CORROSION PERFORMANCE OF BLENDED CEMENT CONCRETES IN THE MARINE TIDAL ZONE

Reinforced concrete (RC) structures exposed to the marine environment hardly meet their serviceability expectations due to early deterioration problems associated with chloride-induced reinforcement steel corrosion. To curb the impact of this, the use of blended cement, using supplementary cementitious materials (SCMs) has been adopted worldwide due to their improved durability performance. However, their performance under different marine exposure conditions varies due to differences in physical, chemical and mineralogical composition. This study assesses the corrosion performance of selected SCMs in the marine tidal zone through an automated cycle change system, resembling the tide change in the marine tidal zone. Three binders (100%PC, 70%PC/30%FA, and 50%PC/50%GGBS), two w/b ratios (0.45 and 0.65) and two cover depths (20 mm and 40 mm) were used to make corrosion specimens. A total of 12 specimens were cast, each with an embedded high tensile mild steel to act as an anode and two stainless steels which served the function of cathode. The specimens were exposed to a simulated marine tidal zone in the laboratory comprising of a continuous cycle of 6 hours wetting with 5% NaCl solution and 6 hours air-drying for a period of 3 months. Corrosion current was monitored weekly in all specimens. The experimental programme is ongoing but some results will be presented in this paper.