Evaluation of wood fly ash as a cement replacement material in concrete

Abstract

Biomass is the largest source of renewable energy in the European Union, of which 60% comes directly or indirectly from forests. The most common way of producing energy from biomass is combustion, and this process yields substantial quantity of ash. The cement and concrete industry has been identified as one of the main potentials for biomass ash utilization. This paper presents the results of an experimental study aimed at determining the influence of wood fly ash on the properties of concrete. Wood ash was sampled from three power plants using different technologies of incineration and different types and parts of wood were used as a fuel which consequently had a large impact on the properties of ash. Subsequently, workability, heat of hydration, stiffness development, 28-day compressive strength, apparent porosity, and capillary absorption were determined on concrete mixes prepared with WFA as cement replacement from 5–45% by weight. Cement replacement up to 15% with the finest WFA accelerated hydration, stiffness development, and increased compressive strength of concrete up to 18%, while replacement with coarser WFA's led to a decrease in compressive strength of up to 5% and had more gradual heat liberation. The dominant effect that could explain these findings is attributed to the filler and filling effect mechanisms.