Improving recycled coarse aggregate (RCA) and recycled coarse aggregate concrete (RCAC) by biological denitrification phenomenon

摘要

Biomineralisation induced by ureolytic bacteria is usually utilized for enhancing concrete. However, ammonia (NH3) was usually generated unavoidably with an unpleasant smell. Denitrification bacteria can use organic carbon and nitrate salt to induce biomineralisation without supplying urea. This study investigates the use of biomineralisation induced by denitrification bacteria to improve the properties of recycled coarse aggregate (RCA) and RCA concrete. Calcium carbonate crystals were found on the surface of RCA and the matrix inside RCA concrete by SEM analysis. For RCA treated by this method, a maximum 14% reduction of water absorption, a 4% increase of apparent density and a 10% reduction of crushing value were detected compared with RCA soaked in the non-bacterial solution. The concrete contains treated RCA with bacteria solution added to the mixing water, which can significantly improve the 28-day compressive strength, tensile splitting strength, and elastic modulus, which improved 24.6%, 24.1%, and 7.5%, respectively. Ultrasonic pulse velocity test also indicated the bacteria increased the compactness of concrete. The paper presents a new approach to achieve improvement without the consumption of urea and ammonia release.