Corrosion behaviour of blended cements in low and medium strength concretes

The corrosion behaviour of steel in concrete with blended cements like Portland pozzolana cement and Portland blast furnace slag cement were studied in comparison to their corresponding ordinary Portland cements from the same production facility with the same clinker used in their production. The different cements studied were – two Portland pozzolana cements (PPCs) and their corresponding ordinary Portland cements (OPCs) from the same cement plant, and two blast furnace slag cements (BFSCs) along with the corresponding OPCs from the same factory. Three concretes of compressive strengths 15, 30 and 45 MPa were designed. The corrosion characteristics of fly ash and slag cement concretes were studied through measurement of resistivity, pH, carbonation, and corrosion rate. The resistivities of both fly ash and slag concretes were found to be more than the corresponding ordinary concretes. The pH of fly ash and slag concretes were found to be around 12.0 indicating no significant lowering compared to OPC concrete. However, carbonation was higher in both blended cement concretes, particularly in slag concretes. The corrosion rates of steel in both fly ash and slag concretes were much lower than the corresponding OPC concretes, with slag concretes showing higher resistance than fly ash concretes. From these studies it is evident that fly ash and slag blended cements performed better than their corresponding ordinary cements, with slag cements showing the best corrosion resistance.