Influence of the amount of mixed recycled aggregates on the properties of concrete for non-structural use

This article presents the results of an experimental campaign on the influence of replacing natural aggregate with mixed recycled aggregate (MRA) in the mix design of non-structural concrete. Mixed recycled aggregates are those that come from construction and demolition waste treatment and include concrete waste, unbound aggregates and ceramic products as their predominant components. Specifically, a mix design suitable for manufacturing low-strength blinding concrete (15 MPa), medium-strength blinding/backfill concrete (25 MPa) and non-structural concrete for high-resistance precast elements (65 MPa) is proposed. According to the properties of mixed recycled aggregates, the conclusion drawn is that it is feasible to substitute about 40% of coarse aggregate in such a way that the resulting coarse aggregate mix complies with all the regulatory requirements analysed. The higher absorption capacity of mixed recycled aggregates means that special precautions in the mix design are required, since consistency may be affected. In a hardened state, the compressive, tensile and flexural strength properties decrease when the proportion of MRA increases. This decrease is proportionately higher when the concrete’s average compressive strength increases. At 90 days, the reduction in average compressive strength is less than 15% for replacements around 20% of the coarse aggregate.

► Real Mixed Recycled Aggregates (MRA) produced in a treatment plant were used.
► Substitutions of up to 40% could be assumed to meet all the specified requirements.
► Three different concrete mixes were tested: 15 MPa, 25 MPa and 65 MPa.
► Compressive, tensile and flexural strength decrease when the MRA amount increases.
► MRA additions of up to 20-25% produce decreases in strength of less than 15%.