Efficiency factors of recycled concrete aggregate concrete bottle-shaped struts

A comparison with code-based predictions of efficiency factors of bottle-shaped struts computed using strut-and-tie models from shear test results of coarse recycled concrete aggregate concrete beams reported in the literature is presented. The objective of the comparison was to ascertain whether strut efficiency factors in current design codes originally meant for natural coarse aggregate concrete can be conservatively applied to concrete made with coarse recycled concrete aggregate or not. In addition to the codal provisions, a strut efficiency factor model developed from first principles was also used in the comparative study. The results of the comparison indicate that the AASHTO LRFD code provisions and the proposed efficiency factor model gave conservative predictions for the coarse recycled concrete aggregate concrete bottle-shaped struts although the ACI 318-08 predictions were unconservative. The most accurate predictions were obtained from the Eurocode 2 model, although with an erratic degree of conservatism. The lack of conservatism vis-à-vis the ACI code recommended strut efficiency factors does not per se indicate inferior strength of coarse recycled concrete aggregate concrete but may be attributed to the insensitivity of the ACI code efficiency factors to strut inclination with adjoining tie(s).