cutting by air-water jets will not be permitted for concrete surfaces
congested with reinforcing steel or if they are relatively inaccessible.
If, for any other reason, it is considered undesirable to disturb the
surface of a lift before it has hardened, the use of sandblasting or
high-pressure water jet after hardening will be required. Regardless of
the method used, the resulting surface shall be free from all laitance and
inferior concrete so that clean, well-bonded coarse aggregate particles are
exposed uniformly over the lift surface. Application of the joint
treatment method shall be such that the edges of the larger particles of
aggregate are not undercut. Where joint preparation occurs more than 2
days prior to placing the next lift or where the work in the area
subsequent to the joint preparation causes dirt or debris to be deposited
on the surface, the surface shall be cleaned as the last operation prior to
placing the next lift. The surface of the construction joint shall be kept
continuously wet for the first 12 hours of the 24 hours prior to placing
concrete, except that the surface shall be damp with no free water at the
time of placement.
3.2.5.2
Air-Water Cutting
Air-water cutting of a construction joint shall be performed at the proper
time, generally between 4 and 12 hours after placement and only on
horizontal construction joints. This period may be modified if a retarder
is used to prolong the setting of the cement at surface of the concrete.
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 a surface 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 its application. After cutting, the surface shall be washed
and rinsed until the wash water is no longer cloudy. If air-water cutting
does not produce acceptable results, the surface shall be prepared by
high-pressure water jet or sandblasting.
3.2.5.3
High-Pressure Water Jet
A stream of water under a pressure of not less than 21 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
high-pressure water jet is incapable of a satisfactory cleaning, the
surface shall be cleaned by sandblasting.
3.2.5.4
Wet Sandblasting
This method of joint preparation may be used when the concrete has reached
sufficient strength to prevent undercutting of coarse aggregate particles.
The operation shall be continued until all accumulated laitance, coatings,
stains, debris, and foreign materials are removed. The surface of the
concrete shall then be washed thoroughly to remove all loose material.
This method may be used on both horizontal and vertical surfaces.
3.2.5.5
Waste Water Disposal
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NOTE: Specification Writer will fill in the section
number for the Environment Protection Plan.
SECTION 03700
Page 57
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