Physico-mechanical properties of metakaolin and diatomite-based geopolymers

Abstract

Geopolymers (inorganic polymers) are sustainable materials obtained from the dissolution of an aluminosilicate precursor by a high-alkaline liquid medium. Many studies point out that the properties of such materials depend on essential parameters, such as precursor, activating solution, SiO2 source, curing temperature, and others. This work evaluated the combination of two aluminosilicates (metakaolin and calcined diatomite) with Na-based alkaline liquid reagents (containing sodium silicate or colloidal silica) and how they affected the physico-mechanical properties of the prepared geopolymers after curing at 40 °C for 24 h. The following tests were carried out to characterize the compositions: in situ Young’s modulus evolution as a function of time; cold crushing strength; apparent porosity; and structural analyses via XRD and FTIR measurements. The synthesized geopolymers showed amorphous inorganic structure containing residual crystalline phases (quartz and illite), which are in tune with the Si-O-Si and Si-O-Al bonds identified in the ATR-FTIR spectra. The samples presented cold crushing strength and Young’s modulus up to 39.4 MPa and 13.4 GPa, respectively. The geopolymerization reactions were favored when using colloidal silica suspension, which led to the development of silicate-free geopolymers with enhanced performance at low temperature.