Modification of cement pore fluid compositions by pozzolanic additives

The impact of blending agents on the internal environment of cement systems is assessed by chemical analysis of the pore fluid in cured blends. The short-term behaviour of PFA blends is complicated by the presence of soluble alkali. In general, pore fluid sodium levels are not much altered by PFA while potassium is reduced. SiO 2 fume has a more immediate impact on the pore fluid chemistry: 10–20% additions can lead to order-of-magnitude reductions, especially in caesium content. The potential of cement to uptake chloride anions is assessed: the correlation with the sum of tricalcium aluminate (C 3 A) and ferrite phases is more significant than with C 3 A alone. Blast furnace slags can markedly affect the internal redox potential, which decreased from +100mV in Portland cement to minus 200–225mV in slag-rich blends.