entering the mixer shall be free from ice, snow, or frozen lumps. Salt,
chemicals or other materials shall not be incorporated in the concrete to
prevent freezing. Upon written approval, an accelerating admixture
conforming to ASTM C 494/C 494M, Type C or E may be used, provided it
contains no calcium chloride. Calcium chloride shall not be used.
3.8.4
Hot Weather Requirements
**************************************************************************
NOTE: If desired, placement of floor slabs may be
specified to be delayed until a roof is in place.
Additional information concerning hot weather
concreting may be obtained from ACI 305R.
**************************************************************************
When the ambient temperature during concrete placing is expected to exceed
30 degrees C 85 degrees F, the concrete shall be placed and finished with
procedures previously submitted and as specified herein. The concrete
temperature at time of delivery to the forms shall not exceed the
temperature shown in the table below when measured in accordance with ASTM
C 1064/C 1064M. Cooling of the mixing water or aggregates or placing
concrete in the cooler part of the day may be required to obtain an
adequate placing temperature. A retarder may be used, as approved, to
facilitate placing and finishing. Steel forms and reinforcements shall be
cooled as approved prior to concrete placement when steel temperatures are
greater than 49 degrees C 120 degrees F. Conveying and placing equipment
shall be cooled if necessary to maintain proper concrete-placing
temperature.
Maximum Allowable Concrete Placing Temperature
Relative Humidity, Percent,
Maximum Allowable Concrete
During Time of
Temperature
Concrete Placement
Degrees
Greater than 60
33 C 90 F
40-60
30 C 85 F
Less than 40
27 C 80 F
3.8.5
Prevention of Plastic Shrinkage Cracking
During hot weather with low humidity, and particularly with appreciable
wind, as well as interior placements when space heaters produce low
humidity, the Contractor shall be alert to the tendency for plastic
shrinkage cracks to develop and shall institute measures to prevent this.
Particular care shall be taken if plastic shrinkage cracking is potentially
imminent and especially if it has developed during a previous placement.
Periods of high potential for plastic shrinkage cracking can be anticipated
by use of Fig. 2.1.5 of ACI 305R. In addition the concrete placement shall
be further protected by erecting shades and windbreaks and by applying fog
sprays of water, sprinkling, ponding or wet covering. Plastic shrinkage
cracks that occur shall be filled by injection of epoxy resin as directed,
after the concrete hardens. Plastic shrinkage cracks shall never be
troweled over or filled with slurry.
3.8.6
Placing Concrete Underwater
**************************************************************************
NOTE: Delete this paragraph when not applicable.
SECTION 03300A
Page 43
Previous Page
