Optimum proportion of fly ash or slag for resisting concrete deterioration due to carbonation and chloride ingress

Chloride ingress is considered as the primary reason causing corrosion of steel inside reinforced concrete (RC). Carbonation can also result in significant corrosion of RC structures in locations where CO2 concentration is high due to atmospheric condition or environmental hazards. Consequently, RC structure could experience considerable degradation if carbonation occurs in conjunction with chloride induced corrosion. However, from the available literature, inconsistent outcome has been found regarding the effect of amount of supplementary cementing materials (SCMs) such as fly ash and slag on concrete's carbonation. In this study, an attempt has been made to establish interaction zones from the contrasting results observed between carbonation and chloride penetrability of concrete with respect to fly ash or slag addition. The findings of the study were based on results obtained from Rapid Chloride Permeability Test (RCPT) and carbonation tests of 108 mixes with a range of water to binder (w/b) ratios, binder contents, aggregate gradations and fly ash/slag percentages. An apparent optimum proportion of 20% replacement of cement by fly ash or slag has been proposed considering combined action of chloride ingress and carbonation. Moreover, tentative service life has been estimated using fib model with the observed carbonation depth data. In addition, replacing cement with the optimized amount of fly ash or slag will reduce cost and provide a sustainable solution to concrete construction.

Automated summary

This study aims to investigate the impact of different supplementary cementing materials on the carbonation and chloride penetrability of concrete. Based on the experimental results, an optimal proportion of 20% replacement of cement has been proposed, and the preliminary service life has been estimated. This is of significant importance for the durability and cost-effectiveness of concrete structures.