Dae-Wook Park

Evaluation of Predicted Pavement Response with Measured Tire Contact Stresses

A uniform circular vertical contact stress is commonly assumed in representing wheel loads in pavement analysis procedures. However, experimental measurements have shown that actual loading conditions are nonuniform and depend on tire construction, tire load, and tire inflation pressure. Predicted pavement response from three-dimensional (3D) finite element (FE) and layered elastic programs were compared to establish guidelines for modeling wheel loads in current layered elastic pavement analysis programs to provide a better approximation of pavement response parameters for design and evaluation. Tire contact pressure was measured with the stress-in-motion pad. In addition, tire contact pressure measurements from a previous study conducted at the University of California at Berkeley were obtained. Available contact pressure measurements on four tires were used to predict pavement response with a 3D FE program, which permitted input of measured tire contact pressures at various tire loads and tire inflation pressures. Horizontal strain at the bottom of the asphalt layer, compressive strain at the top of the subgrade, and principal stresses at different depths were predicted. Similar predictions were generated with layered elastic theory with two different representations of contact pressure and contact area. From predicted strains, service life for a range of pavements, tire load, and tire inflation pressures were estimated with limiting strain criteria. In addition, Mohr-Coulomb (MC) yield function values were calculated from predicted principal stresses at different depths. The MC yield function values and pavement life estimates from 3D FE and layered elastic analyses were compared with established guidelines for modeling wheel loads using existing layered elastic procedures.

Evaluation of Asphalt Mixture Modified with Graphite and Carbon Fibers for Winter Adaptation: Thermal Conductivity Improvement

AbstractConventional asphalt concrete is relatively low conductive. This paper focus on the improvement of thermal properties of asphalt mixtures using conductive fillers, and investigating the conduction performance by two-dimensional (2D) simulation. Also, the microstructure of asphalt mixture was analyzed with extremely high magnification to observe the distribution of conductive fillers in the mixture. Indirect tensile (IDT) strength was additionally investigated. Different asphalt mixtures used in this study was modified with milled carbon fiber, chopped carbon fiber, and graphite powder. The study also evaluated the effect of mixed fillers combined carbon fiber with varying admixtures of graphite contents. The thermal properties of modified asphalt mixtures were measured and calculated to evaluate their conduction effects to obtain the appropriate kind and quantity of carbon fibers and graphite. Based on the results of thermal properties of the asphalt mixtures, the 2D simulation was performed on a ...

Estimation of pavement rehabilitation cost using pavement management data

Estimation and scheduling of future pavement maintenance and rehabilitation (M&R) works are one of the primary concerns of highway agencies due to the limited allocations in budget and resources. Two approximate methods for estimation of pavement rehabilitation cost are presented and compared in this study based on highway present condition index (HPCI) and rehabilitation history. The former is based on pavement condition, while the latter is based on historical and statistical trends. Database from a pavement management system (PMS) of various highway sections surveyed in Korea were used in this study to establish a relationship between HPCI and pavement service life and to analyse the trends of rehabilitation periods. The two simple methods presented provide useful information and probable range for the various highway agencies to guide them in the preliminary planning, budgeting, estimating and scheduling of their future pavement M&R works.

Thermal properties of permeable friction asphalt mixture and estimation of temperature profiles

The compaction of asphalt mixture at a proper temperature range is a very important factor to get the desired density of the asphalt mixture. The aim of this study was to determine the time at which the desired temperature is achieved and to investigate the effect of the permeable friction course (PFC) asphalt mixture properties on thermal conductivity. The thermal conductivity was measured using a surface probe type, and the values of thermal conductivity of PFC mixtures were smaller compared to dense-graded mixture. The relationships between thermal conductivity and asphalt mixture properties were investigated. Compaction temperature profiles were predicted using a simulation program that is developed based on one-dimensional (1D) heat conduction equation, finite difference method and environmental conditions. The results of the predicted temperature profiles were evaluated by comparing the measured in situ temperature profiles during compaction. From the results, it was found that the predicted time at a specified temperature could be used to determine the compaction time.

Traffic loadings considering temperature for pavement rutting life

The procedures for obtaining Temperature Conversion Factor (TCF) are described. This factor accounts for the pavement temperature variation during full-scale truck trafficking. This variation results from changes in air temperature and the distribution of temperature with depth in the pavement structure. Repeated load triaxial tests at multiple temperatures were conducted to consi der temperature effects on an asphalt mixture in terms of permanent deformation. The TCF was calculated using the results of repeat ed load triaxial tests and layered strain procedures based on field temperature distribution with depth. The TCF was applied to convert ESALs at the field temperatures to ESALS at the standard temperature, which can be used in temperature controlled laboratory accelerated pavement tests (APT) or material property tests. The TCF provided a simple, convenient way to convert traffic loading at various temperatures to its equivalent at a standard temperature

Simulation of Rutting Profiles Using a Viscoplastic Model

The development of high speed computers has encouraged researchers to increasingly utilize the finite element method (FEM) to simulate more realistic pavement structures and loading conditions in their efforts to predict the performance of asphalt pavem ents. Analysis of pavement materials using mechanistic constitutive materials models is an integral part of these efforts. An elastic viscoplastic continuum model based on Perzyna’s viscoplastic theory and the Drucker-Prager yield function is proposed to simula te the permanent deformation of a hot mix asphalt (HMA) mixture at WesTrack. Compressive strength tests were performed at differen strain rates and confinement pressures to obtain the elastic-viscoplastic constitutive material parameters. The test temperature was 60 °C based on the critical temperature for permanent deformation at 12.5 mm of the WesTrack replacement section. Permanent deformation of the replacement section was simulated by the three dimensional FEM program, ABAQUS. The same trend of rutting profiles was obtained for both the measured and the simulated rutting profiles.

Aggregate gradation theory, design and its impact on asphalt pavement performance: a review

ABSTRACT Gradation is one of the crucially important features of aggregate blend. The objective of this paper is to present a review on the theory and design method of aggregate gradation, followed by its effect on asphalt pavement performance. The results indicate that, (i) Theory of maximum density curve, particle interfering theory and fractal theory are the main theories for aggregate gradation. (ii) The gradation design of asphalt mixture has two types by aggregate morphology-continuous and gap gradation, or three types by air voids of mixture-dense, open and semi-open gradation. However, the only constant principle of aggregate gradation design is to strictly follow the requirements of pavement performance. (iii) Aggregate gradation significantly influences almost all of the pavement performances. The performance-based design method for asphalt mixture should pay more attention on aggregate gradation. (iv) The variability of aggregate gradation cannot be eliminated due to its objective existence from aggregate production in quarry to mixture compaction in field. Several effective control measures are summarized to limit gradation variability under an acceptable range. (v) The latest developments and the trend for gradation analysis are numerical simulation based on virtual reconstruction, image-based modelling and computer-generated modelling.

Investigation of Asphalt Track Behavior Under Cyclic Loading: Full-Scale Testing and Numerical Simulation

In this study, the full-scale testing of asphalt track and numerical simulation using the viscoelastic material property of asphalt mixtures under cyclic loading was investigated. Dynamic modulus tests were conducted to characterize the linear viscoelastic property of asphalt mixtures. The full-scale test was performed to simulate train movement on the rail track with cyclic loading using the rail load simulator. The full-scale test and numerical simulations were implemented on three different layers of the asphalt with different thicknesses. The results were then subsequently compared to prove the reliability of the methods. The laboratory testing results indicate that the asphalt mixture for the surface layer, a polymer-modified asphalt, provides a high elastic modulus and behaves more elastically at low-frequency loading compared to the conventional mixtures for the intermediate and base layers. The full-scale test indicates that all cases of asphalt layer thickness satisfy the settlement criteria. However, only the asphalt layer with a 35-cm thickness attains the earth pressure requirement. The numerical simulation results are reasonable and reliable by fitting the measurement curves of cyclic loading test.

Lightweight Treated Soil As a Potential Sustainable Pavement Material

AbstractRecycling of poor soil becomes very important when good-quality construction materials are limited. This paper investigates the properties of lightweight treated soil such as strength properties based on the stress-strain behaviors, durability by simulating the freeze-thaw cycle (FTC), and evaluation of the road performance when lightweight treated soil was used as a subbase layer. Lightweight treated soil was made by mixing dredged soil waste, cement, air-foam, and water with the determined proportion. Test specimens were prepared with various cement contents and air-foam contents. Several series of unconfined compression tests, FTC tests, and thermal conductivity tests were then conducted. From the results of the experiments, it is observed that the strength of lightweight treated soil increased with an increase in cement content, but decreased with an increase in air-foam content or number of FTCs. The thermal conductivity of lightweight treated soil decreases with increasing air-foam content. ...

Anti-Oxidants’ Effect on Bitumen Rheology and Mixes’ Mechanical Performance

The oxidation mechanism in polymer-modified bitumen tends to alter physical and chemical properties. In this study five anti-oxidants are evaluated to examine their potential to mitigate polymer-modified bitumen oxidation. Styrene copolymers and hindered phenol additives are evaluated at low, intermediate and high temperature using aging indices. The styrene copolymers were effective at high temperature while the hindered phenols were effective at low and intermediate temperature. Two blends of both additives were introduced to cover a wide spectrum of temperature. Frequency and temperature sweep testing suggested that the blend improved the recoverable imposed energy at wide range of temperature/frequency. The blends have also improved resistance to rutting and moisture susceptibility for the asphalt mixes.