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論文

Impact of interatomic structural characteristics of aluminosilicate hydrate on the mechanical properties of metakaolin-based geopolymer

Kim, G.*; Cho, S.-M.*; Im, S.*; Suh, H.*; 諸岡 聡; 菖蒲 敬久; 兼松 学*; 町田 晃彦*; Bae, S.*

Construction and Building Materials, 411, p.134529_1 - 134529_18, 2024/01

 被引用回数:6 パーセンタイル:64.44(Construction & Building Technology)

This study explores the influence of the interatomic structure of sodium aluminosilicate hydrate (N-A-S-H) with varying silica contents on the mechanical properties of metakaolin-based geopolymer. Geopolymer pastes comprising Si/Al ratios between 2.0 and 3.0 were synthesized. A larger number of Si-O-Si linkages compared to Si-O-Al linkages and a higher atomic number density were found in the geopolymers with higher silica contents, which enhanced the compressive strength of the geopolymer pastes up to the optimal Si/Al ratio of 2.5. The paste with a Si/Al = 2.5 exhibited a greater portion of Q$$^{4}$$(1Al and 2Al) and denser morphology compared to the other geopolymer pastes. Furthermore, in-situ high-energy synchrotron X-ray scattering experiments were conducted to assess the elastic modulus of the aluminosilicate structure at a local atomic scale. The modulus value in real space decreases with increasing silica contents up to Si/Al = 2.5 and increases with the presence of excessive unreacted silica fume. The modulus value in reciprocal space for the axial and lateral directions both presented a positive value at the geopolymer comprising a Si/Al ratio higher than 2.5, indicating that the load-bearing property of N-A-S-H changed at higher Si/Al ratios. Moreover, the smallest difference between the strains along the axial and lateral directions was detected for the geopolymer with Si/Al = 2.5 in both the real and reciprocal space, owing to the most interconnected and flexible nanostructure, which led to the highest mechanical strength.

論文

Characteristic microstructural phase evolution and the compressive strength development mechanisms of tricalcium silicate pastes under various initial carbonation curing environments

Cho, S.*; Suh, H.*; Im, S.*; Kim, G.*; 兼松 学*; 諸岡 聡; 町田 晃彦*; 菖蒲 敬久; Bae, S.*

Construction and Building Materials, 409, p.133866_1 - 133866_20, 2023/12

 被引用回数:9 パーセンタイル:76.50(Construction & Building Technology)

The effects of various initial carbonation curing environments on the phase evolution and resulting mechanical characteristics of tricalcium silicate paste were studied. For the analyses of the reaction products and microstructure, synchrotron X-ray diffraction, thermogravimetry, Fourier transform-infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy and high-resolution X-ray computed tomography were utilized. C$$_{3}$$S cured under carbonation environment pressurized by 0.1 MPa showed excellent mechanical properties owing to the highest degree of reaction and homogeneous generation of CaCO$$_{3}$$ with low-Ca/Si calcium silicate hydrates, resulting in a dense matrix with refined pore structure. C$$_{3}$$S paste treated under other carbonation conditions underwent deteriorative microstructural phase transitions, including void evolution by decalcification of C-S-H and an inhomogeneous composition of crystalline phases, resulting in inferior properties.

論文

Insight on the mechanical properties of hierarchical porous calcium-silicate-hydrate pastes according to the Ca/Si molar ratio using ${it in situ}$ synchrotron X-ray scattering and nanoindentation test

Im, S.*; Jee, H.*; Suh, H.*; 兼松 学*; 諸岡 聡; Choe, H.*; 西尾 悠平*; 町田 晃彦*; Kim, J.*; Lim, S.*; et al.

Construction and Building Materials, 365, p.130034_1 - 130034_18, 2023/02

 被引用回数:14 パーセンタイル:76.08(Construction & Building Technology)

Nanocrystalline calcium-silicate-hydrate (C-S-H) is a typical heterogeneous material with a multiscale structure spanning a wide length scale from angstrom to micrometer, and whose structure is determined by the Ca/Si ratio. In this study, we directly applied compressive loads on synthetic C-S-H pastes with Ca/Si ratios of 0.6-1.2 and investigated their mechanical properties using the elastic modulus calculated at three length scale levels (i.e., angstrom to nanometer, micrometer, and millimeter) via in-situ synchrotron X-ray scattering, nanoindentation tests, and strain gauges, respectively. Further, $$^{29}$$Si nuclear magnetic resonance spectroscopy was conducted on the C-S-H pastes to elucidate the alterations in the silicate polymerization. The experimental results confirmed the deformation behavior of the C-S-H paste with different Ca/Si ratios under external loading, which was demonstrated to be transferred from the surface of the pastes to particles owing to the presence of multiscale pores.

論文

Analysis of atomistic structural deformation characteristics of calcium silicate hydrate in 53-year-old tricalcium silicate paste using atomic pair distribution function

Bae, S.*; Jee, H.*; Suh, H.*; 兼松 学*; 城 鮎美*; 町田 晃彦*; 綿貫 徹*; 菖蒲 敬久; 諸岡 聡; Geng, G.*; et al.

Construction and Building Materials, 237, p.117714_1 - 117714_10, 2020/03

 被引用回数:21 パーセンタイル:66.56(Construction & Building Technology)

Although the atomistic structure and the deformation characteristics of calcium silicate hydrates (C-S-H) are of primary interest in cement chemistry, they have not been fully investigated. In this study, pair distribution function (PDF) analysis was conducted on a 53-year-old fully hydrated tricalcium silicate (C$$_{3}$$S) paste using in situ synchrotron high-energy X-ray scattering to probe the atomic structural deformation of C-S-H under external loading. The results were compared with those from our previous PDF study of a 131-day-old C$$_{3}$$S paste in order to elucidate the effect of aging on the mechanical characteristics of C-S-H. Three different strains measured by the strain gauge, by the lattice shifts (d-spacing) in the reciprocal space, and by the shift of the interatomic distance (r) in the real space were compared. In the range of r $$<$$ 20 ${AA}$, where most of the information was derived from C-S-H, the 53-year-old C$$_{3}$$S paste had a higher overall elastic modulus (18.3 GPa) and better resistance to compressive stress than the 131-day-old C$$_{3}$$S paste (elastic modulus: 8.3 GPa). Moreover, it was found that the macroscopic strains of the 53-year-old C$$_{3}$$S paste were presumably induced by mechanical deformation such as microcracks at the macroscale. The results provide experimental evidence for the atomistic and mesoscale mechanical behavior of C-S-H in the early and late ages.

論文

Reduction of contaminated concrete waste by recycling aggregate with the aid of pulsed power discharge

Arifi, E.*; 石松 宏一*; 飯笹 真也*; 浪平 隆男*; 坂本 浩幸*; 舘 幸男; 加藤 博康*; 重石 光弘*

Construction and Building Materials, 67(Part B), p.192 - 196, 2014/09

 被引用回数:5 パーセンタイル:24.79(Construction & Building Technology)

福島第一原子力発電所の事故によって多量の放射性汚染コンクリートが発生している。放射性廃棄物としての汚染コンクリートの減容化に対するパルスパワー放電の適用可能性が調査された。汚染コンクリートは、パルスパワー放電過程で、非汚染粗骨材を汚染マトリクスから分離することにより除染される。本研究では、放射性汚染コンクリートを模擬するために、Csの安定同位体を用いた。試験の結果、汚染コンクリートから回収された骨材の体積は最大で60%であり、一方で、回収骨材中のCsはおおよそ3%であった。大部分のCsは、放電過程で水中に移行した。これらの結果より、パルスパワー法によって、骨材の再利用による汚染コンクリートの減容できる可能性が示された。本手法の実際の廃棄物への適用性を評価していくため、より実際の廃棄物に近い条件で試験を実施する必要がある。

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