No description available.

Not available / text

Pavement performance prediction in terms of fatigue cracking and surface rutting are essential for any mechanistically-based pavement design method. Traditionally, the estimation of the expected fatigue field performance has been based on the laboratory bending beam test. Full-scale Accelerated Pavement Testing (APT) is an alternative to laboratory testing leading to advances in practice and economic savings for the evaluation of new pavement configurations, stress level related factors, new materials and design improvements. This type of testing closely simulates field conditions; however, it does not capture actual performance because of the limited ability to address long-term phenomena. The same pavement structure may exhibit different response and performance under APT than when in-service. Actual field performance is better captured by experiments such as Federal Highway Administration's Long-Term Pavement Performance (LTPP) studies. Therefore, to fully utilize the benefits of APT, there is a need for a methodology to predict the long-term performance of in-service pavement structures from the results of APT tests that will account for such differences. Three models are generally suggested to account for the difference: shift factors, statistical and mechanistic approaches. A reliability based methodology for fatigue cracking prediction is proposed in this research, through which the three models suggested previously are combined into one general approach that builds on their individual strengths to overcome some of the shortcomings when the models are applied individually. The Bias Correction Factor (BCF) should account for all quantifiable differences between the fatigue life of the pavement site under APT and in-service conditions. In addition to the Bias Correction Factor, a marginal shift factor, M, should be included to account for the unquantifiable differences when predicting the in-service pavement fatigue life from APT. The Bias Correction Factor represents an improvement of the currently used "shift factors" since they are more general and based on laboratory testing or computer simulation. By applying the proposed methodology, APT performance results from a structure similar to an in-service structure can be used to perform four-point bending beam tests and structural analysis to obtain an accurate estimate of the necessary Bias Correction Factor to estimate in-service performance.

Not available / text

Research, tests and analysis are presented on several reinforcements placed in the asphalt overlay of a roadway built over soft organic soils. Non-destructive Evaluation (NDE) methods and statistical analysis were used to characterize the pavement before and after rehabilitative construction. Before reconstruction, falling weight deflectometer, rut and ride tests were conducted to evaluate the existing pavement and determine the statistical variability of critical site characteristics. Twenty-four 500ft. test sections were constructed on the roadway including sixteen reinforced asphalt and eight control sections at two test locations that possessed significantly different subsoil characteristics. NDE tests were repeated after reconstruction to characterize the improvements of the test sections. Test results were employed to quantify the stiffness properties of the pavement based on load-deflection data to evaluate the relative performance of the reinforced sections. Statistical analysis of the data showed the stiffness of the reinforced sections was consistently higher than the control sections. / by Daniel D. Pohly. / Thesis (M.S.C.S.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

An inverted base pavement is a new pavement structure that consists of an unbound aggregate base between a stiff cement-treated foundation layer and a thin asphalt cover. Unlike conventional pavements which rely on upper stiff layers to bear and spread traffic loads, the unbound aggregate inter-layer in an inverted base pavement plays a major role in the mechanical response of the pavement structure. Traditional empirical pavement design methods rely on rules developed through long-term experience with conventional flexible or rigid pavement structures. The boundaries imposed on the unbound aggregate base in an inverted pavement structure change radically from those in conventional pavements. Therefore, current empirically derived design methods are unsuitable for the analysis of inverted base pavements. The present work documents a comprehensive experimental study on a full-scale inverted pavement test section built near LaGrange, Georgia. A detailed description of the mechanical behavior of the test section before, during and after construction provides critically needed understanding of the internal behavior and macro-scale performance of this pavement structure. Given the critical role of the unbound aggregate base and its proximity to the surface, a new field test was developed to characterize the stress-dependent stiffness of the as-built layer. A complementary numerical study that incorporates state-of-the-art concepts in constitutive modeling of unbound aggregates is used to analyze experimental results and to develop preliminary guidelines for inverted base pavement design. Simulation results show that an inverted pavement can deliver superior rutting resistance compared to a conventional flexible pavement structure with the same fatigue life. Furthermore, results show that an inverted base pavement structure can exceed the structural capacity of conventional flexible pavement designs for three typical road types both in rutting and fatigue while saving up to 40% of the initial construction costs.

The emergence of analytically-based pavement design has encouraged investigations toward a better understanding of the behaviour of pavement layers under cyclic loading. Unbound granular base (UGB) materials are commonly placed as base course layers in the design of pavement foundations. Due to their nature and geometry they are unsaturated geo-materials and therefore, it is desirable to study their behaviour using the framework of unsaturated soil mechanics. Current literature reflects very limited achievements in this direction. This thesis presents the development of a cyclic triaxial testing system and associated testing methodology that meets the challenges of testing an UGB material as an unsaturated soil. The testing system enables the initialisation of a specimen to target matric suction and facilitates direct measurement of its evolution under cyclic loading. In conjunction with the use of accurate on-specimens strain measurement transducers, ???clean??? strain and matric suction cyclic responses are obtained. Two types of cyclic triaxial testing are investigated: with constant cell pressure (i.e., CSeries testing) and with varying (cyclic) cell pressure where both axial and radial stress components are simultaneously (and in phase) pulsed (i.e., V-Series testing). Different initial matric suctions, si will be imposed in the testing program and the influence of si on material behaviour is analysed. This is investigated in a similar manner for C- and V-Series testing. The influence of si appears to be significant for both cyclic and permanent strain responses. A strong stress path dependency is found to characterise the behaviour of the UGB material. Under a wide range of cyclic deviator stress magnitudes, permanent strain response is found to correlate with that of matric suction response. Both appear to indicate better the relative performance of a UGB material than the response of resilient modulus. Another particular aspect investigated is the influence of additional fines on the behaviour of the UGB material. To ???isolate??? the effects of additional fines the cyclic and permanent strain responses of ???equivalent??? specimens with equivalent compaction and unsaturation condition, but different fines content, are compared. The results showed that the relative performance of the two materials (distinguished by the different percentage of fines content) in intertwined with the strong stress path dependency. It is also found that a material compacted at higher dry density may not improve its behaviour under cyclic loading, but may worsen with load cycles. Soil-water characteristic curve tests are conducted for the UGB materials investigated, showing high sensitivity of initial matric suction to moisture content, which increases further for the material with additional fines. This explains the notion of ???sensitivity??? of UGB materials as commonly suggested by practicing pavement engineers.

No description available.

No description available.