Bituminous Matrix Research Articles

Investigation of bituminized waste products swelling behavior due to water uptake under free leaching conditions: Experiments and modeling

AbstractBituminized waste products (BWPs) were produced by conditioning in bitumen the co‐precipitation sludge resulting from industrial reprocessing of spent nuclear fuel. Underground geological disposal is a solution for the long‐term disposal of some intermediate level long‐lived (ILW‐LL) categorized BWPs in France. After one or several hundred thousand years, the water from the host rock will fully saturate the disposal cells. By an osmotic phenomenon enabled by the semi‐permeable capacity of the bituminous matrix, water in direct contact with BWPs could cause them to swell, which would lead to pressure on the host rock and may damage the disposal facility. Therefore, the BWPs’ swelling behavior has to be taken into account in safety studies for disposal facilities. This paper presents an experimental and numerical investigation of BWPs’ swelling behavior due to water uptake. Experimentally, water uptake, swelling and released salts were monitored for about 4 years during free leaching tests of simplified BWPs. The numerical model presented is extended from an existing one that incorporates transport mechanisms (diffusion, permeation, osmosis) with mechanics via Maxwell's viscoelastic model. An original coupled homogenization of transport terms is proposed to better capture the role of the semi‐permeable membrane played by the bitumen and the porosity dependency of coupled transport coefficients during water uptake. The presented numerical model is able to reproduce the experimental results of free leaching tests and shows its validity for the entire leaching process.

Heterogeneous numerical modeling of fatigue damage for asphalt mixtures through complex mechanical impedances

Asphalt mixes, also known as bituminous concrete and asphalt concrete (AC), which are one of the most widely used materials in pavement engineering, are complex, multi-scale composite materials. AC is a heterogeneous material composed of a bituminous matrix and aggregates featuring viscoelastic and elastic behavior, respectively. Fatigue under cyclic loading of this material is one of the main pavement degradation phenomena. Under cyclic loading, the viscoelastic behavior of this material converts part of the energy brought by the loading into dissipated energy due to the viscous effects of the bituminous matrix. It is a heat source that leads to the increase of temperature during phase I of fatigue (self-heating). The second part of the energy is restituted and is the growth driving force of the damage. This work deals with a new thermodynamic approach to describe rheological models applied to viscoelastic materials under mechanical cyclic loading. The dissipation and the energy-released rate are determined based on an electromechanical analogy to simulate damage growth and the temperature increase. Both thermal and mechanical aspects and their coupling are taken into account leading to complete constitutive modeling to simulate the decrease of the AC complex modulus. Using the image processing technique, a heterogeneous microstructure is used to model the AC.

Filled bituminous compositions in the construction industry

Objective. The properties of road bitumen, when interacting with the components of building compositions, are always transformed relative to their original properties. Therefore, when working with materials based on filled bitumen compositions, regardless of their field of application, the main task is to monitor the dynamics of changes in characteristics and control in the required direction, as well as maintaining properties such as viscosity, flexibility and fluidity. The purpose of the work is to study the effect of modifying additives of various bases (fillers, plasticizers and waxes) on the properties of a bituminous binder and to evaluate the effectiveness of their contribution to the formation of filled bitumen compositions for the construction industry.Method. The methodological basis of the work is the principle of bitumen structure formation. Experimental studies were carried out using standard and special methods.Result. The results obtained showed that fiberglass fiber proved to be the best filler in the bitumen composition. In the study of plasticizers, it was revealed that the most pronounced positive plasticizing effect is observed from the use of an extract of selective oil purification, which allows you to control the flexibility of the system in a wide range. It has been established that the plasticizer polyalkylbenzene effectively regulates the properties of the composition at negative temperatures, slightly affecting the heat resistance. The results of the wax study show that Titan synthetic wax and Viscobit polyethylene wax are evenly distributed in the volume of the bituminous binder and provide stabilization of the system properties.Conclusion. In the process of performing the study, as well as analyzing the results obtained, 3 groups of bituminous matrix filler additives were studied. It has been established that the directed regulation of the properties of bitumen systems is possible due to the rational choice of the type of additive-filler. Thus, using complex fillings of the bitumen matrix when designing bitumen compositions with the possibility of regulating and normalizing their properties (optimization indicators), it is possible to obtain economic and operational effects.

Influence of polymeric molecular chain structure on the rheological-mechanical behavior of asphalt binders and porous asphalt mixes

This manuscript reports on two Styrene-Butadiene-Styrene (SBS) polymeric molecular chains so-called 1101AT and D0243, used to modify a 50/70 pen grade neat asphalt binder sample, generating the matrixes 60/85 E and Highly Modified Asphalt (HiMA), respectively. Some research gaps still exist and need to be investigated further, principally on why and how these distinct molecular chains influence the rheological-mechanical behavior of the asphalt binders and asphalt mixes, even pertaining to the same polymeric group. Dynamic Shear Rheometric (DSR) analyses describe the rheological spectra of the binder samples, considering the dynamic stiffness modulus in the complex plane |G*|. Porous asphalt mixes were evaluated considering the French formulation methodology and the following aspects: compaction ability, deleterious action of water, seepage speed and resistance to rutting. The results obtained indicate that HiMA matrix presented superior long-term rheological and mechanical behavior compared to 60/85 E, due to the more elaborate polymeric chain being associated to a bituminous matrix with rheological spectra providing less thermal and kinetic susceptibility, although its highest dynamic viscosity implies little reduction in the air void content and, consequently, lower seepage speeds to the porous asphalt mixes, but greater rutting resistance.

Investigations on the rheological and swelling-degradation behavior of crumb rubber within the bituminous matrix

This paper focuses on the rheological and swelling-degradation behavior of crumb rubber within the bituminous matrix. Three different penetration-grade asphalts were modified by crumb rubber in a four-paddle mixer at various curing times and treatment temperatures. Rotational viscosity, dynamic shear rheometer, solubility and gel permeation chromatography tests were conducted to evaluate the viscosity, rheological property, crumb rubber solubility and molecular weight distribution of the rubber-modified asphalts, respectively. Moreover, the microstructure of the rubber-modified asphalts was characterized by fluorescence microscopy and Fourier transform infrared spectroscopy tests. The results reveal that the viscosity and complex modulus of the rubber-modified asphalts decrease and the infiltrating ability of crumb rubber within the bituminous matrix increases with increasing treatment temperature (or curing time). However, serious degradation of crumb rubber and asphalt ageing happen with the increased treatment temperature or prolonged curing time, which causes a noticeable increase in viscosity and stiffness. The increase in asphaltenes content within the bituminous matrix causes an enhancement in viscosity and complex modulus, and releases of the large (or medium) molecules, improving rutting deformation resistance. There is no obvious difference in small molecules, illustrating that asphalt type does not affect the distribution of small molecular size. When the treatment temperature increases from 200 °C to 220 °C, the curing time required to achieve 60 % solubility of crumb rubber in asphalt X is from 25 h to 15 h, which indicates that the higher the treatment temperature, the shorter the curing time required to reach the maximum solubility. Moreover, the swollen crumb rubber molecules are degraded into some small molecule substances dissolving into asphalt binder for modification. It makes the adsorption peaks of typical function groups increase significantly. The outputs from this study can provide the guidance for the selection of preparation conditions and asphalt binders that fabricate the rubber-modified asphalt with desired properties.

PH and microbial community determine the denitrifying activity in the presence of nitrate-containing radioactive waste.

An important fraction of the currently stored volume of long-lived intermediate-level radioactive waste in Belgium contains large amounts of NaNO3 homogeneously dispersed in a hard bituminous matrix. Geological disposal of this waste form in a water-saturated sedimentary formation such as Boom Clay will result in the leaching of high concentrations of NaNO3, which could cause a geochemical perturbation of the surrounding clay, possibly affecting some of the favorable characteristics of the host formation. In addition, hyper-alkaline conditions are expected for thousands of years, imposed by the cementitious materials used as backfill material. Microbial nitrate reduction is a well-known process and can result in the accumulation of nitrite or nitrogenous gases. This could lead to the oxidation of redox-active Boom Clay components, which could (locally) decrease the reducing capacity of the clay formation. Here, we compared nitrate reduction processes between two microbial communities at different pH related to a geological repository environment and in the presence of a nitrate-containing waste simulate during 1 year in batch experiments. We showed that the microbial community from in Boom Clay borehole water was able to carry out nitrate reduction in the presence of acetate at pH 10.5, although the maximum rate of 1.3 ± 0.2 mM NO3 -/day was much lower compared to that observed at pH 9 (2.9 mM NO3 -/day). However, microbial activity at pH 10.5 was likely limited by a phosphate shortage. This study further confirmed that the Harpur Hill sediment harbors a microbial community adapted to high pH conditions. It reduced twice as much nitrate at pH 10.5 compared to pH 9 and the maximum nitrate reduction rate was higher at pH 10.5 compared to that at pH 9, i.e., 3.4 ± 0.8 mM NO3 -/day versus 2.2 ± 0.4 mM NO3 -/day. Both communities were able to form biofilms on non-radioactive Eurobitum. However, for both microbial communities, pH 12.5 seems to be a limiting condition for microbial activity as no nitrate reduction nor biofilm was observed. Nevertheless, pH alone is not sufficient to eliminate microbial presence, but it can induce a significant shift in the microbial community composition and reduce its nitrate reducing activity. Furthermore, at the interface between the cementitious disposal gallery and the clay host rock, the pH will not be sufficiently high to inhibit microbial nitrate reduction.

A Numerical Simulation of Electrical Resistivity of Fiber-Reinforced Composites, Part 2: Flexible Bituminous Asphalt

Asphalt concrete pavements are vulnerable to freeze-thaw cycles. Consecutive cracking and penetration of corrosive agents can expedite the degradation of asphalt pavements and result in weight loss and reduced strength. Fiber reinforcement in flexible bituminous asphalt bridge cracks limits the crack width and enhances the toughness of the composite. Furthermore, steel fibers facilitate asphalt heating during maintenance and repair operations. Electrical resistivity is a vital parameter to measure the efficiency of these operations and to identify the state of degradation in fiber-reinforced asphalt concrete. The significant difference between conductivities of steel fibers and bituminous matrix warrants in-depth investigations of the influence of fiber reinforcement on the measured surface electrical resistivity of placed pavements. Numerical simulations endeavor to predict the resistivity and associated deviations due to randomly distributed fiber reinforcement. Results and discussions reveal the sources and magnitudes of fiber geometry and content adjustments. Outcomes investigate associated errors for practical applications.

Reliability study on rheological and cracking behavior of mastics using different sized particles

The objective of this present work was to evaluate the rheological and cracking behavior of mastics fabricated with different sized particles and asphalt types. Two asphalts (base and modified) and three fillers with different sized particles (C, M and F) were investigated. The rheological functions including the creep and recovery property and the fatigue property were measured by multiple stress creep-recovery (MSCR) and time sweep (TS) tests, respectively, while the cracking behavior of asphalt materials was investigated using extensile (ES) tests. Moreover, the dispersion characteristics of various sized particles inside a bituminous matrix and the associated mastic morphology were assessed by a scanning electron microscope (SEM). The results revealed that the presence of coarse-sized particles in matrix increased the non-recoverable compliance and fracture energy but decreased fatigue life of the mastics. The presence of medium-sized particles in matrix enhanced the high-temperature elasticity recovery behavior and degraded the low-temperature fracture energy and the cohesive strength of asphalt mastics, regardless of asphalt types. When filler particle size dropped down to a minimum dimension, asphalt type had negligible effects on the fatigue response and exerted a positive effect on the low-temperature cohesive strength for the related mastics. In addition, the dispersion characteristics of various sized particles inside a bituminous matrix and the associated mastic morphology can account for the rheological response and cracking behavior of the corresponding mastics.

A heterogeneous micromechanical model for bituminous composites containing rigid and flexible particulates

This paper uses a heterogeneous micromechanical model to evaluate the resistance to thermal cracking in bituminous composites containing granular particulates. Thermal cracking is mainly caused by temperature fluctuations leading to accumulated stress that exceeds the strength of the materials. The presence of various granular particulates significantly affects a material's strength and capacity to release stress. Here, we use a two-dimensional heterogeneous numerical finite element model to evaluate and predict the thermal cracking characteristics of bitumen containing granular particulates such as crumb rubber and taconite. To develop the model, randomly distributed polygons using the Delaunay triangulation method were used to represent taconite and crumb rubber inside a bitumen matrix. The elastic properties of taconite and crumb rubber were assigned to the particulates, and the viscoelastic properties of the bitumen were modeled using a Prony series by implementing a simple fractional viscoelastic model. The study results showed that the flexural creep stiffness and creep rate calculated by the model were in good agreement with the measurements of experiments: the maximum errors were 6.15% for bitumen containing crumb rubber and 13.72% for bitumen containing taconite. Considering that flexural creep stiffness and creep rate are commonly used as indicators of thermal cracking resistance, the newly developed heterogeneous micromechanical model can be used to evaluate the thermal cracking resistance of bituminous matrices containing granular particulates. The model was further used to study the effects of temperature, elasticity, and concentration of particulates on the cracking resistance of the bituminous matrix. For instance, it was found that introducing 16% particulates with an elasticity of 1.02 MPa (representing crumb rubber) to bitumen improves its critical cracking temperature from −25 °C to −29.3 °C. This model provides insights to help the design of bituminous composites with desired cracking resistance properties by incorporating the proper particulates.

Effect of Used Engine Oil Addition on the Rheological Properties of a Plastic Bag Waste–Modified 40/50 Grade Bitumen

AbstractThe oily fraction allows expansion and dissolution of the polymer particles within the bituminous matrix. This contribution studies the effects of adding a small quantity of a used engine o...

Phenolic compounds to amplify the effect of sulfur on Bitumen’s thermomechanical properties

This paper evaluates effects of phenolic compounds on the role of sulfur in a bituminous matrix. This is especially important because the concentration of sulfur in bitumen has been increasing mainly after a strict restriction was placed on sulfur content of marine fuel, which led refineries to divert sulfur from fuel to bitumen. There are documented challenges associated with the use of high-sulfur bitumen, such as sulfur’s oxidation to hazardous hydrogen sulfide during bitumen application as well as increased moisture susceptibility in bitumen. This paper specifically examines how specific bitumen constituents can promote sulfur reactions that in turn amplify the effect of sulfur on bitumen’s thermo-mechanical properties. To do so, we use density functional theory (DFT) and rheometry to examine and compare the effects of sulfur on bitumens that contain different concentrations of polar aromatics and phenolic compounds. Our DFT results highlight the role of polar groups and heteroatoms in the addition reactions of sulfur radicals to CC bonds, which mostly improve the formation of organo-sulfur compounds. Our results show that presence of phenolic compounds can work as an activator for sulfur interactions within bitumen. This in turn indicates that the effect of sulfur can be more noticeable in a bituminous matrix having a high content of phenolic compounds. Our DFT results are further supported by experiments showing that among studied asphalts, those modified with wood-based bio-oil containing 76% polar compounds including nearly 41.8% phenolic structures (among molecules recognized by chromatography) had the highest change in their thermomechanical properties when sulfur was introduced. In contrast, asphalts modified with waste vegetable oil containing 12% polar compounds and nearly no phenolic structures showed the least change due to the addition of sulfur. This in turn shows effects of sulfur on bitumen’s property can be tuned by introducing specific compounds. The outcomes of the study provide insights about variational role of sulfur in bitumen containing various bio-modifiers to allow more informed use of sulfur to promote sustainability of construction.

Behavior Evaluation of Bituminous Mixtures Reinforced with Nano-Sized Additives: A Review

This article presents a comparative review of the most commonly used nano-additives for bituminous mixtures: nanoclays (NC), nanosilicates, carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), nano-calcium oxide (CaO), and nano-titanium dioxide (TiO2). In this study, the mechanical behavior of the obtained additive mixture is evaluated. According to the revised literature, the results strongly depend on type, concentration, and dispersal of used nano-additive. In fact, it has been seen that simple shear mixing followed by sonication homogenizes the distribution of the nanoparticles within the bituminous matrix and favors the bonds’ formation. The viscosity of the mixture of bitumen with nanoparticles improves with the increase of the percentage of additive added: it indicates a potential improvement to permanent deformation and rutting. Another benefit is an increased resistance of the binder to aging. Furthermore, it has been shown that the nanoparticles are able to prolong the service life of a bituminous mixture by means of various interdependent chemical–physical mechanisms that can influence the resistance to fatigue failure or the ability to self-heal. However, the effectiveness of these improvements depends on the particle type, added quantity and mixing technique, and the tests carried out.

Heterogeneous visco-hyperelastic numerical modelling of crumb rubber-modified asphalt binders

ABSTRACT Three-dimensional numerical finite element (FE) biphasic models verified against the experimental data were developed aiming to study the accuracy of FE modelling in the prediction of viscoelastic properties of crumb rubber-modified asphalt binders. In the numerical models, crumb rubber-modified asphalt binders are considered as a heterogeneous composite material consisting of the original asphalt binder and rubber particles which respectively have viscoelastic and hyperelastic behaviours. Three different dosages of crumb rubber including 10, 15 and 20 wt% of the original asphalt are added. To capture rubber particles distribution within the bituminous matrix, a random generation method by using the MOA software (French acronym for random object modeller) was implemented based on rubber’s minimum and maximum particle sizes. In order to determine the viscoelastic properties of the original asphalt binder as well as the crumb rubber-modified ones, the dynamic shear rheometer (DSR) was used. The excellent agreement between the numerical FE modelling and experimental results witnessed the capability of biphasic finite element models to predict the visco-hyperelastic behaviour of crumb rubber-modified asphalt binders having an error lower than 9%.

Investigating Change of Polydispersity and Rheology of Crude Oil and Bitumen Due to Asphaltene Oxidation

This paper examines the effect of oxidation of asphaltene molecules on the overall polydispersity and rheology of a bituminous matrix. The research hypothesis is that oxidation of asphaltene molecu...

Water-soluble bitumen degradation products can fuel nitrate reduction from non-radioactive bituminized waste

An important fraction of the currently stored volume of long-lived intermediate level radioactive waste in Belgium is immobilized as Eurobitum. This type of waste typically contains large amounts of NaNO3 homogeneously dispersed in a hard bituminous matrix. Geological disposal of Eurobitum in a water-saturated sedimentary formation such as Boom Clay will result in the leaching of high concentrations of NaNO3 in the Boom Clay formation. This could cause a geochemical perturbation of the surrounding clay, possibly affecting some of the favorable characteristics of the host formation such as its hydraulic conductivity, sorption potential or the redox conditions. The latter might result in a decrease of its reducing capacity and an increase in the mobility of redox-sensitive radionuclides. Microbial nitrate reduction is a well-known process, which could be stimulated by the chemical and radiolytical water-soluble organic bitumen degradation products. The present study carried out different series of long-term anoxic batch experiments to investigate the ability of the microbial community of Boom Clay borehole water to reduce nitrate, leaching from thermally aged non-radioactive Eurobitum in the presence or absence of acetate, formate and oxalate, being part of the most important organic bitumen degradation products. Obtained results indicate that all three organic bitumen degradation products can be used as electron donor to fuel microbial nitrate reduction, albeit with a different efficiency. The highest nitrate reduction rate was observed in the presence of acetate, while oxalate was the least efficient electron donor for nitrate reduction. Moreover, organic compounds that leached from the Eurobitum during the course of the experiment were used as electron donor for microbial nitrate reduction in all conditions. Furthermore, calcium oxalate crystals were observed, indicating that if oxalate is present, it will probably be less bioavailable compared to other organic compounds.

Phase separation and thermal degradation of plastic bag waste modified bitumen during high temperature storage

Phase separation and thermal-oxidative degradation can occur during storage and transportation of polymer modified bitumens (PmB), and both phenomena may substantially erode the properties of the PmB. In this paper, we investigate the phase separation and thermal degradation issues of waste plastic bag modified bitumen (WPmB) samples stored under quiescent conditions, as suggested by the standard storage stability testing procedures, and under a low continuous agitation. As for the phase separation, empirical basic tests, dynamic rheological tests and dissolution in a diluent of a small quantity taken from each section; top, intermediate and bottom, of the WPmB stored samples are used to evaluate the potential of segregation and migration of plastic particles within the stored samples under static and agitation conditions. As for the WPmB degradation, FTIR spectra analysis and different binder ageing testings were used to estimate the effect of both heat and air on the properties of the WPmB during its storage at high temperature for a duration of 48 h. The phase separation results demonstrated that the totality of the plastic particles have separated completely from the bitumen during static storage. However the plastic remains well distributed in the bituminous matrix of the agitated samples thanks to the low continuous agitation, which obviously manage to prevent plastic particles from flocculating and then from separating. Moreover, the thermal degradation results indicate that no considerable adverse effects of the high temperature storage are observed on the ageing of the modified bitumen as well as on the thermal degradation of the waste plastic bag additive.

Elemental Composition and Organic Petrology of a Lower Carboniferous-Age Freshwater Oil Shale in Nova Scotia, Canada.

A 59 m-thick section of a freshwater oil shale interbedded with marlstone of Lower Carboniferous (Tournaisian) age from the Big Marsh area in Antigonish Basin, Nova Scotia, Canada, was examined using reflected light microscopy, Rock-Eval pyrolysis, X-ray diffractometry analysis, inductively coupled plasma-mass spectrometry for elemental analysis, and prompt γ for boron concentration. The oil shale was deposited in a lacustrine environment based on geology, sedimentology, variation in organic matter, and boron content (28–54 ppm). Organic petrology classified the oil shale into three broadly distinct types. Type A oil shale is a coastal facies shale containing terrestrially derived macerals, such as vitrinite and inertinite, sporinite, with some lamalginite, and amorphous bituminous matrix. Type B oil shale was deposited in a shallow-water facies and contains mostly lamalginite and some vitrinite and sporinite. Type C oil shale is a relatively deep-water facies, associated with open-water Torbanite-type oil shale and contains mostly Botryococcus colonial telalginite. The oil shale is thermally mature (Tmax is 441–443 °C). Total organic carbon (TOC) varies from 5.8 to 7.3 wt %, and the hydrogen index is between 507 and 557 mg HC/g TOC. The rate of sedimentation as determined by the Th/U ratio indicates possibility of three sedimentation periods: an irregular but mostly slow rate of sedimentation from the base of the section up to 68 m, followed by a regular and slow rate between 68 and 53 m, and a regular and fast rate between 53 m and the top of the section. The higher Th/U ratio during deposition of the shallow-water facies was due to the input of allochthonous U. The redox conditions, as reflected in the variation of Cr to Mo, U, and Ni + V, indicate that the oil shale was deposited under suboxic–dysoxic conditions. The high organic productivity by phytoplankton and bacteria is characterized by a low Cr and high V/Cr ratio and suboxic conditions. In contrast, the well-oxygenated and uniform, warm-temperature upper water level supports a dysoxic environment. Variation of Sr/Ca vs Mn/Ca ratios indicates that most samples have low values, a characteristic of colder water and high terrigenous influx. The post-Archean Australian shale (PAAS)-normalized rare earth elements (REEs) follow three trends. Type A oil shale has the highest concentration of total REEs (648 ppm) and light REEs (LREEs, 605 ppm) as compared with type C (269 and 233 ppm), which are less than half of type A. Type B oil shale has the lowest total REEs (184 ppm) and LREEs (152 ppm). The concentration of heavy REEs decreased from 43 ppm in type A oil shale to 36 ppm in type C oil shale. Comparison of PAAS-normalized REEs for the three oil shale types indicates a reduction of the negative Eu anomaly with depth, which is possibly related to sedimentary sorting as a result of accumulation of fine sediments in the deeper water zone of the lake. The concentration of most elements of environmental concern is similar to and/or lower than the world shale. However, there are instances of higher concentrations of hazardous elements (e.g., As, Cd, Mo, and Se).

Effects of filler particle size and ageing on the fatigue behaviour of bituminous mastics

Fatigue cracking is caused by repeated traffic loads and environmental conditions (temperature, ageing, etc.); it predominantly initiates within the mastic phase in the form of micro-cracks. In this sense, bituminous mastics (comprised of a binder, filler and entrapped air) play a significant role in the anti-fatigue performance of asphalt mixes. In this paper, the effects of filler particle size and ageing on the fatigue behaviour of bituminous mastics were evaluated. Prior to this, the rheological properties of the studied samples were evaluated using physical tests and frequency sweep tests. Moreover, the mastic morphology and filler distribution inside a bituminous matrix were characterized by Scan Electronic Microscope (SEM). The results revealed that ageing had a greater effect than filler particle size on the rheological behaviour of SBS-modified bituminous mastics, especially for mastics containing coarse filler particles. According to the ageing responses derived from log-log fatigue law plots, aged mastics containing coarse filler particles had higher slopes (represented by coefficient B) and lower intercepts (identified by coefficient A) than un-aged mastics. However, opposite fatigue behaviour was observed with fine filler granules, where coefficient B slightly decreased while coefficient A slightly increased after ageing. In addition, mastic morphology and filler dispersion inside a bituminous matrix were characterized by SEM, providing insight to possible relationships between morphological characteristics and fatigue performance.

Multi-Scale Numerical Viscoelastic Simulation of Fatigue Behavior of Asphalt Mixtures Modified with Polyphosphoric Acid

Fatigue cracking is one of the main distresses affects the service life of asphalt mixture. Recently, polyphosphoric acid (PPA) widely used as a modifier to improve mechanical and rheological characteristics of asphalt binders and mixtures especially at high and low service temperatures. While there are several studies devoted to investigate high and low service temperature of PPA modified asphalt binder and mixture, its fatigue behaviour needs to be studied in more detail. The main objective of this paper is to develop a multiscale heterogeneous numerical finite element (FE) model as well as experimental program to investigate the effect of PPA modification on fatigue behaviour of different bituminous composites from neat asphalt binder to asphalt mixture. The experimental program includes frequency sweep test at test temperature of 25°C by implementing dynamic shear rheometer (DSR) for neat and PPA modified asphalt binder and also indirect tensile fatigue (ITF) at frequency of 1 Hz (0.1 s loading time and 0.9 s rest time) under constant stress of 300 kPa at test temperature of 25°C by using a UTM-25kN. Three different contents of PPA is used for modifying neat asphalt binder including 0.5, 1 and 1.5 wt.% of neat binder to consider the variation of modifier extent on fatigue behaviour of neat asphalt binder and mixture. The mixture specimens were prepared with granite aggregate and asphalt binder of 85/100 penetration grade. The asphalt mixture is modeled as a biphasic medium composed of granular inclusions with linear elastic properties and bituminous matrix exhibiting linear viscoelastic behavior at small strain values. The generalized Maxwell rheological model was used to simulate viscoelastic behavior of the asphalt binder and PPA modified asphalt binder. In order to create the aggregate skeleton of the bituminous composites, a custom software (called “MOA”, French acronym for Random Object Modeler) developed in University of Limoges, has been used to generate random inclusions of various sizes and shapes. The experimental results of asphalt binder and mixture indicated that modification with PPA has a significant effect on improving asphalt mixture’s fatigue life especially in dosage of 1%. On the other hand, results of numerical simulation have shown a good agreement with experimental results.

Chemo-Rheological Study of Hardening of Epoxy Modified Bituminous Binders with the Finite Element Method

The chemical irreversible hardening of epoxy modified bitumen is affected by various physical factors and the successful application of this technology is directly linked with full understanding of chemo-rheological material characteristics. This study proposes a model to describe the material viscosity evolution during hardening of epoxy modified bitumen. The findings from numerical analyses performed to assess the mechanical response of epoxy modified bituminous binders are presented. Information of the chemical interaction of epoxy within a bituminous matrix was collected and all the influential factors have been determined. The proposed chemo-rheological model accounting for the polymerization of the epoxy in the bitumen was formulated and the sensitivity of material parameters, such as activation energy, reaction order and extent of hardening reaction until the gel point of epoxy modified binders, was demonstrated. Results of the analyses suggest that lower levels of activation energy increase the degree of hardening and the rate of viscosity development. By decreasing the hardening reaction until the gel point the achieved viscosity of epoxy modified bitumen was increased showing the importance of gel reaction extent on material viscosity evolution. The numerical studies have shown also that the polymerization rate in the epoxy modified bitumen is highly dependent on the temperature under various (non-) isothermal conditions. Also, the polymerization rate should be considered through all the material curing processes to avoid unwanted variations in the mechanical properties.