Influence of nanoclays on flowability and rheology of SCC pastes

Abstract

SCC rheology is the key factor of fresh performance and its control is required to overcome cast in place issues regarding pumping and formwork lateral pressure that still limits its widespread use. Nanoclays are good candidates to improve rheological properties of cement pastes as yield stress, viscosity and thixotropy, controlling paste flow behavior. However, some interactions between nanoclays and admixtures can limit their efficiency. In this study, a comparative analysis on rheology and flowability of SCC cement pastes blended with limestone filler and 2% by cement weight of four types of nanoclays, attapulgite, bentonite, and sepiolite in powder form and dispersed in water, is presented. Two water to binder ratios (w/b), 0.35 and 0.45, were considered and a high range water reducing admixture (HRWRA) was used to reach the required flowability. Water adsorption of nanoclays, flowability and rheological properties of SCC cement pastes with nanoclays were evaluated. It was found that HRWRA was less effective on pastes with nanoclays and low w/b, particularly bentonite. Sepiolite showed larger water adsorption and improved rheological properties. It was observed that, the relation of nanoclays and HRWRA was decisive to produce flowability on pastes with low w/b. Besides, flowability was deeply affected by w/b, as water saturation of nanoclays increased HRWRA efficiency. All nanoclays modified rheological properties due to its different particles morphology characteristics. However, sepiolite showed the largest effects and reached the higher values of yield stress, viscosity and thixotropy ratios used.