Room-temperature alkaline activation of feldspathic solid solutions: Development of high strength geopolymers

Amorphous fraction, grains defects and the incongruent dissolution of solid solutions (pegmatite, trachyte, and granite) were used to design high strength geopolymer composites with crystalline content in the range of ∼70–85%. The geochemical history of the natural solid solutions affects the dissolution and polycondensation/geopolymerization. These solid solutions were altered with 15, 20, 25 and 30% of metakaolin and activated with alkaline solution. Experimental results (phase evolution, three-point flexural strength, microstructure, mercury intrusion porosimetry and water absorption) indicated that polycondensation/polymerization is enhanced in trachyte, granite and pegmatite based specimens, compared to sand, due to the increase in N-A-S-H secondary phases. The amorphous/crystalline ratio of the solid precursors were used to understand the role of dissolved and undissolved fraction into the strength development of geopolymer composites. It was concluded that high strength geopolymer composites of chemico-mechanical equilibrium can be achieved with solid solutions having reduced fraction of pores volume and pore-size.