• 한국해안·해양공학회논문집
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• 제21권6호
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• pp.437-443
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• 2009

콘크리트 구조물의 안전성이나 내구성을 파악하기 위해 비파과 검사를 실시하는데, 충격공진법을 이용하면 동탄성계수를 얻을 수 있다. 동탄성계수는 일축압축실험에서 얻을 수 있는 일반적인 정탄성계수와는 절대값에서 차이가 있다. 본 연구에서는 현장 항만 콘크리트 구조물에서 채취된 코어시료에 대한 실내실험을 통해 동탄성계수와 정탄성계수의 상관관계를 규명하고자 하였다. 현장 항만 콘크리트 코어는 완도항, 마산항, 인천항에서 채취하였으며, 노출환경에 따라 대기부, 비말대, 간만대로 나누어 작업을 실시하였다. 채취된 시료는 실험실로 이송하여 충격공진법과 일축압축실험을 실시하였다. 충격공진법을 이용하면 개별시료의 공진주파수를 측정할 수 있으며, 이를 바탕으로 동탄성계수를 계산할 수 있다. 일축압축실험을 수행하면 시료의 응력-변형률 곡선을 얻을 수 있는데, 이를 바탕으로 일반적으로 설계에 사용되는 정탄성계수(현탄성계수)와 낮은 응력수준의 초기현탄성계수를 구하였다. 동탄성계수와 정탄성계수 및 초기현탄성계수의 상관관계는 채취 지역에 따라 차이가 있었지만 같은 안벽 내에서의 노출 환경에 따라서는 거의 차이가 없었다. 또한, 압축강도와 동탄성계수의 상관관계도 코어채취지역에 따라 조금씩 차이가 있었다. 그러나, 압축강도와 정탄성계수는 코어채취지역에 따라 차이가 발생하지 않았다.

• 한국산학기술학회논문지
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• 제13권3호
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• pp.1385-1390
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• 2012

바톰애시와 현장발생토사를 혼합한 유동성뒤채움재에 실험적 연구를 수행하였다. 유동성과 일축압축강도를 이용하여 4가지 다른 배합조건에 대한 각각의 최적배합비를 결정하였다. 현장발생토 25-45%, 바톰애시 30%, 플라이애쉬 10-20%, 고무분말 0-3%, 시멘트 3% 및 물 22%의 범위에서 최적배합비가 결정되었다. 각각의 혼합물은 20cm 이상의 유동성, 3일 양생시 127 kPa 및 28일 양생시 206-980 kPa 일축압축강도 조건을 만족하였다. 시험재료는 상온양생 및 습윤양생 2가지 조건을 이용하였다. 전체 혼합물에 대한 변형계수(E50)는 0.07-0.08 * $q_u$로 나타났다. 또한, 습윤양생 시편의 일축압축강도가 상온양생 시편에 비해 약 10% 정도 큰 값을 나타나내었다. 전체혼합물의 내부마찰각은 36.5-46.6도, 점착력은 49.1-180 kPa 범위로 측정되었다. 고무분말이 추가된 case 4번의 경우 다른 case에 비해 점착력은 크게, 내부마찰각은 작은 값을 나타내었다. 유동성채움재의 공용 성능을 위해 실시한 pH실험 결과 배합초기 12이상 강알칼리성으로 평가되었다.

• 한국도로학회논문집
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• 제17권3호
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• pp.85-95
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• 2015

PURPOSES : Recently, bonded concrete overlay has been used as an alternative solution in concrete pavement rehabilitation since its material properties are similar to those of the existing concrete pavements. Deteriorated concrete pavements need rapid rehabilitation in order to prevent traffic jams on Korean expressways. Moreover, speedy and effective repair methods are required. Therefore, the use of bonded concrete overlay with ultra-rapid hardening cement has increased in an effort to reopen promptly the expressways in Korea. However, mobile mixer is required for ultra-rapid hardening cement concrete mixing in the construction site. The use of mobile mixer causes various disadvantages aforementioned such as limitation of the construction supply, open-air storage of mixing materials, increase in construction cost, and etc. In this study, therefore, hydration accelerator in-situ mixing on polymer modified concrete produced in concrete plant is attempted in order to avoid the disadvantages of existing bonded concrete overlay method using ultra-rapid hardening cement. METHODS : Bonded concrete overlay materials using ultra-rapid hardening cement should be meet all the requirements including structural characteristics, compatibility, durability for field application. Therefore, This study aimed to evaluate the application of hydration accelerator in-situ mixing on polymer modified concrete by evaluating structural characteristics, compatibility, durability and economic efficiency for bonded concrete overlay. RESULTS : Test results of structural characteristics showed that the compressive, flexural strength and bond strength were exceed 21MPa, 3.15MPa and 1.4MPa, respectively, which are the target strengths of four hours age for the purpose of prompt traffic reopening. In addition, tests of compatibility, such as drying shrinkage, coefficient of thermal expansion and modulus of elasticity, and durability (chloride ions penetration resistance, freezing-thawing resistance, scaling resistance, abrasion resistance and crack resistance), showed that the hydration accelerator in-situ mixing on polymer modified concrete were satisfied the required criteria. CONCLUSIONS : It was known that the hydration accelerator in-situ mixing on polymer modified concrete overlay method was applicable for bonded concrete overlay and was a good alternative method to substitute the existing bonded concrete overlay method since structural characteristics, compatibility, durability were satisfied the criteria and its economic efficiency was excellent compare to the existing bonded concrete overlay methods.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 추계 학술발표회 2차
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• pp.61-67
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• 2010

Thick soft clay deposits which are generally located at the west and south coast of the Korean peninsula have complicated characteristics according to their orientation and formation history. Thus, several geotechnical problems could possibly occur when those soft clay deposits are used as foundations for marine structures. Deep cement mixing (DCM) method is one of the most widely used soft soil improvement method for various marine structures, nowadays. DCM method injects binders such as cement into the soft ground directly and mixes with the in-situ soil to improve the strength and other geotechnical properties sufficiently. However, the natural impacts induced by dynamic motions such as ocean waves, wind, typhoon, and tusnami give significant influences on the stability of marine structures and their underlaying foundations. Thus, the dynamic properties become important design criteria to insure the seismic stability of marine structures. In this study, the dynamic behavior of cemented Busan clay is evaluated. Laboratory unconfined compression test and resonant column test are performed on natural in-situ soil and cement mixed specimens to confirm the strength and strain-dependent dynamic behavior variation induced by cement mixing treatment. Results show that the unconfined compressive strength and shear modulus increase with curing time and cement content increment. Finally, the optimized cement mixing ratio for sufficient dynamic stability is obtained through this study. The results of this study are expected to be widely used to improve the reliability of seismic design for marine structures.

• Advances in concrete construction
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• 제9권6호
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• pp.537-545
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• 2020

In order to reduce the usage of cement slurry in grouting engineering and consume the tunnel excavation waste soil, a new geopolymeric grouting material (GGM) was prepared by combine completely weathered granite (CWG) and blast-furnace slag (BFS), which can be applied to in-situ grouting treatment of completely weathered granite strata. The results showed CWG could participate in the geopolymerization process, and GGM slurry has the characteristics of short setting time, high flowability, low viscosity, high stone rate and high mechanical strength, and a design method of grouting pressure based on viscosity evolution was proposed. By adjusted the content of completely weathered granite and alkali activator concentration, the setting time of GGM were ranged from 5 to 30 minutes, the flowability was more than 23.5 cm, the stone rate was higher than 90%, the compressive strength of 28 days were 7.8-16.9 MPa, the porosity were below 30%. This provides a novel grouting treatment and utilizing excavated soil of tunnels in the similar strata.

• 한국농공학회지
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• 제40권5호
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• pp.68-79
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• 1998

In the years, the concern about high-strength concrete which is new material has been heightened as a result of active research and development. Recently, as the building structure has been being bigger, higher, longer and more specialized, the demand of material with high-strength concrete for building has been increasing. The demand of high -strength concrete is expected to increase with expansion of usage about the complex concrete structures such as bridge structure as well as nuclear plants, underground structures, hydraulic structures and arctic area sturctures. In this research, silica-fume was used as an admixture in order to get a high-strength concrete. Water/binder ration was limited no more than 18 percent and the amount of unit cement was increased. In this study, a number of trial in concrete mix was carried out to get optimal mix design, and the target slump with $10{\pm}2cm$ was set for in-situ construction. High-strength concrete with cylinder strength of 1,200kgf/$cm^2$ in the 28-days was produced and tested. The static test was carried out to measure the ultimate load, the initial load of flexural and diagonal cracking, crack patterns, fracture modes. The load versus strain and load versus deflection relations were obtained form the static test. The test results were compared with the shear strengths predicted by the equations of ACI code 318-89 and orther researchers. Based on the test results, shear strength equation of reinforced concrete beam using high strength concrete was proposed. Form an evaluation of the results of this experimental investigation, it was concluded that shear strength after diagonal tention cracking diminished with the increase in compressive strength for beams.

• 한국재료학회지
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• 제18권6호
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• pp.289-293
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• 2008

Porous HAp with three-dimensional network channels was prepared in a polymer foam process using a in-situ formation. HAp/polyol with various HAp solid contents was formed with an addition of isocyanate. Under all conditions, the obtained porous HAp had pore sizes ranging $50\;{\mu}m$ to $250\;{\mu}m$. The influence of the HAp content on the physical and mechanical properties of porous HAp scaffolds was investigated. As the solid content increased, the porosity of the porous HAp decreased from 79.3% to 77.9%. On the other hand, the compressive strength of the porous HAp increased from 0.7 MPa to 3.7 MPa. With a HAp solid content of 15 g, the obtained porous HAp had physical properties that were more suitable for scaffolds compared to other conditions.

• 한국구조물진단유지관리공학회 논문집
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• 제22권2호
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• pp.98-104
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• 2018

콘크리트 비파괴강도 추정식은 일반적으로 콘크리트 강도를 결정하는데 사용된다. 그러나 기존의 추정식들은 대부분 제한된 실험 변수를 토대로 제안되어 배합조건, 강도특성 등이 다양한 실제 공용중 교량의콘크리트 압축강도 추정시 많은 오류를 포함한다. 본 연구에서는 297개 공용 교량의 정밀안전진단 결과 중 콘크리트 비파괴시험 및 현장 코어강도 시험결과를 토대로 콘크리트 부재의 코어강도와 비파괴 추정강도 평가결과를 비교분석하였다. 분석결과 분석이 이루어진 기존 추정식들 중 일본건축학회 CNDT소위원회 강도계산식이 다른 추정식에 비하여 실제파괴강도와의 오차가 가장적고 상관분석의 신뢰도도 가장높은 것으로 검토되었다. 그러나 이 추정식은 코어강도가 30 MPa이상일때 추정강도는 과소평가되는 것으로 나타났다. 이에 본 논문에서는 추정식에 의한 강도와 현장 코어강도사이의 관계를 활용하여 회귀분석을 통한 개선된 비파괴강도 추정식을 제안하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(II)
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• pp.497-500
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• 2005

This study was performed to evaluate the characteristics which are slump, air content and time of set in fresh concrete and compressive strength of hardened concrete containing slag powder and fly-ash. Replacement rate of FA is fixed on 10$\%$ and replacement rate of slag powder are 0$\%$, 20$\%$ and 30$\%$. Also AE water-reducing agents(standard type, accelerating type) are used. The results were as follows. (1)Slump flow of concrete using AE water-reducing agents is similar. Flowability is incresed when replacement rate of slag powder is increased due to slag powder's ball bearing reaction.(2)Time of set of concrete using accelerating type agent is more faster than that of concrete using standard type agent because of ettringite generation that promote setting.(3)Early strength of three-component concrete using accelerating type agent is higher than that using standard type agent. Therefore cumulative pore is reduced due to ettringite

• 대한토목학회논문집
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• 제29권5C호
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• pp.207-215
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• 2009

시멘트 혼합토나 콘크리트는 일반적으로 습윤상태를 유지하면서 양생이 되며 양생기간이 늘어남에 따라 수화작용으로 강도는 증가한다. 하지만 양생기간 동안 시멘트 혼합토에 충분한 수분이 공급되지 않을 경우 이는 수화작용에 영향을 미치고 결국 시멘트 혼합토의 강도 변화를 가져오게 된다. 본 연구에서는 시멘트비가 20% 미만인 시멘트 혼합토가 현장에서 시공 될 때 발생할 수 있는 수분공급 조건을 고려하여 네 가지 양생방법(대기중 양생, 밀봉 양생, 습윤 양생, 수중 양생)으로 제작된 고결모래의 양생조건에 따른 일축압축강도의 특성을 비교하였다. 전기간(3일) 대기중 양생한 공시체의 강도는 시멘트비가 10% 미만인 경우 밀봉 및 습윤 양생한 공시체보다 크지만 시멘트비가 10% 이상인 경우는 더 작았다. 시멘트비에 관계 없이 대기중 양생한 공시체가 수중 양생한 공시체보다 더 큰 강도를 발휘하였다. 양생방법이 동일한 경우 시멘트비 4%의 강도를 기준으로 시멘트비 증가에 따른 강도 증가율은 대기중 양생한 공시체가 가장 낮았으며, 밀봉, 습윤 및 수중 양생한 공시체의 강도는 시멘트비 증가율의 제곱으로 증가하였다. 공시체를 2일 양생 후 1일 동안 수침시켰을 때 밀봉 또는 습윤 양생한 공시체의 강도는 수침시키지 않은 공시체보다 시멘트비에 관계없이 평균 10% 정도 저하되었으나, 대기중 양생한 공시체는 시멘트비가 낮은 경우 최대 30% 정도까지 크게 저하되었다. 본 연구 결과는 현장에서 발생하는 수분공급 조건과 수침에 따른 시멘트 혼합토의 강도 변화를 예측하여 시멘트 혼합토를 사용한 댐과 같은 지반구조물의 안정성 확보에 기여할 수 있다.