Biomass bottom ash in different types of recycled concrete. Mechanical, acoustic and thermal properties

Due to the global emergency associated with the use of planet Earth's natural resources, the accumulation of waste from human activity and the existence of high noise levels, especially concentrated in large cities, this work focuses on the development of thermally-insulating concrete mixes and noise sinks with recycled materials in their matrix. Two series of concrete mixes were manufactured: series 1 of five self-compacting concrete mixes (SCC) and series 2 of five lightweight concrete mixes (LC) including biomass bottom ash (BBA) with different processing in substitution of fine aggregate.

A physicochemical characterisation including elemental analysis of the materials was carried out. The concrete series were tested for mechanical performance, durability, thermal conductivity and sound insulation. The self-compacting concrete mixes with fine aggregate and limestone filler substitutions showed a reduction of between 14 % and 40 % of the strength of the long-term control mix. With respect to the lightened concrete series, the strengths of the concrete mixes with recycled materials incurred a drop of between 7 % and 16 % of the mechanical performance of the conventional concrete. The series of lightweight concrete mixes including biomass bottom ash, in terms of acoustic and thermal insulation, performed better than the conventional lightweight concrete mix. This study shows the possibility of applying ash from olive biomass bottom ash to two types of concrete. The use of this by-product leads to improvements in thermal and acoustic insulation properties. Thermal insulation improved by 35 % compared to the insulation of the conventional lightweight concrete mix. The notable improvement in acoustic insulation occurred in the medium and high frequencies, between 1000 Hz and 8000 Hz. The exhaustive study of the thermal and acoustic performance of concrete with recycled materials yielded positive results, demonstrating that the inclusion of bottom ash from biomass slightly decreases the mechanical performance while improving the thermal and acoustic comfort performance.