Long-term pozzolanic reaction of fly ash in hardened cement-based paste internally activated by natural injection of saturated Ca(OH)(2) solution

The pozzolanic reaction of fly ash in hardened cement-based paste internally activated by a natural injection of saturated Ca(OH)(2) solution from the age of 1month was investigated. This investigation was conducted with the aim of comprehensively evaluating the long-term effectiveness of this technique. The Ca(OH)(2) content, degree of the fly-ash reaction, and pore structure were measured using thermal gravimetric analysis, selective dissolution, and mercury intrusion porosimetry, respectively. The Ca(OH)(2) consumption was calculated from the Ca(OH)(2) content in the pastes with 0 and 40% replacements of cement by fly ash. The cement hydration and pozzolanic reactions of fly ash in the pastes proceeded gradually up to 12months, but were negligible from 12 to 24months regardless of whether solution was injected. An injection of alkali solution increased both the Ca(OH)(2) consumption and the degree of the fly-ash reaction after aging for 12months. The relationship between the Ca(OH)(2) consumption and degree of the fly-ash reaction indicated that the injection of alkali solution activated the surface of the fly-ash particles at early ages, whereas the injection of water did not activate these particles but accelerated the cement hydration, which promoted the pozzolanic reaction. The refinement of the pore structure in the pastes confirmed the effectiveness of the solution injection. Consequently, the injection of saturated Ca(OH)(2) solution from the age of 1month directly activated fly-ash particles and accelerated the long-term pozzolanic reaction (i.e., up to 24months) in hardened cement paste with 40% replacement by fly ash, although it was not effective in further enhancing the pozzolanic reaction from 12 to 24months.