A fractal dimension-modified stochastic damage model for bond-slip responses of corroded steel rebar embedded in different types of geopolymer concrete

Abstract

The performance of reinforced concrete (RC) structures may experience significant deterioration in harsh environments, and geopolymer concrete becomes an alternative to ordinary Portland cement (OPC) concrete due to its high corrosion resistance. However, the interfacial bond behavior of steel rebar to geopolymer concrete may significantly vary, and hence totally 68 central pull-out specimens were tested to gain insight into this issue. Several potential influenced factors on bond behavior were systematically discussed, covering rebar type, concrete type, as well as corrosion degree. Based on the test results, the calculated fractal dimension is found to be significant for the corroded rebar embedded in geopolymer concrete, indicating that more uniform corrosion occurred under this scenario. Furthermore, geopolymer concrete can provide a strong chemical adhesion at the bond interface, leading to a conspicuous enhancement of the bond strength. The interfacial chemical adhesion, however, tends to be damaged by the corrosion effect, and more significant bond deterioration is detected with the increase in corrosion degree for slag-based geopolymer (SG) and metakaolin-based geopolymer (MKG) specimens. Nevertheless, the corrosion extent as well as the bond deterioration can be alleviated to some extent by using hydrophobic metakaolin-based geopolymer (HMKG) concrete. Based on the stochastic damage theory, a spring system is assumed to describe the stochasticity of bond-slip responses, and a new model is proposed with the consideration of the corrosion degree and fractal dimension. The proposed model can provide desirable predictions for the bond strength and bond-slip responses of corroded rebar to different types of concrete.