• Advances in concrete construction
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• 제5권4호
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• pp.313-330
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• 2017

Geopolymer is a sustainable concrete, replaces traditional cement concrete using alternative sustainable construction materials as binders and alkaline solution as alkaline activator. This paper presents the strength characteristics of geopolymer concrete (GPC) developed with fly ash and GGBS as binders, combined Sodium silicate ($Na_2SiO_3$) and Sodium Hydroxide (NaOH) solution as alkaline activators. The parameters considered in this research work are proportions of fly ash and GGBS (70-30 and 50-50), curing conditions (Outdoor curing and oven curing at $600^{\circ}C$ for 24 hours), two grades of concrete (GPC20 and GPC50). The mechanical properties such as compressive strength, split tensile strength and flexural strength along with durability characteristics were determined. For studying the durability characteristics of geopolymer concrete 5% $H_2SO_4$ solutions was used and the specimens were immersed up to an exposure period of 56 days. The main parameters considered in this study were Acid Mass Loss Factor (AMLF), Acid Strength Loss Factor (ASLF) and products of degradation. The results conclude that GPC with sufficient strength can be developed even under Outdoor curing using fly ash and GGBS combination i.e., without the need for any heat curing.

• Restorative Dentistry and Endodontics
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• 제6권1호
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• pp.123-132
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• 1980

The author conducted a dental survey of a college girl students and compared with that of E college students 10 years ago which based on the same criteria. The items of this survey included the prevalence of dental caries, DMFT and the kinds of restored material. All college students 1,414 were examined in May 1978, with the recommended criteria and method of W.H.O.. Among them, the data of 1,393 were analyzed for this study. The following results were obtained: 1. The average number of present teeth were 28.97${\pm}$1.64. 2. The prevalence of dental caries was 84.92% and D.M.F. index was 15.51. Average D.M.F. teeth were 4.49${\pm}$3.69. 3. The average number of decayed (D) teeth were 2.09${\pm}$2.16. 4.30% of the present decayed teeth was secondary decay, and 2.44% of the decayed teeth was indicated for extraction. 4. The average number of missing(M) teeth were 0.32${\pm}$0.79. It included 8.56% of root fragements. 5. Average number of filled(F) teeth were 2.09${\pm}$3.17. F-ratio of this group was 46.45%. The analysis revealed 50.88% of amalgam alloy, 31.41% of gold inlays, and 1.20%, the least among the filling materials, silicate cement or composite resin. 6. While the prosthodontic treatment, such as crown and bridge has reduced than that of 10 years ago, the fillings and inlays as the conservative means has increased.

• Advances in concrete construction
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• 제10권3호
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• pp.237-245
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• 2020

Past research efforts already established geopolymer as an environment-friendly alternative binder system for ordinary Portland cement (OPC) and recycled aggregate is also one of the promising alternative for natural aggregates. In this study, an effort was made to produce eco-friendly mortar mixes using geopolymer as binder and recycled fine aggregate (RFA) partially and study the resistance ability of these mortar mixes against the aggressive environments. To form the geopolymer binder, 70% fly ash, 30% ground granulated blast furnace slag (GGBS) and alkaline solution comprising of sodium silicate solution and 14M sodium hydroxide solution with a ratio of 1.5 were used. The ratio of alkaline liquid to binder (AL/B) was also considered as 0.4 and 0.6. In order to determine the resistance ability against aggressive environmental conditions, acid attack test, sulphate attack test and rapid chloride permeability test were conducted. Change in mass, change in compressive strength of the specimens after the immersion in acid/sulphate solution for a period of 28, 56, 90 and 120 days has been presented and discussed in this study. Results indicated that the incorporation of RFA leads to the reduction in compressive strength. Even though strength reduction was observed, eco-friendly mortar mixes containing geopolymer as binder and RFA as fine aggregate performed better when it was produced with AL/B ratio of 0.6.

• Computers and Concrete
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• 제20권6호
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• pp.705-710
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• 2017

The effectiveness of mineral additives in suppressing alkali-silica reactivity has been studied in this work. Experimentation has been performed in accordance with the procedures prescribed in ASTM C 1567. In the scope of the investigation, a quarry aggregate which was reactive according to ASTM C 1260 was tested. In the experimental program, prismatic mortar specimens measuring $25{\times}25{\times}285mm$ were produced. Ten sets of production, three specimens for each set, were made. Length changes were measured at the end of 3, 7, 14 and 28 days and then expansions in percentage have been calculated. Fly ash, silica fume, and metakaolin have been used as cement replacement in different ratios for the testing of the alkali-silicate reactivity of the aggregate. In the mixes performed, the replacement ratios were 20%, 40%, and 60% for the fly ash, and 5%, 10%, and 15% for the silica fume, and 5%, 10%, and 15% for the metakaolin. Mixes without mineral additives were also produced for comparison. The beneficial effect in suppressing alkali-silica reactivity is highly noticeable as the replacement ratios of the mineral additives increase regardless of the type of the mineral additive used. Being more concise, the optimum concentrations of using silica fume and metakaolin in mortar in suppressing ASR is 10%, respectively, while it is 20% for fly ash.

• Advances in concrete construction
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• 제7권4호
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• pp.263-275
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• 2019

In the present work, Granulated Blast Furnace Slag (GBFS) and Fly ash (FA) were used as partial replacement of Natural Sand (NS) and Ordinary Portland Cement (OPC) by weight. One control mix, one with GBFS, three with FA and three with GBFS-FA combined mixes were prepared. Replacements were 50% GBFS with NS and 20%, 30% and 40% FA with OPC. Preliminary investigation on development of compressive strength was carried out at 7, 28 and 90 days to ensure sustainability of waste materials in concrete matrix at room temperature. After 90days, thermo-mechanical study was performed on the specimen for a temperature regime of $200^{\circ}-1000^{\circ}C$ followed by furnace cooling. Weight loss, visual inspection along with colour change, residual compressive strength and microstructure analysis were performed to investigate the effect of replacement of GBFS and FA. Although adding waste mineral by-products enhanced the weight loss, their pozzolanicity and formation history at high temperature played a significant role in retaining higher residual compressive strength even up to $800^{\circ}C$. On detail microstructural study, it has been found that addition of FA and GBFS in concrete mix improved the density of concrete by development of extra calcium silicate gel before fire and restricts the development of micro-cracks at high temperature as well. In general, the authors are in favour of combined replacement mix in view of high volume mineral by-products utilization as fire protection.

• Geomechanics and Engineering
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• 제25권1호
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• pp.31-40
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• 2021

Injection grouting is one of the most common ground improvement practice to increase the strength and reduce the hydraulic conductivity of soils. Owing to the environmental concerns of conventional grout materials, such as cement-based or silicate-based materials, bio-inspired biogeotechnical approaches are considered to be new sustainable and environmentally friendly ground improvement methods. Biopolymers, which are excretory products from living organisms, have been shown to significantly reduce the hydraulic conductivity via pore-clogging and increase the strength of soils. To study the practical application of biopolymers for seepage and ground water control, in this study, we explored the injection capabilities of biopolymer-based grout materials in both linear aperture and particulate media (i.e., sand and glassbeads) considering different injection pressures, biopolymer concentrations, and flow channel geometries. The hydraulic conductivity control of a biopolymer-based grout material was evaluated after injection into sandy soil under confined boundary conditions. The results showed that the performance of xanthan gum injection was mainly affected by the injection pressure and pore geometry (e.g., porosity) inside the soil. Additionally, with an increase in the xanthan gum concentration, the injection efficiency diminished while the hydraulic conductivity reduction efficiency enhanced significantly. The results of this study provide the potential capabilities of injection grouting to be performed with biopolymer-based materials for field application.

• Advances in concrete construction
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• 제11권2호
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• pp.127-140
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• 2021

In this study, twenty-five geopolymer (GP) mixes were prepared by varying the alkaline solids to Metakaolin (MK) and sodium silicate to NaOH ratios from 0.1 to 0.5 and 0.2 to 1.0, respectively, thus giving a wide range of molar ratios of silica to alumina, sodium oxide to alumina and water to sodium oxide. The compressive strength of these GP mixes was determined for four curing schemes involving oven curing at 100℃ for 24 h and three ambient curing with the curing ages of 3, 14, and 28 days. The test results revealed that for the manufacture of GP binder for structural applications of strength up to 90 MPa, the molar ratio of silica to alumina should be greater than 2.3, sodium oxide to alumina should be between 0.6 to 1.2, and water to sodium oxide should not exceed 12. The compressive strength of ambient cured GP mortar gets stabilized at 28 days of ambient curing. Experimental findings were also corroborated by GP microstructure analysis. The embodied energy of MK-based GP mortars, especially of high strength, is significantly less than the cement mortar of equivalent strength.

• 콘크리트학회논문집
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• 제18권1호
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• pp.125-132
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• 2006

최근 들어 툭별한 물리적 방법을 사용하지 않고 내구성능이 저하된 콘크리트의 성능을 회복시키는 방법의 일환으로서 콘크리트 표면보호재에 대한 관심이 높아지고 있다. 표면보호는 직접적인 의미로서는 콘크리트 구조물의 표면을 보호하는 것뿐만아니라 다양한 열화요인의 침투를 억제함으로서 내부의 콘크리트 및 철근의 열화를 억제하여 콘크리트 구조물을 보호하게 된다. 이와 같은 표면보호재 중 함침계 표면보호재는 콘크리트 표면층의 공극에 충전 혹은 생성물을 석출시켜 치밀한 층으로 하느 충전계와 콘크리트 표면층의 외부 및 내부표면의 성질을 개선하는 표면계로 분류하는 것이 가능하다. 따라서 본 연구는 규플르오르화염을 주성분으로 하는 표면형 함침계 표면보호제 도포에 의한 콘크리트 표면의 세공구조의 변화 및 중성화, 염해, 화학적 침식 등의 내구성 향상을 실험실증적으로 검토함으로서 콘크리트 구조물의 내구성향상 방안을 제시하고자 한다. 그 결과, 표면보호제를 도포함으로서 모든 물시멘트비에서 도포전과 비교하여 전세공용적이 감소하고 있으며, 특히 50nm이상의 비교적 큰 세공경인 모세관공극의 용적이 감소함으로서 물흡수성, 중성화 저항성, 내황산성, 염소이온침투 저항성 등의 내구성 향상에 기여하는 것으로 나타났으며, 그 효과는 물시멘트비가 클수록 높게 나타났다.

• 한국건설순환자원학회논문집
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• 제5권4호
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• pp.114-121
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• 2010

포틀랜드 시멘트 제조 시 다량의 이산화탄소를 배출함으로써 많은 문제가 발생하고 있다. 그리고 화력발전소 및 제철소의 산업부산물인 플라이애쉬 및 고로슬래그 미분말은 시멘트와 일부 대체하여 콘크리트로 일부 재활용되고 있으나, 42% 정도를 해안 및 육상에 매립함으로써 환경적인 문제를 유발하고 있다. 최근 결합재로 시멘트를 사용하지 않은 알칼리 활성 콘크리트에 대한 연구가 활발히 진행되고 있다. 결합재로 플라이애시 또는 고로슬래그 미분말을 단독으로 사용한 연구는 많으나, 이들 결합재의 혼합사용에 대한 연구는 부족한 실정이다. 따라서 본 논문에서는 시멘트를 전혀 사용하지 않고 결합재로서 플라이애쉬와 고로슬래그 미분말을 혼합한 알칼리 활성 콘크리트를 개발할 목적으로 결합재의 혼합비율 및 양생온도가 알칼리 활성 모르터의 시공성, 압축강도 등 특성에 미치는 영향에 대해 검토하였다. 그 결과, 플라이애쉬와 고로슬래그 미분말의 혼합비는 시공성 및 강도에 큰 영향을 주지만, 양생온도는 비교적 큰 영향을 주지 않는 것으로 나타났다. 플라이애쉬와 고로슬래그 미분말을 50%씩 혼합하고, 9M NaOH과 쇼듐실리케이트를 1:1의 비율로 제조한 알칼리 활성화제를 사용할 경우에는 $20^{\circ}C$의 상온양생에서도 재령 28일에서 압축강도 65 MPa의 알칼리 활성 모르터를 제조할 수 있는 것으로 나타났다.

• 지질공학
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• 제11권1호
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• pp.81-99
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• 2001

터널의 차수그라우팅 효과를 확인하기 위하여 영천댐 도수터널 건설공사 중에 현장 그라우팅 시험을 수행하였다. 시험은 그라우팅 시기에 따라 굴착전, 굴착후 및 콘크리트 라이닝일 설치된 이후의 압밀 그라우팅 등으로 구분하였고, 주입재료, 암종 및 지질인자, 그라우팅공의 천공방향 및 주입단계에 따른 효과를 비교하도록 계획하였다. 재료의 특성에 따른 차수효과는 포틀랜드시멘트, 마이크로시멘트, 마이크로시멘트 마이크로시멘트+규산에 비해 우레탄이 가장 뛰어났으며, 시공시기에 따라서는 라이닝후 및 굴착후에 비해 굴착전 그라우팅시 차수효과가 뛰어났다. 암종에 따라서는 화산암 및 화강암지반에 비해 퇴적암지반에서 차수효과가 낮게 나타났는데 이는 퇴적암에 발달하는 절리틈새가 적고 절리 충전물이 많아서 주입재의 침투성 저조에 기인한 것으로 사료된다. RMR값과는 직접적인 상관성이 없으나 RMR 요소 중 절리틈의 간극이 클수록 차수효과가 높게 나타났다. 천공방향은 차수효과에 영향을 미치지 않았으나 주입방법은 천공 및 주입의 단계를 세분할 수록 높은 차수 효과를 기대할 수 있다.