Effect of the Incorporation of Mineral Admixtures and Shrinkage-Mitigating Ingredients on the Plastic Shrinkage of Concrete

Abstract

In recent years there has been a rapid increase in the use of supplementary cementitious materials, such as fly ash and ground granulated blastfurnace slag, for high performance and durable concrete, as well as to reduce clinker requirement. Such materials being fine and not as reactive as cement, increase the setting time and water demand, and reduce bleeding in concrete. If the rate of evaporation is high enough, plastic shrinkage cracking occurs in slabs and other elements that have high surface area to volume ratios. Such premature surface cracks may accelerate the ingress of harmful agents, and impair durability and serviceability of the structures. The present study has two objectives: firstly, to investigate the influence of supplementary cementitious materials on plastic shrinkage cracking, in hot and dry environmental conditions; and secondly, to control plastic shrinkage cracks using fibers and shrinkage reducing admixtures. Four synthetic fibers — polyacrylonitrile, polyester, glass and polypropylene fibers at commonly-used dosages are evaluated. The results indicate that the addition of supplementary cementitious materials increases the cracking potential as the dosage increases. The incorporation of fibers and shrinkage reducing admixtures reduce crack widths, suggesting that they are viable solutions for combating plastic shrinkage cracking in concretes with supplementary cementitious materials.