서울시와 같은 도심지의 경우 상수도관, 하수관, 가스관, 통신․전기선과 같은 인프라 시설물을 도로포장 하부에 매설하고 있다. 그 러나 도로 지하에 각종 시설물을 매설하거나 유지보수 등으로 인해 노면을 굴착할 경우, 포장체 구성에 불연속면을 생성하여 이에 대 한 복구가 적절하지 않았을 경우 지반침하, 포장 노면 균열, 평탄성 불량 등의 발생으로 도로 이용자의 승차감 저하 및 노면배수 불량 으로 인한 차량 주행의 안전성 저하, 보도의 경우 통행인의 불편 초래 및 안전사고를 유발할 수 있다. 그러나 현재 서울시의 도로굴착복구 공사는 도로 이용자의 편의를 위해 당일 굴착·당일 복구를 원칙으로 하고 있으며, 이를 위해 주 간 공사 및 장시간 교통통제를 지양하고 있어, 하루 중 야간 8시간 정도로 공사 시간이 부족하고 수많은 공사가 산발적으로 시행됨에 따라 관리 감독이 어려워 시공 품질관리가 미흡하며, 특히 지하 매설물 공사 이후 포장층 하부의 되메우기 공정은 다짐 작업이 제대 로 이루어지지 않는다. 일반적으로 서울시 도로굴착복구 공사는 공사 당일 임시포장을 시행하고, 일정 기간 경과 후 차로 단위로 항구 포장 복구를 시행하고 있으며, 이로 인한 도로 평탄성 불량으로 소음․진동 발생 및 포장 조기 파손의 원인으로 작용하고 있다. 특히 되메우기 공정의 경우, 현행 시방서에 따르면 신속한 되메움 복구 및 관로 주변의 조밀한 충진을 목적으로 관로 주변을 양질의 모래로 시공하는 것을 원칙으로 하고 있으나, 기존 되메움 재료인 모래는 결속력이 약해 인접 구간 공사 시 세굴로 인한 사고 발생 위험 요소를 내재하고 있으며, 누수에 의한 세굴 발생시 편토압 등으로 인해 주변 지반의 침하 등 2차 파손을 발생시킬 수 있다.

In this study, we report the microstructure and characteristics of Ag-SnO2-Bi2O3 contact materials using a controlled milling process with a subsequent compaction process. Using magnetic pulsed compaction (MPC), the milled Ag-SnO2-Bi2O3 powders have been consolidated into bulk samples. The effects of the compaction conditions on the microstructure and characteristics have been investigated in detail. The nanoscale SnO2 phase and microscale Bi2O3 phase are well-distributed homogeneously in the Ag matrix after the consolidation process. The successful consolidation of Ag-SnO2-Bi2O3 contact materials was achieved by an MPC process with subsequent atmospheric sintering, after which the hardness and electrical conductivity of the Ag-SnO2-Bi2O3 contact materials were found to be 62–75 HV and 52–63% IACS, respectively, which is related to the interfacial stability between the Ag matrix, the SnO2 phase, and the Bi2O3 phase.

The Mn-Zn ferrite powders were prepared by high energy ball milling, then compacted and sintered at various temperatures to assess their sintering behavior and magnetic properties. The initial ferrite powders were spherical in shape with the size of approximately 70 m. After 3 h of ball milling at 300 rpm, aggregated powders ~230 nm in size and composed of ~15 nm nanoparticles were formed. The milled powders had a density of ~70 % when compacted at 490 MPa for 3 min. In the samples subsequently sintered at 1,273 K ~ 1,673 K for 3 h, the MnZnFe2O4 phase was detected. The density of the sintered samples had a tendency to increase with increasing sintering temperature up to 1,473 K, which produced the highest density of 98 %. On the other hand, the sample sintered at 1,373 K had the highest micro-hardness of approximately 610 Hv, which is due to much finer grains.

PURPOSES : In a previous study, an error was detected in data pertaining to the direction and velocity of a roller. Hence, in this study, the correlation between these two variables and acceleration data is analyzed. Relevant algorithms are developed by adding variables to existing algorithms. METHODS : A tachometer and GPS are used to acquire the velocity, compaction direction of rollers, and number of compactions. Subsequently, data input to an accelerometer are compared and analyzed. RESULTS : Based on FFT analysis, it is discovered that the data are inaccurate when a forward reverse is performed. Using the GPS, the velocity of the roller is differentiated based on the number of pledges, and then added as a variable to the algorithm. Subsequently, it is evaluated and analyzed only with data during forward movement based on changes in the latitude and longitude. CONCLUSIONS : It is discovered that the acceleration data values from both the left and right rollers differ owing to their weight difference, as indicated by the asphalt gradient. Data changes based on asphalt gradients are analyzed using gyro sensors. If the correlation between the two sets of data is high, then the algorithm is advanced by introducing a cross spectrum after calibrating the acceleration value based on the gradient.

PURPOSES : The driver's ability to make a commitment has resulted in excessive force and a lack of commitment. To solve this problem, we are developing an algorithm that analyzes resolution in real-time by introducing IoT and informs drivers of the completion of compaction. METHODS : Real-time compaction was analyzed by installing accelerometers on the rollers. To evaluate the algorithms, we conducted an apparent density test. RESULTS : The algorithm data and apparent density test data showed similar trends. This means that the proposed algorithms are sufficiently reliable. However, a lack of data samples and the fact that only data prior to completion of the commitment were analyzed may indicate a lack of reliability. CONCLUSIONS : In subsequent studies, the number of samples will be increased and the data after completion of the commitment analyzed to increase reliability. Introducing a tachometer will prevent the TVL from falling sharply when the direction of the rollers' progress changes. In addition, it is also planned to upgrade the algorithms by researching cases in which the algorithms did not produce satisfactory results owing to problems such as temperature and speed.

Ti-based alloys are widely used in biomaterials owing to their excellent biocompatibility. In this study, Ti- Mn-Cu alloys are prepared by high-energy ball milling, magnetic pulsed compaction, and pressureless sintering. The microstructure and microhardness of the Ti-Mn-Cu alloys with variation of the Cu addition and compaction pressure are analyzed. The correlation between the composition, compaction pressure, and density is investigated by measuring the green density and sintered density for samples with different compositions, subjected to various compaction pressures. For all compositions, it is confirmed that the green density increases proportionally as the compaction pressure increases, but the sintered density decreases owing to gas formation from the pyrolysis of TiH2 powders and reduction of oxides on the surface of the starting powders during the sintering process. In addition, an increase in the amount of Cu addition changes the volume fractions of the α-Ti and β-Ti phases, and the microstructure of the alloys with different compositions also changes. It is demonstrated that these changes in the phase volume fraction and microstructure are closely related to the mechanical properties of the Ti-Mn-Cu alloys.

Accurate and effective powder compaction analyses are performed for brittle materials such as graphite, utilized as a solid lubricant, by using the discrete element method (DEM). The reliability of the DEM analysis is confirmed by comparing the results of graphite powder compaction analyses using the DEM particle bonding contact model and particle non-bonding contact model with those from the powder compaction experiment under the same conditions. To improve the characteristics, the parameters influencing the compaction properties of the metal-graphite mixtures are explored. The compressibility increases as the size distribution of the graphite powder increases, where the shape of the graphite particles is uniform. The improved compaction characteristics of the metal-graphite (bonding model) mixtures are further verified by the stress transmission and compressive force distribution between the top and bottom punches. It is confirmed that the application of graphite (bonding model) powders resulted in improved stress transmission and compressive force distribution of 24% and 85%, respectively.

In this paper, a durability study is presented to enhance the mechanical properties of an Fe-Si-Al powderbased magnetic core, through the addition of graphite. The compressive properties of Fe-Si-Al-graphite powder mixtures are explored using discrete element method (DEM), and a powder compaction experiment is performed under identical conditions to verify the reliability of the DEM analysis. Important parameters for powder compaction of Fe-Si-Algraphite powder mixtures are identified. The compressibility of the powders is observed to increase as the amount of graphite mixture increases and as the size of the graphite powders decreases. In addition, the compaction properties of the Fe-Si-Al-graphite powder mixtures are further explored by analyzing the transmissibility of stress between the top and bottom punches as well as the distribution of the compressive force. The application of graphite powders is confirmed to result in improved stress transmission and compressive force distribution, by 24% and 51%, respectively.

The present study demonstrates the effect of magnetic pulse compaction and spark plasma sintering on the microstructure and mechanical property of a sintered W body. The relative density of green specimens prepared by magnetic pulse compaction increases with increase in applied pressure, but when the applied pressure is 3.4 GPa or more, some cracks in the specimen are observed. The pressureless-sintered W shows neck growth between W particles, but there are still many pores. The sintered body fabricated by spark plasma sintering exhibits a relative density of above 90 %, and the specimen sintered at 1,600 oC after magnetic pulse compaction shows the highest density, with a relative density of 93.6 %. Compared to the specimen for which the W powder is directly sintered, the specimen sintered after magnetic pulse compaction shows a smaller crystal grain size, which is explained by the reduced W particle size and microstructure homogenization during the magnetic pulse compaction process. Sintering at 1,600 oC led to the largest Vickers hardness value, but the value is slightly lower than that of the conventional W sintered body, which is attributed mainly to the increased grain size and low sintering density.

PURPOSES : For the compaction control on the subgrade layer, dynamic cone penetration test (DCPT) is being applied to the Korea pavement subgrade construction guidelines. The existing equation in the Korean guidelines for estimating the resilient modulus, MR, from the DCPT test result penetration rate (PR), is a correlation developed from a small amount of data and does not consider the degree of compression. Therefore, this study attempts to propose an advanced MR-DCPT PR correlation through the correction of existing data and additional field tests. METHODS : The in-situ DCPT tests were conducted according to the types of subgrade soils in the field. Thereafter, the existing guideline‘s data were collected and corrected with the degree of compaction, R. RESULTS : In this study, the correlation coefficient is improved such that it is considerably higher than the existing equation using additional field data and converting the data used in the existing equation into data with over 95% degree of compaction. CONCLUSIONS : Through verification, it was found that the relative errors of the proposed correlations in this study were reduced when compared with the existing equation.

Cell adhesion plays an important role in the differentiation of the morphogenesis and the trophectoderm epithelium of the blastocyst. In the porcine embryo, CDH1 mediated adhesion initiates at compaction before blastocyst formation, regulated post-translationally via protein kinase C and other signaling molecules. Here we focus on muscle RAS oncogene homolog (M-RAS), which is the closest relative to the RAS related proteins and shares most regulatory and effector interactions. To characterize the effects of M-RAS on embryo compaction, we used gain- and loss-of-function strategies in porcine embryos, in which M-RAS gene structure and protein sequence are conserved. We showed that knockdown of M-RAS in zygotes reduced embryo development abilities and CDH1 expression. Moreover, the phosphorylation of ERK was also decreased in M-RAS KD embryos. Overexpression of M-RAS allows M-RAS KD embryos to rescue the embryo compaction and blastocyst formation. Collectively, these results highlight novel conserved and multiple effects of M-RAS during porcine embryo development.

PURPOSES : For compaction control on the subgrade layer, the simple and economical test DCPT (Dynamic Cone Penetrometer Test) is being applied to the Korea Pavement Design Guide. However, compaction control is now difficult and to conduct in the field and is not performed in practice because the compaction degree is evaluated via the field density test as a pretreatment step when the compaction management process is evaluated by DCPT at the same time. Therefore, this study tried to propose a method considering an evaluation for the compaction degree using DCPT, via laboratory tests and field tests. METHODS: The in-situ DCPT tests were conducted according to the types of subgrade soils in the field. Afterward, the field density tests for the compaction degree (R) of field samples and the experiments using DCPT were performed simultaneously in a self-made test container in the lab. RESULTS: Through the DCPT test, compaction degree evaluation from the correlations proposed in this study was determined to be possible. Additional field tests could verify the proposed correlations between compaction degree with DCPT PR on the subgrade. CONCLUSIONS: For the evaluation of the subgrade compaction degree using dynamic CPT, the correlations between compaction degree and DCPT PR on the subgrade layer are proposed from laboratory tests and field tests using DCPT and field density tests.

PURPOSES : The feasibilities of cohesive elastoplastic contact model and discrete element method (DEM) for asphalt concrete mixture compaction process were evaluated. METHODS : The contact models that were used to simulate the dynamic behavior of construction materials were reviewed. The characteristics of cohesive elastoplastic models were discussed from the perspective of integration with existing contact models. Two asphalt mixtures that were fabricated with specific aggregate gradations and binder contents were compacted according to the Superpave gyratory compaction specification. The parameters for the model were determined via trial-and-error method. The heights of the specimens were plotted with respect to number of gyrations. The results of the laboratory tests were compared to those of numerical simulations. The displacement of particles in asphalt mixture specimen was also visualized to understand the effect of gyratory compaction on asphalt mixture specimen. RESULTS : The DEM model exhibited a significant friction coefficient dependency on compaction degree and slop. The DEM model with parameters determined through trial and error demonstrated reasonable simulation results in terms of specimen height at a gyration number. CONCLUSIONS: Even though a little discrepancy was observed between the results of the experimental test and numerical simulation, a combination of DEM with cohesive elastoplastic contact model seems to be applicable for the simulation of asphalt mixture compaction in laboratory. However, the model needs to be enhanced to be used for more realistic compaction processes, including heat transfer, phase change, and vibratory loading.

Roller Compacted Concrete Pavement (RCCP) is placed by roller compaction of a mixture of less cement and unit water content and more aggregates and provides excellent early strength development with the help of interlocking of aggregates and hydration. The unit cement content of RCC pavements accounts for 85% of conventional pavements, with low drying shrinkage. As low drying shrinkage leads to smaller crack widths than ordinary concrete, RCC pavements can help elevate reflecting crack resistance if applied to a base layer of a composite pavement system. In a composite pavement with an asphalt surface laid over a concrete base, pavement temperature change is important in predicting pavement performance. As movement of the lower concrete layer is determined by temperature depending on pavement depth, temperature data of the pavement structure serves as an important parameter to prevent and control reflecting crack. Among the causes of reflecting crack, horizontal behavior of the lower concrete layer and curling-caused vertical behavior of joints/cracks are considered closely related to temperature change characteristics of the lower concrete course (Baek, 2010). Previous studies at home and abroad about reflecting crack have focused on pavement behavior depending on daily and yearly in-service temperature changes of a composite pavement (Manuel, 2005). Until now, however, studies have not been conducted on initial temperature characteristics of concrete in composite pavements where asphalt surface is placed over an RCC base. Annual temperature changes of in-service concrete pavements go up to 60 ℃, and those of asphalt overlays become around the twice at 110 ℃. This study evaluated initial crack behavior of composite pavement by investigating pavement temperature by depth of an RCC base and analyzing joint movement depending on change to temperatures of continuously jointed pavements. Findings from the study suggest that in composite pavements and asphalt overlays, time of laying asphalt has an important impact on crack behavior and reflecting crack.

In this study, several tests such as liquid limit test, compaction test, and XRF analysis were conducted on silty sand (SM) containing air to investigate the saturation collapse phenomenon due to flow liquefaction, which can result to the increase of the saturation degree and water content. The relationship between the flow strength and water content of the test material, which was artificially prepared by mixing Saemangeum dredged soil and water at different mixing ratios, was investigated to determine the strength variation caused by intergranular flow. When silicon dioxide (Si02) and water react with each other, energy is generated from capillary phenomenon and the attractive force between particles increases from 10% to 20% due to matric potential. The maximum flow resistance is maintained at the range of 20% to 30% water content, which is larger than the optimum water content obtained from the compaction test, so that flow resistance is greater in the region where the maximum shearing force is significantly high. However, if the water content is increased to more than 30%, the flow resistance is significantly low.

Molybdenum (Mo) is one of the representative refractory metals for its high melting point, superior thermal conductivity, low density and low thermal expansion coefficient. However, due to its high melting point, it is necessary for Mo products to be fabricated at a high sintering temperature of over 1800-2000 oC. Because this process is expensive and inefficient, studies to improve sintering property of Mo have been researched actively. In this study, we fabricated Mo nanopowders to lower the sintering temperature of Mo and tried to consolidate the Mo nanopowders through ultra high pressure compaction. We first fabricated Mo nanopowders by a mechano-chemical process to increase the specific surface area of the Mo powders. This process includes a high-energy ball milling step and a reduction step in a hydrogen atmosphere. We compacted the Mo nanopowders with ultra high pressure by magnetic pulsed compaction (MPC) before pressureless sintering. Through this process, we were able to improve the green density of the Mo compacts by more than 20% and fabricate a high density Mo sintered body with more than a 95 % sintered density at relatively low temperature.

Powder compaction is a continually and rapidly evolving technology where it is a highly developed method ofmanufacturing reliable components. To understand existing mechanisms for compaction, parameter investigation isrequired. Experimental investigations on powder compaction process, followed by numerical modeling of compaction arepresented in this paper. The experimental work explores compression characteristics of soft and hard ductile powdermaterials. In order to account for deformation, fracture and movement of the particles, a discrete-finite element analysismodel is defined to reflect the experimental data and to enable investigations on mechanisms present at the particlelevel. Effects of important simulation factors and process parameters, such as particle count, time step, particle discret-ization, and particle size on the powder compaction procedure have been explored.

PURPOSES: To ensure appropriate RCC properties with sufficient strength development and workability, it is necessary to secure a proper level of consistency. It is also necessary to secure maximum dry density, which is an important factor for increasing the interaction of aggregate interlocking, leading to an augmentation of RCC strength. On the other hand, the dry density of RCC can be changed owing to the compaction conditions, water content, and particle size distribution. A Proctor test and a modified Proctor test were used for determining the optimum water content needed to achieve maximum dry density with different amounts of compaction energy. A Vebe test, on the other hand, was used for checking the level of consistency, which is important for producing a workable mixture. METHODS : To confirm the degree of compaction at various particle sizes, RCC mixtures with different sand/aggregate ratios were evaluated. The Proctor test and modified Proctor test were applied to these mixtures to check the effect of the aggregate gradation and compaction energy on the maximum dry density and optimum water content. During each test, three specimens were produced for all types of water content under each aggregate gradation. A compaction curve and the optimum water content and maximum dry density for each aggregate gradation were then obtained for both tests. The range of water content for the appropriate consistency of each aggregate gradation was determined through a Vebe test. The optimum water content was then evaluated based on this range. RESULTS : The compaction test results show that the modified Proctor test provides a higher maximum dry density and lower optimum water content compared with the standard Proctor test. For the modified Proctor test, two cases of aggregate gradation (s/a = 30% and 70%) had the optimum water contents outside of the appropriate water content range. For the standard Proctor test, on the other hand, none of aggregate gradations provided the optimum water content within the desired range. CONCLUSIONS : The modified Proctor test should be used for an RCC mixture design because it can provide adequacy between maximum dry density and consistency. Moreover, the compaction roller has become highly developed for higher compaction energy.