Environmental quality of hardened wood fly ash–cement mixtures

Three different samples of woody biomass fly ash were characterised for their hazardousness level using two different compliance leaching tests (American US EPA 1311 toxicity characteristic leaching procedure and European UNI EN 12457-2). Two types of fly ashes (virgin wood and treated wood ash) were then selected and their environmental acceptability as construction materials was assessed through leaching tests on hardened wood ash–Portland cement mixtures at different cement replacement levels (0, 15 and 30 wt%). Leaching tests were performed using both granular samples (pH-dependent leaching test) and monolithic specimens (long-term dynamic leaching tests at constant pH 6·0). All the studied cementitious materials, except the mixture containing 30 wt% treated wood ash, showed good environmental quality when they were tested in the monolithic form and the dynamic leaching test results were analysed through different judgement criteria. The appropriateness of using leaching tests on granular samples of hardened cementitious materials was questioned.