Shrinkage mitigation of metakaolin-based geopolymer activated by sodium silicate solution

Abstract

Geopolymers seem to be a good alternative to ordinary Portland cement to reduce the carbon footprint of the construction industry. However, their durability over time is still a subject of discussion. One of the major problems blocking their marketing is shrinkage, which can induce excessive cracking and circulation of aggressive agents. The aim of this study is to evaluate the autogenous deformation and desiccation shrinkage of a metakaolin-based geopolymer activated with sodium silicate solution. Several shrinkage measurement methods are used and criticized. Then, twenty-two formulas were tested to reduce shrinkage: varying the cure or the environmental conditions, changing the water-to-binder ratio, adding filler or fibres, incorporating chemical admixtures (plasticizers, water repellents, water retainers) or using curing products. Coupled with these results, showing a shrinkage reduction reaching 35 %, a model was developed to explain the involved mechanisms specific to geopolymers. It might offer prospects for improving the durability of geopolymers.