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Published in Bujang B. K. Huat, Arun Prasad, Sina Kazemian, Vivi Anggraini, Ground Improvement Techniques, 2019
Bujang B. K. Huat, Arun Prasad, Sina Kazemian, Vivi Anggraini
XRD analyses (Figure 10.25) identified the magnesium based phases of dypingite, hydro-magnesite, and nesquehonite as being responsible for strength development following carbonation with pressure of 200 kPa at 7, 24 and 168 hours of carbonation time. As can be seen by increasing the carbonation time, the amount of these crystals peak increases and the strength of the treated soil increases according to UCS results.
Effect of hydrated magnesium carbonate grown in situ on the property of MgO-activated reactive SiO2 mortars
Published in Journal of Sustainable Cement-Based Materials, 2022
Tingting Zhang, Ziyu Zhou, Min Li, Ziming He, Yuan Jia, Christopher R. Cheeseman, Caijun Shi
Nesquehonite is a low-temperature carbonate normally found in alkaline soils, deposits in caves and as a weathering product of ultramafic rocks. It is unstable at temperatures >50 °C and is therefore unsuitable for use in applications involving high temperatures. In such cases, nesquehonite transforms into the thermodynamically more stable hydrated magnesium carbonates, dypingite and hydromagnesite [29].
Influence of soil type on strength and microstructure of carbonated reactive magnesia-treated soil
Published in European Journal of Environmental and Civil Engineering, 2020
Song-Yu Liu, Guang-Hua Cai, Jing-Jing Cao, Fei Wang
Figure 9 presents the X-ray diffractograms of carbonated reactive MgO-treated soils for varying wL after 12-hr carbonation. To scrutinise the evolution of the products, the intensity of X-ray diffraction is set on the semi-logarithmic scale. Evidently, there are some strong quartz peaks such as at two theta of 26.59° (3.35 Å), 20.83° (4.26 Å), 50.05° (1.82 Å) in all samples with different wL. Moreover, two weak MgO peaks at two theta of 42.87° (2.11 Å) and 62.23° (1.49 Å) are detected in samples S1 and S2, indicating that reactive MgO in low wL silty samples is not fully hydrated. The peaks of brucite are also detected at two theta of 38.04° (3.63 Å) and 18.60° (2.76 Å) in all of the tested samples, and the peak values of carbonated samples S4, S5, S6 and S7 are significantly higher than those of carbonated samples S1, S2 and S3, suggesting that high wL samples (S4, S5, S6 and S7) have lower carbonation degree than low wL samples (S1, S2 and S3). Compared with the XRD peaks of raw materials and carbonated soils, the new detected peaks of nesquehonite and dypingite or hydromagnesite should be ascribed to MgO addition and further carbonation, and these hydrated magnesium carbonates are consistent with those detected in carbonated cements or soils of previous studies (Cai et al., 2015b; Liska & Al-Tabbaa, 2008, 2012; Liska et al., 2008; Unluer & Al-Tabbaa, 2013, 2014a, 2014b; Vandeperre & Al-Tabbaa, 2007; Yi et al., 2013a, 2013b). Figure 9 shows that the XRD peaks of carbonation products of S1, S2 and S3 are significantly higher than those of S4, S5, S6 and S7, showing that the lower the wL, the more the carbonation products. Furthermore, it is noticed from Figure 9 that some overlaps exist in some peaks such as those at two theta of 15.1° (e.g. dypingite and hydromagnesite) and those at two theta of 42.9° (e.g. magnesia and magnesite). These overlap peaks suggest that it is difficult to distinguish every specific carbonation product through the XRD analysis.