have floors constructed with two-course construction. Two-course floor
shall be constructed by placing a bonded topping on the thoroughly hardened
concrete base slab which has been left with a rough slab finish left 50 mm
2 inches below final grade as shown on the drawings. Topping shall be
applied at an approved time late in the contract period. The floor topping
mixture shall have a specified compressive strength of 34.5 MPa 5000 psi at
28 days, a 50 mm 2 inch maximum slump, 12.5 mm 1/2 inch maximum size coarse
aggregate, and shall be proportioned to obtain required finishability. The
surface of the base slab shall be thoroughly cleaned by sandblasting or
high-pressure waterjet immediately before placing topping. The temperature
of the fresh concrete topping shall not vary more than 5 degrees C 10
degrees F plus or minus from the temperature of the base slab. The ambient
temperature of the space adjacent to the concrete placement and of the base
slab shall be between 10 and 30 degrees C 50 and 90 degrees F. The base
slab shall be kept continuously wet for the first 12 hours during the 24
hour period immediately prior to placing the finished floor. After all
free water has evaporated or has been removed from the surface, a grout
shall be scrubbed in. The grout shall be a 1:1 mixture of portland cement
and sand passing the 2.36 mm No. 8 sieve mixed to a creamlike consistency.
The grout shall be scrubbed into the surface just ahead of the concrete
topping placing operation. While the grout is still damp, the top course
shall be spread and screeded and darbied or bull floated. When the surface
moisture has disappeared, the surface shall then be floated with disc-type
power float with integral impact mechanism followed by a minimum of two
power trowelings. Trowel marks left by the machine shall be removed by a
final, hard steel troweling by hand. Joints shall be formed to match those
in the base slab. Concrete shall be maintained in a moist condition and
shall be protected against rapid temperature change, mechanical injury, and
injury from rain or 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 F 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 be started immediately as soon as free water has
disappeared from the surface of the concrete 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 topping during the curing period.
3.13
FLOOR HARDENER
**************************************************************************
NOTE: If the drawings do not indicate the areas to
receive floor hardener, they must be specified here.
Normally, floor hardener is not needed. Use only
where extreme dust-free area is required or where
requested by using service.
**************************************************************************
[Areas as indicated on the drawings] [The following areas [_____]] shall be
treated with floor hardener. Floor hardener shall be applied after the
concrete has been cured and then air dried for [14] [28] days. Three coats
shall be applied, each the day after the preceding coat was applied. For
the first application, 0.5 kg one pound of the silocofluoride shall be
dissolved in 4 liters one gallon of water. For subsequent applications,
SECTION 03300A
Page 58
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