• Journal of the Korea Concrete Institute
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• v.24 no.1
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• pp.37-44
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• 2012

Recently, due to developments in construction technology, the use of high-performance concrete became popular. High-performance concrete when compared to the ordinary concrete can better satisfy required performances by using mineral admixture and superplasticizer. Various studies on the effect of admixture materials on the quality of high-performance concrete have been reported. But there exist limited number of reported results on the effect of cement qualities, which is the most important constituent material in concrete. Therefore, in this study, the relationship between the quality of cement and the flowability of high flowing concrete is investigated. Qualities of domestically produced cement were identified, and then the influence of the qualities of cement on the flowability of high flowing concrete is evaluated. The result showed that the dosage of required superplasticizer was dependent on cement fineness, to brain, free-CaO, and interstitial phase, which all trigger initial hydration process of cement. Particularly, the results showed that fineness of cement has a high impact on the dosage of the superplasticizer. For strength property of concrete, the dosage of superplasticizer had a significant effect on the early age strength, but had negligible effect in the long term strength.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.4
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• pp.113-119
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• 2019

Many researches on alternative materials as construction materials is continuing by recycling industrial byproducts due to shortage of sitereclamation and natural aggregates. In this paper, engineering properties in early-aged OPC (Ordinary Portland Cement) and GGBFS (Ground Granulated Blast Furnace Slag) concrete are evaluated with EOS aggregate replacement. The related experiments were carried out with 0.6 of water to binder ratio, three levels of EOS replacement ratios (0%, 30% and 50%) for fine aggregate, and two levels of cement replacement with GGBFS (0% and 40%). Several tests such as slump air content, and unit mass measurement are performed for fresh concrete, and compressive strength and diffusion coefficient referred to NT BUILD 492 method are measured for hardened concrete. Through the tests, it was evaluated that the compressive strength in concrete with EOS aggregate increased to 3 days and 7 days but slightly decreased at the age of 28 days. In the accelerated chloride penetration test, GGBFS concrete showed reduced diffusion coefficients by 60 - 67% compared with OPC concrete. The lowest chloride diffusion coefficient was evaluated in the 50% replacement with EOS aggregate, which showed an applicability of EOS aggregate to concrete production.

• Journal of the Korea Concrete Institute
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• v.14 no.5
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• pp.766-773
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• 2002

The failure phenomenon of overlaid concrete structures, such as surface crack, and peel-off failure, shear bond failure in the end contact zone, was investigated due to humidity changes. To investigate this failure phenomenon, the surface tensile stress, and the shear stress, the vertical tensile stress in the contact zone were analysed using the non-linear stress-strain relationship of material such as strain-hardening- and strain-softening diagrams. Overlay thickness and overlay material were the main variables in the analyses. It is assumed that the initial surface humidity of overlaid concrete structures was 100％ r.H. With a atmospheric humidity of 55％ r.H. and two load cases for drying(LCI), curing and drying(LC2), the stress states of overlaid concrete structures were calculated. The result shows that only fictitious cracks occurred in the overlay surface of CM2O, ECM25, and no shear bond failure occurred in the contact zone without CM2O. The peel-off failure was proved to be the main cause of the damage in the overlaid concrete structures. Only for overlay thickness of 1cm occurred no peel-off failure in the case of drying after a long-term public use(LC1). In the case of curing and drying during overlay work(LC2) occurred the peel-off failure within 1.5days for all the overlaid concrete structures.

• Journal of the Korea Institute of Building Construction
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• v.13 no.3
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• pp.218-226
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• 2013

Of construction materials, cement and steel are the representative material that carbon dioxide. to reduce carbon emissions in the use of these materials The purpose of this study is low heat type blended cement, which is manufactured using a amount of cement than ordinary low heat blended cement. Low heat blended cement, mixing ratio of 10%, was investigated hydration properties and adiabatic temperature of concrete. The study in order to activate the reaction mineral admixture, a separate source of CaO and $SO_3$ areneeded. gypsum and lime, it expected amount of cement, low-carbon low-heat blended cement could reduce the hydration heat concrete than currentlyused low heat blended cement.

• Journal of the Korea Institute of Building Construction
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• v.15 no.1
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• pp.1-7
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• 2015

The objective of this study is to develop a high-performance foamed concrete made with a new mixture proportioning as an alternative of autoclaved lightweight concrete (ALC) block. For the early-strength gain of the foamed concrete under an atmospheric curing condition, the binders and chemical agents were specially contrived as follows: 3% anhydrous gypsum was added to ordinary portland cement (OPC) in which $3CaO{\cdot}SiO_2$ content was controlled to be above 60%; and the content of polyethylene glycol alkylether in a polycarboxylate-based water-reducing agent was modified to be 28%. Using these binders and chemical agents, 11 mixes were prepared with the parameters of W/B ratio (30% to 20% in a interval of 2.5%) and unit binder content ($400kg/m^3$ to $650kg/m^3$ in a interval of $50kg/m^3$). The quality and availability of the mixed foamed concrete were examined according to the minimum requirements specified in the KS for ALC block and existed conventional foamed concrete. The measured properties satisfied the minimum requirement of KS for ALC block and proved that the developed high-performance foamed concrete had considerable potential for practical application.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.91-96
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• 2011

The design, construction and management of underground facilities as infrastructure of nation should be properly carried out. One of reasons for underground facilitie's failure is a non-proper construction of backfill materials. This is common for circular underground pipes. A non-proper compaction is the cause of settlement and decrease of performance of underground facilities. The use of controlled low strength materials is an alternative to reduce the couple of failure problems. The flowability, self-cementation, and non-compaction are the major advantages to use the controlled low strength materials. In this research, couple of recycled materials, such as in-situ soil, water-treatment sludge, and crumb rubbers, were adopted. The basic properties of each materials were determined according to KS or ASTM. Also, couple of laboratory tests were carried out to get the design parameters for geotechnical and roadway area.

• Journal of the Korean Recycled Construction Resources Institute
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• v.9 no.2
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• pp.117-126
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• 2021

An experimental study was carried out to investigate the applicability of cement-based materials for green soil which is a soil for promoting plant growth. The results show that the shear strength of the green soil mixed with gypsum cement (No.3) was low, but the hardness (23.6mm) and pH value (7.4) was most suitable for the vegetation environment. In addition, the initial vegetation germination of green soil, which improved performance by adding a moisturizer, was slower than that of general green soil, and the conductivity value tended to be slightly higher. On the other hand, the slope adhesion of advanced green soil was high, and it was found that the plant growth rate and the regeneration capacity were superior after time passed.

• Proceedings of the Korean Society of Dyers and Finishers Conference
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• 2012.03a
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• pp.64-64
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• 2012

아라미드는 일반적인 유기섬유와는 다른 우수한 역학적 성질을 바탕으로 보호의류 중에서 방탄방호 및 방검보호 의류에 사용되는 고부가 소재이다. 현재까지 ATY기계에서 사의 구조와 물성에 큰 영향을 미치는 Nozzle의 구조에 대한 연구결과는 많이 발표되어왔다. 그러나 최근 들어 소방방화방 검용 보호의류에 많이 사용되는 아라미드사에 ATY 공정 중에서 Nozzle의 직경이 ATY사의 물성에 어떤 영향을 미치는가에 대한 연구는 발표된 바가 없다. 따라서 본 연구에서는 Para-aramid/Nylon hybrid사를 이용하여 ATY로 제조할 경우, 표면에 생기는 loop로 인하여 타 소재와 접착시, 접착제 담지 성능이 향상되어 접착력이 상승되는 반면 아라미드 Hybrid사의 역학물성은 ATY가 가공되기 전의 물성보다 저하되는 약점을 가지고 있다. 따라서 본 연구에서는 ATY 제조공정에서 Nozzle의 직경을 달리할 때 Aramid/Nylon Hybrid ATY사의 물성변화를 분석함으로서 방화복과 방검용 보호의류에 적합한 아라미드 ATY사를 개발하고자 한다. 본 연구에서는 ATY 제조공정 중 다른 공정조건은 동일하게 하고 Nozzle의 직경을 0.6, 0.75, 1, 1.2mm로 변경하여 4가지 시료를 준비하고 물성분석을 위하여 제조된 시료의 강신도, 초기탄성률을 각각 측정하여 인장특성을 확인하였으며, 건열수축률과 습열수축률을 측정하여 시료의 열 수축률을 측정 분석하였다. 표면의 루프 발현 정도를 보기위하여 형태 불안정성을 측정 평가하였으며 영상현미경시스템을 사용하여 표면특성을 측정 평가하여 다음과 같은 결론을 얻었다. Nozzle의 직경이 증가함에 따라 절단강도는 30% 감소하였고 초기탄성률은 3배 가까이 감소하였다. 그리고 절단신도는 2배정도 증가하는 경향을 나타내었다. 또한 Nozzle의 직경이 증가함에 따라 ATY hybrid사의 건 습열수축률이 증가하다가 직경이 1.2mm일 때 감소하는 경향을 나타내었고 직경 변화에 따라 4~6%의 열 수축률의 분포를 보였다. Para-aramid/Nylon hybrid사의 형태불안정성은 0.3~0.5%를 분포를 나타내었고 Nozzle의 직경이 0.6, 1mm일 때 상대적으로 낮은 ATY의 불안정성이 확인되었다. Nozzle의 직경이 감소할수록 loop의 엉킴이 적으며 flat하였으며 직경이 1.2mm일 때 가장 조밀하고 표면에 loop가 많이 형성된 것을 확인하였다.

• Polymer(Korea)
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• v.36 no.6
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• pp.789-794
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• 2012

Poly(lactic-co-glycolic acid) (PLGA) has been most widely used due to its advantages such as good biodegradability, controllable rate of degradation and metabolizable degradation products. We manufactured composite scaffolds of PLGA scaffold penetrated DBP gel (PLGA/DBP gel) by a simple method, solvent casting/salt leaching prep of PLGA scaffolds and subsequent soaking in DBP gel. Chondrocytes were seeded on the PLGA/DBP gel. The mechanical strength of scaffold, histology (H&E, Safranin-O, Alcian-blue) and immunohistochemistry (collagen type I, collagen type II) were performed to elucidate in vitro and in vivo cartilage-specific extracellular matrices. It was better to keep the characteristic of chondrocytes in the PLGA/DBP gel scaffolds than that PLGA scaffolds. This study suggests that PLGA/DBP gel scaffold may serve as a potential cell delivery vehicle and a structural basis for in vivo tissue engineered cartilage.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.477-484
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• 2004

As a part of durability improvement of concrete-structure, penetrating water repellency of liquid type is applied to concrete surface. Besides, a related standard is made recently, but the standard has been prescribe for initial settlement state of penetrating water repellency of liquid type, to the exclusion of performance variation depending time and outdoor environment factor. For measurement of performance variation, we measured the weight of outdoor exposure specimen every regular intervals and check a measured value against a measured value of different condition specimen. Moreover, after the application of penetrating water repellent, measured a adhesive strength in tension between cement-polymer modified waterproof coatings and surface of specimen. The applied penetrating water repellent is a emulsified silicon type with a deep penetration depth. In view of the results so far achieved, the more a Quantity of application and active solid content does get, the deeper penetrating water repellency of emulsion type Penetrate get longer and supplied moisture increase in quantity, a penetrating water repellency of liquid type penetrates more deep, but a quantity of water absorption increase gradually. Perhaps this result is caused by a reduction of active solid content on concrete surface, because active ingredient is moved into the concrete by dissolution.