Study on the disposition of water in fly ash-based geopolymers using ATR-IR

Abstract

This paper addresses the question of whether the main product of low calcium fly ash-based geopolymer is a hydrate, namely, sodium aluminosilicate hydrate (N-A-S-H). The answer to this question is important for understanding geopolymer characteristics. One of these is its fire resistance. In this study, fly ash-based geopolymers were synthesized using the combination of Na2CO3 and Ca(OH)2. Samples were cured at ambient temperature for 7 days, then placed in the oven at 105°C for 24 h, and then calcined at 1050°C for 48 h. IR was used to examine the produced geopolymers at each stage so as to further knowledge on the following issues: the possibility of co-existence of calcium aluminosilicate hydrate (C-A-S-H) and N-A-S-H, the roles of cations as compensator and network modifier as well as the role of water. The results obtained suggest that the primary geopolymerization products, which are potentially good fire-resistant, are unlikely to contain hydrates. Even if there were hydrates, their amount must be very small such that the escaping of water does not compromise the structure's integrity.