Pavement condition index | EPFL Graph Search

The pavement condition index (PCI) is a numerical index between 0 and 100, which is used to indicate the general condition of a pavement section. The PCI is widely used in transportation civil engineering and asset management, and many municipalities use it to measure the performance of their road infrastructure and their levels of service. It is a statistical measure and requires manual survey of the pavement. This index was originally developed by the United States Army Corps of Engineers as an airfield pavement rating system, but later modified for roadway pavements and standardized by the ASTM. The surveying processes and calculation methods have been documented and standardized by ASTM for both roads and airport pavements: ASTM D6433 - 20: Standard Practice for Roads and Parking Lots Pavement Condition Index Surveys ASTM D5340 - 20: Standard Test Method for Airport Pavement Condition Index Surveys The method is based on a visual survey of the number and types of distresses in a pavement. First, the type and extent of existing distresses, their severity level is collected. Next, distress density is calculated for each type of distress. The density values are translated into deduct value (DV) and corrected deduct value (CDV) using a set of curves proposed by the ASTM. The ASTM does not include the formulae of these curves, but they are recalculated by researchers. Finally, the value of the PCI is calculated in an iterative process. The result of the analysis is a numerical value between 0 and 100, with 100 representing the best possible condition and 0 representing the worst possible condition. Pavement distress types for asphalt pavements include: Alligator cracking Bleeding Block cracking Bumps and sags Corrugations Depressions Edge cracking Joint reflections Lane/shoulder drop-off Longitudinal and transverse cracking Low ride quality Patching and utility cut patching Polished aggregate Potholes Rutting Shoving Slippage cracking Swelling Weathering and raveling For relatively small pavement systems, the entire system may be surveyed.

Modélisation et prédiction du comportement rhéologique des mélanges bitume caoutchouc

Mehdi Ould Henia

Asphalt rubber is a modified binder widely used in pavement construction. Composition design methods of asphalt rubber blends are exclusively empiric and rely on the selection of the optimal combination of parameters after a long experimental program. The understanding of the phenomena affecting the asphalt rubber behaviour starts with the proposal of a rational theory and its validation with experimental data. To do so, a set of experiments were carried out including three main factors considered as significant for the rheological behaviour of the final binder. These factors are the bitumen chemical composition, the rubber content and its maximum mesh size. The binder complex shear moduli were measured within the viscoelastic linear domain. The measurements allowed a full characterisation of the rheological behaviour of asphalt rubber for the service temperatures and rates of loading. Base bitumen composition leads to final binders with rheological behaviours that are radically different despite the fact that the base bitumen belong to the same commercial grade. The rubber content increase showed significant changes on the properties of the binder, especially an increase of its elasticity and a decrease of its temperature sensitivity. The rubber powder maximum mesh size has no significant effect on the rheological properties of the blends within the service conditions. An analysis of physical and chemical changes was carried out on the phases formed after the curing process. A method for the isolation of the phases without affecting their physical and chemical properties was proposed. A centrifuging process was applied to asphalt rubber thanks to the design of an appropriate equipment adapted to the binder features. An experimental protocol was established to obtain a good separation of the phases with a limited aging. The SARA bitumen group analyses were carried out before and after the curing process. They allowed the determination the bitumen fractions kinetics during the blending. Light fractions of bitumen are the main chemical groups that migrate toward the cross-linked rubber network causing its swelling. The rheological behaviour of the separated bitumen phase has proven that the residual bitumen exhibits a lowered thermal sensitivity which is confirmed by the increase of the colloidal instability index. The rubbery phase has showed an extent of swelling varying between 200 and 400% which modifies considerably the rheological behaviour of the rubber by transferring to it a part of the thermal sensitivity of the bitumen. The influence of the factors was evaluated and their relative importance determined through a statistical model. Micromechanical modelling of the asphalt rubber composite has allowed the validation of observed phenomena that are mainly physical ones. To do this, two main homogenisation procedures were implemented and carried out on the heterogeneous medium: The classical self-consistent approach widely referenced as the equivalent medium approach (EMA) and the generalised self-consistent approach frequently referenced as the equivalent field approach (EFA). A satisfactory modelling of the composite is achieved by taking into account two changes occurring in the phases: their volumetric fractions influenced by the swelling, and their rheological properties due to the diffusion of bitumen into the rubber. An acceptable estimation of the rheological behaviour of the rubbery phase is obtained from the base materials properties with a three-phase self-consistent modelling according to EFA approach. The consideration of an adsorbed fraction of the bitumen on the surface of the rubber particle has allowed a qualitative and a quantitative description of the properties of the rubbery phase. The difficulty of predicting the rheological behaviour of a bitumen from its chemical composition is discussed. Future investigation ways are proposed.

EPFL2005

Modélisation et prédiction du comportement rhéologique des mélanges bitume caoutchouc

Mehdi Ould Henia

EPFL2005