Leaching performance of concrete eco-blocks: Towards zero-waste in precast concrete plants

This work presents a case study of waste incorporation, where precast concrete block rejects were reincorporated into the production of new recycled concrete blocks which stands for a technically and environmentally viable alternative to natural aggregates. This study therefore evaluated the technical feasibility, first, and the leaching performance, after, of recycled vibro-compacted dry mixed concrete blocks using different percentages of substitution of recycled aggregates (RA) coming from precast concrete block rejects in order to identify those that presented a better technical performance. According to the results, concrete blocks with a 20% of RA incorporation presented an optimum physic-mechanical behaviour. The environmental evaluation based on leaching tests was carried out to identify the most conflictive elements legally regulated according to their pollutant release levels and investigate their different release mechanisms. The leaching study performed in concrete monoliths showed that in blocks with 20% of RA incorporation: Mo, Cr, and sulphate anions presented a higher mobility during the diffusion leaching tests; Sb and Cu presented an average mobility; Ba and Zn exhibited lower mobility levels and their corresponding release mechanisms for each of them. However, the limits for pollutant release in construction materials in a monolithic state were not surpassed by far.