Characteristics of boroaluminosilicate geopolymers

In this work, a new method for incorporating fly ash in constructional technology was developed by production of boroaluminosilicate geopolymers. These new class of geopolymers were appropriately synthesized from mixtures of fly ash and anhydrous borax and compressive strengths as high as 64 MPa are achievable by using suitable amount of borax. Different types of microstructures were observed by changing mixture proportion of the specimens. All of specimens revealed a brittle fracture with no crack branching in the mixture. Additionally, less unreacted fly ash particle was observed in the considered pastes indicating a totally different fracture mechanism in boroaluminosilicate geopolymers with respect to aluminosilicate ones. FT-IR analyses of the mixtures revealed an additional B-O bond with respect to aluminosilicate geopolymers. It was shown that this bond is a key factor to determine compressive strength and specimens with no B-O bond have the lowest strength.