Synergic effect of fly ash and calcium aluminate cement on the properties of pumice-based geopolymer mortar

Abstract

• FA and CAC increase the workability of pumice-based geopolymers. • CAC and FA significantly increase the early age strength of pumice-based geopolymers. • CAC increases the resistance of pumice-based geopolymers to wetting–drying and seawater. • Heat curing significantly reduces efflorescence. • Replacing pumice with FA and CAC reduces cracks and voids in the geopolymer matrix. This paper reveals the synergic effect of fly ash (FA) and calcium aluminate cement (CAC) on the properties of pumice-based geopolymer mortars. Geopolymer mortar samples produced by replacing 0, 10, 20, and 30% of the pumice with FA and/or CAC are cured at ambient temperature, and 60C°. Physical properties, compressive strength (7, 28, and 90-days), durability, and microstructure of these samples are investigated in this study. While CAC and heat curing greatly reduce the setting time, FA has a limited effect on the setting time. However, both FA and CAC significantly increase the workability of the mortar mix. By replacing the optimum amount of the pumice with FA and CAC, the 7-day compressive strength of heat-cured geopolymer mortars can achieve 68.0 MPa. On the other hand, CAC significantly increases the compressive strength of the geopolymer mortars and their resistance to the wetting–drying and seawater. In addition, the FA has a limited effect on the enhancement of the mechanical properties and durability of the geopolymer mortars. Efflorescence is slightly reduced by FA and CAC additives, however, is greatly reduced by heat curing. The SEM/EDS show that CAC creates C-A-S-H gel and together with FA they reduce cracks and voids in the geopolymer matrix. The findings reveal that the properties of both fresh and hardened geopolymer mortars can be improved by replacing pumice with a suitable amount of FA and CAC.