Pavement skid resistance has long been recognised as the primary factor to reduce traffic accidents Skid resistance is affected by a large number of parameters This is the first in a series of two papers dealing with the road surface contribution to tire-pavement skid resistance giving special emphasis to the effect of a water film development on the pavement surface Pavement surface texture is expressed by micro⧹macrotexture depth and density Relative regression equations giving pavement skid resistance values have been reviewed and a well fitting regression equation has been derived The mathematical background of fractal interpolation functions is then presented An attempt is described to approximate the pavement surface texture with fractals by taking into account its accurate geometry Through this approximation the procedure of pavement surface wetting is evaluated, in respect with its effect to skid resistance values This attempt yields encouraging results, although it is apparent that further research is required

Fractal Evaluation of Pavement Skid Resistance Variations. I: Surface Wetting

Pavement skid resistance has long been recognized as the most important parameter to reduce traffic accidents. The factors affecting skid resistance are numerous and very complicated. It is a difficult task to estimate the extent and direction of their overall contribution. This paper deals with the road surface contribution to tire-pavement skid resistance. Pavement surface is expressed through micro/macrotexture depth and density. An attempt is made to approximate this pavement surface texture with fractals, in order to take into account its accurate geometry. A qualitative relationship between pavement surface texture, expressed through fractal concepts, and skid resistance is recognized. This attempt yields encouraging results, although it is apparent that further research is required.

Skid resistance and fractal structure of pavement surface

The paper illustrates the importance of load/stress inputs in pavement design on pavements with relatively thin asphalt surfacings, typically used in southern Africa. The investigation concentrates on the quantification of several pavement response parameters as a result of non-uniform and non-circular shaped contact stresses at different asphalt moduli, compared to the traditional circular uniformly loaded tire patch. The finite element method (FEM) was used for the detailed analyses. The responses of an un-cracked and cracked pavement structure were also compared, under circular and rectangular loading shapes of varying levels of loads and contact stresses using a customized semi-analytical FEM code. The response data were benchmarked with multilayered linear elastic theory, and also indicated the importance of both load shape and level of contact stress on pavement performance. The paper highlights the importance of using and managing actual tire-pavement contact stress data for more rational design and analysis of pavements incorporating thin asphalt layers.

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Evaluation of non-uniform tyre contact stresses on thin asphalt pavements

Because approximately 85 percent of the total volume of hot-mix asphalt (HMA) mixtures consists of aggregates, the performance of HMA mixtures is greatly affected and influenced by properties of the aggregate blend. The angularity, shape, and texture of the aggregate particles have a significant effect on the performance of HMA mixtures by controlling the mixture's strength and rutting resistance. Rough, angular aggregates have been proved to produce higher-quality HMA pavements than smooth, round aggregates. Current aggregate tests are primarily based on experience and empirical characterization tests. A study was conducted to evaluate test methods that could be used to characterize aggregate properties that are related to HMA rutting potential of heavy-duty pavements. Specifically, FAA aggregate properties and aircraft loading conditions were addressed. The aggregate particles were characterized with the particle index (ASTM D3398), uncompacted void content for fine aggregate (ASTM C1252), modified ASTM...

Influence of aggregate properties on performance of heavy-duty hot-mix asphalt pavements

Pavement surface texture greatly contributes to tire-pavement skid resistance. Pavement surface irregularities are continuous from pavement macrotexture to pavement microtexture. Their pattern is also roughly repetitive. This existence of self-similarity encourages an attempt to approximate the pavement surface texture with fractals in order to take advantages of fractal modeling. The mathematical background is based on \iC\u0 and \iC¹ fractal interpolation curves. Through this approximation, the procedure of pavement surface wear is evaluated, in respect to its effect to skid resistance values. Fractal potential is simultaneously tested in representing pavement surface contamination. A qualitative relationship between the skid resistance values of characteristic pavement surface texture profiles and the fractal dimension of their interpolation function is recognized. The whole attempt yields encouraging results, although it is apparent that further research is required.

Consideration of Fractals Potential in Pavement Skid Resistance Evaluation

A field evaluation of Texas highway pavements was conducted to provide evidence that sand-size aggregate particles have a significant influence on rutting. A laboratory investigation was performed in order to (1) quantify the influence on resistance to rutting when rounded, smooth, sand-sized aggregate particles are replaced by rough, angular, porous particles while other aggregates and the total gradation remain unchanged, (2) evaluate the ability of certain test procedures to differentiate between rut-susceptible and rut-resistant mixtures, (3) develop a new rutting model for predicting pavement performance which incorporates characteristics of the aggregate, and (4) examine fractal dimension analysis as a method of quantifying aggregate angularity and surface texture. Octahedral shear stress theory was employed to compare the rutting potential of asphalt concrete mixes containing low quality sand-size particles (rounded, smooth, non-absorptive) and high quality sand-size particles (rough, angular, absorptive). Five mixtures with varying amounts of the different aggregates were tested. A state-of-the-art theoretical approach was developed in which hyperbolic equations are introduced to model the compressive creep and recovery compliances. The new compliance equations are further developed into a rutting prediction model. The aggregate's role in the permanent deformation behavior of the mixture is assessed by means of a novel parameter termed "p" value. A new technique, known as fractal dimension analysis, offers a great deal of potential in providing a direct quantitative measure of aggregate angularity and surface texture which has heretofore been impossible. A combination of the new theoretical approach, the long-term laboratory performance of the mix, and the octahedral shear stress analysis is recommended as the preferred approach to evaluate the influence of sand-sized aggregate particles on permanent deformation in asphalt concrete mixtures.

J W Button

Papers

Identifying and correcting rut-susceptible asphalt mixtures