EFFECT OF INTERNAL ALKALI ACTIVATION ON LONG-TERM POZZOLANIC REACTION OF FLY ASH IN CEMENT PASTE

In recent years, alkali activation on fly ash particles has been suggested for accelerating their pozzolanic reaction, which enhances the durability of concrete. It was reported that the alkali activations become most effective when high temperature curing is applied, but it is limited for many applications. Therefore, alkali activation at normal temperature on fly ash cement paste 1 month after casting was investigated and it was found that the alkali activation was effective in accelerating the pozzolanic reaction at the age of 2 months. This study deals with the effects of internal alkali activation on the long-term pozzolanic reaction of fly ash up to the age of 12 months in the cement paste cured at normal temperature by examining the Ca(OH)(2) (CH) content, consumption of CH, and porosity. Cement pastes were prepared with a water to binder ratio of 30%. Fly ash replacement ratios were 0% (FA0) and 40% (FA40) by mass. A saturated Ca(OH)(2) solution was used for an internal alkali activation and water was used for comparison. The internal activation was carried out by supplying the solution naturally through an installed syringe from the age of 1 month. As a result, the injection of water or saturated Ca(OH)2 solution increased the CH content in FA0 at the age of 12 months when compared with no injection. Meanwhile, the injection of saturated Ca(OH)(2) solution from the age of 1 month was more effective in decreasing the CH content and the volume ratio of 20-330 nm pores to the total pore in FA40 and increasing the consumption of CH than the injection of water from the age of 1 month. It indicates that the internal activation from the age of 1 month by using saturated Ca(OH)(2) solution accelerated the pozzolanic reaction of fly ash particles in the cement paste up to the age of 12 months more than that by using water. In addition, the internal activation from the age of 1 month reduced the total pore volume in FA0 and FA40. It can be concluded that internal alkali activation was effective in accelerating the pozzolanic reaction of fly ash in cement paste up to the age of 12 months.