Geopolymerization process of alkali–metakaolinite characterized by isothermal calorimetry

The geopolymerization process of metakaolinite activated by alkali and alkali silicate solutions was revealed. The effects of alkali concentration, modulus of alkali silicate solution and reaction temperature on geopolymerization were studied systematically by isothermal calorimetry, as well as X-ray diffraction and 27Al/29Si MAS NMR. Results show that the geopolymerization process of metakaolinite under alkali activation condition can be reasonably supposed into three stages: (I) destruction, (II) polymerization and (III) stabilization. The rate of geopolymerization in KOH solution is higher than in NaOH solution and reaches the maximum in 15 mol/L KOH solution during stage II. The extent of geopolymerization increases with increasing of alkali content regardless of the existence of silicate anions in activator.