Combined Effects of Internal Curing, SCMs, and Expansive Additives on Concrete Shrinkage

Internal curing (IC) using prewetted lightweight aggregate (LWA) has often been used to improve the cracking performance of concretes with low water-to-binder (w/b) ratios (<0.42) when autogenous shrinkage and self-desiccation are of concern. Shrinkage-compensating admixtures (SCAs) are also used to improve the cracking performance of concrete. A modified version of ASTM C157, Standard Test Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete, in which length-change measurements begin 5 1/2 ± 1/2 h after casting concrete, was used to evaluate the effects of IC obtained through the use of intermediate-sized prewetted LWA, partial replacements of cement with the supplementary cementitious materials slag cement and silica fume (SCMs); incorporation of calcium oxide–based and magnesium oxide–based SCAs; and combinations of IC, SCMs, and SCAs using eleven concrete mixtures with moderate w/b ratios (0.45). The results show that the modified ASTM C157 method helps to capture the early-age behavior of concrete mixtures. IC provided by partial replacement of total aggregate with intermediate-sized prewetted LWA is effective in reducing drying shrinkage in concrete made with moderate w/b ratios. Partial replacements of cement with slag cement and silica fume induce increased first-day expansion and reduce shrinkage. A further increase in first-day expansion and a reduction in shrinkage is obtained when IC is used in conjunction with slag cement and silica fume. The SCAs evaluated in this study reduce the tendency to develop shrinkage strain. The calcium oxide–based SCA induces the more rapid expansion of greater magnitude, while the magnesium oxide–based SCA expands more gradually. When the calcium oxide–based SCA is incorporated in a mixture containing SCMs or SCMs and IC, expansion is further increased. The same observation cannot be made for mixtures incorporating SCMs with the magnesium oxide–based SCA.