• Resources Recycling
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• v.15 no.4 s.72
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• pp.52-59
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• 2006

The purpose of this study was to evaluate the effects of ground granulated blast-furnace slag on strength development and durability of ordinary portland cement concrete (OPC) with steam curing types. Main experimental variables were slag contents(0%, 10%, 30%, 50%, 70%) and curing types (standard, accelerated curing). It were performed to check the basic properties of concretes that compressive strength, rapid chloride ion permeability and chemical resistance. From the result, we have found that increasing the amount of blast-furnace slag produced concrete with increased compressive strength and permeability resistance. Rapid freezing-thawing test showed that they were good enough to protect the concrete structures and to carry out cyclic freezing and thawing. The freeze-thaw resistance of blast-furnace slag produced concretes maintained above 90% of relative dynamic modulus after 300 freezing-thawing cycles. Increasing the amount of blast-furnace slag produced concretes with increased chemical resistance.

• Journal of the Korea Institute of Building Construction
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• v.19 no.1
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• pp.1-7
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• 2019

This study evaluated the mechanical properties of the alpha-calcium sulfate hemihydrate replaced concrete to reduce the cracking in a box culvert power transmission. After setting the replacement ratio of alpha-calcium sulfate hemihydrate at 0, 6, 9, 12, and 15%, the setting time, compressive strength, and drying shrinkage were measured and the microstructure and crystal structure were analyzed. As a result, it was confirmed that as the replacement ratio of alpha-calcium sulfate hemihydrate increased, the setting time decreased and the compressive strength declined. On the other hand, when the alpha-calcium sulfate hemihydrate was set with 15% of replacement ratio, about 60% reduction in the drying shrinkage was shown compared to that of ordinary Portland cement. Therefore, it is thought that when the concrete replacing the alpha-calcium sulfate hemihydrate is applied to a box culvert power transmission, the cracking reduction performance will be improved, and the improvement of compressive strength will be required.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.47-54
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• 2023

In this study, the tensile behavior of concrete specimens reinforced with GFRP (Glass Fiber Reinforced Polymer), BFRP (Basalt Fiber Reinforced Polymer), and CFRP (Carbon Fiber Reinforced Polymer) bars was experimentally analyzed. The tensile strength of the FRP bars is appeared to be similar to the design strength, but the elastic modulus was somewhat lower. Additionally, the specimens for tension stiffening effect were manufacured using OPC (Ordinary Portland Cement) and SFRC (Steel Fiber Reinforced Concrete), with dimensions of 150(W)×150(B)×1000(H) mm. The crack spacing of specimens was most significant for GFRP reinforcement bars, which have a lower elastic modulus and a smoother surface, while BFRP and CFRP bars, with somewhat rougher surfaces and higher elastic moduli, showed similar crack spacings. In the load-strain relationship, GFRP bars exhibited a relatively abrupt behavior after cracking, whereas BFRP and CFRP bars showed a more stable behavior after the cracking phase, maintaining a certain level of tension stiffening effect. The tension stiffening index was somewhat smaller as the diameter increased, and GFRP, compared to BFRP, showed a higher tension stiffening index.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.805-811
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• 2004

In this paper, effects of mixture proportion and material condition on both fundamental properties, drying and autogenous shrinkage of high performance concrete are discussed. According to the results, for the effect of mixture proportion on the fundamental properties, decrease in W/B and unit water content results in reduction of fluidity, while air content has no variation. Compressive strength exhibits an decreasing tendency with an increase in W/B and unit water content do not remarkable affect the compressive strength. For the effect of materials on the fluidity, the fluidity of low heat portland cement(LPC) is smaller than that of ordinary portland cement(OPC). The use of Polycarbonic acid based superplasticizer(PS) has more favorable effect on enhancing fluidity than Naphtalene based superplasticlzer(NS) and Melamine based superplasticizer(MS). Air content of concrete using LPC is larger than that using OPC. The effects of superplasticizer type on the air content is larger in order of MS, PS and NS. The use of LPC exhibited lower strength development at early age than OPC, whereas after 91days, similar level of compressive strength is achieved regardless of cement type. Compressive strength of concrete is not affected by SP type. For the effect of mixture proportion and materials on drying and autogenous shrinkage, an increase in W/B results in reduction of drying shrinkage and an decrease in water content leads to reduce drying shrinkage. Autogenous shrinkage is not observed until 49 days with the concrete mixture with $35\%$ of W/B and $145 kg/m^3$ of water content. This is due to the combination effects of expansion admixture and shrinkage reducing admixture, which causes an offset of autogenous shrinkage. The use of LPC results in a reduction in autogenous shrinkage compared with OPC. SP type has little influence on the autogenous shrinkage. It is found from the results that mixture proportioning of high performance concrete incorporating fly ash, silica fume, expansion admixture and shrinkage reducing admixture is need to focus on the increase in W/B and the reduction in water content and the use of LPC and MS is also required to use to secure the stability against shrinkage properties.

• Journal of the Korea Institute of Building Construction
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• v.9 no.5
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• pp.63-70
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• 2009

This study is part of an ongoing research project on the development of a sound-absorbing lightweight foamed concrete manufactured by a hydro-thermal reaction between silica and calcium. As the silica source, pulverized bottom ash was used, and as several cementitious powders of ordinary portland cement, alumina cement and calcium hydroxide were used. Manufacture of foamed concrete was accomplished using the pre-foaming method to make a continuous pore system, which is the method of making the foam by using a foaming agent, then making the slurry by mixing the foam, water, and powders. The experiment factors are W/B, foam agent dilution ratio, and foam ratio, and test items are compressive strength, dry density, void ratio, and absorption rate, as evaluated by NRC. The experiment results showed that the sound absorption of lightweight foamed concrete satisfied NRC requirements for the absorbing materials in most of the experiments. It is thus concluded that foam ratio was the most dominant factor, and significantly affected all properties of lightweight foamed concrete in this study. W/B rarely affected total void ratio and continuous void ratio as well as compressive strength, and dry density and foam agent dilution ratio also had little effect onalmost all properties. The analysis of the correlation between NRC, absorption time, continuous void ratio, and absorption time showed that the interrelationship of the continuous void ratio was high.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.5
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• pp.293-300
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• 2021

In this study, the microstructure and thermal conductivity correlation was investigated for concrete materials used in concrete thermal energy storage (CTES) among real-time energy storage devices. Graphite was used as admixture to increase the thermal conductivity performance of the CTES. Concrete specimens of 10% and 15% substitution of cement by mass with graphite, as well as ordinary portland cement (OPC) specimens were prepared, and the microstructural changes and effects on thermal conductivity were analyzed. Porosities of OPC and concrete with graphite were compared using micro-CT, and the microstructural characteristics were quantified using probability functions. Three-dimensional virtual specimens were constructed for thermal analysis, to confirm the effect of microstructural characteristics on thermal conductivity, and the results were compared with the measured conductivity obtained using the hot-disc method. To identify thermal conductivity of graphite for thermal analysis, solid phase conductivity was inversely determined based on simulation and experimental results, and the effect of graphite on thermal conductivity was analyzed.

• Journal of Ceramic Processing Research
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• v.19 no.5
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• pp.378-382
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• 2018

It is a known fact that the cement production is responsible for almost 5% of total worldwide $CO_2$ emission, the primary factor affecting global warming. Geopolymers are valuable as ordinary Portland cement (OPC) substitutes because geopolymers release 80% less $CO_2$ than OPC and have mechanical properties sufficiently similar to those of OPC. Therefore, geopolymers have proven attractive to eco-friendly construction industries. Geopolymers can be fabricated from aluminum silicate materials with alkali activators such as fly ash, blast furnace slag, and so on. Integrated gasification combined cycle (IGCC) slag has been used for fabricating geopolymers. In general, IGCC slag geopolymers are fabricated with finely ground and sieved (<128 mesh) IGCC slag. The grinding process of as-received IGCC slag is one of the main costs in geopolymer production. Therefore, the idea of using as-received IGCC slag (before grinding the IGCC slag) as aggregates in the geopolymer matrix was introduced to reduce production cost as well as to enhance compressive strength. As-received IGCC slag (0, 10, 20, 30, 40 wt%) was added in the geopolymer mixing process and the mixtures were compared. The compressive strength of geopolymers with an addition of 10 wt% as-received IGCC slag increased by 19.84% compared to that with no additional as-received IGCC slag and reached up to 41.20 MPa. The enhancement of compressive strength is caused by as-received IGCC slag acting as aggregates in the geopolymer matrix like aggregates in concrete. The density of geopolymers slightly increased to $2.1-2.2g/cm^3$ with increasing slag addition. Therefore, it is concluded that a small addition of as-received IGCC slag into the geopolymer can increase compressive strength and decrease the total cost of the product. Moreover, the direct use of as-received IGCC slag may contribute to environment protection by reducing process time and $CO_2$ emission.

• Journal of the Korea Institute of Building Construction
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• v.15 no.3
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• pp.281-289
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• 2015

Carbonation of concrete causes reduction of pH and subsequently causes steel corrosion for reinforced concrete structure. However, for plain concrete structure or PC product, it can lead to a decrease in porosity, high density, improvement of concrete, shrinkage-compensation. Recently, based on this theory, research of $CO_2$ curing effect has been performed, but it was mainly focused on its effects on compressive strength using only ordinary portland cement. Researches on $CO_2$ curing effect for concrete containing $CO_2$ reactive materials such as ${\gamma}-C_2S$, MgO haven't been investigated. Therefore, this study has performed experiments under water-binder ratio 40%, and the replacement ratios of ${\gamma}-C_2S$ and MgO were 90%. Micro-chemical analysis, measurement of compressive strength according to admixtures and $CO_2$ curing were investigated. Results from this study revealed that higher strength was measured in case of $CO_2$ curing compared with none $CO_2$ curing for plain specimen indicating difference between 1.08 and 1.26 times, in case of ${\gamma}-C_2S$ 90, MgO 90 specimen, incorporating high volume replaced as much as 90%, it was proven that when applying $CO_2$ curing, higher strength which has difference between 14.56 and 45.7 times, and between 6.5 and 10.37 times was measured for each specimen compared to none $CO_2$ curing. Through micro-chemical analysis, massive amount of $CaCO_3$, $MgCO_3$ and decrease of porosity were appeared.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.4A
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• pp.565-571
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• 2008

Recently, the evaluation technique using NDT (Nondestructive Technique : NDT) is widely utilized because it makes little damage on RC (Reinforced Concrete : RC) structures. The techniques using electromagnetic properties (EM properties) are also attempted for the evaluation of the performance of concrete which is nonmetallic. For the economic manufacturing of concrete material, sea-sand is often used as aggregate, however, chloride ion in concrete has direct effects on steel corrosion and EM properties. In this study, OPC mortar specimens with 5 different chloride amount (0.0, 0.6, 1.2, 2.4, and $3.6kg/m^3$) and 3 different water-cement ratios (45%, 55%, and 65%) are prepared in order to investigate the EM properties corresponding to concrete properties. The EM properties of conductivity and dielectric constant are measured in the frequency range over 0.2~20 GHz. To facilitate the comparison of EM properties with chloride content, average values are taken respectively for the conductivity and dielectric constant measured over the 5~20 GHz frequency range. According to the results of this experiment, dielectric constant and conductivity are increased with lower W/C ratio and larger amount of chloride content.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.349-356
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• 2016

This report presents the results of an investigation on the early strength development of pastes high volume slag cement (HVSC) activated with different concentration of sodium carbonate ($Na_2CO_3$). The ordinary Portland cement (OPC) was replaced by ground granulated blast furnace slag (GGBFS) from 50% to 90% by mass, the dry powders were blended before the paste mixing. The $Na_2CO_3$ was added at 0, 2, 4, 6, 8 and 10% by total binder (OPC+GGBFS) weight. A constant water-to-binder ratio (w/b)=0.45 was used for all mixtures. The research carried out the compressive strength, ultrasonic pulse velocity (UPV), water absorption and X-ray diffraction (XRD) analysis at early ages(1 and 3 days). The incase of mixtures, V5 (50% OPC + 50% GGBFS), V6 (40% OPC + 60% GGBFS) and V7 (30% OPC + 70% GGBFS) specimens with 6% $Na_2CO_3$, V8 (20% OPC + 80% GGBFS) and V9 (10% OPC + 90% GGBFS) specimens with 10% $Na_2CO_3$ showed the maximum strength development. The results of UPV and water absorption showed a similar tendency to the strength properties. The XRD analysis of specimens indicated that the hydration products formed in samples were CSH and calcite phases.