ITEM 520 PNEUMATICALLY PLACED MORTAR
520.01
Description
520.02
Materials
520.03 Removal
of Concrete
520.04
Reinforcement
520.05
Preparation of Repair Area
520.06 Mixing
520.07
Proportions
520.08 Pressures
520.09
Preconstruction Testing
520.10 Placing
520.11
Inspection and Testing
520.12 Method
of Measurement
520.13 Basis of
Payment
520.01 Description. This work consists of
repairing the surface of concrete structures using pneumatically placed mortar
where the depth of repair generally is less than 6 inches (150 mm).
520.02 Materials. Furnish materials conforming to:
Reinforcing
steel........................................................... 509
Portland cement
................ 701.01 through 701.05, 701.09
Fine aggregate.............................................
703.02, 703.03
Welded steel wire
fabric.......................... 709.10 or 709.12
Use
water free from sewage, oil, acid, strong alkalis, vegetable matter, clay, and
loam. Potable water is satisfactory for use in mortar.
520.03 Removal of Concrete. In areas
to be repaired, remove all loose, soft, honeycombed, and disintegrated
concrete, plus a 1/4-inch (6 mm) depth of sound concrete. Remove
additional concrete as necessary to permit the placement of the minimum
specified mortar thickness of not less than 1 1/2 inches (38 mm),
except on top horizontal surfaces where it shall not be less than 3/4 inch (19
mm). Perform all work in such a manner as not to damage or shatter the
concrete that is to remain in place. Make square or, preferably, slightly
undercut shoulders at the edge of all repair areas.
Encase
reinforcing bars exposed after concrete removal, as required above, with
pneumatically placed mortar. If these bars are less than 1 inch (25 mm) from
the proposed finished surface of mortar, drive them back, if practical, into
recesses cut in the masonry to obtain that coverage. If this is
impractical because of large concentrations of reinforcing bars, provide the
minimum specified mortar coverage by modifying the finish surface as the
Engineer approves.
If
the bond between the concrete and a primary reinforcing bar has been destroyed,
or if more than one-half of the periphery of a bar has
been exposed, remove the adjacent concrete to a depth that will provide a
minimum 3/4-inch (19 mm) clearance around the bar, except where other
reinforcing bars make this clearance impractical. Adequately support reinforcing that has become loose, and tie it back
into place. Replace reinforcement that is damaged during construction
operations.
Only
use pneumatic or hand tools that give results satisfactory to the Engineer in
the removal of concrete and in preparing and shaping the areas to be repaired.
If
working around reinforcing steel, avoid loosening the steel, or shattering the
concrete around it, beyond the repair area.
520.04 Reinforcement. If pneumatically placed
mortar is specified to repair areas of unsatisfactory concrete, or for surface
coverage of exposed reinforcing steel, place wire fabric in all areas where the
thickness of the mortar patch is 1 1/2 inches (38 mm) or more.
For areas where the thickness of the mortar patch exceeds 4 inches (100 mm),
use a single layer of wire fabric to reinforce each 4-inch (100 mm) thickness
of patch or fractional part thereof. Use fabric that is either 2 x 2
inches (50 x 50 mm) using wire size number W 0.9, or 3 x 3 inches (75 x 75
mm) using wire size number W 1.4. Place all
fabric parallel to the proposed finished surface. Completely encase each
layer of fabric in mortar that has taken its initial set before the succeeding
layer of fabric is applied. Ensure that fabric supported adjacent to the
prepared masonry surface is no closer than 1/2 inch (13 mm) to that
surface. Overlap adjacent sheets of fabric by 6 inches (150 mm), and
securely tie them together. Carefully pre-bend fabric
before installation to fit around corners and into re-entrant angles.
Never spring fabric into place.
Place
all steel items, including reinforcing bars and wire fabric, no closer than 1
inch (25 mm) to the proposed finished surface of mortar.
Support wire
fabric with anchor bolts except where existing reinforcing steel in the repair
area is considered by the Engineer to be satisfactory for this purpose.
Construct anchors of 1/4-inch (6 mm) minimum diameter expansion hook bolts, and
ensure that each bolt has sufficient engagement in sound masonry. For
repairs that are generally 4 inches (100 mm) thick or less, space anchors no
more than 12 inches (0.3 m) and 18 inches (0.5 m), center-to-center, on
overhead and vertical surfaces, respectively, and 36 inches (1.0 m),
center-to-center, on top horizontal surfaces. For repairs that exceed 4
inches (100 mm) in thickness, ensure that the anchor bolts are capable of
supporting three times the weight of suspended mortar and two times the weight
of mortar on vertical surfaces. Use at least three anchors for each
patch.
If specified,
thoroughly clean reinforcing exposed in the original structure, or exposed
after removals as required above, and restore any
appreciable reduction in steel area as directed.
520.05 Preparation of Repair Area. After
removing all unsatisfactory concrete, properly shaping the sound concrete surface,
placing dowels and expansion hook bolts, and restoring steel area as directed,
and within 24 hours before placing the mortar, blast clean all surfaces to
which the mortar is to bond, including exposed reinforcing steel, existing
concrete, and the work face of any previously placed mortar, to remove all
spalls, laitance, and contaminants detrimental to the achievement of an
adequate bond. The Contractor may blast clean these surfaces using
high-pressure water blasting with or without abrasives in the water, abrasive
blasting with containment, or vacuum abrasive blasting. If a bonding
compound is not specified, drench the prepared masonry surface with water and
keep the prepared surface wet during the 2 hours preceding the placement of the
mortar. Ensure that all surfaces are damp, but without free water, while
placing mortar. The Engineer will approve the preparation and condition
of all surfaces immediately before the application of the mortar.
520.06 Mixing. Thoroughly dry mix the materials
in a batch mixer. Before placing the mixture in the hopper of the cement
gun, remove all materials and lumps over 1/4 inch (6 mm) in size by screening.
Apply
the screened sand and cement to the masonry surface within 1 hour after being
combined.
520.07 Proportions. Ensure that the mixture as
placed in the hopper has a ratio of one volume of portland cement to three volumes of sand.
520.08 Pressures. Use at least 35 pounds per square
inch (240 kPa) pneumatic pressure at the cement gun
in placing the mixed material. If more than 100 feet (30 m) of hose or a
greater lift than 25 feet (7.5 m) is used, increase the pressure
proportionately. Maintain the water at a uniform pressure of not less
than 25 pounds per square inch (170 kPa) above the
pressure of the air on the gage at the cement gun.
520.09 Preconstruction Testing. Before
the start of placing any mortar, perform a preconstruction test to verify the
operation of the equipment, to confirm the application crew’s capability, and
to ensure the pneumatically placed mortar will be of acceptable quality.
Fabricate the
test panel by gunning mortar onto the plywood bottom of an open box 4-foot (1.2
m) square and 4 inches (100 mm) deep. Install reinforcement in the
test panel that matches the largest size and tightest spacing found for the
reinforcement in the bridge. Mount the box vertically and apply the
mortar using the same personnel, equipment, and procedures that will be used on
the project, until the box is full. Adjust the mixing water to provide
mortar of the proper consistency, but do not exceed a total water content,
including the free moisture in the aggregate and water added at the nozzle, of
4.5 gallons (17 L) per sack of cement (94 pounds = 42.6 kg).
Take three cores
from the test panel, and test them for compressive strength at an independent
testing laboratory. Ensure that the strength at 28 days is a minimum of
4200 pounds per square inch (29.5 MPa) or at a
minimum compressive strength of 3200 pounds per square inch (22.5 MPa) at 7 days.
After taking the
cores, break the test panel and allow the Engineer to carefully examine the
interior portions. Ensure that they are substantially free of hollow
areas and sand pockets, and ensure that the mortar is well bonded to the
reinforcement.
Have each crew
proposed to perform this work fabricate a satisfactory panel before allowing
that crew to apply mortar to the structure.
520.10 Placing. Place the premixed dry cement and
sand by pneumatic equipment with the proper amount of water applied in the
mixing nozzle for the correct placement consistency. Apply the mortar as
dry as practical to prevent shrinkage cracking. Use shooting strips to
ensure square corners, straight lines, and a plane surface of mortar, except as
otherwise permitted by the plans or approved by the Engineer. Place
shooting strips so as to keep the trapping of rebound at a minimum. At
the end of each day’s work, or similar stopping periods requiring construction
joints, slope the mortar off to a thin edge. In shooting all surfaces,
ensure that the stream of flowing material from the nozzle impinges as nearly
as possible at right angles to the surface being covered, and hold the nozzle 2
to 4 feet (0.6 to 1.2 m) from the working surface.
Apply
a sufficient number of mortar coats to obtain the required thickness.
Finish mortar repairs flush with the original masonry surface, except as noted
for areas of exposed reinforcing steel. On vertical and overhead
surfaces, do not apply any coat thicker than 1 inch (25 mm), except as the
Engineer approves, and place each coat so that it will neither sag nor decrease
the bond of the preceding coat. If a successive coat is applied on mortar
that has set for more than 2 hours, clean and dampen the mortar surface as
required in 520.05 for the prepared masonry
surface. Remove deposits of rebound from previous shooting, whether loose
or cemented.
After
mortar has been placed to the desired thickness, cut off all high spots with a
sharp trowel, or screed them to a true plane as
determined by shooting strips or by the original masonry surface, or as
directed. If using screeds, apply them lightly to all surfaces so as not
to disturb the mortar for an appreciable depth, and work them in an upward
direction when applied on vertical surfaces. Unless otherwise directed,
give the finished mortar surface a flash coat about 1/8 inch (3 mm)
thick. Take special care to obtain a sightly
appearance on all exposed surfaces.
Cover
the pneumatically placed mortar patches with burlap or cotton mats, and keep
them wet for 7 days after placing. If it is not practical to use mats,
keep the surface wet by sprinkling for the same length of time. If the
Engineer determines that the above curing procedures are impractical because of
the inaccessibility of isolated repair areas, the Contractor may cure the final
mortar surface according to 511.17, Method
B. Do not place pneumatically placed mortar when the air temperature is
below 50 °F (10 °C) or against a surface in which there remains any
frost. Protect all mortar against cold weather according to 511.15.
520.11 Inspection and Testing. After
curing and before final acceptance, sound all patched areas. Remove and
replace all unsound or cracked areas. In addition to sounding all patches, the
Department will base acceptance of the pneumatically placed mortar on 4-inch
(100 mm) diameter cores taken from patched areas and tested for compressive
strength. The Engineer will determine the location of the cores, with one core
being taken for each 200 square feet (20 m2) of pneumatically placed
mortar. Drill the cores completely through the patched area and into the
underlying sound concrete at least 1/2 inches. Ensure that the depth of
the cores is at least 4 inches. The Engineer will visually inspect the
cores at the site for hollow areas, sand pockets, and voids around reinforcing
steel. Test the cores at an independent laboratory for compressive
strength. The required minimum average compressive strength is 3000
pounds per square inch (21 MPa) at 7 days, with no
single core test less than 2600 pounds per square inch (18 Mpa).
The
Engineer will waive coring on small quantities or overhead patches if it is
determined by sounding and visual inspection that the patches are
sound.
Remove,
replace, re-inspect, and re-test all defective patches, as determined by
sounding, visible cracks, or unacceptable
cores.
Fill
core holes with concrete according to 519.
520.12 Method of Measurement. The
Department will measure Pneumatically Placed Mortar by the number of square
feet (square meters) as determined under Method A, unless Method B or another
method is specified.
A.
Method A. The Department will
measure the actual area of exposed surfaces of all completed, tested, and
approved patches, irrespective of depth or thickness of the patch. If a
patch includes corners or edges of such members as beams, columns, or curbs,
the Department will include all of the exposed surfaces; or if a patch extends
completely through a member or a slab, the Department will include both exposed
surfaces.
B. Method B. For unreinforced mortar repairs, the Department
will measure the actual area of exposed surfaces of all completed, tested, and
approved patches, irrespective of depth or thickness of patch. If a patch includes corners, or edges of such members as beams,
columns, or curbs, the Department will include all of the exposed surfaces.
For fabric reinforced mortar repairs, the Department will measure the actual
surface area of fabric, complete and in place. The Department will
consider fabric laps and layers of fabric closer than 2 1/2 inches (65 mm),
center-to-center of layer, as a single layer in area measurements. The
Contractor and the Engineer will agree on the measured area of wire fabric
before said fabric is encased in mortar, otherwise the Department will obtain
the area of the patch for pay purposes as described for unreinforced mortar
repairs.
The
Contractor is responsible for all test panels, coring repair of core holes,
independent laboratory testing of the cores, and replacement of rejected areas
and shall include them under Pneumatically Placed Mortar.
520.13 Basis of Payment. The
Department will not pay for additional reinforcement to replace that damaged by
the Contractor’s operations.
The
Department will not pay for removing, replacing, and re-inspecting of defective
patched mortar as determined by sounding, visible cracks, or unacceptable
cores.
The
Department will pay for accepted quantities at the contract price as follows:
Item
Unit
Description
520
Square
Foot
Pneumatically Placed Mortar
(Square Meter)