Abstract

KHUZWAYO, Bonga. Interfacial tensile bond strength between precast rib and cast-in-situ concrete for beam and block slab systems. Acta structilia (Online) [online]. 2024, vol.31, n.1, pp.222-240. ISSN 2415-0487.  http://dx.doi.org/10.38140/as.v31i1.7668.

The beam and block slab system, also referred to as rib and block slab, is widely used in South Africa as a preferred suspended flooring system owing to its structural efficacy and economic viability. According to SANS 1879 (2021) guidelines for precast concrete suspended slabs, the removal of temporary propping for beams and block slabs is recommended once the cast-in-situ concrete's compressive strength surpasses 17 MPa. Notwithstanding, the limited availability of literature on the matter means that 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. 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 is 3 mm, the delamination experiments exhibit 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 revealed the interfacial tensile bond stress between precast rib and cast-in-situ concrete, which manufacturers and structural engineers can use in conjunction with Annex B (B1) of SANS 1879 (2021). This allows temporary props to be removed once the concrete reaches 17 MPa. The test results show sufficient interfacial tensile bond strength between precast ribs and cast in-situ concrete if the interfacial surface is adequately prepared and the rib supports its own weight.

Keywords : beam and block slab system; rib and block slab system; voided slabs.

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