PURPOSES : A mechanistic-empirical (ME) predictive design logic that can compute the reflective cracking life of hot-mix asphalt (HMA) overlaid on top of a composite pavement is proposed herein. METHODS : The overlay thickness design and analysis logic of the HMA were formulated based on the ME concept of reflection crack propagation. Climate data, traffic load data, the pavement material properties, and the thickness of each layer of the pavement are the main inputs for the ME-Reflective Cracking Rate (RCR) prediction algorithm. An Microsoft Excel Virtual Basic for Application (VBA) program was created to aid designers in assessing the expected performance of an HMA overlay design. Calibration was done using data from the Long-Term Pavement Performance (LTPP) sections. Sensitivity analysis was conducted to compare the results yielded by the program and data from a report by the Texas Transportation Institute. RESULTS : The predictive model performance effectively generates the dynamic and relaxation modulus curves. The correlation value of the calibration factors, R2, is 0.79. The calibration factors used for the Asphalt Overlay Thickness Design (AOTD) program and the sensitivity analysis, i.e., k1, k2,, and k3,, are set to 5, 5, and 150, respectively. The sensitivity of the AOTD program affords reasonable results. Additionally, the program yields results similar to the trends presented in a report by the Federal Highway Administration. CONCLUSIONS : The proposed ME design logic is successfully translated into an Excel VBA program, AOTD, which can perform routine assessments of laboratory tests for HMA overlays. The program can effectively perform numerous iterations and computations to predict an HMA overlay. The predictive model can generate reasonable dynamic modulus and relaxation modulus curves for the characterization of HMA overlays. Under the same asphalt binder grade and HMA type, doubling the HMA overlay thickness yields three times the expected reflective cracking service life.

In recent years there has been an increased number of cases where geogrid have been incorporated into unbound road base layers to promote roadway optimization. The term optimization in this context refers to the use of geogrid to form a mechanically stabilized base course layer which leads to an improved performance of unbound layers by controlling particle movement and reducing permanent deformations. A mechanistic based pavement design approach offers a better means to accommodate the geogrid effect within the pavement structure. Guidance published by AASHTO recommends that pavement designs incorporating the effect of a geosynthetic need to be based upon experimentally derived input parameters. Performance data obtained from full scale accelerated pavement test studies and monitored field trials can be used to determine the influence of a geogrid on performance over the life of the pavement. This paper will highlight the concept of pavement optimization and present several cases where both post construction and long term evaluation methods were utilized in the quantification of the effectiveness of geogrid stabilized pavement structures.

PURPOSES : Recently, the mechanistic-empirical overlay pavement design program that is linked with Korea Pavement Research Program (KPRP) has been developed. This paper focused on establishing the framework and developing the program for the asphalt overlay design over the existing asphalt concrete pavement. METHODS : The overlay pavement design program developed in this study was investigated to assess the sensitivity to various pavement conditions, such as the damage level and thickness of existing layers. In addition, the actual overlay design on currently performing pavement was carried out as a practical example. RESULTS : From the sensitivity analysis, it was found that the thickness and damage level of existing asphalt layer mostly affect the overlay design results. In addition, under the same condition, the overlay pavement would better perform in cold region. From the overlay design with the actual condition, it is noted that the overlay thickness varies depending on the given condition. CONCLUSIONS : Based on various evaluations, it was concluded that the overlay design program developed in this study is a reliable and reasonable tool to be used in the actual pavement design.

역학적-경험적 포장설계 프로그램 중에서, 미국 AASHTO 설계법을 기초로 개발된 MEPDG는 교통량, 기상, 재료물성, 포장구조 등을 입력변수로 하여 기술자가 최적의 대안을 찾도록 한다. 하지만 MEPDG에서 기술적 문제가 발견되고 있기 때문에 이를 해결하여 프로그램을 개선하기 위한 노력이 계속되고 있다. 한편, 국내에서도 KPRP 연구과제에서 역학적-경험적 포장설계 프로그램이 개발되어 왔다. 이 한국형 포장설계 프로그램을 더욱 합리적으로 개발하고 개선하기 위해서는 이미 사용되고 있는 MEPDG를 분석하여 서로 비교할 필요가 있다. 콘크리트 포장설계의 경우, 피로균열은 다른 공용성 인자와는 달리 매우 복잡한 로직을 통해 예측된다. 따라서 본 논문에서는 MEPDG 버전 0.5, 버전 1.0, 그리고 버전 1.1의 피로균열 전이함수를 분석하였다. 그리고 버전별 MEPDG와 KPRP 입력변수들의 누적피로손상에 대한 민감도를 서로 비교하였다.