Shear strength of plain concrete made of recycled low-strength concrete aggregates and natural aggregates

This paper reports the results of an experimental study of the shear strength of plain concrete made using recycled low-strength concrete coarse aggregates (RCA) and natural coarse aggregates (NCA). Ninety push-off specimens were cast and tested. Three types of coarse aggregates were used: recycled low-strength waste concrete, limestone, and gabbro. The other variable in the concrete was the water to cementitious materials ratio (w/cm), which varied from 0.31 to 0.72. The push-off shear strength (vpo), the cube compressive strength (fcu), and the shear failure surfaces were investigated. The results showed that recycled aggregates concrete (RAC) had lower push-off shear and compressive strengths relative to the natural aggregates concrete (NAC) of similar w/cm ratios. However, the relationship between vpo and fcu was similar for the NAC and the RAC. This indicates that the effects of using RCA on the shear strength can be accounted for indirectly by consideration of their effects on fcu. The tests also showed that failure surfaces were more smooth in the concrete with lower w/cm ratios. In addition, the use of RCA affected the failure surfaces slightly. Based on a linear-elastic finite element analysis, a relationship between the tensile cracking strength σcr and vpo for the push-off specimen was established. Consequently, the experimental results suggest that the equation σcr=0.43fcu can be used to relate the tensile strength to the compressive strength of concrete.