• International Journal of Railway
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• 제7권3호
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• pp.85-89
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• 2014

The use of pozzolanic materials in concrete mixtures can enhance the mechanical properties and durability of concrete. By reactions with pozzolanic materials and calcium hydroxide in cement matrix, calcium-silicate-hydrate (C-S-H) increases and calcium hydroxide decreases in cement matrix of concrete. Consequently, the volume of solid materials increases. The pozzolanic particles also fill spaces between clinker grains, thereby resulting in a denser cement matrix and interfacial transition zone between cement matrix and aggregates; this lowers the permeability and increases the compressive strength of concrete. Moreover, the total contents of alkali in concrete are reduced by replacing cements with pozzolanic materials; this prevents cracks due to alkali-aggregate reaction (AAR). In this study, nanosilica is incorporated in cement pastes. The differences of microstructural compositions between the hydrated cements with and without nanosilica are examined using nanoindentation, XRDA and $^{29}Si$ MAS NMR. The results can be used for a basic research to enhance durability of concrete slab tracks and concrete railway sleepers.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.637-642
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• 2002

In this study, the experiments of recycled aggregate concrete with fly ash and special blended slag powder or diatom calcined at 650$\circ$ were performed on compressive strength, shrinkage and creep. The compressive strength of concrete with recycled aggregate and pozzolanic materials were higher than that of concrete with crushed stone and OPC. On the other hand, the shrinkage and creep of concrete with recycled aggregate and pozzolanic materials was smaller than that of concrete with crushed stone and OPC. Futhermore, the shrinkage and creep of recycled aggregate concrete with fly ash and special blended slag powder was a little decreased that of recycled aggregate concrete with fly ash and diatom. Relationship between compressive strength and creep coefficient was shown to the linear relation like as $\sigma$$_{c}$= -30CF＋404.4.

• Computers and Concrete
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• 제13권1호
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• pp.97-115
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• 2014

Silica fume is a by-product of induction arc furnaces and has long been used as a mineral admixture to produce high-strength, high-performance concrete. Due to the pozzolanic reaction between calcium hydroxide and silica fume, compared with that of Portland cement, the hydration of concrete containing silica fume is much more complex. 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 concrete containing silica fume. The heat evolution rate of silica fume concrete is determined from the contribution of cement hydration and the pozzolanic reaction. Furthermore, the temperature distribution and temperature history in hardening blended concrete are evaluated based on the degree of hydration of the cement and the mineral admixtures. The proposed model is verified through experimental data on concrete with different water-to-cement ratios and mineral admixture substitution ratios.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2014년도 추계 학술논문 발표대회
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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.

• Computers and Concrete
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• 제27권2호
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• pp.175-184
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• 2021

The incorporation of pozzolans to Portland cement pastes adds value in the development of new materials for the construction industry. This study presents a new computational method, complementary to the pozzolanic identification by compressive strength at 28 days method, for supporting the validation of pozzolanic mortars for non-structural purposes. An algorithm capable of classifying the pixels of micrographs of specimens fragments was developed. Therefore, comparative analyses were generated from fractional Gaussian representations in four intervals of the same amplitude that indicated the predispositions to form larger void indices (intervals 1 and 2). The results showed that the computational method indicators are in accordance with the physical and chemical indicators.

• 시멘트
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• 통권158호
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• pp.40-44
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• 2003

• Advances in concrete construction
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• 제10권4호
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• pp.301-310
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• 2020

The following paper concentrates on the objective of studying the influences of extent of duration and temperature on the Pozzolanic properties as well as reactivity of locally existing natural clay of Nai Gaj, district Dadu, Sindh Pakistan. The activation of the clay only occurs through heating when temperature in a furnace chamber reaches 600, 700 and 800oC for 1, 2 and 3 hours and at 900 and 1000℃ for 1 and 2 hours. Furthermore, the strength activity index (SAI) of advanced pozzolanic material happens to be identified through 20% cement replacement for different samples of calcined clay as per ASTM C-618. The compressive strength test of samples had been operated for 7 and 28-days curing afterwards. The maximum compressive strength had been seen in mix E in which cement was replaced with clay calcined at 700℃ for 1 hour that is 27.05 MPa that is 24.31% more than that of control mix. The results gathered from the SAI verdicts the optimal activation temperature is 700℃ within a one-hour time period. The SAI at a temperature of 700℃ with a one-hour duration at 28 days is 124.31% which happens to satisfy the requirements of the new Pozzolanic material, in order to be applied in mortar/concrete (i.e., 75%). The Energy- dispersive spectrometry (EDS) along with the X-ray diffraction (XRD) have been carried out in means of verifying whether there is silica content or amorphous silica present in metakaolin that has been developed. The findings gathered from the SAI were validated, as the analysis of XRD verified that there is in fact Pozzolanic activity of developed metakaolin. Additionally, based on observation, the activated metakaolin holds a significant influence on the increase in mortar's compressive strength.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 봄 학술발표회 논문집
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• pp.166-171
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• 1996

This study examines whether the raw diatomaceous rock, after thermally activated for converting into a pozzolanic form, can improve cement quality(i.e., compressive strength) of the cement-mortar. The diatomaceous rock, heat-treated at 75$0^{\circ}C$ for 30minutes as an optimum pozzolanic form was mixed with OPC(Ordinary Portland Cement) on a weight basis from 0, 2.5, 5.0, 10, 20, 40%. The cement quality was then assessed by the compressive strength and analysis of XRD(S-Ray Diffraction) and SEM(Scanning Electron Microscope).

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1991년도 가을 학술발표회 논문집
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• pp.11-14
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• 1991

Apparent diffusion coefficients of Cl-ions through hardened cement paste(HCP), which were partly substituted blending materials, were determined. Also, pore solution was extracted from HCP which were immersed in NaCl solution, and Cl- concentration of the solution were analyzed. Partly substitution of pozzolanic materials considerably reduced the diffusion rate for Cl-ions and Cl- concentration of pore solution. Binding capacity of Cl- is related to the content of Al2O3 and pozzolanic reactivity.

• Computers and Concrete
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• 제11권2호
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• pp.93-104
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• 2013

The use of rock wool waste, an industrial by-product, in cement-based composites has positive effects on the environment because it reduces the problems associated rock wool disposal. The experiments in this study tested cement-based composites using various rock wool waste contents (10, 20, 30 and 40% by weight of cement) as a partial replacement for Portland cement in mortars. The pozzolanic strength activity test, flow test, compressive strength test, dry shrinkage test, absorption test, initial surface absorption test and scanning electron microscope observations were conducted to evaluate the properties of cement-based composites. Test results demonstrate that the pozzolanic strength activity index for rock wool waste specimens is 103% after 91 days. The inclusion of rock wool waste in cement-based composites decreases its dry shrinkage and initial surface absorption, and increases its compressive strength. These improved properties are the result of the dense structure achieved by the filling effect and pozzolanic reactions of the rock wool waste. The addition of 30% and 10% rock wool wastes to cement is the optimal amount based on the results of compressive strength and initial surface absorption for a w/cm of 0.35 and 0.55, respectively. Therefore, it is feasible to utilize rock wool waste as a partial replacement of cement in cement-based composites.