Prevention of steel corrosion in concrete containing calcium aluminate cement

Abstract

The present study concerns a development of inhibition technique for steel in concrete using a mixture of calcium aluminate cement (Hereinafter CAC). The CAC is partially replaced for ordinary Portland cement (OPC) in concrete, accounting for 5, 10 and 15% to total binder, to avoid unnecessary flash set. To assess the inhibition effect, chloride binding capacity and corrosion propagation were mainly measured using mortar specimen, assuming that gravel has no chemical influence on the chemical modification of the cement matrix and pore solution, which directly affect the corrosion resistance. Simultaneously, a development of concrete strength was monitored to confirm the applicability to in-situ. As a result, a mixture of CAC with OPC imposed a high resistance to corrosion, as being ensured by monitoring of galvanic current, corrosion potential and corrosion rate, when concrete specimens cast with a centrally located steel bar were containing the variation level in the chloride ions ranging from 0.5 to 3.0% by weight of binder. The corrosion resistance of CAC seems to arise from the higher binding capacity of chlorides in the cement matrix, due to the high portion of C3A, which chemically reacts with chloride ions to form an immobile crystallised salt. Despite the benefits of CAC in mitigating corrosion risk, the strength of CAC mixture was 20-30% lower than OPC concrete in the condition of a damp curing at approximately 20°C, at which the hexagonal hydration phase may be converted to the cubic phase, leading to an increase in the porosity in the cement matrix.