Influence of carbonation on the resistance of concrete structures to chloride penetration and corrosion

Abbas S Al-Ameeri,M Imran Rafiq,Ourania Tsioulou,M.G Grantham,C Mircea

doi:10.1051/matecconf/201928908001

Abbas S Al-Ameeri, M Imran Rafiq + Show 3 more

Open Access

https://doi.org/10.1051/matecconf/201928908001

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Abstract

Chloride-induced corrosion of steel rebar embedded in concrete is one of the major concerns influencing the durability of reinforced concrete structures. It is widely recognized that the carbonation in concrete affects the chloride diffusivity and accelerates the chloride-induced reinforcement corrosion. However, only very limited studies have dealt with this issue in the literature. The presence of service load related cracks also affects the reinforcement corrosion. This study aims to investigate the potential impact of concrete carbonation on the chloride penetration resistance, and degree of corrosion, in RC structures subjected to service related microcracks.The experimental programme involves casting of concrete prisms (100 x 100 x 500 mm) with different water-cement ratios (w/c) of 0.4, 0.5 and 0.6 and with four different crack widths (0, 0.05-0.15 mm, 0.15-0.25 mm and 0.25-0.35 mm). These samples were exposed initially to accelerated carbon dioxide (CO2) environment and then exposed to the accelerated chloride environment. Carbonation depth, chloride penetration, and the degree of corrosion (using half-cell) were experimentally measured. The results indicated that (i): The depth of carbonation increases with the increase in crack width and w/c ratio, (ii) chloride penetration depth in concrete structures increases significantly due to the influence of carbonation and (iii) half-cell corrosion potential increases significantly when carbonated concrete samples are exposed to the chloride environment relative to the uncarbonated concrete samples.

Highlights

Carbon dioxide and chloride ion attack seem to be significant factors which affect the sustainability of concrete structures
The results indicated that (i): The depth of carbonation increases with the increase in crack width and w/c ratio, (ii) chloride penetration depth in concrete structures increases significantly due to the influence of carbonation and (iii) half-cell corrosion potential increases significantly when carbonated concrete samples are exposed to the chloride environment relative to the uncarbonated concrete samples
The depth of carbonation (DoC) as a function of w/c ratio for the mixes used in this study is shown in Table 2, where M 0.4, M 0.5 and M 0.6 refers to w/c ratio of 0.4, 0.5 and 0.6 respectively

Summary

Introduction

Carbon dioxide and chloride ion attack seem to be significant factors which affect the sustainability of concrete structures. The diffusivity of CO2 in concrete leads to changes in the mineralogical composition (due to carbonation) of concrete and has the potential to reduce the pH of the pore water in concrete. It may break down the chloride binding (calcium chloroaluminate), which free up more chloride leading to the deeper penetration of chloride in the concrete. It is a result of the reaction between one of the cement components, namely tricalcium aluminate (C3A) and chloride ions within the pore water in concrete [4]. Carbonation is a significant factor in reducing the pH and liberation of bound chlorides for cement mortar samples [5]

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