Studying different silica sources for preparation of alternative waterglass used in preparation of binary geopolymer binders from metakaolin/boiler slag

Abstract

The production of geopolymeric binders based on metakaolin (MK), coal boiler slag (BS) and alternative silica sources (rice husk ash (RHA) and silica fume (SF)) to produce potassium waterglass was successfully carried out. The binders were characterized microstructurally and mechanically at different ages. Monitoring of the reactions of the cements was carried out by techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA/DTG). The results show that byproducts such as BS and RHA can be used with MK as starting materials for the preparation of geopolymer binders. The using of by-product rich on silica produces materials with microstructures similar to those traditionally obtained with commercial potassium silicate (PS). Regarding SF-based binders, the strength declines over time, with late-age instability. The most stable or homogeneous binders over time are those based on RHA. The MK/BS30 binder exhibits good mechanical performance 42.1, 51.04 and 48.3 MPa at 7, 180 and 360 days respectively. The MK/BS30 binder shows a high degree of geopolymerization, a more homogeneous and enhanced connectivity between the grains and geopolymer gel and likewise, a lower content of MK unreacted. In general, the results indicate that geopolymers manufactured with RHA could replace materials produced with commercial silicates.