Addition of bottom ash from biomass in calcium silicate masonry units for use as construction material with thermal insulating properties

•Bottom ash from biomass as a source of added value for building application.•The samples were prepared with bottom ash, lime and Portland cement.•The properties of silico-calcareous samples were studied following EN standards.•Bottom ash and cement show the best compressive strength. This paper studies the effect of adding bottom ash from the combustion process of biomass plants to calcium-silicate samples for use as construction material with thermal insulating properties. After a process of physical, chemical and mineralogical characterization of the raw materials, calcium-silicate samples were manufactured by mixing bottom ash (CF) with different sources of lime (calcium oxide-OC and calcium hydroxide-HC) and Portland cement (CM). The amount of bottom ash added ranged from 10% to 90% of the dry weight of the mixtures. The experimental program included a wide range of testing methods of the developed material such as water absorption, mechanical strength, porosity, microstructure, freeze–thaw and thermal conductivity. The optimal values are those containing a 1:1 ratio of SiO2/CaO, with compressive strength ranging from 25.21MPa (CF/HC) to 61.11MPa (CF/CM) and thermal conductivity from 0.564W/mK (CF/OC) to 0.773W/mK (CF/HC). The initial results obtained make it possible in principle to obtain calcium-silicate samples with low thermal conductivity according EN standard 771-2:2011.