Synergistic gel formation in  geopolymers of superior mechanical strength synthesized with volcanic ash and slag

Abstract The present work studies gel evolution and microstructure of geopolymers synthesized with volcanic ash (VA) and blast furnace slag (BFS). The synthesis parameters such as BFS proportions on geopolymers formation were investigated. Gel evolution and microstructure of the geopolymers were studied by FTIR, X-ray diffraction (XRD), 29Si NMR spectroscopy, and scanning electron microscopy measurements. Silicate gels (N−S−H) were mainly formed in VA based geopolymers of low compressive strength (14.07 MPa). While with VA and BFS each account for 50%, VA-BFS based geopolymers possessed a compressive strength of 55.6 MPa, as well as the homogeneous C−(A)−S−H and N−A−S−H gels were formed. The C−(A)−S−H and N−A−S−H gels show synergistic effects on mechanical property of the geopolymers. This work provides a clue for the synthesis of geopolymers with superior mechanical properties in areas of architecture.