Effect of mixed recycled aggregates on mechanical properties of recycled concrete

Abstract

The use of construction and demolition waste in concrete manufacture allows the concept of sustainability to be included in the construction industry and helps to alleviate both the large consumption of natural resources and the high generation of waste. The present research assesses first the suitability of two different mixed recycled aggregates as coarse aggregates for concrete according to the code on structural concrete (EHE-08), and subsequently evaluates the effect of their use as a partial (50%) replacement of natural coarse aggregate (gravel) on the mechanical properties (compressive strength, splitting-tensile strength, flexural strength, stress–strain curves and modulus of elasticity) in concrete mixes of 25 MPa strength grade. The secondary material characterisation shows that, although presenting promising properties in terms of granulometry, particle size, density and shape, the recycled aggregates should be pretreated in order to comply with the quality of fines and water absorption, and their resistance to fragmentation limits their application in concrete mixes with a strength grade below 30 MPa. Regarding the results of the tests performed on the hardened concrete, the values obtained suggest that the use of mixed recycled aggregates is feasible, but at the expense of minor losses of the mechanical characteristics.