Portland cement concrete
pavement must be constructed so that it provides a smooth-riding surface
satisfactory to the traveling public. It must be 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 no more important than durability and
structural strength. All desirable
elements of a good pavement are a product of the Contractor’s workmanship 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.
This item includes the
construction of a Portland cement concrete pavement that contains reinforcing
steel.
The concrete specified for
use in reinforced Portland cement concrete pavement is defined in Item 499.
The coarse and fine
aggregates used in the Contractor’s JMF to produce a well graded aggregate in
the Class
QC 1 concrete for exposed concrete pavements (Items 451
and 452)
have additional requirements found in 703.02.A. The fine aggregate used in the concrete must
be natural sand; manufactured sand is not permitted. Coarse aggregate must be provided in
accordance with 703.13,
in addition to the requirements of 703.02.
In addition to the
requirements of 703.02,
the following aggregate requirements apply per 703.13.
Where gravel, crushed ACBFS,
or limestone is selected, and the total combined quantity of the plan items (451,
452
or 305)
is greater than 10,000 square yards (8,000 m2), the coarse aggregate
must be No. 57 or 67 size.
If the total combined
quantity of the plan items (451,
452,
or 305)
is less than 10,000 square yards (8,000 m2), the coarse aggregate
can be one of the following sizes: No.
7, 78, 8, 57, or 67.
Freeze-thaw resistance
testing is required for all No. 57 or No. 67 gravel or limestone coarse
aggregate used in 451
(or 452
or 305)
to help eliminate the concrete pavement’s potential for D-cracking in
accordance with ASTM C666,
Procedure B. Testing is performed by
the Department. Contact the Aggregate
laboratory to validate if your coarse aggregate sources are approved.
D-cracking is cracking caused
by freeze-thaw deterioration of the aggregate within the concrete. This type of cracking can be observed in
about 7 to 10 years after construction of concrete pavement. D-cracks are closely spaced cracks parallel
to transverse and longitudinal joints which multiply outward from the joints
toward the center of the pavement panel.
D-cracking is a function of the pore properties of certain types of aggregate
particles and the environment in which the pavement is placed. Due to the natural accumulation of water
under pavements in the base and subbase layers, the aggregate may eventually
become saturated. With freezing and
thawing cycles, cracking of the concrete starts in the saturated aggregate at
the bottom of the slab and progresses upward until it reaches the wearing
surface. This problem can be reduced by
either selecting aggregates that perform better in freeze-thaw cycles or where
marginal aggregates must be used by reducing the maximum particle size. Also,
installation of effective drainage systems for carrying free water out from
under the pavement may be helpful.
Figure
451.A – D-cracking in concrete pavement
Expansion joint sealer must
be a 705.04
hot-applied joint sealer conforming to ASTM D 6690, Type II.
These curing materials are
burlap cloth, sheet-curing materials, and liquid membrane-forming
compounds. The liquid membrane-forming
compounds used on the project must be on the Department’s Qualified Products
List.
Tie bar steel used in the
longitudinal joints in concrete pavement must meet the epoxy coated reinforcing
steel requirements of 709.00.
The reinforcing steel must
comply with 709.09,
709.10,
and 709.12
Dowel bars and dowel bar
assemblies (dowel baskets used to support the dowels at the proper position)
must be coated with a fusion-bonded epoxy coating, which conforms to AASHTO M
254, with the exceptions listed in 709.13,
Requirements for all Dowel Bars
Dowels should be inspected to
ensure the epoxy 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. The coating
must be free from holes, voids, contamination, cracks, and there shall be no
more than two holes (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 in addition to being
completely coated.
Where project pavement has a
bid item ending in “with QC/QA,” the Contractor will provide a quality control
plan (QCP), quality control (QC) testing, and quality control inspection. The Engineer initially accepts the QCP. All requirements for the QCP submittal, what
is required in the Contractor’s QCP, minimum QC testing, and the Engineer’s
quality assurance (QA) responsibilities are in Item 455.
Reinforced Portland cement
concrete pavement is placed by a series of equipment called a paving
train. A paving train normally consists
of a concrete spreading machine, a mesh cart, a mesh depressor, a finish paving
machine, a work bridge and a cure/texture machine.
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 help to eliminate
surface irregularities.
The Contractor is responsible
for equipment adjustments. Department
personnel are not expected to adjust or advise the Contractor on 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 is 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 the
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,
which meet the specified requirements.
The specifications give the Contractor the option of using slip form or
fixed form pavement construction methods.
Vibrators are used for the
full-width and depth of the concrete slabs to provide consolidation of the
fresh concrete. They must be internal
type, using a tube or multiple spuds.
Internal means the vibrators must be immersed in the fresh
concrete. External vibration is not
allowed. Vibrators 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 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 must
operate at a frequency of 7,000 to 11,000 impulses per minute. The vibrators should be connected to an
electronic monitoring device equipped with an automatic recorder. The monitoring device should display the
operating frequency of each internal vibrator.
The readout display should be located near the paving operator’s
controls and must operate continuously when paving and display all vibrator
frequencies with manual or automatic sequencing between individual
vibrators. The automatic recorder must
record the following information for every 25 feet (8 m) of paving or at every
5 minute time interval.
·
The time of day.
·
Station location.
·
Paving machine
track speed.
·
The frequency of
each vibrator.
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 ensure
that adequate consolidation for the full-depth and width is achieved without segregation.
Vibrators must be connected
so they turn off when the machine on which they are mounted stops.
Concrete plants and trucks
hauling concrete are inspected annually by the District Laboratories. 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 will be checked to ensure proper calibration within
specified tolerances. The scales will be
checked for accuracy (the specifications require that concrete materials be
measured by weight).
Central mix plants should be
checked to see that the mixer drum 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 buildup and excessive wear.
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.
Figure
451.B – Transit Mixer Truck
Even after the annual
inspections, transit mixers should be checked to determine that the counters
are functioning properly. After having
been mixed for no 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.
Figure
451.C – Non-Agitation Concrete Delivery Trucks
Dump-Crete Truck (left), Dump Truck (right)
When
the concrete is transported to the paving site in dump trucks or other
non-agitating units, check the bodies to ensure that they are water-tight and
free of objectionable corners or internal ribs where concrete may
accumulate. Canvas covers that shield
concrete from sun and wind shall be provided when required by the Engineer.
Contractors build aggregate
stockpiles at locations where concrete will be mixed. In all cases, aggregate stockpiles can be
placed on areas which are paved, or they may be placed directly on the ground
if the existing ground is firm, cleaned of foreign material, and shaped to
provide drainage. No aggregate is to be
removed from the stockpile within 1 foot of the ground during production of
concrete.
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.
Coarse aggregate stockpiles
must be constructed to prevent segregation.
In building the stockpiles of coarse aggregate, the Contractor is to
prevent segregation through proper handling.
Methods that allow the aggregate to be deposited close to the surface of
the pile helps prevent aggregate from rolling to the bottom of the stockpile
and aggregate segregation. As the pile
increases in height, each layer of aggregate should be benched back to help
limit rolling and segregation.
Rubber tire front-end loaders
are often used to construct stockpiles.
Rubber tires must be kept clean and the bucket drops kept short. If the front-end loader is on the pile, it
should not be moved on and off the stockpile.
This can cause contamination of the stockpile. Using a bulldozer to push
coarse aggregate is not permitted; this causes segregation and the use of steel
treads on the pile crushes 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 can
result in segregation, degradation, or contamination is not permitted. Aggregate stockpiles that appear segregated
should be tested for gradation at the lab.
Slag aggregate and any other
aggregate with a reported absorption above 3 percent must be managed in
stockpiles to ensure uniform moisture content at the time of batching (499.07). A stockpile watering system must be used that
raises the aggregate moisture to saturated surface dry (SSD) or above. The Contractor is responsible for collecting
samples to confirm the aggregate moisture requirement. Additionally, the Contractor is responsible
for maintaining the aggregate stockpile at or above SSD until dewatering prior
to batching in the concrete mix. During
production of concrete, the Contractor is required to test and maintain the
aggregate moisture. Variation in
moisture of more than 1 percent requires more frequent testing such that the
correct information is used in concrete batching.
Where QC/QA is required, the
Contractor is required to test aggregate gradations conforming to Item 455.
This construction method
requires the Contractor to 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 be
self-propelled and uniformly distribute and consolidate the concrete without
segregation. Fixed form construction is
used on small or irregular paving jobs because of slower productivity and
potential issues with smoothness.
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.
Pavers for fixed form
construction must be able to spread, consolidate, and finish the concrete
pavement to the cross-section and profile required using one or more
machines. The machines must be able to
distribute and consolidate the fresh concrete without causing segregation. Consolidation must be for the full-depth of
the concrete thickness being placed.
Forms for use on ODOT
projects must meet the following requirements:
·
Made of steel.
·
Straight and must
not be less than 10 feet (3 m) in length.
·
Have a depth
equal to the pavement thickness specified.
·
Base width of at
least 3-inches or greater. Older forms
will likely have a base width equal to the depth of the forms.
·
Built-up and
shimmed forms are not allowed
·
Forms that are
bent or damaged are not permitted.
Figure
451.D – Sections of Steel Concrete Paving Forms (left), Forms in Place (right)
Forms must be cleaned and
oiled each time they are used. 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 for the entire project. All
forms must have adequate joint locks to tightly join the ends of abutting
sections together.
The surface left by the
transverse screed must be uniform and satisfactory.
This method of construction
permits pavement placement without the use of fixed side forms. In lieu of forms, a slip form paver spreads
concrete uniformly across the paving area with an auger or spreader plow,
consolidates the concrete with spud vibrators, and strikes off the top of the
concrete and then feeds the concrete under a profile pan that provides the
correct elevation and proper cross-section.
Many slip form pavers have a tamping bar that tamps larger aggregate
into the top of the slab before it enters under the profile pan. When the concrete
leaves the mold, the slab should retain its shape and position. Some slip form pavers utilize an oscillating
float (auto-float) or tube float after the slab is extruded. These floats are used to smooth and seal the
top of the slab; however, in some cases, they can cause the slab to be
bumpy. Excessive finishing after the
slab is extruded should not be necessary if the slip form paver is set-up
correctly.
The base must be constructed
as outlined in the specifications.
Stability of the base is critical for slip form construction. The base must be graded to the plan elevation
by a properly designed machine. The
track area for the paving train 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. See Fine Grading
of Subgrade or Subbase below for more details.
Stabilization in the paving
machine track area in order 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 industry-standard,
approved slip form paver must be used to spread, consolidate, screed, and
finish the concrete in one pass. The
machine must consolidate the full-width and depth of pavement being placed to
provide a dense homogeneous pavement slab which requires a minimum of hand
finishing.
For the placement of steel
mesh, two machines may be used with the leading machine, 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 it does not interfere with the second paving machine.
Figure
451.E – Slip Form Paving
Preset grade lines are
required for slip form paving equipment to ensure acceptable riding quality of
the pavement. Paving equipment must have
controls that trace the grade line and automatically adjust the screed. String lines offset from and parallel with
the edge of pavement are most often used.
Sensors on the paver follow the string line and automatically adjust the
screed.
The use of string lines will
not ensure riding quality. All lines,
grades, and controls should be frequently checked. The electronic controls of a slip form paver
utilizing a string line merely follow the ups and downs of the string line;
thus, any dips, bumps, and errors in the string line set-up are mirrored on the
surface of the new pavement. String line
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. The
stringline tension must be taut enough so excessive sag does not occur.
For best results using a slip
form paver, the concrete slump should be maintained at about 1-1/2 inches. Too much slump will cause the slab edges to
sag and too little slump will result in a torn or open surface. In either case, the slab will require hand
finishing to make repairs. Good construction
results are achieved by operating the slip form paver with continuous forward
motion and a minimum of starting and stopping.
When the paving machine stops, all vibrating, tamping, and oscillating
elements must stop.
The slip form paver must not
be used like a dozer to push large quantities of concrete piles. The Contractor is responsible for placing
concrete that requires as little rehandling as possible, including pushing
mounds of concrete or using hand vibrators to move concrete. See Placing Concrete below.
Figure
451.F – Improper Concrete Placement in Front of Slip Form Paver
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 slip
form paver can be positioned at the joint when production is resumed. The trailing side forms do not bind and spall
the slab edges when this leeway is provided on each side.
Inspection of slip form
paving should include checking the pavement edges. The pavement’s edge should be perpendicular
to the pavement’s surface. Since no
forms are used to screed against or to hold the edge in place, the edge can
slump downward or lean outward. Use a
straightedge placed perpendicular to the pavement’s edge to check transversely
and longitudinally for slumping or leaning.
Edges must be corrected while the concrete is plastic. The Contractor is required to make changes to
the slip form paving process to prevent edge slump.
Where pavement will be placed
against an outside edge, the pavement must not vary more than 1/4 inch (6 mm)
below the typical section.
Where pavement will not be
placed against an outside edge, the pavement must not vary more than 1/2 inch
(13 mm) from the typical section.
All pavement edges must be
nearly vertical with no projections or keyways exceeding 1/2 inch (13 mm). If edge projections exceed 1/2 inch (13 mm),
concrete must be removed by hand methods and the edge should be troweled
smooth.
Forms serve as the “tracks”
for the paving equipment, 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. They must have sufficient
pin pockets for setting securely so that they will withstand the operation of
the paving equipment. Forms are to be
set so they do not vary more than 1/8 inch in 10 feet (3 mm in 3 m) on the top
face or more than 1/4 inch in 10 feet (6 mm in 3 m) on the vertical face. If they cannot be reset or repaired to meet
this tolerance, they cannot be used.
Forms are reused continuously.
Therefore, inspection of forms must be continuous. Any time forms are found out of tolerance,
they must be rejected. Forms that are
rejected should be marked so they are not incorporated into the work.
Figure
451.G – Forms are Set in Position and Pinned to the Base
Forms are to be set true to
line and grade on a thoroughly compacted base with uniform bearing throughout
their entire length and width. Using
loose earth pebbles or other shims 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.
Figure
451.H – Built-up and Shimmed Forms are not Allowed
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 prior to placing concrete and tightened if
necessary. Make a final visual check at
the same time to ensure 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 the placing of concrete.
When hook bolts or wiggle bolts are fastened to the forms, the forms
must be oiled prior to placing these units.
After the embankment has been
placed and compacted, the subgrade is brought to the required grade, cross-section,
and density in accordance with 203. Base
material is provided by plan for all concrete pavements with only a few
exceptions. The typical plan section
indicates the depth and width of compacted base materials. Generally, base material is 304
Aggregate Base and must be placed, shaped, and compacted in accordance with
that specification. Fine grading of the
base material should be done in advance of the concrete paving operation to
allow the Engineer to check the established grade for conformance to the plan
elevation. After the grade has been
checked and accepted, no further disturbance of the base material is allowed.
For both fixed form and slip
form construction, the surface of the base material is left approximately 1
inch (25 mm) above grade after compaction has been completed to the required
density. After forms have been set to
grade for form paving, or the string line is set for slip form construction,
the slight excess is removed with a subgrade planer (subgrader). The 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 regarding, which results in a delay in progress of
fine grading.
When automatic subgraders are
used, they will precede the setting of forms.
Grade will be maintained from a preset string line 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 to restore surface density. This rolling operation also smooths the
surface and reduces the friction between the base and the pavement.
For fine grading between
forms, the resulting base surface can be checked using a multiple pin template
operated on the forms or a stringline stretched between 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. Where the subgrader
is operated on a string line, the grade will be checked based on the grade
stakes for the pavement. The Inspector
should record the limiting stations of the area checked and conformance to the
specification requirements in project records.
The subgrader is usually one
of the heaviest pieces of equipment operating on the forms. Therefore, this is a good 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.
Moisture is controlled by
spraying the base prior to fine grading, preferably in the late afternoon
before fine grading. This provides the
uniform moisture distribution necessary for density. After removal of excess material during fine
grading, moisture is present for the final surface compaction.
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
ensure 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.
Prior to placing concrete,
the subbase must be thoroughly moistened with water. This keeps the subbase material from
absorbing water from the plastic concrete, thus affecting its workability and
decreasing its set-up time. Different
moisture levels throughout the depth of concrete can build in stresses that
lead to cracking.
The concrete must be placed
as close to the paving and finishing operation as possible to limit
rehandling. Excessive handling of
plastic concrete can reduce the air entrainment, and therefore, the long term
durability of the pavement.
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 operations are started. 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 the 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 either transit mixer or dump truck delivery.
Concrete must be vibrated
using internal vibration for the full-width and depth of the pavement being
placed. When using dowel basket
assemblies, the Contractor is required to use a separate handheld internal
vibrator to consolidate the concrete around the assembly. This requirement is sometimes overlooked and
must be required to ensure complete and adequate consolidation at the dowel
basket assemblies. Internal vibrators,
mounted on a paver, must automatically shut off when the machine stops. Vibrators that continue to run cause
segregation of the coarse aggregate from the paste which results in weak areas
in the pavement.
Workers should not walk in
the concrete unless they are wearing clean boots that do not have dirt, earth,
clumps, or other foreign matter on them.
Workers should never walk on concrete that has been struck off; these
boot tracks can fill with mortar which will develop as low and weak spots on
the surface of the slab.
Concrete must not be allowed
to displace dowel bar assemblies or expansion joints.
A separate concrete
placer/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). When using a slip form paver with a dowel bar
inserter (DBI), the placer/spreader requirement may be waived. When a slip form paver with DBI is used,
there are no dowel baskets; therefore, concrete delivery vehicles can deposit
concrete directly and evenly in front of the paver.
Placer/spreaders must be
industry standard equipment that is self-propelled and receives concrete in a
hopper adjacent to the area being paved and delivers the concrete using a
conveyor system evenly and uniformly in front of the paver. Placer/spreaders must be adjusted to deposit
the proper amount of concrete for the required slab thickness. The amount of concrete deposited is
determined by the elevation of a strike-off plate located behind the screw
augers, paddle, or hopper that distributes the concrete.
Figure
451.I – Concrete Placer/Spreaders
The elevation of the bottom
of the strike-off plate 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.
The initial placing of the
concrete should be just enough so that a slight excess is carried ahead of the
placer/spreader as it levels the concrete to a uniform surface. Unless this is done, there will be an
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.
Concrete should not be mixed,
placed, or finished after dark without operating an adequate and approved
lighting system.
When the air temperature is
35 °F (2 °C) or below, the concrete temperature must be between
50 °F and 80 °F (10 °C and 27 °C) at the point of placement.
When the air temperature is
greater than 35 °F (2 °C), the concrete temperature cannot exceed 95 °F (35 °C). When placing higher
temperature, concrete setting and finishing can become an issue. Cure and delivery time also becomes critical. Ensure that the cure is immediately being
applied and do not allow curing to lag behind the paver. See Hot Weather Construction.
Concrete cannot be placed on
any surface that is frozen or has frost.
Two test beams are to be made
for each 7,500 square yards of concrete or fraction of 7,500 square yards that
is placed each day.
The running yield of concrete
may be determined at any time during concrete paving and can provide an easy,
accurate method to ensure that the proper thickness is being placed. When a constant width and thickness is
placed, a 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 1 foot length (one meter) of
finished pavement of the width and depth required. This factor is computed by using Equations
451.2 and 451.3:
Yield Factor
= Width (ft) x Thickness (ft) x 1 ft
27 ft3 / yd3
Yield Factor
= Width (m) x Thickness (mm) x 1 m
1000 mm / m
Equation
451.3 – Yield Factor (metric)
Running Yield
= (Yield Factor) x Length Placed
Equation
451.4 - Running Yield
Example:
A
Contractor is placing a 24-foot wide slab that is 9 inches thick. Determine the yield factor and running yield
for this cross-section when the Contractor placed 4,254 linear feet. Using Equation 451.2, the following
calculation results:
Yield Factor = 24 ft x (9 in/12 in/ft) x 1 ft =
0.667 yd3 per foot of length
27 ft3/yd3
Once the 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.
For this example: Running Yield = 0.667 yd3 per
foot of length x 4,254 ft = 2,830 yd³
This is the volume of concrete that should be used for this length of
pavement if it is placed to the plan width and thickness. A comparison to the quantity of concrete used
will show whether the Contractor is over or under running on yield.
Example:
Actual quantity used = 2,880 yd³
Running yield (from above calculation) = 2,830 yd³
Over/Under run = Actual used – Running Yield =
Difference
2,880 yd³ - 2,830 yd³ = + 50 yd³
difference
(50 yd³ ÷ 2,830 yd³) x 100 % = 1.77%
overrun
A 1 to 3 percent greater than
that required is generally due to wasting over the forms, spillage, etc. An overrun of 3 percent or more should be
investigated to determine the cause.
Overruns may be caused by several factors, including inaccurate
weighing, low subgrade/base, excessive waste, line and grade, etc. Similarly, an under run in concrete may be
due to inaccurate weighing, high subgrade/base, insufficient width, thickness
of slab, settlement of forms, etc.
When high air temperatures,
low humidity, and winds are encountered during concreting operations, the rate
at which concrete hydrates (hardens) increases.
High temperatures, especially when accompanied by wind and low humidity,
tend to cause a rapid loss of moisture from the surface of the plastic concrete
resulting in early setting and a reduction in time allowed for finishing.
Lowering the concrete
temperature to 75 ºF (24 ºC) or below will help offset the effects of high
ambient temperatures. Selection of a
cool water supply is the most effective means of lowering the mix
temperature. Watering of coarse
aggregate stockpiles for moisture control also aids in controlling the mix
temperature.
When form paving, it is good practice to maintain
the slump of concrete near the top limit during hot weather. Increasing
the slump will help delay hydration, thereby making more time available for the
finishing operations.
During hot weather
operations, there may be a tendency to add water to the surface of the concrete
to aid in finishing. This practice cannot
be allowed. Using water on the surface
during finishing results in an increase in the water-cement ratio and reduces
the entrained air content of the concrete at the surface. Both of these changes adversely affect the
long-term durability of the pavement’s surface.
The use of the whitewash brush to sprinkle water has caused the majority
of scaling that occurs in concrete surfaces.
Under extreme drying
conditions caused by high temperatures, coupled with low humidity and high
winds, mixing water may evaporate quickly from the concrete’s surface. 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 straight edged after the fog spray. This provision should be carefully controlled
and should be the exception rather than the rule.
An approved Type B or D (705.12)
set retarding admixture is required when the concrete temperature exceeds 75
°F. Set retarders help slow down the
setting time, thereby providing more time for finishing. The use of this admixture will result in less
slump loss and result in higher strength concrete.
Concrete paving must not be
undertaken in rainy conditions; however, in the course of paving, rain can
occur and the Contractor must take steps to protect the plastic concrete from
damage. If the pavement is adequately
protected from rain, extensive 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. When
the concrete hasn’t 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
resulting in a sandy appearance along with a speckled or splattered surface
pattern. If the surface hasn’t 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 be used for several passes
to restore the surface finish. When
correcting damage to newly placed concrete surfaces, the excess surface water
must first be removed, not worked into the concrete. Cement must 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 and must not be allowed.
When rain persists for a
lengthy period, it will be necessary to remove any protective covering to
finish and texture the concrete before it sets.
Membrane curing should not be applied when the surface is wet. 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.
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.
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.
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 the cure period.
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 sufficient strength.
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 thereafter to retain
the heat of hydration during curing. If
the air temperature is 35 ºF (2 ºC) or below when concrete is being placed, the
concrete must have a temperature from 50 ºF to 80 ºF (10 ºC to 27 ºC) when
placed. The Contractor is responsible
for ensuring that the concrete temperature is in the required range.
If the concrete temperature
is less than 50 °F the mixing water or aggregates may be heated. The heated water and aggregate should be
introduced into the mixer before the cement so 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 effectiveness.
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.
All material being used in
the production of concrete shall be sampled, 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
for use in pavements must meet the specified requirements for air, slump and
yield. Tests must be conducted to check for compliance with these
requirements. The test results must be
within the following limits:
AIR |
SLUMP |
YIELD |
6 ± 2% |
1 to 3
inches |
± 1% |
Under QC/QA, the Contractor
will perform tests and report this information to the Engineer. If random QA tests find out of tolerance concretes,
the Contractor must be notified of out of specification test results and make
immediate adjustments to the mix.
Production should be stopped and check tests made to confirm
non-compliance 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 limits of the water-cement ratio. If slump is excessive, the concrete should not
be used.
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 District
Laboratory 48 hours after casting. Notify the Laboratory when the cylinders are
to be tested for compressive strength (normally at 28 days of age.)
Results of air, slump, and
yield tests must be recorded on the Concrete
Inspector’s Daily Report and in SiteManager. See either 499
or SiteManager help documents for required entry. Results of flexural tests on beams are to be
recorded in the project records. Results
of compression tests on cylinders (if made) will be reported by the Laboratory.
Distributed steel or
reinforcement used in reinforced pavement (Item 451)
is welded wire fabric or mesh.
Reinforcing mesh details for 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).
The longitudinal wires are to be spaced at 6-inch (150 mm) centers. A W4 or D4 (MW26 or MD26) wire is used
transversely and has a nominal diameter of 0.225 inches (5.7 mm). Transverse wires are to be spaced at 12-inch
(300 mm) centers.
The mesh holds together the
slab after cracks have formed. Adequate
load transfer across the crack is ensured, and the infiltration of
incompressible material into the crack is prevented or delayed. Mesh does not increase the flexural strength
of the slab. 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 prevent bonding with the
concrete. Any mesh that has been bent
or has broken welds should be rejected.
Mesh with rust, mill scale, or a combination of both will be considered
satisfactory provided the minimum dimensions are not less than specified. Research indicates that tight, scaly, and
pitted rust does not prevent bond.
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. 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.
Figure
451.J – Concrete Spreader with Mesh Cart
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
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 or soil.
The specifications allow
three methods of installing reinforcing mesh. The allowable methods are:
1. Place one layer of concrete, place the mesh on top of
this layer so that it is located at its final location without any further
manipulation, and place the second layer of concrete on top of the mesh. 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
2. The mesh may be supported on chairs at the correct
elevation and securely anchored to the base and the concrete placed in one
layer.
3. 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. 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.
Figure
451.K – Placing Two Layers of Concrete (left), Mesh Supported (right)
Figure
451.L – Using a Mesh Depressor
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 so there is 2
inches (50 mm) clearance from a longitudinal joint or pavement edge to the
reinforcing wires and 12 ± 2 inches (300 ± 50 mm) from any transverse joint.
Figure
451.M – Location of Mesh in the Slab
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.
Two types of machines have
been approved to vibrate 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
self-propelled and consists of long tapered longitudinal runners across the
width being placed. This machine
gradually depresses the mesh into position in 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 ensure that
the specified clearance of 12 ± 2 inches (305 ± 51 mm) is being maintained on
each side of the center of the transverse joint. If the mesh position is found to be out 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 confirm that the machine
is placing mesh to the required depth.
Standard when mesh depth is out of tolerance, immediate adjustments must
be made by the Contractor.
Reinforcing mesh is normally
shipped in lengths of 19 feet (5.9 m) by 11 feet 8 inches (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 with the steel working up into the finishing
operations.
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. See Standard
Construction Drawing BP-2.1 for longitudinal joint details and BP-2.2
for transverse joint details. The
Inspector should know the requirements of the specifications and the drawings
before inspecting joint construction.
All transverse joints are to
be constructed normal (perpendicular) to the centerline of the pavement lane
unless otherwise noted on the construction plans and are to be coated with a
thin, uniform coat of new light form oil.
Only new oil should be used. The
oil coating should be applied no sooner than 2 hours prior to concrete
placement. For example, it is not
acceptable for the Contractor to oil the dowels the day before the concrete is
placed. For slip form construction which
uses mechanical dowel bar inserter, the dowels must be oiled just prior to
loading the dowels into the machine.
Joint sawing is required to
prevent uncontrolled cracking of concrete pavement and is required for all
transverse contraction joints. Joint sawing is also required for all
longitudinal joints when concrete pavement has been placed across two or more
lanes at the same time.
The timing of the sawing
operation is critical. The use of HIPERPAV software is required to determine
the sawing time limits to help protect from early, uncontrolled cracking. The software is available as detailed in Supplement
1033 as well as the requirements for analysis. Note: the use of HIPERPAV does not relieve the Contractor of
his responsibilities under 451.17
regarding the repair of cracks in the completed pavement.
The HIPERPAV analyses must be run 24 hours
prior to placing concrete and for every pour.
The HIPERPAV files and printout
must be provided to the Engineer. If HIPERPAV predicts early age slab cracking
will occur, whether due to standard construction practices, joint sawing
methods, mix design or curing, the Contractor cannot start construction until
modifications have been made to eliminate HIPERPAVs
predicted slab cracking.
If HIPERPAV predicts that joint sawing can
exceed 24 hours, all joints must be cut by the twenty-fourth hour.
Sawing must be done after the
concrete has sufficiently hardened and is able to support the sawing equipment
and to avoid spalling and raveling. This
operation cannot be tied to normal working shifts. A standby saw is required at the paving site
in the event of the breakdown or inability of one machine to maintain necessary
progress.
Inspection should include
random checking of each day’s sawing to ensure the width and depth specified is
achieved. Saw blades will wear with use,
so continued checks must be made. Since
the timing of sawing is critical, inspectors assigned to this operation must be
aware of the importance and document the actual time of sawing.
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).
Joints between adjoining
lanes of pavement or shoulders 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, and are often
called longitudinal butt joints. Most
pavement lanes are 12 feet wide.
Epoxy coated tiebars or hook
bolts are required at longitudinal joints to tie the lanes and 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.
Both tiebars and hook bolts
should be placed in accordance with the requirements of standard construction
drawings called out in the plans.
Tiebars are 5/8 inch (16 mm) in diameter, deformed 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 placed
approximately at right angles and placed at one-half the thickness of the
pavement. For example, if the slab is 10
inches thick, the tiebars are to be placed at 5 inches as measured from the surface
of the slab.
Tiebars may be set on chairs
prior to concrete placement or inserted in the plastic concrete using a
mechanical device on a slip form paver.
Chaired tiebars must be adequately anchored to the base material. A mechanical inserter must be able to install
the tiebars at mid-depth in the plastic concrete. Tiebars must be inserted after the concrete
has been placed to its full-depth and after the reinforcing mesh is placed (mesh
is not required for 452 or 305 pavement).
Pushing tiebars into the plastic concrete by hand is not acceptable.
Figure
451.N – Mechanical Tie Bar Inserters
Center Tie Bar (left), Edge Tie Bar
(right)
Figure
451.O – Tie Bars can be Supported prior to Concrete Placement
When a standard (water-cooled
diamond bladed) concrete saw is used to make the longitudinal joint between
simultaneously placed lanes, the following applies:
·
Pavement ≤
10 inches thick: Saw the joint to a minimum depth of one-fourth the specified
pavement thickness.
·
Pavements > 10
inches (255 mm) thick: Saw the joint to a minimum depth of one-third the
specified pavement thickness.
·
Saw joints 1/4 ± 1/16 inch (6 ± 1.6 mm) wide as measured at the time of sawing.
When using early-entry (dry
cut, light weight) saws, only use saw blades and skid plates as recommended by
the manufacturer. Perform the early entry sawing after initial set and before
final set as follows:
·
Saw the joint
2-1/4 to 2-1/2 inches (56 to 63 mm) deep.
·
Saw joints
approximately 1/8 inch (3 mm) wide as measured at the time of sawing.
Standard, 30-inch long
tiebars can be installed in the slip formed edge of the pavement using a
mechanical inserter at longitudinal joints when lanes are placed
separately. This is normally done by a
mechanical ram which pushes a tiebar 15 inches into the edge of the slab along
the joint and at the center of the slab.
Tiebars cannot be placed by hand.
Bent tiebars are not permitted in longitudinal construction joints.
(Note that
spec now requires epoxy coated hook bolts)
The epoxy coated hook bolt or
an epoxy coated hook bolt alternate (wiggle bolt) may be used in longitudinal
joints when using fixed form paving. An
epoxy coated coupling attached to 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 after removal of the forms.
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 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 inside and outside edges
of the paved lane must be edged to a 1/8-inch (3 mm) radius. 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. Tool marks left by the
edging tool must be removed. Since the
final texturing is to follow edging, this operation must not be permitted to
lag.
Figure
451.Q – Radius Edger and Removal of Tooling Marks
Longitudinal joints (butt
joints) between separately placed lanes require extra care to ensure that a
smooth transition from one lane to the other will result. Good workmanship is necessary at these joints
to obtain satisfactory results. Hand
finishing and straight edging should be performed carefully so that each lane
will be at the same elevation. The
surface of the pavement in the joint area should not vary more than 1/8 inch (3
mm) from a 10 foot (3.0 meter) straightedge in both longitudinal and transverse
directions.
Figure
451.R – Edging and Finishing a Longitudinal Butt Joint
Transverse joints include
contraction joints, expansion joints, or expansion joints. All transverse joints are constructed normal
(perpendicular) to the centerline of the pavement lane unless otherwise shown
on the plans. All transverse joints
require the use of smooth, epoxy coated, round dowels. The size of dowels is dependent on the
thickness of the pavement as shown in Table 451.09-1 in the specifications.
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 |
Dowels can be placed in
concrete pavement using dowel basket assemblies. Dowel basket assembly wires, as well as the
dowels, are required to be epoxy coated according to 709.13
of the Specifications. Dowel basket
assemblies shall conform to Standard
Construction Drawing BP-2.2.
Dowel basket assemblies are
not to exceed the maximum spacing for the type of pavement specified (reinforced
or non-reinforced) and must be perpendicular to the centerline and edge of
proposed pavement or forms. Locating the
transverse alignment may be by any method that ensures a right angle to the
centerline. On curves, the joints should
be approximately on radial lines.
Transverse contraction joints
must be continuous across the full-width of pavement placed. Therefore, the joint in a lane already placed
must be continued across all other adjoining lanes.
Figure
451.S – Dowel Baskets are Pinned to the Base Material
When properly located and placed,
dowel basket assemblies are anchored in place with steel pins. At least eight 1/1/2-inch (13 mm) diameter
steel pins, 18 inches (460 mm) in length, are required to hold each 12-foot
(3.6 m) basket assembly. 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. The assembly should not be hit
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 any 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.
While the specification
allows the use of steel bearing plates when placing basket assemblies on
granular material that may distort, this practice is not common and should not
be used for standard construction purposes.
If there is a base stability problem this must be corrected before
pinning basket assemblies.
Shimming of basket assemblies
with pebbles, stones, wood, 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.
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 as the dowels. Dowel basket assemblies must be anchored to
the base before the shipping and spacer wires are removed.
Figure
451.T – Shipping Wires Fully
Removed (left) and Only Cut (right)
Specifications require that
dowel basket assemblies be preset prior to the beginning of paving unless the
Engineer determines that it is impractical to do so. This allows time to check the baskets to
ensure they are parallel to the base and centerline of the pavement. Checking of the assemblies is to be done
after the removal of the shipping and spacer wires. Measurement checks of the distance between
the dowel and the forms (made at each end of the dowel) or the proposed edge of
pavement 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
visual when fixed form paving since dowels out of alignment are easy to spot in
relation to the forms.
Figure
451.U – Checking Dowel Level with
an A-Frame Level
An adjustable A-frame level
is used to check several dowels in every assembly unit to ensure 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. The level is then 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. Check as many dowels as possible, but at
least three dowels should be checked in each 12-foot (3.6 m) section, , one at
each end and in 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.
The Contractor may propose to use a slip form paver
with a mechanical device that automatically inserts dowels in the plastic
concrete during the paving operation.
Dowels placed using a DBI must be placed in the full thickness of the
concrete pavement slab. A DBI is
integral to a slip form paver and is located behind the vibrators and the
initial strike-off of the paver. The
DBI consists of a rack located above the slab and in the correct transverse
locations across the slab. The loose
dowels are loaded into the rack, and the dowels drop into place and are pushed
into the fresh concrete using metal forks that push (and sometimes vibrate) the
dowel to the correct elevation in the slab. The metal forks must insert each
dowel so that it is parallel to the base and the pavement centerline and be at
the center of the slab thickness. After
the dowels are placed at mid-depth, the forks are withdrawn leaving the dowels
in position and supported by the concrete.
The dowels are to be installed after the concrete is placed to its full
depth, and if required, after the mesh is positioned properly. The only operations permitted after
positioning the dowels are the machine’s final strike-off, mechanical float
finishing, and hand finishing the concrete’s surface.
The specifications require the Contractor to submit to
the Engineer details and specifications of the proposed slip form paver with
DBI at least 14 calendar days prior to bringing the equipment to the
project. The use of the slip form paver
with DBI must be demonstrated using a test section and specialized scanning
equipment to verify the location of dowels in the completed pavement.
Verification of dowel placement is done using MIT Scan-2 equipment and software. The MIT Scan-2 uses magnetic tomography to locate the dowels in
three dimensions. The equipment provides
an immediate print out in the field and a detailed report of each dowel in the
joint including all measurements and a color depiction of the dowels in the
joint.
Figure 451.V – Checking Dowel Alignment Using a MIT
Scan-2 after Placement with DBI
Dowels placed using a slip form paver with DBI have a
required placement tolerance as shown in the Table 451.09-2. Note: dowel basket
assemblies have tolerances as shown on Standard
Construction Drawing BP-2.1. These are the manufacturing tolerances for
the basket and dowels in the basket. As
noted above, the dowel basket assemblies require checking for level and
perpendicular placement with the joint.
Dowel misalignment can result in poor load transfer
and joint locking which is detrimental to the performance of the pavement.
451.09-2 states the allowable tolerances for each of the following misalignment
parameters:
Table 451.09-2
Individual Dowel Bar Alignment Tolerances
Alignment Parameter |
Acceptance Tolerance (inches) |
Rejection Criteria (inches) |
Horizontal
Translation a |
±2.0 |
±3.0 |
Longitudinal
Translation b |
±2.0 |
±4.0 |
Vertical
Translation c |
±1.0 |
± T/6 |
Horizontal
Skew d |
±0.60 |
±1.0 |
Vertical
Tilt e |
±0.60 |
±1.0 |
Cover f |
- |
2.5 minimum |
a.
Horizontal Translation
- the total difference, measured horizontally, between the actual dowel bar
location and the plan required dowel bar location along the transverse
contraction joint.
b.
Longitudinal
Translation - the total difference, measured in the longitudinal direction,
from the center of the transverse contraction joint to the actual dowel bar
center. Also termed as “side shift”.
c.
Vertical
Translation - the total difference, measured vertically, between the centerline
of the actual dowel bar location and the mid-depth of the slab. (T = Pavement
Thickness in inches)
d.
Horizontal Skew -
the total difference, measured from end to end of a dowel bar, of the dowel in
the horizontal plane.
e.
Vertical Tilt -
the total difference, measured from end to end of a dowel bar, of the dowel bar
in the vertical plane.
f.
Cover - the least
distance between the surface of embedded reinforcement and the outer surface of
the concrete.
Rotational misalignments (horizontal skew and vertical
tilt) must be evaluated using a Joint Score Analysis per an FHWA publication
called Best Practices for Dowel Placement Tolerances (CPTP Tech Brief, FHWA-HIF-07-021). The Joint Score is a measure of the combined
effects of rotational misalignment.
The Joint Score (JS) is calculated using a weighting
system that assigns a number to each dowel bar in a joint depending on the
amount of deviation. The deviation is
referred to as Single Dowel Misalignment (SDM), and is the resultant
misalignment of a dowel. SDM is calculated as the square root of the sum of squares
of horizontal skew and vertical tilt.
Horizontal and vertical misalignments are the skew and
tilt measurements determined using the MIT Scan 2. Once the
SDM is calculated for each dowel in the joint; determine the weighing factor
(W) for each bar from Table 451.09-3; sum the W values for every dowel in the
joint and add one (1) to calculate the Joint Score (JS).
Table
451.09-3
Weighting Factors in
Joint Score (JS) Determination
Single
Dowel Misalignment (SDM) |
W,
Weighting Factor |
SDM ≤ 0.6 in. (15 mm) |
0 |
0.6 in. (15 mm) < SDM ≤ 0.8 in. (20 mm) |
2 |
0.8 in. (20 mm) < SDM ≤ 1 in. (25 mm) |
4 |
1 in. (25 mm) < SDM ≤ 1.5 in. (38 mm) |
5 |
1.5 in. (38 mm) < SDM |
10 |
Joint Score (JS) – Evaluated for a single transverse joint between
adjacent longitudinal joint(s) and/or pavement edge(s) (i.e., a typical
where:
n = number of
dowels in the single joint
Wi = weighting factor
(Table 451.09-3) for dowel i
The Joint Score threshold for a
locked joint of 10 (JS=10), was developed for a nominal pavement width of 12ft
and must be adjusted to account for differing pavement widths. This adjustment
is made using the Joint Score Trigger (JST).
Joint Score Trigger (JST) – A scaling of the Joint Score risk value to account for
the actual number of dowels required in a single joint for pavement
width other than 12 ft (3.6 m), calculated as:
Include the
Joint Score and Joint Score Trigger for every joint
scanned in the report to the Engineer. Any joint with a Joint Score equal to or
greater than the Joint Score Trigger is considered locked and rejectable.
·
Excel spreadsheet
from MIT Scan-2 software for Joint No. 24
·
Horizontal and
vertical misalignments shown on the spreadsheet as “sh” and “sv.”
·
Calculate the
resultant misalignment (deviation) as the square root of the squares of
horizontal and vertical misalignments.
·
Assign a weight
for each dowel based on the resultant misalignment.
·
Multiply the
number of bars in each weight category times the weight.
·
Total products of
number of bars x weight and add 1.
·
In this example,
the Joint Score = 14.
In this example the joint being measured is 24 feet
wide so the number of dowels required is 24. The JST should then be calculated
as follows:
We now check to ensure that the JS < JST and (14
< 20) so the joint has an acceptable joint score. Keep in mind that the JS
is not the only a measure for a compliant joint. All other parameters of
Table
451.09-2 must be met
as well.
Prior to
using a slip form paver with DBI on a project, the Contractor is required to
perform a test section of at least 500 feet.
Every joint in the test section must be verified for accuracy of dowel
bar placement using the MIT Scan-2 equipment. The
slip form paver and DBI can be accepted for production paving if the following acceptance criteria are met:
1.
Each Joint Score (JS) is less than Joint Score Trigger
(JST);
2.
Ninety percent (90%) of the dowel bars meet the Acceptance
Tolerances of Table 451.09-2;
3.
None of the dowels exceed the Rejection Tolerances of 451.09-2.
When the test strip does not pass the stated
requirements, the Contractor must make adjustments to the paver, mix or other
parameters and retest. In some cases,
the Contractor may have to remove and replace the test section pavement.
New test strips are required at the beginning of every
construction season, after any major paver repair or maintenance, at every
mobilization and remobilization to a project, and after any major concrete mix
design change. A paver that is approved
for use on one project must still pass the test section requirement on every
other project it is used on.
Any ferrous metal, namely tie bars, that is too close
to the dowels being measured can reduce the accuracy of the MIT Scan-2 device. Determine during the test section if embedded
tiebars or other project conditions are affecting the Rejection Tolerances and
JS’s. If the test section demonstration
shows interference, exclude from the JS and JST calculations any dowel bar(s)
closer than 12 in. (300 mm) in any direction to tiebars in the longitudinal
joint(s). At the Engineer’s discretion,
establish the location of excluded dowels by another equivalent non-destructive
method or by probing.
After completion and acceptance of the test section,
the Contractor can begin using the approved slip form paver and DBI. During production paving, the Contractor is
required to scan every 10th joint. The Engineer can request
additional scans be performed if needed.
The Contractor is required to provide a report of the
scanning within 24 hours of each day’s production. The report shall include the Joint Score as
well as the Excel files and graphical output for each joint. The report should include a summary where the
results from each scanned joint are presented and easily reviewed. An initial report can be used by the Engineer
to determine whether paving can continue.
The Engineer will base the decision to keep paving as
described below:
1. When the daily Quality Control Testing (QCT) finds
more than 10 percent of the joints scanned have dowels exceeding the acceptance
tolerances of Table 451.09-2 but the JS is less than the JST, increase the
scanning frequency to every 5th joint.
Evaluate the paving process to reduce/eliminate misalignments and
mislocations and continue to pave. The
QCT frequency will revert back to every 10th joint when two consecutive days of
scanning every 5th joint show no dowels exceeding the acceptance tolerances of
Table 451.09-2 and all JSs are less than the JST.
2. When QCT finds any individual dowel bars exceeding the
rejection criteria of Table 451.09-2 or the JS is found to exceed the JST, the
joint is considered to be locked and immediate investigation needs to be made
as follows:
a) Scan joints in front and behind the locked joint
location until five (5) consecutive joints in both directions are found with no
dowel bars exceeding the rejection criteria of Table 451.09-2 and no JS is
found to exceed the JST.
b) If the additional scanned joints show no additional
dowel bars exceeding the rejection criteria of Table 451.09-2 and no JS
exceeding the JST, evaluate equipment to determine what caused the original
problem. Before continuing paving
increase the frequency of QCT to conform every 5th joint.
c) If the additional scanned joints show additional dowel
bars exceeding rejection criteria of Table 451.09-2 or joints with a JS
exceeding the JST, stop paving.
Investigate to determine the cause of the dowel bar rejection issues and
provide the causes and alternative corrections to the Engineer.
The Engineer
will determine if the corrections will correct the problem and may allow paving
to temporarily continue to validate if the corrections work. During any evaluation, scan all joints to
determine if the corrections were successful.
If successful, continue QCT scanning at the frequency of every 5th
joint. If not successful, discontinue
paving, repair or replace the slip form paver and DBI, and repeat the Test
Section
All dowel bars found beyond rejection criteria of
Table 451.09-2 or joints with a JS exceeding the JST require a corrective
action proposal conforming to 451.09.B.5, Corrective Action.
The
contractor must submit a proposal for corrective action to the Engineer for any
dowel that exceeds the rejection criteria in Table 451.09-2 or any joint that
has a JS greater than the JST. The Engineer should evaluate the proposal and
approve of any corrective actions prior to them being performed by the
contractor.
Corrective
action for all JS exceeding the JST may not be required, if they are random in nature.
Up to two (2) consecutive joints with a JS exceeding the JST may be accepted,
provided that the adjacent three (3) joints before or after do not have dowels
exceeding Table 451.09-2 rejection limits and have JS’s less than the JST.
Corrective action is required where there are more than two (2) consecutive
joints with a JS exceeding the JST.
Relief for compressive forces
that are caused by movement in the pavement (typically in hot weather) is
provided at bridges, structures, and intersections in the form of expansion
joints. Expansion joints permit contraction
and expansion of the concrete pavement.
The first two regularly
spaced joints in the concrete pavement adjacent to a bridge approach slab must
be expansion joints (when a pressure relief joint is not included in the
plans). Other expansion joints may be detailed
in the plans at locations at other structures and intersections. Standard
Construction Drawing, BP-2.2 provides additional information on the
installation of expansion joints. All
expansion joints are doweled and allow the pavement to expand or grow due to
temperature variations. A standard
expansion joint allows for 1 inch (25 mm) of expansion.
Figure
451.W – Typical Expansion Joint (left), SCD BP-2.2 Detail of Expansion Joint
Section
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.
Preformed compressible material,
1 inch (25 mm) thick, is installed in the dowel assembly at the location of the
expansion joint. It must be set
perpendicular to the dowel as well as perpendicular to the line of forms and
the pavement centerline. The material
must extend down to 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 pavement surface. It is permissible to place the expansion
material closer to the pavement surface to facilitate sawing of this joint,
provided all material is removed to a depth of 1 inch (25 mm). The 1 inch by 1
inch area at the top of the expansion joint shall be sealed using a hot applied
joint sealer which meet the requirements of 705.04.
Standard 18 inch (460 mm)
long epoxy coated dowels are required for load transfer in all expansion
joints.
Inspectors must ensure that
the 1 inch (25 mm) thick, preformed expansion joint filler is held rigidly in
position and extends the full-width of all lanes. The preformed 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 the holes
with no gaps in which concrete could flow through.
The dowels are oiled 2 hours
prior to placing the concrete with new form oil as is required for contraction
joints. After oiling, an expansion cap,
also called a sleeve, is placed on the opposite ends of adjacent dowels (each
dowel will have one cap, but on alternate ends) to create a void in the
concrete to permit expansion movement.
The cap contains a crimp or stop that provides for the 1-inch (25 mm)
void. These caps must not be forced
beyond the crimp; otherwise, the space for expansion will be compromised and
the joint will not function properly.
The Contractor must provide
adequate consolidation throughout the slab depth, adjacent to the preformed
expansion joint filler, and around dowels by use of hand-held internal
vibrators. The top of the joint must be formed
to a 1-inch (25 mm) wide and 1-inch (25 mm) deep opening, carefully edged using
an edger having a 1/8-inch (3 mm) radius on top of the preformed expansion
joint filler, and sealed with 705.04 joint sealer.
Contraction joints in
concrete pavement are constructed at right angles across a pavement lane unless
otherwise specified by the plans. These
joints control cracking of concrete pavement that result from stresses from
volume changes during curing of the concrete.
These joints are designed to transfer the loading from traffic from one
slab to the next and require the use of dowel bars to accomplish this function. These dowel bars are called load transfer
devices. Dowel bars can be pre-installed
using dowel bar assemblies (basket assemblies) or can be installed using dowel
bar inserters during slip form paving.
Dowels must be spaced at
12-inch (300 mm) centers beginning 6 inches (150 mm) from the longitudinal
joint. 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 Standard
Construction Drawing BP-2.2 or the plan construction drawings. The maximum contraction joint spacing for
reinforced concrete pavement (Item 451) is 21 feet (6.5 m). For non-reinforced concrete pavement (Item
452) and concrete base (Item 305), the maximum spacing is 15 feet (4.6 m).
To function properly, dowels
must be placed parallel to the surface and parallel to the centerline of the
pavement since expansion and contraction movements occur in this
direction.
When a standard (water cooled
diamond bladed) concrete saw is used to cut the contraction joint, the
following applies:
·
Pavement ≤
10 inches thick: Saw the joint to a minimum depth of one-fourth the specified
pavement thickness.
·
Pavements > 10
inches (255 mm) thick: Saw the joint to a minimum depth of one-third the
specified pavement thickness.
·
Saw joints 1/4 ± 1/16 inch (6 ± 1.6 mm) wide as measured at the time of sawing.
When using early-entry (dry
cut, lightweight) saws, only use saw blades and skid plates as recommended by
the manufacturer. Perform the early
entry sawing after initial set and before final set as follows:
·
Saw the joint
2-1/4 to 2-1/2 inches (56 to 63 mm) deep.
·
Saw joints
approximately 1/8 inch (3 mm) wide as measured at the time of sawing.
Joints should be spot checked
to make sure that the Contractor is sawing the pavement to the required depth.
Figure
451.X – Standard Water Cooled Saw (left), Early Entry Saw (right)
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 skipped joints. The standby saw may be put into service to
saw the skipped joints 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 following day, the
pavement is normally subjected to expansive forces when the temperature
rises. When temperatures drop during the
evening of the following day, the pavement experiences shrinkage stresses and
all joints originally bypassed must be sawed before these stresses result in
random cracking.
A HIPERPAV analysis for each day’s paving is
required to be completed by the Contractor.
HIPERPAV software is used to help
determine the correct time for sawing and potential for early age cracking
based on mix design, pavement configuration, and environmental factors. HIPERPAV generates
the critical stress-to-strength of the pavement for the first 72 hours after
placement. Supplement
1033 provides HIPERPAV details. HIPERPAV files
must be provided to the Engineer prior to paving. If the critical
stress-to-strength ratio is 98 percent or greater, the Contractor is required
to modify the paving operation and rerun the HIPERPAV
analysis.
Generally pavement should be
sawed the same day, usually 6 to 8 hours after placing. Concrete placed late in the day may not
harden to permit sawing until the next day, but sawing should be completed
before the following late afternoon temperature change, as shrinkage will occur
as temperatures drop. The Contractor is
responsible for determining the optimal sawing time to prevent uncontrolled
cracking.
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 an existing concrete pavement, which 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 contraction
joints in the previously placed lane of pavement must be in-line with those in
the newly placed lane.
·
The joint sawing
must be done as soon as the saw can be operated on the newly placed pavement
lane without damaging or excessive raveling of the joint.
·
Full-depth joint
cracking in the previously placed lane indicate movement. Therefore, joints in the newly placed lane,
which are in line with the cracked joints, 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,
wide variations in day and night temperatures, or a cold rain cause thermal
changes and add stress, thus making the timing of sawing especially
critical. When these conditions occur
or are anticipated, increased attention to the sawing operation to assure
control of cracking is needed.
Construction joints are
transverse joints 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 doweled 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.
Locate construction joints at
or between contraction joints. If
located between contraction joints, construct the construction joint no closer
than 10 feet (3 m) to the last contraction joint.
In non-reinforced 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 provisions 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.
Figure
451.Y – Transverse Construction Joints Are Doweled
Smooth epoxy-coated dowels
must be used in construction joints placed parallel to the surface of the
base. The dowel size and spacing is the
same as required for standard contraction joints. See 451.09.B for those details.
Finishing behind the concrete
paving operation can be done by a variety of methods. In all cases, a 10-foot straightedge must be
used to continually check the pavement surface for smoothness.
Paving operations may include
floats of different configurations behind the paver. Some slip form pavers include oscillating
longitudinal floats or other types of “automatic” floats attached to the
paver. Regardless of the type of machine
floating, a straightedge should be used to check the pavement surface.
The Contractor is required to
round the edges of the pavement slab to the radius specified before the
concrete sets. For an inside slab edge,
the radius is to be 1/8 inch (3 mm), and for an outside slab edge, the radius
is typically 1/2 inch (13 mm). Any tool
marks left by the edging tool must be eliminated.
Some slip form paving
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 straight edged. However, straight edging should not be
confined to the area of the trailing forms.
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 to produce an acceptable surface that
complies with the specifications. The
preferred method is to keep the machines in proper adjustment and limit the
amount of handwork that is required. 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. Inspection
of tools should be done daily to correct for wear. Tools should be restored to the desired
accurate form. They must be rigid enough
to remain straight with no bending while in use.
After 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
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.
Figure 451.Z – Highway Straightedges/Bump Cutters
behind the Automatic Float
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, the aggregate
grading, mix design, and the method of placing the concrete must be evaluated
and corrected. A properly proportioned
mix along with correct paver operation should not require excessive hand
floating.
No water is to be added to
the surface during this or any other operation.
This includes sprinkling of water on the surface using a brush,
spraying, or otherwise introducing additional water into the finishing process. Adding water reduces the air entrainment in
the surface causing a mortar layer that will not be resistant to freezing and
thawing. This thin weak surface layer
will pop off over time.
The final surface texture
should be applied when most of the water sheen has disappeared, but before
concrete becomes non-plastic. Finishing
methods used must produce the texture as described in the appropriate
specification item.
Unless otherwise specified,
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 longitudinal 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.
Figure
451.AA – Machine Brooming in Longitudinal Direction (left), Transverse
Direction (right)
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.
The broom drag provides 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.
Immediately after brooming,
the pavement is longitudinally tined using a uniform tine spacing of 3/4
inches, 1/8 inch wide, and 1/8 inch deep.
Longitudinal tining must be applied using a machine specifically made for
this application and must be controlled from a stringline that controls the
line and grade of the tining operation.
Longitudinal tining shall be kept 3 inches from the edge of pavement and
any longitudinal joint.
Small areas, as defined by
the Engineer, may be longitudinal tined with non-machine operations. The finished longitudinal tining will be
straight to within 3/4-inch in 20 feet (20 mm in 6.4 m).
Figure 451.BB – Longitudinal Tining
The Contractor is required by
specification to stencil complete station numbers into the plastic concrete
pavement (Item 451 and 452) each 100 feet (50 meters) before the concrete
sets. The dies used to form the station
numbers must be 3 to 4 inches (75 to 100 mm) high and 1/4 inch (6 mm) in
depth. The numbers are placed parallel
to the pavement edge, centered 12 inches (0.30 m) from, and facing the right
edge of the pavement. For the purposes
of placing station numbers, the right edge is the edge to the right of the
normal 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.
For divided highways, station
numbers must be provided for each pavement direction.
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).
Curing is the treatment or
protection provided to concrete during the curing period. Proper curing consists of keeping the
concrete moist and preventing rapid evaporation of the mix water to ensure
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 pavement. Strength loss due to lack of moisture during
this period is difficult to regain even with subsequent curing.
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 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.
Prior to the application of
any curing material, ensure that it meets the requirements of 705.05,
705.06,
or 705.07
Type 2. This also applies to any
equipment used in the application.
For concrete pavement, an approved
curing membrane must be sprayed on all exposed surfaces using a self-propelled
mechanical sprayer with adequate shielding to prevent overspray to adjacent
areas from wind. The curing membrane
must be applied at a minimum rate of 1 gallon per 150 square feet (1 liter per
3.6 square meters) as soon as the free water has dissipated from the
surface. Approved liquid membrane curing
compounds are white in color so that coverage can be readily observed. They are sprayed over the exposed concrete
faces while the concrete is still plastic.
Hand spraying can be used on pavement with integral curb, for small
irregular areas, sections of variable width, and on pavement edges after form
removal.
Project inspection should
include a daily check of the Contractor’s curing compound application rate to
ensure that the correct amount of curing membrane was applied to the
pavement. To do this check, determine
the amount of curing compound required for the day’s placement and compare it
to the amount of curing compound actually used by the Contractor.
To calculate the amount of
curing compound required, the area in square feet (square meters) of pavement
that is to be cured must be determined.
This area includes the top surface of the pavement plus the area of any
pavement edges that are to be cured if the Contractor is slip form paving. Once the area has been calculated, it is
divided by the specified application rate in gallons per square yard (liters
per square meter). The formula below is
used to calculate the required amount of curing compound in gallons (liters):
Required Gallons =
Area (square feet)
Rate (gallons/ square feet)
Required
Liters = Area
(square meters)
Rate (liters/square meter)
The above equations give the
amount of curing compound required in gallons (liters). The amount of gallons (liters) required is
compared to the amount that was actually used during the day’s work. The amount of gallons (liters) of curing
actually used must be equal to or greater than the required amount of gallons
(liters).
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 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 the
concrete pavement will be affected. It
should be noted that concrete with a grooved (tined) surface may require more
curing compound to obtain complete coverage than a base pavement without
tining. The specified application rate
is a minimum and the Contractor must use more if the visual coverage is
lacking.
White pigmented compound is
the only membrane curing compound 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.
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 provides a uniform protective
covering. Streaks, lines, and dribbles
indicate malfunctioning sprayers. The
Contractor must correct the equipment to provide uniform, consistent coverage
over the entire pavement.
Figure
451.CC – Cure/Texture Machine
A water cure using wet burlap,
waterproof paper, or polyethylene sheeting may be used; however, this type of
curing must remain in place for 7 days unless test beams have attained a
modulus of rupture of 600 psi. This type
of curing should be placed as soon as possible without marring the surface.
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 kept wet at all times. This type of curing requires constant
checking throughout the curing period.
This method is not used very frequently; therefore, it is not discussed
in detail.
Waterproof paper or
polyethylene meeting specification requirements (705.05
and 705.06)
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 combination of wet burlap
and waterproof paper or polyethylene sheeting is less labor intensive than a
burlap-only cure, because it will keep the concrete wet and does not require
regular wetting.
Curing blankets, sheeting,
and burlap 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.
Curing materials 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 ensure edges along forms are sealed so
there is no possibility of air getting under the curing material. This is important because air can circulate
over the pavement drying out the surface and resulting in inadequate
curing. In addition, heavy winds will
get under the blankets and rip them off leaving the pavement without any curing
at all.
All physical curing blankets,
sheeting, etc., must be free of holes and torn areas and must be securely
anchored against blowing. These types of
curing methods must be checked daily.
The presence of forms during
early curing protects the pavement edges against damage and serves as a curing
method (for the pavement edges only).
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 be loosened
first, 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 honeycombed areas filled with
mortar. Inspect filled areas to make
sure the entire areas are tightly packed and struck off flush with surface of
the pavement edge.
Curing must be applied to the
edges as soon as forms have been removed and edge patching has been
completed. This ensures curing was
satisfactory as well as prevents the
loss of water necessary for hydration of the cement.
There are two methods that
could be used to check the smoothness of a completed concrete pavement. Item 451.13
requires the use of a 10-foot rolling straightedge or Proposal
Note (PN) 420 that requires the use of a non-contact profiler to measure
smoothness. When PN
420 is required as part of the Contract documents, 451.13
does not apply.
When 451.13
applies, the Contractor is required to check the surface smoothness of the
completed pavement using a 10-foot rolling straightedge or equipment conforming
to Supplement
1058 and output using ProVal software
conforming to PN
420 for a 25-foot localized roughness criteria (see the section on PN
420 below). The rolling straightedge
can be two- or four-wheeled 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 and cleaning 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 an 8 degree curvature or 6
percent grade, the tolerance is 1/4 inch in 10 feet (6 mm in 3.0 m).
Figure
451.DD – 10 foot Rolling Straightedge
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.
Larger concrete paving
contracts (those exceeding 1 mile in centerline length) generally include Proposal
Note (PN) 420 Surface Smoothness Requirements for Pavements. When this proposal note is included, the
provisions of 451.12
do not apply and the Contractor is required to use the information included in PN
420 to determine surface smoothness.
This proposal note requires testing of the surface of completed pavement
with a non-contact profiler and ProVAL software
that will produce an International Roughness Index (IRI).
The non-contact profiler must
meet the requirements of Supplement
1058. The equipment and operator
must be previously approved by the Department.
All equipment and operators that are approved are listed on the
Department’s website. The equipment and
Operator must be checked against the Contractor’s approval letter and against
the Department’s website. The Contractor
must demonstrate the use of the equipment prior to its use on the project.
Figure
451.EE – Non-contact profilers
Low-speed
type used for daily checks (left) and high-speed type for payment (right)
The Contractor is paid a
bonus for exceptionally smooth concrete pavement and there are deductions if
the pavement is not constructed smooth enough.
The pavement must be of a certain level of smoothness to be accepted,
otherwise, corrective work is required.
The IRI is measured for localized roughness (bumps) for any 25-foot
section and for smoothness of any 0.10 mile section. Where there is localized roughness with an
IRI greater than 160 inches per mile in 25 feet, corrective work is required. For an IRI greater than the requirements of PN
420 (currently 95 inches per mile) in any 0.10 mile section, corrective
work is also required.
Defective work, as described
under PN
420, includes removal and replacement or diamond grinding to restore the
surface to within the tolerances required.
When 451.13
applies, and the surface deviations as measured with the 10-foot rolling
straightedge must be ground, the diamond grinding equipment must conform to
Item 257. Bush hammering, carbide tipped grinders, or
any method that may damage the bond of the aggregate or shatter the aggregate
is not permitted.
A 10-foot (3.0 meter)
straightedge must be used to check for compliance when corrective work is in progress. The straightedge can 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.
It may be necessary to
restore grooves in concrete pavement after the concrete has hardened when the
finishing operation does not conform to 451.10 and/or when the tining operation
does not provide the correct pattern or depth.
Grinding to restore trueness leaves a corduroy texture in the
longitudinal direction. The randomly
spaced transverse grooves must be restored as detailed to the dimensions given
in 451.10.
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 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.
Note: When pavement is ground to meet the
requirements of 451.13
Surface Smoothness or PN
420, the restoration of transverse grooving is not required.
Only expansion joints are required
to be sealed. This should be done as
soon as possible after saw cutting and before the pavement is open to
construction equipment or any other traffic.
Proper sealing prevents intrusion of stones and debris into the joint
that would keep it from opening and closing as designed with the movement of
the pavement.
The Engineer may allow the
use of a temporary seal material to allow opening to traffic. This material must be removed prior to the
final sealing of the 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.
Hot-applied joint sealer (705.04)
is required for sealing expansion joints.
Since the hot applied sealer requires heating, frequent checks should be
made to avoid overheating to a temperature higher than the manufacturer’s
recommendation.
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 enter 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.
As air temperature increases,
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.
Prior to final acceptance of
the pavement, any unsatisfactory joint 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.
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 the modulus of
rupture of the test beams is 600 pounds per square inch (4.2 Mpa) or greater.
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 modulus of rupture of 600
pounds per square inch (4.2 Mpa) or greater.
In no case should concrete pavement be opened in less than 3 days.
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.
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.
Slump, air, and yield tests
shall be made and recorded each time beams are cast. Concrete for these tests shall be obtained
from the same batch of concrete that was used in casting the beams.
The Contractor is responsible
for repairing cracked or deficient pavement at no cost to the Department. These deficiencies include:
o
There is an
exception for reinforced 451
pavement that accepts a tight, mid-panel transverse crack. See 451.17.
Repair methods are specified
in 451.17
and include the following:
A. Transverse or diagonally cracked full-depth pavement.
Repair
with a full-depth repair according to
Item 255
and applicable standard construction drawings. Repair
cracks by replacing the pavement the full-width and full-depth between
longitudinal joints, perpendicular to the centerline, and at least 6 feet (1.8
m) longitudinally. Install smooth dowel
bars at the interface between the original pavement and the replaced pavement
section. Locate and size the repairs to
ensure that the repair limits are at least 7 feet (2.1 m) away from any
transverse joint. Item 255
and Standard
Construction Drawing BP-2.5 applies.
B. Longitudinal cracking cracked full-depth
pavement.
Repair
longitudinal cracks within 15 inches (380 mm) of a tied longitudinal joint by
routing and sealing the crack according to Item 423. For longitudinal cracks beyond 15 inches (380
mm), repair the same as for transverse or diagonal cracks stated above.
C. Spalled pavement surfaces.
Repair
spalled pavement with Item 256
Bonded Patching of Portland Cement Concrete Pavement.
D. Pavement panels which have cement or mud balls.
Repair
cement balls or mudballs by coring out the area, full-depth with a diamond core
bit, and replacing the removed concrete with the same concrete as in the
pavement. Remove and replace any
pavement panel with 5 or more cement balls or mudballs. Locate the limits of the repair along the
longitudinal joints and at least 1 foot (0.3 m) past the transverse joints to
remove any existing dowel bars. Install
smooth dowel bars at the transverse limits of the repairs. Install Type D (Drilled Tied Longitudinal)
Joint along the longitudinal limits.
The Contractor must cut cores
from the completed pavement to check the pavement thickness and to determine a
price adjustment if necessary. When the constructed pavement thickness is less
than plan by more than 0.2 inches, a deduction to the contract bid unit price
is made.
One random core must be taken
for every (sublot) 2,000 square yards (1,650 square meters) of a pavement unit
or a major fraction thereof. No less
than three cores will be cut for any pavement unit. For the purpose of coring, the Department
will consider the entire pavement area of a specified thickness a unit. The Engineer will determine the locations for
the random cores according to Supplement
1064.
Core thickness must be
measured by the Engineer in accordance with AASHTO T 148. When a core shows a deficiency in thickness
of more than 1/2 inch (13 mm) from the specified thickness, the Contractor must
take additional cores as directed by the Engineer to determine the limits of
the deficiency. Follow the procedures
below to determine how and when to cut additional cores:
1. Take a core 5 feet (1.5 m) longitudinally on both
sides of the deficient core. If both
cores are less than 1/2 inch (13 mm) deficient in thickness, the zone of
deficiency has been determined.
2. If either or both cores are more than 1/2 inch (13 mm)
deficient in thickness, cut a core 50 feet (15 m) longitudinally from the
deficient core(s). If the 50-foot (15 m) core(s) is more than 1/2
inch (13 mm) deficient, cut additional cores in 100-foot (30 m) longitudinal
intervals until a core is less than 1/2 inch (13 mm) deficient in thickness,
until the pavement ends, or until overlapping an adjacent pavement lot’s core
in the same lane.
3. If a pavement sublot has cores more than 1/2 inch (13
mm) deficient in thickness, and the sublot’s constructed width is greater than
12 feet (3.6 m), obtain cores transverse to the location of the more than 1/2
inch (13 mm) deficient cores. Obtain transverse
cores at a location one-half the distance from the deficient core to the
furthest edge of pavement. Obtain
transverse cores for each core more than 1/2 inch (13 mm) deficient in
thickness.
4. The Engineer will use the cores that measure less than
1/2 inch (13 mm) deficient in thickness to define the limits of the
deficiency. The price adjustment would
apply to these limits of deficiency.
Note: The zone of deficiency is also called zone of deficient thickness.
Whether the concrete pavement
item is “with QC/QA” or not, additional strength cores will be obtained from
the sample location as the thickness cores.
The Contractor is required to
obtain the cores at the same location as 451.18.A
for the Engineer. The Contractor
determines when he wants all the cores tested (from 28 to 90 days) and notifies
the Engineer.
If the concrete is QC/QA the
Contractor’s laboratory performs the QC core testing conforming to the accepted
QCP and Item 455. The Engineer will require a QA core be
obtained for every 10 sublots for verification testing. Those QA cores will be provided to the
Engineer for curing and testing by the District Laboratory. The Department will test the core at the
number of Contractor specified days. QA
Results are compared to the companion Contractor QC core result. Acceptable results are defined in Item 455.
An average strength and a
standard deviation are calculated using the Contractor’s verified QC core
results. Follow the procedures of Supplement
1127.
If the concrete is not QC/QA,
the Department will obtain the strength cores from the Contractor and the
District Laboratory will perform the testing of the cores for acceptance. Strength acceptance will be based on the
individual core results not an average and standard deviation.
Price adjustments are based
on the pavement average thickness. The pavement
is to be constructed such that the thickness is not more than 0.2 inches (5 mm)
less than the specified thickness at any location. When this criterion is met, the Contractor
receives 100 percent of the contract bid price.
When a core or cores are
greater than 1 inch deficient in thickness, the pavement must be removed and
replaced. The Zone of Deficiency for the
removal is determined as outlined above.
For zones of deficiencies
with pavement thickness 1/2 inch to 1 inch deficient, the Engineer must
calculate the average thickness of concrete pavement to determine price
adjustments.
Two averages must be
calculated as follows:
1. Calculate a Project Average Thickness (PAT) using all
cores from all lots that are ≤ 1/2 inch deficient in thickness.
2. Calculate a Deficient Zone Average (DZA) using all
cores with a thickness deficiency of >1 1/2 inch.
Note: When calculating PAT, cores > 1/2 inch
thicker than the plan thickness are considered to be plan thickness + 1/2 inch
for the PAT calculation. For example, if
plan thickness is 10 inches and the core measured 10.75 inches, use 10 inches +
1/2 = 10.5 inches when calculating the PAT.
The PAT and DZA are used to
determine the price adjustment for each section of deficient pavement using the
zone of deficiency area previously determined based on the coring operation.
The following table
illustrates how the price adjustment is applied:
Deficiency
in Thickness as Determined by Cores |
Proportional
Part of Contract Price |
0.0 to .2 inch (0.0 to 5 mm) |
100 percent |
0.3 to 0.5 inch (6 to 13 mm) |
|
0.6 to 1.0 inch (15 to 25 mm)* |
|
Greater than 1.0 inch (25 mm) |
Remove and replace |
* The District
Construction Administrator will determine whether pavement areas from 0.6 inch (15
mm) up to 1 inch (25 mm) deficient in thickness will be allowed to remain in
place at the reduced price or must be removed and replaced.
If any deficient core is
greater than 1 inch (25 mm) deficient in thickness, determine the limits of
over 1 inch (25 mm) deficiency by following 451.17,
Steps 1 through 4, to determine the limits. Remove and replace those areas
greater than 1 inch (25 mm) deficient in thickness.
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.
The pavement areas
represented by the PAT of DZA are to be calculated and paid separately.
Deductions are determined and
applied to each separately placed width of pavement.
If any pavement area is
removed and replaced, the replaced pavement must be cored, and core values
determined are to be included in the average calculations.
A
Contractor places 150,000 square yards of 10-inch concrete pavement. The contract price is $38 per square
yard. If the Project Average Thickness
(PAT) is 9.7 inches and the Plan Specified Thickness (PST) is 10 inches, what
would the Contractor be paid?
The
thickness deficiency is: 10 inches – 9.7
inches = 0.3 inches
From
Table 451.17-1, look up the price adjustment for a 0.3 inch thickness
deficiency.
Use
that formula to determine the Proportion Part of Contract Price as follows:
Proportion Part of the Contract Price = = 0.8330
Then
the Contractor’s Payment for 150,000 sq. yards is calculated as follows:
(150,000
sq. yards) x ($38.00 per sq. yards) x (0.8330) = $4,748,100
Note:
this results in a deduction of $951,900 for this pavement area.
Record the compressive
strength results for each sublot of concrete.
High-early strength mixes, QC MS and QC FS mixes, are calculated
separately. Determine the strength pay
factor according to Table 451.19-2.
TABLE 451.19-2 |
CONCRETE PAVEMENT STRENGTH PAY
FACTOR |
Design Strength = f’c from 499 or as per plan Individual Sublot Core
Strength = x Project Average
Strength () = Project Standard
Deviation (δ) = Project Required
Strength (f’cr) = f’c + 1.65 δ Strength Pay Factor (PFS)
= / f’cr * |
* When PFS
is greater than 1.00, pay the unit bid price |
For high-early strength sublots, determine the pay factor
separately as follows: ·
If the individual sublot core strength (x) is greater than f’c, PFS = 100% of the Unit
bid price for the quantity represented. ·
If the individual sublot core strength (x) is less than f’c, then PFS = /f’c) of the unit bid price for the
quantity represented. |
When the Project plans
include Proposal Note 420 determine a lump sum payment adjustment following the
requirements of Proposal
Note 420.
When a pavement exhibits
multiple deficiencies for thickness and strength, the reduced unit price will
be calculated for each deficiency and the lowest reduced unit price will be
used. Adjustment for smoothness under 451.19.C
will conform to the lump sum requirements of 451.19.C.
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. The Engineer will measure the
length along the 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 involve
concrete pavement quantities must be shown fully documented. In addition, any areas found to be deficient
in thickness must be documented and the adjustment made in the pay quantity.
Payment is made for accepted
quantities of pavement by the square yard (square meter) at the contract bid
price. If pavement is found to be
deficient in thickness or compressive strength, the Department will pay a
reduced price according to 451.19.
When a pavement exhibits
multiple deficiencies for thickness and strength, the reduced unit price will
be calculated for each deficiency and the lowest reduced unit price will be
used. Adjustment for smoothness under 451.19.C
will conform to the lump sum requirements of 451.19.C.
There is no additional
payment for any pavement constructed and found to have an average thickness in
excess of the thickness specified.
1. Document subgrade/subbase preparation.
2. Document contraction, expansion, and longitudinal
joints dowel and tiebar sizes, type, coating, support, placement, and spacing.
3. Document forms set 100 percent bearing, correct
alignment and grade, rigid, clean and oiled.
4. Document length of lap, clearance maintained on steel
mesh.
5. Document contraction joint spacing, dowels oiled,
dowel assembly tie wires removed, number and size of pins used to hold dowel
assembly, and alignment of dowels.
6. For slip form construction document:
a. Test section results.
a. Approval of slip form paver.
b. Alignment of dowels using MIT Scan-2.
c. Corrective action as required.
7. Document concrete placement, including all quality
control testing, method of placement, finishing, tining, curing (type and
amount), stamping of stationing, and weather conditions.
8. Document use of HIPERPAV
software, time of sawing, depth, and width of sawed joints.
9. Document coring for thickness verification and
results.
10. Record results of beam breaks and opening to traffic.
11. Measure length and width for pay.
12. Document on CA-D-3A
or CA-D-3B or other approved forms.