Effect of particles' characteristics and road surface's texture on the tire/road friction

This paper presents a laboratory study to investigate the lubrication induced by particles deposited on road surfaces which is responsible for the increase of accidents at the first rain after a long dry period. Particles are extracted from sediments collected at a catchment area and characterized by their chemical composition and size distribution. Protocol to simulate the particle deposit on the road surface and their compaction by the traffic is described. The test program includes variables such as particle concentrations, particles' size fractions and surface textures. Dry friction tests are conducted using the Skid Resistance Tester which simulates the sliding friction between a rubber slider and the test surface. Friction is lowered when the surface is covered by particles, compared with a clean surface. Repeated passages of the slider induce an increase of friction coefficient until reaching a stable value. Particles' flows during a friction run are separated into those ejected from the sample, those stored by the surface macrotexture and those that stay on the test surface; this study demonstrated that the friction coefficient is closely related to the quantity of particles available on the test surface. SEM analysis shows on the other hand that these particles are mainly trapped by the surface microtexture. Similar behavior between fine particles and powder in terms of lubrication mechanisms is observed

Observations of dry particles behaviour at the tyre/road interface

Previous studies highlighted that friction value measured on real road surface textures covered by particles depends on particle sizes. This paper focuses on identification of particles behaviours at the tyre/road interface in the presence of particles. Identification is made by visual observations through high-speed camera, focus-variation microscopy and Scanning Electron Microscopy on the contaminated surface as scratch analysis on the surface. Two particle types were collected into samples picked next to roads. They are composed of clay and quartz which have different behaviours at the interface and affect the friction. Clay has a lasting effect due to its adhesive behaviour. Quartz has a scratching and rolling behaviour and is quickly ejected to the contact area due to a pinching effect

Lubrication of the tire/road interface by fine particles : Tribological approach

Accidents increase during the first rain after a long dry period. This trend is due to the accumulation of fine particles originated from different sources such as atmosphere, road and tires debris, fuel emissions, etc. These particles accumulate on the road surface during a long dry period and induce a friction loss between the tire and the road surface. In the road field, the tire/road skid resistance on dry conditions is considered satisfactory (considering the road surface as clean) and the loss of skid resistance is attributed to the sole action of water. Thus, there is an unexplored field concerning the particles' effect, alone in dry period and mixed with water in wet period, on the skid resistance. In this paper, we investigate the action of the particles during a dry period using two approaches developed in tribology: the third body approach, particularly the mass analysis inspired from Fillot et al. [1], to understand the particles flows at the tire/road interface; and the dry lubrication theories developed for powders (as molybdenum disulfide MoS2 ) [2] [3] to understand and model the friction.  Experiments are conducted in laboratory to understand and model this phenomenon. Particles are collected, by drying and sieving, from sediments sampled from a catchment area which collects runoff water. Analyses are performed to determine the particles' chemical composition and size distribution. Experimental protocol allows simulating the particles' build up process on the road surface. The specimen surface, representative of a road surface, includes a microtexture scale, representing the asperities of the aggregates, and a macrotexture scale, representing the space between the aggregates. Friction measurements are realized by means of the so-called Skid Resistance Tester Pendulum, widely used in the road field, which simulates the friction between a rubber pad sliding at 3 m/s on the specimen surface. On a surface initially covered with particles, successive friction runs are performed, without resupplying particles between two consecutive runs. Specimen's weight is recorded before and after each friction run. Results show that friction drops significantly, compared to a clean state, when the surface is covered by particles. Successive runs induce an increase of friction coefficient until reaching a stable value which is below that of a clean surface. Three particles' flows are calculated: particles ejected from the contact area between the friction slider and the test surface; particles trapped by the surface microtexture; particles stored by the surface macrotexture. Close relationship was found between the friction coefficient and the flow of particles trapped by the microtexture. Similarities are found, in terms of lubrication mechanisms, between the behavior of studied particles and powder [3].  Discussions allow understanding the relationship between particles' characteristics and Stribeck curves' parameters such as viscosity, lubricant film thickness and pressure. A first attempt of modeling allows to calculate the friction coefficient from the fraction of surface covered by particles. This study has allowed to see the contribution of tribology to the understanding of complex phenomena in the road field such as skid resistance on contaminated road surfaces. Perspectives, especially in terms of study of water and particles mixing, are presented.   [1] Fillot, N., Iordanoff, I., and Berthier, Y. Wear modeling and the third body concept. Wear, 262, 949-957, 2007. [2] Higgs, C.F., Wornyoh, E.Y.A. An in situ mechanism for self-replenishing powder transfer films: Experiments and modeling. Wear, 2008, 264, 131-138. [3] Heshmat, H. Wear reduction systems for coal-fueled diesel engines ? Experimental results and hydrodynamic model of powder lubrication. Wear, 1993, 162-164, 518-528

Adhérence des chaussées contaminées par des particules

The thesis aims to predict the skid resistance of road surfaces contaminated by fine particles. These particles are deposited on the road during dry periods and act, alone or mixing with rainwater, as a lubricant at the tire / road interface. The research methodology is based on the third body approach by distinguishing the phases of deposit and washing of particles by rain. Particles are characterized by their size distribution and their chemical and mineralogical compositions. The study is conducted at three scales: global, by measurements of friction and third body masses (particles during the deposit phase and the water / particles mixture during the washing phase); in the contact area by analyses of third body flows; and at the particle level by SEM observations. Particle flows during the deposit phase are identified by visualizations with a high-speed camera. The interaction between the particles and the road surface texture is highlited by microscopic observations. Flow modeling is used to estimate the coverage rate of a surface that, in turn, is used as a weighting factor to calculate the coefficient of friction during the deposit phase. In the presence of water, the volume fraction of the particles is used to estimate the viscosity of the mixture. The coefficient of friction during the washing phase depends on this viscosity and the coverage rate of the surface. Results are discussed in terms of the influence of particle characteristics (concentration,size) and road surface texture.La thèse vise à prédire l’adhérence des chaussées contaminées par des particules fines. Ces particules se déposent sur la chaussée pendant les périodes sèches et agissent, seules ou se mélangeant avec l’eau de pluie, comme un lubrifiant à l’interface pneu/chaussée. La démarche de recherche est basée sur l’approche du troisième corps en distinguant les phases de dépôt et de lessivage des particules par la pluie. Les particules sont caractérisées par leur distribution granulométrique et leurs compositions chimique et minéralogique. L’étude est menée à trois échelles : globale, par des mesures de frottement et de masses du troisième corps (particules pendant le dépôt et le mélange eau/particules pendant le lessivage) ; dans l’aire de contact par des analyses de flux du troisième corps ;et au niveau des particules par des observations au MEB. Les flux de particules pendant la phase de dépôt sont identifiés par des visualisations avec une caméra rapide. L’interaction entre les particules et la texture de la chaussée est mise en évidence par des observations microscopiques. La modélisation des flux permet d’estimer le taux de recouvrement d’une surface qui, à son tour, est utilisé comme un facteur de pondération pour calculer le coefficient de frottement pendant la phase de dépôt. En présence d’eau, la fraction volumique des particules est utilisée pour estimer la viscosité du mélange. Le coefficient de frottement pendant la phase de lessivage dépend de cette viscosité et du taux de recouvrement de la surface. Les résultats sont discutés en termes d’influence des caractéristiques des particules(concentration, taille) et de la texture de la chaussée

The skid resistance of roads contaminated by particles

La thèse vise à prédire l’adhérence des chaussées contaminées par des particules fines. Ces particules se déposent sur la chaussée pendant les périodes sèches et agissent, seules ou se mélangeant avec l’eau de pluie, comme un lubrifiant à l’interface pneu/chaussée. La démarche de recherche est basée sur l’approche du troisième corps en distinguant les phases de dépôt et de lessivage des particules par la pluie. Les particules sont caractérisées par leur distribution granulométrique et leurs compositions chimique et minéralogique. L’étude est menée à trois échelles : globale, par des mesures de frottement et de masses du troisième corps (particules pendant le dépôt et le mélange eau/particules pendant le lessivage) ; dans l’aire de contact par des analyses de flux du troisième corps ;et au niveau des particules par des observations au MEB. Les flux de particules pendant la phase de dépôt sont identifiés par des visualisations avec une caméra rapide. L’interaction entre les particules et la texture de la chaussée est mise en évidence par des observations microscopiques. La modélisation des flux permet d’estimer le taux de recouvrement d’une surface qui, à son tour, est utilisé comme un facteur de pondération pour calculer le coefficient de frottement pendant la phase de dépôt. En présence d’eau, la fraction volumique des particules est utilisée pour estimer la viscosité du mélange. Le coefficient de frottement pendant la phase de lessivage dépend de cette viscosité et du taux de recouvrement de la surface. Les résultats sont discutés en termes d’influence des caractéristiques des particules(concentration, taille) et de la texture de la chaussée.The thesis aims to predict the skid resistance of road surfaces contaminated by fine particles. These particles are deposited on the road during dry periods and act, alone or mixing with rainwater, as a lubricant at the tire / road interface. The research methodology is based on the third body approach by distinguishing the phases of deposit and washing of particles by rain. Particles are characterized by their size distribution and their chemical and mineralogical compositions. The study is conducted at three scales: global, by measurements of friction and third body masses (particles during the deposit phase and the water / particles mixture during the washing phase); in the contact area by analyses of third body flows; and at the particle level by SEM observations. Particle flows during the deposit phase are identified by visualizations with a high-speed camera. The interaction between the particles and the road surface texture is highlited by microscopic observations. Flow modeling is used to estimate the coverage rate of a surface that, in turn, is used as a weighting factor to calculate the coefficient of friction during the deposit phase. In the presence of water, the volume fraction of the particles is used to estimate the viscosity of the mixture. The coefficient of friction during the washing phase depends on this viscosity and the coverage rate of the surface. Results are discussed in terms of the influence of particle characteristics (concentration,size) and road surface texture

Effect of fine particles on road skid resistance

8th Symposium on Pavement Surface Characteristics: SURF 2018 - Vehicle to Road Connectivity, BRISBANE, AUSTRALIE, 02-/05/2018 - 04/05/2018Fine particles originated from road and tires debris or traffic and industry emissions can be at the origin of some safety-related issues such as accidents at the first rain after a long dry period or seasonal variations of skid resistance. This paper presents a laboratory study reproducing under controlled conditions the process of particles' buildup and washing by runoff water. Surfaces composed of rough and worn aggregates are studied. The test protocol is described. Friction is measured by means of the British Pendulum. On a surface initially covered with particles, dry and wet tests are performed. Results show that on a contaminated surface, the friction coefficient drops significantly, compared to a clean state, and then increases. Mechanisms related respectively to dry and wet lubrications are presented. In parallel, mass of particles are monitored. It was found that friction and mass of particles evolves similarly but in opposite directions. Discussions are made in terms of the effect of particles' size and surface's microtexture

Evolution of the road bitumen/aggregate interface under traffic-induced polishing

Road skid resistance decreases under traffic and climate actions. For a surface made of bituminous concrete, the skid resistance evolution involves a removal of the bitumen layer and a polishing of the aggregates. Previous researches have been focused on polishing mechanisms and less is known about bitumen removal phase. This paper presents a laboratory study to better understand the behavior of the stone mastic asphalt under simulated actions of traffic. Due to its formulation, this bituminous concrete contains more bitumen than other materials used for road surfacing. Polishing tests are performed on circular cores using tWehner/Schulze machine, which simulates the traffic-induced polishing by means of rolling rubber cones and measures the tire friction by means of sliding rubber pads. Tests are stopped at predefined numbers of passes for friction measurements, 3D cartographies of surface texture and scanning electron microscopic observations of the cores' surface. Statistical tests are performed to identify relevant texture parameters to explain friction evolution. During bitumen removal phase (i.e. before 20,000 passes of polishing), Ssc (average curvature of peaks) and Sdq (average quadratic slope of asperities) are correlated with friction values. After 50,000 passes, volume parameter Vvc is more adapted due to the abrasion of asphalt mix surface. Then, scanning electron microscopic observations show that a layer composed by bitumen and particles (small aggregates and sand) is a third-body surrounding aggregates, which evolves in thickness and size of aggregates during polishing. The system composed of the aggregates, the bitumen-particles layer and the polishing cones can be assimilated to a tribosystem with a tribological circuit at the interface. The bitumen-particles layer acts as an internal flow, before leaving the contact area. The movement of the layer under the shear stress induced by the polishing cones explains the ejection of big aggregates and the heterogeneity of the layer around aggregates