• Cement
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• s.168
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• pp.69-74
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• 2005

서울시, 자연녹지에 레미콘공장 허용(2005.7.15)/ 매출 다각화 나섰다, 시멘트업계 건자재 증대, 신사업 진출(2005.7.20)/ "직원과 함께 땀흘린다" 라파즈 그룹 CEO 현장 경영(2005.7.25)/ 한일, "레미탈, 전국권 시멘트로 육성"(2005.7.27)/ 중국산 저질건자재 활개, 비규격 철근 · 시멘트, 국산으로 둔갑/ 중국, 상반기 시멘트 생산량 7.4% 증가(2005.8.2)/ 2010년 일본 건설투자, 51조엔(2005.8.16)/ 건교부, 건설폐기물 재활용 촉진(2005.8.25)/ 시멘트업계 '첨단경영 시대' 성신양회 · 한일 등 정보인프라 시스템 구축(2005.8.31)/ 8.31 부동산종합대책 발표(2005.8.31)/ 동양, 고온가스 재활용 일석이조(2005.9.1)/ 쌍용, 11월 워크아웃 졸업(2005.9.2)/ 일본, 시멘트 수요 호조세(2005.9.12)/ 골재 공급물량 넘친다(2005.9.19)/ 레미콘 공장은 '늘고', 수요는 '줄어'(2005.9.20)

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.6 s.58
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• pp.135-147
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• 2009

In order to develop the ultra high strength concrete over 400Mpa at 28 day, Low-heat portland cement, ferro-silicon, silica-fume and steel fiber were mixed and tested under the special autoclave curing conditions. Considering the influence of Ultra high strength concrete. normal concrete is used as a comparison with low water-cement ratio possible Low-heat portland cement. Additionally, as a substitution of aggregates, we analyzed the compressive strength of Ferro Silicon by making the states of mixed and curing conditions differently. In addition, SEM films testified the development of C-S-H hydrates of Type III & Type IV, and tobermolite, zonolite due to the high temperature, high pressure of autoclave curing. Fineness of aggregate, filler and reactive materials in concrete caused 420Mpa compressive strength at 28day successfully.

• 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.

• Journal of the Korean Geotechnical Society
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• v.26 no.1
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• pp.75-83
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• 2010

Controlled low strength material (CLSM) is a flowable mixture and does not need to be compacted. It is produced by mixing portland cement, fly ash, fine aggregates, water and chemical admixtures. Sand is the most commonly used fine aggregates in the conventional CLSM, but it is getting more and more difficult to obtain sand in Korea. In this study, the characteristics of unconfined compressive strength, flow and applicability of a new CLSM that is produced by mixing of pond ash, fly ash, water, cement are examined. An unconfined compressive strength satisfies the standard unconfined compressive strength (0.5~1.0 MPa) were obtained when the mixture ratio of pond ash and fly ash is 30:70~70:30, cement ratio is 3.0~5.0%, and water content is 31~34%. The results of flow test indicate that the mixture ratio of pond ash and fly ash which satisfy the standard How value (0.2 m) is 30:70~70:30.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.329-340
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• 2016

Increase in demotion and repair works on buildings in the construction market generates a large amount of construction waste. Recycling of construction waste is important for saving of resources, preservation of environment and constant advance of the construction industry. Accordingly, the environmental and economic value of recycled aggregate, which is produced after waste concrete is crushed, is increasingly highlighted. It is generally known that compared to concrete made of ordinary aggregate, concrete made of recycled aggregate has low quality, and the low quality is dependent on the amount of the bonding heterogeneous (cement paste and mortar) as well as the amount of the pores within the bonding heterogeneous. Reports on carbonation mechanism shows that the pores of cement-based materials are filled up by the progress of carbonation. Therefore, this study aims at an estimation of the period for optimum carbonation reforming appropriate for the thickness of the bonding heterogeneous of recycled aggregate, based on carbonation mechanism, with a view to improving the product quality by means of filling up the pores of the bonding heterogeneous of recycled aggregate. This study drew the carbonation depth according to the passage of age by calculating the bonding ratio and bonding thickness of the bonding heterogeneous as against the particle size distribution of recycled aggregate as well as by chemical quantitative analysis according to the age of accelerated carbonation of mock-up samples imitating bonding heterogeneous. Based on the correlation between the age of accelerated carbonation and carbonation depth, this study also proposed the estimated period of carbonation reforming of recycled aggregate appropriate for the thickness of the bonding heterogeneous.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.3
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• pp.93-100
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• 2005

The purpose of this study is to investigate the physical properties of porous concrete according to the aggregate shape and size which is produced by con crusher and impact crusher. For this purpose, the selected test variables were the aggregate size and shape, the ratio of water to cement and the ratio of paste to aggregate. The results of this study showed that its economic performance and physical properties were improved using the aggregate made by impact crusher. The coefficient of permeability and compressive strength of porous concrete had a close correlationship with the void ratio, and it was suggested as a function of void ratio.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.660-667
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• 2002

The effects of polymer-cement ratio and antifoamer content on the durability of ultrarapid-hardening polymer-modified mortars using redispersible polymer powder are examined. As a result, regardless of the antifoamer content, the setting time of the ultrarapid-hardening polymer-modified mortars using redispersible polymer powder tend to delay with increasing polymer-cement ratio. The water absorption and chloride ion penetration depth of the ultrarapid-hardening polymer-modified mortars using redispersible polymer powder decrease with increasing polymer-cement ratio and antifoamer content. The resistance of freezing and thawing and chemicals improvement is attributed to the improved bond between cement hydrates and aggregates because of the incorporation of redispersible polymer powder

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.4C
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• pp.265-273
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• 2006

This study aims at evaluation of the fire resistance performance of cementitious materials for fire protection of tunnel. For this purpose, the research procedure was divided into three parts. First, base mix proportion with different material type were determined by fire test. Second, the fire test of cementitious materials for fire resistance were performed on base mix proportions to evaluated their performance. Third, the performance of cementitious materials for fire resistance compare to the target value and existing commercial products. If the performance of developed cemetitious materials for fire resistance were satisfied the target value, this studies were stopped. But, this research return to first process if the performance of cementitious materials for fire resistance are not satisfied the target value. As a result of this study, the spalling did not happen for develop and existing commercial product. Also, developed cementitious materials for fire resistance are shown with excellent compressive strength, flexural strength, and bond strength, because it used a height density aggregate. And developed cementitious materials has sufficient resistance for fire.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.1
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• pp.35-44
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• 2015

Two main parameters were examined such as CSA content and polymer-binder ratio to find effects on the strength, water absorption, chloride ion penetration depth, carbonation depth, length change and chemical resistance of polymer-modified mortar with CSA and EVA polymer powder (EVAPP). As results, compressive, flexural, tensile, adhesive strengths, and length change of the polymer-modified mortar with CSA and EVAPP increases with increasing CSA content and polymer-binder ratio, although the water absorption, chloride ion penetration depth, and carbonation depth decrease with increasing polymer-binder ratio and CSA content, and also the chemical resistance decreases. Such strength and durability development is attributed to the high tensile strength of EVA polymer and the improved bond between cement hydrates and aggregates because of the addition of EVAPP and CSA.

• Journal of the Korea Concrete Institute
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• v.20 no.5
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• pp.557-563
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• 2008

Recently, the amount of disposed construction materials like demolished concrete is growing fast and the shortage of natural concrete aggregate is becoming serious. Therefore, recycling of aggregate extracted from the demolished concrete is getting important and use of the recycled aggregate for concrete has been seriously considered. However, the use of the recycled aggregate even for low performance concrete is very limited because recycled aggregate which contains large amount of old mortar has very low quality. Therefore, removing the paste sticked to the recycled aggregate is very important in the manufacturing of high quality recycled aggregate. We have studied a series of research according to complex crushing method, which is removed the ingredient of cement paste from recycled fine aggregate using both the low speed wet abrasion crusher as mechanical process and the acid treatment as chemical processes. This paper is to analyze the quality of the recycled fine aggregate produced by those complex method and investigate optimum manufacturing condition for recycled fine aggregate by the design of experiments. The experimental parameters considered are water ratio, coase aggregate ratio, and abrasion time. As a result, data concerning the properties of recycled sand were obtained. It was found that high quality recycled fine aggregate could be to obtain at the condition of the fifteen minute of abrasion-crusher time and the over 1.0 of recycled coarse aggregate ratio.