Microstructure-Based Modeling for Water Permeability of Hydrating Cement Paste

Qian

et al. 2021

J. Mater. Civ. Eng.

Accurate prediction of transport properties in cementitious materials remains a challenge since it is difficult to experimentally obtain the realistic three-dimensional (3D) pore network of cement paste.In this study, the 3D pore network of cement paste is quantitatively characterized using Nano X-ray microtomography coupled with the metal centrifugation porosimetry (MCP). First, the MCP technique is carried out to impel the liquid metal into the pore network of cement paste. Subsequently, the 3D pore network of cement paste with the intruded metal is reconstructed using high-resolution X-ray microtomography. Finally, based on the X-ray microtomography images, the transport properties of cement paste including ionic diffusivity and fluid permeability are simulated using a set of lattice Boltzmann transport models. The results show that the metal alloy can significantly enhance the contrast between the pore network and solid phase, and the realistic 3D pore network can be 2 successfully reproduced. For cement paste with water-to-cement (w/c) ratios of 0.5 and 0.6, the transport properties are dramatically increased with increasing w/c ratio. A similar increasing trend in transport properties can be found for effective porosity of cement paste ranging from 27.56% to 36.11%.

Section: Simulation Results Of Transport Propertiesmentioning

confidence: 99%

Section: Simulation Results Of Transport Propertiesmentioning

confidence: 99%

See 1 more Smart Citation

Three-Dimensional Modeling of Transport Properties in Hardened Cement Paste Using Metal Centrifugation-Based Pore Network

Qian

et al. 2021

J. Mater. Civ. Eng.

“…In the context of nuclear power plants, capturing the temperature dependency of this dynamic microstructure (related data has been reported by ) is critical for a more accurate estimation of the moisture transport, such as in a recent trial by Li and Xu (2019). To the authors' knowledge, no similar data for mid-range periods have been reported thus far.…”

Section: Introductionmentioning

confidence: 90%

Cement and Concrete for Nuclear Waste Management

Nakarai¹,

Kosakowski²

2022

ACT

The safe management and disposal of radioactive wastes are of critical importance for maintaining a sustainable society. In nuclear waste management, cement and concrete are commonly used to immobilize radioactive waste. Cementation is a common technique used for conditioning low-level and intermediate-level radioactive wastes, which should ensure safe interim storage of waste packages, and act as a first long-term barrier during waste disposal. In addition, cement-based materials are utilized for construction and barrier materials in surface disposals for very low-level to low-level waste and deep geological disposals for low-level, intermediate-level, and high-level wastes.Furthermore, recovery from the nuclear disaster at the Fukushima Daiichi Nuclear Power Station (F1NPS) is an important and urgent issue in Japan. To solve the difficult problems associated with radioactive contaminated materials in the plant and in the environment, contributions of cement and concrete technologies are highly expected.The understanding end prediction of the long-term evolution of cement materials interacting with wastes and other barrier materials during interim and final storage is indispensable and needs to be studied by experts from different scientific and engineering disciplines. The very long times associated with the safe disposal of radioactive waste, which are well beyond the lifetime of ordinal engineered structures and therefore not experimentally accessible, make this task even more demanding.In the first part of this special issue, three technical contributions summarize research and development projects for nuclear waste management with cement and concrete technologies in Japan. and Ichikawa and Hamamoto (19-1275) give general overviews on the use of cement-based materials for low-level radioactive waste (LLW) and for high-level radioactive waste (HLW), respectively. Furthermore, Abe and Iida (20-236) present a comparative discussion of approaches used for LLW in Japan and Belgium.In the second part, the contributions concentrate on processes and applications related to the performance assessment of cement and concrete for nuclear waste management. The scientific papers describe sorption experiments with Cl, I, HTO, and C by Nedyalkova et al. (19-811), diffusion experiments with NaCl of leached cement paste by Kurmisawa et al. (19-426), leaching experiments of cement paste with quick setting admixture by Yokozeki et al. (19-1173), immersion experiments of cement-bentonite samples by Nakarai et al. (19-433, 19-447), and chemo-mechanical modelling of degraded concrete by Oda et al. (19-1075).Finally, the third part contains contributions that investigate, in a broad sense, how cement and concrete technologies can be used to deal with the aftermath of the F1NPS nuclear disaster. At first, a technical paper by summarizes the outcome of a research initiative that aimed at identifying the cause and extent of radioactive contamination of concrete at the F1NPS.A set of scientific contributions is related to water abso...

“…In the context of nuclear power plants, capturing the temperature dependency of this dynamic microstructure (related data has been reported by Maruyama and Rymeš (2019)) is critical for a more accurate estimation of the moisture transport, such as in a recent trial by Li and Xu (2019). To the authors' knowledge, no similar data for mid-range periods have been reported thus far.…”

Section: Introductionmentioning

confidence: 90%

Temperature-Dependent Water Redistribution from Large Pores to Fine Pores after Water Uptake in Hardened Cement Paste

Kiran

Samouh

Igarashi

et al. 2020

ACT

During sorption, the microstructural evolutions of two different cement pastes (with water-to-cement ratios of 0.40 and 0.55) are studied via proton-nuclear-magnetic-resonance relaxometry. The water uptake test is performed for samples dried at 105°C under three different temperatures of 20°C, 40°C, and 60°C for the first twenty-six days of sorption. It is observed that the water went first to the larger pores before migrating to the finest ones. This behavior is accelerated with increasing temperature. The rate of water exchange between fine and large pores is estimated and found to increase with temperature for both studied mixtures. The activation energy corresponding to this water movement is calculated and found to be higher for the lowest water-to-cement ratio, owing its finer microstructure. Finally, the activation energy related to the local water transport in re-distribution from large pores to fine pores is calculated and found to be inferior to the experimental results, which can be explained by the dynamic microstructure not being considered in the classical theories. Recently, based on the proton nuclear magnetic resonance ( 1 H-NMR) relaxometry technique, the dynamic