Abstract
The early mechanical performances of low-calcium fly ash (FFA)-based geopolymer (FFA–GEO) mortar can be enhanced by soda residue (SR). However, the resistance of SR–FFA–GEO mortar to acid or sulfate environments is unclear, owing to the various inorganic calcium salts in SR. The aim of this study was to investigate the long-term mechanical strengths of up to 360 d and evaluate the resistance of SR–FFA–GEO mortar to 5% HCl and 5% Na2SO4 environments through the losses in compressive strength and mass. Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS) and Fourier Transform Infrared Spectrometer (FTIR) experiments were conducted for the SR–FFA–GEO mortars, both before and after chemical attack, to clarify the attack mechanism. The results show that the resistances of the SR–FFA–GEO mortar with 20% SR (namely M10) to 5% HCl and 5% Na2SO4 environments are superior to those of cement mortar. The environmental HCl reacts with the calcites in SR to produce CaCl2, CO2 and H2O to form more pores under HCl attack, and the environmental Na+ cations from Na2SO4 go into Si-O-Al network structure, to further enhance the strength of mortar under Na2SO4 attack. These results provide the experimental basis for the durability optimization of SR–FFA–GEO mortars.
Highlights
Accepted: 4 February 2021In recent years, geopolymer material has obtained rapid development and wide interest in the industry of building material [1,2]
hydrochloric acid (HCl) reacts with the calcites in soda residue (SR) to produce CaCl2, CO2 and H2 O to form more pores under HCl attack, and the environmental Na+ cations from Na2 SO4 go into Si-O-Al network structure, to further enhance the strength of mortar under Na2 SO4 attack. These results provide the experimental basis for the durability optimization of strengthsdevelopment development (SR–)flyfly ash (FFA)–GEO mortars
The fresh and physical properties of SR–FFA–GEO at 90, 150 and 360 d were shown in Table 4 and Table 5, including fluidity, bulk density, porosity and the shrinkage behavior in height
Summary
Accepted: 4 February 2021In recent years, geopolymer material has obtained rapid development and wide interest in the industry of building material [1,2]. As a kind of alkali-activated aluminosilicates, geopolymer material possesses similar (or superior) mechanical properties to Ordinary Portland Cement (OPC)-based material, as well as durable performances, such as high compressive strength, high compatibility with organic components [6], high hardness, high thermal-stability, high fire-resistance, high chemical erosion-resistance, etc. Some industrial solid wastes composed of aluminosilicate phases, such as fly ash (FA), blast furnace slag, red mud, etc., can be employed for preparing geopolymer products by alkali-activation [8,11,12]. Low-calcium fly ash (FFA), as one of most commonly used raw materials and most available solid wastes for geopolymer preparation, mainly consists of amorphous spherical beads with aluminosilicate compositions [2,13,14,15]. The amorphous geopolymer can be manufactured with FFA and basic alkaline solution with Na+ or K+ cations, such as Published: 7 February 2021
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