Determination of structural layer properties of aggregate and asphalt surfaced roads Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/2b88qg120

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  • This study involved the determination of the structural layer properties of aggregate and asphalt surfaced pavements for use in the evaluation of pavement load carrying capacity and the seasonal effects of moisture. This was achieved by the use of Nondestructive Testing Methods (NDT) and backcalculation techniques. Pavement surface deflection measurements were taken using three NDT devices, namely the Dynaflect, Road Raterand Falling Weight Deflectometer (FWD). Soil moisture cells were implanted in the subgrade to monitor the moisture content and temperature of the subgrade. Samples of the pavement materials and subgrade were taken for evaluation in the laboratory using standard methods. A total of 27 project sites were studied. The deflection data collected using NDT devices were used to backcalculate pavement layers and subgrade moduli. The backcalculation procedures used were BISDEF, MODCOMP2, and SEARCH. The backcalculated moduli obtained from different equipment for any test site were compared to each other. Also, the backcalculated moduli were compared to laboratory determined values. Attempts were made to develop regression equations relating subgrade moisture content to easy-to-measure variables, such as rainfall, site aspect, pavement thickness and elevation. Also, for a known stress state, attempts were made to develop a regression equation which can be used to predict modulus as a function of dry density and moisture content. Finally, a regression equation was developed for the prediction of backcalculated modulus from pavement surface deflection basin for aggregate surfaced roads. The results from the study show that backcalculation methods can be used to determine the moduli of aggregate and asphalt surfaced pavement layers. These methods are limited in that they cannot take into account the stress sensitivity of the pavement materials and subgrade. As such, the backcalculated modulus denotes the relative stiffness of the pavement layer and cannot be compared to the modulus obtained in the laboratory at a specific loading situation. Nevertheless, it was shown that the backcalculated modulus changes with the moisture content and, therefore, can be used to evaluate the seasonal effects of moisture. The results can be used in the management of low volume roads, first by providing a means of evaluating the in situ pavement conditions at any given time. This can be used to develop rational load restriction policies during the critical season of the year. The backcalculated moduli can also provide a reliable input in overlay and reconstruction design. Finally, the prediction equations can provide an easy method for obtaining the resilient modulus for input into a mechanistic design method.
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