Plastic shrinkage cracking of blended cement concretes under hot weather conditions

Abstract

In order to inhibit the deterioration of concrete structures in the Arabian Gulf environment, emphasis has been shifted from the requirements of concrete strength towards to its durability, especially the selection of materials. Towards this end, silica fume and other types of blended cement materials are being used. However, silica fume cement concrete is also more susceptible to plastic shrinkage cracking, and under hot weather conditions, this cracking could be further aggravated. This research was conducted to investigate the effect of the type and dosage of silica fume and other blended cements on the plastic shrinkage cracking of concrete. The effect of cement type, super plasticizer type, temperature relative humidity and wind velocity on the plastic shrinkage strains, cracking and the microstructure were conducted. Additional studies to evaluate the effect of the type of silica fume on the early age properties, such as the compressive strength; the split tensile strength and the ultrasonic pulse velocity were also conducted.

Results of this research indicated that it is the fineness of the silica fume and its state of densification that determine its plastic shrinkage strain response. The fineness of the silica fume must be evaluated in terms of not only its specific surface area, but also its average pore radius.

The plastic shrinkage strain increased with increasing temperature and wind velocity and decreasing relative humidity. The decrease in the relative humidity presented the most severe condition that promoted higher plastic shrinkage strains and cracks. A threshold value of plastic shrinkage strain was determined in plain and blended cement that will initiate plastic shrinkage cracks. This threshold value was found to be independent of the exposure conditions.

The type of super plasticizer had a significant effect on the plastic shrinkage strains in silica fume cement concretes. The effect of the fineness of the silica fume played the most important role in determining the plastic shrinkage strains in the concrete. Incompatibility between the type of super plasticizer and the silica fume cement concrete was also noted. Statistical analysis of the early age properties, such as the compressive strength, split tensile strength and pulse velocity of plain and blended cements suggested that the material variability as represented by the type and dosage of silica fume was comparable to that of plain cement concrete.