• Computers and Concrete
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• v.9 no.3
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• pp.179-193
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• 2012

The hydration of cement contributes to the performance characteristics of concrete, such as strength and durability. In order to improve the utilization efficiency of cement and its early properties, the particle size distribution (PSD) of cement varies considerably, and the effects of the particle size distribution of cement on the hydration process should be considered. In order to evaluate effects of PSD separately, experiments testing the isothermal heat generated during the hydration of cements with different particle size distributions but the same chemical composition have been carried out. The measurable hydration depth for cement hydration was proposed and deduced based on the experimental results, and a PSD hydration model was developed in this paper for simulating the effects of particle size distribution on the hydration process of cement. First, a reference hydration rate was derived from the isothermal heat generated by the hydration of ordinary Portland cement. Then, the model was extended to take into account the effect of water-to-cement ratio, hereinafter which was referred to as PSD hydration model. Finally, the PSD hydration model was applied to simulate experiments measuring the isothermal heat generated by the hydration of cement with different particle size distributions at different water-to-cement ratios. This showed that the PSD hydration model had simulated the effects of particle size distribution and water-to-cement ratio on the hydration process of cement with satisfactory accuracy.

• Journal of the Korean Ceramic Society
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• v.37 no.7
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• pp.681-685
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• 2000

The influence of ZnCl2 in portland cement hydration was studied. The hydration reaction was progressed with ZnCl2 solution to observe the adiabatic hydration exothermic and hydration products. To compare with cement hydration, Ca(OH)2 solution reacted with ZnCl2 was carried out. The addition of ZnCl2 solution to the portland cement was retarded hydration quantitatively. Because ZnO which was produced in certain pH adsorbed with unhydrated cement made retarded the hydration reaction.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.883-887
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• 1998

Hydration is the main reason for the growth of the material properties. A exact parameter to control the chemical and physical process is not the time, but the degree of hydration. Therefore, it is reasonable that development all material properties should be formulated in terms of degree of hydration. Mathematical formulation of degree of hydration is based on combination of reaction rate functions. The effect of moisture conditions as well as temperature on the rate of reaction is considered in the degree of hydration model. This effect is subdivided into two contributions: water shortage and water distribution. The former is associated with the effect of on the progress of hydration. The water needed for progress of hydration do not exist and there is not enough space for the reaction products to form. The latter is associated with the effect of free capillary water distribution in the pore system. Physically absorption layer does not contribute to progress of hydration and only free water is available for further hydration.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2014.11a
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• pp.13-14
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• 2014

Ultra high performance concrete (UHPC) consists of cement, silica fume (SF), sand, fibers, water and superplasticizer. Typical water/binder-ratios are 0.15-0.20 with 20-30% of silica fume. The development off properties of hardening UHPC relates with both hydration of cement and pozzolanic reaction of silicafume. In this paper, by considering the production of calcium hydroxide in cement hydration and its consumption in the pozzolanic reaction, a numerical model is proposed to simulate the hydration of UHPC. The degree of hydration of cement and degree of reaction of silica fume are obtained as accompanied results from the proposed hydration model. The properties of hardening UHPC, such as degree of hydration of cement, calcium hydroxide contents, and compressive strength, are predicted from the contribution of cement hydration and pozzolanic reaction. The proposed model is verified through experimental data on concrete with different water-to-binder ratios and silica fume substitution ratios.

• Journal of the Korean Ceramic Society
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• v.21 no.2
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• pp.143-148
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• 1984

In this study we mainly dealt with the effects of organic retarder(calcium lignosulfate) on the early hydration process of clinker minerals. From a consideration of the hydration process of tricalcium silicate $(C_3S)$ tricalcium silicate $(C_3S)$-tricalcium aluminate $(C_3A)$ tricalcium silicate $(C_3S)$-tetracalcium aluminof-errite $(C_4AF)$ systems with calcium lignosulfate the following results were obtained. 1. when 0.25wt% of CLS was added to $C_3S$ the hydration process was progressed normally but adding of 0.5wt% its hydration was greatly retarded. 2. The hydration of $C_3S$-$C_3A$ system was progressed normally up to 0.5wt% but by adding gypsum its hydration was retarded slightly. 3. The hydration of $C_3S$-$C_4AF$ system was greatly retarded even with 0.25wt% of CLS but by adding gypsum its hydration process was recovered normally.

• Computers and Concrete
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• v.11 no.4
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• pp.271-289
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• 2013

In this research, a developed microstructural model of cement particles was presented to describe the cement hydration procedure. To simplify the hydration process, the whole hydration was analyzed in a series of sub-steps. In each step, the hydration degree, as well as the microstructural size of the hydration cell, was calculated as a function of the radius of the unreacted cement particles. With the consideration of the water consumption and the reduction of the interfacial area between water and hydration products, the micro-level expressions of the cement hydration kinetics were established. Then the heat released and temperature history of the concrete was carried out with the hydration degree obtained from each sub-steps. The equivalent age method based on the Arrhenius law was introduced in this research. Based on the equivalent age method, a maturity model was applied to describe the evolution of the mechanical properties of the material during the hydration process. The finite element program ANSYS was used to analyze the temperature field in concrete structures. Then thermal stress field was calculated using the elasticity modulus obtained from code formulate. And the risk of thermal cracking was estimated by the comparison of thermal stress and concrete tensile strength.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.21-21
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• 2011

A series of Quasi-Elastic Neutron Scattering (QENS) experiments helps us to understand the single-particle (hydrogen atom) dynamics of a globular protein and its hydration water and strong coupling between them. We also performed Molecular Dynamics (MD) simulations on a realistic model of the hydrated hen-egg Lysozyme powder having two proteins in the periodic box. We found the existence of a Fragile-to-Strong dynamic Crossover (FSC) phenomenon in hydration water around a protein occurring at TL=$225{\pm}5K$ by analyzing Intermediate Scattering Function (ISF). On lowering of the temperature toward FSC, the structure of hydration water makes a transition from predominantly the High Density Liquid (HDL) form, a more fluid state, to predominantly the Low Density Liquid (LDL) form, a less fluid state, derived from the existence of a liquid?liquid critical point at an elevated pressure. We showed experimentally and confirmed theoretically that this sudden switch in the mobility of the hydration water around a protein triggers the dynamic transition (so-called glass transition) of the protein, at a temperature TD=220 K. Mean Square Displacement (MSD) is the important factor to show that the FSC is the key to the strong coupling between a protein and its hydration water by suggesting TL${\fallingdotseq}$TD. MD simulations with TIP4P force field for water were performed to understand hydration level dependency of the FSC temperature. We added water molecules to increase hydration level of the protein hydration water, from 0.30, 0.45, 0.60 and 1.00 (1.00 is the bulk water). These confirm the existence of the FSC and the hydration level dependence of the FSC temperature: FSC temperature is decreased upon increasing hydration level. We compared the hydration water around Lysozyme, B-DNA and RNA. Similarity among those suggests that the FSC and this coupling be universal for globular proteins, biopolymers.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.805-808
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• 2002

This study is designed to reduction of hydration heat of 4 layer division-placed mass concrete considering the difference of setting time of super retarding agent. According to the results, peak temperature of plain concrete by hydration heat show $63^{\circ}C$ around the age of 1 days. Hydration heat is lowest in the bottom layer, and highest in the middle of 3rd layer from the bottom. Hydration heat of mock up structure, which is division-placed at the same interval of 1 and 2 days by setting time difference of super retarding agent, is highest in the bottom layer because after peak temperature of 4th layer, hydration reaction progresses in order of 3rd, 2nd and 1st layer. But in mock up structure which is division-placed at the various interval. peak temperature by hydration heat is reduced by about $13^{\circ}C$, compared with plain concrete because after first peak hydration heat of 4th layer (plain concrete), hydration reaction progresses after the drop of hydration heat in order of 3rd, 2nd and 1st layer.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2017.05a
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• pp.230-231
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• 2017

The addition of a limestone filler(LF) to fill into the voids between cement and aggregate particles can reduce the cementitious paste volume. This paper aim to evaluate the influence of LF contents on the hydration kinetics and compressive strength. Hydration kinetics were evaluate using heat of hydration, ignition loss and thermal analysis. The heat of hydration was measured using Isothermal Calorimetry. The degree of hydration was measured using ignition loss. Hydration product analysis was carried out by Thermal Gravimetric and Differential Thermal Analysis. The results show that the addition of LF reduces not only the initial setting time and heat of hydration peak, also degree of hydration and rate of strength development at early age increase with the addition of LF. It can be concluded the LF fills the pore between cement particles due to formation of carboaluminate, which may accelerate the setting of cement pastes.

• Journal of Korean Academy of Nursing
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• v.37 no.5
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• pp.781-789
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• 2007

Purpose: The study was conducted to investigate the skin hydration level in various body sites and identify the influencing factors in neonates. Methods: An exploratory comparison study was designed to measure the stratum corneum hydration, using a National DM-R2 on the forehead, abdomen, buttocks, and the back of the hands and feet of 198 neonates including 92 premature infants. Results: The results showed 32.7%-36.5% of stratum corneum hydration for all sites. Premature infants revealed a higher hydration level on the peripheral sites (dorsal hand and feet) than those of the full-term infants, possibly resulting from therapeutic regimens including an incubator or radiant warmer. Infants in an incubator showed a higher hydration level than those in radiant warmers, suggesting more attention to fluid management for infants in the open environment. In addition, all stratum corneum hydration measurements except one, from the forehead, showed a positive correlation with postnatal age in full-term infants while showing no relation to any measurements in premature infants. Conclusion: The study demonstrated the very low skin hydration levels in hospitalized neonates, particularly in premature neonates with more susceptible skin hydration instability despite therapeutic interventions for fluid balance. More vigilant fluid management is imperative in neonates, particularly those in the open environment.