Ferhat Hammoum

Experimental and Numerical Analysis of Crack Initiation and Growth in Thin Film of Bitumen

ABSTRACT In order to estimate the influence of bitumen on the resistance to cracking and fatigue behaviour of bituminous mixes, a specific test has been developed to estimate fracture properties. A thin film of binder between two steel protuberances, simulating the pseudo contact of two aggregates, is subjected to successive tension loads with a constant strain rate during the test. Formation and evolution of the crack size during the test was investigated using numerical methods. This paper deals with the combination of the experimental evolution of the sample stiffness and modelling of the considered test by finite element method. The modelling method, described here, integrates both viscoelasticity with Prony series and the sample geometry. A quantitative method using stress intensity factor and displacement intensity factor is also presented to study the effect of strain rate on propagation of crack.

Quantifying Expansion Effects Induced by Freeze-Thaw Cycles in Partially Water Saturated Bituminous Mix: Laboratory Experiments

Contraction/expansion effects induced by freeze-thaw cycles are thought to be at the origin of important and sudden deteriorations of pavement surface course, observed on some road sections in North-East of France. Therefore following these events and observations, it was decided to investigate in laboratory the phenomenon of freeze-thaw on partially water saturated bituminous materials specimen. This article presents some aspects of this beginning research work. We report an experimental investigation on the effect of the freezing-thaw cycles of bituminous materials. Some specimens are subjected to laboratory freeze-thaw cycles under a freezing rate without moisture change with the environment. In addition to basic mechanical properties and pore distribution, the measurement is also performed for freezing expansion of material of the specimen in each cycle. From these results, it is observed that the freezing expansion can be measured for high degree of saturation of the material. The results indicate also that the specimens experiment significant swelling at the beginning of the freezing periods. It is believed that the phenomenon could be detrimental to pavements, especially in the case of differential horizontal strains appearing within the structure layers, due to different swelling conditions depending on the materials and their moisture content.

Bitumen healing investigation using a specific fracture test

ABSTRACT In order to estimate the influence of bitumen on the fatigue behaviour of bituminous mixes, a test was developed and allows to estimate fracture properties and healing capacity of bitumen. A thin film of binder between two steel protuberances, simulating the pseudo contact of two aggregates, was subjected to successive tension loads with a constant strain rate during the test. Applying a rest period between every tension stage allows healing in the thin bitumen film. Evolution of the crack size during the test was investigated using different methods. This paper deals with the combination of the experimental evolution of the sample stiffness, modelling of the considered test and ultrasonic measurement. The modelling method, shortly described here, integrates both viscoelasticity and the sample geometry. A quantitative method using ultrasonic measurement is also presented to study crack size evolution when the test is repeated several times.

A 4pt bending bond test approach to evaluate water effect in a composite beam

Abstract Considering that water may cause a separation of interfaces between layers of pavement structures, specific test on bi-layer specimens is performed in a water bath. For the study of the bond between layers made of cement concrete overlay on bituminous material, four-point bending results show a competition between different failure mechanisms. Actually a very good bond resistance between layers compared to the fracture tension resistance of the cement concrete layer is preliminary observed in dry conditions. In this work, first results of the water effect on the behaviour of such a material interface are presented. The final fracture length of the specimen and the corresponding curve of force-displacement highlight the influence of water immersion on the debonding failure mode. The field displacement measurement obtained by Digital Image Correlation is used to improve the understanding of the fracture scenario.

Mixed-Mode Debonding Approach to Evaluate Water Sensibility in Bi-Layer Composite Pavement

In order to evaluate water sensibility on the interface between layers of composite pavements, a four-point bending (4PB) test on bilayer structure in a water bath is proposed. Using the virtual crack closure technique, the individual strain energy release rates are calculated with a specific model. The debonding mode I should be recognized as the main failure mode. For bilayer specimens made of a cement concrete overlay on bituminous material, the specific test has shown a competition between the different failure mechanisms. A very good bond resistance between layers compared to the fracture tension resistance of the cement concrete layer is observed. In this work, first results of the effect of water on the behavior of such a material interface are presented. An aquarium is built in order to submerge under water the bi-layer specimen. The final fracture length of the specimens, curves of force-displacements and first digital image correlation results show the influence of water immersion on the debonding failure mode.

Quantifying Expansion Effects Induced by Freeze-Thaw Cycles in Partially Water Saturated Bituminous Mix

ABSTRACT Contraction/expansion effects induced by freeze-thaw cycles are thought to be at the origin of important and sudden deteriorations of pavement surface course, observed on some road sections in North-East of France. Therefore following these events and observations, it was decided to investigate in laboratory the phenomenon of freeze-thaw on partially water saturated bituminous materials specimen. This article presents some aspects of this beginning research work. We report an experimental investigation on the effect of the freezing-thaw cycles of bituminous materials. Some specimens are subjected to laboratory freeze-thaw cycles under a freezing rate without moisture change with the environment. In addition to basic mechanical properties and pore distribution, the measurement is also performed for freezing expansion of material of the specimen in each cycle. From these results, it is observed that the freezing expansion can be measured for high degree of saturation of the material. The results indicate also that the specimens experiment significant swelling at the beginning of the freezing periods. It is believed that the phenomenon could be detrimental to pavements, especially in the case of differential horizontal strains appearing within the structure layers, due to different swelling conditions depending on the materials and their moisture content.

Effects of Ageing on Warm Mix Asphalts with High Rates of Reclaimed Asphalt Pavement

Within the framework of the European Project SUP&R ITN a Ph.D. thesis is carried out to study the durability of asphalt mixtures made with the combination of high rates of reclaimed asphalt pavement (RAP) and warm mix asphalt technologies. For this purpose the complex modulus and fatigue resistance of three different asphalt mixtures, including surfactant modified and foamed warm mix asphalts, combined with RAP has been studied. The extra value is given by the application of an ageing procedure based on the oxidation of compacted materials in laboratory. It follows the recommendations of the RILEM TC-ATB TG5, which distinguishes between short and long term ageing. Fourier Transform InfraRed (FTIR) tests were carried out on the extracted bitumens to quantify the oxidation levels. An increase of the norm and a decrease of the phase angle of \( \left| {{\text{E}}^{*} } \right| \) at 15 °C 10 Hz with ageing and RAP addition are experienced for all the mixtures. Similarly the slopes of the fatigue laws tend to increase with ageing. A consistent correlation is observed between these evolutions and the evolution of the carbonyl index. In general, the tendency is similar for all procedures, so the use of warm technologies combined with high RAP amounts may need to be considered.

GB5 mix design: a new approach for aggregate grading optimization for heavy duty flexible pavements

Since 2008, EIFFAGE has developed an aggregate optimization method (maximum contact and minimum space between aggregate particles) combined with the use of special binders (pure, multigrade or polymer-modified bitumen depending on the traffic concerned), to formulate the high-performance asphalt bituminous mix known as GB5®. During that time, numerous roads designed for heavy traffic have been built using this innovative technique, representing more than 1,000,000 tons at the end of 2014, mainly in France and, more recently, in South Africa. This article presents the result of collaboration between IFSTTAR and EIFFAGE aimed at scientifically relating the specific characteristics of the aggregate skeleton of GB5® to its outstanding mechanical properties, via 2D-image analysis and complete mechanical characterization.

A Mineralogical Approach of the Interactions Between Bitumen, Clay and Water in Hot Mix Asphalt (HMA)

Clay fines are known to reduce the water resistance of bitumen-aggregates binding and cause stripping in Asphalt Concrete (AC) mixtures. To address this phenomenon, a better understanding of the mineralogical composition of aggregates is needed as well as an assessment of the bitumen-clay-water interactions. This paper contributes to reach this goal from a mineralogical perspective. The most common clays in natural aggregates, kaolinite, illite and montmorillonite, were used to prepare thin clay films and artificial clay-rich aggregates. The bitumen-clay interaction was studied using the sessile drop and the Oliensis spot tests on those thin clay films, whereas Duriez tests allowed measuring the stripping potential of AC mixtures containing the clay-rich aggregates. The results show that the water-bitumen-clay interaction and water resistance of the AC mixture are specific to the clay mineralogy. Furthermore, they show that the bitumen-clay interaction may be captured upon determining the surface energy of bitumen, the chemical composition and pH value of the clay and the bitumen-clay compatibility. Hence, predicting the water resistance of clay rich AC mixtures from mineralogical properties of the bitumen-clay interaction seems feasible.