Understanding the Formation of Geopolymer Foams: Influence of the Additives

Abstract

Geopolymer foams are innovative materials synthetized at low temperature, resulting from the activation of an aluminosilicate source with an alkaline solution. The purpose of this study is to understand the role of additives, such as surfactants and fillers, on foam formation. Four different geopolymer foams were synthetized and analyses on their microstructure, density, mechanical resistance and thermal conductivity were carried out. Then, the reactive mixtures of dense geopolymers were studied by the means of FTIR, viscosity and surface tension measurements. The addition of surfactants leads to an increase in the volume expansion up to 4.03, in the porosity rate with a homogeneous microstructure and therefore the foam thermal conductivity and the compressive strength decrease to 57 mW/m.K and from 4950 to 52 kPa respectively. Besides, it modifies the polycondensation reaction by delaying the beginning of the reaction by up to 80 minutes. However, it appears the addition of silica fibers does not impact the geopolymer formation and improves the mechanical properties by 70%. This study also reveals that the ratio of surfactant (300) to metakaolin is crucial in order to stabilize the wet foam before its consolidation.