• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.145-146
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• 2015

When using non KS aggregate muck pile in general, compared to when using KS aggregate, when obtaining an identical slump a high unit quantity of water was confirmed, and when designing the concrete mix the compressive strength of concrete decreased due to an increase in W/B. Therefore because the use of non KS aggregate decreases the liquidity, strength and durability etc. qualities of concrete from an overall performance point of view, there is a need for the used of KS aggregate and when using aggregate that does not adhere to KS standards, it is determined there is a need for appropriate concrete mix design and care.

• Magazine of the Korea Concrete Institute
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• v.6 no.5
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• pp.149-157
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• 1994

보통 포틀랜드 시멘트와 수용성 고분자 물질인 hydroxy propyl methyl cellulose(HPMC), 미세골재 및 혼화재료를 사용하여 W/C=0.1이 되도록 물을 첨가하고 twin roll mill로 혼합 성형한 후 60일간 양생하여 고강도 시멘트 경화체를 제조하였다. 이 경화체에 대한 휨강도 및 파괴인성을 검토하였다. SiC 분말 및 백색시멘트를 첨가한 경우 휨강도는 약 100MPa정도, 탄성계수는 80-95GPa의 값을 나타내었다. 실리카흄을 첨가한 경우 휨강도는 80MPa, 탄성계수는 60GPa의 값을 나타내었다.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.55-56
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• 2023

Recently, large and high-rise buildings are increasing, and accordingly, concrete weight reduction is required. Lightweight aggregate concrete can provide economic feasibility and large space, but safety can be reduced due to problems such as low strength and poor durability. Since the development of such low strength of concrete is important in the early construction stage, it is necessary to evaluate the vertical formwork demolding period at the early age. The correlation was analyzed by measuring the compressive strength and ultrasonic pulse velocity. As a result, the ultrasonic pulse rates of normal and lightweight aggregate concrete at the time of 5 MPa expression, which is the time of vertical mold deformation, were 3.07 km/s and 2.77 km/s for W/B 41, and 2.89 km/s and 2.73 km/s for W/B 33.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2023.05a
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• pp.409-410
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• 2023

In this study, the compressive strength and ultrasonic pulse velocity were evaluated according to the elapsed time on concrete mixed with normal and lightweight aggregates at early age. For evaluation in various strength ranges, the design compressive strength was set to 30, 45, and 60MPa and evaluated. As a result of the experiment, the compressive strength of concrete mixed with lightweight aggregates developed 5MPa earlier compared to normal aggregate concrete, and the UPV showed a similar tendency.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.649-656
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• 2006

In this study, powered superplasticizer(PSP) agents to improve the slump loss rate of recycled aggregate concrete were developed. To evaluate the variation of fluidity against elapsed time and the mechanical properties, twenty four specimens whose main variables had the mixing condition of aggregates, such as natural and recycled gravels, and natural and recycled fine aggregates, were tested. The concrete slump with a liquid superplasticizer greatly decreased against the elapsed time and dropped by less than 50% of initial slump after two hours. However the concrete slump with the PSP agents hardly varied until after half an hour and maintained more than 85% of initial slump even after an hour. Also the PSP agents made the compressive, splitting tensile, and flexural strength of concrete increased and the shrinkage strain decreased. Considering the properties improvement of concrete, it can be recommended that optimum mixing amount of the PSP agents should be 5% of the amount of cement.

• International Journal of Highway Engineering
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• v.14 no.1
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• pp.45-53
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• 2012

This study was performed to analyze test results on drying shrinkage for concrete specimens mixed with various constituents in concrete mixes. Test variables are coarse aggregate types(Limestone, Sandstone, Granite, Andesite, Gneiss), fine aggregate types(natural sand, crushed sand) and cement amounts(normal strength, high strength). Epoxy coating of(U&V-H(A,B)) was applied onto the specimen surface to simulate diverse volume surface ratios(22.2, 40, 85.7, 150, 200, 300) with different specimen sizes. The experiments had been executed during 1,014 days at a condition of $20^{\circ}C$ and relative humidity of 60% in environmental chambers. Test results showed that shrinkage strain from the specimen equivalent to real pavement decreased to 39% compared to the standard specimen recommended by KS. Test results also showed that shrinkage strain of the specimen mixed with Limestone was 56~76% of that with Sandstone, thus Limestone mix seems to be suitable to the concrete pavement.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.4
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• pp.270-278
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• 2005

Recycled aggregate concrete has lower strength and durability compared to concrete with natural aggregate. Therefore, metakaolin is used to improve the properties of recycled aggregate concrete. Main components of metakaolin are $SiO_2$ and $Al_2O_3$. and specific surface area is 9 times larger than that of ordinary portland cement. Quality of demolished-recycled aggregate(DRA) satisfies the type 1 of KS F 2573, but quality of source-recycled aggregate(SRA) does not satisfy with the type 2 of KS F 2573. When metakaolin was replaced with 20% of cement, compressive strength of concrete with SRA and DRA develops about 40~64% of control concrete. Water absorption ratio was reduced about 2% by replacing 20% metakaolin and it represents low compared to the natural aggregate concrete without metakaolin. In addition, the resistance to freezing and thawing, of concrete with DRA is indicated to remarkably enhanced due to the contribution of metakaolin. However, when metakaolin is replaced with 20% of cement, relative dynamic modulus of elasticity of concrete with SRA was below 60% at 210 freezing and thawing cycles.

• Resources Recycling
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• v.15 no.2 s.70
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• pp.24-31
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• 2006

The duality of recycled fine aggregate (RS) which was produced at the waste concrete crushing was investigated. The compressive strength, flexural strength and absorption of mortar utilized with RS were examined. It was evaluated on the application of RS as precast concrete aggregate. The density and absorption of RS were $2.31g/cm^3$ and 8.07% respectively, the quality of RS was satisfied with the criterion of KS F 2573 type 2. The maximum 28days compressive strength of mortar mixed with blended cement MRS1, MRS2 and MRS3 were developed with 15.8, 27.4 and 48.7MPa respectively, in condition to curing temperature $40^{\circ}C$ and water-cement ratio 37.5%. When blended cement MRS1 and MRS2 were used, the maximum flexural strength of mortar was developed at curing temperature $40^{\circ}C$ and water-cement ratio 35.0%. When blended cement MRS3 was used, the maximum flexural strength of mortar was developed at curing temperature $40^{\circ}C$ and water-cement ratio 37.5%. The absorption of mortar mixed with blended cement MRS1, MRS2 and MRS3 were indicated the range of $8.3{\sim}7.3%,\;6.5{\sim}8.5%$ and $3.5{\sim}6%$ respectively. Therefore, when the ratio of blended cement and RS is appropriately centre]led, it would be expected that MRS1, MRS2 and MRS3 will be able to apply the variable low strength, medium strength and high strength precaste concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.789-792
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• 2008

Blast furnace slag doesn't have self-hydraulicity and it needs stimulants such as alkali to hydrate. Therefore using recycled aggregates erupted calcium hydroxides and blast furnace slag acquiring alkali stimulate could make a complementarily use of a recycling architectural material possible. In this study, we have discussed about characters of blast furnace slag and recycled aggregate firstly, and make recycled aggregate mortar and concrete using blast furnace slag for the experiment. The experiment is about mortar and concrete using recycled aggregate as a substitutional material of blast furnace slag. In this experiment, I replace blast furnace slag and aggregate with recycled aggregate. Conclusions through the test results analysis are as follows. And then, we added field experiment using concrete with composited materials.

• Economic and Environmental Geology
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• v.37 no.5
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• pp.555-568
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• 2004

The demand of aggregate resources in Korea has been increased with a rapid economic growth since the 1980s. About 25% of the total aggregate production is derived from riverine aggregates, 20% to 25% from marine sands, 40% to 45% from crushed aggregate and the rest 5% to 15% from old fluvial deposits. The abundance of crushed coarse aggregates varies in the uniform distribution of country, but in general it can be concentrated in the most densely populated areas, five main cities. Typical rock types of the Korean crushed stones are classified as plutonic rocks of 27%, metamorphic rocks of 32%, sedimentary rocks and volcanic rocks of 18%, respectively. The most abundant coarse aggregate used in the country is obtained from granite (25% of total) and subordinately gneiss (20%), sandstone (10%) and andesite (10%). Although rock types using as dimension stone are only fifteen, those as aggregate amount up to twenty nine rocks. These rocks consist of plutonic rocks such as granite, syenite, diorite, aplite, porphyry, felsite. dike and volcanic rocks such as rhyolite, andesite, trachyte, basalt, tuff, volcanic breccia and metamorphic rocks such as gneiss, schist, phyllite, slate, meld-sandstone, quartzite, hornfels, calc-silicate rock, amphibolite. And sandstone, shale, mudstone, conglomerate, limestone, breccia, chert are main aggregate sources in tile sedimentary rocks. The abundance of plutonic rocks is the highest in Chungcheongbuk-do, and decreases as the order of Jeollabuk-do, Gangwon-do and Gyeonggi-do. In Jeollanam-do, volcanic aggregates occupy above 50%, on the contrary sedimentary aggregates are above 50% in Gyeongsangnam-do.