Performance of concrete mixes with OPC–PFA blends

This paper describes a comprehensive programme of testing for strength, durability (sorptivity, carbonation, drying shrinkage, sulphate attack and chloride ingress) and fresh-state properties (slump, slump loss, setting time, temperature rise and plastic shrinkage) of grade 25 and 35 concretes, where the ordinary Portland cement (OPC) binder was replaced with 15% and 25% of pulverised fuel ash (PFA). Three types of OPC–PFA mixes, designated ‘safe’, ‘workable’ and ‘economical’, were investigated. In general, the results from the PFA mixes were similar to or better than the OPC control mixes. The charge passed in the indirect chloride ion penetration test and the heat of hydration temperature rise were considerably reduced in the PFA mixes. They were however more susceptible to plastic shrinkage cracking. It was also found that the strength ratio between PFA mixes and OPC controls was slightly greater at 3 days than at 7 days, after which this ratio increased again, as expected.