Pierre Hornych

Review of glass fibre grid use for pavement reinforcement and APT experiments at IFSTTAR

Reinforcement using an interlayer system has been demonstrated for more than four decades as a multi-purpose solution to improve performance, to extend service life and thus to reduce maintenance costs of road pavements. Among a large number of existing interlayer systems, glass fibre grids have shown effective use in pavement reinforcement with a hot mix asphalt overlay. Recently they have received increasing attention from the pavement community. However, as for other types of interlayer systems, the mechanisms underlying the effectiveness and proper installation of this type of reinforcement system are still not fully understood, and the choice of the most appropriate grid (e.g. mesh size, tensile strength) and its optimal location in the pavement system are mainly based on experience. This article presents firstly a literature review on the use of glass fibre grids in pavement reinforcement. Then some results of recent full-scale tests on the accelerated pavement testing facility of the IFSTTAR are presented. They confirm that glass fibre grid properly installed near the bottom of the asphalt layer improves significantly the fatigue life of the reinforced pavement. They also demonstrate the efficiency of glass grid use under only a thin asphalt overlay. Finally, first results obtained using an original instrumentation of glass grid strands by means of strain gages, to understand better the mechanical behaviour of the glass fibre reinforcement in a new pavement structure are described.

Water Influence on Bearing Capacity and Pavement Performance: Field Observations

This chapter presents a mechanical behaviour study, i.e. the bearing capacity as a function of the moisture degree. The field point of view is expressed and the chapter summarises a number of observations on road behaviour, in relation to variations of moisture. First, the road structure is recalled with respect to the mechanical analysis point of view. Then some observations on field under temperate climate, humid, are given. In a second step, the specific case of frost and thawing are discussed.

Prediction of Permanent Deformations of Unbound Granular Materials in Low Traffic Pavements

ABSTRACT Permanent deformations of unbound granular layers and soils, caused by unfavourable moisture conditions, are one of the most common mechanisms of deterioration of low traffic pavements, with unbound granular bases. The paper presents permanent deformation models, developed by LCPC and by the University of Limoges, for the prediction of permanent deformations of unbound granular materials: a simple empirical model and two elastoplasticity based models for cyclic loading: one of them is based on the time independent plasticity with kinematic hardening, and the second one on the shakedown theory. The model parameters have been determined with cyclic triaxial tests performed on a granular base course material, at different moisture contents. An application of the models to finite element calculation of permanent deformations in a pavement structure is presented.

Creep tests on bituminous mixtures and modelling

In order to study the permanent deformations of bituminous mixtures, a temperature-controlled triaxial test has been set up. By means of triaxial creep tests at imposed stress, the influence of different parameters on the behaviour of bituminous materials (confining pressure, deviatoric stress and temperature) has been investigated. A viscoelastic–viscoplastic model has been developed to simulate the creep tests and has shown good ability for simulating the test results.

Cyclic triaxial tests on bituminous mixtures

In the framework of a study on rutting of bituminous layers, thermo-controlled triaxial tests under constant confining pressure on homogeneous asphalt concrete specimen have been performed. These tests are cyclic sinusoidal tests, with the aim to reproduce in some way the loading and unloading phases due to traffic on roads. The influences of confinement and load frequency have been studied. Tests have highlighted that confinement notably decreases the strain rate as well as the level of strain reached at the end of the test. The tests did not allow to clearly observe the influence of frequency on the response of the material, due to problems of repeatability. In order to avoid such problems, another test procedure was adopted. It consisted in changing either confinement or frequency during the test, with the purpose to see an evolution of strain rate, and to establish correlations. These tests have clearly shown the influence of cyclic loading and the relative influence of loading frequency on the response of asphalt concrete. The main objective of this triaxial programme is to develop a numerical model, based on rheological laws, able to predict the behaviour of bituminous layers.

Recycling of road materials into new unbound road layers - main practice in selected European countries

Most European countries are active in the field of recycling road materials, but knowledge and practice differ between countries. The European project DIsmantling and RECycling Techniques for road MATerials – Sharing knowledge and practices aims at sharing knowledge and practice in this field among the 15 participating countries, with the view of drafting European best-practice guidelines. This paper reports on the first step towards this goal, which consists of summarising documented practices within these countries concerning demolition and recycling of road materials back into new unbound road layers. Common documented practice and major differences between European countries are highlighted and put in perspective, thanks to a broader international document review.

Experimental and Theoretical Investigation of Three Dimensional Strain Occurring Near the Surface in Asphalt Concrete Layers

Several pavement failures have been observed to be initiated at or near the surface of the hot-mix asphalt layers and some of them propagate downward through the surface layer (top-down cracking). These modes of failure are affected by heavy vehicular loading configuration, pavement structure and their interaction at the tire-pavement contact. This paper documents an experimental investigation of surface strain induced under the entire tire by using specific instruments based on fiber optic sensors. Two innovative retrofit techniques which allow measuring strains in the upper parts of the asphalt layer have been used on the IFSTTAR’s test track facility. The association of these two techniques allows obtaining the strains, few centimeters below the surface, in three directions: longitudinal, transverse and vertical. Two pavement structures with two temperatures (moderate and hot) have been tested. Shape of the signal under the tire and magnitude of strain are compared with viscoelastic model pavement calculations.

Water Influence on Mechanical Behaviour of Pavements: Constitutive Modelling

This chapter deals with the effects of water on the mechanical behaviour of pavements. The analyse is based on constitutive considerations. Constitutive models devoted to both routine and advanced pavement analysis and design are introduced and both the resilient behaviour as well as the long term elasto-plastic approaches are presented. As soon as the approach considers the material as a two phase (solid matrix and a fluid), the introduction of the effective stress concept is required. In the last section an analysis is made on the extension of the constitutive models to the characterisation of partially saturated materials.This chapter deals with the effects of water on the mechanical behaviour of pavements. The analysis is based on constitutive considerations. Constitutive models devoted to both routine and advanced pavement analysis and design are introduced and both the resilient behaviour as well as the long term elasto-plastic approaches are presented. As soon as the approach considers the material as a two phase (solid matrix and a fluid), the introduction of the effective stress concept is required. In the last section an analysis is made on the extension of the constitutive models to the characterisation of partially saturated materials

Laboratory characterisation of the fatigue behaviour of a glass fibre grid-reinforced asphalt concrete using 4PB tests

This paper presents a complete experimental study of the fatigue behaviour of a glass-fibre-reinforced asphalt concrete, respecting EN 12697-24:2012, Annex D. The study is based on 38 four point bending tests, performed on 18 non-reinforced asphalt specimens and 20 geogrid-reinforced asphalt specimens. Both non-reinforced and reinforced asphalt specimens are tri-layered beams. The reinforced specimens contain two glass fibre grids, each one placed at the interface between two asphalt concrete layers. The objectives of the study were: (1) to characterise the fatigue behaviour of reinforced asphalt concrete, and to determine fatigue parameters, which can be used for pavement design, following the French pavement design method, (2) to show that glass fibre grid delays fatigue crack propagation and (3) to estimate the gain in fatigue due to the geogrid. The comparison of the fatigue curves of non-reinforced and reinforced asphalt concrete indicates that the geogrid increases fatigue life for the testing conditions, which were: fully reverse loading, displacement control, sinusoidal waveform, T = 10°C and f = 25 Hz.

Detecting Unbounded Interface with Non Destructive Techniques

The French road network has been built more than 30 years ago, and consists mainly of bituminous pavements. Some of them have also been maintained several times by thin overlays. On these pavements, a lot of damage such as potholes and alligator cracking has been observed, in particular after periods of heavy rain or freeze/thaw. Frequently, this type of damage is assumed to be linked with interface debonding between these overlays and the old pavement, associated with moisture effects. To detect such damages, some non destructive techniques (NDT), as electromagnetic techniques (GPR, step-frequency radar or infra-red) or as mechanical techniques (from static deflection measurements to seismic wave propagation methods), appear as promising approaches. This paper compares two differents NDT to detect debonding during an experiment carried out on the large pavement fatigue carrousel of IFSTTAR in Nantes.