Search

Many methods have been applied to monitor fugitive methane gas from landfills. Recently, there have been suggestions to use a framework utilizing an unmanned aerial vehicle (UAV) for landfill gas monitoring, and several field campaigns have proved that a rotary UAV-based measurement has advantages of ease of control and high-resolution concentration mapping on the target planes. However, research on the evaluation of error-inducing factors in the suggested system is limited so far. This study prepared a measurement system with a lightweight methane detector and a rotary UAV to support the applicability of rotary UAV in landfill gas monitoring. Then, the validity of the system was tested experimentally and theoretically. In the detector reliability test, the methane detector had sufficient resolution for field application. The critical UAV velocity required was obtained to ensure the credibility of the proposed measurement system. When spatial interpolators were applied to field data from the measurement system, the empirical Bayesian kriging demonstrated the best prediction of methane concentrations at unmeasured points. With the verifications provided in this study, this proposed method may contribute to reducing uncertainty in estimating fugitive landfill gas emission.

In this research, a test-bed large-span Hanok which adopts new structural system compared to the traditional structural system has been introduced, and the structural analysis and seismic design for it have been performed to test possibility as a large-span Hanok. The test-bed Hanok is composed of two parts, that is, 1st story part and 2nd story part. The roof structure of 1st story part is similar to that of the traditional Hanok, but that of 2nd story part is new-styled and different from the traditional Hanok. The two parts are joined together side by side. The largest span of this test-bed Hanok is 14.4m in 1st story part and 10.8m in 2nd story part. The structural design was done to extract optimal member size for both raw wood and glued laminated wood with satisfying safety and serviceability conditions. The comparison of the sectional area between raw wood and glulam showed that glulam required less member size than raw wood. The area ratio of the glulam compared to the raw wood is from 0.60 to 0.92, and this shows that, glulam is more economical than raw wood in large-span Hanok from the viewpoint of the required volume of the timber which affects much in cost and construction. Conceptual seismic design methods for the test-bed large-span Hanok were proposed and the structural characteristics of each method were discussed. The proposed method is summarized as addition of shear wall, reinforcing existing shear wall and isolating the basement of the structure from the ground.

Conventional hot mix asphalt overlaying on trench infrastructure typically necessitates extended cooling times for further works and can have adverse effects on buried components, such as electricity cables and hot water pipes. Therefore, this research aims to investigate the use of warm guss mastic asphalt (at an installation temperature of 160 °C) as an overlaying material for mini-trenches, which can reduce the cooling time required for traffic opening and improve the efficiency of the construction process. This research involved two stages: first, lab testing and related research results were used to generate the thermal conductivity and specific heat necessary for simulation work. Second, a finite element model analysis was conducted to evaluate the thermal transmission of the overlaying surface and the buried conduit based on the summer pavement temperature distribution through the Korean Pavement Research Program. Afterward, the field test bed was constructed to verify the simulation. The results indicate that the optimal thickness of the overlaying material and the concrete covering should be designed to ensure thermal durability and meet traffic opening requirements. The overlaying depth of the mini trench using warm mix guss mastic asphalt should be less than 100 mm to meet with the traffic opening time, while the thickness of the concrete covering should be designed to be more than 100 mm to ensure thermal durability. Additionally, the findings suggest that the application of warm guss asphalt could reduce the opening time by 30 min to 1 h and 25 min compared to conventional hot guss asphalt materials. When the pavement surface temperature for the traffic opening is controlled at 50 °C, the asphalt mixture requires at least 2 h to 5 h to meet the cooling criteria for traffic opening, respectively. Overall, this research confirms the potential benefits and optimal use of warm guss mastic asphalt in the construction process of mini-trenches.

The objective of this study is to provide a process that can be applied in preparation for the introduction of an efficient and systematic pavement management system. This process includes features for selecting pavement segmentation (for management) and priority based on a cumulative difference approach(CDA), starting from the development of an index that reflects the pavement condition and current distribution status. For the index, which can reflect the current pavement conditions of sections to be managed, this study proposes a basic model form and establishes a simple modeling plan that uses only 3 points (maximum value, minimum value, and management standard) for typical flaws. For pavement segmentation, this study establishes a plan that uses a moving average combined with a minimum maintenance length standard to reflect existing condition distribution characteristics as much as possible. Finally, for priority, this study establishes a plan that performs selections using the averages of the index values of the sections that require maintenance, as determined via the segmentation step.

We successfully designed an optimized plenum fan with a three-dimensional, smooth, curved blade. The optimized model revealed that the static pressure in the channel had been increased uniformly and stably, and the flow separation at the leading edge was significantly reduced. According to simulations, the three-dimensional blade stabilized the fluid flow, and the flow friction was reduced by suppressing the flow separation as much as possible so that both the static pressure and the static efficiency were clearly improved in comparison with those of the original model. As a result, the static efficiency was improved by 6.3% compared with that of the original model.

Owing to the increasing usage of nanomaterials, it is imperative to assess their potential impacts on natural systems, and in particular, investigate if existing barriers can prevent nanomaterial emission in landfills because they will be disposed in landfills at the end of their useful lives. This study inspected the behavior of colloidal fullerene (nC

This study aims to evaluate the effect of different rejuvenators and antistripping agents on the healing performance of hot mix asphalt (HMA). Two damage HMA series (e.g., moisture damage and aged damage) were subjected to either induction or microwave heating. A PG64-22 virgin and aged binder were used and modified with several additives. Three long-term aged binders (e.g., PAV5, PAV15, and PAV20) were conducted by pressure aging vessel (PAV) test. The moisture damage series fabricating with a new binder was further categorized into four different freeze-thaw (FT) cycles (e.g., 0FT, 1FT, 3FT, and 5FT). Also, the aged series was fabricated with three different aged binders. A total of eight damage-healing cycles were applied to all asphalt mixtures, examined by the three-point bending test. The moisture resistance of modified asphalt mixture was examined by indirect tensile strength test. Overall, asphalt mixtures modified with either antistripping additives or rejuvenators not only obtained higher moisture resistance but also gained better healing performance under moisture damage. In addition, the study showed a probable correlation between moisture damage and long-term aging in terms of healing performance, such as PAV15 and 3FT cycles and PAV20 and 5FT cycles.

Solid waste landfills are one of the primary anthropogenic sources of methane emissions which are often estimated by flux chamber measurements on landfill surfaces. Due to the small footprint of the flux chamber on the surface coverage, however, it is important to design a proper spatial deployment of the chambers with an optimal number of measurement points such that the measured fluxes are correctly scaled up to the whole landfill area. In order to improve the design of flux chamber network, several deterministic interpolation models were applied and results of reproducibility tests with 22 flux measurement data sets from ten municipal solid waste landfills in the Republic of Korea were compared one another. The bilinear model and natural neighbor model among the deterministic models showed stable results in all cases. The surface methane emissions estimated from arithmetic or geometric mean resulted in significant under- or overestimation compared to spatial interpolation methods in all data sets. As a result of this study, minimal number of flux measurement points could be determined for target error levels. Innovative flux chamber network design with proper measurement points will improve the accuracy of methane emission estimate from solid waste landfills.

Most products containing engineered nanomaterials are disposed at landfills in the final stage of their lifecycle. This study aims to assess landfill liners as a final barrier of disposed silver nanoparticles (AgNPs). Sorption and transport of AgNPs were investigated in the laboratory-scale simulation of landfill liner conditions. Field soil (silt loam) and bentonite were tested in batch sorption experiments respectively. To test transportation, 3 cm thick mixture of the field soil and the bentonite constituted the porous media to meet the criteria for compacted clay liner of landfill. Mathematical modeling in the experimental and actual landfill conditions was also conducted. The results demonstrated considerable extent of sorption by both types of sorbents. The breakthrough of AgNPs was not observed for 200 days (over 20 pore volume). In general, the experimental results indicated that AgNPs cannot easily pass through the landfill clay liner under present standards. Modeling results also showed that AgNPs could be blocked effectively. Although long-term tests are still required, these results clearly show resistance to current sanitary landfill liners against AgNP penetration. As the trial to assess the safety of landfills against AgNP migration, this work provides insights into the fate and transport of nanomaterials in the landfill environment.

PURPOSES: The objective of this study is to investigate the properties of recycled asphalt binders with five different rejuvenators, in order to evaluate the applicability of the recycled asphalt binders compared with the original asphalt binder. METHODS: In order to simulate recycled asphalt binders, fresh asphalt binders are aged by various Superpave aging procedures, such as the rolling thin-film oven (RTFO) and the pressure aging vessel (PAV). Then, selected rejuvenators are added to the aged asphalt binders in the amount of 5%, 10%, and 15%. The asphalt binder properties are evaluated by the dynamic shear rheometer (DSR), the rotational viscometer (RV), and the bending beam rheometer (BBR). In this study, AP-5 (penetration grade 60-80, PG 64-16) asphalt binder is used. A total of five types of rejuvenators are employed. RESULTS AND CONCLUSIONS : When considering aged asphalt without a new asphalt binder, it seems that the percentage of rejuvenator used in Korea is a bit too low, and that it fails to possess the characteristics of the original binder. From the current practice of evaluating the properties of recycled binder based on penetration ratio only, the amount of rejuvenator required is similar for the long-term-aged binder, but is excessive for the longest-term aged binder, causing deterioration of workability and stiffness of the recycled binder.

In this research, surface moisture contents of columns and roof deflection of three Korean traditional timber houses were monitored. The monitored houses are composed of two different types of Hanok, that is, a one-story traditional Hanok built by traditional construction method, and two two-storied new-styled Hanok built by modernized construction method. The monitoring of traditional Hanok and new-styled Hanok1 has been carried out for about two and a half years, and that of the new-styled Hanok2 is 14 months. The monitored moisture contents were analyzed according to column location to the sun, wood types and relative humidity. The moisture contents of the northern columns are 0.71% higher than those of the southern columns, and moisture contents of raw wood was 0.83% higher than that of the glued structural wood. The mean vertical deflection of angle rafters is 11.6mm in traditional Hanok, 4.2mm in new-styled Hanok1 and 2.1mm in new-styled Hanok2. Meanwhile, the mean vertical deflection of plane rafters is 21.5mm in traditional Hanok, 9.7mm in new-styled Hanok1 and 20.3mm in new-styled Hanok2. Angle rafters and plane rafters showed meaningful deformations and that were affected mainly by roof weight and supporting member.

Recently in Korea, extensive research on developing a new style of Korean traditional wooden house, Hanok, has been conducted for duplicating architectural plan composition and appearance of the Hanok and for improving construction and economic efficiencies. The beam–column joint of the new Hanok is composed of general timber and steel plates for ensuring workability on site and enhancing the structural performance while a traditional Hanok simply adopts general mortise and tenon joints. In this study, the lateral stiffness of a 2-story new Hanok was evaluated by conducting the static lateral loading tests using a 1/4 scale specimen. The ‘I’ shaped plan part of the specimen was first tested and the effective rotational stiffness of the joints with steel plates was estimated by comparing roof displacements of the test specimen and a numerical model. The effective stiffness of the specimen increased with increasing vertical loads and decreased with increasing roof displacements. An equation for estimating the joint rotational stiffness was proposed with regard to the steel plate type based on the test result from the ‘I’ shaped plan specimen. The effectiveness of the equation was verified by showing that roof displacement of the test specimen with ‘L’ shaped plan could be approximately estimated by using an analytical model having joint rotational stiffness determined by using the proposed equation.

PURPOSES: The objectives of this study were to develop a new polymer-modified emulsion for application to tack coats and to evaluate its properties by comparing it with other types of asphalt emulsions, with the goal of providing an enhanced tack coat material for use in construction. METHODS: Modified asphalt binders were developed from using SBS and SBR latex in the laboratory, and their fundamental properties, such as their penetration index and PG grade, were evaluated. Based on the properties, a new tack coat material was developed. To evaluate the newly developed asphalt emulsion, the bonding strength between the two layers of HMA was measured by applying a uniaxial tensile test and shear test. For the tests, a total of four different conditions were applied to the specimens, including the developed asphalt emulsion, latex modified asphalt emulsion, conventional asphalt emulsion, and non-tack coating. RESULTS AND CONCLUSIONS: Overall, the developed asphalt emulsion exhibits the best bonding strength behavior among all of the three types. Also, the two types of polymer-modified emulsions were found to be better for application for use as a tack coat than a conventional emulsion. Especially, at a high temperature (), the conventional asphalt emulsion no longer acts as a tack coating material. Therefore, the polymer-modified emulsion should be considered for application to tack coat construction during the summer.

This research performed deformation monitoring for a Korean traditional wooden house called a Hanok to figure out its long-term deformational characteristics and hence, to establish basic data for the maintenance and management of Hanok. The monitored buildings are composed of two different types of Hanok, one is a one-story traditional Hanok built by traditional construction method, and the other is a two-storied, new-styled Hanok built by modernized construction method. The vertical deflection of roof structural members was measured for about two years. The mean vertical deflection of the angle rafter, called Chuneo, which is located on the corner of eaves, is 10.0mm in the traditional Hanok and 1.7mm and 5.7mm both in the new-styled Hanok's 1st and 2nd roof, respectively. The traditional Hanok showed 2~5times more deflection than the new-styled Hanok, and this result can be deduced from the fact that the roof weight of the traditional Hanok is 2~3 times more than that of the new-styled Hanok, so the traditional Hanok showed more long-term deflection than the new-styled Hanok.

PURPOSES : The objective of this study is to develop new pothole repair materials using polyurethane-modified asphalt binder, and to evaluate them relative to current pothole repair materials in order to improve the performance of repaired asphalt pavement. METHODS : In the laboratory, polyurethane-modified asphalt binder is developed, and then asphalt binder is added to produce pothole repair materials. In order to evaluate the properties of this new pothole repair material, both an indirect tension strength test and a direct tension strength test are performed to measure the material strength and bond strength, respectively. Additionally, the basic material properties are evaluated using the asphalt cold mix manual. The strength characteristics based on curing times are evaluated using a total of 7 types of materials (3 types of current materials, 2 types of new materials, and 2 types of moisture conditioned new materials). The indirect tension strength tests are conducted at 1, 2, 4, 8, 16, and 32 days of curing time. The bond strength between current HMA(Hot Mix Asphalt) and the new materials is evaluated by the direct tension strength test. RESULTS AND CONCLUSIONS : Overall, the new materials show better properties than current materials. Based on the test results, the new materials demonstrate less susceptibility to moisture, faster curing times, and an improved bond strength between HMA and the new materials. Therefore, the use of the new materials reported in this study may lead to enhanced performance of repairs made to asphalt pavement potholes.

PURPOSES : The objective of this study is to compare the densities of asphalt pavements measured both in the field and in the laboratory, and also to evaluate the applicability of field density measuring equipment, such as the pavement quality indicator (PQI), by using statistical analysis. METHODS : For the statistical analysis of the density measured from asphalt pavement, student t-tests and a coefficient of correlation are investigated. In order to compare the measured densities, two test sections are prepared, with a base layer and an intermediate layer constructed. Each test section consists of 9 smaller sections. During construction, the field densities are measured for both layers (base and intermediate) in each section. Core samples are extracted from similar regions in each section, and moved to the laboratory for density measurements. All the measured densities from both the field and laboratory observations are analyzed using the selected statistical analysis methods. RESULTS AND CONCLUSION : Based on an analysis of measured densities, analysis using a correlation coefficient is found to be more accurate than analysis using a student t-test. The correlation coefficient (R) between the field density and the core density is found to be very low with a confidence interval less than 0.5. This may be the result of inappropriate calibration of the measuring equipment. Additionally, the correlation coefficient for the base layer is higher than for the intermediate layer. Finally, we observe that prior to using the density measuring equipment in the field, a calibration process should be performed to ensure the reliability of measured field densities.

3-차원 원통 구조의 공명관에 Krylov-Schur 순환 법을 적용하였다. 균질한 메질에서 공명파의 세기를 기술하는 벡터Helmholtz 방정식을 FEM을 이용하여 분석하였다. 고유 방정식은 사면 배위 구조 요소의 변-접선 벡터에 기반을 두어 구성하였다. 이 방정식은 Helmholtz 작용자의 curl-curl과 연관된 정방형 행렬들로 이루어져 있다. 고유-값들과 고유-모드들은 이들에 대하여 Krylov-Schur 순환 법을 적용하고, Schur 행렬의 대각 성분들과 변환 행렬들로 부터 구하였다. 결과로써 이들 고유-값과 고유-모드 쌍들을 시각적으로 묘사하였다. 그리고 각각의 경계조건에 따른 고유-쌍들을 서로 비교하였다.

This research performed dynamic tests on a 1/4 scale test model of a new-styled Korean traditional wooden house to study its dynamic characteristics. The dynamic tests were performed both by the impact hammer test and the shaking table test of an El-centro N-S seismic wave. Together with these dynamic tests, structural analysis was also performed and the results were compared. The natural frequency from the impact hammer test was slightly higher than that from the shaking table test. The natural frequency from the eigenvalue analysis was about 16~33% lower than that from both the impact hammer test and the shaking table test. It can be deduced that the rotational stiffness of joints of analysis model were somewhat underestimated than those of experiment model.

In this study the section tables were developed which help to decide appropriate section size of lateral members of 3-ridge and 5-ridge roof hanok, such as, ridgepole, Jusim-Dori, Dori and Jangyeo, Pyung-Bang and Chang-Bang, and rafters. The main items which were considered in developing section tables are roof structure types, timber species and material properties, overburden loads, length and disposition of members. We proposed schemes for computing allocation loading area for each lateral members according to geometric shapes and topological disposition between members. The length of members and size of sections are restricted to a field applicable ranges. The filed applicability of the developed section tables were evaluated using a test-bed hanok in Myongji University and a pilot hanok in Eunpyeong hanok village. The evaluation was carried out by comparing three results of sections from detailed structural design, section tables and actual construction. It turns out that the sections from section tables are somewhat conservative but has sufficient field applicability in early design stage.

Krylov-Schur 반복법을 활용하여 2-차원 사각 도파관에서 나타나는 고유특성을 밝혔다. 고유 행렬 방정식은 삼각형 그물 요소의 접선을 기저벡터로 사용한 FEM(유한요소법)으로 구성하였다. 우선 Arnoldi 분해법을 이용하여 이 방정식에 대한 상위 Hessenberg 행렬을 구하였다. 그리고 QR 알골리즘을 통하여 이것을 삼각형 대각 행렬인 Shur 형태로 변형하였다. 수렴 조건에 부합된 몇몇 고유 값들이 삼각형 대각 행렬의 대각 요소에 나타났다. 이들에 대응하는 고유 모드들을 역-반복법으로 구하였다. 수렴조건에 부합되는 고유 값들은 Shur 행렬의 대각선 선두 부분으로 재배열시켰다. 이들은 나머지 고유값 및 고유모드의 쌍을 구하는 반복 과정에서 변형되지 않도록 배제되었다. 이 과정이 연속하여 서너 번 반복되었는데, 그 결과 충분한 신뢰도를 갖는 주요한 몇 개의 TM 및 TE 고유 쌍들이 구하여졌다.

South Gobi road of 240-km flexible pavement was constructed from UKHAA KHUDAG to GASHUUN SUKHAIT in South Gobi, Mongolia in 2011. However, due to the heavy traffic and severe weather condition, early distresses have occurred from a length of 100-km flexible pavements in South Gobi road after one year service life. In order to enhance crack and rutting resistances and to improve paving quality control in South Gobi road, polymer modifier is selected to reduce rutting at high temperature and cracking at low temperature and warm-mix asphalt (WMA) additive is selected to reduce the mixing and compacting temperatures and provide better compaction on the road and the ability to haul paving mix for longer distances. This paper adopted comprehensive asphalt tests to evaluate physical and rheological characteristics, and crack potential at low temperature for use in a South Gobi road. Laboratory tests were performed on asphalt binder with a polymer modifier and warm-mix asphalt additive by conducting the following tests: softening test, ductility test, SuperpaveTMtest and cold bending test. These test results of asphalt binder with SBS polymer modifier and warm-mix asphalt additive were significantly more positive than those of typical asphalt binder. On the basis of test results, it can be concluded that the asphalt binder with SBS polymer modifier and WMA additive is stronger and less susceptible to rutting and crack than typical asphalt binder used in South Gobi.

PURPOSES : Compared to the criteria from advanced countries, Korea has conservative criteria for the buried depth of pipeline (about 30~70cm deeper) causing the waste of cost and time. Therefore, this research investigated the effect of various buried depths of pipeline on pavement performance in order to modify the criteria to be safe but economical. In addition, a recycled aggregate which is effective in economical and environmental aspect was evaluated to be used as a refilling material. METHODS : In this study, total 10 pilot sections which are composed with various combinations of pavement structure, buried depth of pipeline, and refilling material were constructed and the telecom cable was utilized as a buried pipeline. During construction, LFWD (Light Falling Weight Deflectometer) tests were conducted on each layer to measure the structural capacity of underlying layers. After the construction is completed, FWD (Falling Weight Deflectometer) tests and moving load tests were performed on top of the asphalt pavement surface. RESULTS : It was found from the LFWD and FWD test results that as the buried depth decrease, the deflections in subbase and surface layer were increased by 30% and 5~10%, respectively, but the deflection in base layer remained the same. In the moving load test, the longitudinal maximum strain was increased by 30% for 120mm of buried depth case and 5% for 100mm of buried depth case. Regarding the effect of refilling material, it was observed that the deflections in subbase and surface layer were 10% lager in recycled aggregate compared to the sand material. CONCLUSIONS : Based on the testing results, it was found that the change in buried depth and refiliing material would not significantly affect the pavement performance. However, it is noted that the final conclusion should be made based on an intensive structural analysis for the pavement under realistic conditions (i.e., repeated loading and environmental loading) along with the field test results.

FEMhasbeenusedtoobtaintheeigen-modesofPCFinvolvingthevarieddistributionofthedielectricholes.PCFwasassumedtobeconstructedwiththebackgroundmaterialofhigh-indexdielectricandtheseveralcircularholesoflow-indexone.TheseholeswerethedielectricsuchliketheairandsurroundedthecentralregionofPCF.FEMhasgiventheresultsthatthespectrawerevariedaccordingtothepositionanddimensionofthedielectricairholes.Eacheigen-modeshavebeenidentifiedbasedonthespectraoftheconventionalopticalfiber.Thespectrahaveshownthatthebackgroundmaterialrestrictedthedistributionofelectromagneticfieldtothecentralregion.Fromtheseresults,ithasreconfirmedthattheairdielectricholescombinedwithbackgroundmaterialtoconfinetheelectromagneticfieldintothesmallcentralregionofPCF. Keywords:FEM,PCF,eigen-mode,dielectric,waveguide.

PURPOSES : This study evaluated the field applicability and laboratory performance of warm-mix asphalt (WMA) as an alternative technology in asphalt pavement. METHODS : The pilot road using two different types of WMA mixture and one HMA mixture was constructed in Waegwan-Seokjeok road construction site and the mixtures were sampled at the asphalt plant for laboratory testings. The field applicability was assessed in environmental aspects, such as emission, and in aspects of constructibility using the existing equipment and procedure, i.e., thickness and density measurement. The laboratory testings included the moisture susceptibility test by AASHTO T283, dynamic modulus test, triaxial repeated load permanent deformation test, and the fatigue test. RESULTS : The temperatures for production and compaction of WMA were lower than those for HMA and therefore, the noxious gas emission were significantly reduced. The field density of WMA pavements was similar or better than that of HMA pavement. From the laboratory testings, it was found that WMA mixtures exhibit comparable performance to HMA mixture in moisture susceptibility, permanent deformation, and fatigue performance. CONCLUSIONS : With these results, it would be concluded that WMA could replace the existing HMA technology without any significant issue. To support this conclusion, it is necessary to track the long-term performance of WMA in pilot road.