High-strength low-alloy steel is one of the widely used materials in onshore and offshore plant engineering. We investigated the alloying effect of solute atoms in α-Fe based alloy using ab initio calculations. Empirical equations were used to establish the effect of alloying on the Vicker’s hardness, screw energy coefficient, and edge dislocation energy coefficient of the steel. Screw and edge energy coefficients were improved by the addition of V and Cr solute atoms. In addition, the addition of trace quantities of V, Cr, and Mn enhanced abrasion resistance. Solute atoms and contents with excellent mechanical properties were selected and their thermal conductivity and thermal expansion behavior were investigated. The addition of Cr atom is expected to form alloys with low thermal conductivity and thermal expansion coefficient. This study provides a better understanding of the state-of-the-art research in low-alloy steel and can be used to guide researchers to explore and develop α-Fe based alloys with improved properties, that can be fabricated in smart and cost-effective manners.

PURPOSES : The purpose of this study is to confirm the thermal expansion characteristics of concrete mixed with 1% waste glass fine aggregates, which is the amount stipulated for recycled aggregates in the current quality standard. METHODS : The coefficient of thermal expansion was measured by applying AASHTOT 336-10 using a LVDT. The results measured were used as physical properties in a finite element analysis to confirm the change in tensile stress and the displacement of the right angle section of the upper slab of a concrete pavement due to admixture substitution. RESULTS : The thermal expansion coefficients of concrete based on the replacement rate of the admixture when the waste glass fine aggregates are replaced are within the range of the thermal expansion coefficients of concrete specified in the Federal Highway Administration report. As the replacement rate of the admixture increases, the thermal expansion coefficient of concrete decreases. As the thermal expansion coefficient decreases, the slab pavement curling displacement and the tensile stress of the center of the upper slab of concrete decrease. CONCLUSIONS : In the short term, the presence or absence of waste glass fine aggregates does not significantly affect the thermal expansion coefficient of concrete. However, in the long term, waste glass fine aggregates are reactive aggregates that causes ASR, which creates an expandable gel around the aggregates and results in concrete expansion. Therefore, the relationship between ASR and the thermal expansion coefficient must be analyzed in future studies.

PURPOSES : The purpose of this study is to suggest a thermal expansion coefficient measurement method using an embedded strain transducer (EST) and vibrating wire gauge (VWG), as well as to evaluate the reliability of the proposed methods by comparing them with the AASHTO T 336-10 standard method. METHODS : To apply the AASHTO 336-10 test method, which is the criterion for reliability evaluation, a reference specimen using stainless steel (sus304) is manufactured, and a thermal expansion coefficient of 17.308με/°C is obtained based on ISO regulations. Using the reference specimen, the correction factor of the thermal expansion coefficient measurement equipment is measured to be 2.93με/°C, and using this value, the thermal expansion coefficient of the mortar specimen containing the embedded gauges is measured accurately. The reliability of the proposed experimental method is evaluated by measuring the thermal expansion coefficient of the embedded gauge with temperature compensation and then comparing it with that of the reference specimen. RESULTS : The coefficient of thermal expansion of the mortar specimen is measured to be 12.423με/°C based on AASHTO 336-10, 11.963με/°C using the EST method, and 12.522με/°C using the VWG method. Based on the results obtained using the AASHTO method, the embedded gauges show a difference of 1%~3% in terms of the average results, as well as a difference in the standard deviation of 0.059~0.186. Therefore, our level of confidence in the thermal expansion coefficient experiment using the embedded gauges is high. CONCLUSIONS : When using the AASHTO 336-10 test method, the thermal expansion coefficient should be obtained by measuring the length change of the specimen; however, some engineering judgment of the experimenter is required when the measurement values fluctuate during the temperature stabilization period. In the thermal expansion coefficient test using embedded gauges (EST and VWG), temperature compensation must be performed. Furthermore, it is assumed that the temperature difference between the water tank and test specimen does not significantly affect the thermal expansion coefficient measurement because the important point is not the actual temperature value but the temperature gradient. For reliability evaluation, a statistical significance review of the strain distribution by measurement method is performed via a T-test comparing with the AASHTO test result (12.423με/°C) and the reliability level for each measurement method remains confidential.

PURPOSES : The objective of this study is to understand blow-up distress and causes in concrete pavement. METHODS : Feasible causes of blow-up and existing models were reviewed based on the literature. Three analytical models were adopted to perform a sensitivity analysis. Input parameters reflected the typical concrete pavement of national expressways. Evaluation of blow-up models was based on the amount of temperature increase and zero stress temperature of the concrete pavement. RESULTS : A review of the literature indicated that the five major causes of blow-up were: increase in temperature and solar radiation, alkaliaggregate reaction (AAR), friction characteristics between the concrete slab and subbase, joint closure (incompressible), and joint freezing. The sensitivity analysis revealed that the coefficient of thermal expansion had the greatest influence on the blow-up safety temperature. CONCLUSIONS : From existing blow-up model results, it could be concluded that the construction of concrete pavement during the winter season was not effective at preventing blow-up. In addition, an equivalent coefficient of thermal expansion that considers slab expansion due to AAR was proposed as a model input parameter for concrete pavement sections damaged by AAR.

고준위폐기물을 처분하기 위한 심층처분시스템의 구성 요소로는 처분용기, 완충재, 뒷채움 및 근계 암반이 있다. 이 중 완충재는 심층 처분시스템에 있어 필수적인 요소이다. 처분용기에서 발생하는 고온의 열량은 완충재로 전파되기에 완충재의 열적 특성은 처분시스템의 안정성 평가에 상당히 중요하다고 할 수 있다. 특히, 고온의 열량은 완충재의 열적 팽창을 야기 하여 근계 암반에 열응력을 야기할 수 있기에 완충재의 열팽창 특성 규명은 반드시 필요하다고 할 수 있다. 따라서 본 연구에서는 국내 경주산 압축 벤토나이트 완충재(KJ-II)에 대한 열팽창 거동 특성을 실내 실험을 통해 분석하고 선형 열팽창계수 에 대한 추정 모델을 제시하고자 하였다. 압축 벤토나이트 완충재의 선형 열팽창계수는 딜라토미터 장비를 이용하여 승온 속도, 건조밀도, 온도 범위에 따라 측정되었으며 선형 열팽창계수 값은 대략 4.0~6.0×10-6/℃ 로 측정되었다. 또한 실험 데이터를 토대로 비선형 회귀분석 방법을 이용하여 건조밀도에 따른 경주 압축 벤토나이트 완충재의 선형 열팽창계수를 추정 할 수 있는 모델을 제시하였다.

최근 철도 주변에서 엄청난 양의 폐 콘크리트 침목이 적재 되어 있음을 쉽게 발견될 수 있다. 이는 열차에서 떨어진 금속가루 및 기름 때문에 폐 침목이 환경 유해물로 분류되기 때문이다. 보통 폐 콘크리트 침목은 50MPa 수준의 고강도 콘크리트로 되어 있어, 이를 활용하면 양질의 순환골재를 확보할 수 있다. Yang 등과 Kim 등은 순환골재에 붙어있는 구모르타르(RM)를 콘크리트 배합에 필요한 신모르타르(NM)의 일부로 간주하는 수정 등가모르타르체적(EMV) 배합법을 제안한 바 있다. 순환골재를 사용한 기존 배합법에서는 콘크리트 탄성계수의 저감 및 건조수축의 증가를 가져온 반면 수정 EMV 배합법에서는 천연골재를 사용한 기준 콘크리트에 비해 동등한 물성을 확보함을 보여주었다. 본 연구를 통해 위의 두 가지 배합법에 의해 제작된 콘크리트의 열팽창계수 실험을 수행하였다. EMV 배합법에 의해 제작된 순환골재 콘크리트의 열팽창계수가 기존 배합법에 의해 제작된 순환골재 콘크리트보다 작게 나옴을 보여 주었다. AASHTO-TP60 실험방법을 이용하여 10∼50℃의 범위에서 SUS304(열팽창계수 18.3m/m/℃)를 보정시편으로 사용하였다.

플랜트의 유황 저장 탱크는 강재로 구성되며, 탱크 저면은 앵커볼트에 의해 Ring Wall 형상의 콘크리트 기초와 연결된다. 탱크 내 유황이 내부 열원에 의해 고온상태를 유지하기 때문에, 유황 저장 탱크는 상온의 유체를 저장하는 다른 탱크에 비해 큰 체적팽창을 겪게 된다. 일반적으로 탱크 기초의 구조설계는 기초의 내외부의 온도차를 하중으로 적용한 구조해석이 수행 되는데, 이 방법은 탱크의 열팽창 특성이 앵커볼트에 의해 집중하중 형태로 콘크리트 기초에 전달되는 현상을 고려할 수 없 다. 이는 온도하중의 영향을 과소평가하게 되며, 앵커볼트에 인접한 콘크리트의 균열을 야기한다. 본 연구는 앵커볼트에 의 한 온도 하중전달 메커니즘을 고려한 하중 평가식을 제안함으로써, 콘크리트 기초에 작용하는 하중을 보다 합리적으로 결정 하고자 한다. 이를 위해 탱크 바닥판과 앵커볼트가 포함된 유한요소모델을 이용해 앵커볼트 개수 증감에 따른 온도하중의 변화를 분석하였으며, 분석결과를 이론해와 결합해 앵커볼트에 의해 전달되는 하중을 평가할 수 있는 명시적인 형태로 해를 제시하였다. 제안된 식의 유효성을 확인하기 위해 실제 플랜트 현장의 유황 저장 탱크 설계에 적용하였으며, 실무적으로 사 용 가능함을 보였다.

PURPOSES : This study was performed to determine a systematic approach for measuring the coefficient of thermal expansion (COTE) of concrete specimens. This approach includes the initial calibration of measurement equipment. Test variables include coarse aggregate types such as natural aggregate, job-site produced recycled concrete aggregate, and recycled aggregate processed from an intermediate waste treatment company. METHODS: First, two cylindrical SUS-304 specimens with a known COTE value of 17.3×10-6m/m/℃. were used as reference specimens for the calibration of each measurement system. The well-known AASHTO TP-60 COTE apparatus for concrete measurement was utilized in this study. Four different measurement apparatuses were used with each LVDT installed and a calibration value was determined using each measurement apparatus. RESULTS : In the initial experimental stage, calibration values for each measurement apparatus were assumed to be almost identical. However, using the SUS-304 samples as a reference, the calibration values for the four different measurement apparatuses were found to range from 3.49 to 8.86 ×10-6m/m/℃. Using different adjusted values for each measurement apparatuses, COTE values for the three different concrete specimens were obtained. The COTE value of concrete made with natural coarse aggregate was 9.91×10-6m/m/℃, that of job-site produced recycled coarse aggregate was 10.45×10-6m/m/℃, and that of recycled aggregate processed from the intermediate waste treatment company was 10.82×10-6m/m/℃. CONCLUSIONS: We observed that the COTE value of concrete made from recycled concrete aggregates (RCA) was higher than that of concrete made from natural coarse aggregate. This difference is due to the fact that the total volumetric mortar proportion in the RCA mix is higher than that in the concrete mix made with natural coarse aggregate.

The aim of this paper is to consider the effect of annealing on the coefficient of thermal expansion (CTE) of electroplated Invar Fe-Ni alloy. The CTE of the as-electroplated alloy is lower than those of alloys annealed at 400˚C and 800˚C. XRD peaks become sharper as the as-electroplated alloy is annealed, which means the grain growth. The average grain sizes of as-electroplated and as-annealed alloys at 400˚C and 800˚C are 10 nm, 70 nm, and 2μm, respectively, as determined by TEM and EBSD analyses. The CTE variation for the various grain sizes after annealing may come from the magnetostriction effect, which generates strain due to changes in the magnetization state of the alloys. The thermal expansion coefficient is considered to be affected by nano grain size in electroplated Fe-Ni Invar alloys. As grain size decreases, ferromagnetic forces might change to paramagnetic forces. The effect of lattice vibration damping of nano grain boundaries could lead to the decrease of CTE.

복합재료 구성성분은 수 마이크로미터 수준의 크기를 가지고 있으므로 시험을 통한 정확한 물성 측정이 매우 어렵다. 그러므로 본 논문에서는 역해석을 이용하여 복합재료 구성성분의 열팽창계수를 예측할 수 있는 기법을 제안한다. 복합재료에 대한 등가 열팽창계수를 예측할 수 있는 Mori-Tanaka 기법과 결합된 역해석기법을 이용하면, 라미나 수준의 목적함수를 최소화함으로써 구성성분의 열팽창계수를 효율적으로 구할 수 있다. 본 연구에서 제안한 기법을 검증하기 위하여 다양한 섬유(glass fiber, P75, P100, M55J)에 대한 열팽창계수를 예측하고 이를 시험결과와 비교하였다. 또한 라미나와 기지 물성치에 대한 불확실성이 섬유 물성치 예측에 미치는 영향을 분석하였다.

PURPOSES: The purpose of this study is to provide the method of how to measure the coefficient of thermal expansion of concrete using temperature compensation principle of electrical resistance strain gauge. METHODS : The gauge factor compensation method and thermal output(temperature-induced apparent strain) correction method of selftemperature compensation gauge were investigated. From the literature review, coefficient of thermal expansion measurement method based on the thermal output differential comparison between reference material(invar) and unknown material(concrete) was suggested. RESULTS: Thermal output is caused by two reasons; first the electrical resistivity of the grid conductor is changed by temperature variation and the second contribution is due to the differential thermal expansion between gauge and the test material. Invar was selected as a reference material and it、s coefficient of thermal expansion was measured as 2.12×10-6m/m/℃. by KS M ISO 11359-2. The reliability of the suggested measurement method was evaluated by the thermal output measurement of invar and mild steel. Finally coefficient of thermal expansion of concrete material for pavement was successfully measured as 15.45×10-6m/m/℃. CONCLUSIONS: The coefficient of thermal expansion measurement method using thermal output differential between invar and unknown concrete material was evaluated by theoretical and experimental aspects. Based on the test results, the proposed method is considered to be reasonable to apply for coefficient of thermal expansion measurement.

콘크리트포장은 시공초기의 품질관리수준에 따라 전체수명이 결정될 정도로 시공초기의 품질관리가 매우 중요하다. 이러한 초기 품질관리는 콘크리트포장의 초기거동을 잘 파악하여 초기거동을 조절할 수 있는 방안을 도출하는 것이 중요하다. 콘크리트포장의 초기거동에 영향을 주는 요소는 크게 두 가지가 있다. 첫째는 콘크리트의 건조수축이고, 두 번째는 수화열 및 대기온도 변화에 따른 포장체의 온도변화이다. 따라서, 콘크리트의 열팽창계수와 건조수축은 콘크리트의 초기거동에 매우 중요한 요소라 할 수 있다. 지금까지의 열팽창계수는 완전히 양생된 콘크리트에 대해 실험하는 것이 일반적이었기 때문에 시공초기에 열팽창계수를 얻는데 한계가 있어 왔다. 또 건조수축도 시간방법의 한계로 초기 건조수축을 측정하는데 어려움이 있어 왔다. 본 연구에서는 콘크리트포장의 초기 거동을 조절할 수 있는 방안을 도출하기 위하여, 콘크리트의 초기 건조수축과 열팽창계수를 측정하고 이를 통해 콘크리트포장의 초기 거동 예측프로그램의 입력변수들과 적용 모델들에 대한 자료제공 및 검증을 위 한 기초자료를 제공하는데 그 목적을 두었다. 본 연구에서 얻은 결론은 현장에서 초기 콘크리트의 열팽창계수 값을 측정한 결과 8.9~10.8×10-6/℃ 값을 나타내었으며, 콘크리트의 건조수축에 있어서 깊이별 effect와 size effect가 존재하는 것으로 분석되었다.

To improve the practical application of the thermal expansion of closed long pipeline exposing to external heating sources such as solar energy, safety engineering and system optimization for relief valve in the closed piping system are suggested through theoretical approach, correlation in view of temperature and pressure increase caused by external solar energy in the closed piping system. The profile for thermal relief valve including relieving capacity, influx heat energy, sizing criteria, set pressure, selection against back pressure is also presented. It is noted that following topic on solar relief valve should be applied to engineering, installation and commissioning.