Production of sustainable green mortar by ultrahigh utilization of fly ash: Technical, economic and environmental assessment

Abstract

Fly ash (FA) utilization in mortar/concrete as partial replacement of cement is commonly around 30 wt% and globally most of the FA is disposed of in landfills which possess environmental burden. The aim of this experimental work is to present a cost effective and practical solution for potential ultra-high-volume utilization of FA for synthesis of three types of mortar as specified in ASTM C1329. At first, the pozzolanic activity of FA was evaluated through modified Chapelle test, thermogravimetric analysis and strength activity index. Then mortar was prepared by replacing cement with FA up to 100% and the targeted compressive strengths were obtained through cementing and by alkali activation (geopolymerization). Different parameters such as; molarity of alkaline activators, liquid to solid ratio and sodium silicate to sodium hydroxide ratio, that influence the properties of geopolymer mortar were also studied. Tensile strength test and interfacial split tensile strength test was also conducted to evaluate its compatibility with conventional concrete. Characterization of all types of mortar was carried out by the Fourier-transform infrared spectroscopy analysis and verified the geopolymerization as well as their mechanical performance. Finally, comparative analysis was carried out in terms of sustainability, evaluation of technical-economic-environmental indicators. It was concluded that formulation of green geopolymer mortar is the sustainable solution, having better mechanical strength, least CO2 footprints and economical. Results revealed that 60% FA replacement is possible through cementing while for higher replacement levels, alkaline activation was needed to reach the targeted strength.