The First 20 Hours of Geopolymerization: An in Situ WAXS Study of Flyash-Based Geopolymers

Abstract

This study followed the first 20 h of flyash geopolymerization at 70˝C using time resolved Wide Angle X-ray Scattering (WAXS). The extent of dissolution of the amorphous phase of the flyash was determined to range from 29% to 54% for the different formulations trialed. The dissolution rate of the flyash significantly reduced after the first 5 h for all samples. During the formation stage of the geopolymer there were significant temporal variations in the chemistry of the dissolved solution due to the rate of flyash dissolution, with a relative standard deviation of 20%, 57% and 24% for the Si/Al, Na/Al and H/Si ratios, respectively. Utilizing the Power Law, scattering in the low angle region of the WAXS pattern combined with the geopolymer peak area yielded a measure which correlated with the compressive strength-providing a new method to measure the flyash dissolution and geopolymer formation processes independently. The evolution of several zeolite-like phases was followed, noting there are different formation mechanisms involved even within the same sample. Four samples were examined with compressive strengths ranging from 14(2)-50(9) MPa, each was synthesized with flyash from Collie Power Station (Western Australia) activated with sodium silicate solution of varying concentrations.

Recent progress in low-carbon binders

“…Hence, in comparison with SEM, this method is well-suited for resolving nanometer-scale surface morphologies and porosity present in rough and irregular fractured samples, including alkali-activated binders. Scattering and diffraction-based techniques have been used to provide insight into AAMs during the initial [109][110][111], medium-term [112], and later-age [113] evolution of gel, crystallite, and pore structure in AAMs. The combination of neutron and X-ray scattering, applied in parallel to provide different aspects of the required information, has also given important new insight into the highlyconnected nature of the pore structure in metakaolin-based AAMs [114].…”

Alkali-activation of CaO-FeOx-SiO2 slag: Formation mechanism from in-situ X-ray total scattering

“…The maximum intensity cannot be directly related to the nanoscale morphology of the material, therefore, but instead will be a combination of scattering from the material and contributions from the experimental setup. By examining SAS data from the literature for AAMs [43][44][45], however, the intensity at 0.3-0.4 Å -1 can be used to qualitatively analyze the formation of pores or a layered structure in the paste as it evolves. Although previous studies on metakaolin-based IPs have shown that this SAS region is attributed to pores in the paste [43], a layered structure cannot be discounted at this stage of the investigation as calcium-silicate-hydrate-type gels typical of Portland cements and Ca-rich AAMs/IPs can give rise to a basal peak in reciprocal space positioned between ~ 0.35 ≤ Q ≤ 0.8 [46].…”

Micromechanical Response of Crystalline Phases in Alternate Cementitious Materials using 3-Dimensional X-ray Techniques

“…At Load 0, in the case of the cubic iron oxide phase, there is a large distribution in the strain values (−2 × 10 −3 to 4 × 10 −3 ), much greater than the per component uncertainty of ~10 −4 which has been previously determined for this technique 58 . This large variation in strain across the cubic iron oxide crystals can be attributed to variation in lattice parameter (calculated to be in the range of 8.344–8.404 Å) due to substitution of Fe atoms by Ca, Al, Mg, Mn or Ti during coal combustion 47,59 and possible local variations of shrinkage stresses. Comparing elastic strains in the loading direction at various load steps, it can be seen that on average the compressive elastic strains in both phases increased as the macroscopic load applied to the specimen was increased (refer to lines plotted across Fig.…”