Optimization and characterization of sustainable geopolymer mortars based on palygorskite clay, water glass, and sodium hydroxide

Abstract

The synthesis of ambient-cured sustainable geopolymer mortars (GMs) was studied throughout this work. To reduce carbon dioxide emissions, new materials must be used in the production of sustainable concrete and mortars. Many types of binders are used in the synthesis of GM and concrete (GPC), especially clay minerals. These clay minerals are considered sources of alumina and silica in GM and concrete. The geopolymerization process relies on the alkaline solution activating the alumino-silicate to produce geopolymer gel products. The palygorskite (PA) clay mineral, sodium hydroxide (NaOH), and sodium silicates (Na2SiO3) were chosen as a binder (solid material) and alkaline activator solution to synthesize GM at ambient temperature. PA was thermally treated at 550, 650, 700, and 750°C, respectively, to convert into high-reactive PA (HRP) HRP550, HRP650, HRP700, and HRP750, respectively. The characteristics of PA clay, HRP powders, and HRP-based GM were evaluated using compressive strength (CS) testing, X-ray fluorescence analysis, carbon footprint analysis, X-ray diffraction (XRD) diffractograms, Fourier transform infrared spectroscopy (FTIR) spectroscopy, scanning electron microscopy (SEM) images, and energy-dispersive X-ray spectroscopy (EDS) analysis. The maximum CS of 25.1 MPa was acquired for geopolymer synthesis utilizing HRP700-based GM cured at 30°C for 28 days. FTIR spectroscopy demonstrated that HRP-based GM showed the presence of Si–O, Al–O, and O–C–O bonds stretching vibrations in the alumino-silicate network. The results showed that the CO2 emissions had a reduction in the HRP-based GM compared with the reference mix of ordinary Portland cement mortar (OPM). The percentage of reductions was 14.1, 13.7, 13.1, and 12.4 for HRP550, HRP650, HRP700, and HRP750, respectively, compared with the OPM mixture. SEM images/EDS analysis and XRD diffractograms confirmed the presence of sodium alumino-silicate hydrates, magnesium silicate hydrate, and calcium silicate hydrate gels with high quantities particularly in the HRP700-based GM than that in HRP550, HRP650, and HRP750, respectively. The results indicate the suitability of HRP calcined at 700°C (HRP700) in the synthesis of the GM.

Keywords

• sustainable material
• alkaline solution
• calcination temperatures
• carbon footprint
• high-reactive palygorskite