We have published many posts about cracking in concrete members. Of this plastic shrinkage cracking is generated by the adverse affect of weather. Here we will try to summarize some preventive measure to control such cracking.
While concreting in adverse weather condition which leads to moisture losses at very rapid rates, plastic shrinkage cracks is generated. The factors that influence the moisture loss are follows:
a. Air temperature
b. Concrete temperature
c. Relative humidity
d. Wind velocity
These factors have to be considered at concrete surface and surroundings. The combination of these factors can accelerated the rate of evaporation at surfaces; these may be either in cold or hot weather.
Now prevention of plastic shrinkage cracking means preventing rapid moisture loss. Moisture loss, as discussed above, due to hot weather and dry winds. We have publish some useful information regarding hot weather concreting according to ACI 305R. Here we are listing the measures to reduce moisture loss:
a. Application of fog nozzles; these method saturates the air surrounding (above) finish surface.
b. Application of sheeting over concrete; most common is plastic sheeting. This method also retards moisture loss. Sheets cover the surface between consecutive finishing operation.
c. Wind breaks; these reduce the velocity of wind; thus reducing moisture loss due to dry wind. The flat work is scheduled in such way that erected wind breaks start working.
d. Sunshades; this also reduce the temperature of surface.
Besides this scheduling placement or starting concreting operation at night, is sometimes advised, which works good without external preventive measures discussed above. This is advised during hot day time with low humidity in windy weather.
We have witnessed concreting in Burj khalifa at night to avoid unfavorable weather of Dubai. You can visit “special feature of concrete in Burj Dubai” for more information.