horizontal surfaces shall be covered, immediately before the concrete is
placed, with a layer of mortar proportioned similar to that in the concrete
mixture. The mortar shall be covered with concrete before the time of
initial setting of the mortar.
3.2.4
Construction Joint Treatment
Construction joint treatment shall conform to the following requirements.
3.2.4.1
Concrete surfaces to which additional concrete is to be bonded shall be
prepared for receiving the next lift or adjacent concrete by cleaning with
either air-water cutting, sandblasting, high-pressure water jet, or other
approved method. Air-water cutting will not be permitted on formed
surfaces or surfaces congested with reinforcing steel. Regardless of the
method used, the resulting surfaces shall be free from all laitance and
inferior concrete so that clean, well bonded coarse aggregate is exposed
uniformly throughout the lift surface. The edges of the coarse aggregate
shall not be undercut. The surface shall be washed clean again as the last
operation prior to placing the next lift. There shall be no standing water
on the surface upon which concrete is placed.
3.2.4.2
Air-Water Cutting
Air-water cutting of a construction joint shall be performed at the proper
time and only on horizontal construction joints. The air pressure used in
the jet shall be 620 to 760 kPa 90 to 110 psi, and the water pressure shall
be just sufficient to bring the water into effective influence of the air
pressure. When approved by the Contracting Officer, a retarder complying
with the requirements of COE CRD-C 94 may be applied to the surface of the
lift to prolong the period of time during which air-water cutting is
effective. Prior to receiving approval, the Contractor shall furnish
samples of the material to be used and shall demonstrate the method to be
used in applications. After cutting, the surface shall be washed and
rinsed as long as there is any trace of cloudiness of the wash water.
Where necessary to remove accumulated laitance, coatings, stains, debris,
and other foreign material, high-pressure water jet or sandblasting will be
required as the last operation before placing the next lift.
3.2.4.3
High-Pressure Water Jet
A stream of water under a pressure of not less than 20.7 MPa 3,000 psi may
be used for cleaning. Its use shall be delayed until the concrete is
sufficiently hard so that only the surface skin or mortar is removed and
there is no undercutting of coarse-aggregate particles. If the water jet
is incapable of a satisfactory cleaning, the surface shall be cleaned by
sandblasting.
3.2.4.4
Wet Sandblasting
This method may be used when the concrete has reached sufficient strength
to prevent undercutting of the coarse aggregate particles. The surface of
the concrete shall then be washed thoroughly to remove all loose materials.
3.2.4.5
Waste Disposal
The method used in disposing of waste water employed in cutting, washing,
and rinsing of concrete surfaces shall be such that the waste water does
SECTION 03301A
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