Gel Composition and Strength Properties of Alkali‐Activated Oyster Shell‐Volcanic Ash: Effect of Synthesis Conditions

Abstract

The gel composition and mechanical properties of alkali‐activated oyster shell‐volcanic ash were investigated at different NaOH concentrations (8, 12, and 15M) and curing temperatures (60°C and 80°C) in wet and dry conditions. XRD, FTIR, SEM‐EDS, and TGA‐DSC were used for microstructural characterization of the binder. The gel composition of the system was found to be influenced by NaOH concentration and was not affected when curing temperature was varied from 60°C to 80°C. The main phase was N,C–A–S–H for all alkali‐activated oyster shell‐volcanic ash, with C–S–H as secondary phase for some samples and contains high percentage of iron. The splitting at υ3 = 1400–1494 cm−1 on FTIR spectra corresponded to the elimination of the degeneracy due to the distortion of CO32− group. The high degree of splitting indicated that this carbonate group is linked to Ca2+. The compressive strength was influenced by curing temperature and the formation of a secondary phase. The compressive strength in dry condition increased roughly between 28 and 180 d for some samples, while in wet condition, the partial dissolution of Si–O–Si bonds of some silicate phases resulted in a reduction of strength.

The Compressive Strength and Microstructure of Alkali-Activated Binary Cements Developed by Combining Ceramic Sanitaryware with Fly Ash or Blast Furnace Slag

“…Given the low CaO content in the original CSW and FA (lower than 4 wt %; see Table 4), a N-A-S-H or a N-(C)-A-S-H gel was expected to form, with calcium provided mainly by the 4 wt % Ca(OH) 2 addition. The XRD results agree with those obtained by DTG as the main dehydration band slightly displaced toward higher temperatures with increasing BFS contents, and hardly moved in the CSW/FA blended systems cured at 20 • C, but exhibited a minor displacement when these CSW/FA blended pastes were cured at 65 • C. As observed by Ismail et al [29] and Djobo et al [41], these higher dehydration temperatures denote a modification in the gel structure, with free water more tightly bound or with smaller pores. Thus, in the CSW/BFS blended cements, the slightly higher dehydration temperatures would be attributed to the incorporation of calcium into the binding gel, while they would be explained by the formation of a more cross-linked structure with smaller pores in the CSW/FA pastes cured at 65 • C.…”

“…They cross-link to form oligomers, which arrange to form an aluminosilicate gel. Si and Al are tetrahedrally bonded with oxygen so that the basic monomer units (AlO 4 − ) are negatively charged [41]. Although these charges are balanced by the alkali cations in the system (Na + ), they may also be balanced by Ca 2+ in the presence of reactive calcium.…”

Fly ash and zinc slag blended geopolymer: Immobilization of hazardous materials and development of paving blocks

“…Geopolymer technology provides a sustainable solution towards waste utilization, pollution mitigation and resource conservation by using waste materials as precursor (Fernández-Jiménez and Palomo, 2003;Onisei et al, 2012;Lee et al, 2016;Kumar et al, 2017;Koplík et al, 2018;Nie et al, 2019;Xia et al, 2019). As a result, a huge number of industrial byproducts and wastes have been examined for solidification/stabilization through geopolymer technology (Xu et al, 2014;Nazari and Sanjayan, 2015;Djobo et al, 2016;Lirer et al, 2017;Kiventera et al, 2018;Koplík et al, 2018;Nath, 2018;Hassan et al, 2019;Luhar et al, 2019;Nie et al, 2019).…”

Characterization and Leachability Behaviour of Geopolymer Cement Synthesised from Municipal Solid Waste Incinerator Fly Ash and Volcanic Ash Blends

“…The series of bands in the 450-650 cm −1 range is assigned to Si deformation vibrations [40,41]. The peaks at around 1420 cm −1 and the one at 872 cm −1 were attrib The last mineral belongs to the zeolite type and was also observed earlier during alkali activation of volcanic ash with a calcium source by hydrothermal treatment (60 • C and 80 • C) [32]. In this study, zeolitic phases were obtained at room temperature due to the rapid dissolution of glassy MSWI-FA which promoted the formation of crystalline and amorphous alumina-silicates phase [33].…”

“…The EDS analysis of the different phases formed after reaction highlight that their respective compositions are constantly modified according to the composition and the alkaline medium of the synthesis. In the present study, the (M(II),M(I))-(A)-S-H, and (M(I),M(II))-A-S-H formed resulted from the C-S-H and N-A-S-H, respectively; where M(II) = Ca, Mg and (M(I) = Na, K.The heterogeneity of the gel is due to the high reactivity of its ingredients gel[32].…”