Study on the cause of pop-out defects on the concrete wall and repair method

Concrete pop-outs are a common occurrence in foreign countries; however, this has not been the case in Korea, until recently when pop-outs were observed on the concrete walls of an apartment. Our investigation revealed that the electric arc furnace (EAF) slag, as fine aggregates in the concrete caused the pop-out.This study discusses the cause that EAF slag as fine aggregates for concrete create the pop-outs, and an appropriate repair depth for deteriorated concrete as suggested by finite element (FE) analysis.Results show that the free CaO and free MgO in the EAF slag were primarily responsible for creating the pop-outs. These findings led us to conclude that the defect could occur to the depth of 34 mm in the concrete with 21 MPa strength as the EAF slag size was up to 5 mm. As an effective repair method for pop-outs, replacing concrete up to 23 mm in depth from the surface with polymer mortar of 50 MPa design strength was suggested, and the proposed method is verified through experimentation.