Effect of sulphate content on the hydration and strength of cement/fly ashsystems with and without a water-reducing admixture

Earlier studies of the optimum SO₃, contents of cements in the presence of chemical admixtures have been extended to mixes containing cement (both OPC and SRPC), sub-bituminous high-lime fly ash and water-reducing admixture. The hydration character istics have been studied by means of conduction calor imetry; and measurements of the compressive strength of mortars up to 56 days have been used to assess optimum SO₃, contents. The optimum SO₃, content of the plain cement mixes in the presence of the admixture was 1% higher than the as-received cement. The optimum SO₃, content of the cement/fly ash/admixture mixes was found to be close to that of the as-received cements, It is suggested that, where large volumes of a concrete containingjy ash and admixture are to be produced, it may he worthwhile determining the optimum SO₃, con tent of the particular mix, to assess whether adjusting the SO₃, content of the mix at the batching plant may be cost and energy-efective.