A study on pozzolanic reaction of fly ash cement paste activated by an injection of alkali solution

The purpose of this study is to investigate the pozzolanic reaction of the fly ash cement paste by an injection of an alkali solution after hardening. Cement pastes with 0%, 20%, and 40% of fly ash replacement ratios were used. An NaOH or saturated Ca(OH)2 solution was injected into the paste through a syringe 1 month after casting at normal temperature. In addition to the reduction of the Ca(OH)2 content, the consumptions of Ca(OH)2 in the paste with 40% replacement of fly ash activated by NaOH and Ca(OH)2 solution were observed to be 2.6 and 4.5 times as large as that with 20% replacement of fly ash. It indicates the alkali solution accelerates the pozzolanic reaction, together with the promotion of cement hydration. The results of pore structure analysis also confirmed this activation. As a result, it can be concluded that the 1-month alkali solution injection was effective in accelerating the pozzolanic reaction of the cement paste with 40% replacement of fly ash.