• Cement
• /
• s.175
• /
• pp.62-66
• /
• 2007

• Applied Chemistry for Engineering
• /
• v.3 no.4
• /
• pp.639-648
• /
• 1992

For recycling cement hydrate(CH) as waterproofers for mortar and concrete or a filler for rubber & plastics, the cement hydrates were treated with stearic acid(SA). And the bonding characteristics and the water repellency of the CH-SA compounds were investigated by using FT-IR, TGA, SEM, XRD, and contact angle measuring apparatus. Water tightness of the remitars used CH-SA compounds was also tested. The results are summarized as follows : 1) If the cement hydrates are treated with over 2.0% of stearic acid, the CH-SA compounds show very strong water repellency. 2) The stearic acids are solidified on the surfaces of cement hydrate in calcium stearate and aluminium stearate. 3) If CH-SA compounds which is cement hydrate treated with 5~10% of stearic acid are used 3%~6% in remitar, water absorption ratio and water permeatility ratio of remitar are decreased in below 30% of those of the ordinary remitar.

• Journal of the Korea Concrete Institute
• /
• v.19 no.5
• /
• pp.613-621
• /
• 2007

Due to the increasing significance of durability, much researches on carbonation, one of the major deterioration phenomena are carried out. However, conventional researches based on fully hardened concrete are focused on prediction of carbonation depth and they sometimes cause errors. In contrast with steel members, behaviors in early-aged concrete such as porosity and hydrates (calcium hydroxide) are very important and may be changed under carbonation process. Because transportation of deteriorating factors is mainly dependent on porosity and saturation, it is desirable to consider these changes in behaviors in early-aged concrete under carbonation for reasonable analysis of durability in long term exposure or combined deterioration. As for porosity, unless the decrease in $CO_2$ diffusion due to change in porosity is considered, the results from the prediction is overestimated. The carbonation depth and characteristics of pore water are mainly determined by amount of calcium hydroxide, and bound chloride content in carbonated concrete is also affected. So Analysis based on test for hydration and porosity is recently carried out for evaluation of carbonation characteristics. In this study, changes in porosity and hydrate $(Ca(OH)_2)$ under carbonation process are performed through the tests. Mercury Intrusion Porosimetry (MIP) for changed porosity, Thermogravimetric Analysis (TGA) for amount of $(Ca(OH)_2)$ are carried out respectively and analysis technique for porosity and hydrates under carbonation is developed utilizing modeling for behavior in early-aged concrete such as multi component hydration heat model (MCHHM) and micro pore structure formation model (MPSFM). The results from developed technique is in reasonable agreement with experimental data, respectively and they are evaluated to be used for analysis of chloride behavior in carbonated concrete.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
• /
• v.10 no.2
• /
• pp.125-132
• /
• 2012

The dehydration schemes of rare earth (La, Ce, Nd, Pr, Sm. Eu, Gd, Y) chloride hydrates was investigated by using a dehydration apparatus. To prevent the formation of the rare earth oxychlorides, the operation temperature was changed step by step ($80{\rightarrow}150{\rightarrow}230^{\circ}C$) based on the TGA (thermo-gravimetric analysis) results of the rare earth chloride hydrates. A vacuum pump and preheated Ar gas were used to effectively remove the evaporated moisture and maintain an inert condition in the dehydration apparatus. The dehydration temperature of the rare earth chloride hydrate was increased when the atomic number of the rare earth nuclide was increased. The content of the moisture in the rare earth chloride hydrate was decreased below 10% in the dehydration apparatus.

• Journal of the Korea Concrete Institute
• /
• v.27 no.3
• /
• pp.265-272
• /
• 2015

In this study, a method to reduce temperature rise due to hydration in mass concrete is investigated. It is to use retarder (glucose) for reducing heat of hydration and to use calcium silicate hydrate (C-S-H) for compensating the retardation effect due to its role as a nucleation seed. For this purpose, the temperature rise of cement paste due to hydration was measured and the effect of using both C-S-H and glucose on setting and 28-day compressive strength of mortar specimens was investigated. According to the experimental results, using C-S-H and glucose caused the reduction in the maximum temperature but accelerated the time to reach the maximum temperature compared to that of retarded cement paste using glucose. In addition, using C-S-H and glucose did not show significant effect on 28-day compressive strength of mortar specimens, indicating that the method shown in this study can be a successful alternative to control maximum temperature rise in mass concrete.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1998.05a
• /
• pp.369-373
• /
• 1998

증기발생기에서 부식에 의한 전열관 손상은 전열관과 관판사이의 틈새에서 대부분 발생되고 이 틈새에서의 수질환경에 좌우된다. 틈새에서는 과열도가 높아 미량의 불순물이 농축되면서 틈새수화학 (crevice chemistry)은 증기발생기 내부수 수화학과는 달라진다. 전열관 손상을 억제하기 위해서는 틈새수질을 적절히 제어하여야 하는데 이는 틈새수화학을 정확히 분석평가할 수 있는 기술을 기반으로 하여야 한다. .기존의 틈새수질을 계산하는 방법으로는 증기발생기 내부수에 비해 틈새에서 화학종들이 얼마나 농축되는지를 가정하는 농축도 (concentration factor) 방법이 있으나 가정에 의한 불확실성으로 인해 틈새수질을 정확히 해석할 수 없었다. 그러나 원전 증기발생기의 잠복불순물 방출시험 자료로부터 틈새수질을 보다 정확히 평가할 수 있는 새로운 개념의 몰비지수(molar ratio index) 방법이 최근 EPRI에서 제시되었고 EPRI 산하의 많은 발전소에서 적용중이다. 본 연구에서는 PWR 원전 증기발생기의 틈새수화학을 평가할 수 있는 기술을 개발하기 위해 잠복불순물 방출시험 자료로부터 틈새에서의 몰비지수를 계산할 수 있는 CRAP (CRevice-chemistry Analysis Program) 전산프로그램을 작성하였다 CRAP를 국내원전에 적용하여 증기발생기 및 그 틈새에서의 수화학을 평가하였다.

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.06a
• /
• pp.501-503
• /
• 2007

오호츠크해 사할린 북동 해저사면지역은 세계적인 가스수화물 산출지역으로 알려져있다. 이미 2005년 탐사에서 50 cm 두께의 순수 가스수화물 시료를 해저면에서 채취한 지역이다. 2006년 탐사에서는 다양한 주파수대역의 고해상도 지구불리장비를 사용하여 탐사를 실시하였다. Side-scan Sonal와 3.5 kHz SBP 탐사, 수중음향 탐사를 통해 대규모 하도구조가 가스수화물지역의 북쪽 경계를 형성하고 있음을 밝혔다. 가스수화물의 BSR은 수심에 얕아짐에 따라 계속해서 심도가 감소하여 수심 약 300 m에서 해저면에 다다름. 이는 연구지역에서의 가스수화물 안정대의 상부경계가 약 300 m임을 시사한다 가스수화물 분출구조들은 약 1000m 수심을 경계로 천부에 분포하고, 해저면에는 원형의 가스분출구조들이 특징적으로 나타난다. 반면에 1000 m 수심보다 깊은 지역에서는 mud-dirpir의 상승구조로 판단되는 상승구조들이 해저면에 굴곡지형을 형성하고 있다. 해수중으로 분출하는 가스기둥들은 수심 111.2 m에서 1226.4 m 지점까지 다양한 수심에서 분포하며, 상승높이는 최대 750 m에 이르며, 약 150 m 수심까지 도달한다. 이는 해저에서 분출되는 메탄가스가 해수에 흡수되지 않고 해수면까지 이동하여 대기중으로 발출될 수 있음을 시사한다.

• Journal of the Mineralogical Society of Korea
• /
• v.23 no.2
• /
• pp.151-159
• /
• 2010

The effect of calcite and gypsum on the hydration of Portland cement was investigated using GEM-PSI, a geochemical model. Addition of calcite and gypsum up to 5 wt% of total cement clinker into Portland cement was found to influence the hydrate assemblage of the hydrated cement in different ways. The results of geochemical modelling showed that the fraction of calcium monocarbonate increased by the hydration of cement with the increase of calcite addition. The results of modelling also indicated that gypsum increased the fraction of ettringite in the assemblage of hydrated cement as the amount of gypsum added increases. This study showed that porosity generated by the hydration of cement had a significant relation with the amount of calcite and gypsum added. The porosity of hydrated cement was lower when calcite added up to 3 wt% of cement clinker compared to the hydrated cement with the same amount of gypsum addition. However, when calcite added more than 3% of cement clinker, the porosity of hydrated cement were higher than that of hydrated cement with the same amount of gypsum addition.

• Journal of the Korean Recycled Construction Resources Institute
• /
• v.9 no.1
• /
• pp.1-12
• /
• 2021

The present study proposes the modified-stoichiometric model for describing hydration of sodium silicate-based alkaliactivated slag(AAS), and compares the results with the thermodynamic modelling-based calculations. The proposed model is based on Chen and Brouwers(2007a) model with updated database as reported in recent studies. In addition, the calculated results for AAS are compared to those for hydrated portland cement. The maximum difference between the proposed model and the thermodynamic calculation for AAS was at most 20%, and the effects of water-to-binder ratio and activator dosages were identically described by both approaches. In particular, the amount of non-evaporable water was within 10% difference, and was in excellent agreement with the experimental results. Nevertheless, notable deviation was observed for the chemical shrinkage, which is largely dependent on the volume of hydrates and pores.

• Journal of the Korea Concrete Institute
• /
• v.27 no.1
• /
• pp.85-92
• /
• 2015

The chloride ions, responsible for the initiation of the corrosion mechanism, intrude from the external medium into the concrete. A part of the intruding chloride ions will be retained by the hydration products of the binder in concrete, either through chemical adsorption or by physical adsorption. Since the hydration products of cement are responsible for the chloride binding in concrete, this study focused on the chloride binding in individual hydrate. The purpose of this study is to explore the time dependant behaviors of chloride ions adsorption with cement hydrates, focused on its mechanism. AFt phase and CH phase were not able to absorb chloride ion, however, C-S-H phase and AFm phase had a significant chloride adsorption capacity. In particular, AFm phase showed a chemical adsorption with slow rate in 40 days, while C-S-H phase showed binding behaviors with 3 stages including momentary physical adsorption, physico-chemical adsorption, and chemical adsorption. Based on the results, this study suggested theoretical approach to depict chloride adsorption behavior with elapsed time of C-S-H phase and AFm phase effectively. It is believed that the approach suggested in this study can provide us with a good solution to understand the mechanism on chloride adsorption with hydrates and to calculate a rate of chloride penetration with original source of chloride ions, for example, marine sand at initial time or sea water penetration later on.