Effect of water glass performance on fly ash-based geopolymers

The effects of water glass with different moduli and solid content (mass ratio of solid to water) on the compressive strength of fly ash-based geopolymers are described, and the effects of sodium water glass silicate and sodium potassium water glass on the compressive strength of fly ash-based geopolymers are compared. The results show that the compressive strength of fly ash-based geopolymers increases when the water glass modulus is increased, but when the modulus exceeds 1.4, the compressive strength decreases, and it decreases markedly when the modulus is greater than 2.0. The compressive strength improves with the increase of water glass solid content. For sodium water glass, when the solid content is 32%, the compressive strength of fly ash-based geopolymers reaches the maximum and then decreases with the solid content increase. For sodium potassium water glass, when the solid content is increased from 16% to 36%, the compressive strength improves continuously. Comparison of the activation effect shows that the activation effects on fly ash vary with the modulus and the solid content of water glass. The results indicate that using sodium water glass with 32% solid content and modulus 1 and sodium potassium water glass with 36% solid content and modulus 1.2 can prepare fly ash-based geopolymers with compressive strengths of 38.5 MPa and 42.1 MPa, respectively. The microstructures of fly ash and geopolymers are described based on X-ray diffraction and Fourier transform infrared analyses. At last, the activation mechanism of water glass on fly ash is discussed.