A comparative review on foam-based versus lightweight aggregate-based alkali-activated materials and geopolymer

TL;DR: In this paper, the authors provide an updated information on recent advances while stressing the sustainability of lightweight geopolymer materials over ordinary Portland cement products that are vastly in use, including perlite, pumice, shale, ceramsite, and slate sand.

Abstract: Alkali-activated materials and geopolymer are major sustainable alternative binding materials to ordinary Portland cement products with higher thermal resistance and often better durability properties. In lightweight form, they have an unmatched lowered thermal conductivity and insulating properties making them a perfect fit for optimized structural components with highest strength to density ratio and major energy savings in green buildings. For them to produce lightweight materials, generally either certain foaming agent or some types of lightweight aggregates in virgin, expanded, or recycled form are utilized that reduce the overall density through higher overall porosity. In accordance, this review provides an updated information on recent advances while stressing the sustainability of lightweight geopolymer materials over ordinary Portland cement products that are vastly in use. In the end, recent mechanical and durability properties developed and documented are reviewed and provided for future applications. Based on the result of this review, the most common lightweight aggregates used in literature are perlite, pumice, shale, ceramsite, and slate sand, in expanded and porous form, along with recycled thermosetting (e.g., rubber), or thermoplastic (e.g., polyethylene) materials. In foam form, chemical and mechanical foaming are the most commonly used foaming techniques to increase porosity of final materials. The pore mechanism of foam-based geopolymer is found to be different from that of lightweight aggregate-based geopolymer. This variation results in different physico-mechanical and durability properties such as better insulation properties (and lower thermal conductivity) for foam-based versus better mechanical properties for lightweight aggregate-based geopolymer.