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2 results on '"Go Igarashi"'

1. New insight on the thermal impact on cementitious materials due to high-temperature with water supply: Continuous expansive spalling in water

Author

Taito Miura, Shintaro Miyamoto, Ippei Maruyama, Abudushalamu Aili, Takumi Sato, Yuji Nagae, and Go Igarashi

Subjects
Cementitious materials, High temperature, Water immersion, Water vapor pressure, Lime expansion, Continuous expansive spalling, Materials of engineering and construction. Mechanics of materials, TA401-492
Abstract

In this study, the expansion behavior of cement materials after high-temperature heating and water immersion was observed experimentally. Two experiments were conducted using mortar specimens with different sand-to-cement ratios subjected to different high-temperature histories up to 1000 °C. In Case 1, the specimens were immersed in water after high-temperature heating and then cooled naturally; in Case 2, the specimens were immersed in water at high temperatures without the cooling process. Based on the results, it was confirmed that lime expansion due to the rehydration of CaO by heating occurred in Case 1. In contrast, dynamic continuous explosive spalling occurred in Case 2 because of water penetration into the specimen at a high temperature. The explosive spalling in water observed in Case 2 is a phenomenon that has not been reported to date. Possible failure mechanisms for lime expansion and continuous expansive spalling in water are suggested.

Published
2024
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2. Microstructural changes in white Portland cement paste under the first drying process evaluated by WAXS, SAXS, and USAXS

Author

Go Igarashi, Kunio Matsui, Ippei Maruyama, and Naoki Sakamoto

Subjects
Materials science, 0211 other engineering and technologies, 02 engineering and technology, law.invention, chemistry.chemical_compound, Drying (A), law, Desorption, 021105 building & construction, Monolayer, General Materials Science, Calcium silicate hydrate, Composite material, Adsorption (C), Small-angle X-ray scattering, Scattering, Building and Construction, 021001 nanoscience & nanotechnology, Microstructure, Portland cement, chemistry, Microstructure (B), Calcium–silicate–hydrate (C–S–H) (B), 0210 nano-technology, Small-angle X-ray scattering (B), White Portland cement
Abstract

Meso- and micro-scale structural changes in matured hardened cement paste dried slowly for 1.5 years at different relative humidities (RHs) are evaluated by small-angle X-ray scattering profiles covering a q range of 0.017 nm − 1 –30 nm − 1 with a fractal disc-shaped particle analysis and Guinier approximation. The fractal disc-shaped particle analysis revealed that calcium–silicate–hydrate (C–S–H) agglomerations are very thin (~ 2.5 nm) and of relatively large width (~ 35 nm) under high RH conditions. However, the agglomerations are segmented (in width) into ~ 10 nm below an RH of 40%. The Guinier approximation found the possibility that the scattering profiles in the range of 2 nm − 1 –8 nm − 1 correspond to a spacing between C–S–H monolayers and it showed stepwise changes at 40%–50% RH. The stepwise behavior of the distance between C–S–H monolayers may explain a kink in water vapor desorption at around 40% RH.

Published
2017

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