Efficiency factors of recycled concrete bottle-shaped struts

Abstract

Reported test results of reinforced concrete beams made with coarse recycled concrete aggregate have been re-analysed using strut-and-tie models and the efficiency factors of the recycled concrete aggregate concrete bottle-shaped struts compared with those made of natural coarse aggregate. The objective was to ascertain whether strut-and-tie model provisions for efficiency factors of bottle-shaped struts in current design codes and the recent literature, originally meant for natural coarse aggregate concrete, can be conservatively applied to recycled concrete aggregate concrete, or not. The results of the re-analysis indicate that the efficiency factors of the natural coarse aggregate as well as the recycled concrete aggregate concrete bottle-shaped struts were comparable and conservative when benchmarked against the predictions of CSA A23.3-04 and an efficiency factor model proposed by the authors. However, both ACI 318-08 and Eurocode 2 gave unsafe efficiency factor predictions for the recycled concrete aggregate as well as the natural coarse aggregate concrete bottle-shaped struts under investigation. This is attributed to the insensitivity of these two codes to strut inclination with adjoining tie(s) and does not per se indicate any inherent inferiority as far as recycled concrete aggregate concrete is concerned. This investigation indicates that recycled concrete aggregate concrete bottle-shaped struts can be designed using the efficiency factors recommended for natural coarse aggregate concrete bottle-shaped struts in CSA A23.3-04.