Early Age Drying Shrinkage Evaluation of Self-Compacting Concretes and Pastes with Mineral Additions

Abstract

Early age (EA) drying shrinkage of cement based materials is a complex process because it comprises reaction evolution, microstructure development, stiffening and water evaporation due to environmental conditions. The occurrence of EA shrinkage can increase early age cracking risk which can compromise durability. Due to the larger amount of paste, moderate strength powder-type self-compacting concrete (SCC) is more prone to EA drying shrinkage than conventional concrete. To evaluate the effect of limestone filler, microsilica (MS), nanosilica (NS) and metakaolin (MK) on EA free drying shrinkage of cement pastes and SCC, an experimental program was carried out. Free shrinkage and mass loss were monitored on paste and SCC samples during 24 hours, subjected to surface desiccation to evaporate all the bled water during 6 hours, while temperature and Relative Humidity remained constant. It was observed that evaporation and free shrinkage were not related directly, although a physical relationship could be identified. Evaporation during EA shrinkage of pastes and SCC compositions showed similar values, while drying shrinkage depended on the presence of the aggregates. The effect of the paste components’ amount and type, the volumetric fraction of aggregates and the evaporation were assessed and some equations were proposed to estimate EA drying shrinkage of moderate strength powder-type self-compacting pastes and concretes.