Nakseok Kim

Use of surface free energy properties to predict moisture damage potential of Asphalt concrete mixture in cyclic loading condition

The synergistic effects of microdamage due to repeated loading in Asphalt-Aggregate system at a high temperature (40°C) and moisture damage analysis based on surface free energy theory are presented in this paper. The introduction of moisture in either a liquid or vapor state during cyclic loading may well be more damaging than simply moisture conditioning an asphalt concrete sample prior to testing. This difference may be due to the presence of a dynamic “network” of adhesive fracture, which potentially provides a channel for moisture movement within the sample. The percentage of the surface area of aggregate that has been exposed to water was used as a significant index to quantify the level of adhesive fracture. This index is calculated with the surface free energies of aggregate and asphalt which are measured by two methods, the universal gas adsorption and the Wilhelmy plate, respectively. The relation between the percentage of the surface area of the aggregate exposed to water and the number of cycles of loading assists in quantifying adhesive fracture in the asphalt-aggregate mixture.

Development of Performance Prediction Models in Flexible Pavement Using Regression Analysis Method

The capability to forecast future pavement condition has been questions of common interest for the economic reason for pavement management systems and the need to develop an intelligent prioritization schedule became ever more important for the sake of efficiency. If the pavement performance prediction model can be developed based on the past pavement performance data, the remaining service lives for pavements can be forecasted. It would help to optimize the scheduling of the rehabilitation activit ies and to determine the funding level required to achieve a predetermined level of performance. However, the results of the previous attempts to develop general pavement condition forecasting models have not been satisfied reliable because of the difficulties of collection pavement performance data, complexity of the pavement construction situation and different properties of pavement materials. The Georgia Department of Transportation (GDOT) has used the Pavement Condition Evaluation System (PACES) to evaluate the pavement conditions for the entire highway system in Georgia annually for the past 15 years. In this paper, the as phalt pavement performance prediction models for the state highways and the interstate highways have been developed applying simple and multiple regression analysis methods using the PACES data and PACES rating. The multiple linear regression model is effective to forecast pavement performance when ratings with various AADT. If this pavement performance prediction model using multiple linear regression analysis is implemented into the Pavement Management System, it could play an important role in the decision making process for the asphalt pavement management system.

Angular Fuzzy Logic Application for Pavement Maintenance and Rehabilitation Strategy in Ohio

Pavement deterioration can lead to pavement distress, which then causes many problems to the pavement structure as well as to he pavement itself. The continued deterioration of highway pavements has led to recognition of the importance of pavement maintenance and rehabilitation (M&R) strategy in pavement management. During the maintenance and rehabilitation of pavements, experts’ experiential knowledge plays an important role. This paper introduces an approach which employs an expert system and fuzzy modus ponens deduction technique to automate a pavement management system so as to produce consistent and reliable strategies for maintenance, rehabilitation, and repair of pavement.

A comparative study on measured vs. Predicted pavement responses from falling weight deflectometer (FWD) measurements

Falling weight deflectometer (FWD) drops were applied on the entire 24 test sections, and the resulting surface deflections were measured simultaneously using FWD geophones. The MODULUS 4.0 backcalculation program developed by the Texas Transportation Institute (TTI) was used to backcalculate the asphalt concrete layer moduli values of each test section. then the backcalculated moduli values were entered into a forward calculation program, WES-5, with known pavement layer thicknesses, assumed Poissons ratio, and the magnitude and geometry of FWD loading to calculate the surface and depth deflections. The surface and depth deflections were used to calculate the average vertical strains of different layers at the centerline of loading. In the validation process, the comparisons between the measured and predicted pavement responses were made.

Evaluation of rutting performance of asphalt concrete layers using multi-depth deflectometers (MDD)

The multi-depth deflectometer (MDD) is an linear variable differential transformers (LVDT) deflection measuring device which is retrofitted into pavement layers. A maximum of six modules may be installed in a single 1.5 inch (3.8 cm) diameter hole. The modules are clamped against the sides of the hole at the required depths and the center core is attached to an anchor located approximately seven feet below the pavement surface. The MDD can measure the permanent deformation (rutting) of each layer in the pavement system. By placing multiple modules in a single hole, the vertical strains induced in pavement layers can be measured. This paper presents the evaluation of the rutting performance of asphalt concrete layers in various flexible pavement structures as well as the traffic measurement using weigh-in-motion (WIM) device installed in the field. It has been found that, at least for reasonably stiff supporting materials, most pavement rutting is confined in the asphalt concrete layer. In addition, the majorportion of the total surface permanent deformation in the flexible pavement stems from the upper part (top 3.6 inches (9.1 cm)) of the asphalt concrete layer. The permanent deformations from base, subbase, and subgrade layers were negligible if any.

A Thermal Conductivity Model for Hydrating Concrete Pavements

Hydrating concrete pavement is typically subjected to temperature-induced stresses that drive cracking mechanisms at early concrete ages. Undesired cracking plays a key role in the long-term performance of concrete pavement systems. The loss of support beneath the concrete pavement due to curling caused by temperature changes in the pavement may induce several significant distresses such as punch out pumping, and erosion. The effect of temperature on these distress mechanisms is both significant and intricate. Because thermal conductivity dominates temperature flow in hydrating concrete over time, this material property is back-calculated by transforming governing equation of heat transfer and test data measured in laboratory. Theoretically, the back- calculated thermal conductivity simulates the heat movements in concrete very accurately. Therefore, the back- calculated thermal conductivity can be used to calibrate concrete temperature predicted by models.

Micromechanics Analysis of Granular Soils to Estimate Inherent Anisotropy

This paper presents micromechanics models to estimate resilient properties of unbound aggregate materials. Micromechanics models account for the effect of particle orientation and the ratio of the normal contact stiffness to shear contact stiffness among particles. The results demonstrate that aggregate orientation and shape influence the level of inherent anisotropy, which has a substantial effect on the pavement responses that impact pavement design. The micromechanics analysis predicted an inherent anisotropy (ratio of horizontal to vertical modulus) ranging from 1.0 to 0.4. The effect of this increased anisotropy on the performance of a pavement with an unbound aggregate base is substantial.

Aggregate Gradation Effects on Cracking-Related Displacements in Concrete Pavement

Aggregate gradation effects on cracking-related displacements of concrete are investigated in the laboratory using the German cracking frame. Concrete workability was assessed by use of the slump and drop tests for two different concrete mixtures consisting of gap-graded and dense-graded aggregates. Shrinkage strain, cracking frame strain, and concrete strain were measured and used to compare to strength gain and creep development. The measured and calculated strains of the different aggregate gradations were compared each other. Gradation effects on strength and stress development relative to tensile cracking at saw-cut tip were also investigated. Test results revealed that the gap-graded concrete has indicated larger shrinkage and creep strains than dense-grade concrete perhaps because of its higher volume concrete of cement mortars in the mixture.

Multi-Laboratory Validation Study on Resilient Modulus of Asphalt Concrete Using SHRP LG Device

The Strategic Highway Research Program (SHRP) Load Guide (LG) Device was developed as a part of the Strategic Highway Research Programs Long—Term Pavement Performance project. This device was recommended by the National Co-operative Highway Research Program (NCHRP) Project 1–28 as the most promising testing equipment after extensive comparisons among conventional testing equipments. Also, the NCHRP Project 1–28 proposed a new resilient modulus testing procedure of asphalt concrete using the SHRP LG Device. However, the feasibility of a new testing procedure using the SHRP LG Device should be proved by other testing agencies in order to be accepted as a standardized method. In addition, the test results should be reproduced with ease by investigators. Based on these backgrounds in mind, the resilient modulus test of asphalt concrete was conducted by two laboratories.The resilient modulus test results demonstrated that the moduli values determined from the calculated Poissons ratio showed greater difference between the laboratories than those from the assumed Poissons ratio. In particular, when the calculated Poissons ratios were used in computation, the moduli values from North Carolina Department of Transportation (NCDOT) were always higher than those from North Carolina State University (NCSU). Based on these two observations, assumed Poissons ratios may become a better choice for more consistent moduli in order to minimize the operator-to-operator variation. Also, the graphical comparison and statistical analysis results obviously demonstrated the possible effect of operator-to-operator variation. The effect of tested versus untested specimens on resilient moduli values was negligible within the given size of experiment, which could be attributed to the reduction of load levels proposed as a result of NCHRP Project 1–28.