Optimization of calcium silicate based high density structural flame-retardant composites developed using waste marble powder and sugarcane bagasse ash for flame retardancy applications

Calcium silicate powder was produced by calcining a mixture of 1:1 weight of acetic-treated waste marble powder and hydrochloric acid-treated sugar cane bagasse ash. Waste marble powder was calcined at 700, 800, and 900 °C. Ordinary Portland cement binder was added before compressing at pressures of 15, 20, and 25 MPa. The composites were formulated with 10–30 g of cement binder and 15 wt% water in each mixture. Box-Behnken response surface methodology was used to determine the effects of calcination temperature, Ordinary Portland cement binder amount and pressing pressure on density, thermal conductivity, water absorption and compressive strength. XRF, XRD and SEM were used to determine the chemical compositions, phases and microstructures. XRD results showed that the developed high density structural flame-retardant composites were crystalline and consisted of tobermorite and calcium silicate hydrate (C-S-H), which were responsible for enhancing the flame-retardant and mechanical strength. SEM images showed the existence of micro-pores which affected the thermal conductivity behavior. The optimized high density structural flame-retardant composite had the maximum compressive strength of 62.8 MPa, thermal conductivity of 0.02 W·m -1 ·K -1 , water absorption 6.5% and density of 2058.24 kg·m -3 . This further suggests that the developed high density structural flame-retardant composites produced from these wastes may be used to thermally insulate the internal lining of buildings.