Properties of sustainable self-compacted concrete with recycled concrete and waste tire crumb rubber aggregates

The concrete building industry has to adhere to stringent sustainability standards. In previous investigations, the utilization of recycled concrete aggregates (RCA) from construction and demolition waste (CDW) or crumb rubber (CR) from waste tires in producing sustainable self-compacted concrete (SCC) was well studied; however, the combined effect of RCA and CR on the performance of SCC is scarce. Therefore, the main purpose of this study is to evaluate the feasibility of developing SCC mixtures containing both RCA and CR and their influence on the performance of SCC. Three distinct series of SCC mixes were designed so that the water-to-binder ratio and total binder content were kept at 0.32 and 505 kg/m3. In the first series, the effect of RCA content (0%, 50%, and 100%) in place of natural coarse aggregate (NCA) on the performance of SCC mixtures was studied. Moreover, the effect of various CR contents (0%, 10%, 20%, 30%, and 40%) as a sand substitution and 50% RCA was investigated in the second series. In the third series, the influence of CR inclusion and 100% RCA was utilized to promote the sustainability of SCC. The fresh behavior of the mixtures was assessed by measuring followability, viscosity, and segregation resistance. Density, water absorption, and apparent porosity for all mixes were also examined. The mechanical properties were assessed for compressive, splitting tensile, and flexural strengths. The findings show that the inclusion of RCA and CR has an adverse impact on the fresh, physical, and mechanical properties of SCC, excluding segregation resistance. However, it is possible to produce a SCC using 100% RCA and 40% CR with a slump flow diameter of 605 (SF1 class) and a compressive strength of greater than 31 MPa, which is applicable for structural applications. Moreover, the ACI and Euro code CEB-FIP proposed models can predict the mechanical properties of the developed SCC made with recycled materials. This research could contribute to a more sustainable SCC by substituting recycled materials for natural aggregates.