Effect of partial substitution of recycled concrete aggregate in reinforced concrete beams: analysis of dry and pre-saturated conditions.

Abstract

The preservation of natural resources and the pursuit of sustainability in civil construction have promoted academic interest in research related to the reuse of construction and demolition waste (CDW). The partial replacement of conventional aggregates with CDW in cementitious materials has yielded satisfactory results in terms of the mechanical and rheological behavior of the resulting material. However, further studies are needed to demonstrate the feasibility of this application in a standardized manner. Accordingly, the present study aims to assess the impact of recycled concrete aggregates (RCAs) on the behavior of reinforced concrete (RC) beams. To this end, natural coarse aggregates were replaced with RCAs at substitution levels of 0% and 30%, while maintaining the same mixture composition across all samples. The main properties of concrete with RCAs were evaluated, including the slump test, compressive strength, tensile strength, and modulus of elasticity after 7 days and 28 days of curing. Subsequently, RC beams containing RCAs were analyzed through for four-point bending tests. The prototypes were cast using RCAs in water saturated and unsaturated conditions. The results revealed that incorporating RCAs enhanced workability by 62.5% while reducing compressive concrete strength by less than 15% in 28 days. Despite this reduction, concrete incorporating RCAs achieved the projected compressive strength of 25 MPa. No significant changes in tensile resistance were observed. Regarding the beams containing RCAs, it was observed that the failure mode remained unchanged, and their collapse loads did not differ significantly from those of the conventional reference RC beam, with variations of less than 10%. These findings are significant, given that several studies have documented notable changes in the mechanical properties of concrete containing RCAs. Overall, it can be concluded that using RCAs at a 30% substitution level is a viable option for RC beam applications. Furthermore, although saturating RCAs might enhance the adhesion between the aggregate and the cement matrix, this effect was not confirmed in the present study.