Dolomite can be used as a source of aluminosilicate to produce geopolymers; however, this approach is limited by its low reactivity. This study analyzes the viability of producing geopolymers using dolomite/fly-ash with sodium silicate and NaOH solutions (at multiple concentrations) by determining the resultant geopolymers’ compressive strengths. The dolomite/fly-ash-based geopolymers at a NaOH concentration of ~22 M resulted in an optimum compressive strength of 46.38 MPa after being cured for 28 days, and the SEM and FTIR analyses confirmed the denser surface of the geopolymer matrix. The synchrotron micro-XRF analyses confirmed that the Ca concentration exceeded that of Si and Mg, leading to the formation of calcium silicate hydrate, which strengthens the resulting geopolymers.

Low calcium fly ash is used as the main material in the mixture and the crumb rubber was used in replacing fine aggregates in geopolymer mortar. Sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) which were high alkaline solution were incorporated as the alkaline solution. The fly ash reacted with the alkaline solution forming alumino-silicate gel that binds the aggregate to produce a geopolymer mortar. The loading of crumb rubber in the fly ash based geopolymer mortar was set at 0% (CRGM-0), 5% (CRGM-5), 10% (CRGM-10), 15% (CRGM-15), and 20% (CRGM-20), respectively. NaOH solution (12M) and Na2SiO3 solution ratio is set constant at 2.5 for all geopolymer mixture and the fly ash to alkali activator ratio was kept at 2.0. The CRGM at 28 days of curing time was exposed to elevated temperature at 200°C, 400°C, 600°C and 800°C. The weight loss of the CRGM increases with increasing temperature at all elevated temperatures. However, the density and compressive strength of CRGM decrease with an increase of crumb rubber loading for all elevated temperature exposure. The compressive strength of CRGM reduced due to the fact that rubber decomposes between 200°C and 600°C thereby creating voids. CRGM-15 and CRGM-20 showed cracks developed with rough surface at 800°C. Image obtained from scanning electron microscope (SEM) showed that, the CRGM changed significantly due to the decomposition of crumb rubber and evaporation of the free water at 400°C, 600°C and 800°C.