Influence of metal ions on formation of silico-aluminophosphate geopolymer

Abstract

Portland cement as the most widely used construction material plays a significant role on the global urbanization. However, numerous crises (e.g., environmental issues) coming with this progress have been emerging. Geopolymer cement (or chemically-activated cement [CAC] defined by other researchers) is an attractive alternate to the traditional Portland cement because such a type of cement can be calcination-free and derived through chemical reactions (e.g., gels formation and geopolymerization) between industrial by-products or natural minerals (i.e., aluminosilicate precursors) and activating solutions (e.g., alkali-silica or phosphate). This thesis focuses on the influences of metal ions on the microstructural modification during the formation of silico-aluminophosphate geopolymer. An in-depth understanding of the material formation mechanism is believed to be a key to tailor this type of geopolymer to meet specific performance requirements in different engineering applications. The study mainly involves four dimensions: (1) Synthesis of silico-aluminophosphate geopolymer based on a theoretical Si-Al-P ratio which is supported by a hypothetical molecular structure; (2) Improvement of the workability and setting time of silico-aluminophosphate geopolymer by incorporating aluminate species into the phosphate activator; (3) Use of dead-burnt magnesia-doped aluminosilicate precursor to induce acid-base reaction during the geopolymerization for improving the early age performance of silico-aluminophosphate geopolymer; (4) Use of high-calcium coal fly ash as the calcium donor during geopolymerization to acquire the castable silico-aluminophosphate geopolymer with high early strength. Aluminum-incorporated phosphate activation and magnesium/calcium-doped aluminosilicate precursors (e.g., dead-burnt magnesia and high-calcium coal fly ash) were extensively studied and found to be effective to modify both the fresh and hardened properties of silico-aluminophosphate geopolymer. The knowledge arisen from the thesis has facilitated a solid basis for a wide range of engineering applications of this new category of geopolymer cement.