Microstructure Stability and Thermal Resistance of Ash-Based Geopolymer with Sodium Silicate Solution at High Temperature

Abstract

Current cement-based building materials have a huge disadvantage that they are easily broken due to thermal decomposition at high temperature (over 500°C) of structures of hydrated cement. This is easily observed at construction works when burned, the cement-based mortar and concrete materials and plaster are susceptible to collapse causing damage to buildings or structures. More seriously, these accidents easily cause injuries or loss of life for residents and people working there. Therefore, research on fire resistance and structural stability at high temperatures of building materials is always an interested topic of many scientists. This study utilized resources of highly active alumino silicate materials such as coal bottom ash and rice husk ash to produce geopolymer using sodium silicate solution as an alkaline activator. The ash-based geopolymer has good engineering properties responding to requirements of ASTM C55 and C90 for lightweight concrete brick. It is interesting to note that the geopolymer product was tested for thermal properties at 1000°C such as heat resistance, volumetric shrinkage, mass loss. The experimental results show that the ash-based geopolymer material has high thermal stability with increasing significantly of compressive strength after heated at 1000°C. Moreover, the geopolymer was also carried out to characterize microstructure before and after exposed at high temperature using methods of X-ray diffraction (XRD), scanning electron microscope (SEM). Thermal analysis methods such as thermogravimetric (TG), differential thermal analysis (DTA), and dilatometry-thermal expansion (CTE) were used to evaluate microstructural stability of the geopolymer-based materials.

Influence of Curing Regimes on Engineering and Microstructural Properties of Geopolymer-Based Materials from Water Treatment Residue and Fly Ash

“…The FTIR spectra in Figure 6 detected asymmetrical elastic oscillation regions of Si-O-T bonding (in which T represents Si or Al) (Panias et al, 2006). This oscillation region is within the wavenumbers from 1100 to 900 cm −1 (Schoonheydt et al, 2018;Nguyen et al, 2020b;Nguyen, 2021). The geopolymer formation displaced the absorption peak position of the Si-O-T bonding toward the lower frequency.…”

“…Figure 5 XRD patterns of WTR, FA, and the samples cured in different conditions This is evident in geopolymer formation (Davidovits, 2020;Nguyen et al, 2020a;Nguyen et al,2020b;Nguyen, 2021). In addition, crystals such as quartz (SiO2), kaolinite (Al2O3.2SiO2.2H2O), hematite (Fe2O3), and mullite (3Al2O3.2SiO2) still exist, as is known in the initial raw materials.…”

“…It is related to the dissolution of the activated SiO2 and Al2O3 from the raw materials into alkaline solution, forming the amorphous structure of the aluminosilicate gel in the geopolymeric network (Lee et al, 2000;Nguyen, 2020a). This is evident for restructuring after the aluminosilicates were dissolved in alkaline solution to form Si-O-Al bonds in the inorganic polymer chains (Davidovits, 2020;Nguyen, 2021).…”

“…The products based on WTR have very low strength (Waijarean et al, 2013;Geraldo et al, 2017) due to the weak alkaline activity of WTR. Therefore, WTR treatment should be combined with materials of high activity, such as FA (Suksiripattanapong et al, 2015Horpibulsuk et al, 2016Janani and Santhi, 2018;Susanto et al, 2020), metakaolin (Geraldo et al, 2017), rice husk ash (Waijarean et al, 2014;Poowancum et al, 2015), and others (Nguyen, 2020a;Nguyen, 2020b;Do et al, 2020a;Do et al, 2020b;Nguyen, 2021, Petrus et al, 2021.…”

“…The H2O molecules supply [OH] − to enter into the structures of Na2O, SiO2, and Al2O3; hence, this is called hydrothermal process. Finally, at atmospheric pressure, the water is removed from the structures to form polymer bonds in the geopolymer-based material by drying (Alas and Ali, 2019;Nguyen, 2021;Nguyen and Dang, 2021;Nguyen et al, 2021a;Nguyen et al, 2021b). Swanepoel and Strydom (2002) suggested that the optimal condition for strength development of geopolymer samples is at 60°C for 48 h. Palomo et al (2004) concluded that geopolymer samples based on fly ash (FA) were cured at 65°C for one week or 85°C for 24 h, which had enough energy to achieve levels of reactions and strength responding to the engineering requirements.…”