Optimization of geopolymer synthesis by calcination and polycondensation of a kaolinitic residue

In this work a kaolinitic residue has been used for the synthesis of geopolymer-based building materials. The synthesis takes place through a calcination step followed by a polycondensation step. The calcination step was carried out at temperatures ranging from 500 to 750degreesC and times ranging between 2 and 6 h. Optimum calcination conditions were found by evaluating the reactivity of the calcined products by differential scanning calorimetry (DSC). The polycondensation step was carried out at temperatures ranging from 25 to 85 degreesC by reaction with sodium or potassium silicate. The compositions of polycondensation systems stoichiometric for the synthesis of polysialate (PS), polysialatesiloxo (PSS) and polysialatedisiloxo (PSDS) geopolymers were tested, but only the first two were successful. An original quantitative analytical method was employed to determine the amounts of reacted silicate and water after polycondensation. The products obtained were tested for unconfined compressive strength, apparent density, porosity, surface area and pore size distribution. The results show that it is possible to produce good quality building materials starting from a kaolinitic residue. (C) 2003 Elsevier B.V. All rights reserved.