Abstract: This study first prepares high purity Al2O3-SiO2 powders or geopolymer precursor using the sol-gel method, and then synthesizes alkali-activated geopolymers using water-solid ratios of 0.50, 0.75, 1.00, 1.25 and 1.50, eliminating the effect of complex composition of the raw mineral materials on product properties in conventional geopolymer research. Compressive strength of the geopolymer samples activated by NaOH is experimentally measured, with microstructure observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM), and chemical bond characterization tested via Fourier transform infrared (FTIR). The results show the geopolymer synthesized with a water-solid ratio of 1.00 performs best in compressive strength after 3 day curing. A too low ratio may lead to incomplete geopolymerization reaction, uneven mixing, insufficiently dense microstructure, excessive porosity of the samples, and poor mechanical properties; while under a too high ratio, moisture would hinder the alkali activator’s reaction with Al2O3-SiO2 powders, thereby causing serious bleeding of the samples and affecting the progress of geopolymerization. When NaOH is used to activate the geopolymer precursor synthesized using the sol-gel method, water-solid ratio has significant effects on its mechanical properties and microstructure. Determining an appropriate water solid ratio helps improve the performance of special geopolymers.

Key words: hydraulic structure material, compressive strength, test and analysis, geopolymer, water-solid ratio, mechanical properties, sol-gel method