Minh Tan Do

Modeling of the Road Surface Polishing Based on Contact-mechanics Approach

ABSTRACT In this paper, a new contact-mechanic-based model for road polishing is presented. According to this model, the local polishing rate is controlled by the pressure distribution between the car tire and the road surface. The Boussinesq load-displacement relation is used to calculate this pressure distribution taking into account the surface roughness, the applied load, the mechanical and geometrical properties of the bodies in contact. Coupling the pressure distribution with a wear law, the local evolution of the pavement roughness can be evaluated. The proposed wear law is based on the Preston equation and is proportional to the contact pressure, the relative velocity and the Micro-Deval coefficient of the aggregates used in the mix-designing. To validate this model, polishing tests are performed on road specimens, using the so-called machine Wehner-Schulze. Results show that the predicted road profile evolution is consistent with that given by experiments.

Road surface texture and skid resistance

This paper deals with the relationship between road surface texture and skid resistance. Mechanisms underlying the tire/wet road friction are first described. Definitions of road surface irregularities scales are given. The rest of the paper is then focused on the macrotexture and microtexture scales and their respective roles in what happens at the tire/road interface. Existing methods to measure and characterize the road surface texture are presented. On the one hand, problems encountered when using sensors developed for machined surfaces for the measurement of road surface profiles or cartographies are discussed. On the other hand, potential improvements when applying characterization methods developed for machined surfaces to road surfaces are highlighted. The paper presents finally modeling approaches to calculate friction forces from road surface texture. The generalized form of the models is presented from which terms related respectively to the macrotexture and the microtexture are identified. Approaches used to calculate these terms, integrating eventually other variables, are presented.

Friction/water depth relationship—In situ observations and its integration in tire/road friction models

The purpose of this paper is to provide new experimental evidences about the friction/water depth relationship and to improve the formulation of friction models in terms of consideration of the effect of water depth. Tests are conducted on test tracks. Friction forces are measured by means of a dedicated trailer providing a locked-wheel (full sliding) friction coefficient. The test surfaces are wetted by an on-board wetting system providing water depths varying from 0.1 mm to 1.50 mm. Effect of the road surface texture on the friction/water depth variation is shown and commented. Inputs newly provided by field tests, compared with laboratory tests, are highlighted. The obtained friction/water depths curves are assimilated to Stribeck curves and analyses, assuming conditions of a starved lubricated contact, are conducted to determine the lubrication regimes experienced by the tire/road contact when the road surface changes from dry to wet. A new friction model is formulated using the three-zone description of the tire/road contact area. The formulation is focused on the water drainage term reflected by a so-called hydrodynamic term FHL. It was assumed that FHL is a product of elementary functions expressing the respective effects of water depth, speed, tire tread depth, and road surface macrotexture on water drainage. Form of the elementary functions is derived from experimental evidences and consideration of previous friction models. Fitting of the new model to experimental data is shown and comparison with previous models is discussed.

Kinematic wave approach to model water depth on road surfaces during and after rainfall events

Water on road surfaces significantly degrades the available skid resistance. Indeed, 25% of injury accidents occur on wet roads in France due to lack of skid resistance. Some research results advocate an exponential decrease in skid resistance with increase in water depth. The above conclusions show the importance of knowing the water depth present on road surfaces during and after rainfall events in order to evaluate the available skid resistance for driver safety. In this paper, a prediction model of water depth on road surfaces during and after rainfall events is presented. This model takes into account the road surface characteristics such as macrotexture, slope and porosity, and weather conditions such as temperature, wind speed, relative humidity and rainfall rate. The model is based on the kinematic wave simplification of the Saint Venant equations, which represents the balance of flows from rainfall, run-off, infiltration and evaporation. The model is validated from comparisons to experimental measurements of water depth performed on four different surfaces of the IFSTTAR test track. The experimental device for the validation is composed of sensors that measure water depth, rainfall intensity, wind velocity, air humidity and temperatures. The model predictions on these four surfaces are very satisfactory.

Effect of Aggregate and Asphalt on Pavement Skid Resistance Evolution

When designing pavement, engineers must optimize some requirements such as user safety (skid resistance), environmental impact (noise, rolling resistance...)... However, this skid resistance evolves during the entire pavement life. So it is a common practice to perform laboratory tests to forecast the evolution of skid resistance. Previous works done in the French Laboratory of Bridges and Roads (Laboratoire Central des Ponts et Chaussees, LCPC) have identified phenomena such as binder removal, aggregate polishing and seasonnal variations to be responsible of these variations. This paper focuses on the polished stone values of aggregates and the aging of asphalt on the evolution of pavement skid resistance. Skid resistance of different specimens of nude aggregates and asphalt mixes that are submitted to polishing and aging was studied. On skid resistance point of view, aging of aggregates can be neglected in comparison to those of asphalt. Rocks with high polishing resistance offer less variation of skid resistance. Aging of asphalt tends to increase skid resistance until 12 month and remains this latter constant after.