• International Journal of Concrete Structures and Materials
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• 제8권2호
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• pp.173-182
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• 2014

An experimental investigation was carried out to evaluate the mechanical properties of concrete mixtures in which coarse aggregate was partially (30, 50 or 70 %) replaced with pre-washed municipal solid waste incineration (MSWI) bottom ash. Results indicated that bottom ash reduced the compressive strength, elastic modulus, and levels of heavy metals in leachate when used as a replacement for gravel, and that the maximum amount of MSWI bottom ash in concrete should not exceed 50 %. To analyze the effect mechanism of bottom ash in concrete, the degree of hydration and the following pozzolanic reaction characterized by the pozzolanic activity index, and the porosity distribution in cement mortar. The study indicates that improved properties of concrete are not solely later strength gain and reduced levels of heavy metals in leachate but also the progression of pozzolanic reactions, where a dense structure contains a higher proportion of fine pores that are related to durability.

• 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 1994년도 봄 학술발표회 논문집
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• pp.169-173
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• 1994

Recently, the use of crushed stones is increased due to the shortage of natural aggregates. In the previous papers of part 1 and 2, we got the conclusions that some of crushed stones have the characteristic of alkali-silica reaction(ASR). And these reactions are influenced by the amount and type of alkali in cement. The purpose of this paper is how to prepare for the prevention against alkali-silica reaction. As a solution of problems, we have conducted the experiments of two methods. One was the replacement of innocuous aggregates instead of reactive aggregates, the other was the addition of various pozzolanic materials. As a result, we found that the expansion by alkali-silica reaction in mortar bar could be effectively decredsed by upper methods.

• 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.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회 논문집(I)
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• pp.183-186
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• 1998

This paper deals with 28, 56, 91 days age compressive strength and ratio of weight when OPC and Low-Heat cement mortar immersed in chemical solution. As a result of experiment, the resistance of Low-Heat Cement motar in chemical attack is more effective than that of OPC, because of lower $C_3$A content and Pozzolanic reactions. Especially in long term age compressive strength, Low-Heat cement mortar shows higher strength in all kind of chemical solution compared with compressive strength of OPC motar.

• International Journal of Concrete Structures and Materials
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• 제7권4호
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• pp.287-293
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• 2013

Strength and some durability properties of concrete containing rice husk ash (RHA) predominantly composed of amorphous silica at a specific surface of 235 $m^2/kg$ produced using a charcoal incinerator were determined. The maximum ordinary Portland cement (OPC) replacement with the RHA increased with increase in water/binder (w/b) ratio of the concrete mixes. The results show that 15 % OPC could be substituted by the RHAwithout strength loss at w/b ratio of 0.50. The split tensile strength generally increased with increase in RHA content for the mixes.

• 콘크리트학회논문집
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• 제27권2호
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• pp.115-125
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• 2015

본 연구는 물-결합재비 20%를 가지는 고강도 고함량 고로슬래그 혼합 시멘트 페이스트의 유동성, 수화열, 응결시간 그리고 강도 발현 특성, 수화 및 포졸란 반응 특성 등을 실험을 통해 관찰하고, 이를 통해 고로슬래그 미분말의 치환률과 분말도가 수화 및 포졸란 반응에 미치는 영향을 분석하였다. 연구 결과에 따르면 물-결합재비가 낮은 고강도 배합에서는 고로슬래그 미분말로 시멘트를 대체함으로써 시멘트와 결합하는 자유수가 상대적으로 증가하는 dilution effect에 의해 시멘트의 초기 수화가 촉진되어 재령 3일부터 28일까지의 초기 강도는 보통 포틀랜드 시멘트만을 사용한 배합보다 더 높게 나타났다. 반면, 재령이 증가하면서 수화반응속도가 급격히 낮아지고, 고로슬래그 미분말로 시멘트를 대량 치환함에 따라 수산화칼슘이 충분히 공급되지 못하므로 포졸란 반응도가 낮아져 장기강도의 발현이 억제되는 것으로 나타났다. 또한 고로슬래그의 분말도가 높으면 자유수를 더 많이 흡착함으로써 유동성이 저하되고 수화도가 낮아져 강도가 오히려 저하되는 것으로 나타났다. 이와 같은 결과는 보통 강도 콘크리트와는 다른 경향을 나타내는 것으로 향후 콘크리트 배합에 대해 추가 검증이 필요하며, 고로슬래그 미분말을 대량 혼합한 고강도 콘크리트의 개발을 위해서는 장기 강도의 발현율을 더 높일 수 있는 방안에 대한 연구가 필요하다.

• Advances in concrete construction
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• 제11권4호
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• pp.299-306
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• 2021

The alkali-silica reaction (ASR) is a highly complex chemical reaction which causes damage to concrete and thus adversely affects the durability and service life. Significant damage can occur in concrete structures due to cracking because of the chemical reactions taking place. Various mineral and chemical additives have been used so far to mitigate ASR and/or to reduce its adverse effects. In this study, ground trachyte and rhyolite provided from Rize-Çağrankaya region, Turkey, were used to investigate their effectiveness in controlling ASR-induced damage by substituting them with cement at certain ratios. In this context, initially the possible use of trachyte and rhyolite as pozzolanas was determined in accordance with BS EN 450-1 and TS 25 standards by considering their pozzolanic activities and then their effectiveness in mitigating the ASR was evaluated as per ASTM C 1567-13. In experimental study, blends of trachyte and rhyolite were prepared by substituting them by cement at 25%, 35%, and 50% percentage. Totally 7 mixes were prepared and three samples of 25×25×285 mm mortar bars were prepared from each batch. The length changes of the mortar bars were determined at the end of 3, 7, 14 and 28 days of exposure. SEM, along with XRD analyses were performed to examine and elementally determine the ASR products that have been formed. The results obtained have shown that ground trachyte and rhyolite used in this study can be used as pozzolanas in concrete and they can also significantly mitigate ASR-induced damage as the substitution ratio increases.

• Structural Engineering and Mechanics
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• 제83권1호
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• pp.79-92
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• 2022

In this paper, the impact of a vernacular pozzolanic kaolinite mine on concrete alkali-silica reaction and strength has been evaluated. For making the samples, kaolinite powder with various levels has been used in the quality specification test of aggregates based on the ASTM C1260 standard in order to investigate the effect of kaolinite particles on reducing the reaction of the mortar bars. The compressive strength, X-Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) experiments have been performed on concrete specimens. The obtained results show that addition of kaolinite powder to concrete will cause a pozzolanic reaction and decrease the permeability of concrete samples comparing to the reference concrete specimen. Further, various machine learning methods have been used to predict ASR-induced expansion per different amounts of kaolinite. In the process of modeling methods, optimal method is considered to have the lowest mean square error (MSE) simultaneous to having the highest correlation coefficient (R). Therefore, to evaluate the efficiency of the proposed model, the results of the support vector machine (SVM) method were compared with the decision tree method, regression analysis and neural network algorithm. The results of comparison of forecasting tools showed that support vector machines have outperformed the results of other methods. Therefore, the support vector machine method can be mentioned as an effective approach to predict ASR-induced expansion.

• International Journal of Concrete Structures and Materials
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• 제8권2호
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• pp.157-164
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• 2014

Ground granulated blast-furnace slag (GGBS) is a green construction material used to produce durable concrete. The secondary pozzolanic reactions can result in reduced pore connectivity; therefore, replacing partial amount of Portland cement (PC) with GGBS can significantly reduce the risk of sulfate attack, alkali-silica reactions and chloride penetration. However, it may also reduce the concrete resistance against carbonation. Due to the time consuming process of concrete carbonation, many researchers have used accelerated carbonation test to shorten the experimental time. However, there are always some uncertainties in the accelerated carbonation test results. Most importantly, the moisture content and moisture profile of the concrete before the carbonation test can significantly affect the test results. In this work, more than 200 samples with various water-cementitious material ratios and various replacement percentages of GGBS were cast. The compressive strength, electrical resistivity, chloride permeability and carbonation tests were conducted. The moisture loss and microstructure of concrete were studied. The partial replacement of PC with GGBS produced considerable improvement on various properties of concrete.