Chloride Threshold Value for Steel Corrosion considering Chemical Properties of Concrete

The present study assesses the chloride threshold level for corrosion of steel in concrete by examining the properties of four different binders used for blended concrete in terms of chloride binding, buffering of cement matrix to a pH fall and the corrosion behaviour. As binders, ordinary Portland cement (OPC), 30% pulverised fuel ash (PFA), 60% ground granulated blast furnace slag (GGBS) and 10% silica fume (SF) were used in a concrete mix. Testing for chloride binding was carried out using the water extraction method, the buffering of cement matrix was assessed by measuring the resistance to an artificial acidification of nitric acid, and the corrosion rate of steel in mortar with chlorides in cast was measured at 28 days using an anodic polarisation technique. Results show that the chloride binding capacity was much affected by content and physical adsorption, and its order was 60% GGBS>30% PFA>OPC>10% SF. The buffering of cement matrix to a pH fall was varied with binder type and given values of the pH. From the result of corrosion test, it was found that the chloride threshold ranged 1.03, 0.65, 0.45 and 0.98% by weight of cement for OPC, 30% PFA, 60% GGBS and 10% SF respectively, assuming that corrosion starts at the corrosion rate of . The mole ratio of []:[], as a new presentation of the chloride threshold, indicated the value of 0.008-0.009, irrespective of binder, which would be indicative of the inhibitive characteristic of binder.