Influence of limestone filler and viscosity-modifying admixture on the shrinkage of self-compacting concrete

Abstract

The aim of this experimental work is to study shrinkage evolution with age in self-compacting concretes (SCC) made with w/c=0.6 and different limestone filler and viscosity-modifying admixture (VMA) contents. The results show that limestone fillers speed up hydration reactions and provide a finer porous structure. As a result, when specimens are hardened under water, SCC made with limestone fillers tends to shrink, since the water only penetrates the outer layers of the specimen, while the interior is subject to self-desiccation. If the concrete contains substantial air content (3.2%) the water finds it easier to penetrate and the concrete swells. When hardening takes place in the open air, autogenous shrinkage in SCC is lower than in normally-vibrated concretes (NVC) and the higher the fines content, the lower the shrinkage. This is more than likely due to the use of limestone filler as addition, finer porous structure and higher amount of absorbed water from the aggregate which compensates for the auto-desiccation of the concrete. On the whole, drying shrinkage in SCC is greater than in NVC. However, when filler is replaced by VMA the porous structure is coarser and shrinkage is reduced by 33%, thanks to the lower capillary pressure. This means that due to the reduction in autogenous and drying shrinkage, SCC made solely with VMA presents 7.7% lower total shrinkage than NVC. In SCC made with limestone filler, total shrinkage is only slightly higher than in NVC, the differences being under 9.2%.