Pullout behaviour of deformed steel bars in high-strength recycled aggregate concrete

The results of 30 pullout tests carried out on 8-mm and 10-mm dia. deformed steel bars concentrically embedded in high-strength recycled aggregate concrete with coarse recycled concrete aggregate (RCA) replacement levels of 25%, 50%, 75% and 100% are reported. The measured bond–slip relationships indicate similar mechanisms of bond resistance in the RCA and the natural coarse aggregate concretes, and relatively accurate bond strength predictions of the RCA concretes are obtained from a model in the literature. For both the bar sizes, normalised bond strengths of the high-strength RCA concrete – besides being higher than those of the comparable natural coarse aggregate concrete – are observed to increase with an increase in the RCA replacement level. This behaviour is explained in terms of fracture toughness evaluated using an analogous parameter from rock mechanics. An empirical bond stress against slip relationship is proposed and it is conservatively suggested that anchorage lengths of the 8-mm and the 10-mm dia. deformed steel bars in the high-strength RCA concretes of this investigation may be taken as the same as that found in comparable natural aggregate concrete.