Durability analysis of sustainable mortars with biomass fly ash as high-volume replacement of Portland cement

Utilization of various supplementary cementitious materials was in the last decades considered beneficial for the replacement of the energy-intensive Portland cement to meet sustainable targets. However, structural changes in energy production and heavy industry in Europe significantly limit the availability of coal fly ash and blast furnace slag for blended cement production. On the other hand, the increasing production of biomass ash (BA) presents not only challenges for its disposal but also new opportunities for the concrete industry. In this paper, the durability of cement composites containing up to 70 wt.% of BA as Portland cement (PC) replacement was analyzed, taking into consideration also microstructure and mechanical properties. The experimental results showed a preservation of good mechanical performance up to the 30 wt.% limit. The freeze-thaw resistance was not affected significantly up to the 40 wt.% BA dosage during the first 300 cycles. The analyzed composites also exhibited a good overall resistance to alkali silica reaction- and sulfate-induced expansion up to the 50 wt.% PC replacement. BA can thus be considered as a prospective future alternative to coal fly ash and blast furnace slag to meet the sustainable development goals in the building industry.