Prediction of Shear Strength of Reinforced Recycled Aggregate Concrete Beams without Stirrups

For decades, recycled coarse aggregate (RCA) has been used to make recycled aggregate concrete (RAC). Numerous studies have compared the mechanical properties and durability of recycled aggregate concrete (RAC) to those of natural aggregate concrete (NAC). However, test results on the shear strength of reinforced recycled aggregate concrete beams are still limited and sometimes contradictory. Shear failure is generally brittle and must be prevented. This article studies experimentally and analytically the shear strength of reinforced RAC beams without stirrups. Eight RAC beams and two controlled NAC beams were tested under the four-point flexural test with the shear span-to-effective depth ratio (a/d) of 3.10. The main parameters investigated were the replacement percentage of RCA (0%, 25%, 50%, 75%, and 100%) and longitudinal reinforcement ratio (rho(w)) of 1.16% and 1.81%. It was found that the normalized shear stresses of RAC beams with rho(w) = 1.81% at all levels of replacement percentage were quite similar to those of the NAC counterparts. Moreover, the normalized shear stress of the beam with 100% RCA and rho(w) = 1.16% was only 6% lower than that of the NAC beam. A database of 128 RAC beams without shear reinforcement from literature was analyzed to evaluate the accuracy of the ACI 318-19 shear provisions in predicting the shear strength of the beams. For an RCA replacement ratio of between 50% and 100%, it was proposed to apply a reduction factor of 0.75 to the current ACI code equation to account for the physical variations of RCA, such as replacement percentage, RCA source and quality, density, amount of residual mortar, and physical irregularity.

Automated summary

This article experimentally and analytically studied the shear strength of reinforced recycled aggregate concrete beams without stirrups. It was found that the shear stresses of RAC beams with certain replacement percentage and longitudinal reinforcement ratio were similar to those of NAC counterparts. It was proposed to apply a reduction factor of 0.75 to the current ACI code equation for an RCA replacement ratio of between 50% and 100% to account for physical variations of RCA.