Shear strength of concrete interfaces with infra-lightweight and foam concrete

Ceiling and floor slabs made of horizontal layers of regular and lightweight concrete could lead to an efficient use of materials. In this context, the bond between the different types of concrete is of particular importance. This paper shows the shear strength and failure mode of unreinforced concrete interfaces with high-quality, lightweight concretes in dependence of different interface roughness. To achieve this, a regular and a structural lightweight concrete were bonded to an infra-lightweight and a foam concrete. Small-scale shear specimens consisting of five layers were manufactured and loaded to investigate their shear behavior as a whole. Both concrete and interface failures were detected in dependence of interface roughness and the type of core layer concrete. Additionally, it is shown that the observed behavior can be satisfactorily reproduced by a finite-element model using the material parameters of concrete standard tests. The experimental and numerical investigations provide clearly defined interface parameters to design efficient load-bearing slabs made of different concrete layers.