Resistivity-based chloride-induced corrosion rate prediction models and hypothetical framework for interpretation of resistivity measurements in cracked RC structures

Abstract

To present resistivity-based chloride-induced corrosion rate prediction models and hypothetical framework for interpretation of resistivity measurements in cracked RC structures. Parallel corrosion experiments were carried out by exposing one half of 210 beam specimens (120 × 130 × 375 mm) to accelerated laboratory corrosion (cyclic 3 days wetting with 5 % NaCl solution followed by 4 days air-drying) while the other half were left to undergo natural corrosion in a marine tidal zone. The specimens were cast using five concretes made using two w/b ratios (0.40 and 0.55) and three binders (100 % CEM I 42.5N (PC), 50/50 PC/GGBS and 70/30 PC/FA). Other variables in the experiments included cover depth (20 and 40 mm), crack width (0, 0.4 and 0.7 mm). Corrosion rate and resistivity were monitored bi-weekly in the specimens. The results relevant to this paper are presented and discussed. Experimental results (both natural and accelerated) show that there is an inverse relationship between corrosion rate and concrete resistivity in both cracked and uncracked RC structures. The results also show that for a given concrete resistivity value, corrosion rate of steel in concrete of a given binder type and w/b ratio increases with increase in crack width. Furthermore, for a given crack width, corrosion rate in cracked concrete is also shown to be influenced by concrete quality. Resistivity-based chloride-induced corrosion rate prediction models for cracked RC structures are proposed. This paper also advocates for the improvement in the interpretation of concrete resistivity measurements with respect to steel corrosion in cracked RC structures. A hypothetical framework to aid in this is proposed.