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Abstract

The corrosion of steel in ordinary Portland cement (OPC) mortars of low water/OPC ratio (w/OPC) was examined during immersion in chloride solutions. Steel in mortar with equal volumes of sand and 0PC, immersed in aerated simulated sea water, was passive for 550 days with a corrosion current (I_cor) typically of the order of 0·1 μA cm⁻². In 3:1 and 2:1 sand/OPC mortars steel depassivated under apparent anodic control. Corrosion potentials were more negative than —800 mV(SCE) and corresponded to I_cor values between 5·0 and 8·0 μA cm⁻², limited by oxygen diffusion. It is suggested that some gas filled porosity was retained despite prolonged immersion. Reduction of mix water content from 0·4 to 0·3 w/0PC decreased mortar and cement paste porosity but did not improve the corrosion performance of embedded steel. This may be due to reduced compaction efficiency during placement and lower Ca(OH)₂ content in the hardened OPC paste (particularly at the steel/mortar interface). Steel in mortar showed similar anodic polarisation behaviour to steel in alkaline chloride solution, with two anodic reaction peaks before passivation but little evidence of general depassivation at low potentials (more negative than —800 mV(SCE)). In deoxygenated mortars, anodic current, at —850 mV(SCE), decayed with time, which may be due to the formation of partially protective oxides.

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Effect of Mix Specification on Corrosion of Steel in Mortars Immersed in Chloride Solutions

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