• Nuclear Engineering and Technology
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• v.56 no.9
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• pp.3942-3949
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• 2024

This study focuses on investigating the chemical degradation characteristics of cementitious barriers used in low-and intermediate-level radioactive waste repository by reactive transport modeling. The impact of the blending with supplementary cementitious materials (SCMs) in the barriers on the chemical degradation was evaluated to find the optimum barrier design. A number of different barrier designs were examined by replacing ordinary Portland cement (OPC) by SCMs (i.e., fly ash, silica fume, and blast-furnace slag). The simulation results showed that silica fume blended barrier has better durability against chemical degradation by rainwater compared to fly ash or blast-furnace slag blended barriers. In addition, the chemical durability of silica fume-based barrier increased with increasing replacement level up to about 20 %. It seems that the amount of formed calcium silicate hydrate (CSH) in the initial cement-based barrier highly affects the overall chemical durability. The newly developed reactive transport model demonstrated its capability for understanding the barrier performance and investigating the optimal design of the barrier system.

• Computers and Concrete
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• v.19 no.1
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• pp.19-31
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• 2017

This paper uses modelling and experiment to perform a quantitative analysis for the gypsum and ettringite formations in cement pastes subjected to sulfate attack. Firstly, based on Fick's law and chemical reaction kinetics, a diffusion model of sulfate ions in cement pastes is proposed, and then the model of the gypsum and ettringite formations is established to analyze its contents in cement pastes with corrosion time. Secondly, the corrosion experiment of the specimens with cement pastes immersed into 2.5%, 5.0% and 10.0% $Na_2SO_4$ solutions are carried out, and by using XRD-Rietveld method, the phases of powder samples from the specimens are quantitatively analyzed to obtain the contents of gypsum and ettringite in different surface depth, solution concentration and corrosion time. Finally, the contents of gypsum and ettringite calculated by the models are compared with the results from the XRD experiments, and then the effects of surface depth, corrosion time and solution concentration on the gypsum and ettringite formations in cement pastes are discussed.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.111-119
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• 2023

Recently, a variety of new cement-based materials have been developed, and attempts to predict the properties of these new materials are increasing. In this study, we aimed to predict the rheological properties of binary blended pastes. The cementitious materials used in the study included Portland cement (PC), fly ash (FA), blast furnace slag (BS), and silica fume (SF). The three binder components, fly ash, blast furnace slag, and silica fume, were blended with cement as the foundational composition. We predicted the yield stress and plastic viscosity of the pastes using the YODEL (Yield stress mODEL) and Krieger-Dougherty's equation. The predictive model's performance was validated by comparing it with experimental results obtained using a rheometer. When the rheological properties of the binary blended paste were predicted by reconstructing the properties and parameters used to predict the individual materials, it was evident that the predictions made using the proposed method closely matched the experimental results.

• Advances in concrete construction
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• v.9 no.6
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• pp.547-556
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• 2020

This study aimed to develop reference materials (RMs) that are chemically stable and can simulate the flow characteristics of cement paste. To this end, the candidate components of RMs were selected considering the currently required properties of RMs. Limestone, slag, silica, and kaolin were selected as substitutes for cement, while glycerol and corn syrup were selected as matrix fluids. Moreover, distilled water was used for mixing. To select the combinations of materials that meet all the required properties of RMs, flow characteristics were first analyzed. The results revealed that silica and kaolin exhibited bilateral nonlinearity. When an analysis was conducted over time, slag exhibited chemical reactions, including strength development. Moreover, fungi were observed in all mixtures with corn syrup. On the other hand, the combination of limestone, glycerol, and water exhibited a performance that met all the required properties of RMs. Thus, limestone, glycerol, and water were selected as the components of the RMs. When the influence of each component of the RMs on flow characteristics was analyzed, it was found that limestone affects the yield value, while the ratio of water and glycerol affects the plastic viscosity. Based on this, it was possible to select the mixing ratios for the RMs that can simulate the flow characteristics of cement paste under each mixing ratio. This relationship was established as an equation, which was verified under various mixing ratios. Finally, when the flow characteristics were analyzed under various temperature conditions, cement paste and the RMs exhibited similar tendencies in terms of flow characteristics. This indicated that the combinations of the selected materials could be used as RMs that can simulate the flow characteristics of cement paste with constant quality under various mixing ratio conditions and construction environment conditions.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.120-121
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• 2021

The organic insulation material has excellent thermal insulation property, but it is difficult to expect fire stability, and semi inorganic insulation only delays combustible hour but it is difficult to expect fire stability. In this study, thermal insulation property of cement-based non-combustible inorganic insulation using cement and non combustible materials and redispersible polymer powder was studied. As a result of the experiment, the thermal insulation property decreased as the use of redispersible polymer powder increased, but the heat insulation property improved when using the appropriate amount.

• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.3-10
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• 2011

Theoretical models for prediction of the mechanical properties of cement mortar are developed based on the morphology and interactions of cement hydration products, capillary pores and microcracks. The models account for intermolecular interactions involving the nano-scale calcium silicate hydrate (C-S-H) constituents of hydration products, and consider the effects of capillary pores as well as the microcracks within the hydrated cement paste and at the interfacial transition zone (ITZ). Cement mortar was modeled as a three-phase material composed of hydrated cement paste, fine aggregates and ITZ. The Hashin's bound model was used to predict the elastic modulus of mortar as a three-phase composite. Theoretical evaluation of fracture toughness indicated that the frictional pullout of fine aggregates makes major contribution to the fracture energy of cement mortar. Linear fracture mechanics principles were used to model the tensile strength of mortar. The predictions of theoretical models compared reasonably with empirical values.

• Journal of the Korea Concrete Institute
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• v.28 no.6
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• pp.665-672
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• 2016

This study is conducted to investigate the effect of phase change materials (PCM) on hydration heat and strength characteristics of cement mortar. Two types of Barium and Strontium-based PCMs were used in this study and the addition ratio of each PCM to the cement mortar ranged from 1% to 5% by cement weight. Flow test, semi-adiabatic temperature rise test, compressive strength and flexural strength test were carried out to examine the PCM effect on heat and mechanical properties of cement mortar. Test results indicated that PCMs used in this study were effective to control hydration heat of cement mortar, and Barium-based PCM slightly reduce flow value. The compressive and flexural strength of cement mortar with PCM decreased with increasing the adding mount of PCM. The prediction model for compressive strength of cement mortar with different addition levels of PCMs are suggested in this study.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.06a
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• pp.21-22
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• 2020

In this study, the pile filling materials of the pile in drilled piling was studied. cement milk is mostly used as the filling materials of bored pile. The use of filling material based on cement milk is inefficient at field construction because it needs a lot of the charging mass. thickening agent was added to the cement milk to perform settlement estimation experiment on a circular cylinder, and as a result of examining the compressive strength of the day, it was found that the settlement estimation was significantly reduced. However, the strength was relatively low, it was confirmed that there was no problem with the regulation because the main surface fixative required relatively low strength.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.2
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• pp.123-129
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• 2018

The aim of the research is providing a fundamental idea of reducing viscosity of cement based materials by replacing powder based material. With developing concrete technology, high performance concrete with high solid volume fraction has been used widely. Under the conditions of the high solid volume fraction due to the low w/c and replacement of SCMs, decreased fluidity is one of the critical problem, and thus plasticizer has been used to improve fluidity of the mixture. However, in rheological aspect, the fluidity of cement based materials can be defined with yield stress and viscosity, and using plasticizer only decreases yield stress without least controlling on viscosity. Therefore, based on the idea of Krieger-Dougherty model, a feasibility of wasted limestone powder from cement manufacturing process was used to decrease the viscosity of the mixture by replacing cement powder. According to a series of experiment, by replacing wasted limestone powder solely, there was a possibility of reducing viscosity was observed. Thus, in this research scope, it is considered to contribute on providing a fundamental idea of reducing viscosity with powder replacement and it is expected to contribute on further research using various conditions of replacing powders for reducing viscosity of cementitious materials.

• Journal of the Korean GEO-environmental Society
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• v.19 no.4
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• pp.17-26
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• 2018

This study systematically examines the changes in the compressive and tensile strength of soil cement reinforced by natural hair fiber, which is regularly produced from human. Extensive experimental tests of various test specimens have been carried out in a laboratory. Several factors are considered, including the soil type, amount of cement, amount of fiber, fiber length, loading type, and curing age. The test results indicate that both the compressive and tensile strengths are significantly affected by the fiber, either increasing or decreasing depending on the conditions. The increase in tensile strength is significant in the sand-based soil cement due to the tensile resistance of the fiber which is interlocked with the surrounding soil or cement particles. The natural fiber provides a larger strain to failure due to its extensibility, which allows greater deformation. Based on the test results, natural hair fibers can be an effective and environmentally friendly way to improve soil ground subjected to tensile loading, such as an embankment slope, road subgrade, or landfill, thus reducing the cost for cement and waste treatment. The study results provide a useful information of better understanding the mechanical behavior of natural hair fiber in soil cement and the practical use of waste materials in civil engineering. The findings can be practically applied for improving earth structures under tensile loading.