A study was conducted to determine the effect of reinforcement on the fatigue lives of asphalt beams of size 76 × 76 × 610 mm, which were prepared in the laboratory with a typical surface layer asphalt mix. Three sets of nine beams each contained no reinforcement (control beams) and reinforcements consisting of nonwoven paving fabric and composite (woven grid and nonwoven fabric composite). Each set of beams was subjected to three different load levels (three beams were tested at each load level), and their fatigue lives were determined. The fatigue testing of these beams was carried out by placing the beam on an elastic foundation (approximately 150 mm deep, 76 mm wide, and 660 mm long) and loading the beam at the center. A fatigue load at a frequency of 2 cycles/sec was applied to each beam. Each load cycle consisted of a half sine wave of 0.1-sec duration and a rest period of 0.4 sec. The total number of fatigue loads to crack the entire depth of beam was recorded as its fatigue life. The data obtained from three different sets of the beams were analyzed to determine the effect of reinforcement on the fatigue lives of the beams. These analyses indicated that the beams reinforced with composite performed significantly better than the beams containing paving fabric alone, and the beams reinforced with fabric alone performed better than the unreinforced control beams. Further details of the study and the results are described.

The theories related to the strength-thickness relationship of solid-asphalt-solid systems are discussed and their limitations in explaining the “strength-thickness” rule are presented. It is postulated that the restraining action of the boundary conditions is responsible for the observed strength-thickness rule. With respect to the failure mechanism of the solid-asphalt-solid systems, it is indicated that the three types of failure, brittle fracture, tensile rupture, and shear failure, observed in thin films of asphalt are related to the restraining action of the boundary conditions. It is also indicated that, according to thermodynamic principles and concept postulated by Bikerman, the failure in the “properly formed” solid-asphalt-solid systems can be considered as cohesional rather than adhesional. Using the time-temperature superposition principle, the temperature-dependence function of solid-asphalt-solid systems is also determined. It is shown that in confirmation with previous investigations in solid-asphalt-solid systems the temperature-dependence function of asphalt is considerably reduced. A master curve has also been prepared for the tensile-strength-film-thickness relationship of asphalt.

The paper discusses application of fracture mechanics to the analysis of fatigue characteristics of paving mixtures. A method of determination of crack growth parameters for asphaltic beams resting on elastic foundation is presented. The finite element method of analysis is used for the determination of stress intensity factors for various crack sizes. The effect of material characteristics, foundation modulus, and mode of loading on the crack growth process of asphaltic mixtures, is discussed. The effect of asphalt content, mixture density, and asphalt penetration on the Paris crack growth law is shown. It is also shown that fracture mechanics principles can be used to predict fatigue life of pavement material.

This investigation deals with the influence of several mix variables in respect to asphaltic concrete on its fatigue response. The investigation was based on a simple model representation comprising a beam supported on elastic foundation subjected to sinusoidal repeated loading, thus providing a two-dimensional simulation of actual pavement conditions under traffic loads. The dimensions of the beam were designed such that plan strain conditions prevailed during fatigue loading. Fracture mechanics concepts using linear elastic theory were employed to analyze test data, including stress and deformation near the crack tip. It was also hypothesized that the parameter, A, in the rate-of-crack-growth equation, dc/dN = A K4 would adequately reflect the changes induced in the fatigue response of the mix by the selected mix variables. The effect of mixture variables such as the amount of binder, density, aging, and viscosity on the parameter A is investigated.

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