Analysis of wood fly ash as a sustainable alternative to cement replacement in concrete

Supplementary cementitious materials (SCMs) can contribute to reducing the carbon dioxide footprint of concrete. One of these SCMs is biomass fly ash (BFA), which is waste from wood production. Although different researchers have used BFA as SCM, it is fundamental to know the behaviour of concrete with local materials (including available BFAs) to reduce the environmental impact of transportation. In particular, the Biobío region produces 57% of Chilean wood, concentrated in Eucalyptus globulus and Pinus radiata production. This paper describes the behaviour of concrete mixtures with replacements of eucalyptus BFA (BFAE) or pine BFA (BFAP) at 0, 10 and 20% by weight of cement. Workability, compressive and flexural tests were performed, and the specimens were examined using scanning electron microscopy as well. The results showed that BFAE reduced the slump of fresh concrete and BFAP increased it in all cases due to their morphology. An increase in resistance at later ages was evident due to an increase in pozzolanic activity and an improvement in BFA morphology. The results indicate that BFAE and BFAP are suitable for replacing at least 10% of cement, because those mixes present similar, and even higher, compressive and flexural strengths than the control mix.