In order to improve the durability of the asphalt pavement, the glass fiber reinforced asphalt which reinforces the aggregate and the binder in three - dimensional form by adding glass fiber to the asphalt mixture has been studied and the durability improvement effect of the asphalt pavement has been confirmed. Porous pavement has been increasingly applied due to reduced traffic accidents and noise reduction, but durability problems such as aggregate stripping and pot-hole are emerging. This study evaluated the durability enhancement effect by adding glass fiber to the porous mixture. The cantabro loss ratio and the indirect tensile strength test were performed to evaluate the performance of the glass fiber reinforced porous mixture. The glass fibers were added to the mixture using PG76-22 and PG64-22 binder and not to the mixture using PG82-22 binder. The mixture using the PG76-22 binder was added 1.4% (PEGS 0.6%, Micro PPGF 0.2%, Macro PPGF 0.6%) glass fiber based on the weight of the mixture. The mixture using the PG64-22 binder was added 1.4% (PEGS 0.6%, Micro PPGF 0.2%, Macro PPGF 0.6%) and 2.1% %(PEGS 0.9%, Micro PPGF 0.3%, Macro PPGF 0.9%)glass fibers by weight of the mixture. The glass fibers were used at the same ratio as that applied to the conventional asphalt mixture test. As a result of the cantabro loss rate test, the mixture using the PG82-22 binder showed a loss rate of 10.7% at 20 ℃ and 22.4% at -20 ℃. The mixture using PG76-22 binder and 1.4% glass fiber showed a loss ratio of 13.2% at 20 ℃ and 26.7% at -20 ℃. The mixture using PG64-22 binder and 1.4% glass fiber showed a loss rate of 12.5% at 20 ℃ and 35.9% at -20 ℃. The mixture using PG64-22 binder and 2.1% glass fiber showed a loss rate of 11.9% at 20 ℃ and 26.6% at -20 ℃. The three mixtures (using of PG82-22 binder, PG76-22 binder + 1.4% glass fiber and PG64-22 binder + 2.1% glass fiber) satisfied quality standard of Ministry of Land, Infrastructure and Transport. As a result of the indirect tensile strength test, the mixture using the PG82-22 binder showed 0.73 N/㎟. The mixture using PG76-22 binder and 1.4% glass fiber showed 0.88 N/㎟. The mixture using PG64-22 binder and 1.4% glass fiber showed 0.62 N/㎟. The mixture using PG64-22 binder and 2.1% glass fiber showed 0.74 N/㎟. In this study, the durability enhancement effect was confirmed by adding glass fiber to the drainage mixture. We will do further research to confirm the optimal combination of glass fibers.

PURPOSES: Evaluation of the wind speed effect on the temperature drop of an asphalt mixture during construction, by using the transient heat transfer theory and dominant convective heat transfer coefficient model. METHODS: Finite difference method (FDM) is used to solve the transient heat transfer difference equation numerically for various wind speeds and initial temperature conditions. The Blasius convective heat transfer coefficient model is adapted to account for the effect of wind speed in the temperature predictions of the asphalt mixture, and the Beaufort number is used to select a reasonable wind speed for the analysis. As a function of time and depth, the temperature of the pavement structure is predicted and analyzed for the given initial conditions. RESULTS : The effect of wind speed on the temperature drop of asphalt mixture is found to be significant. It seems that wind speed is another parameter to be accounted for in the construction specifications for obtaining a better quality of the asphalt mixture. CONCLUSIONS: It is concluded that wind speed has a significant effect on the temperature drop of the asphalt layer. Although additional field observations have to be made to reflect the effect of wind speed on the construction specifications, it appears that wind speed is a dominant variable to be considered, in addition to the atmospheric temperature.

PURPOSES: Implementation and verification of the simple linear cohesive viscoelastic contact model that can be used to simulate dynamic behavior of sticky aggregates. METHODS: The differential equations were derived and the initial conditions were determined to simulate a free falling ball with a sticky surface from a ground. To describe this behavior, a combination of linear contact model and a cohesive contact model was used. The general solution for the differential equation was used to verify the implemented linear cohesive viscoelastic API model in the DEM. Sensitivity analysis was also performed using the derived analytical solutions for several combinations of damping coefficients and cohesive coefficients. RESULTS : The numerical solution obtained using the DEM showed good agreement with the analytical solution for two extreme conditions. It was observed that the linear cohesive model can be successfully implemented with a linear spring in the DEM API for dynamic analysis of the aggregates. CONCLUSIONS: It can be concluded that the derived closed form solutions are applicable for the analysis of the rebounding behavior of sticky particles, and for verification of the implemented API model in the DEM. The assumption of underdamped condition for the viscous behavior of the particles seems to be reasonable. Several factors have to be additionally identified in order to develop an enhanced contact model for an asphalt mixture.

PURPOSES : In this study, a fracture-based finite element (FE) model is proposed to evaluate the fracture behavior of fiber-reinforced asphalt (FRA) concrete under various interface conditions. METHODS: A fracture-based FE model was developed to simulate a double-edge notched tension (DENT) test. A cohesive zone model (CZM) and linear viscoelastic model were implemented to model the fracture behavior and viscous behavior of the FRA concrete, respectively. Three models were developed to characterize the behavior of interfacial bonding between the fiber reinforcement and surrounding materials. In the first model, the fracture property of the asphalt concrete was modified to study the effect of fiber reinforcement. In the second model, spring elements were used to simulated the fiber reinforcement. In the third method, bar and spring elements, based on a nonlinear bond-slip model, were used to simulate the fiber reinforcement and interfacial bonding conditions. The performance of the FRA in resisting crack development under various interfacial conditions was evaluated. RESULTS : The elastic modulus of the fibers was not sensitive to the behavior of the FRA in the DENT test before crack initiation. After crack development, the fracture resistance of the FRA was found to have enhanced considerably as the elastic modulus of the fibers increased from 450 MPa to 900 MPa. When the adhesion between the fibers and asphalt concrete was sufficiently high, the fiber reinforcement was effective. It means that the interfacial bonding conditions affect the fracture resistance of the FRA significantly. CONCLUSIONS: The bar/spring element models were more effective in representing the local behavior of the fibers and interfacial bonding than the fracture energy approach. The reinforcement effect is more significant after crack initiation, as the fibers can be pulled out sufficiently. Both the elastic modulus of the fiber reinforcement and the interfacial bonding were significant in controlling crack development in the FRA.

PURPOSES: Evaluation of thermal conductivity and convection properties of asphalt mixture by using thermodynamics. METHODS: In this research, temperature prediction model based on thermodynamics is derived for asphalt mixture in transient state and it is verified with laboratory test results. RESULTS: The derived temperature prediction model shows good agreement with laboratory test results. CONCLUSIONS: It is concluded that the derived model based on thermodynamics and thermal properties in the literature are good enough to capture temperature variation in laboratory test. The approach based on thermodynamics can be applied to more complex temperature simulations.

PURPOSES: Evaluation of input parameters determination procedure for dynamic analysis of aggregates in DEM. METHODS: In this research, the aggregate slump test and angularity test were performed as fundamental laboratory tests to determine input parameters of spherical particles in DEM. The heights spreads, weights of the simple tests were measured and used to calibrate rolling and static friction coefficients of particles. RESULTS : The DEM simulations with calibrated parameters showed good agreement with the laboratory test results for given dynamic condition. CONCLUSIONS: It is concluded that the employed calibration method can be applicable to determine rolling friction coefficient of DEM simulation for given dynamic conditions. However, further research is necessary to connect the result to the behavior of aggregate in packing and mixing process and to refine static friction coefficient.

PURPOSES : Determination of particle packing model variables that can be used for formulation of new DEM based particle packing model by examining existing particle packing models METHODS : Existing particle packing models are thoroughly examined by analytical reformulation and sensitivity analysis in order to set up DEM based new particle packing model and to determine its variables. All model equations considered in this examination are represented with consistent expressions and are compared to each others to find mathematical and conceptual similarity in expressions. RESULTS : From the examination of existing models, it is observed that the models are very similar in their shapes although the derivation of the models may be different. As well, it is observed that variables used in some existing models are comprehensive enough to estimate particle packing but not applicable to DEM simulation. CONCLUSIONS : A set of variables that can be used in DEM based particle packing model is determined.

PURPOSES: Simulation of aggregate slump test using equivalent sphere particle in DEM and its validity evaluation against lab aggregate slump test METHODS : In this research, aggregate slump tests are performed and compared with DEM simulation. To utilize spheric particles in YADE, equivalent sphere diameter concept is applied. As verification measures, the volume in slump cone filled with aggregate is used and it is compared with volume in slump cone filled with equivalent sphere particle. Slump height and diameter are also used to evaluate the suggested numerical method with equivalent concept RESULTS : Simulation test results show good agrement with lab test results in terms of loose packing volume, height and diameter of slumped particle clump. CONCLUSIONS : It is concluded that numerical simulation using DEM is applicable to evaluate the effect of aggregate morphological property in loose packing and optimum gradation determination based on the aggregate slump test simulation result.

PURPOSES: To characterize the aging effect on asphalt binder, dynamic shear modulus mastercurve of two typical asphalt binders are developed. METHODS: To develop dynamic shear modulus mastercurve, dynamic shear modulus at high temperature and creep stiffness at low temperature are measured by temperature sweep test and bending beam rheometer test, respectively. RESULTS: It is observed that the aging effect on asphalt binder can be clearly observed from dynamic shear modulus mastercurve and the mastercurve can be utilized to predict behavior of asphalt binder at wide range of temperature. CONCLUSIONS: It is confirmed that SBS 5% modified binder has more desirable mechanical property at low and high temperature as a pavement material comparing to PG64-22 binder and the mastercurve is an effective tool to evaluate the property of asphalt binder.

PURPOSES: As pavement generally provides service shorter than an expected life cycle, maintenance cost increases gradually. In order to help extending the service life and reduce maintenance cost, a new multi-functional composite pavement system is being developed in Korea. METHODS: This study is a part to develop the multi-functional composite pavement and is to investigate the mechanical performances of fiber-reinforced lean concrete for pavement subbase. The inherent problem of fiber reinforced concrete is dispersion of fibers in concrete mix. This study additionally evaluated fiber dispersion characteristics with respect to different fiber types. RESULTS: From the test results, the compressive strengths of the concretes satisfied the required limit of 5MPa at 7days. The standard deviation of the measured number of fibers were lower in the order of nylon, steel fiber and polypropylene. CONCLUSIONS: Reject ash was shown to be satisfactory as a replacement material to Portland cement in lean concrete base. The fiber volume fraction is suggested to be 0.4% even though the fracture toughness did not vary significantly with respect to fiber types. However, fracture energy absorbed up to complete failure increased with the increased fiber volume fraction increment.

최근 도로포장에 수분이 많이 침투한 상태에서 중차량 교통량의 증가로 아스팔트 포장에 파손이 증대되어 그 중 하나인 포트홀이 많이 발생한다. 이에 따라 도로안전운전에 심각한 장애가 되며 교통사고가 빈번하게 발생하여 기준에 미달하는 자재 사용으로 도로의 조기 파손을 불러온다는 지적이 제기되고 있다. 다양한 포트홀 보수 방법이 사용되고 있지만, 보수 후 포트홀 발생 부위에 적절하지 않은 보수 방법으로 인하여 다시 포트홀이 발생되고 있으며, 그로 인한 잦은 재보수로 유지 보수 비용역시 증가되고 있는 실정이다. 이에 따라 본 연구에서는 아스팔트 혼합물의 내구성을 증진하여 도로포장에 발생하는 포트홀을 방지할 수 있는 포장 재료를 개발하는데 목적이 있다. 산업 부산물인 유리섬유 파분을 이용하여 골재형태로 제조한 석분대체용 유리 파분 골재와 유리섬유를 이용하여 실내 실험에서 검증된 유리 섬유 혼합물을 현장 적용성을 평가 하였다. 실내 배합설계를 통하여 최적 보강 섬유량을 결정하였으며, 유리 섬유 보강 아스팔트 혼합물의 적정 생산 온도 및 다짐 횟수를 결정해 현장 적용을 실시하였다. 수원 국토 관리 사무소 관내 국도 38호선에 2회에 걸쳐 시험 포장을 진행하였고, 총 500m 구간 중 100m에 적용하였으며, 현장 적용도를 비교 평가하기 위해 1차 시험 포장의 경우 전체 생산 혼합물량 대비 유리 보강 섬유량 1.3%(유리 장섬유 펠렛 0.66%+ 리사이클 펠렛 0.66%), 2차 시험 포장의 경우 유리 보강 섬유량 1.0%(유리 장섬유 펠렛 0.5%+ 리사이클 펠렛 0.5%)로 각각 다른 보강 섬유량을 결정하여 생산하였다.