An evaluation of bottom ash from plant biomass as a replacement for cement in building blocks

This paper presents the results of research on the effect of adding bottom ash from the combustion of plant biomass to construction material, substituting the ash for Portland cement in proportions ranging from 10% to 90% in mass. After determining the physical, chemical, and mineralogical character of the raw materials, sample building blocks were formed through compression at 20 MPa. The experimental program included a wide range of testing methods such as mechanical strength, XRD, porosity, microstructure, freeze-thaw, thermal conductivity, and environmental safety (heavy metal leachability). The results demonstrate that the addition of bottom ash increases the material's porosity, thereby decreasing its thermal conductivity and compressive strength. The mixture with a 1:1 Si/Ca ratio shows the best mechanical characteristics (61.11 MPa) with acceptable thermal conductivity value (0.773 W/mK) and could potentially be used in products such as building blocks, since partially replacing the cement with ash produced samples based on criteria of the EN standards. Heavy metal concentration in the leachates of the bottom ash and samples formed are far lower than those recommended in the Spanish legislation (OM AAA/661/2013) and US-EPA standard. (C) 2013 Elsevier Ltd. All rights reserved.