Use of recycled concrete aggregates from precast block for the production of new building blocks: An industrial scale study

Large amounts of construction and demolition (C&D) waste are generated annually and will increase in the future. Until now, only a small fraction of concrete by-products is re-used as recycled concrete aggregates (RCA) for the manufacture of concrete. In this paper, the feasibility of using RCA obtained from old precast concrete block was investigated for the industrial scale production of new blocks. Concrete building blocks with different substitution rates (0%, 30% and 100%) of natural aggregates (NA) by the same volume fraction of RCA were manufactured in a factory and the mechanical properties and durability of concrete blocks were monitored. The results show that incorporating RCA slightly decreases the compressive strength and impairs the durability of concrete blocks. However, the compressive strength of concrete blocks made with 100% RCA could reach 11.1 MPa after 28 days, which is within the requirement in Belgian codes for this type of block. The concrete blocks produced with 30% and 100% of RCA reached the strength, capillary water absorption, drying shrinkage and freeze-thaw resistance requirements for concrete blocks specified by Belgian codes. A cradle-to-gate life cycle assessment (LCA) was performed on both "classical" blocks with only NA and with substitution of NA by RCA. When considering the additional use of RCA from a nearby C&D waste recycling centre, the substitution of 30% or 100% of NA by RCA led to a reduction in the land use category, in addition to supporting the implementation of the circular economy.