Bond strength of deformed steel bars in high-strength recycled aggregate concrete

The results of thirty pullout tests carried out on 8 and 10 mm diameter deformed steel bars concentrically embedded in high-strength recycled aggregate concrete designed using equivalent mix proportions with coarse recycled concrete aggregate (RCA) replacement levels of 25 %, 50 %, 75 % and 100 % are reported towards investigation of bond behaviour of RCA concrete. Analysis of the measured bond–slip relationships indicates similar mechanisms of bond resistance in the RCA and the natural aggregate (NA) concrete and relatively the most accurate and conservative predictions of the measured bond strengths were obtained from the fib Model Code 2010. For both the bar sizes, normalised bond strengths of the high-strength RCA concretes were not only higher than those of the comparable NA concrete but were also higher than those of the normal-strength RCA concrete. For the RCA concrete, the normalised bond strength was observed to increase with an increase in the RCA replacement level, a behaviour which has been explained in terms of fracture toughness of the RCA concrete calculated using an analogous parameter from rock mechanics. An empirical bond stress-versus-slip relationship has been proposed and it is conservatively suggested that anchorage lengths of the 8 mm and the 10 mm diameter deformed bars in the high-strength RCA concretes of this investigation may be taken the same as in NA concrete of comparable strength.