Abstract
On 16th of November 2021, the PC slab had been fallen out and dropped to approximately 10M downstairs slab during the PC slab concrete pouring work on the rooftop floor of new logistics warehouse construction in Hwaseoung, Gyeonggi-do, and this accident was mainly caused by the bending fracture of concrete since the weaker strength of the upper compressed concrete compared to the tensile strength of central lower parts failed to withstand the high stress of upper topping concrete pouring. For the investigation of root-cause for above mentioned accident, the design compressive strength had been tested by utilizing the core sampling(extracting) method for the PC slab which was fallen out while pouring topping concrete, and as a result, the average compressive strength of three(3) concrete specimens collected from the relevant member through the destructive test was observed as 21.7MPa (No.1 – 20.6MPa, No.2 – 18.1MPa, No.3 – 26.5 MPa) which is only 55% level of the design compressive strength of 40MPa. The main cause that the average compressive strength was observed at about 55% level of the design compressive strength of 40MPa is the failure to comply with the required standard/specification for steam curing during the PC production processing. The required conditions to be complied for the steam curing are 60±10℃(Max. 80℃ or less) of curing temperature, 20℃/h or less of temperature rise rate and shall be managed by the concrete maturity, however, it was reported as a result of investigating the PC manufacturer that the strength had not reached to the standard strength before the mold deformation due to the steam curing with low temperature condition at opened space. The logistics warehouses have been continuously requested to be expanded after COVID-19 Pandemic, and the demand of PC which has merit in logistics warehouse construction work has been rapidly increasing. As a result, the operation rate of PC manufacturers currently reaches the maximum production limit, instead, PCs have been indiscriminately produced at small workplaces which have not able to satisfy the design compressive strength, construction quality and safety requirements. In the current situation, the construction site and workers are exposed to the potential risk of falling accidents since any relevant law or regulation on non-securing quality requirements such as the compressive strength is not stipulated yet. For this reason, the PC products with secured quality requirements shall delivered and construction safety management shall be improved by implementation of PC Factory Certification System at the earliest. For the purpose of this study, the PC factory certification system should be introduced, the research method was selected based on PC drop accidents and domestic and international operational cases of each country's certification system.
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