EFFECT OF CEMENT TYPE ON CHLORIDE BINDING AND CORROSION OF STEEL IN CONCRETE

Chloride binding and its influence on the rate of reinforcement corrosion has been investigated in a range of mixes by, respectively, pore solution analysis and measuring the galvanic current in macro corrosion cells formed by embedding mild steel bars in two layers of concrete. For chloride derived from NaCl and introduced at the time of mixing, chloride binding occurred in the order of: GGBS>PFA>OPC>SF and the amount of unbound tie free) chloride increased with increasing chloride content. However the corrosion rates occurred in the order of PFA>SF>GGBS>OPC at 1% Cl- and PFA>OPC>GGBS>SE at 3% Cl-. The corrosion rates increased with increasing chloride content for all mixes due to an increase in the amount of free chloride. The higher rates of corrosion for PFA (and GGBS at 1% Cl-) compared with OPC was attributable to a reduction in the OH concentration as a result of the pozzolanic reaction. The relatively low rate of corrosion for SF at 3% Cl- is thought to largely depend upon the physical characteristics of the matrix rather than the pore solution chemistry.