Effect of Portland cement on the properties of geopolymers prepared from granite powder and fly ash by alkali-thermal activation

Abstract

Recycling granite powder (GP) and fly ash (FA) is of great significance for ensuring the sustainable development of the stone processing and thermal power industries. In this study, the reactivity of GP and FA was enhanced via alkali-thermal activation (ATA) and subsequently applied to the synthesis of one-part geopolymers. The results showed that the framework of raw material was severely disrupted, and the content of reactive silicon components was increased after ATA, which enhanced their potential as geopolymeric precursors. Furthermore, the effect of a small amount of ordinary Portland cement (OPC) on the mechanical properties of geopolymers cured at room temperature and 60 °C was investigated. The results demonstrated that the incorporation of OPC at room temperature promoted the degree of geopolymerization and the formation of additional calcium-rich aluminosilicate gels, which led to a significant improvement in the microstructure and compressive strength of geopolymers. When the dosage of OPC is 10%, the compressive strength of geopolymers reaches 32.72 MPa at 28d. However, OPC addition deteriorated the strength of geopolymers cured at 60 °C. The reduction in the strength of geopolymers was attributed to the reduction of hydration products and the efflorescence of geopolymers. This study provides a novel approach for preparing prefabricated building products and on-site cementitious material using GP and FA.