Compressive strength of fly ash magnesium oxychloride cement containing granite wastes

► Granite waste and fly ash are incorporated into magnesium oxychloride cement (MOC). ► The water absorption of granite waste from the slurry results in increased hydration product of 5Mg(OH)2⋅MgCl2⋅8H2O. ► The excess water absorption of granite waste from low-concentration brine leads to compact microstructure of GFMOC, whereas from the high concentration of brine leads to porous microstructure. ► The sound composition and compact microstructure of the hydration product lead to high compressive strength of GFMOC. ► Incorporated granite waste can increase the compressive strength of fly ash MOC. This paper presents the results of an experimental investigation on compressive strength of granite waste fly ash magnesium oxychloride cement (GFMOC). Various GFMOC specimens were prepared with 23°Bé or 25°Bé brine and different proportions of granite fragment (GF) or granite sludge (GS) ranging from 0% (for the control mixture) to 40% of magnesia weight. Compression tests were conducted at the age of 3, 7, and 28days. The hydration products and paste microstructure were analyzed by XRD and SEM, respectively. The results demonstrated that the water absorption and filling role of the fine particles of granite waste in GFMOC slurry are favorable for 5Mg(OH)2⋅MgCl2⋅8H2O (P5) and dense microstructure, respectively. The quantity ratio of P5 to Mg(OH)2 (MH) and microstructure are important factors responsible for the compressive strength of GFMOC. The incorporation of granite wastes as aggregate can increase the compressive strength of fly ash magnesium oxychloride cement (FMOC).