The effect of curing on the hydration and pore structure of hardened cement paste containing pulverized fuel ash

Tests were carried out on ordinary Portland cement (OPC) and OPC/pulverized fuel ash (PFA) paste specimens stored at a range of relative humidities in order to study the effects of curing on the hydration and development of pore structure. The results of thermogravimetric analysis show that P FA pastes are more susceptible to inadequate curing with no significant reaction between PFA and Ca(OH)₂ observed in early age pastes nor in pastes stored at low relative humidities (below 80%). For pastes cast at equal water/solid ratios, methanol adsorption studies show that PFA pastes have a larger total porosity than OPC pastes, but with adequate curing the PFA paste develops a more refined pore structure (i.e. smaller volume of large pores). However, in early age or poorly cured (storage at low humidity following short curing periods) pastes with equal water/solid ratios, those containing PFA may have a considerably coarser pore structure. Generally, for pastes stored at low relative humidity, PFA paste required an additional curing period of one day in order for the volume of large pores (< 36·8 nm dia.) not to exceed that ofOPC paste. A comparison of OPC and PFA pastes cast at the water/solid ratios used in equal strength grade OPC and PFA concretes, show the PFA paste to have a more refined pore structure, even under conditions of poorest curing (i.e. stored at low humidity following demoulding at 24 h).