The effect of shrinkage reducing admixtures on drying shrinkage, autogenous deformation, and early age stress development of concrete

Abstract

The current study investigates the effect of shrinkage reducing admixtures (SRA) on volume changes that may lead to shrinkage cracking and early age cracking. Drying shrinkage (DS) and autogenous deformation (AD), the impetus for shrinkage cracking, were measured over 2.5 years for three concretes with and without 1% SRA addition: an ordinary Portland concrete, a fly ash concrete and a slag concrete. The latter two concretes were also tested in the Temperature-stress testing machine (TSTM), which measures AD, thermal dilation (TD) and restrained stress development for a concrete subjected to realistic temperature curing conditions. SRA was found to have a substantial and permanent impact on DS and AD for all three concretes (up to 32% reduction of the total deformation after 2.5 years). The higher the shrinkage, the higher the effect of SRA. For the slag concrete, where AD was found to be the main impetus of early age volume changes, SRA had a clear beneficial effect on the cracking tendency. For the fly ash concrete, where TD provided the main contribution to the volume changes, SRA had a less pronounced effect. The test results were also compared with AD and DS modeled by Model Code 2010.