Biomass electrostatic precipitator fly ash treatment methodologies to maximize cement replacement in mortar and concrete

The dwindling resources of conventional supplementary cementitious materials (SCMs), such as coal fly ash and blast-furnace slag, have spurred considerable research into alternative SCMs. Landfilled at a high environmental and economic cost, biomass precipitator fly ash (BFA) is a major byproduct of burning biomass as a renewable source of energy. Despite interest in BFA as an alternative SCM, its inherent properties have limited its use to less than 10 % of cement weight. This comparative study aims to maximize the cement replacement ratio by BFA through various treatment methodologies. The treatment methodologies include calcination (i.e., 350 – 1000°C), milling and combined calcination and milling. The compressive strength and workability of the mortars indicate that two hours of calcination at 800°C is the optimal calcination treatment. Various BFA contents have been adopted to replace cement (i.e., 0 – 50 %). The influence of water/binder (W/B) ratio on calcined and untreated BFA mortars are also studied by considering W/B of 0.5 and 0.35. The results suggest that a 28-day compressive strength of 42 MPa can be reached by replacing 50 % of the cement with calcined ash, which satisfies the requirements of most engineering structures. As such, the cement replacement ratio with BFA, which has traditionally been limited by its low strength and workability, can be increased substantially through simple calcination. A conservative life-cycle carbon dioxide emission calculation indicates a 47.5 % reduction in CO 2 emissions with 50 % replacement of cement with treated BFA, and a tenfold reduction on a per-kilogram basis. • The influence of calcination temperature and milling pretreatment methods was studied. • Two-hour calcination at 800°C was the optimum treatment method to induce the best workability and strength synergy. • Concrete mixes with untreated biomass fly ash were highly viscous despite the high superplasticizer contents. • The required amount of superplasticizer was drastically reduced after calcination. • Concrete samples with 30 % calcined fly ash reached equal strength to traditional concrete after 56 curing days.