The effect of the steel–concrete interface on chloride-induced corrosion initiation in concrete: a critical review by RILEM TC 262-SCI

Abstract

This article has been prepared within a framework of RILEM TC 262-SCI. The article has been reviewed and approved by all TC members.

Chloride‐induced steel corrosion in alkali‐activated fly ash mortar: Increased propensity for corrosion initiation at defects

“…The importance of spatially varying characteristics of the steel–concrete interface, including microstructural or chemical heterogeneities, has been highlighted recently for the case of conventional cement‐based materials. [ 8,24 ] The present findings emphasize the need for a similar approach to alkali‐activated materials, that is, studies dedicated to understanding the causes and the relative importance of various defects and microstructural alterations at the steel–concrete or steel–mortar interface in these materials.…”

“…As alterations of the steel surface due to welding were not at the origin of the preferential corrosion at the joints, another mechanism must underly its occurrence. The most economic explanation appears to be the preferential formation of corrosion‐promoting defects such as air voids [ 8,24 ] at the welding joints in the alkali‐activated fly ash mortar specimens, but not in the Portland cement mortar.…”

“…While extensive data regarding the critical chloride content in concretes and mortars based on Portland cement and blended cement have been compiled, [ 6–8 ] much less data in this regard are available for concretes or mortars based on alkali‐activated binders. [ 9 ] Early work showed that carbon steel in chloride‐free alkali‐activated fly ash mortars attains a passive state and indicated that chloride contents up to 0.4 wt% with respect to binder (wrtb) do not cause steel corrosion in these mortars.…”

Determination of the Corrosion Rate of Steel Bars in Concrete Based on the Porosity of Interfacial Zone

“…A change of the chloride threshold can have a significant effect on the corrosion process of the steel bars. Observation of the corroded concrete structures shows that corrosion of steel bar initiates at the surface voids and steel-concrete interface with lower porosity can delay the initiation of corrosion (Angst et al, 2019), indicating that lower porosity of the interfacial zone can increase the chloride threshold. Kenny and Katz (2020) conducted a statistical analysis of the relationship between the chloride threshold and steel-concrete interfacial zone properties.…”

“…However, the anode-cathode ratio a/c is difficult to be quantified, due to the uncertainty of cathode area and anode area of the steel bar. Research (Angst et al, 2019) shows that the corrosion of steel bars occurs at the surface contacting with concrete pores, which is mainly because pores at the interfacial zone provide a primary pathway for chloride ingression, which can induce corrosion of steel bars. In addition, the chloride diffusion coefficient in the interfacial zone is 6-12 times greater than that in the bulk paste (Wu et al, 2015;Zhu et al, 2017), which decreases the resistivity of the concrete and accelerate the corrosion process due to the high porosity (Soylev and François, 2003).…”