• Magazine of the Korea Concrete Institute
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• v.9 no.3
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• pp.149-156
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• 1997

In order to improve compressive strength of cement mortar, powder admixture(FAS) was mmufactured by mixing fly ash. Il-anhydite and silica hume, and superplasticizer was used for the control of fluidity reduction with the use of this admixture. Cement was substituted by 10, 20wt% of FAS respectively. At W/S = 0.40, the fluidity of' cement paste substituted by PAS was decreased. NSF and NT-2 were very effective fbr the control of fluidity reduction. As the particle size of U -anhydrite was fine, the fluidity of cement mortar was increased. The fluidity reduction of cement mortar substituted by 10wt% of FAS was controlled. The compressive strength of cement mortar substituted by 10wt% of FAS showed higher. value than that of 20wt%, expecially specimen(C1) substituted by 10wt% of $\gamma$ had the highest compressive strength value.

• International Journal of Highway Engineering
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• v.15 no.2
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• pp.113-119
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• 2013

PURPOSES : The objectives of this study are to develop the eco-friendly pavement material using polyurethane binder and evaluate mechanical properties of the developed binder and concrete. METHODS : The bending beam test was conducted to select the sample candidates of polyurethane binder based on the bending strength. The characteristics of viscosity, curing time, and temperature change of sample binder was examined on different temperature conditions. The mechanical properties of polyurethane binder was estimated using the dynamic modulus testing. The indirect tensile strength test was conducted on polyurethane binder concrete with different gradation and binder content for evaluating the mechanical properties of concretes. RESULTS : Based on the beading beam test, four different binder samples were prepared for estimate the mechanical properties. The viscosity of polyurethane binder tends to increase with increase of liquid temperature and the hardening phenomenon begins 10 to 15 minutes at room temperature after mixing the resin and hardener. It is observed that the dynamic modulus of binder increases as loading frequency increases and change of modulus is found to be the highest in the PU-2I binder type. The PU-2I binder concretes shows the largest value of indirect tensile strength and indirect tensile energy. CONCLUSIONS : The use of polyurethane binder as pavement materials is capable of increasing the pavement performance and reducing the detrimental environmental effect during the highway construction.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.294-300
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• 2001

The effectiveness of bottom ash on the mechanical and physical properties of Controlled Low-Strength Material(CLSM) is investigated in this study, CLSM is defined by the ACI Committee 229 as a cementitious material that is in a flowable state at the time of placement and having a specified compressive strength of 83 kgf/$\textrm{cm}^2$ or less at the age of 28 days. This study was undertaken on the use of bottom ash as a fine aggregate in CLSM. Four different levels of bottom ash with fly ash contents, 25%, 50 %, 75%, 100%, are investigated. Laboratory test results conclude that inclusion of bottom ash increases the demand for mixing water in obtaining the required flow. However, the sand was reduced because it was adjusted to maintain a constant total volume. Miかe proportions were developed for producing CLSM at three 28-day strength levels: removal with tools (less than 7 kgf/$\textrm{cm}^2$), mechanical means (less than 20 kgf/$\textrm{cm}^2$), and power equipment (less than 83 kgf/cm\`). The physical and mechanical properties supports the concept that by-product bottom ash can be successfully used in CLSM.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.549-555
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• 2002

Tensile strength of CFRP (Carbon Fiber Reinforced Polymer) is approximately 10 times higher than that of the steel reinforcement, but the design strength of CFRP is normally limited by unpredictable bond failure between RC and CFRP. Many researches concerned with bond behavior between RC and CFRP have been carried out to prevent the bond failure of RC beam strengthened by CFRP, but the national design code for design bond strength of CFRP has not been constructed. In this study, three beam specimens strengthened by CFRP under the parameters of bonded length were tested to derive the design bond strength of CFRP for the RC flexural members. Each bonded length was calculated based on the bond strength of JCI and CFRP manufacturing company. Also, another two beam specimens strengthened by CFRP were tested to inspect the construction environment effects such as mixing error of epoxy resin, and the amount of epoxy primer. From the test results, it is concluded that the maximum design bond strength of CFRP to RC flexural member is considered to be $\tau$a =8 kgf/㎠.

• Magazine of the Korea Concrete Institute
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• v.5 no.4
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• pp.156-166
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• 1993

The results of an experimental study on the manufacture and the mechanical properties of steel fiber reinforced polyester resin composites utilizing industrial waste products(fly ash) are presented in this paper. The composites using steel fiber, fly ash, unsaturated polyester resin, styrene monomer, catalyst (cobalt octate) and accelerator(methyl ethyl ketone peroxide), fine and coarse aggreates were prepared using various mixing conditions. As the test results show. the mechanical and physical properties, such as the compressive, tensile and flexural strengths, and the setting shrinkage of fly ash$\cdot$polyester resin composites were improved considerably by increasing the fly ash-binder ratio. And the workability of steel fiber reinforced fly ash$\cdot$polyester resin composites was reduced with increasing the fly ash-binder ratio and steel fiber content. Also, the compressive, flexural strength and toughness of the composites were remarkably increased by increasing steel fiber content.

• Journal of the Korea Concrete Institute
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• v.15 no.3
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• pp.386-391
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• 2003

Ready mixed mortar has been originated from lime industry of Germany and is being used widely in the world at present. In recent years, the studies of mortar with new faculty have been progressed. In this study, we used elvan instead of using sand in order to make cement mortar and investigated characteristics of elvan and mortar that used elvan. The major compositions of elvan were $SiO_2$ and $Al_2O_3$. The crystal phases of elvan were composed of quartz and sillimanite. Elvan had a lot of pore and absorption ratio was 2.09%. The compressive strength of mortar that used elvan satisfied korean industrial standards under 1:3 (mixing ratio) and water retentivity increased according to increase of elvan contents. Far infrared radiation and deodorization ratio increased and thermal conductivity decreased according to increase of elvan contents.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.677-680
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• 2008

The surface of particles was energetically modified by inter-grinding OPC and BFS in vibration mill for improvement of the early strength and low-heat evolution of concretes. BFS was pre-grinding in ball-mill to 2535(BS2) and 3245 $cm^2/g$(BS3), in blaine surface area. The inter-grinding time in vibration mill was changed from 10 minutes to 30 minutes. And Mixing ration of BFS to OPC was changed in 60, 70, 80%. After inter-grinding, the change of specific surface area, particle size distribution, hydration heat of cement and compressive strength of mortar were measured. As the result of comparison test with LHC, it was found that the mixture and inter-grinding time satisfying the value of over 100% of compressive strength for 7 days and under 170J/g of heat of hydration for 72 hours. and it was confirmed that the possibility of low heat slag cement utilizing blast furnace slag(BS2, BS3) with the low fineness in high volumes.

• Magazine of the Korea Concrete Institute
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• v.6 no.4
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• pp.141-152
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• 1994

The results of an experimental study on the development and the evaluation of lightweight and high strength composites utilizing by-products and calcium silicates for construction materials are presented in this paper. The composites using early strength portland cement, by-Products( f1y ash, silica fume), silica powder, quick lime, gypsum, A1 powder and fibers(PAN-derived CF, alkali-resistance GF) were prepared using various mixing conditions. As the test results show, PAN-derived CF and alkali-resistance GF were suitable for rein-forcing fiber of the composites. And the mechanical properties,such as compressive tensile flexural strength, and toughness of Lt. Wt. fiber reinforced calcium silicates cement comp-osites were improved by increasing the fly ash and silica fume contents, and fiber contents, especially by increasing fiber contents the toughness of the composites were remarkably in-creased. Also, compressive tensile flexural strength,and toughness of the composites rein-forcing PAN-derived CF were higher than those of the composites reinforcing alkali-resistance GF..

• Magazine of the Korea Concrete Institute
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• v.3 no.3
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• pp.101-110
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• 1991

Results of an experimental study on the manufacture, the mechanical properties and watertightness of pitch - based carbon fiber reinforced fly ash. cement composites are presented in this paper. The carbon fiber reinforced fly ash. cement composites using early strength cement silica powder and a small amount of stylene butadiene rubber latex are prepared with carbon fiber, foaming agents and mixing conditions. As a result, the mechanical and physical properties such as compressive , tensile and flexural strengths, watertightness and drying shrinkage of lightweight carbon fiber reinforced fly ash cement composites are Improved by using a samll amount of stylene butadiene rubber latex. Also, the manufacturing pnx:ess technology of carbon fiber reinforced fly ash . cement composItes is developed. The development and applications of precast products of lightweight carbon fiber remforced cement composites are expected in the near future.

• Journal of the Korea Institute of Building Construction
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• v.18 no.1
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• pp.51-57
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• 2018

The objective of the present study is to examine the feasibility on the development of high-insulation concrete using aerogels with hydrophilic surface treatment. To prevent the segregation and enhance the dispersibility of agerogels in the cement pastes, the substrate of aerogels was modified to be hydrophobic property using surfactant. The modified aerogels were added from 0% to 100% of the cement volume at the interval of 25% under the constant cement content. Some cement pastes showed segregation phenomenon and flocculation of aerogels during mixing phase. The addition of aerogels decreased the compressive strength of cement pastes but enhanced the thermal conductivity. The thermal conductivity of pastes with 100% aerogels was lower by 43% when compared with that measured in the conventional paste. To improve the compressive strength and insulation capacity of concrete containing aerogels, a reliable surface treatment method of aerogels needs to be further investigated.