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

Abstract

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. 

Die balk- en blokbladstelsels, ook bekend as rib- en blokblad, word wyd in SuidAfrika gebruik as ’n voorkeur-hangvloerstelsel vanweë hul strukturele doeltreffendheid en ekonomiese lewensvatbaarheid. Volgens SANS 1879 (2021)-riglyne vir voorafvervaardigde beton- hangblaaie, word die verwydering van tydelike stutte vir balke en blokblaaie aanbeveel sodra die in-situ beton se druksterkte 17 MPa  oorskry. Sekere vervaardigers en strukturele ingenieurs het bekommernisse met betrekking tot die strukturele egtheid van die grensvlak trekbindingsterkte wat bestaan tussen voorafvervaardigde rib en in-situ beton, veral wanneer die druksterkte van beton 17 MPa is. Ten  einde die strukturele egtheid van grensvlak trekbindingsterkte te meet, is uittrektoetse uitgevoer op voorafvervaardigde, geruwde  betonribbe en in-situbeton. Die studie het vasgestel dat, wanneer die oppervlakruwheid 3 mm is, die delamineringseksperimente ’n  trekspanning van 0.15 MPa toon, wat gelykstaande is aan ’n druksterkte van 17 MPa vir in-situ beton. Verder het die studie aan die lig  gebring  at die treksterkte ’n waarde van 0.21 MPa bereik by die bereiking van ’n druksterkte van  25 MPa vir beton, gegewe ’n oppervlakruwheid van 3 mm. Die studie het die grensvlak trekbindingspanning tussen voorafvervaardigde rib en in-situ beton  geopenbaar, wat vervaardigers en strukturele ingenieurs kan gebruik in samewerking met Bylae B (B1) van SANS 1879 (2021). Dit laat toe  dat tydelike stutte verwyder word sodra die beton 17 MPa bereik. Die toetsresultate toon voldoende grensvlak trekbindingsterkte  tussen voorafvervaardigde ribbes en gegote in-situ beton indien die grensvlak-oppervlak voldoende voorberei is en die rib sy eie gewig  dra.