Effects of Nanoclays on SCC Paste Rheology

Self-compacting concrete is an efficient and advantageous technology that increases cast in place speed while reduces energy consumption and health risks. However, some difficulties regarding pumping and lateral pressure on the formwork still limits its widespread use. A promising alternative for reducing the formwork pressure is the use of nanocomponents. Among them, nanoclays such as sepiolite, attapulgite, and montmorillonite can modify the rheological properties of fresh concrete, increasing early age thixotropy and structural build-up. These nanoclays have different morphology and nature, but similar size or BET surface area. In order to evaluate the effect of nanoclays on early rheology of SCC pastes, an experimental study was carried out. A reference paste with ordinary Portland cement blended with limestone filler, 3:1 by weight, was designed and two water-to binder ratios (w/b), 0.35 and 0.45, were considered. Then, four types of nanoclays were incorporated: attapulgite, montmorillonite and two types of sepiolite, one in powder form and the other dispersed in water. Water adsorption was tested using the tea-bag method in tap water and alkaline pore water. Paste consistency was measured by slump flow adjusted using a high range water reducing admixture (HRWRA). The rheological behaviour of the mixtures was tested using the mini-slump flow test. The final spread diameter and time to final spread after mixing were assessed. The aim of this study is to understand and evaluate the effect of nanoclays on the rheological parameters of pastes with cement and limestone filler, which may improve the rheology and the structural build-up at rest, overcoming the problems identified for SCC.