Investigating the mechanical property and reaction mechanism of geopolymers cement with red Pisha Sandstone

Abstract Alkali-activated geopolymers cement based on natural red Pisha Sandstone (RPS), which causes severe soil erosion, was examined. The compressive strength and softening coefficient of the alkali-activated red Pisha Sandstone cement (AAPC) were investigated at different blast furnace slag replacement levels, NaOH dosages, and curing durations. This paper also investigated the strength and reaction mechanism of the AAPC samples with 40 wt% blast furnace slag at different NaOH dosages by replacing RPS with ISO Standard Sand (referred to as G group samples). Scanning electron microscopy/energy dispersive X-ray, Fourier transform infrared spectroscopy, and X-ray diffraction were used to analyze the hydration products and reaction mechanism of the samples at the curing ages of 28 days after the strength test. The results showed that the compressive strength and softening coefficient of the cement improved significantly when blast furnace slag was used as the mineral additive. When 1.5 wt% NaOH was used as the activator, the compressive strength and softening coefficient of the AAPC sample curing for 90 days increased from 6.9 to 56.2 MPa and 0.4 to 0.95, respectively, with an increase in the slag dosages from 0 to 40 wt%. The reaction mechanism of AAPC was essentially different from that of the alkali-activated blast furnace slag cement. The blast furnace slag significantly promoted the polymerization reaction of Si–Al gels. The Si–Al and C-S-H gels strengthened the AAPC system. However, the C-S-H gels and reinhardbraunsite, which are formed by the hydration of blast furnace slag, strengthened the alkali-activated blast furnace slag cement. In the AAPC samples with blast furnace slag as the mineral additive, the hydration reaction of the slag and the polymerization reaction of the Si–Al gels promoted each other.