ACCIONA and ACCIONA Energía have carried out an innovation pilot project to reuse biomass slag in the construction works of the A-68 Arrúbal – Navarrete highway, in La Rioja, Spain.

The road works are being carried out by ACCIONA’s Construction business, commissioned by the Ministry of Transportation, and the pilot was led by ACCIONA Energía’s Innovation department.

The pilot has reused 1,500 tonnes of biomass slag –a common term to refer to boiler bottom ash– generated during the combustion process to produce renewable electricity at the Sangüesa biomass plant to replace natural excavated soil. The road section included a subbase of high-quality selected soil and a base of graded aggregates with a simple surface dressing on top.

Biomass slag has successfully replaced selected soil of the subbase, providing a high bearing capacity and rigidity to the road, complying with all technical requirements that rules road construction in Spain. The pilot includes an environmental monitoring plan.

This project follows preliminary pilots carried out to build access roads at the Celada Fusión wind farm, where ACCIONA Energía reused 352 tonnes of slag from the Briviesca biomass plant, and at the Miajadas biomass plant, where it reused 966 tonnes of slag from the Miajadas plant itself. These projects tested the load-bearing and self-cementing capacities of biomass slag and demonstrated its good mechanical and environmental performance.

The reuse of biomass slag contributes to the goal of ACCIONA and ACCIONA Energía to provide a second life to the waste and by-products derived from its activity, while promoting circular economy and reducing CO₂ emissions from the construction process in an outstanding example of industrial symbiosis among its businesses. All ACCIONA Energía's biomass plants have the Bureau Veritas certification "Zero Waste Management (Minimization of waste to landfill)", which promotes committed and appropriate management of waste to avoid landfill, using it as a resource.