Interfacial tensile bond strength between precast rib and cast-in-situ concrete for beam and block slab systems

Abstract

The beam and block slab systems, also referred to as rib and block slab, are widely used in South Africa as a preferred suspended flooring system owing to their structural efficacy and economic viability. According to SANS 1879:2021 guidelines for precast concrete suspended slabs, it is recommended to remove temporary propping for beams and block slabs once the cast-in-situ concrete’s compressive strength surpasses 17 MPa. Notwithstanding the limited availability of literature on the matter, certain manufacturers and structural engineers have raised apprehensions regarding the structural soundness of the interfacial tensile bond strength that exists between precast rib and cast-in-situ concrete, particularly when the compressive strength of concrete is 17 MPa, hence the study. In order to measure the structural soundness of interfacial tensile bond strength, pull-out tests were conducted on precast roughened concrete ribs and cast-in-situ concrete. The study determined that, when the surface roughness was 3 mm, the delamination experiments exhibited a tensile stress of 0.15 MPa, which equates to a compressive strength of 17 MPa for cast-in-situ concrete. Furthermore, the study revealed that the tensile strength attains a value of 0.21 MPa upon attainment of a compressive strength of 25 MPa for concrete, given a surface roughness of 3 mm. The study suggests that an independent mechanism should be devised and implemented to guarantee the structural soundness of the interfacial tensile bond strength between precast ribs and cast-in-situ concrete topping, owing to the low bond strengths.