Activated fly ash cements: tolerable limit of replacement for durable steel reinforced concrete

At present the utilisaton of fly ash in cement and concrete in India is very minimal. Therefore, enhancing the activity of fly ash is the critical key to large scale applications. Physical, thermal and chemical activation methods have been effected and their performance characteristics tested by aggressive macro cell corrosion technique. The salient features of the investigations were: steel embedded in ordinary Portland cement (OPC) and unprocessed fly ash incorporated cements suffered severe corrosion under macro cell corrosion conditions. But OPC containing treated fly ashes improved the corrosion resistant properties to a greater extent. Chemically treated fly ashes showed superior performance when compared to thermally treated and physically treated systems. The tolerable limit of replacement level for various treated fly ashes under aggressive macro cell corrosion condition is found to be 20%–30%. Under 30% replacement level, chemically activated fly ash (CFA) system showed lowest corrosion rate, highest durability factor and lowest macro cell current under accelerated macro cell corrosion conditions.