Effects of fly ash on Portland limestone cement under sulfate attack at low temperature

摘要

The effects of type-F fly ash (FA) on the performance of Portland limestone cement (PLC) under sodium sulfate or magnesium sulfate attack at 5 degrees C were evaluated. The degree of damage to the ternary blended cement exposed to 5 wt% sulfate solutions was assessed based on the evolution of the blended cement's appearance, compressive strength and volume. The sulfate product compositions from the blended cement under sulfate attack were analysed by Fourier transform infrared spectroscopy and quantitative X-ray powder diffraction. The results indicated that the PLC containing 40 wt% type-F FA was more resistant to sulfate attack than the control specimen without FA with similar mechanical properties, which was tested at a low temperature. The PLC containing 20 wt% type-F FA showed few effects in terms of improved resistance to sulfate attack. Analysis suggested that active aluminium in the FA glassy phase weakened the blended cement's resistance to sulfate attack because more ettringite was easily formed during the attack, which might accelerate thaumasite formation by means of the woodfordite route at low temperature. Therefore, the effects of type-F FA containing high contents of aluminium phase on the sulfate attack of PLC at low temperature need to be carefully evaluated and studied.