Emmanuel Chailleux

A mathematical-based master-curve construction method applied to complex modulus of bituminous materials

ABSTRACT This paper gives a mathematical-based procedure in order to construct master-curves from complex-modulus measurements. The method is based on the Kramers-Kronig relations linking modulus and phase angle of a complex function. Three pure bitumens, one polymer-modified-binder and two mixtures are chosen to validate the possible use of this methodology and apply it. Assumptions which are needed to apply this procedure, are verified on complex-modulus data measured from these materials. Hence, master-curves can be built without introducing error from manual adjustement. The method seems to be suitable for binders and mixtures as soon as their behaviour is in agreement with the time-temperature equivalency principle. In conclusion, some interpretations of the WLF constants are given.

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.

Thixotropic Behavior of Paving-Grade Bitumens under Dynamic Shear

A material exhibits thixotropic behavior if its apparent viscosity decreases under stress and if it recovers its initial viscosity when unloaded. This thixotropy is well defined for fluids, but it is not well understood for viscoelastic materials. For bituminous binders, it a priori corresponds to a decrease in material stiffness under cyclic loading and a recovery of this stiffness after rest. Rheological tests, in which the stress distribution in the material is simple and controlled, appear interesting to gain relevant observations concerning the thixotropic behavior of bitumens. The materials were tested under simple shear flows with the help of a controlled stress rheometer, and the influence of temperature, frequency, and conditioning time were studied. This paper proposes a new experimental procedure for studying binder thixotropy in cyclic mode by means of shear tests. The procedure relies on the observation of the breakdown curves in the nonlinear domain and modulus recovery curves at different frequencies and temperatures. Stiffness variations are demonstrated to be linked to a rearrangement of molecular structure and not to crack formation and healing. Moreover, fatigue performance appears better for the binder that shows the most important capacity to be destructured.

Characterisation of ageing processes on the asphalt mixture surface

Ageing of asphalt binders leads to evolution of pavements mechanical performances, due to changes in their rheological behaviour and in the binder composition. Ageing leads to a hardening of asphalt, mainly due to the oxidation of the asphalt binder itself. Oxidation rate is influenced by several parameters, namely outside temperature, ultraviolet (UV) radiation and intrinsic characteristics of the mixture constituents. In order to assess physical and chemical characteristics of the binders in aged pavements, mixture samples of several centimetres in thickness are usually cored from the field. Binders are extracted from these asphalt samples. This process of extraction is typical but it does not allow differentiating bulk and surface characteristics. Indeed, only the surface binder is exposed to UV rays and weathering. In order to assess the ageing of only the surface layer, to verify, for instance the influence of ageing on adhesion characteristics, it is necessary to extract and recover only the surface asphalt binder. A new test protocol, presented in this paper, has been developed to fulfil this purpose. This protocol consists in sampling only small particles at the surface layer, extracting the binder from the particles and performing Fourier transform infrared spectroscopy (FTIR) tests to assess the ageing of the binder. As the quantity of binder is very small, a specific FTIR test method is used. This method consists in keeping the binder diluted in the solvent and placing the solution in the ray of the spectrometer to perform the measurement. This new method has been compared to a more typical one, which consists in applying the binder on a transparent plate after having extracted the binder from the solvent. Once it has been checked that the two methods provide the same results for three kinds of binders, surface ageing tests have been performed. Two different ageing processes were considered: an ageing on site and an accelerated ageing protocol using a climate chamber named Weatherometer (SUNTERTXXL+). In this chamber, temperature, humidity and rain are controlled. The comparison between the ageing in the laboratory and the field allowed correlating both processes to establish an accelerator factor with respect to the increase in carboxyl group.

Non Linearity in Bituminous Materials during Cyclic Tests

ABSTRACT In the recent years rheology has been taking an increasing importance in the characterization of bituminous materials. Rheological parameters are suggested by many studies as good indicators of the performance of these materials and tools to efficiently predict the performance and durability of asphalt pavements.Bituminous materials exhibit a non-linear mechanical response beyond a certain level of solicitation. This behaviour is important as it is a source of error in linear stiffness measurements. Fatigue tests on bituminous materials are typically performed in the non-linear region. In the present study, non-linearity of bituminous binders and mixtures was investigated through strain sweeps and fatigue tests. The development of non-linearity was described and quantified. It was found the strain level effect has the same impact on mechanical properties as the accumulation of cycles. A phenomenological description of this behaviour is proposed, based on the destruction of supra-molecular structures.

Exploring the Ageing Effect of Binder on Skid Resistance Evolution of Asphalt Pavement

ABSTRACT One of the most important safety requirements of a road is its capability of preventing skidding of vehicles. However, this requirement so called “skid resistance” evolves during the whole pavement life. Phenomena that are identified to be responsible of this evolution are binder removal, aggregate polishing and seasonnal variations. In addition, ageing of bitumen is also identified to play a significant role on skid resistance evolution. One of the main results of previous works about skid resistance evolution was a model that takes into account two of the above listed phenomena such as bitumen scrouring and aggregates polishing. This present work is a continuation of the previous ones. It tries to include the effect of ageing in the above model. An updated model of evolution of skid resistance including this latter effect is proposed. This model is composed by a set of elementery functions in which some of them can be easily identified. The model can predict the evolution of skid resistance by combining effects of ageing, polishing and binder removal.

Development of an accelerated pavement test reproducing the effect of natural ageing on skid resistance

This study deals with the development of a new test method simulating the effect of ageing on skid resistance. This test is applied to bituminous mixes in this study, but can also be applied to concrete. This test relies on two machines, the Wehner–Schulze machine, to measure the friction, and the Weatherometer sunset machine, to simulate weather effects (rain, wind, sunlight, etc.). The relevance of this test is evaluated from comparisons between changes in friction and a chemical function linked to bitumen ageing: the carbonyl index. Validation is performed on bituminous mixture samples exposed to natural and accelerated ageing modes. Three very thin asphalt concrete (VTAC) slabs are manufactured in the laboratory with three different types of bitumens. Two specimens are extracted from each slab: one for natural ageing and the other for accelerated ageing. The evolutions of friction and carbonyl index measured on these samples submitted to the two ageing modes exhibit similar tendencies for all three bitumen types, thus confirming the relevance of the test. A conversion factor describing the correspondence between the durations of accelerated ageing and those of natural ageing is proposed for each type of bitumen. Video abstract Read the transcript Watch the video on Vimeo

Source dependency of rheological and surface characteristics of bio-modified asphalts

Asphalt industry has been looking to reduce their dependence on petroleum-based binders and apply non-petroleum binders as partial or full replacement for asphalt binders. This motivated several attempts by researchers to produce bio-modified asphalts from various materials including woody biomass, waste cooking oil, and bio-oil from animal manure. Accordingly, attempts have been made to incorporate bio-oils/bio-binders (BBs) made from these feedstocks mainly as partial replacements for petroleum-based asphalt. However, this effort has been found to be challenging mainly due to the high variations, in both the feedstock sources and the resulting bioproducts. Accordingly, aforementioned bio-modified asphalts behave differently in terms of their physicochemical and morphological properties, making them to be highly different in terms of their performance as well as their susceptibility to thermal and oxidative ageing. While there have been several studies on the application of various biomass-derived alternative binders, their effects on the physicochemical characteristics of asphalt before and after oxidative ageing have not been studied thoroughly. Therefore, this paper investigates the effects of introduction of four different BBs made from Swine Manure, Miscanthus Pellet, Corn Stover, and Wood Pellet on the rheological and chemical properties of a selected asphalt binder (PG64-22) before and after oxidative ageing. To study the effect of oxidative ageing on the chemical structure of bio-modified asphalt binder, Infrared Attenuated Total Reflectance Spectroscopy (Fourier transform infrared) was utilised. In addition, a Drop Shape Analyser, Rotational Viscometer, and Dynamic Shear Rheometer were used to evaluate the surface properties and rheological behaviour of each bio-modified asphalt binder. Overall, bio-modifiers (bio-oil/BBs) were found to be significantly different in terms of their ageing characteristics. Accordingly, their surface and rheological properties were found to be ranked differently before and after ageing when compared to that of control asphalt binder. The results showed that the BB from swine manure is less susceptible to ageing compared to plant-based bio-oils. This can be further attributed to the chemical structure and the high lipid contents of the BB from swine manure, making it less affected by oxidative ageing.

Molecular weight distribution of asphaltic paving binders from phase-angle measurements

Based on previous works on polymers and regular bitumens, a new method for determining the molecular weight distribution (MWD) of asphaltic paving binders, using the phase angle () of the complex modulus measured in the linear viscoelastic domain, has been developed in this paper. MWDs of pure petroleum bitumens, natural bitumens, modified bitumens and artificially aged bitumens are calculated by this method and compared with MWDs obtained by gel permeation chromatography. The two methods give comparable results, but the δ-method developed here is more sensitive to the molecular weight of species. This method is very simple to implement, and seems a powerful tool in the determination of MWD of bitumens, in the visualisation and repartition of modifiers in the bitumen matrix and in the ageing monitoring and quantification.

Differential Scanning Calorimetry Applied to Bitumen: Results of the RILEM NBM TG1 Round Robin Test

The application of Differential Scanning Calorimetry (DSC) has been proven useful in characterizing bituminous binders, distillates and crude oils. In this paper, results of the round robin test, organized by the Rilem TC 231 Nanotechnology-based Bituminous Materials (NBM) TG1 group are reported. The purpose is to investigate the repeatability and reproducibility of standard DSC measurements when applied to bituminous binders. In the full test program of the Rilem NBM group, DSC measurements are further compared to observations made in atomic force microscopy (AFM), AFM measurements are reported in a separate paper. Seven laboratories have participated in this round robin test. Four bituminous binders were investigated, containing various amounts of natural or added wax. The test program consisted of a well-defined isothermal annealing procedure, followed by a first heating and cooling scan, and afterwards followed by a second heating scan. At this stage, the data, as they were reported by the different participants, were compared. For the glass transition (Tg), mid temperatures, can be defined with a reasonable reproducibility, which improves if natural wax is not present. Regarding melting and crystallization, the shape of the melting curve is highly dependent on the thermal history of the samples. Peak temperatures of melting and crystallization phenomena were reported with a good reproducibility, while the reproducibility of melting enthalpies (or surface area’s under the melting and crystallization signals) was not satisfactory. Different reasons for this and recommendations for improving the results are discussed in the paper.