Dr. Y.R.Kim's Home Page

Dr. Y. Richard Kim

Research Groups

Aspahlt Materials Analysis Group

Pavement Analysis Group

Accelerated Pavement Testing Group

Sponsored Research Projects

1.      “Top-Down Fatigue Cracking of Hot-Mix Asphalt Layers,” NCHRP 1-42A, Subcontract from the University of Florida, $120,000.
Abstract: In this research, the viscoelastic continuum damage model implemented in the finite element program (VECD-FEP++) will be used to investigate the top-down fatigue cracking mechanism in hot-mix asphalt pavements. The VECD model and the dynamic modulus from the IDT test will serve as the primary experimental tools. The resulting VECD-FEP++ will be used to simulate the behavior of asphalt pavements with varying loading, environmental, and pavement factors. The results from the simulation will be investigated to develop mechanistic procedures to evaluate the top-down cracking propensity of asphalt pavement as a function of various factors and to predict the top-down cracking performance of asphalt pavement.

2.      “Development of a Multiaxial VEPCD-FEP++ and Its Extension to the Indirect Tension Test,” Federal Highway Administration, Sep. 1, 2005-Aug. 31, 2007, $499,907.
Abstract: Over the past decade, the NCSU research team has been successful in developing HMA models that can accurately capture various critical phenomena such as microcrack induced damage, strain rate – temperature interdependence, and viscoplastic flow that is critical for high temperature modeling; the resulting model is termed the viscoelastoplastic continuum damage (VEPCD) model. The primary objectives of this research are: (1) to extend the VEPCD model to multiaxial state of stress; (2) to develop a three-dimensional finite element program with the multiaxial VEPCD model; and (3) to extend the principles used in the VEPCD modeling to the indirect tension mode.

3.      “Calibration of Rutting Models for HMA Structural and Mix Design,” NCHRP 9-30A, Subcontract from Applied Research Associates, Inc., June 1, 2005-Aug. 31, 2008, $70,000.
Abstract: The objective of this research effort is to recommend revisions to the HMA rut depth prediction model in the mechanistic-empirical pavement design guide and software developed in NCHRP Project 1-37A for consideration by the NCHRP Project 1-40 panel and the AASHTO Joint Task Force on Pavements. The recommended revisions will be based on the calibration and validation of distress models with measured materials properties and performance data from existing field and other full-scale pavement sections that incorporate modified as well as unmodified asphalt binders.

4.      “Implementation Plan for the New Mechanistic-Empirical Pavement Design Guide,” NCDOT, May 1, 2005-June 30, 2006, $90,422.
Abstract: The goal of the proposed research is to develop an implementation plan for the Guide. This goal will be attained by accomplishing the following objectives:

develop a summary of the design practices outlined in the Guide that differ from the current design practice used by the NCDOT;

perform a sensitivity analysis on the design input parameters using realistic input ranges;

develop a local calibration plan; and

develop a local training program

5.      “Quantifying the Benefits of Improved Rolling of Chip Seals,” NCDOT, July 1, 2005-June 30, 2007, $264,638.
Abstract: The proposed research is aimed at “low hanging fruit,” that is, relatively low cost changes in compaction procedures that could significantly improve the chip seal performance in North Carolina. The performance measures to be evaluated in this study include aggregate embedment depth, aggregate retention, skid resistance, bleeding, and rutting. The research approach utilizes the chip seal performance test methods that have been used and refined in the ongoing NCDOT HWY 2003-09 project, Optimizing Gradations for Surface Treatments. The experimental program involves both laboratory and field experiments.

6.      “Viscoelastoplastic Continuum Damage Modeling of Modified and Unmodified Asphalt Mixtures,” Dwight David Eisenhower Transportation Fellowship to Mr. Benjamin Shane Underwood, US Department of Transportation, Sep. 1, 2004-Sep. 1, 20065, $60,800.
Abstract: The objective of this research is to verify the viscoelastoplastic continuum damage model for a wide range of mixtures, including modified mixtures. To verify the results, mixtures whose life is known must be compared to the model predictions. Pavements tested under the Accelerated Loading Facility (ALF) at the Federal Highway Administration Turner-Fairbank Highway Research Center in McLean, Virginia will be used for this purpose.

7.      “Development of the Asphalt Pavement Performance Prediction Methodology Based on the Viscoelastoplastic Continuum Damage Theory,” Korea Highway Corp., Sep. 1, 2004-Dec. 18, 2006, $335,021.

      Abstract: The primary objectives of the proposed research are: (1) standardization of test and analysis methods for the determination of viscoelastic properties and performance of asphalt mixtures used in the KHC Test Road project; (2) development of the multiaxial viscoelastoplastic continuum damage (VEPCD) models for six asphalt mixtures used in the KHC Test Road project using the indirect tension (IDT) test and triaxial permanent deformation test; (3) development of the VEPCD finite element program in C++ language (VEPCD-FEP++); (5) calibration of the VECPD-FEP++ using the pavement response and performance data measured from the KHC Test Road project pavements; (6) development of transfer functions for the 33 asphalt pavements in the KHC Test Road project; and (7) development of a user-friendly graphic interface for pre- and post-processing of the VEPCD-FEP++ and user’s manuals.

8.      “Investigation of the Causes for Cracking on Longitudinal Joints in Glassgrid Reinforced Asphalt Pavements,” Saint-Gobain Technical Fabrics, June 15, 2004-Sep. 30, 2004, $13,808.

      Abstract: The primary objective of the proposed research is to investigate the effects of vibratory compaction and grid opening size on the density of asphalt pavement over the GlasGrid longitudinal joint. Two grid materials, GlasGrid 8501 with half inch openings and GlasGrid 8511 with one inch openings, are investigated in this study.

9.      “Characterization of ALF Mixtures Using the Viscoelastoplastic Continuum Damage Model,” FHWA, Aug. 15, 2003-Aug. 14, 2005, $199,795.

      Abstract: The primary objectives of the proposed research are: (1) to verify the time-temperature superposition principle in damaged states for various asphalt mixtures used in the current ALF study; (2) to characterize the ALF mixtures using the viscoelastoplastic continuum damage model; and (3) to predict the performance of various ALF pavements using finite element analysis and the VEPCD model.

10. “Optimizing Gradations for Surface Treatments,” NCDOT, July 1, 2003-June 30, 2005, $215,576.

      Abstract: Due to the ongoing commitment to pavement preservation and the growing number of miles of low volume roads, the use of surface treatments has increased substantially in recent years and is likely to continue to rise in the future. This increase in the use of surface treatments has led state agencies to invest in reviewing their design procedures and to modify their existing specifications and develop new mix design systems. Such systems would address material selection, mixture characteristics, performance evaluation, and other influencing factors such as traffic, climate, and existing pavement conditions. The primary objective of this proposed research project is to evaluate the current mixture characteristics of surface treatments used in North Carolina and recommend modifications to the current specifications, particularly those related to aggregate gradations, if needed. In addition, the effects of different mixture characteristics on performance will be identified and incorporated in mix design guidelines.

11. “Determination of Dynamic Moduli for Typical North Carolina Asphalt Mixtures Modified with Lime,” Chemical Lime Company, May 15, 2003-May 14, 2004, $24,966.
Abstract: The objective of this proposal is to develop a dynamic modulus database for typical asphalt mixtures modified with lime in parallel with the NCDOT database. Only the axial compression test method will be used in this project with the anticipation of adding the indirect tension test method later when funds are avaiable. Also, the applicability of Witczak’s predictive equation to lime-modified mixtures will be evaluated. The dynamic modulus database to be developed from this project will yield necessary information for the NCDOT to design asphalt pavements with lime-modified mixtures using the new AASHTO pavement design guide.

12. “Typical Dynamic Moduli for North Carolina Asphalt Concrete Mixes,” NCDOT, July 1, 2002-June 30, 2004, $210,810.

      Abstract: The dynamic modulus of asphalt concrete will be used as the key parameter in the 2002 AASHTO Design Guide as well as in the Superpave simple performance test protocol that complements the volumetric mix design. The release of the new AASHTO pavement design guide in 2002 makes it urgent to obtain dynamic moduli values of typical asphalt mixes used in North Carolina. The objective of this proposal is to develop a database of dynamic moduli values and their variability for asphalt mixes used in North Carolina. In addition to dynamic modulus testing of the representative mixes, surrogate methods will be evaluated, including the impact resonance method and Witczak’s predictive equation.

13. “Impact of Price Reductions on the Long-Term Pavement Performance of HMA Mixes in North Carolina,” NCDOT, July 1, 2001 - June 30, 2003, $271,742.

      Abstract: Article 105-3 of the North Carolina Department of Transportation (NCDOT) Standard Specifications for Road and Structures provides guidance on price adjustments for hot mix asphalt pavements that are not within reasonably close conformity with the specifications but for which the work is to be accepted and remain in place. The primary objective of the proposed research herein is to determine whether price reduction under the provisions of Article 105-3 is adequate. The research objective will be accomplished by conducting both field and laboratory analyses of deficient pavements and specification pavements with similar structures and traffic history. The types of deficiency to be addressed in this research include asphalt content and in-situ density. Both fatigue and rutting performance will be evaluated.

14. “Laboratory Evaluation of Lime-Modified Asphalt Mixtures for City of Charlotte,” Chemical Lime Company, November 1, 2000 – October 31, 2001, $14,949.

      Abstract: The primary objective of this project is to evaluate the effect of lime modification in asphalt mixtures. Unmodified and lime-modified asphalt mixtures are acquired from the overlay job of a test road in City of Charlotte. These mixes will be characterized for fatigue cracking and rutting using the following three types of specimens: (1) laboratory-compacted specimens by Superpave Gyratory Compactor (SGC); (2) 150 mm diameter cores obtained from the pavement immediately after the construction; and (3) scaled-down laboratory pavements.

15. “Development of Nondestructive Test Methods and Performance Prediction Models for Asphalt Concrete Pavements Using Model Mobile Loading Simulator and Dispersion Analysis of Surface Waves,” National Science Foundation Research Experiences for Undergraduates Program, September 1, 1998 – August 31, 2001, $12,000.

      Abstract: This project is in support of the NSF research project “A Unified Approach to Predicting Long Term Performance of Asphalt-Aggregate Mixtures.” The REU students will assist graduate students in all of these activities with their focus specifically on the following research issues: (a) development of relationships between number of loading applications and the pavement performance; (b) refinement of surface wave testing device; (c) development of relationships between the performance and dispersive surface wave properties; and (d) evaluation of effects of temperature, rest periods, and aging on these relationships.

16. “Development of Specification Testing to Promote Fracture Fatigue Resistance and to Optimize Microdamage Healing,” Texas A&M Research Foundation/Western Research Institute/FHWA, July 1, 1999 – June 30, 2003, $300,000, Co-PI: Y. Horie.
Abstract: The ultimate goal of this project is “to be able to classify/specify/improve asphalts by their healing rates and efficiencies using chemical data that can be acquired more rapidly than by mechanical methods.” To accomplish this goal, the viscoelastic, continuum damage model developed by the PI will be tied to the micromechanical properties of component materials using DM2, a discrete element code developed by the Co-PI. Various test methods will be explored for binder specification testing using the viscoelastic, continuum damage formulation and DM2 simulation with an objective to promote fatigue resistance and to optimize the microdamage healing potential.

17. “A Unified Approach to Predicting Long Term Performance of Asphalt-Aggregate Mixtures,” National Science Foundation, September 1, 1998 – December 31, 2002, $454,793, Co-PI’s: R. H. Borden, Y. Horie.
Abstract: The research objective is to develop test methods and models for predicting long term performance of asphalt concrete that can account for viscoelasticity, damage, volumetric/deviatoric coupling, temperature, and aging. The objective will be accomplished by applying the elastic-viscoelastic correspondence principle and the continuum damage theory. The constitutive model will be incorporated into the ABAQUS finite element code, and used to predict the response and performance of laboratory pavements loaded by the Model Mobile Load Simulator. Nondestructive surface wave tests will be performed to determine the change in material properties due to fatigue damage growth.

18. “Fatigue Performance Evaluation of WesTrack and Arizona SPS-9 Asphalt Mixtures Using Viscoelastic Continuum Damage Approach,” FHWA/NCDOT, July 1, 1998 – June 30, 2000, $224,610.
Abstract: It is proposed herein to apply the viscoelastic continuum damage model developed from the previous FHWA project to the investigation of the fatigue performance of various mixtures in WesTrack and Arizona SPS-9 test pavement projects. To better simulate the condition of these mixtures in the pavements, the continuum damage fatigue model will be extended to include other factors, such as temperature, confining pressure, and moisture. A simplified fatigue test and analysis method will be developed and verified using actual performance data from the experimental pavement sections.

19. Dwight David Eisenhower Transportation Fellowship, U.S. Department of Transportation, September 1, 2000 – August 31, 2001, $78,100.

      Abstract: This fellowship is given to prepare a Ph.D. student, Jo Sias Daniel, for a career in transportation. The Dwight David Eisenhower Transportation Fellowship Program was created to attract, enhance, and retain the Nation’s brightest minds in the transportation research and engineering professionals.

20. “Development of Visco-Elasto-Plastic Continuum Damage Model for Asphalt-Aggregate Mixtures,” Arizona State University, March 1, 2000 – August 09, 2003, $212,496.

      Abstract: This project is a subcontract from Arizona State University as a part of the NCHRP 9-19 project “Superpave Support and Performance Models Management.” The objective of this project is to develop test protocols and models for characterization of asphalt concrete that are needed for structural design and mix design. The NCSU research team will perform experimental/analytical research to evaluate elastic, viscoelastic, viscoplastic responses of asphalt concrete under varying conditions and to develop a constitutive model that can be implemented in finite element analysis for performance prediction of asphalt pavements.

21. “Numerical Modeling of Pavement Materials and Structures Using Finite Element and Discrete Element Methods,” North Carolina Supercomputing Center, November 1, 1999 – October 31, 2000, 4800 SGI Origin hours.

      Abstract: This project utilizes the high-level computing in NCSC for simulating the behavior of asphalt concrete materials and pavements. ABAQUS finite element program is used to compute responses in various pavement structures subjected to FWD loads using dynamic analysis and nonlinear material models. The data will be used to train artificial neural networks that will be used as an inversion method. Also, the viscoelastic discrete element code will be run at NCSC to simulate the evolution of fatigue cracking under cyclic loading. This code will be used to estimate the fatigue cracking resistance of asphalt concrete based on component material properties.

22. “Use of FWD Multi-Load Data for Pavement Strength Estimation,” NCDOT, July 1, 1999 - June 30, 2001, $139,810.

      Abstract: The objective of the proposed research is to develop analysis tools for the evaluation of multi-load level deflection data to obtain improved or additional information about the strength and/or remaining life of asphalt concrete pavements. This objective will be accomplished by adopting nonlinear, dynamic finite element analysis of asphalt pavements as a means of developing a synthetic database composed of pavement properties and responses from which various models can be developed. These models will be verified/calibrated using multi-load level deflection data measured from pavements located in three different climatic regions in North Carolina.

23. “Determination of Subgrade Strength under Intact Portland Cement Concrete Slabs for Rubblization Projects,” NCDOT, July 1, 1998 – June 30, 2000, $128,778.
Abstract: The primary objective of the research is to develop an analysis method that enables the estimation of subgrade modulus after rubblization from deflection measurements on intact PCC slabs before rubblization. The research objective will be accomplished by investigating nonlinear behavior of subgrade soils using multiple-levels of FWD loading. The final product of this research will be a computer program that can be readily implemented by NCDOT to assist in developing rehabilitation strategies for PCC pavements. The guideline on realistically estimating subgrade strength under intact PCC slabs will result in more accurate assessment on preoverlay repair and overlay design.

24. “Dynamic Finite Element Analysis for Condition Assessment of Distressed Pavements,” North Carolina Supercomputing Center, July 1, 1998 – June 30, 1999, 2400 Cluster hours.
Abstract: The supercomputing time allotted to this project is used to run ABAQUS finite element code to calculate surface deflections of pavements under Falling Weight Deflectometer loading. Both intact and distressed pavements will be modeled using axisymmetric finite elements, and their behavior under FWD loading will be simulated using dynamic analysis and nonlinear material models for unbound layer materials. The deflection data base generated from ABAQUS will be used in developing condition assessment algorithms for asphalt pavements in support of the National Cooperative Highway Research Program 10-48 project.

25. “Nondestructive Evaluation of Structural Condition of Timber Piles,” North Carolina Department of Transportation, July 1, 1997 – December 31, 1999, $111,773, Co-PI: S. R. Ranjithan.
Abstract: The principal objective of the proposed research is to develop a nondestructive test and analysis method, that can be readily implemented, for determining structural condition of installed timber piles using the stress wave test method currently used by NCDOT for the evaluation of in-place length of timber piles. The outcome of this research will be a comprehensive stress wave testing system that can quantitatively evaluate the structural condition of installed timber piles from routine inspection. Test results obtained from this system will enable NCDOT calculating the load bearing capacity of deteriorated timber piles.

26.   “Development of a Mechanistic Fatigue Prediction Model for Aging Asphalt-Aggregate Mixtures,” Federal Highway Administration/Western Research Institute, $89,486, August 1996 - May 1997.
Abstract: The primary objectives of this study are to develop aging shift factors to account for the effect of aging on viscoelastic material properties and to establish analytical framework for applying the elastic-viscoelastic correspondence principle and continuum damage mechanics to aging asphalt-aggregate mixtures.

27. “Assessing Pavement Layer Condition Using Deflection Data,” National Cooperative Highway Research Program, $363,637, February 1997 - April 2000, Co-PI: S. R. Ranjithan.
Abstract: The objective of the research is to develop procedures to assess the condition of pavement layers based on deflection measurements. This research is concerned with all layers of rigid and flexible pavements that include an asphalt concrete surface layer. The proposed research approach describes a mechanistic-empirical method of developing a simple, practical deflection interpretation procedure for condition assessment of distressed pavement layers. Validation and implementation of this procedure will be conducted using data collected from distressed pavement sections in various locations in the United States.

28.     “Finite Element Analysis for Condition Assessment of Distressed Pavements,” North Carolina Supercomputing Center, July 1, 1997 – June 30, 1998, 200 Cray T90 hours.
Abstract: Two-dimensional, dynamic finite element analyses were performed using ABAQUS to model the deflection response of distressed asphalt pavements under FWD loading. The deflection database developed from this study was used to develop a numerical algorithm for prediction of layer moduli.

29. "Interpretation of FWD Data When Pavement Layers Are Not Intact,” North Carolina Department of Transportation, $75,000, July 1995 - June 1997.
Abstract: The falling weight deflectometer (FWD) is a principal means of evaluating the structural condition of pavements. Effort has been made to interpret FWD deflection basins for determining rehabilitation strategies and overlay thickness. This research interprets FWD information for condition evaluation of flexible pavements. The objectives are: 1) to determine the effects of cracked or broken layers in flexible pavement systems based on FWD deflection basins; 2) to develop a method for determining the layers in the existing pavement structure at which rehabilitation must be directed; and 3) to verify the recommended procedure using the deflection measured from cracked pavements with known conditions.

30.     "Finite Element Analysis of FWD Deflections Measured from Broken Pavements," North Carolina Supercomputing Center, 499 Cray Y-MP hours, July 1995 - June 1997.
Abstract: Two- and three-dimensional, dynamic finite element analyses were performed using ABAQUS to simulate the deflection response of asphalt pavements under FWD loading. Various material models and input conditions were checked to identify a suitable finite element setup for the pavement study.

31.     "Statewide Calibration of Asphalt Temperature Study from 1992 and 1993,” North Carolina Department of Transportation, $76,422, July 1994 - June 1996.

      Abstract: The temperature prediction and deflection correction procedures developed from the 92/93 study were extended to the statewide models. Surface deflections and air and pavement surface temperatures were measured from seven sections in North Carolina. Heat transfer theory was used along with the field data to develop a mechanistic procedure of predicting the AC layer mid-depth temperature from the surface temperature history. New regional and statewide empirical models for both modulus and deflection corrections have been developed based on a statistical analysis of field data from each respective region. In addition, new analytical models for both modulus and deflection corrections have been developed based on the theory of linear viscoelasticity and the time-temperature superposition principle and make use of the thermo-mechanical properties of the individual mixtures.

32. "Healing of Microcracks in Asphalt and Asphalt Concrete," Federal Highway Administration/Western Research Institute. Subcontract from Texas A&M University, $250,000, April 1993 - March 1997.
Abstract: The objectives of this project are: (1) to prove healing actually occurs in asphalt concrete; (2) to develop a constitutive model of asphalt concrete that accounts for effects of rate of loading, healing during rest periods, fatigue damage growth, and mode-of-loading; and (3) to develop a mechanistic fatigue performance prediction model. The elastic-viscoelastic correspondence principle was applied to evaluate damage growth and healing in cyclic loading separately from time-dependent characteristics of the material. The damage growth during loading cycles and healing during rest periods are modeled using the work potential theory, a continuum damage theory based on thermodynamics of irreversible process. The resulting constitutive model successfully predicts the damage growth of asphalt concrete under monotonic loading of varying strain rates and damage growth and recovery due to complex loading histories, in both controlled-strain and controlled-stress modes, composed of randomly applied multi-level loading with different loading rates and varying durations of rest.

33. "Field Investigation of Microdamage Growth and Healing in Asphalt Concrete," Federal Highway Administration/Western Research Institute. Subcontract from Texas A&M University, $194,079, June 1994 - March 1997.
Abstract: The research objectives are: (1) to demonstrate that the healing in asphalt concrete is indeed a real and significant phenomenon in asphalt concrete pavements; (2) to quantitatively evaluate the change in the elastic modulus of asphalt concrete layer due to damage growth and healing; (3) to investigate the effects of damage level, temperature, rest duration, asphalt content, asphalt viscosity, asphalt modifiers, and asphalt concrete layer thickness on healing; and (4) to develop the relationships between the elastic modulus of asphalt concrete measured by the stress wave technique and other variables such as number of loading applications and pavement cracking survey data. The surface wave test method was applied to pavements in the FHWA Turner-Fairbank Highway Research Center in McLean, Virginia and Mn/ROAD project in Minnesota. Surface wave measurements were analyzed using the dispersive analysis technique developed at NCSU to determine the changes in the elastic modulus of AC layer due to fatigue damage and healing.

34. "Development of a Structural Condition Evaluation Method for Marine Wooden Piling Using Stress Wave Technology," Office of Sea Grant, National Oceanic and Atmospheric Administration, U.S. Department of Commerce, $49,746 plus one graduate student at an annual stipend of $13,500, February 1994 - January 1996, Co-PI: J.S. Fisher.
Abstract:   In this study, stress wave propagation tests were conducted on laboratory wood specimens and field timber piles. The laboratory tests were designed to evaluate effects of varying moisture contents and internal deterioration on stress wave properties. It was found that the attenuation ratio and phase velocity are the most effective indicators that can be used to predict the moisture content and remaining effective area of a wood member. The relationships between the stress wave parameters and moisture contents and remaining effective area were developed from the laboratory data. These relationships were applied to the stress wave test data from installed timber piles located in the fishing pier of Kure Beach, North Carolina, and in-situ moisture contents and remaining effective area of a pile section with significant damage were predicted.

35.     "Nonlinear Viscoelastic Three-Dimensional Analysis of Multi-Layered Pavement Structures," North Carolina Supercomputing Center, 25 Cray Y-MP hours, July 1994 - June 1995.
Abstract: Three-dimensional, dynamic finite element analyses were conducted using ABAQUS to simulate the deflection response of asphalt pavements under FWD loading.

36. "Asphalt Paving Material Properties Affected by Temperature,” North Carolina Department of Transportation, $50,000, July 1992 - December 1993.

      Abstract:   It is proposed in this study that a temperature correction procedure for FWD deflection measurements be developed for the NCDOT by conducting FWD tests on actual pavements along with temperature and moisture data collection and coupling the field data with temperature-dependency of asphalt mixture properties characterized in the laboratory. The developed procedure employs the mid-depth temperature of asphalt layer in correcting FWD maximum deflections and predicts this temperature from the pavement surface temperature and time of day recorded at the time of FWD testing. A field study using FWD deflections and surface temperatures measured from other sections have successfully demonstrated the validity of the NCDOT procedure.

37.     "Investigation of the Fracture Healing Mechanism in Asphalt Cements Using the Theory of Nonlinear Viscoelasticity," Air Force Office of Scientific Research. Subcontract from Texas A&M University, $18,766, July 1991 - August 1992.
Abstract: The nonlinear viscoelastic correspondence principle was applied to densely-graded asphalt-aggregate mixtures. This principle was found to be very effective in describing the hysteretic behavior of sand-asphalt in the previous project, and the same conclusion was made with typical asphalt mixtures used in pavement construction in North Carolina.

38.     "Nondestructive Testing Method Based on Spectral Analysis of Surface Waves," NCSU Faculty Research and Development Fund, $3,500, January 1992 - August 1992.
Abstract: The Spectral Analysis of Surface Waves (SASW) test method was successfully applied to nondestructive evaluation of asphalt pavements with fatigue cracks measure the loss of structural integrity of the pavement due to fatigue cracking.

39.     "Resilient Modulus Testing for Korea Highway Corporation," Korea Highway Corporation. $3,282, October 1992 - December 1992.
Abstract: Typical asphalt-aggregate mixtures used in Korea were tested using the indirect tensile test method developed at NCSU. Resilient moduli values of these mixtures were determined, and their performance was predicted.

40.     "Laboratory Determination of Resilient Modulus for Flexible Pavement Design," National Cooperative Highway Research Program, $425,000, January 1990 - June 1993, Co-PI's: N. P. Khosla, P. C. Lambe, M. S. Rahman.

41.     "Large Sized Aggregate Asphaltic Concrete Mixtures - A Design Approach and Performance Evaluation,” North Carolina Department of Transportation, $117,000, July 1989 - June 1992, PI: N. P. Khosla.

Last updated 04/24/08