Plastic shrinkage cracking in hot weather conditions

Abstract

Deterioration of concrete structures, due to the hot climatic conditions, is one of the major problems in the Arabian Gulf countries. The hot-weather affects both the fresh and hardened properties of concrete. On of the drawbacks of hot weather, which has not been adequately studied is the cracking due to plastic shrinkage. The cracks so formed become the focal point of the ingress of harmful elements into the concrete matrix. This research was conducted to investigate the effect of environment conditions and mix proportions on plastic shrinkage cracking in concrete. The effect of ralative humidity, wind velocity, ambient temperature, cement content, water cement ratio and cement type on the water evaporation, plastic shrinkage cracking, bleeding, shrinkage strains, compressive strength and microstructure was evaluated.

Results of this research indicated that ACI 305 graphical method can only be used to determine the rate of evaporation and cannot provide any indication with regard to plastic shrinkage cracking. Cracking was observed at much lower rates of evaporation than that recommended by ACI 305. Water evaporation and plastic shrinkage cracking increased with an increase in the wind velocity, ambient temperature, cement content, water cement ratio and addition of blended cements. A decrease in the relative humidity had a similar effect. Bleeding increased with cement content as well as water cement ratio. Exposure conditions at the time of casting influenced the properties of hardened concrete. There exists a qualitative relationship between bleeding, water evaporation and plastic shrinkage cracking. However, the total cracked area increased almost linearly with the rate of evaporation. The results also show that lean and stiff mixes crack earlier than rich and plastic mixes, but cracking in the latter was much more than the former. The data also indicate that the technological benefit of using blended cements can be utilized only when adequate measures to control plastic shrinkage cracking are assured.