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This paper applies an innovative digital image processing technique to quantify the orientations of coarse aggregate particles (=: 2 mm) in asphalt concrete mixtures such as hot mix asphalt, stone matrix asphalt, and large stone asphalt compacted in the laboratory or field. The results indicate quantitatively that asphalt concrete specimens compacted in the field or in the laboratory with gyratory compactor have an oriented structure of aggregate particle distribution where the major cross sections of aggregate particles have the tendency to lie horizontally, and that aggregate particles are more randomly oriented in the asphalt concrete specimens compacted in the laboratory with the Marshall compactor.

The paper presents the development of a computer program VIEM for the elastic analysis ofmultilayered elastic pavements under the action of arbitrary tire-pavement contact pressuredistributions. The techniques adapted in VIEM primarily involves the use of a two-dimensional numerical integration to integrate point load solutions over the distributed pressure after discretizing the contact area into a finite number of triangular or quadrilateral elements. Values of contact pressure are inputted at the node points of discretized area. Numerical verification of VIEM indicates that numerical solution of high accuracy caD be efficiently calculated for the elastic response of multilayered asphalt pavements. As a result, the determination of displacements and stresses (strains) can be achieved using a personal computer. With the use of VIEM, a theoretical investigation is further performed to illustrate the effects of tire-pavement contact pressure distributions on the response of asphalt concrete pavements. An in situ measured tire - pavement contact pressure distribution is utilized in the investigation. Theresponse of asphalt concrete pavements due to the action of this measured contact pressure distribution is examined and compared with that due to the action of a uniform and circular contact pressure distribution by taking into account the influences of moduli and thicknesses of structural layers. The results of this investigation confirm theoretically a general consensus that details of the contact pressure distribution affect stresses and strains near the surface of the pavement, whereas the response in the lower layers depends mainly on the overall load. In particular, the contact pressure distributions have a significant effect on the horizontal tensile strains at the bottom of thin asphalt concrete layer which control the fatigue failure of asphalt pavements.

Second International Conference on Computational Methods in Contact Mechanics: 11 July 1995, Ferrara, Italy

1995 CSCE Annual Conference: 01 June 1995, Ottawa, Ontario, Canada

voids, fine particles, sand, and coarse aggregates. A review of the literature reveals that the investigations of AC have mainly concentrated on the macroscopic behavior of the material based on the assumption that the mixture is homogeneous. This assumption is mainly due to the extreme difficulty associated with the quantitative measurements of AC microstructure and the random nature of the aggregate distribution. This paper applies an innovative digital image-processing technique to quantify the distribution, orientation, and shape of coarse aggregates (=2 mm) in AC mixtures. Results of the quantitative measurements of coarse aggregate distribution and shape in AC mixture are then presented and analyzed. The quantitative results of AC microstructure clearly indicate the following findings : (a) the microstructure characteristics of coarse aggregates in AC mixtures can be accurately measured using the digital image-processing technique ; (b) the area gradation of aggregate cross sections by the Feret diameter gives an excellent prediction of the sieve gradation of coarse aggregates (=2 mm) used in the design of AC mixtures ; (c) the major cross sections of coarse aggregate particles have the tendency to lie horizontally in the mixtures ; and (d) comparison among two laboratory and two field compaction techniques provides valuable information related to compaction quality in terms of favorable aggregate distribution within the mixtures.

1995 CSCE Annual Conference: 01 June 1995, Ottawa, Ontario, Canada

CSCE Environmental Engineering Conference: 14 June 1994, Winnipeg, Manitoba

Tests conducted following the mix design stage, are unable to assess the rutting potential of asphalt concrete pavements. They range from moving a rubber tire on a slab and monitoring the rut depth to large-scale field tests using accelerated loading facilities. The Strategic Highway Research Program (SHRP) has proposed evaluating induced damage by determining the accumulated permanent shear strains based on a repetitive simple shear (constant height) test. An investigation conducted at the Centre for Surface Transportation Technology of the National Research Council of Canada is aimed at developing a criteria for measuring rutting potential. A repetitive uniaxialcompression test was used to determine accumulated permanent axial strain. Tests were conducted on cores recovered from the field and others compacted in the laboratory using a SHRP gyratory compactor. Test results indicate that the accumulated permanent axial strain undergoes three distinct stages: strain-hardening (volume change), shear flow, and, finally, fracture failure. During the secondary stage (shear flow) the rate of accumulation of permanent axial strain is constant and is sensitive to asphalt mix's resistance to rutting. Performance-related testing of the mix's resistance to potential rutting was carried out at different temperatures. Based on a proposed rutting criterion, one focused on the constant rate of permanent axial strain, the SHRP gyratory compactor simulates field compaction reasonably well. The influence of sample height, applied pressure, and compaction effort on the proposedrutting criterion also was investigated.

Proceedings - Localized Damage: 01 June 1994, Udine, Italy

Fourth Canadian Conference on Marine Geotechnical Engineering: 1993, St. John's, NFLD, Canada

Thirty-Eight Annual Conference of Canadian Technical Asphalt Association, 1993