Road surface

Résumé

A road surface (English), or pavement (American), is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, macadam, hoggin, cobblestone and granite setts were extensively used, but these have mostly been replaced by asphalt or concrete laid on a compacted base course. Asphalt mixtures have been used in pavement construction since the beginning of the 20th century and are of two types: metalled (hard-surfaced) and unmetalled roads. Metalled roadways are made to sustain vehicular load and so are usually made on frequently used roads. Unmetalled roads, also known as gravel roads, are rough and can sustain less weight. Road surfaces are frequently marked to guide traffic. Today, permeable paving methods are beginning to be used for low-impact roadways and walkways. Pavements are crucial to countries such as United States and Canada, which heavily depend on road transportation. There

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https://en.wikipedia.org/wiki/Road_surface

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Publications associées (27)

Undertaken in the field of design methods for flexible pavement, the present study focuses on the introduction of traffic loads, applied mainly to mechanistic empirical methods. In such research, strains due to traffic loads — calculated by pavement modeling based on linear elastic theory — are used for the evaluation of the life duration of the pavement. Real traffic loads on pavement vary significantly according to their intensity as well as their application modes. Our work aims to evaluate the relevance of the simplifying assumptions used in modeling to determine which parameters used in the description of traffic loads have more influence on the strains in flexible pavements. The study is chiefly based on experimental data. Strain measurements were made on several road structures, varying the main parameters of traffic loads, i.e. load intensity, inflation pressure of the tires and type of wheels. These measurements were carried out at various temperatures. Two structures featuring contrasted rigidities were modeled according to the French design method for flexible pavement. The horizontal strains exerted on these structures were studied at two depths : the bottom of the base course and the bottom of the wearing course. Then, experimental data were systematically compared with the modeling results. Strains at the bottom of the base course were both analyzed related to their maximal value — which corresponds to one of the design criteria used in mechanistic empirical methods — and as signals corresponding to the strain recordings in one given point during the passage of a traffic load. Analysis of maximal values allowed an evaluation of the influence of the studied load parameters and lead on to solutions to include them in calculations for equivalent traffic. The study of strain signals resulted in the definition of values allowing to express strain variations in function of time. The said values apply principally to notions like strain rates and the definition of frequencies that will best model strain variation in time with a sinusoidal curve. Such frequencies are obtained by decompositions in Fourier series. A relation between load speed and frequency has been defined. At the bottom of the wearing course, the study focused on strain signals only, with strange variations — which have been called "irregularities" — appearing in the horizontal strains at low depth. The scrutiny of these irregularities showed that bituminous materials located near to the road surface of flexible pavements are paradoxically more stressed horizontally than vertically. A situation that tends to link the behavior of bituminous layers in flexible pavements to the performance of a slam structure. Analysis of strain signals was supplemented by linear viscoelastic modeling based on Huet's model. If introducing the viscoelastic behavior of the bituminous layers showed no notable improvement in the quality of modeling, it nevertheless highlighted the necessity to model the pavement structure as a whole. Stress analysis underlined the effects of interactions between layers following different patterns of behavior and the importance of the interface conditions between these layers. Finally, the influence of the real vertical load pressure distribution on stress and strain in bituminous layers has been evaluated with elastic modeling. Variation of the loading conditions showed little effects on stress and strain distribution in the bituminous layers.

EPFL2003

Chargement

Comportement dynamique des dalles de roulement des ponts en béton sollicités par le trafic routier

The management of a network of existing road bridges involves interventions in order to maintain safety and the priority of these interventions is often determined by safety criteria. During the evaluation of safety, the dynamic effect of traffic actions is considered using equivalent static loads determined by multiplying the effect calculated using traffic load models by a dynamic amplification factor. During the evaluation of a deck slab, the application of inappropriate dynamic amplification factors could have significant financial implications, all the more since the local dynamic effects of overloaded trucks are determinant for this type of structural element. Dynamic amplification factors defined in codes have usually been derived from the measurement of global traffic action effects in the main structural elements of bridges. Unfortunately, local dynamic effects in deck slabs have not been studied in detail until now. A better understanding of the dynamic behaviour of deck slabs will lead to the definition of more accurate dynamic amplification factors and avoid the use of values that are too conservative. The behaviour of deck slabs of six typical Swiss highway bridges has been simulated in order to study their dynamic response during the passage of trucks. The structural arrangement of the deck slab was different for each of the six bridges. A parametric study was based on the simulation of various scenarios involving the passage of trucks for various combinations of speed, path and road surface roughness. Deck slab response was obtained by numerical simulation based on models of the bridge, truck and road surface. This system was resolved using a prediction - correction algorithm that considers the dynamic interaction between a bridge and trucks. Dynamic amplification factors were subsequently calculated from strains and deflections obtained from independent static and dynamic simulations. The simulation of numerous scenarios enabled the evaluation of the influence of different parameters on the dynamic response of a deck slab: The road surface roughness was found to be one of the most important parameters, with an increase in roughness leading to an increase in dynamic amplification factors. An overloaded truck produces a lower dynamic amplification factor in a deck slab than an empty truck. The truck speed influences the dynamic interaction, but a clear relationship between speed and dynamic amplification factor could not be identified. The maximum dynamic amplification factor does not vary significantly from one point to another over a deck slab in a girder bridge. The structural arrangement of a deck slab in a girder bridge has little influence on dynamic amplification factors. Overall, the different deck slabs on the girder bridges studied were all equally sensitive to the dynamic effects of road traffic. In many cases considered for the framed slab bridge, the maximum dynamic amplification factor was found to occur over the supports. For such bridges, the sensitivity of the deck slab to the dynamic effects of road traffic is not uniform. Finally, two approaches to evaluating deck slabs of existing road bridges are proposed. The first approach is only applicable in certain situations and involves a simplified evaluation using an updated traffic load model and a dynamic amplification factor. In situations where a simplified evaluation is not applicable, the second approach is to evaluate a deck slab using numerical or experimental analyses.

EPFL1999

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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

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Modélisation et prédiction du comportement rhéologique des mélanges bitume caoutchouc

Mehdi Ould Henia

EPFL2005

Comportement dynamique des dalles de roulement des ponts en béton sollicités par le trafic routier

EPFL1999

EPFL2003