Influence of lightweight aggregates concrete on the bond strength of concrete-to-concrete interfaces

An experimental study carried out to characterize the bond strength of lightweight aggregate concrete (LWAC) to normal density concrete (NDC) and LWAC-to-LWAC interfaces is presented, also including NDC-to-NDC interfaces as reference. A single NDC mixture, with a compressive strength of 50 MPa, and three LWAC mixtures, with density range between 1500 and 1900 kg/m3 and compressive strength between 45 and 75 MPa, were adopted. Slant shear and splitting tests were conducted to evaluate the interface bond strength, considering different methods to increase the surface roughness of the substrate. Results were analysed and compared with predictions according to Eurocode 2 (EC2) and fib Model Code 2010, and showed significant differences, mainly for rough surfaces. It was found that the role of the binding matrix strength and of the type of aggregate, in the interface strength, is dependent of the roughness of the substrate; the coefficients of cohesion and friction exhibited a good correlation with the roughness parameter “mean peak high”, Rpm, being the cohesion also influenced by the matrix strength of the added concrete. It was also concluded that there is no advantage, in terms of shear and tensile strengths of interfaces with LWAC, to increase the surface roughness above a certain limit.