Resistance of Soda Residue–Fly Ash Based Geopolymer Mortar to Acid and Sulfate Environments

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.

Mechanical Properties and Damage Evolution of Concrete Materials Considering Sulfate Attack

“…Sulfate attack is an important factor affecting the service life and durability of concrete buildings and structures [ 1 , 2 , 3 , 4 ]. Soils containing a large amount of sulfate are common in saline areas of Northwest China, seawater in coastal areas, and groundwater.…”

Study on the Compressive Strength of Alkali Activated Fly Ash and Slag under the Different Silicate Structure

“…However, the complex composition of the waterglass solution makes the adjustment and control of geopolymer properties difficult. Therefore, two direction of research have emerged in this respect: (1) reaction mechanism: oligomers (Si [OH] 4 and Al[OH] 4 − ), which are the original raw materials of producing, are easily affect by the dissolution and concentration of active Si and Al components. [9] Based on previous investigations [10][11][12][13][14][15], waterglass can substantially accelerate the geopolymerization of oligomers; this is because of the nature of the silicate (Q n ) group in the solution, which plays an important role in the geopolymerization and production of an amorphous gel and determines the mechanical properties, durability and fire resistance.…”

“…(2) Silicate structure of waterglass solution: FTIR [16], Raman spectroscopy [17] and 29 Si NMR [18] experiments were used to obtain the information of structure of waterglass solution. Vidal [19] found the Q 0 , Q 1 , Q 2 , Q 3 and Q 4 species in the silicate solution. Furthermore, the Si/M molar ratio is a crucial parameter that affects the nature of silicate, and an important change point was approximately 1.0.…”

“…Furthermore, the Si/M molar ratio is a crucial parameter that affects the nature of silicate, and an important change point was approximately 1.0. Hunt [20], Aguiar [21] and Lucas [22] thought that the higher-order Q 4 , Q 3 and Q 2 transform to lower-order (Q 1 and Q 0 because of the breaking of the Si-O-Si bonds to produce Si-O-groups.…”

“…Alkali-activated materials, which are inorganic polymer, are defined as three-dimensional aluminosilicate amorphous structures resulting from the reaction of activated aluminum silicate materials and an alkaline activator, and these have become excellent substitutes to cement materials [ 1 , 2 , 3 ]. In addition to the excellent mechanical properties of harden pastes, alkalai-activated materials also have excellent durability [ 4 , 5 ], fire and acid resistance [ 6 , 7 ] and low energy consumption of during their production [ 8 ]. Due to the excellent properties of geopolymer, they have been extensively used on an industrial scale [ 8 ].…”