Impact of shear span-depth ratio on concrete beams incorporating recycled concrete aggregate

Recycling has become an effective procedure for mitigating the negative environmental impacts of construction and demolition waste. Concrete makes up major part of the waste which can be recycled and incorporated in structural beams as coarse aggregate. The performance of such beams under shear loads is influenced by a critical parameter, shear span-effective depth ratio (a/d). In order to determine the effect of a/d ratio on shear capacity of recycled concrete coarse aggregate (RCA) concrete beams without shear reinforcement, a database of 215 RCA concrete beams tested under two-point loads was assembled. The experimental results from the assembled database, were compared with shear predictions from the old ACI 318-14, more detailed ACI 318-14, more recent ACI 318-19, and the new updated ACI 318-25 codes. A comparative analysis of the predictions by the above models illustrates that the a/d range of 2–3 is critical for the four equations, where a close agreement between the average predicted and experimental shear values is observed. The more detailed ACI 318-14 code demonstrates the impact of the a/d ratio, producing the lowest absolute average error (AAE) values for the a/d ratios of 1 and 2 and the highest Pearson’s coefficient among the four equations. The old ACI 318-14 produced the lowest AAE values of 19, 27, 8, and 8% for the remaining a/d ratios, 3, 4, 5, and 6. The size effect modification factor (λs) utilized in the development of shear equations in ACI 318-19 and ACI 318-25 was similarly negatively impacted by the a/d ratio. Based on the database and comparison, it is recommended that future versions of the ACI code incorporate the a/d ratio. When assessing the shear capacity of RCA concrete beams without shear reinforcement using the new ACI code equations, it is advised to free the $$\lambda_{s}$$ from the square root condition ( $$\lambda_{s1}$$ ) as a precaution to account for the variability in the source of RCA.