451 Reinforced Portland Cement Concrete Pavement

Portland cement concrete pavement must be constructed so that it provides a smooth-riding surface satisfactory to the traveling public and is durable when subjected to natural weathering, traffic abrasion and chemicals used for snow and ice control. It must be capable of sustaining the traffic that it is intended to carry and be of sufficient skid resistance to eliminate slippery conditions when wet.

While the quality of the riding surface is the chief construction element by which the public either approves or condemns a pavement, this element is not more important than durability and structural strength. All desirable elements of a good pavement are a product of the workmanship of the contractor and the engineering and inspection personnel assigned to the work.

Every step of construction, from the preparation of the subgrade and base through concrete curing and opening to traffic, has a definite effect on the rideability, durability, and structural integrity of the finished pavement.

Materials (451.02)

Concrete

The concrete specified for use in reinforced Portland cement concrete pavement is Class C concrete that is defined in Item 499 (Table 499.03-3). The Contractor may substitute Class C concrete with one of the three proportioning options specified in 499.04. If Class C with Proportioning Option 1 or Option 3 is used, they can only be used between April 1 and October 15, unless authorized by the Director. The reason for this restriction is that these options allow the use of fly ash or ground granulated blast furnace slag respectively, which slow the strength gain of the concrete during cool temperatures.

The coarse and fine aggregate used in the Class C concrete for exposed concrete pavements (Item 451 and 452) have additional requirements in addition to the requirements in 703.02. The fine aggregate used in the concrete must be natural sand; therefore, sand manufacture from stone is not permitted. The coarse aggregate, if either gravel or limestone is used, must have been tested in accordance with 703.13. Air-cooled blast furnace slag (ACBFS) coarse aggregate does not have to be tested for freeze thaw resistance.

If crushed air-cooled blast furnace slag (ACBFS) coarse aggregate is used, the contractor must use No. 57 or 67 size.

If the contractor is using gravel or limestone coarse aggregate in the concrete for exposed concrete pavement (451 and 452), then No. 57 or No. 67 size must be used if there are more than 10,000 square yards (8,000 square meters) of pavement area. If the project contains less than 10,000 square yards (8,000 square meters) of these items, the contractor may use No. 7, 78, 8, 57, or 67 size gravel or limestone coarse aggregate. The No. 7, 78, or 8 sizes of gravel or limestone, if used, it must meet requirements of 703.02. If No. 57 or No. 67 gravel or limestone sizes are selected in either of the above cases, the aggregate must meet 703.02 and be tested in accordance with ASTM C 666, Procedure B. This is a test for aggregate freeze-thaw durability (D-cracking susceptibility).

Joint sealer

The joint sealer to be used must be a hot-applied joint sealer conforming to ASTM D 6690, Type II. This material is normally used to seal longitudinal joints in exposed concrete pavement.

Preformed elastomeric joint seal

The preformed elastomeric compression joint seal for concrete must comply with ASTM D 2628 with the modifications listed in 705.11. This material is specified for use in transverse joints. It also can be used for longitudinal joints, but contractors normally use a hot applied material because it is much cheaper.

Preformed filler

The preformed filler used must comply with AASHTO M 153 or AASHTO M 213 with the modification shown in 705.03. This material is used in expansion joints to allow for movement at the joint.

Curing materials 705.05, 705.06, 705.07 Type 2

These curing materials are burlap cloth, sheet-curing materials for curing concrete

Tie bar steel, epoxy coated

Tie bar steel used in the longitudinal joints in concrete pavement must meet the requirements for epoxy coated reinforcing steel requirements of 709.00.

Reinforcing Steel

The steel reinforcing steel must comply with 709.09, 709.10, 709.12

Dowel bars and basket assemblies

Dowel bars and basket wires used to support the dowels at the proper position must be coated with a fusion-bonded epoxy coating conforming to AASHTO M 254 with the exceptions listed in 709.13.

Expansion shield anchors, Type A

Expansion shield anchors used to anchor hook bolts in longitudinal pavement joints must meet Federal Specification FF-S-321, Group II, Type 4, Class 1, and Group VIII, Type 1 (See 712.01).

Equipment (451.03)

The riding qualities of a pavement depend largely on the proper operation of mechanical finishing equipment. The equipment must be in correct adjustment. It is almost impossible to use hand finishing to correct a poor surface left by the equipment. Frequent checking and minor adjustments to compensate for changing conditions will do much to eliminate surface irregularities.

The Contractor’s forces are responsible for equipment adjustments. Department personnel are not expected to adjust or advise the Contractor how to adjust and maintain mechanical equipment, but they are expected to observe the checking of all equipment. The Inspector should be able to recognize when such equipment is out of adjustment or not coordinated with the balance of the paving train. The following information on spreaders and finishing equipment is given to provide some knowledge on the operation of such equipment.

The equipment used must be self-propelled spreading and finishing machines that are capable of consolidating and finishing the concrete and producing a finished surface meeting the requirements specified. The specifications give the Contractor the option of using slip-form or fixed-form pavement construction methods.

Vibrators are used for full width and depth vibration of concrete paving slabs. They must be internal type, either with immersed tube or with multiple spuds. They may be attached to the spreader or the finishing machine, or may be mounted on a separate carriage. They must not come in contact with the joint load transfer devices, subgrade, reinforcing mesh or side forms. Multiple spuds should not be spaced further apart than 2 1/2 feet (0.76 m). Therefore, a minimum of 10 spuds is required for a full 24 feet (7.2 meter) width paving.

Internal vibrators operate at 7,000 to 11,000 impulses per minute. An electronic monitoring device that displays the operating frequency of each internal vibrator is required on all concrete paving machines. There must be a readout display located near the paving operator’s controls. This monitoring device must operate continuously when paving and display all vibrator frequencies with manual or automatic sequencing between individual vibrators. The contractor must record the following information each 25 feet (8 m) of paving or 5-minute time interval:

the time of day
station location
paving machine track speed
the frequency of each vibrator using the monitoring system

If the monitoring system is not equipped with an automatic recorder, the contractor must manually record the above information every 30 minutes. The contractor must provide a record of the data to the Engineer each paving day.

Vibration is required for all concrete pavements. Small irregular areas require vibration by hand-held or machine-mounted equipment to assure that adequate consolidation for the full depth and width is achieved without segregation.

Vibrators must be connected such that they turn off when the machine on which they are mounted is stopped.

Fixed Form Construction (451.03.A)

This construction method requires that the contractor furnish equipment that will spread, screed, and consolidate concrete using one or more machines operating on previously placed side forms. There must be enough equipment with capacity to perform the work at a rate equal to the concrete delivery rate. The equipment must uniformly distribute and consolidate the concrete without segregation.

The equipment must either operate on two side forms, on an adjacent lane and one side form, or on two adjacent lanes as necessary. When operating the equipment on adjacent lanes, the adjacent lanes must be protected from damage from the equipment.

Forms must be made of steel, must be straight, and of a depth equal to the pavement thickness specified. Bent or damaged forms are not permitted. Forms must be clean and oiled each time they are used. Form sections must not be less than 10 feet (3 m) in length with a horizontal joint and base width equal to the depth of the forms. If the radius of the pavement edge is 100 feet (30 m) or less, flexible or curved forms may be used as approved by the Engineer.

The contractor must provide methods and devices that securely set forms and withstand paving equipment operation. Built up forms must not be used unless constructing less than 2,000 square yards (1,650 square meters) of pavement. All forms must have adequate joint locks to tightly join the ends of abutting sections together.

Slip Form Construction (451.03.B)

This method of construction permits pavement placement without the use of fixed side forms. In lieu of forms, the paving machine vibrates, tamps, compresses, and strikes off the concrete while within the machine’s moving forms, and finally extrudes the consolidated concrete slab. Consolidation is such that the vertical side faces of the slab retain their shape and position after the passing of the traveling side forms. Trailing side forms are needed only to protect the slab edges during hand straight-edging operations.

The base must be constructed as outlined in the specifications. Stability of the base is critical for slip form construction. If stability is lacking, the base must be stabilized by added admixes or angular aggregate particles at the Contractor’s expense. The base must be graded to the plan elevation by a properly designed machine. The track area may be brought to grade using a form grader, with a subgrader on crawlers used to grade the area under the pavement. An automatic subgrader operating from a preset grade line is ideal for slip form construction and does not require the use of a form grader.

Stabilization in the paving machine track area to provide traction is permissible, provided the area is scarified after pavement construction to avoid interference with lateral drainage of the subbase. Any method of stabilization proposed by the Contractor must be approved by the Engineer.

An approved slip form paver or combination of pavers must be used to spread, consolidate, screed, and finish the concrete in one complete pass of the machine. The machine must consolidate the full width and depth of pavement being placed to provide a dense homogeneous pavement requiring a minimum of hand finishing. Two machines may be used with the front one striking off the bottom course for placement of the mesh. The width of the bottom course may be 6 inches (150 mm) narrower than plan width so as not to interfere with the second paver.

The concrete slump should not exceed 3 inches (75 mm). If the slump exceeds 3 inches (75 mm), the edges may be subject to settlement after the forms have passed. Slump less than about 1 1/2 inches (40 mm) may result in an open textured surface requiring excessive hand finishing. Therefore, the slump should be maintained between 1 1/2 and 3 inches (40 and 75 mm) for best results.

Good construction results are achieved by operating the paver with a continuous forward motion with a minimum of starting and stopping. When the paver stops, all vibrating, tamping and oscillating elements must stop also.

At the end of the day’s production, pavement at construction joints may be reduced approximately 2 inches (50 mm) in overall width. This allows the Contractor to use an insert just inside each moving side form so that the paver can be positioned at the joint when production is resumed. The trailing side forms do not bind and spall the slab edges when the leeway is provided on each side. The slip form machine must not be used as a dozer to push large quantities of concrete piles out in front. Therefore, some means of depositing and striking off the concrete must be used to permit smooth uninterrupted operation of the paver. The use of spreader boxes, a concrete spreader, or any technique that provides a uniform distribution of concrete is permissible.

Preset grade lines are required for slip form paving equipment to assure acceptable riding quality of the pavement. Preset grade lines may consist of:

a stringline offset from and parallel with the edge of the pavement; or
the compacted and trimmed surface of the subbase.

If string lines are used, they may be set on one or both sides of the pavement; the grade is transferred to the paver through sensors following the grade of the string line. A smoother pavement is normally obtained if two string lines are used, one for each pavement edge.

The grade may be traced from the surface of the base by using skis that electronically control the grade of the slip form paver. When this method is employed on one or both side of the pavement, the base should be thoroughly compacted and the surface grade closely controlled. Skis should be placed in areas where the base is not affected by any of the paving equipment.

The use of string lines and base surfaces alone will not assure riding quality. All lines, grades, and controls should be frequently observed to avoid obvious errors. The electronic controls of the slip form paving equipment are not capable of sensing errors in the gradeline; therefore, they will duplicate errors in grade controls in the pavement surface. In order to attain the riding quality possible with slip form pavers, constant attention must be given to the preset grade lines. When a stringline is used, the stringline should be supported at intervals that eliminate sagging of the string under its own weight. Supports every 25 feet (8 m) produce the most desirable results. In addition to the intervals between supports, the stringline tension must also be taut enough that excessive sag does not occur.

Inspection of slip form paving should include checking the pavement edge. Since no forms are used to screed against or to hold the edge in place, the edge can slump downward or tilt out. This can result in an area of lower elevation which will hold water if pavement is placed against it. The edge of the pavement must not vary more than 1/4 inch (6 mm) below the typical section if pavement is to be placed next to it. A straightedge can be placed perpendicular to the edge to check transversely. In addition, the straightedge can be placed longitudinally at the pavement edge to check in that direction. Areas that do not meet the tolerance must be corrected while the concrete is plastic. The outside edge of pavement (the edge that will not have concrete adjacent to it) must not vary more than 1/2 inch (13 mm) from the typical section.

Types of Slip Form Pavers

Slip form pavers are generally of two basic types. One has an extrusion meter that shapes and extrudes the concrete pavement, while the other type has the same features as the combination float finisher that shapes, consolidates, and then finishes the pavement in a manner similar to conventional methods.

The extrusion meters or screeds and the float must be checked for proper crown setting before using. They should be adjusted if necessary to conform to the typical section.

Slip form machines usually are equipped with both tampers and vibrators. Both should be checked to assure they are in working order before paving starts. A vibration monitoring system is required on all paving equipment to monitor all vibrators and ensure that the specified impulses per minute are being obtained.

Concrete Spreaders

A separate concrete spreader is required when the width of pavement being placed in one operation is 12 feet (3.6 meters) or more and the area of any given width exceeds 10,000 square yards (8,300 square meters). They must be adjusted to leave the proper amount of concrete to build the slab. The amount left is determined by the elevation of a strike-off plate that is located behind the screw augers, paddle, or hopper that distributes the concrete.

The elevation of the bottom of the strike-off in relation to the top of the forms is shown on an indicator that is visible to the operator. The equipment should be checked to make sure that the indicator shows zero when the bottom of the strike-off is exactly even with the top of the forms.

Transverse Finishing Machines

The transverse finishing machine should first be checked for its operating condition. The bearings, especially those of the cranks actuating the oscillating screeds, should fit snugly so that the screed reverses direction without slap (which would rack the forms).

The end plates that slide on the forms should be inspected for wear and reversed or replaced if necessary. The screed should be checked for straightness, or crown if one is required. Perform this check by placing a block on the forms under each end of the screeds and stretching wires at both front and back across from form to form. Check the crown by measuring the offsets from the wire to the screed. Adjusting bolts can be loosened or tightened to secure proper adjustment.

The exact tilt required in each screed cannot be determined until construction begins. However, at the start of paving operations, the front edge of the forward screed should be titled about 3/16 inch (5mm) and the rear screed set level. Adjustments can be made readily by end bolts provided for this purpose.

Springs are used as shock absorbers to prevent slap at the end of the stroke. These should be checked to insure that they are in compression at all times. The screed lift chains must be long enough so that they are not tight at the end of the stroke; otherwise, the screed will be lifted off the forms at every oscillation.

Finally, the wheel scrapers should be tightened so that they will be sure to keep the wheels clean.

Operation of Transverse Finishing Machine

The work of the transverse screed is an intermediate step in the process between placing and distribution of the concrete and the final mechanical finishing. The work performed by the screed should be as nearly complete as possible, so that smoothing and floating is the only operation required by any following equipment.

As the transverse screed begins work, the concrete before it must be distributed to approximately the correct surface level, either by mechanical concrete spreaders or by hand methods. The requirements for correct transverse screed operation are the same regardless of the method of prior distribution, except that local grading by hand work will be more irregular and will require more care in the screeding operation.

The transverse screed must leave the surface with a uniform texture and a uniform, correct elevation for final finishing. Good finish cannot be obtained if the screed does not perform this function. Deep or irregular corrugations behind the screed indicate improper operation.

Satisfactory results depend upon several critical factors. These factors must be considered at all times, and variations in the adjustments or in the operation of the screed must be made, as occasion demands, to keep the factors always in balance.

The head of concrete carried in front of the forward screed must be maintained at a uniform height, about 4 to 10 inches (100 to 250 mm), and in uniform quantity across the full width of the lane.

The concrete head carried in front of the rear screed must be uniform and about 2 to 4 inches (50 to 100 mm) high. The material being moved ahead by the rear screed should roll, not flow or tear, and the mix and timing of operations must be controlled to satisfy this requirement.

The height and tilt of the screeds must be adjusted to compact the particular mix being used and to permit a uniform amount of surge.

The traction speed, screed speed, and length of screed stroke are controlled independently. These must be combined in the proper relation to obtain optimum results. As conditions on the project vary, these relationships should be varied to produce a constant quality of result.

The forms and wheels must be kept clean. If the wheels ride on an irregular surface, the concrete will show corresponding roughness. The screeds must be kept clean, so that they do not leave streaks in the concrete and do not drop lumps of hardened concrete on the fresh surface.

The amount of concrete being carried ahead of the screeds (both forward and rear) controls the amount of surge past the screeds for any given mix. If the head of concrete is too high, an excess will pass under the screed and leave an overload for following equipment. If there is a deficiency of concrete at any point in front of the screed, a low spot develops at that point. If the head varies continually, the surge will also vary and a wavy or rough surface will be left. Therefore, a uniform roll of concrete must be maintained along the front edge of the screeds to provide a uniform amount of surge. At the beginning of a day’s work, a small amount of concrete should be placed in front of the forward screed to provide a working supply for filling in low areas. This accumulation should not be allowed to build up as the work progresses, but should be maintained uniformly. If excess builds up, the excess should be screeded off or a second pass made.

The Inspector should insist on coordination of distribution and transverse screeding to obtain continuous, acceptable results. The forward screed should compact the concrete off at the top of form level, allowing for a very small amount of settlement that usually occurs before the following finisher passes. The difference in the requirements at the two screeds accounts for the difference in the size load each should carry.

Inspectors on transverse screeding work must remember that the finishing machine is not intended for heavy duty. The surface left by this work must be uniform and satisfactory. The transverse screed is capable of meeting these requirements. The Inspector should insist that the operator make full use of the machine’s capabilities in order to obtain a complete and proper integration with the entire paving process.

If one pass of the screed does not result in satisfactory surface conditions, a second pass is necessary. It is preferable that preceding operations be controlled so that a second pass is not required at intermittent points. The Contractor may elect to use two screeds or to pass over the entire area twice with one machine. Different amounts of screeding will result in variable surface conditions and are to be discouraged.

Screeds should be operated with the screed wearing plates working directly on the forms. A straight screed with no tilt results in a concrete surface at or below form level, except for surge. Adjustments in screed elevation and tilt may be required to work certain mixes properly. If the concrete mix is extremely stiff, the screeds normally will tear the surface and leave insufficient mortar for finishing. Under these conditions, the front or first screed should be tilted so that the forward edge is raised slightly. This compacts the concrete as the screed passes and forces a small amount of mortar to the surface. Extremely stiff mixes usually demonstrate an absence of surge which, with combined tearing, leaves the surface below the top of forms. The center of the screed then should be raised slightly by adjusting end screed hanger bolts, leaving the end plates to work on the forms with the remainder of the screed raised. This permits the required amount of concrete to pass the forward screed. The rear screed always should be straight along the rear edge and work directly on the forms.

The amount of tilt of the screeds must be worked out for the particular job conditions. As a starting guide, the following information will be of assistance. With standard Portland cements and with air-entrained concrete of relatively stiff consistency, less than 2-inch (50 mm) slump, the forward screed will likely require a tilt of ¼ inch (6 mm) or less and the rear screed a tilt of 1/16 inch (0 to 2 mm).

The combination of traction speed and screed motion depends on the concrete mix and consistency, and upon the grade or super elevation of the pavement. With stiff mixes, the screed speed should be rapid with a long stroke and the traction should be slow in comparison to more workable mixes. This provides extra working of the concrete and aids in compaction and in providing enough mortar at the surface for finishing. With more fluid mixes, the screed action should be decreased; both in speed and length, and the traction speed should be increased. This will prevent over working or excessive agitation of the concrete, which might cause flowing to the low side of the forms, excessive surge past the screeds, or a pooling of wet mortar on the top. The relation of traction and screed speeds is very important. In most machines, the controls are independent and the proper combination can be made by trial without any difficulty. A change in speed of either screeds to reaction requires only shifting of a lever. The change of length of screed stroke requires a work stoppage and readjustment of the screed drive, but this change should not be required very often unless control of the concrete mix is poor. Poor control of the concrete mix should not be tolerated.

The screed wearing plates are rubbing continuously on the forms or on completed concrete lanes. They are made of abrasion-resisting steel, but may wear rapidly under the heavy punishment they receive. As they wear, they have the effect of lowering the entire center portion of the screed by the amount of wear. Furthermore, the wear may not be the same for the full length of screed stroke, and may vary the strike-off elevation of the screed. They should be checked at the beginning of each job. Adjustments for up to 1/8 inch (3 mm) in wear can be taken care of by adjusting the screed bolts. The plates should be replaced when wear exceeds this amount.

Exercise care when operating the finishing machine over expansion joints to avoid displacing or damaging the preformed expansion material. Any method of operation that does not interfere with the expansion material will be permitted.

Mesh Installer

Pavement mesh may be installed by placing it on top of the full depth of concrete, then vibrating it into position using an approved mesh installer. This method eliminates the need for placing two courses of concrete and thereby eliminates the possibility of a plane of weakness (a cold joint) between two separately placed courses. Control of the mesh placement within the slab is more accurate than when placed between courses, based on measurements of cores removed for checking thickness requirements. Another advantage of this method is that a bulkhead can be placed readily and quickly in the event of breakdown since the concrete is placed full depth, and not in two separate courses.

Two types of machines have been approved for use in vibrating the mesh into position. One type consists of a grid of steel plates approximately 15 feet (4.6 m) in length and extending the full width of pavement being placed. The self-propelled machine is positioned over the mesh, stopped, the mesh depressed into the freshly placed concrete, and moved ahead to repeat the operation.

The other type is also self-propelled and consists of long tapered longitudinal runners across the width being placed. This machine gradually depresses the mesh into position within the fresh concrete using an oscillating tamping motion while continuously moving forward.

Since there is forward movement during placing, the latter type of machine may cause movement of the mesh across transverse contraction joints when not properly adjusted. When using a machine of this type, periodic checks must be made by uncovering the mesh at joint assemblies to assure that the specified clearance of 12 ± 2 inches (305 ± 51 mm) is being maintained on each side of the center of the joint. If the mesh position is found to be outside of tolerance, it should be corrected and the machine adjusted at once, or its use immediately discontinued. Production may be continued without the mesh installer by changing to the two-course method.

Both types of machines can be adjusted to control the depth of the mesh. Therefore, depth checks must be made daily to assure control of the depth of mesh. Specifications require the mesh to be placed below the top surface of the pavement a distance of between 2 1/2 inches and T/3 + 1 inch (64 mm and T/3 plus 25 mm) where T is the thickness of the slab. When mesh is found to be outside of tolerance, immediate adjustments must be made by the Contractor.

It may be necessary to use the two-course method at expansion joints and at abutting pavements if the machine with the long tapered runners cannot position the mesh properly. The two-course method should be employed any time satisfactory performance of the machine is not obtained.

Combination Float Finisher

The combination float finisher is commonly used to provide the final mechanical finish on a pavement. The machine that consists of two screeds and a float is designed for use on a 24-foot (7.2 m) pavement.

The front screed of the machine is a conventional reciprocating screed that rides the forms. The rear screed and float, however, are suspended from an approximately 16 foot (4.9 m) beam platform and do not receive any support from the forms. The elevation of both the rear screed and the float is determined by adjustment of the hangers that connect them to the platform. As a result, variations in forms do not significantly affect the plane of operation of either the rear screed or float. The key to smooth finishing with this machine is the rear screed since it is the final screeding tool and operates from a 16 foot (4.9 m) straightedge essentially free from influence of deviations in the forms.

Spring-loaded shoes are fastened to both ends of the rear screed to keep the screed in contact with the forms. The springs are sufficiently strong so that the rails will be kept clean, but not so strong that they will cause the screed to raise when an undetected highpoint in the forms is being traversed.

The float does not oscillate but moves forward with the machine providing a smooth trowelled surface. It is approximately 30 inches (0.7 m) in length and rides on the slab between the forms. Both of the screeds and the float are provided with devices which permit rapid changes in crown. These devices make it possible to change crown at super-elevated sections without delay.

Operation of Combination Float Finisher

The combination float finisher serves both as a conventional transverse and longitudinal finisher. The transverse screeding is accomplished through the two screeds (front and rear) and the longitudinal finishing by the suspended finishing pan that rides on the slab surface.

All phases of good construction practice must be followed in order to obtain the best finish. Several points, however, must be adhered to closely in order to obtain the best possible finish when the machine is used for the final mechanical finishing operations. These items are described in the following paragraphs.

The concrete must be accurately metered to the machine. Better results are obtained when spreaders and auxiliary screeds (when used), operating ahead of the machine, leave just enough concrete so that a uniform roll of 4 to 6 inches (100 to 150 mm) is carried on the front screed. When this condition does not exist, the equipment operating ahead of the float finisher should be adjusted so that such a concrete roll is obtained.

The screeds and float must be set accurately. Both front and rear screeds should be set flat. When the front screed is flat and carries a 4 to 6 inch (100 to 150 mm) roll, it passes sufficient concrete to form about a 2-inch (50 mm) roll on the rear screed. When this 2-inch (50 mm) roll reduces in size, fresh material should be carried back and placed to obtain a uniform roll. It is essential to keep the roll in front of the rear screed uniform for optimum results.

The rear screed cuts off any excess concrete and leaves the pavement surface at the desired crown and grade. When set to proper crown without tilt, the float just makes contact with the surface and trowels it smooth and free of screed marks. Occasionally, it is desirable to leave the front of the float about 1/16 inch (2 mm) when greater compaction is desirable. This practice, however, generally leaves deeper transverse marks than are considered desirable.

The finishing machine is designed primarily for a one-pass operation. If all operations prior to the pass of the machine are as they should be, it is rarely necessary to make more than one finishing pass. If the forward speed is adjusted properly, the machine moves forward at a uniform rate, eliminating frequent stops that cause variations in the surface. It is true with this machine, as with other types of finishing equipment, that continuous operation provides smoother pavement.

The machine must be kept clean. The bottoms of the screeds and the pan must be absolutely smooth. Accumulations of hardened concrete (or oil and grease) that might drop on the pavement must be cleaned off continually. The machine should be cleaned thoroughly every day.

Transit Mix and Central Mix Equipment

Concrete plants and hauling units must be checked for proper condition prior to paving operations, and at regular intervals during paving. Water and admixture metering devices should be checked to assure proper calibration within specified tolerances.

Transit mixers should be checked to determine that the counters are functioning properly. After having been mixed for not less than 70 revolutions at mixing speed, the mixer should contain concrete of uniform consistency and be able to discharge the batch without segregation. Since this determines acceptability, mixers that do not perform in this manner should not be used, and discontinued if encountered. Sources of trouble are badly-worn mixing blades and leaky valves which prevent mixers from producing uniform concrete. They should not be used until corrected.

Central mixers should be checked to see that the mixer is capable of uniformly mixing and discharging the large volume of concrete. During paving, the Contractor or ready mix supplier must keep mixer blades free from concrete build up and excessive wear.

When the concrete is transported to the paving site in dump trucks or other non-agitating units, check the bodies to see that they are water-tight and free of objectionable corners or internal ribs where concrete may accumulate. Canvass covers to shield concrete from sun and wind shall be provided when required by the Engineer.

Concrete Batch Plants

Aggregate stockpiles should be placed on areas which are paved, prepared by using sheet metal, wood plank, etc., or they may be placed directly on the ground. When building stockpiles on existing ground, the area should be firm, cleaned of foreign material, and shaped to provide drainage. No aggregate is to be removed from the stockpile within one foot of the ground until the final clean up. Aggregate within this area should be processed to meet specifications before permitting its use.

Stockpiles should be built in such a manner that different types or sizes of aggregate do not become mixed and the aggregate does not become segregated.

In building the stockpiles of coarse aggregate, exercise continual care to prevent segregation through improper handling. A clam bucket operated by a crane of sufficient size that the center of the pile can be reached from the edge is best for this work. In depositing the aggregate, the bucket should be lowered close to the level where the aggregate is to be deposited before releasing the aggregate. This prevents rolling of the larger aggregate particles to the bottom of the pile to cause segregation. As the pile increases in height, each layer of aggregate should be benched back to form tiers that will help limit rolling and segregation.

Other equipment may be used in conjunction with a clam bucket. If the Contractor uses front-end loaders to build the pile, they must have clean rubber tires if they are to operate on the pile. As with the clam bucket, the drop should be as little as possible when depositing the aggregate. Once on the pile, the front-end loader should not be permitted to move on and off of the pile as this may cause contamination.

Pushing of large aggregate as with a bulldozer is not permitted, as this causes segregation. Use of steel treads on the pile is not permitted as they tend to crush the aggregate.

Small aggregate does not segregate as easily as large aggregate because the smaller pieces are less likely to roll down the side of the pile.

Any operation which might result in segregation, degradation, or contamination is not permitted. When these conditions appear evident, run a gradation test and, if substantiated, adjust the operation. The specifications require that concrete materials be measured by weight. The scales shall be checked for accuracy with standard test weights as outlined in Item 499.

Materials should be placed in the batch plant bins by dumping into the middle of the bin with as short of a drop as possible. Keeping the drop to a minimum reduces the chance for segregation in handling aggregate, as well as in handling concrete.

Setting Forms (451.04)

Forms are a potential source of trouble because they serve as tracks for all paving equipment, except mixers, in addition to serving as forms for the concrete. Since developments in paving equipment have provided heavier equipment, the forms play an increasingly important role in the construction of smooth pavements.

Before any forms are set on a project, they must be inspected to see that they comply with specification requirements. Forms must not be less than 10 feet (3 m) in length, and must have adequate joint locks for joining ends of abutting form sections tightly. In addition, they must have sufficient pin pockets for setting securely so that they will withstand the operation of the paving equipment. Forms that are distorted more than 1/8 inch (3 mm) on the top or more than 1/4 inch (6 mm) in alignment must be rejected. Forms that are rejected must be conspicuously marked. They are not to be used unless they are repaired so that they comply with requirements.

Forms are reused continuously. Therefore, inspection of forms must be continuous. Anytime forms are found out of tolerance, they must be rejected.

Forms are to be set true to line and grade on a thoroughly compacted base with uniform bearing throughout their entire length and width. The building of pedestals of earth or other shimming to bring forms to the required grade is not permitted. Whenever adequate and uniform form support is not obtained, the forms must be removed, the base corrected and compacted, and the forms reset. At least 3 form pins are to be used in each 10-foot (3-meter) length. These pins must be long enough to hold the form in position during the placing and finishing operations.

Grade for forms is prepared using a form grader. A stringline is set to serve as a guide for controlling the grade during the operation of the form grader. An automatic subgrader operating from a preset grade line may be used to prepare the entire base width before forms are set. If such a machine is used, the forms may be set to correct line and grade, a planer usually is operated on the forms to assure the base is to the proper grade. Whether or not a planer is used, a pin template must be used to check the surface of the base.

Pin keys must be straight and free-moving in the pockets and capable of holding the forms tight against the pins. The joint locks must not be bent or worn and must be capable of holding the ends of the forms in true alignment. The pins and locks are checked when the forms are set but should be rechecked just prior to placing of concrete and tightened if necessary. Make a final visual check at the same time to insure forms are at proper line and grade. Smooth riding pavement with good surface finish is extremely difficult to obtain with poorly aligned and set forms.

The forms are to be cleaned and oiled prior to placing of the concrete. When hook bolts or wiggle bolts are fastened to the forms, the forms must be oiled prior to placing of these units.

Fine Grading of Subgrade or Base (451.05)

After the embankment has been placed and compacted, and excavation has been completed, the subgrade is brought to the required grade, cross section, and density. The subgrade shall be checked after it has been prepared to assure compliance with surface and density requirements.

The surface of the subgrade is shaped to bring it within the allowable tolerance of the typical cross section. The surface shall not vary more than:

1/2 inch (13 mm) from a 10-foot (3 m) straightedge applied parallel to the centerline of the pavement.
1/2 inch (13 mm) from the plan grade.

Proof Rolling

Where proof rolling is specified the compacted subgrade must be checked in accordance with the specifications. Instructions for performing this work are detailed in Item 204.

The completed subgrade must be checked for compliance with the specification requirements. The limits of the area checked should be recorded along with a statement that the subgrade conforms to requirements. This data should be recorded in the project Diary.

Any area found outside of the allowable tolerances must be corrected and rechecked before the area is approved for the base and/or the concrete pavement.

Base

Base is provided by plan for all concrete pavements with only a few exceptions. There may be pavements without base but they will be the exception rather than the rule. The typical plan section indicates the depth and width of compacted base materials. Therefore, the Inspector should check the typical section prior to inspecting this operation.

Stabilized bases may be specified on selected projects. Asphalt, cement, and aggregate lime-fly ash bases have been a design feature on several projects. If encountered, these bases should be constructed in accordance with contract requirements. Cement stabilized base should meet requirements of Supplemental Specification 804. Asphalt bases usually are specified in accordance with 301 or 302. Plan and Proposal Notes should be reviewed for special requirements when stabilized bases are required.

Base material conforming to the grading specified in the plan or proposal must be placed with an approved spreader. The base may be placed in a single lift or layer provided the compacted depth does not exceed 8 inches (200 mm). The moisture content will be determined from the test section. If the material does not contain sufficient moisture when it is spread, it must be sprinkled with water. Exercise care to avoid softening the subgrade when watering.

Base material must be compacted to the specified density once it has been spread. Detailed instructions for compaction and compaction testing are outlined in Item 204.

The surface of the base is left approximately 1 inch (25 mm) above grade after compaction has been completed. Then, after forms have been set to grade for form paving or the stringline is set for slip form construction, the slight excess is removed during the operation of the subgrader. The subgrading or fine grading operation should result in a slight removal so that the trimmed surface is compacted thoroughly without low areas. Low areas require the addition of material, compacting, and regrading resulting in a delay in progress of fine grading.

When automated subgraders are used, they will precede the setting of forms. Grade will be maintained from a preset stringline that will be parallel to the grade line. After final trimming the surface will be treated the same as for conventionally graded base.

Loose base material windrowed along the inside of the forms cannot be removed by machine so removal of this material by use of a shovel is necessary. This shall be done before re-compacting.

The trimmed surface left by the subgrader should be compacted using a light or medium roller to restore surface density. This rolling operation also smoothes the surface and reduces the friction between the base and the pavement.

The base surface must be checked using a multiple pin template operated on the forms. The template must be operated behind the subgrader and roller. Any high or low spots encountered shall be corrected immediately, then rerolled and rechecked before continuing.

Moisture is controlled by spraying the base prior to fine grading, preferably in the late afternoon of the day before fine grading. This provides the moisture necessary for density and provides time during the night for uniform moisture distribution. After removal of excess material during fine grading, moisture is present for the final surface compaction.

Just prior to placing concrete, the base should be sprinkled again to replace moisture lost by surface evaporation so that the base will not absorb water from the concrete. Loss of concrete water can result in a rapid slump loss and early setting of the concrete before it can be finished properly.

The subgrader is usually one of the heaviest pieces of equipment operating on the forms. Therefore, this is an opportune time for the Inspector to observe the forms for excess movement or displacement. Areas where movement or displacement is noticed should be rechecked for compliance with requirements before placing concrete.

It is good practice to recheck the alignment and grade of forms, the form locks, and the pin keys after fine grading. Some contractors assign employees to this job. The Inspector should check these items regardless of the Contractor’s operation to assure that any irregularities have been corrected. Since the paving equipment relies on the forms for support, it cannot be expected to produce a quality-riding surface when yielding or improperly set forms are encountered.

The Inspector should record the limiting stations of the area checked that conformed to the requirements in project records. For slip form paving, spot checks of completed base should be recorded in the project records.

Placing Concrete (451.06)

Concrete is to be evenly deposited upon the base in a manner that requires a minimum of redistribution. Even distribution of concrete on the base, or in each course being placed, is the first step toward an acceptable job.

The most even distribution in initial placing results in minimum variation in final surface settlement. If concrete is deposited in piles, or windrows, unequal consolidation may take place before finishing operation are begun. This never will be overcome throughout the finishing procedure and can be the cause of unequal settlement and rough surfaces after finishing has been completed.

In case of transmit mixer or dump truck delivery, use discharging methods that spread each batch as evenly as possible. Better results are obtained when a hopper-type spreader is used with concrete delivered to the site with either transit mixer or dump truck.

A separate approved spreading machine must be used whenever the pavement being placed in one operation is 12 feet (3.6 m) or more in width and the amount to be placed exceeds 10,000 square yards (8,300 m²). Concrete spreaders are powerful pieces of equipment that will handle heavy accumulations of concrete. However, this is not a reason to permit improper distribution.

The initial placing of the concrete should be just enough so that a slight excess is carried ahead of the spreader as it levels the concrete to a uniform surface. Or, in case a spreader is not required, the concrete can be spread and leveled easily with shovels. Unless this is done there will be irregular surge past the strike-off of the spreader or past the finishing screed. This necessitates excessive manipulation of the surface in order to obtain specified smoothness requirements. Excessive manipulation tends to alter the quality, durability, and wear resistance of the finished pavement.

In addition to these principal precautions in placing operations, there are some others that should be observed. Workers should not track dirt or other debris into the concrete, nor should they walk unnecessarily on the fresh concrete after it has been struck off. Boot tracks often are filled with mortar that will shrink when setting, which may develop into low spots. Foreign material must be kept out of the concrete. The incorporation of such items in concrete can cause defects in the pavement.

Concrete should be shoveled in place around expansion joint assemblies. The concrete should not be dropped directly on dowel basket assemblies from the delivery equipment but should be gradually spread over them by the spreading machines. If a hopper-type spreader is used, it should not be positioned over the dowel basket assemblies while concrete is being discharged. This could result in displacing the dowels.

Internal vibration is required for consolidating concrete for the full width of pavement placed. If internal vibration is attached to the paving machine, separate vibration along the forms and around contraction joint assemblies is not required. However, separate vibration around expansion joint dowel basket assemblies and construction joints is required in fill-in areas not traversed with such equipment. Regardless of the consolidation method used, the vibration must be shut off when the machine stops. If it is permitted to run, rapid segregation of the concrete composition can occur which may cause weak spots in the slab. In addition, this practice may cause the vibration action to be picked up by each dowel and result in water planes and/or soft weak mortar being formed along each dowel. This seriously reduces the strength and ability of the concrete to absorb the bearing stress that each dowel transmits to the concrete under traffic load, and contributes to early faulting of the joint.

The vibration frequency of vibrators used must be maintained between 7,000 and 11,000 impulses per minute. Vibration monitoring devices are required.

Placing Reinforcement (451.07)

Distributed steel or reinforcement used in reinforced pavement (Item 451) is generally welded wire fabric or mesh. Its principal function is to hold together the fractured faces or slabs after cracks have formed. Adequate load transmission across the crack is thus assured, and the infiltration of incompressible material into the crack is prevented or delayed. It does not increase the flexural strength of an unbroken slab. Like tiebars, steel mesh is designed to withstand tensile stresses and hold the slab together.

Mesh is usually delivered to the job in advance of paving operations and stored. It should be carefully stacked and kept clean. Before it is used, it should be inspected to see that it has not been damaged in shipment or in storage, and that it is free from dirt, oil, and mud, which will destroy the bond with the concrete. Any mesh that has been bent or has broken welds should be rejected. If the mesh is repaired, it should be rechecked before using. Mesh with rust, mill scale, or a combination of both will be considered satisfactory provided the minimum dimensions are not less than specified. Recent research indicates that tight, scaly, and pitted rust does not prevent bond, but actually improves it.

Therefore, mesh should not be rejected for rusting unless the rust is so severe that the wire dimensions are reduced to less than the minimum specified. Reinforcing mesh details for 451 pavement are shown on Standard Construction Drawing BP-1.1. The longitudinal wire is designated as a W8.5 or D8.5 (MW55 or MD55) size and has a nominal diameter of 0.329 inch (8.4 mm). A W4 or D4 (MW26 or MD26) wire is used transversely and has a nominal diameter of 0.225 inches (5.7 mm). If it is suspected that the wire dimensions have been reduced, the District laboratory should be requested to check the wire dimensions with a micrometer.

If mesh is placed along the rough grade or the shoulder to be easily accessible during paving, it should not be done so far in advance that mud will accumulate on it. Take care to prevent the mesh from becoming badly bent.

If a mesh cart is used on the forms behind a spreader, the mesh is stacked in cart-sized piles at intervals along the grade. These stacks should be placed on wood blocks or in some manner to keep them from becoming caked with mud from the grade.

The specifications allow three methods of installing reinforcing mesh. The allowable methods are:

Place one layer of concrete, place the mesh on top of this layer so that it is located in its final location without any further manipulation, and place the second layer of concrete on top of the mesh.
The mesh may be chaired at the proper elevation and securely anchored to the base and the concrete placed in one layer.
Place and spread one layer of concrete; while the concrete is still plastic, use a mesh depressor that vibrates or mechanically installs the mesh to the proper depth in the slab.

If the pavement is being placed in two layers, the concrete for the base layer should be distributed uniformly on the base and then struck off by means of a mechanical spreader to the proper depth. The strike off should leave a plane surface without voids or high or low spots on which to place the mesh. Concrete must be placed and struck off uniformly to permit placing the mesh to its specified depth without manipulation.

Mesh is required to be located in the slab within the range of 2 1/2 inches to T/3 + 1 inch (64 mm to T/3 + 25 mm) below the finished concrete surface (where T is the thickness of the pavement). In its final position, reinforcing mesh must not touch either dowel bars or tie bars. Mesh must also be located such that there is 2 inches (50 mm) clearance from a longitudinal joint or pavement edge to the reinforcing wires. Mesh must also be located such that it is 12 ± 2 inches (300 ± 50 mm) from any transverse joints.

If the mesh is bent, it should be straightened before it is placed; if it has a gradual bow, place it so the concave side is down. Workers placing steel must not track mud or dirt into the concrete.

Tieing Reinforcing Mesh

The mesh is to be placed between the forms leaving 2 inches (50 mm) between the ends of the wires and the side forms, pavement edge, or pavement centerline. Reinforcing mesh is normally shipped in lengths of 19 feet (5.9 m) by 11’- 8” (3.6 m) wide which will fit the specified joint spacing of 21 feet (6.5 m) for reinforced concrete pavement with an allowance of 12 ± 2 inches (300 ± 50 mm) from the center of each transverse joint. If shorter lengths are provided, transverse laps must be 12 inches (305 mm) and mesh sheets must be fastened at the edge of the lane and two other locations.

Usually, mesh is not fabricated for lane widths greater than 12 feet (3.6 m). Therefore, when placing pavement lanes in excess of 12 feet (3.6 m) in width it will be necessary to tie additional mesh to the standard width sheet. This is done by tying the outer longitudinal wire of adjacent sheets together. A minimum of four ties should be placed along the overlapped longitudinal wires to hold the two sections of mesh in the same plane until the concrete sets.

If the screeding operation has been done properly and the mesh placed in flat sheets and tied properly, there will be no difficulty from the steel working up into the finishing operations.

Joints (451.08)

Joints are classified as transverse and longitudinal. Transverse joints are further classified as contraction, expansion, and construction joints. Detailed instructions for joints are found in the specifications and in the standard construction drawings. The Inspector should know the requirements of the specifications and the drawings before inspecting joint construction. All transverse joints are to be constructed normal to the centerline of the pavement lane.

Sawing of joints has resulted in improvement in the riding quality of concrete pavements and higher quality concrete in the joint area. With sawing, the concrete is placed and finished in a continuous operation without disturbing the surface at every joint for hand forming a groove. In lieu of this laborious hand operation, the groove is sawed in the hardened concrete after the surface has been machine-finished and has hardened sufficiently to saw. The uniform groove thus created controls transverse cracking and provides a reservoir for the joint sealer if required.

Sawing is required for all contraction joints. Expansion joints may be sawed or hand formed (see 451.08(c)). Longitudinal construction joints may be either hand formed or sawed. When properly done, sawing produces uniform joint openings and is therefore preferable.

Joint openings are to be constructed in accordance with the requirements of the applicable standard construction drawing. Contraction joints are sawed in a progressive manner as soon as possible without causing excessive raveling of the concrete. Slight raveling is not objectionable but rather is an indication that sawing is being done at the proper time.

The timing of the sawing operation is critical for contraction joints. Sawing must be done after the concrete hardens sufficiently to support the sawing equipment and to avoid spalling and raveling. This operation cannot be tied to normal working shifts but must be accomplished when the concrete is ready. A standby saw is required at the paving site in the event of breakdown or inability of one machine to maintain necessary progress.

Inspection should include random checking of each day’s sawing to assure the width and depth specified is attained. Saw blades will wear with use so continued checks must be made.

Since the timing of sawing is of utmost importance for contraction joints, it should be emphasized, and inspectors assigned to this operation must be aware of this importance. However, the control of sawing is the Contractor’s responsibility and the Inspector should avoid making decisions as to when to saw.

Timing of the sawing of longitudinal joints is not as critical. However, specifications require the sawing to be done within three days after concrete is placed.

Sawing may be done wet or dry, and the cut must be cleaned by a jet of water (if sawed wet) or air under pressure (if sawed dry).

Longitudinal Joints (451.08.A)

Joints between adjoining lanes of pavement are longitudinal joints. They are necessary to control cracking in the longitudinal direction due to the warping stresses in wide concrete slabs. Joints between separately-placed adjoining lanes are longitudinal joints as well as construction joints. In general, the maximum pavement width used by the Department without a longitudinal joint is 16 ft (4.9 m) for ramp pavements.

Tiebars or hook bolts are required to tie the lanes to prevent them from moving apart or from settling unevenly. Since they tie the lanes together by bond, tiebars or hook bolts are not to be oiled. Expansion anchors, if used, must be installed per manufacturer’s recommendations and the hook bolt screwed into the anchor.

Longitudinal Joint - (in simultaneously placed lanes)

Both tiebars and hook bolts should be placed in accordance with requirements of standard construction drawings called out in the plans. Tiebars are 5/8-inch (16 mm) diameter, No. 5 (No. 16 M) reinforcing bars, 30 inches (760 mm) in length. The spacing of tiebars or hook bolts varies with the pavement thickness. The maximum spacing of tiebars is 26 inches for pavement that is 10 inches (250 mm) thick or less and 20 inches (508 mm) for pavement that is greater than 10 inches (250 mm) in thickness. Tiebars or hook bolts must be approximately at right angles and centered at the longitudinal joint.

Tiebars may be set on chairs prior to concrete placement or installed in the concrete after it is placed and spread. Chaired tiebars must be adequately anchored to the base or surface on which the pavement is placed. An approved mechanical device must be used to install the tiebars at the proper depth and location when placing them in the plastic concrete. The mechanical installing device must install tiebars after the concrete is placed to its full depth and after mesh is in position for reinforced concrete pavement. The device must be located in the paving train to assure consolidation of the concrete around the tiebars. Pushing tiebars into the plastic concrete using hand methods is not acceptable.

In pavements 10 inches (255 mm) or less in thickness, sawed longitudinal joints between adjoining lanes placed at the same time must have a minimum depth of 1/4 of the pavement thickness. In pavements greater than 10 inches (255 mm) thick, the depth of sawing shall be 1/3 of the pavement thickness. The width must be approximately 1/8 inch (3 mm). The minimum depth is necessary to control cracking due to warping stresses. The width of this joint is not critical except that it should be uniform for ease in sealing.

Longitudinal Joint - (in separately placed lanes)

Hook bolts or the hook bolt alternate (wiggle bolt) may be used in longitudinal construction joints. One half of the device is bolted to the side-form for the first lane placed. Before placing concrete in the adjoining lane, the other half is coupled to the embedded part. The hook bolts are to be securely fastened to the forms so they are positioned properly in the slab. The right-angled hooks on each side of the coupling anchor into the slabs to provide the tie. The position of the hooks is not important, that is, they do not have to be turned down, up, or sideways.

The longitudinal joint between separately poured lanes may be sawed or formed. If formed, an insert 1-inch (25 mm) minimum in depth and tapered 3/8 inch (9.5 mm) at the top to 1/4 inch (6.5 mm) at the bottom must be inserted into the plastic concrete to form a void for the joint filler. The insert must be placed carefully against the existing concrete at the proper depth. When the concrete has set, the edge of the plastic concrete is rounded using an edger of the specified radius. The insert must be removed carefully at the proper time, and the groove should be tooled with an edger if necessary.

The hook bolt alternate (wiggle bolt) with a coupling may be mechanically inserted into the plastic concrete through a hole in the side-form of a slip form paving machine. When this is done, the contractor normally uses a plastic cap in the threaded end of the coupling to keep concrete out of the threads. This plastic cap is removed once the concrete is set and a hook bolt is installed in the coupling.

In lieu of hand forming, the concrete may be placed without an insert and then carefully edged using an edger having a 1/8-inch (3 mm) radius. This edging creates a line for sawing the groove later. The saw cut should have a minimum depth of 1/2 inch (13 mm) and a minimum width of approximately 1/4 inch (6 mm).

Longitudinal joints between separately placed lanes require extra care to assure that a smooth transition from one lane to the other will result. Good workmanship is necessary at these joints to obtain satisfactory results. Edging on both sides of these joints should be done using a 1/8 inch (3 mm) radius tool. Hand finishing and straightedging should be performed carefully so that each lane will be at the same elevation. As a guide the surface of the pavement in the joint area should not vary more that 1/8 inch (3 mm) from a 10-foot (3.0 meter) straightedge in both longitudinal and transverse directions.

Bent tiebars are not permitted in longitudinal construction joints.

When edging the longitudinal joint, an edger having a 1/8-inch (3 mm) radius is required as compared to a 1/2 inch (13 mm) radius edger required for the outside edge of pavements. Edging tools must be inspected to see that they have the edge radius required.

The slab should be edged as soon as the concrete becomes stiff enough to remain firm without running back into the groove. The edge should be cut first with a small trowel and then followed by the edger. The edging tool should be held flat with the pavement surface. A trowel should be used to remove the bead left by the edging tool. Since the final texturing is to follow edging, this operation must not be permitted to lag.

Load Transfer Devices (451.08.B)

Round, straight, smooth epoxy-coated steel dowels must be used in all transverse joints for load transfer across the joint. Exercise care in placing dowels parallel to the surface of the base and at mid-depth. The diameter of the dowel required in the pavement depends on the pavement thickness. The required dowel diameter is shown in Table 451.08-1 Dowel Size below (unless otherwise specified in the plan):

Thickness of Pavement (T)	Diameter of Steel Dowels
Less than 8 1/2 inches (215 mm)	1 inch (25 mm)
8 1/2 to 10 inches (215 to 255 mm)	1 1/4 inches (32 mm)
Over 10 inches (255 mm)	1 1/2 inches (38 mm) or as in the plans

Table 451.08-1 Dowel Size

For pavement lanes of even foot (0.3 m) width increments, dowels will be spaced at 12-inch (300 mm) centers beginning 6 inches (150 mm) from the longitudinal joint. Where other widths are specified, the spacing between the end dowel and the outside edge of the lane may be increased up to 12 inches (300 mm). A dowel must be placed 6 inches (150 mm) from the outer edge of the pavement when the spacing between the end dowel of the basket and the outside edge exceeds 12 inches (300 mm). Contraction joints are required to be spaced in the pavement at intervals not to exceed the maximum spacing indicated in the applicable standard construction drawing. The maximum spacing for reinforced concrete pavement (Item 451) is 21 feet (6.5 m) and for non-reinforced concrete pavement (Item 452) and concrete base (Item 305) the maximum spacing is 15 feet (4.6 m).

Contraction joints are necessary to control transverse cracking that occurs due to shrinkage and contraction as the concrete slab cures and hardens. Load transfer dowels are used to transfer loads across the transverse joints. Dowels are smooth, round steel bars, 18 inches (457 mm) in length, spaced at 12-inch (305 mm) intervals at mid-depth of the pavement slab in accordance with applicable standard construction drawings. All dowels used in concrete pavement are to be epoxy coated as per 709.13. The lateral surface of the dowel is to be epoxy coated. It is not necessary that the dowel end be epoxy coated.

To function properly dowels should be parallel to the surface and parallel to the centerline of the pavement since expansion and contraction movements occur in this direction. To assure proper alignment of dowels, a cage or basket is used. This, together with the dowels, is called a dowel basket assembly. Dowel basket assembly wires as well as the dowel are required to be epoxy coated according to 709.13 of the CMS.

Placing Dowel basket Assemblies

Dowel basket assemblies are to be positioned not to exceed the maximum spacing for the type of pavement specified and must be perpendicular to the centerline and forms. Spacing may be controlled by measurement along the forms. Locating the transverse alignment may be by any method that assures a right angle to the centerline. On curves, the joints should be approximately on radial lines.

After the alignment is established, stretch a string line between forms to assist in placing the dowel assemblies properly. Transverse contraction and expansion joints must be continuous across the full width of pavement placed. Therefore, the line of a joint in a lane already placed must be continued in all other adjoining lanes.

When properly located and placed, dowel basket assemblies are anchored in place with steel pins. At least eight 1/2-inch (13 mm) diameter steel pins 18 inches (460 mm) in length are required to hold each 12-foot (3.6 m) unit. The pins are driven at an angle to brace the assembly from lateral movement and to prevent vertical displacement when concrete is placed. Two of the pins are driven opposite each other at each end of the dowel assembly, and the remaining four are driven in a staggered pattern on each side. Take care to avoid hitting the assembly when driving the anchor pins. If wires of the basket are bent, the dowels may be thrown out of line and require the entire assembly to be rejected unless it can be removed, straightened, and reset properly. Any badly distorted assembly should be rejected. The epoxy coating must not be damaged during the above operation.

If concrete pavement is placed on an existing concrete pavement or stabilized base, the dowel baskets must be held firmly in position by use of power-driven fasteners and appropriate clips or pins driven in predrilled holes of a diameter slightly less than the pin diameter. The Contractor may use either of these methods or a combination of the two in sufficient numbers to adequately anchor the basket assembly. The method used must secure the dowel basket from lateral and vertical displacement during concrete placement.

If the dowel basket assembly is placed on a base consisting of sand, a minimum of 6 steel bearing plates approximately 5 inches (127 mm) square must be placed under each 12-foot (3.6 m) dowel assembly unit. Bearing plates also are required when any base material is used which permits distortion or settlement of the dowel assembly due to poor stability. One bearing plate is to be used with each of the four end anchor pins with the others spaced uniformly along the assembly. Shimming with pebbles, stones, etc. is not permitted. If shimming is necessary, it is obvious either that the base is not prepared properly or the dowel basket assembly is bent or misaligned. In either instance, the base or assembly must be rejected until corrective action has been completed.

Dowel Installing Machine

Specifications allow that dowels may be placed in the full thickness of the concrete pavement by a mechanical device (a dowel bar inserter) approved by the Engineer. If the Contractor contemplates this method of installation, special instruction should be requested from the Office of Construction Administration through the District Construction Engineer. This method of dowel placement has been used successfully in construction of non-reinforced concrete pavements. It is intended to permit this method provided the Contractor is able continuously to install dowels properly.

Loose dowels are placed on an installing rack of a self-propelled machine and installed by vibrating them into the plastic concrete. After the dowels are placed at mid-depth, the rack is withdrawn leaving the dowels in position supported by the concrete. The dowels are to be installed after the concrete is placed to its full depth and after the mesh is positioned properly. The only operations permitted after positioning the dowels are machine and hand finishing of the surface of the concrete.

Preventing Bond to Dowel Bars

For dowels to function properly in the concrete slab, they must be oiled with a thin coating of oil for at least one-half their length to prevent the concrete from bonding to them. Most of the dowel assemblies have one end of the dowel welded to the basket wire. The free end, opposite the welded end, must be oiled. Dowels must be oiled within 2 hours of placing the concrete around them. Exercise care to see that the free end of the dowel is oiled. It is always better to oil more than half the length of each dowel to be certain that bond is prevented so that the joint will function properly.

Epoxy coated dowels should be inspected to assure the coating is continuous on the lateral surface of the dowel and that the coating is not perforated, cracked, or otherwise damaged, in which case it must be rejected. In addition, the coating must be free from holes, voids, contamination, cracks, and there shall not be more than two holidays (pinholes not visually discernable) in any 12-inch (305 mm) length of the coated dowel. The free ends of the dowels must be free of burrs or projections.

Dowel Shipping and Spacer Wires

After dowel assemblies have been set and anchored properly, the shipping and spacer wires used to hold both halves of the dowel basket together during shipping and handling must be removed. The shipping wire is normally cut at two locations and removed immediately prior to placing the concrete. The shipping and spacer wires are usually a small diameter wire parallel to the dowels and hooked or tack welded to the basket assembly wire. Shipping wires run the same direction that the dowels do through the joint.

Checking Assemblies

After being set and anchored the dowels must be checked to assure that they are parallel to the base surface and the centerline of the pavement. Spot measurement checks of the distance between the dowel and the forms (made at each end of the dowel) provide a check for being parallel to centerline. The distance to each end of the dowel must be equal for the dowel to be parallel to the forms and the centerline. After some experience, this check can be a visual check since dowels out of alignment stand out when observing them in relation to the forms.

An adjustable A-frame level is used to spot-check several dowels in every assembly unit to assure that all dowels are parallel with the surface of the base. The level is first placed on the base adjacent to a basket assembly and adjusted to read level. Then the level is placed on the dowels. The bubble will indicate level if the dowel assembly is set properly and is parallel to the surface of the base. At least three dowels are to be checked in each 12-foot (3.6 m) section, one at each end and at the middle. If the dowels are not parallel with the surface when checked, the assembly must be adjusted and rechecked. If proper alignment cannot be obtained, the assembly must be removed and replaced.

Expansion Joints (451.08.C)

Relief for compression stresses in hot weather is provided at bridges and at intersections in the form of expansion joints. Non-extruding compressible material is placed in the transverse joint to relieve expansive forces. The first two regularly spaced joints in the concrete pavement adjacent to the approach slab must be expansion joints. Expansion joints may also be detailed in the plan at other locations. All expansion joints are dowelled and they allow the pavement to expand or grow due to temperature variations. A standard expansion joint allows for 1 inch (25 mm) of expansion.

If the pavement consists of two or more separately placed lanes, the expansion joints must be a continuous straight line for the full width of the concrete pavement, including concrete shoulders. All expansion joints are perpendicular to the centerline adjacent to a skewed approach slab.

Standard 18-inch (460 mm) long epoxy coated dowels are required for load transfer, in all expansion joints. The expansion joint also permits contraction movement in addition to absorbing excessive expansion. Proper size dowel holes must be punched or drilled into the preformed expansion joint filler in order to insure a tight fit when the dowel is pushed through it.

Preformed compressible material 1 inch (25 mm) thick is installed in a dowel assembly at the location of the expansion joint. It must be set perpendicular to the top of the expansion forms as well as perpendicular to the line of forms and the pavement centerline. The material must extend down to the top of the base and to the side forms to allow free movement throughout the entire joint. The top of the expansion material is held 1 inch (25 mm) below the surface. It is permissible to place the expansion material closer to the surface to facilitate sawing of this joint, provided all material is removed to a depth of 1 inch (25 mm). This area shall be sealed using a hot applied joint sealer meeting the requirements of 705.04.

An expansion cap is placed on the free end of each dowel to create a void in the concrete to permit expansion movement. This cap must be placed on the free end after the dowel has been oiled. The cap contains a crimp to position it to provide for the 1-inch (25 mm) void. These caps must not be forced beyond the crimp or there will not be space for expansion and the joint will not function correctly.

Inspectors must assure that the 1-inch (25 mm) thick expansion joint filler is held rigidly in position and extends full width of all lanes. The expansion joint filler must be the required height and must extend to the top of the base (or bottom of the new pavement) so that no concrete is permitted to flow under it. Holes in the expansion joint filler must be neatly punched or drilled, and the dowels must fit tightly through with no gaps in which concrete could flow. The free end of each dowel (the end not welded to the basket wire) must be oiled with a bond breaker and the expansion sleeve attached immediately prior to placing the concrete. The expansion sleeve is required to allow the dowel to slide a distance of 1 inch (25 mm) inside of it.

The Contractor must provide adequate consolidation throughout the slab depth adjacent to the joint filler and around dowels by use of hand-held internal vibrators.

Contraction Joints (451.08.D)

Contraction joints in pavements 10 inches (255 mm) thick or less must be sawed to a minimum of 1/4 of the pavement thickness and to a width shown in the standard, measured at the time of sawing. For pavement greater than 10 inches (255 mm) thick, the sawing depth required is 1/3 the slab thickness. .

The depth of 1/4 or 1/3 of the pavement thickness is the minimum necessary to control transverse cracking. Joints should be spot checked to make sure that the contractor is sawing the pavement the required depth.

Following this initial sawing the Contractor must saw to the width and depth detailed in the applicable standard construction drawing. This additional sawing is necessary to install the preformed elastomeric compression joint seal. Sawed joints should be cut through the pavement edge so that vertical cracking is assured and preformed compression seals can be installed easily all of the way to the outside edge of the pavement.

The width of the saw cut must be controlled to within tolerance to create a uniform width opening necessary for the installation of the joint filler. The filler is designed to function within the width specified, and any variation may affect its performance and create installation problems. The width of the saw cut must be 1/4-inch ± 1/16 inch measured at the time of sawing.

If the Contractor desires, sawing may be accomplished in two operations provided:

The first operation consists of sawing to the minimum depth specified using a 1/4 inch ± 1/16 inch (6 mm ± 1.6 mm) blade.
The second operation consists of sawing to the specified depth using a blade of a width within the specified tolerance. The second sawing should be performed when the temperature is 70° F (21° C) or above.

Sawed joints should be cut through the pavement edge so that vertical cracking is assured and the preformed compression seals can be installed easily.

This method provides relief when critical sawing conditions exist and provides a uniform width opening of desired width for installation of joint seal. Use of a narrow blade permits sawing earlier to avoid random cracking. Any raveled edges are dressed during the second sawing.

There are specifications on active projects to experiment on sawing the joints one time as thin of a width as possible and not sealing the joint created. This is only experimental, however, and not the standard.

If a crack appears ahead of the machine during pavement sawing, it is an indication that sawing is late. When such cracking is noted, stop sawing that joint immediately and move the saw ahead several joints. Saw a joint, move ahead several more joints, and saw another joint. Continue skipping three or four joints and sawing every fourth or fifth joint until sawing is back on schedule. The presence of slight raveling indicates proper timing of sawing. Saw every joint in order when sawing is back on schedule. After sawing has been completed for the day’s production the saw can be returned to saw the joints skipped. The standby saw may be pressed into service to saw the joints skipped if an experienced operator is available.

This procedure of skipping ahead and sawing every fourth or fifth joint relieves the stresses that occur when the concrete hardens and shrinks during curing. Once these stresses are relieved, the sawing of the in-between joints is not as critical but should be done as soon as possible.

The pavement is normally subjected to expansive forces the following day when the temperature rises. When temperatures drop during the evening of the following day, the pavement again experiences shrinkage stresses and all joints originally bypassed must be sawed before these stresses result in random cracking.

Pavement placed should be sawed the same day, usually six to eight hours after placing. Concrete placed late in the day may not harden to permit sawing until the next day, but sawing must be completed before the following late afternoon temperature change as shrinkage will again occur as temperatures drop.

Joints in lanes adjacent to previously-placed lanes that are tied together must be sawed as soon as possible to prevent uncontrolled cracking. If a new lane is tied to existing concrete that is expanding and contracting with changes in temperature, stresses will be transmitted to the new slab unless joints are sawed as quickly as possible. The following provisions are important to obtain quality sawed joints in these areas:

All transverse joints, except construction joints in the second lane of pavement, must be opposite and in-line with those in the first lane.
The joint sawing must be done as soon as the saw can be operated on the pavement without damaging the surface or without excessive raveling of the newly cut joint.
Joints opposite those in the first lane placed where cracking indicates movement , must be sawed first.
The cut is to be made from the old slab to the outside or open edge of the new slab being sawed.

A sudden drop in temperature, a wide range between day and night temperatures, or a cold rain creates additional problems when sawing contraction joints. These conditions add stresses due to thermal changes and shrinkage stresses, and make the timing of sawing doubly critical. When these conditions occur or are anticipated, give increased attention to the sawing operation to assure control of cracking.

Construction Joints (451.08.E)

Construction joints are transverse bulkheads placed at the conclusion of each day’s paving or when production is interrupted for more than 30 minutes. These joints are formed by using an adequate bulkhead that provides a straight joint. Construction joints in all concrete pavements are to be dowelled and perpendicular to the centerline. Construction joints may be located at a contraction joint or between contraction joints. The bulkhead must have openings provided for individual dowels or a dowel basket assembly. The bulkhead must be shaped to conform to the typical section of the pavement. Construction joints are to be sealed as detailed for the type of pavement specified.

Construction joints in reinforced concrete pavement (451) may be located at contraction or expansion joints in concrete pavement but must not be located closer than 10 feet (3.0 meter) to any other parallel joint. In non-reinforced concrete pavement (452) or concrete base (305), construction joints must not be closer than 6 feet (1.8 m) to another transverse joint.

At skewed joints between approach slabs and approach pavement, exercise care to position the dowels parallel to the centerline. Recent experience indicates movement occurs at such joints. Make provision for this movement by placing dowels the same as for contraction joints.

The joint may be hand-formed or sawed to the same dimensions required for transverse joints in adjoining pavement.

Smooth epoxy-coated dowels must be used in construction joints; take care to place them parallel to the surface of the base. The dowel size must be as required for the contraction joints in the adjoining pavement. For pavement lanes of even foot (0.3 m) width increments, dowels will be spaced at 12-inch (300 mm) centers beginning 6 inches (150 mm) from the longitudinal joint. Where other widths are specified, the spacing between the end dowel and the outside edge of the lane may be increased up to 12 inches (300 mm). A dowel must be placed 6 inches (150 mm) from the outer edge of the pavement when the spacing between the end dowel of the basket and the outside edge exceeds 12 inches (300 mm). Contraction joints must be spaced in the pavement at intervals not to exceed the maximum spacing indicated in the applicable standard construction drawing. The maximum spacing for reinforced concrete pavement (Item 451) is 21 feet (6.5 m) and for non-reinforced concrete pavement (Item 452) and concrete base (Item 305) the maximum spacing is 15 feet (4.6 m).

Finishing (451.09)

Diagonal pipe floats suspended from self-propelled machines have been used successfully to machine-finish slip form pavement without damage to the unformed edges. They are equipped with a water spray system that applies a fog spray of water. Such water should always be a fog spray and should be used only at the start of a finishing pass. With pipe floats it may not be necessary to hand straightedge the entire pavement surface. However, a straightedge should be used periodically to check the pavement surface.

Edging is done by an attachment to the machine or the trailing forms. With proper adjustment, such devices can satisfactorily apply the specified edge radius automatically.

Some machines trail several sections of forms while others have no trailing forms. When trailing forms are used, they provide protection to the edges while the surface is straightedged. However, straightedging should not be confined to the area of the trailing forms.

Equipment applying the transverse texture grooves and the membrane curing compound straddle the pavement the same as the paver and the pipe float. This equipment rides on the base or subgrade. Membrane machines are capable of covering the vertical faces, as well as the horizontal surface of the pavement, in one operation.

Final finishing is perhaps the most important step in the paving operation, at least from the public viewpoint, because it determines whether the final surface meets the necessary tolerance for a smooth riding surface. Projects using high-strength, quality concrete and the best of modern paving equipment often end up with substandard surfaces, simply because of careless work and lack of attention to details during final finishing.

The work of the hand finishers will be simplified if forms or string lines are set accurately. The finishing machines must also be adjusted and operated properly. If finishing machines are not operated properly, additional work is required for the hand finishers to correct surface irregularities and produce an acceptable surface that complies with the specifications. The preferred method is to keep the machines in proper adjustment. In any case, it is up to the Inspector to insist that the finishers produce a pavement with the required smoothness and an acceptable uniform final surface texture.

The Inspector should ensure that the finishers check their hand tools before paving operations begin to make sure that they comply with specifications. Straightedges should be tested with a string or a master straightedge to make sure they are straight. This should be done daily and tools trued to correct for wear. They must be rigid enough to remain straight with no bending while in use. Handles must be 3 feet (1 meter) longer than one half the width of the pavement. The straightedge itself must be 10 feet (3.0 meters) long.

After the mechanical finishing, while the concrete is still plastic, minor irregularities and surface marks should be removed with a scraping straightedge. When necessary, remove excess water and laitance from the surface transversely by means of a scraping straightedge. Any such excess should be wasted over the forms or removed from the pavement edge if slip forming..

A number of different types of straightedges have been used satisfactorily. They must be strong enough to maintain a true straightedge and yet light enough to handle. In some cases, they also must be heavy enough to cut or scrape off any high spots left by the machine finishing operations. They must be a minimum of 10 feet (3.0 meters) long to comply with the specifications.

The straightedge is operated from the side of the pavement transversely and should be advanced along the pavement in successive stages. By proper manipulation, it can be used as a float to smooth the surface or as a cutter to remove high spots. Long-handled floats may be used to smooth and fill in open textured areas in the surface, but this must be done before straightedge finishing. The use of such floats should be held to a minimum. If open textured areas persist, it is well to check the aggregate grading, mix design, and the method of placing the concrete. A properly proportioned mix should not require hand floating if the mechanical equipment is properly adjusted.

No water is to be added to the surface during this or any other operation.

Texturing

The final surface texture should be applied when most of the water sheen has disappeared but before concrete becomes non-plastic. Surface textures for concrete pavement vary with the type of construction. Finishing methods used must produce the texture as described in the appropriate specification item.

Unless otherwise specified in the plans, exposed concrete pavement (451 and 452) must be textured by the use of a broom drag in the longitudinal or transverse direction immediately followed by an approved device which produces a random pattern of grooves in the transverse direction. The broom drag must produce a uniform, gritty texture. Brooms suspended from a machine or truss and dragged over the pavement surface have provided satisfactory longitudinal texture. The broom should be lifted clear of the surface when not being used.

Concrete base pavement (Item 305) must have a final surface finish that is a uniform, gritty texture as obtained with a broom drag in the longitudinal or transverse direction. No grooves are put in base pavement because it is normally covered with asphalt concrete prior to opening it to traffic.

Broom drag is used in the longitudinal or transverse direction to provide a more skid resistant pavement. The Department has found that new concrete pavement would lose skid resistance after one year of service with merely a light burlap drag prior to tine grooving. Broom dragging roughens the area of concrete between grooves that results in a longer lasting skid resistance.

The contractor must put random-spaced transverse grooves in the plastic concrete immediately after the broom finishing application. The grooves must be spaced in a random pattern spaced at 3/8 to 1 3/4 inches (10 to 45 mm), with 50 percent of the spacings less than 1 inch (25 mm). All grooves must be 0.15 inch (4 mm) deep and 0.10 inch (3 mm) wide. The use of a wire tine rake for the transverse texture grooving can impart the desired groove depth.

Station Numbers

The Contractor is required by specifications to stencil station numbers into exposed concrete pavement (Item 451 and 452) each 100 feet (50 meters). The dies used to form the station numbers must be 3 to 4 inches (75 to 100 mm) high and ¼ inch (6 mm) in depth. The numbers are placed parallel to the pavement edge and centered 12 inches (0.30 m) from and facing right edge of the pavement in the direction of travel. The numbers should be impressed into the plastic concrete following the texturing of the surface and before curing is applied. If the impression is made too early, the number will tend to close up and not be as distinct as desired. The following information applies to stenciling numbers in a dual lane divided highway pavement project.

The right edge of a pavement is that edge to the observer’s right as he stands on the pavement at the low station and faces toward the high station. The station numbers in the right pavement of a dual pavement project are then impressed in the pavement that they may be read from a car traveling on the paved shoulder from the low station towards the high station or in the normal direction of traffic.

Station numbers also must be stenciled in the left pavement. However, if the same pattern of marking stations is followed on the left pavement of a dual-lane divided highway pavement project, the numbers would be on the pavement edge next to the median. Therefore, for the purpose of stenciling station numbers in the left pavement of a dual-lane divided highway pavement project, the right edge of the pavement shall be considered to be the edge on the right of an observer as he looks from the high station on the project towards the low station. The station numbers then may be read easily from a car traveling on the paved shoulder in the same direction as the regular traffic.

Stations from 0 to 9 should include “ + 00” (“+000”) after the digit, e.g. 1+00 (2+050). From station 10 on, the “+ 00” (“+000”) is not necessary.

If concrete shoulders are placed with a traveled lane, the station numbers should be placed 12 inches (0.3 m) in from the outside edge of the shoulder and facing the pavement.

Station numbers are not required on concrete base (Item 305).

Concrete Curing (451.10)

Curing is the treatment or protection given to concrete during the hardening period. Proper curing consists of keeping the concrete moist and warm to insure adequate hydration of the cement. Curing protects concrete from early shrinkage due to changes in temperature and/or loss of moisture before it has developed sufficient strength to resist the resulting tensile stresses.

It is extremely important to provide adequate curing during the first few days, with the first few hours being most important to obtain a strong durable surface. Strength loss due to lack of moisture during this period is difficult to regain even with subsequent curing.

Any one of the several permitted curing methods give satisfactory results if performed correctly. One method may be used throughout the entire curing period, or it may be considered better to use a combination of two methods, initial and final.

Prior to spraying membrane forming curing compounds, assure that the material has been thoroughly agitated.

Curing should begin as soon as the texturing process is completed, providing that the finished surface does not have free water on the surface. For concrete pavement, normally a membrane-forming liquid curing compound is sprayed uniformly on the exposed surfaces of the concrete pavement. This process is normally done by a curing machine that is also capable of grooving (texturing) the pavement. Specifications require a self-propelled mechanical sprayer with shields to protect the spray from the effects of wind. Liquid membrane curing compound is the most popular method of curing. Liquid membrane curing compounds specified are white in color so that coverage can be observed. They are sprayed over the exposed concrete faces while the concrete is still plastic. Hand operated sprays are used on sections of variable width and on the pavement edges after form removal.

The white pigment used in the membrane acts as an abrasive that tends to enlarge the apertures of the spray nozzles and to reduce the efficiency of pumping equipment. Equipment used to apply membrane should be cleaned frequently and checked to see that it is providing a uniform protective covering.

During windy, hot, dry weather, it is very important that finishing is completed rapidly and the curing be placed before the surface dries out to the extent that plastic shrinkage cracks develop. These cracks can never be sealed, and they are an indication that the surface may have been depleted of the necessary water to properly complete the chemical reaction of cement hydration. Water curing may halt this shrinkage cracking, but even the addition of more water will not correct the cracking once it occurs.

In cold weather, the concrete may continue to bleed after finishing. Take care in placing any type of curing under these conditions so that the surface will not be marked. The minimum period for curing is 7 days, unless specimen beams have attained a beam strength of 600 psi (4.2 Mpa). If beams obtain 600 psi (4.2 Mpa), five days is the minimum cure time. During cold weather, concreting the pavement must be protected from freezing temperatures until beams attain a strength of 600 psi (4.2 Mpa).

Prior to application, inspect the curing material to ensure that it meets specification requirements. This also applies to any equipment used in the application.

Membrane materials must meet specification requirements and be applied at the minimum rate of one gallon per 150 square feet (1 liter per 3.7 square meters) for Items 451 and 452. Concrete base (Item 305) shall be treated at the minimum rate of 1 gallon per 200 square feet (1 liter per 4.9 square meters). Exposed concrete with a grooved (tined) surface requires more curing compound than base concrete due to the additional surface area caused by the grooves as opposed to only broom drag finish on the base pavement.

If properly applied, these membrane-forming compounds prevent evaporation and the retained water provides excellent curing. Therefore, make sure that the specified rate of application is adhered to and that the curing compound is applied evenly. This ensures that a uniform thickness of membrane coating is obtained. If this is not done, the quality of concrete will be affected.

White pigmented compound is the only membrane acceptable on paving projects. This has an advantage over clear type compounds in summer construction in that it provides a coating that reflects heat from the surface. This decreases heat absorption in the pavement and the tendency for transverse cracks to develop during warmer afternoon temperatures. In addition, its white color permits visual inspection for uniform coverage.

Water curing

The contractor may choose to water cure by placing wet burlap on the exposed surfaces followed by waterproof paper or polyethylene sheeting. Make sure that the pavement is wet at all times. This type of curing requires constant checking throughout the curing period. This method is not used very frequently and therefore is not discussed in detail.

Curing with Paper or Polyethylene Sheeting

This method uses waterproof paper or polyethylene meeting specification requirements (705.05 and 705.06). These materials are placed on the concrete as soon as possible after finishing without marring the surface and are left in place for the full curing period.

The advantage of this curing method is that no sprinkling or other attention is necessary after placing, except to make sure that it is anchored against blowing off by wind and that holes or torn areas do not occur. The blankets should be inspected daily during use. Before being reused, small holes or breaks should be repaired.

The blankets should be placed to cover the full lane width and lapped at least 12 inches (0.3 m). Edges should be completely covered when forms are removed. This may be done by turning down the edge of the blankets or narrow strips pulled out from under them. These narrow strips are placed on the concrete before main sheets are laid.

These blankets should never be dragged over fresh concrete and should be placed so as not to mar the surface. One of the principal precautions in this curing method is to make sure edges along forms are sealed so that there is no possibility of air getting under the curing material. This is important because air can circulate over the pavement unless the seal is adequate. This will dry out the surface and result in inadequate curing. In addition, heavy winds will get under the blankets and rip them off leaving the pavement without any curing at all.

Membrane Curing

Curing compounds, especially pigmented ones, tend to separate during storage. The material must be stirred thoroughly prior to application in order to obtain a uniform product, and to avoid waste by leaving heavier fractions of the compound in the drums. Drums are equipped with internal paddles for stirring the material to mix the pigmented compound. A crank is attached externally to a shaft on one end of the drum to engage the paddles. Drums of curing compound stored for any length of time should be placed in storage upside-down so that more thorough mixing will result when they are reversed prior to use.

Accurate timing of application is most important. Membrane should never be sprayed on a surface until all free water has evaporated and the concrete has lost its sheen. If membrane is placed on free water, it tends to float with the result that when the water disappears the membrane will craze or crack and peel from the surface. Whenever the texture of the surface is marred by the application, the concrete either is too wet to too green, and the application should be delayed until the membrane can be applied without disturbing the textured finish.

Any membrane disturbed by foot traffic, or sawing equipment during pavement sawing, or by any other cause must be corrected immediately by making a second application of the curing compound with a hand sprayer over the areas.

At the close of paving each day, check the number of gallons of membrane curing compound used. This quantity should be checked against the square feet (square meters) of pavement placed to assure that minimum application is achieved. This check should be documented in the project records.

Removing Forms (451.11)

The presence of forms during the early curing protects the pavement edges against damage and serves as a curing method for the pavement edges.

During warm weather, the common procedure is to remove the forms approximately 24 hours after the concrete is placed. During cold weather, it may be advisable to leave forms in place for a longer period. In any event, forms should not be removed until the concrete has attained sufficient strength to prevent damage to the concrete surface or breaking of the edges during removal.

The method used to remove the forms should not damage the concrete pavement. In addition, the Contractor should be encouraged to use a method that will not bend or otherwise damage the forms. The method used to move forms away from concrete should ensure that each form section is pulled horizontally away from the edge before it is lifted.

Pin keys should first be loosened, form joint locks unfastened, and nuts removed from the ends of hook bolts (single lane paving). Then, pins should be removed from their sockets using a direct vertical lift without any pressure toward the concrete. The action necessary to exert the vertical lift should be from the forms or the ground outside forms. If any equipment is used to pull pins that may ride on the concrete, make sure that no pressure is on the concrete other than the weight of the equipment.

After pins are removed and other preliminary work finished, light blows with a hammer or careful prying on base flanges may be used to separate forms from concrete. Prying against the concrete edges with bars to break forms loose should never be permitted.

When forms have been removed, edges should be checked immediately and honeycomb areas filled. Mortar should be used to fill all honeycomb areas. Inspect filled areas to make sure the entire areas are tightly packed and struck off flush with surface of the pavement edge.

Curing should be applied to edges just as soon as forms have been removed and edge patching has been completed. This assures satisfactory curing as well as preventing the loss of water necessary for hydration of the cement.

Surface Smoothness (451.12)

The Contractor cleans and tests the completed pavement surface for smoothness by means of a surface-testing device. This device can be a two- or four-wheeled 10-foot rolling straightedge with an indicator wheel in the center that detects high and low areas in the pavement surface. This equipment must alert the operator when encountering any high or low areas of pavement in excess of a preset tolerance. This alert may be by a pointer scale, by audio, or by marking the pavement surface with dye or paint.

Testing is done after the final curing of the pavement to detect any surface variations that are in excess of the allowable tolerances. For pavements, the tolerance is 1/8 inch in 10 feet (3 mm in 3.0 m)). For ramp pavements and for those pavements that exceed the 8-degree curvature or 6-percent grade, the tolerance is 1/4 inch in 10 feet (6 mm in 3.0 m).

The Contractor must tow or walk the equipment over the completed pavement. The Contractor must test two lines, one in each wheel path, in each 12-foot (3.6 meter) lane. The wheel paths are located 3 feet (1 m) measured transversely from the pavement edge on each side.

Profilograph Testing

Larger concrete paving contracts (those exceeding 1 mile in centerline length) include a proposal note entitled Surface Smoothness Requirements For 451 and 452. This specification requires the testing of the surface of completed pavement with a California Profilograph or other non-contact equipment that will produce a California Profilograph trace.

The contractor is paid a bonus for exceptionally smooth concrete pavement. There are deductions if the pavement is not constructed smooth enough. The pavement must be of a certain level of smoothness to be accepted.

Profile Grinding (451.13)

Surface variations indicated by the 10-foot rolling straightedge must be ground off to within tolerance with equipment conforming to 451.13. This section requires the use of diamond grinders. Bush hammering, carbide tipped grinders, or any method that may damage the bond of the aggregate or shatter the aggregate is not permitted. After diamond grinding, transverse grooving with diamond grooving equipment must leave the final surface with transverse grooves in conformance with 451.09. Grooving equipment must comply with 451.14.

A 10-foot (3.0 meter) straightedge must be used to check for compliance when corrective work is in progress. The straightedge can also be used to determine the transverse limits of the area to be corrected. Usually variations extend beyond the wheel path and may require diamond grinding and grooving the entire lane width. This determination can only be made by checking with a straightedge.

Low areas should be corrected by grinding on each side until within tolerance. If these areas cannot be corrected by grinding, they must be repaired or replaced to the satisfaction of the Engineer.

Pavement Grooving (451.14)

It may be necessary to put transverse grooves in concrete pavement after the concrete has hardened. This is required after corrective grinding to remove bumps in the pavement surface. This corrective grinding using a profile grinder, described above, leaves a corduroy texture in the longitudinal direction. The randomly spaced transverse grooves described in 451.09 must be restored on the surface of the areas after they are profile ground.

The equipment required for transverse grooving must be self-propelled, power driven machines specifically designed to groove hardened concrete pavement with diamond impregnated blades or diamond impregnated cylinder rings. The blades or cylinder rings must be mounted on an arbor head so that the resulting grooves are randomly spaced. The grooving equipment must have a depth control device that detects variations in the surface and adjusts the cutting head to maintain the proper groove depth.

Sealing Joints (451.15)

Transverse and longitudinal joints are sealed to prevent infiltration of incompressible material. Sealing also limits entrance of surface water to the base. Pavements contract or shrink when temperatures drop, thereby causing joints to open. When temperatures rise, pavements expand and joints close. The presence of incompressible material in an unsealed joint prevents the joint from closing during expansion and subjects the concrete to compressive stresses. Proper sealing prevents intrusion and permits joints to perform as intended during movement of the pavement slab.

Sealing should be done as soon as is feasible after joints are sawed. All joints must be sealed before the pavement is opened to traffic. The Engineer may approve, upon request, placing a temporary material to protect the joint opening during use by construction traffic. This temporary material can be an oversized closed cell backer rod or similar material installed in the sawed joint.

All joints must be cleaned prior to filling. Cleaning consists of operating a saw blade backward through the saw groove to remove all pebbles, trash, dirt, etc. Any other operation which satisfactorily cleans the groove is permissible. The final step in cleaning consists of blowing out the joint opening using compressed air or by a jet of clean water.

Expansion joints must be clean for the full width of the expansion material, and the top of the expansion material must show over its entire area. The presence of any concrete around the expansion material will prevent free compression of the joint material and may cause spalling along the joint when the pavement expands.

Preformed compression joint seals are required in transverse contraction and construction joints in 451 pavements and 452 pavements. Seals should be checked to assure they meet specification requirements (705.11) and are the width specified in the standard drawing. Installing equipment should be inspected to make sure it is in good working condition and is capable of installing the size of sealer specified. Contraction joints in concrete bases are sealed with a hot applied material meeting the requirements of 705.04.

Hot-applied joint sealer (705.04) or preformed compression joint seals (705.11) may be used for sealing longitudinal joints in non-reinforced or reinforced pavement. Since the hot applied sealer requires heating, frequent checks should be made to avoid overheating to a temperature higher than the manufacturer’s recommendation. Check samples must be taken daily but should not be taken after a long period of heating. These samples are sent to the Laboratory.

Longitudinal joints in Item 305, concrete base do not require sealing. Contraction joints in Item 305 are to be sealed with hot applied joint sealer (705.04).

Joint walls must be inspected just ahead of filling to make sure that they are dry and thoroughly clean. It is essential that the walls be in this condition if the sealer is to function properly. If the sealer fails to adhere to the concrete, water and foreign material will filter into the joint.

Pour liquid sealing compounds in such a manner that complete filling from the bottom of the joint slot to approximately level with the surface of the pavement is assured. With some compounds it may be necessary to fill the joint in several applications. Workers should not allow the sealing compound to spatter or drip onto the adjacent pavement.

The sealing material will run to the low side if the joint is filled too fast. Hot poured compounds may flow out of the joint at the edge of the pavement if some method of plugging the edge is not used. A satisfactory plug can be provided by any one of the following methods:

A ball of mud pressed over the end of the joint.
A small piece of roving jute pressed vertically into the joint end, flush with the face of the pavement edge.
A small piece of masking tape placed over the end of joint.

As the temperatures increase, the pavement will expand or lengthen and the joints will close. Conversely, the slabs contract as the temperature falls, causing the joints to open. Joint filling should be such that the surface of the hot-applied sealing material will be approximately level with the pavement surface when the pavement temperature is about 70° F (21° C).

Never over-fill a joint to the extent that a bump will be produced at the joint. Such a practice is a waste of material, creates an unsightly condition, and affects the riding quality of the finished pavement. The bumps created by the excessive material will be readily noticeable to the traveling public from a smoothness standpoint, as vehicles pass over each joint.

When placing preformed compression seals in contraction and construction joints, seals should be installed by machine or by hand methods in such a manner to avoid excessively stretching the seal. A maximum elongation of 5 percent should be enforced during installation. If hand methods are used, seals that are nicked or cut should be removed and replaced. An approved lubricant adhesive should be used to aid in placing the compressed seals into the joint opening. The seals should be placed so that they are approximately 1/4 inch (6 mm) below the level of the pavement surface.

Prior to final acceptance of the pavement any unsatisfactory seal should be removed and replaced. All low spots in sealing compounds must be brought to the desired level, and any high spots should be cut off and the excess material removed.

Opening to Traffic (451.16)

Concrete test beams are required for each 7,500 square yards (6,500 square meters), or fraction thereof, of pavement placed each day. Instruction for making and testing beams are found in Item 499. Beams are tested at the project by the project personnel.

The completed pavement may be opened to traffic, including construction traffic, after 7 days have elapsed. The pavement may be opened to traffic after 5 days provided a beam strength of 600 pounds per square inch (4.2 Mpa) is attained. If it is determined that it will be necessary to open a portion of the pavement in fewer than 5 days, high early strength concrete shall be used, and the pavement may be opened to traffic after 3 days provided the test beams attain a strength of 600 pounds per square inch (4.2 Mpa). In no case should concrete pavement be opened in less than 3 days.

Beams normally are tested at 5 and 7 days. If results are not needed before the end of 7 days, only one beam break is necessary. This break should be made at the age of 7 days.

The maximum capacity of the beam breaker is 1,000 pounds per square inch (6.7 Mpa) and is marked on the beam breaker dial. The capacity must not be exceeded. Beams that do not break when loaded to the capacity of the breaker should be recorded as >1,000 psi (>6.7 Mpa) or whatever the unbroken strength was when the test was stopped, such as 850 psi + (5.9 MPa +) for example.

A slump, air, and yield test shall be made each time beams are cast. Concrete for these tests shall be obtained from the same batch of concrete as that used in casting the beams.

Pavement Thickness (451.17)

The Contractor will remove cores from the completed pavement to check the pavement thickness in accordance with 451.17 of the specifications. The entire pavement area of a specified thickness is considered a unit for coring purposes. A core is taken at random for every 2,000 square yards (1,650 square meters) of a pavement unit. The Engineer determines locations for random cores according to Supplement 1064. Cores must be measured by the Engineer in accordance with AASHTO T 148. The Contractor must take extra cores as directed by the Engineer.

The pavement is to be constructed such that the thickness is not more than ½ inch (13 mm) less than the specified thickness at any location. Random cores are taken every 2,000 square yards (1,650 square meters) and additional cores must be taken if a core is measured and found to be more than ½ inch (13 mm) deficient from the specified thickness. The additional cores are taken to isolate the area of deficient pavement. A core is taken 5 feet (1.5 m) measured longitudinally on each side of the deficient core. If both of these cores are not deficient in thickness by more than ½ inch (13 mm) do not cut any more cores to isolate the deficient area. In this case the deficient area of pavement will 10 feet long by the width placed.

If either or both of the above additional cores are more than ½ inch (13 mm) deficient from the specified thickness, establish the longitudinal boundaries by cutting additional cores 50 and then 100 feet (15 and 30 m) longitudinally from the location of the first deficient core. If thickness deficiencies greater than ½ inch (13 mm) are found, take additional cores at 100 foot intervals longitudinally until the pavement thickness is within the ½ inch (13 mm) tolerance in both directions or until the end of the pavement is reached.

If the width of the pavement placed consists of two or more lanes and a core from the center of one lane is more than ½ inch (13 mm) deficient, cut additional cores in the center of the adjacent lane or lanes to isolate the deficient area laterally (transverse to the centerline) from the first core. If the transverse core or cores are within the ½ inch (13 mm) tolerance, limit the area of deficient pavement to the lane or lanes found to have deficient thickness. If any of the transverse cores is outside the tolerance, include all lanes that were deficient in the area calculation. Determine the longitudinal boundaries for each deficient lane according to the above.

The project average thickness of each pay item must be 0.2 inch (5 mm) or less than the specified thickness. Any core measurement more than ½ inch (13 mm) greater than the specified thickness will be considered the specified thickness plus ½ inch when determining the project average thickness. The average thickness is the mean thickness in inches (millimeters) of cores taken from the pavement. If there are total deduction areas, use the mean of the two cores limiting the area of the deficient pavement in the average calculation instead of the original cores in the zone. The other cores within the zone of deficiency are not used to compute the project average.

The Contractor must fill all core holes using the same concrete used in constructing the pavement. When filling the core hole, the surface should be damp and should be painted with a grout consisting of cement and water having the consistency of a thick paint. Stiff concrete should then be rodded into the core hole before the grout dries. The surface should be struck off, and curing membrane applied to provide curing essential for a durable repair.

If thickness measurements indicate a deficiency resulting in a price adjustment, the Engineer will adjust the payment to the Contractor. The contractor will receive 100 percent pay if the project average thickness is deficient 0.0 to 0.2 inch (0.0 to 5 mm) from the specified thickness. There will be no payment for pavement when the average thickness is deficient by more than ½ inch (13 mm). If the thickness is deficient by more than ½ inch (13 mm), and the Engineer decides not to remove and replace the pavement, there will be no pay for the area retained.

If the project average thickness is 0.3 to 0.5 inch (6 mm to 13 mm), use Equation 451.1 to determine a ratio of the contract price to pay the contractor:

Equation 451.1– Contract Price Ratio

Example

If the project average thickness is 9.7 inches and specified pavement thickness is 10 inches, what is the proportional part of the bid price to be paid is?

Pavement thickness checks

In order to ensure that the specified thickness of pavement is being constructed, the Engineer should periodically check the depth as follows:

Place metal plates, approximately 5 to 6 inches (125 to 150 mm) square, on the base. These should be in line and spaced at about 4-foot (1.2 meters) intervals between the forms or area of pavement being placed. Sufficient references must be made so that the plates may be located after the concrete is placed. After the concrete at plate locations is in place and the final mechanical equipment passes over it, a small rod, such as a staking pin, is worked down through the concrete at plate locations until it touches the metal plate. The surface of the concrete is marked on the rod and the rod withdrawn and the depth measured.

Whenever the pavement is found to be deficient in thickness all operations and equipment should be checked immediately and corrected where necessary, so that the proper slab thickness will be obtained.

Method of Measurement (451.18)

Concrete pavement is measured by the number of square yards (square meters) completed and accepted in place. The width of pavement used to calculate the area equals the pavement width shown in the typical sections of the plans plus any widening the Engineer directs in writing. The Engineer will measure the length along each centerline of each roadway or ramp.

Irregular areas of pavement should be field measured and the area calculated in square yards (square meters) for payment.

Any plan changes that involves concrete pavement quantities must be shown on the form used to document the final pay quantity. In addition, any areas found to be deficient in thickness must be indicated on the form and adjustment made in the pay quantity.

Basis of Payment (451.19)

Payment for 452 is made for accepted quantities of pavement by the square yard (square meter) area at the contract bid price. If pavement is found to be deficient in thickness, the Department will pay a reduced price according to 451.17.

There is no additional payment for any pavement constructed and found to have an average thickness in excess of the thickness specified.

Running Yield Check

The running yield may be determined at any time during concrete paving and can provide an easy, accurate method of checking that the proper thickness is being placed. Any time that a constant width and thickness is placed a running yield factor in cubic yards per foot (cubic meters per meter) can be calculated. This factor is determined by calculating the amount of concrete required for one foot (one meter) of finished pavement of the width and depth being placed. This factor is computed by using Equations 451.2 and 451.3:

Equation 451.2 – Yield Factor

Equation 451.3 – Yield Factor (metric)

Example

A contractor is placing a 24-foot wide slab that is 9 inches thick. Determine the yield factor for this cross-section. Using Equation 451.2 the following calculation results:

A contractor is placing a 7.2 meter wide slab that is 255 mm thick. Determine the yield factor for the paving operation. Using Equation 451.3 the following calculation would result:

Once this running yield factor has been calculated, it can be used to determine the concrete volume required for any length of slab of the same dimensions. This running yield is determined by multiplying the running yield factor by the length placed as shown in Equation 451.4.

Equation 451.4 - Running Yield

The actual quantity used is easily computed for any length of slab by multiplying the number of batches placed by the number of cubic yards (cubic meters) per batch.

Example

Assume 4,245 linear feet of the above 9-inch thick by 24-foot wide pavement was placed and 360, 8-cubic yard truckloads were used. Calculate the running yield. Determine the volume used. Compare the volume used to the volume required and show which is greater. Determine the difference in volume and the percent over-run or under-run.

Running Yield = (2/3 yd ³ per linear ft) (4,245 linear feet)

= 2,830 yd ³ (required volume)

Volume Used= (360 batches) (8 yd ³ per truck) = 2,880 yd ³ (volume used)

2,880 yd ³ (volume used) > 2,830 yd ³ (volume required)

2,880 yd ³ - 2,830 yd ³ = + 50 yd ³ difference

(50 yd ³ ÷ 2,830 yd ³) x 100 % = 1.77% overrun

Assume that a 1,293-meter length of the above 255 mm thick by 7.2 m wide pavement was placed and 345, 7-cubic meter truck loads were used. Calculate the running yield. Determine the volume used. Compare the volume used to the volume required and show which is greater. Determine the difference and the percent over-run or under-run.

Running Yield = (1.84 m³/m) (1,293 m) x = 2,379 m³ (volume required)

Volume Used= (345 batches) (7 m³/truck) = 2,415 m³ (volume used)

2,415 m³ (volume used) > 2,379 m³ (required volume)

2,415 m³ - 2,379 m³ = + 36 m³ difference

(36 m³ ÷ 2,379 m³) x 100% = 1.51 percent overrun

The quantity used may be from 1 to 3 percent greater than that required, generally due to wasting over the forms, spillage, etc. Whenever this relationship does not occur, immediate steps should be taken to find the cause. Overruns may be caused by several factors, including inaccurate weighing, low base, excessive waste, etc. Similarly, an under run in concrete may be due to inaccurate weighing, high base, loss of crown, insufficient width, thickness of slab, settlement of forms, etc.

Checking Pavement Cross-section

Where concrete pavement is placed in a single lane, the pavement slopes from the low edge to the high edge at 0.016 cross slope and can be readily checked for proper slope with a 4-foot level. Checks should be made frequently to insure that the final pavement surface is as required.

Transverse smoothness should be checked with a 10-foot straightedge or stringline to assure compliance with specified tolerances. Pavement surface variations must not exceed 1/8-inch in 10-foot (3 mm in 3 m) length of pavement. Ramp pavements, any pavements with curvatures greater than 8 %, and pavements on grades exceeding 6 % surface variations must not exceed 1/4-inch in 10-foot (6mm in a 3-m) length of pavement.

The pavement cross slope is shown in the typical sections of the plans. Some normal cross slope arrangements are shown in Figure 451.A.

Figure 451.A - Checking Crown

If the Contractor elects to finish the two lanes of pavement with a center crown in one operation, as when placing 24-foot (7.2 m) pavement, the center 6 feet (1.8 m) of pavement is rounded. If slip form paving is used, the rounding is optional.

A crown check should always be made at the start of paving operations to determine that all equipment is properly set and functioning as it should. Whenever deviations from the specified crown are found, take immediate steps to correct the situation. Checking crown and adjusting equipment and operations should continue until the proper crown is obtained. Make a daily check of crown throughout construction to determine that changes in equipment or procedure, which might affect the crown, have not occurred.

When a 24-foot pavement is constructed with a center crown with a cross slope of 0.016 (3/16-inch per foot) on each side, a straightedge cannot be used to check the final crown. The crown can be readily checked using two 3-inch (76 mm) wood or steel blocks on top of the forms (or on top of the outside corners of the slab) with a piano wire stretched tightly across. The following describes how to check the crown by measuring down from the piano wire.

Calculate, at 2-foot (0.6 meter) intervals, the height that pavement surface should be above a straight line connecting the tops of the forms. For example, in a 24-foot (7.2 meter) pavement with the high point in the center of the slab, these heights are:

Distance from Center		Height above Straight Line
feet	(meters)	inches	(millimeters)
12	(3.6)	0	(0)
10	(3.0)	3/8	(10)
8	(2.4)	3/4	(19)
6	(1.8)	1 1/8	(29)
4	(1.2)	1 9/16	(38)
2	(0.6)	1 15/16	(48)
0	(0.0)	2 5/16	(58)

Subtract the values determined in (1) to establish the distance the pavement surface should be below the piano wire line 3 inches (76 mm) above and parallel to the line connecting the tops of the forms. In the example given above these values will be:

Distance from Center		Height above Straight Line
feet	(meters)	inches	(millimeters)
12	(3.6)	3	(76)
10	(3.0)	2 5/8	(66)
8	(2.4)	2 1/4	(57)
6	(1.8)	1 7/8	(47)
4	(1.2)	1 7/16	(38)
2	(0.6)	1 1/16	(28)
0	(0.0)	11/16	(18)

Set the blocks on the cleaned forms (or on top of the outside corners of the slab) and stretch the wire across the slab. Then measure the distance the surface of the slab is below the wire. The measured distance should closely match those calculated in (2) in order to comply with the specified cross-slope.

Hot Weather Construction

Specifications do not cover the necessary precautions for placing concrete during hot weather. However, when high air temperatures, low humidity, and winds are encountered during concreting operations, make adjustments to assure quality. Any one of these factors speeds up the rate at which concrete hardens. High temperatures, especially when accompanied by wind and low humidity, tend to cause a rapid loss of moisture from the surface of the pavement resulting in early setting and a reduction in time allowed for finishing.

In order to counteract the adverse effects of hot weather, it is necessary to control the temperature of the concrete mix. Lowering the concrete temperature to 75° F (24° C) or below will offset the effects of hot weather. Selection of a cool water supply is the most effective means of lowering the mix temperature. Sprinkling of coarse aggregate stockpiles for moisture control also aids in controlling the mix temperature.

It is a good practice when form paving, to maintain the slump of the concrete near the top limit during hot weather. Increasing the slump will delay the stiffening, thereby making more time available for the finishing operations. Make sure that any additional water added at the job site is thoroughly blended into the mix to provide workability.

Using water on the surface during finishing results in an increase in the water-cement ratio and washes out the entrained air in the concrete at the surface. Both of these changes adversely affect the durability at the surface. The use of the whitewash brush has probably been the cause of the majority of scaling occurring in concrete surfaces. Therefore, the use of water on the surface during finishing must not be tolerated.

Under extreme drying conditions, mixing water may evaporate quickly from the surface of the concrete. This water may be restored by applying a fog spray of water on the surface, provided the surface has been completely finished and will not be screeded or straightedged. This provision should be controlled carefully and should be the exception rather than the rule.

Use of an approved set retarding type admixture may be desirable in hot weather to retard the setting time thereby providing more time for finishing. Project personnel must be aware that a water-reducing retarding admixture (705.12, Type D) is required in the concrete (for any concrete usage) if the concrete temperature exceeds 75° F (24° C). The use of this admixture will result in less slump loss and result in high strength concrete. Admixtures for accelerating the set will be permitted only when provided for in the contract or upon the written permission of the Director.

Protection from Rain

If the pavement is protected from rain, much time and expenditure in corrective work can be avoided. A roll of polyethylene sheeting on the finishing machine or the curing machine can be quickly unrolled to protect large areas of pavement and thus avoid corrective measures. When the concrete has not been protected and has been damaged by rain, increased attention to corrective measures will be necessary to obtain durable concrete.

Concrete that has been exposed to rain will have some mortar or paste washed from the surface. The surface usually has a sandy appearance when the cement paste is removed. In addition, it will have a speckled or spattered appearance. Quality can be restored to the surface by several methods.

If the surface has not been machine finished, it should be screeded with the machine. This screeding will eliminate the sandy texture and force grout to the surface. For a surface which has been machine finished, the machine may be used to make a single pass over the area affected, or the surface may be dragged with the burlap to remove the sand and work grout to the surface. A broom drag may have to be used for several passes to restore the surface finish.

Pavement that has been damaged by heavy rain should be reworked with the finishing machine, if the concrete has not taken its initial set. If it has, the broom drag alone should be used repeatedly until the surface has been corrected.

When correcting damage to newly placed concrete surfaces, the excess surface water must first be removed; it definitely should not be worked into the concrete. Cement should not be placed on the surface in an attempt to restore cement paste washed away by the rain . Such a practice is detrimental to the concrete rather than helpful.

When a rain persists for a lengthy period, it will be necessary to remove any protective covering to finish and texture the concrete before it stiffens and sets. The concrete may be recovered after this has been accomplished. Membrane curing should not be applied when the surface is wet and may be delayed until paving is resumed. If polyethylene sheeting is used as a covering, curing may be delayed indefinitely provided the sheeting is maintained in accordance with the specifications. However, membrane curing should eventually be applied to provide a surface uniform in appearance.

If rain damages the curing membrane, the surface should be re-sprayed after the excess water has dissipated to restore the impervious covering and retain moisture necessary for curing.

Concrete subjected to rain can be restored to its original quality provided attention is given to the details mentioned above. The usual difference between a rain-damaged pavement that is satisfactory and one that is undesirable is that the finishing crew did not quit but persevered until satisfactory results were obtained.

If, for any reason, measures taken by the Contractor to produce a surface that meets specifications are unsuccessful, the affected portions of the pavement must be repaired or replaced to comply with contract requirements.

There is equipment available that can groove the transverse texture into pavement that does not have adequate texture. The equipment must be approved by the Engineer and meet the requirements of 451.14.

Cold Weather Construction

During cold weather, provisions must be made to prevent concrete from freezing until it has attained adequate strength. Concrete that has been frozen prior to gaining sufficient strength may be permanently damaged; and may never achieve the design strength. Therefore, it is necessary to protect the concrete from freezing temperatures during curing in order to prevent damage and to obtain the design strength.

The temperature of the concrete and the surrounding air directly control the rate of hardening of the concrete. As the ambient temperature decreases, the rate of hardening decreases. The rate of hardening ceases at the freezing point. If the concrete is maintained just above freezing, it will not be damaged. However, it will require a lengthy curing period before it will harden and gain strength sufficient for removing forms. Under these conditions, it is necessary to provide heat to the concrete so that it will harden and gain desired strength within seven days.

The Contractor is responsible for protecting concrete during cold weather. If damage might possibly occur, the surface shall be protected by any means that prevents the concrete from freezing and retains the heat of hydration.

In order to control the rate of hardening and strength gain, it may be necessary to control the temperature of the concrete being placed and to protect the concrete to retain the heat of hydration during curing. If the air temperature is 35° F (2° C) or below when concrete is being placed, the concrete must be heated to a temperature from 50° to 80° F (10° C to 27° C) when placed.

Heating mixing water is the most effective way of heating the concrete. Aggregate may be heated, if necessary, in addition to the water. The heated water and aggregate should be introduced into the mixer before the cement, so that the temperature is reduced before cement is added to avoid the possibility of a flash set. One further precaution is to delay the introduction of the air-entraining agent until the temperature has been reduced, because hot water tends to reduce its potency.

The subgrade or base and forms must be free from frost when concrete is placed. Covering these areas usually prevents frost and avoids delays.

Any request to incorporate an accelerating admixture during cold weather construction must be submitted and approved as previously discussed.

Job Control Testing and Sampling

Concrete for use in pavements must meet specified requirements for air, slump and yield. Tests must be conducted to check for compliance with these requirements. The Inspector will conduct these tests after the concrete has been delivered and deposited on the base. The test results must be within the following limits:

Air 6 ± 2 percent (8 ± 2 with No. 8 size coarse aggregate)

Nominal Slump 1 to 3 inches (25 to 75 mm)

Maximum Slump 4 inches (100 mm)

Yield ± 1 percent

Immediate adjustments must be made if tests indicate the concrete is not within these limits. Production should be stopped and check tests made to confirm noncompliance of the original tests. Concrete that does not meet specification requirements must not be used unless adjustments can be made to correct the deficiency prior to incorporating it into the work. The fact that concrete has been produced and transported to the project does not justify its use unless it conforms to requirements.

Insufficient air may be corrected by the addition of an air-entraining agent and remixing the load to generate additional entrained air. Variations in yield should not be cause for rejection; however, immediate adjustments must be made in the batch weights and must be followed by additional yield tests until conformance is obtained. Slump may be increased by the addition of water provided it remains within the above limits. If slump is excessive, the concrete should not be used.

All material being used in the production of concrete shall be sampled and tested and approved or accepted by certification before being used. Material that has not been sampled before delivery to the project must be sampled and submitted for testing. Such material must not be used until approval has been given by the Laboratory. Sampling must be done in accordance with the specifications and as outlined in Item 499.

Concrete cylinders are not required for pavement concrete. However, if for some reason cylinders are desired, they should be cast from concrete obtained at the paving site and are to be made in accordance with Item 499. Cylinders are to be shipped to the Laboratory on the fourth day after casting where they are tested for compressive strength at 28 days of age.

Results of air, slump, and yield tests must be recorded on the Concrete Inspector’s Daily Report as outlined in Item 499. Results of compression tests on cylinders submitted will be reported by the Laboratory in the Construction Management System (CMS) under Test Data Reports. Results of flexural tests on beams are to be recorded in the project records.