• Title/Summary/Keyword: cement pastes

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Numerical simulation on integrated curing-leaching process of slag-blended cement pastes

  • Xiang-Nan Li;Xiao-Bao Zuo;Yu-Xiao Zou;Guang-Pan Zhou
    • Computers and Concrete
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    • v.32 no.1
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    • pp.45-60
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    • 2023
  • Concrete in water environment is easily subjected to the attack of leaching, which causes its mechanical reduction and durability deterioration, and the key to improving the leaching resistance of concrete is to increase the compaction of its microstructure formed by the curing. This paper performs a numerical investigation on the intrinsic relationship between microstructures formed by the hydration of cement and slag and leaching resistance of concrete in water environment. Firstly, a shrinking-core hydration model of blended cement and slag is presented, in which the interaction of hydration process of cement and slag is considered and the microstructure composition is characterized by the hydration products, solution composition and pore structure. Secondly, based on Fick's law and mass conservation law, a leaching model of hardened paste is proposed, in which the multi-species ionic diffusion equation and modified Gérard model are established, and the model is numerically solved by applying the finite difference method. Finally, two models are combined by microstructure composition to form an integrated curing-leaching model, and it is used to investigate the relationship between microstructure composition and leaching resistance of slag-blended cement pastes.

Effects of Fly Ash on Chloride Binding Capacity in Cement Pastes (시멘트 페이스트 내의 염화물 고정화에 미치는 플라이 애쉬의 영향)

  • 소승영;소양섭
    • Magazine of the Korea Concrete Institute
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    • v.7 no.6
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    • pp.209-215
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    • 1995
  • Corrosion of steel reinforcment is the most significant factor of deterioration in reinforced concrete structures. Chloride ion is considered one of the most common culprits in the corrosion of steel in concrete. It breaks down the passive film and allows the steel to corrode actively at a high rate. The main objective of this study is to determine the critical chloride ion concentrations in the pore solutions and chloride binding effect of cement pastes made with and without fly ash. Cement pastes with water-binder ratio of 0.5, allowed to hydrate in sealed containers for 28 days and to express pore solution. The expressed pore fluids were analyzed for chloride and hydroxyl ion concentrations. Evaporable water on paralled specimens was determined a.s the loss of weight per 100g of unhydreded cement when the specimens were heated to constant weight at 105'C. It was found that the replaced cement with fly ash has negligible influnce on the chloride binding and chloride binding capacity and rises the $Cl^-$ /$OH^-$ ratio in pore solution.

Prediction of Rheological Properties of Cement-Based Pastes Considering the Particle Properties of Binders (결합재의 입자특성을 고려한 시멘트 기반 2성분계 페이스트의 유변특성 예측)

  • Eun-Seok Choi;Jun-Woo Lee;Su-Tae Kang
    • 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.

Characterization of Reinforcing Efficiency in Hybrid Fiber Reinforced Cementitous pastes (하이브리드 섬유보강 시멘트 페이스트의 보강효율에 대한 특성화)

  • Park, Tae-Hyo;Noh, Myung-Hyun;Park, Choon-Keun
    • Proceedings of the Korea Concrete Institute Conference
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    • 2004.05a
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    • pp.644-647
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    • 2004
  • Modulus of rupture (MOR) and flexural toughness in hybrid fiber reinforced cement pastes mixed with micro-fiber (carbon fiber) and macro-fiber (steel fiber) and replaced with silica fume according to the fixed ratio were researched. Reinforcing efficiency in specimens were estimated by two factors, such as strengthening factor $(F_s)$ and toughening factor $(F_t)$, which were calculated from the analysis of variance (ANOVA) of the response values, such as MOR and absorbtion energy $(W_0)$. According to the experimental design by the fractional orthogonal array, nine hybrid fibrous reinforced paste series and one non-reinforced control paste were manufactured. Specimens of each series were tested by the INSTRON Inc. 8502(model) equipment in three-points bending and then measured the load-deflection response relationships. Considerable strengthening of cement pastes resulted in' the case of other factors without carbon fiber and toughening of cement pastes about all factors showed high. Based on the significance of factors related to response values from ANOVA, following assessments were available; $F_s$ or MOR: silica fume $\gg$ steel fiber $\gg$ carbon fiber; $F_t\;or\;W_0$: steel fiber > carbon fiber > silica fume. Optimized composition condition was estimated by steel fiber of $1.5\%$, carbon fiber of $0.5\%$ and silica fume $7.5\%$ in side of strengthening and steel fiber of $1.5\%$, carbon fiber of $0.75\%$ and silica fume $7.5\%$ in side of toughening.

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염용액에 침지한 콘크리트의 열화에 대한 연구

  • 문한영;김기형;김성수
    • Proceedings of the Korea Concrete Institute Conference
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    • 1989.10a
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    • pp.25-30
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    • 1989
  • In this paper, morter and concrete specimens made with four cements were immersed in Mgcl2, MgSO4 Solution and artifical Seawater which was corresponded with Seawater. The hydration products of immersed cement pastes were looked over by using SEM, EDS and X-ray diffraction method. The results show that the concrete made with domestic flyash cement and blast-frrnace slag cement is superior to that of ordinary portland cement in resistance to chloride and sulphate solution. Especially, it is found that the attack of Cl-ion on the concrete plays an important role of the deterioration of concrete.

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Effects of Sugar and Hydrated Cement Powder on the Reduction in Heat of Hydration (당분과 수화시멘트 분말이 수화열 저감에 미치는 효과)

  • Moon, Hoon;Kim, Ji-Hyun;Cho, Yong-Hun;Lee, Jae-Yong;Chung, Chul-Woo
    • Journal of the Korea Institute of Building Construction
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    • v.14 no.2
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    • pp.135-142
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    • 2014
  • The heat of hydration can be reduced through the use of retarding agents. Typical retarding agents include sugar and glucose. However, these significantly delay the setting of cement paste. For the efficient use of sugar and glucose for mass concrete construction, it is necessary to develop a technique that can provide a setting behavior equivalent to that of plain concrete. In this work, the temperature rise of cement paste was monitored with the addition of various retarders including sugar and glucose. Hydrated cement powder was made with a water to cement ratio of 5 in order to accelerate the retarded cement pastes. It was found that the addition of hydrated cement powder in retarded pastes reduced the maximum temperature of cement paste. The use of hydrated cement powder could also successfully reduce the time to reach the maximum temperature.

Application of Antifungal CFB to Increase the Durability of Cement Mortar

  • Park, Jong-Myong;Park, Sung-Jin;Kim, Wha-Jung;Ghim, Sa-Youl
    • Journal of Microbiology and Biotechnology
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    • v.22 no.7
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    • pp.1015-1020
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    • 2012
  • Antifungal cement mortar or microbiological calcium carbonate precipitation on cement surface has been investigated as functional concrete research. However, these research concepts have never been fused with each other. In this study, we introduced the antifungal calcite-forming bacteria (CFB) Bacillus aryabhattai KNUC205, isolated from an urban tunnel (Daegu, South Korea). The major fungal deteriogens in urban tunnel, Cladosporium sphaerospermum KNUC253, was used as a sensitive fungal strain. B. aryabhattai KNUC205 showed $CaCO_3$ precipitation on B4 medium. Cracked cement mortar pastes were made and neutralized by modified methods. Subsequently, the mixture of B. aryabhattai KNUC205, conidiospore of C. sphaerospermum KNUC253, and B4 agar was applied to cement cracks and incubated at $18^{\circ}C$ for 16 days. B. aryabhattai KNUC205 showed fungal growth inhibition against C. sphaerospermum. Furthermore, B. aryabhattai KNUC205 showed crack remediation ability and water permeability reduction of cement mortar pastes. Taken together, these results suggest that the $CaCO_3$ precipitation and antifungal properties of B. aryabhattai KNUC205 could be used as an effective sealing or coating material that can also prevent deteriorative fungal growth. This study is the first application and evaluation research that incorporates calcite formation with antifungal capabilities of microorganisms for an environment-friendly and more effective protection of cement materials. In this research, the conception of microbial construction materials was expanded.

Effects of Absorbent Polymer on the Moisture Resistance and Hydration Characteristics of Cement Pastes (시멘트 페이스트의 특성에 미치는 흡수성폴리머의 영향)

  • 나종균;김창은;이승규
    • Journal of the Korean Ceramic Society
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    • v.36 no.5
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    • pp.539-546
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    • 1999
  • Absorbent polymer-cement composites were fabricated by the semi-powder mixing OPC(ordinary Portland cement) with an absorbent polymer. The effects of absorbent polymer on the mechanical properties and the hydration characteristics were observed and the polymer-cement interaction also discussed. Absorbent polymer-cement composites showed the value of total porosity of 8vol% the value of 28 days flexural strength was up to 280 Kgf/cm2 in the case of absorbent polymer-cement composite at 1 wt% absorbent polymer content and microstructure of absorbent polymer-cement composite has been observed more dense than that of OPC paste. Accordingly the permeability of compositewas improved and so the moisture resistance was also increased. Adding polymer did not retard the hydration of OPC. It was considered from the results of IR(infrared) analysis that the functional group of absorbent polymer would be changed from unidentate to bidentate during by the hydration of cement minerals.

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Investigation on alkalinity of pore solution and microstructure of hardened cement-slag pastes in purified water

  • Hu, Ya-Ru;Zuo, Xiao-Bao;Li, Xiang-Nan;Jiang, Dong-Qi
    • Advances in concrete construction
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    • v.12 no.6
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    • pp.507-515
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    • 2021
  • To evaluate the influence of slag on the alkalinity of pore solution and microstructure of concrete, this paper performs a leaching experiment on hardened cement-slag pastes (HCSP) slice specimens with different slag content in purified water. The pH value of pore solution, average porosity, morphology, phase composition and Ca/Si of HCSP specimens in the leaching process are measured by solid-liquid extraction, saturated-dried weighing, scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) and X-ray diffraction (XRD). Results shows that the addition of slag can mitigate an increase in porosity and a decrease in Ca/Si of HCSP in the leaching process. Besides, an appropriate slag content can improve the microstructure so as to obtain the optimum leaching resistance of HCSP, which can guarantee the suitable alkalinity of pore solution to prevent a premature corrosion of reinforced bar. The optimum slag content is 40% in HCSP with a water-binder ratio of 0.45, and an excessive slag causes a significant decrease in the alkalinity of pore solution, resulting in a loss of protection on reinforced bar in HCSP.