surface of the base slab shall be thoroughly cleaned with an air-water jet
immediately before placing the topping. A thin coat of neat cement grout
of about the consistency of thick cream shall be thoroughly scrubbed into
the existing surface immediately ahead of the overlay placing. At the time
the neat cement grout is placed, the existing concrete surface shall be
damp but shall have no free water present. The overlay concrete shall be
deposited before the grout coat has had time to stiffen.
3.12.8.3
Placing and Finishing
Concrete shall be placed, as nearly as practicable in final position, in a
uniform layer. The overlay shall be placed and screeded slightly above the
required finished grade, compacted by rolling with rollers weighing not
less than 4.5 kg/linear 25 mm 10 pounds/linear inch of roller width or by
approved tamping equipment and finish screeded to established grade. Grid
type tampers shall not be used. The concrete, while still green but
sufficiently hardened to bear a person's weight without deep imprint, shall
be floated to a true even plane with no coarse aggregate visible. Floating
shall be performed with an approved disc-type mechanical float which has
integral impact mechanism. The surface of the overlay shall then be left
undisturbed until the concrete has hardened enough to prevent excess fines
from being worked to the top. Joints shall be formed to match those in the
base slab.
3.12.8.4
Curing and Protection
Concrete shall be maintained in a moist condition and shall be protected
against rapid temperature change, mechanical injury, and injury from rain
or flowing water, for a curing period of not less than 10 days. Concrete
shall be maintained in a moist condition at temperatures above 10 and below
30 degrees C above 50 and below 90 degrees F throughout the specified
curing period. Concrete shall be protected from a temperature change
greater than 3 degrees C 5 degrees F per hour and from rapid drying for the
first 24 hours following the removal of temperature protection. Curing
activities shall begin as soon as free water has disappeared from the
concrete surface after placing and finishing. Curing shall be moist curing
accomplished by the following method. Surfaces shall be covered with a
double layer of burlap, wetted before placing, and overlapped at least 150
mm 6 inches. Burlap shall be kept continually wet and in intimate contact
with the surface. Burlap shall be kept covered with a polyethylene
sheeting at least 0.1 mm 4 mils thick. All traffic shall be kept from the
floor during the curing period and heavy traffic shall be kept off till
28-day age.
3.12.9
Two-Course Floor Construction
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NOTE: Where it is anticipated that the surface of a
floor slab may be damaged during construction
operations, a two-course floor may be specified with
the second course applied late in the contract. If
the drawings do not indicate areas to receive
two-course floor construction, they must be
specified here. Delete this subparagraph when
two-course floor is not required. Edit bracketed
items.
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[Areas as indicated on the drawings] [The following areas [_____]] shall
SECTION 03300A
Page 57
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