Technical specifications for highway noise barriers made of coal bottom ash-based sound absorbing concrete

• We manufacture a product composed of 80% of coal bottom ash.
• It is applied to develop highway noise barriers at semi-industrial scale.
• Acoustic properties of recycled product similar to commercial materials.
• It complies with the European specifications for highway noise barriers.

This paper focuses on developing a highway noise barrier prototype mainly composed of bottom ash from the traditional pulverised coal combustion at semi-industrial scale, following a simple and low-cost manufacturing procedure similar to that used to cast commercial concrete noise barriers. In order to obtain good sound absorption coefficients, a multilayer product was designed, with a porous layer in the incident noise face followed by the finest material in the back layer. The characterisation of the recycled multilayer product was carried out in accordance with the current European standard for road traffic noise reducing devices and the results have been compared to the specifications stated by the regulations. The acoustic performance has been evaluated by determining the sound absorption coefficient and the airborne sound insulation in a reverberation room. Regarding the non-acoustic performance, the physical (open void ratio, unit weight), mechanical (compressive strength, Young’s modulus, flexural strength, fracture energy, indirect tensile strength, characteristic length, impact strength) and fire resistance properties were determined. From the results obtained, bottom ash from traditional pulverised coal combustion can potentially be recycled by manufacturing a multilayer product that complies with the specifications required for road traffic noise reducing devices according to the European standards, and that reaches the same acoustic category as other commercial products used for the same application.