Impact of different ageing levels on binder rheology

This paper evaluates the variability of binder rheology for different ageing levels and the influence of ageing at different testing temperatures. Three different ageing levels were applied on a single type of bitumen with a penetration grade of 70/100.The artificial ageing of the binder was performed using the rolling thin-film oven test and the pressure ageing vessel. The rheological behaviour was investigated at low temperatures with the bending beam rheometer (BBR) and at medium and high temperatures with the dynamic shear rheometer (DSR). Several experiments were conducted to determine the range of stiffness and complex modulus results, the type of distribution comparing real and theoretical models, and the effects of ageing on the variability of the rheological behaviour. It was shown that not only the mean results from BBR and DSR tests change with ageing, but also the variability of the results changes with ageing. This would have an impact on mechanistic-empirical pavement design because it would influence the calculated stresses and strains as well as the calculated reliability.     

Influence of commercial waxes and polyphosphoric acid on bitumen and asphalt concrete performance at low and medium temperatures

The influence of adding four types of commercial wax and one polyphosphoric acid to a non-waxy bitumen was investigated with regard to binder and asphalt concrete mixture performance. Binder properties were determined using dynamic shear rheometer (DSR), bending beam rheometer, force ductilometer and various conventional test methods. Asphalt concrete performance was investigated using tensile stress restrained specimen test (TSRST), creep test at −25,^˚C, dynamic creep test at 40,^˚C and complex modulus test at 0, 10 and 20,^˚C. Totally eleven binders and eight asphalt mixtures were investigated. TSRST fracture temperatures of the asphalt mixtures were marginally influenced by the addition of any of the additives, and significant physical hardening of the binders, observed by BBR testing, could not be established using TSRST. Also in creep testing of asphalt mixtures at −25,^˚C, recorded effects were less pronounced compared to binder testing. In dynamic creep testing, the smallest permanent strains were recorded for the asphalt mixtures containing FT-paraffin or montan wax, indicating better resistance to rutting. Adding polyethylene wax or polyphosphoric acid to the non-waxy bitumen used, showed considerable positive stiffening effects on the binder at medium and higher temperatures. However, this increase in stiffness could not be shown in dynamic creep testing (at 40,^˚C) of asphalt concrete mixtures containing these additives.     

Fatigue and healing properties of bituminous mastics reinforced with nano-sized additives

The research work described in the paper focused on fatigue and healing properties of bituminous mastics reinforced with nano-sized additives.Commercially available multiwall carbon nanotubes (CNTs) and montmorillonite nanoclay (NC) were combined with a single base bitumen and a standard mineral filler to produce bituminous mastics. These blends were prepared in the laboratory by making use of a technique consisting in simple shear mixing followed by sonication.Fatigue behaviour of mastics under repeated loading was investigated by means of time sweeps performed in the strain-controlled mode at various amplitudes. Healing potential was assessed by adopting a testing protocol specifically conceived to discriminate between recovery of damage induced by fatigue loading and other artefact phenomena which may affect material response. All rheological measurements were carried out with a dynamic shear rheometer in the parallel plates geometry.Outcomes of the experimental investigation were found to be highly dependent on the nature of additive type, as a result of the key role played by interaction mechanisms that nano-particles can establish within the bituminous mastic.     

Evaluation of waste materials as alternative sources of filler in asphalt mixtures

There are many different ways to reduce the construction industry’s impact on environment. The incorporation of waste in the fabrication of construction materials may be beneficial for both the waste management sector and the construction industry. The aim of this research was to investigate the use of three different waste materials (construction and demolition waste, brick powder and fly ash) as filler in asphalt mixtures. Limestone filler was used as reference material. The materials were characterized in terms of their geometrical, physical and chemical properties, and the interaction with bitumen was assessed with two mastic test methods using four different bitumens. The specific surface of waste materials shows a wide-ranging variation due to material specific shape and texture of particles. However, the Rigden voids and bitumen number tests adequately measure the stiffening effect of these materials. The delta ring and ball test results showed there is a good relation with the filler content when the results are affected by the bitumen type. The f/b ratio for a specific bitumen–filler combination can be determined from the maximum filler-to-bitumen ratio and the recommended stiffening increase. The mastics with these waste materials showed strong resistance to water damage.     

Mechanism and behavior of bitumen strength reinforcement using fibers

This paper investigates the reinforcement mechanism of bitumen mixed with fibers. Fibers including cellulose, rock wool and polyester types were added to bitumen. The viscosity, toughness and tenacity, microscopy and rheological tests were conducted to characterize the engineering properties of bitumen-fiber mastics. Test results indicate that the reinforcing effect increases with increasing fibers up to a critical fraction. With higher mixing temperatures, there is a higher viscosity ratio of mastic to bitumen. The tensile strength of bitumen-fiber mastics also increases with increasing fiber concentrations because the fibers carry parts of tensile loads. With the increasing tensile strength, it is implied that there is a good adhesion between bitumen and fibers. Scanning electron micrographs show that fibers reinforce bitumen through a three dimensional structure. However, there is a critical fiber fraction when fibers start to interact with each other, resulting in lower toughness. The optimum fiber content is dependent on fiber type, length and diameter.     

碱侵蚀对玄武岩纤维/沥青流变性能的影响

为增强玄武岩纤维（BF）/沥青流变性能,采用1.0 mol/L及2.5 mol/L NaOH溶液对BF进行侵蚀,通过ESEM试验和FTIR试验对其表面细观形貌进行了细观观测及分析。结果表明：原样BF表面光滑,NaOH侵蚀后的BF呈现明显的NaOH产物包裹BF现象,且随着NaOH的浓度及侵蚀时间的增加,BF的-OH含量增加;通过ESEM试验、动态剪切流变仪（DSR）试验及低温弯曲流变仪（BBR）试验,研究了BF/沥青的拉拔断口形貌及流变性能。结果表明：随着BF的侵蚀程度越严重,沥青与BF粘结性能和BF/沥青流变性能越好,且得到了NaOH对BF侵蚀的最佳侵蚀时间和浓度分别为45 min和2.5 mol/L。     

基于关联性的玄武岩纤维沥青胶浆及其混合料性能研究

为全面提升玄武岩纤维沥青混合料性能,研究了纤维类型及玄武岩纤维长度、掺量等因素对沥青胶浆抗裂性能、抗剪性能及流变特性的影响规律;基于纤维胶浆与纤维沥青混合料性能的关联性分析,揭示了玄武岩纤维对沥青混合料性能的细观增强机制。结果表明:玄武岩纤维对沥青胶浆的抗裂性能及流变特性影响显著,其极限拉力和车辙因子分别达到原沥青胶浆的4.5倍及1.08倍;纤维沥青胶浆高温流变特性与其沥青混合料高温稳定性变化规律存在差异,而前者抗裂性能与后者低温抗裂性能关联性较强;玄武岩纤维与沥青胶结料、集料之间形成三维网状结构,有利于抑制裂缝扩展。     

Styrene butadiene styrene polymer modification of road bitumens

This paper describes the polymer modification of road bitumens with SBS. Six polymer modified bitumens (PMBs) were produced by mixing bitumen from two crude oil sources with an SBS copolymer at three polymer contents. The rheological characteristics of the SBS PMBs were analysed by means of dynamic mechanical analysis using a dynamic shear rheometer (DSR). The results of the investigation indicate that the degree of SBS modification is a function of bitumen source, bitumen-polymer compatibility and polymer concentration. When the polymer concentration and bitumen-polymer compatibility allow a continuous polymer network to be established, modification is provided by a highly elastic network which increases the viscosity, stiffness and elastic response of the PMB, particularly at high service temperatures. However, ageing of the SBS PMBs tends to result in a reduction of the molecular size of the SBS copolymer with a decrease in the elastic response of the modified road bitumen.     

Characteristics of two-component epoxy modified bitumen

Coal tar bearing emulsions were used in the Netherlands as binder in anti-skid surfaces for runways because of their perfect adhesion and fuel resistance properties. They are however toxic and will not be allowed anymore after 2010. Therefore alternatives need to be developed. As one of the alternatives, two types of two-component epoxy modified bitumen have been investigated by means of direct tensile tests (DTT), relaxation tests (RT) and dynamic shear rheometer (DSR) tests. The effect of the curing temperature on the strength development of the epoxy modified bitumen was tested. The results show that the tensile strength increases with increasing curing time and temperature. DTT and RT results indicate that this new epoxy modified bitumen has a much higher tensile strength, cures faster than a bitumen emulsion as a binder. Furthermore, it shows a good stress relaxation even at lower temperatures. The curing speed and the ultimate tensile strength after full curing can be easily adjusted. The DSR results show that the complex modulus of this epoxy modified binder is less susceptible to changes in temperature. The results also suggest that this epoxy modified bitumen has better anti-crack properties at lower temperature and less permanent deformation than bituminous binders at higher temperatures. All these results shows that this type of two-component epoxy modified bitumen can be promising as a binder in anti-skid layers.     

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.     

On the representative volume element of asphalt concrete at low temperature

The feasibility of characterizing asphalt mixtures’ rheological and failure properties at low temperatures by means of the Bending Beam Rheometer (BBR) is investigated in this paper. The main issue is the use of thin beams of asphalt mixture in experimental procedures that may not capture the true behavior of the material used to construct an asphalt pavement.For the rheological characterization, three-point bending creep tests are performed on beams of different sizes. The beams are also analyzed using digital image analysis to obtain volumetric fraction, average size distribution, and spatial correlation functions. Based on the experimental results and analyses, it is concluded that representative creep stiffness values of asphalt mixtures can be obtained from testing at least three replicates of the thin (BBR) mixture beams.Failure properties are investigated by performing strength tests using a modified Bending Beam Rheometer (BBR), capable of applying loads at different loading rates. Histogram testing of BBR mixture beams and of larger beams is performed and the failure distribution is analyzed based on the size effect theory for quasibrittle materials. Different Weibull moduli are obtained from the two specimens sizes, which indicates that BBR beams do not capture the representative volume element (RVE) of the material.     

Characterization of bitumens modified with SEBS, EVA and EBA polymers

A laboratory evaluation of the modified bitumens containing styrene-ethylene-butylene-styrene (SEBS), ethylene vinyl acetate (EVA) and ethylene butyl acrylate (EBA) copolymers is presented. The morphology, storage stability and rheological and ageing properties of the modified binders were studied using fluorescence microscopy, dynamic mechanical analysis, creep test (bending beam rheometer) and conventional methods. The results indicated that the morphology and storage stability of the modified binders were largely dependent on the polymer content and were influenced by the characteristics of the base bitumens and the polymers. At a low polymer content (3% by weight), the modified binders showed dispersed polymer particles in a continuous bitumen matrix. At a sufficiently high polymer content (6% by weight), a continuous polymer phase was observed. Regardless of the nature of the two phases, the storage stability of the modified binders decreased as polymer content increased. Polymer modification improved bitumen rheological properties such as increased elastic responses at high temperatures and reduced creep stiffness at low temperatures. The degree of improvement generally increased with polymer content, but varied with bitumen source/grade and polymer type. Polymer modification also influenced bitumen ageing properties. Evaluation of ageing effect was dependent on testing conditions (e.g. temperature and frequency).     

Rheological characterisation of bitumen diffusion

Diffusion is considered important in the process of mixing old and new binders during asphalt recycling. The degree of mixing is presumed to greatly influence the final properties of recycled asphalt concrete. Previously, studies have been undertaken to investigate diffusion using FTIR-ATR (Fourier Transform Infrared Spectroscopy using Attenuated Total Reflectance). A need was identified to verify, if the rates of diffusion detected using FTIR-ATR were accompanied by changes in rheological properties. In this paper, a dynamic shear rheometer (DSR) with parallel plates is used for monitoring diffusion. Diffusion coefficients obtained at 60, 80 and 100 °C from tests of a soft bitumen (rejuvenator) diffusing into a stiff one are presented. The diffusion coefficients determined are compared with the corresponding diffusion coefficients obtained using FTIR-ATR. The comparison shows that the rates of diffusion detected by the DSR are of the same magnitude, but somewhat higher than the ones detected by FTIR-ATR.     

Rheological behavior of short sisal fiber-reinforced polystyrene composites

The rheological behavior of short sisal fiber-reinforced polystyrene composites containing short sisal-fiber has been studied using an Instron capillary rheometer. The effect of fiber length, fiber loading, shear rate, shear stress and temperature on the rheological behavior of the composites was studied. Unlike other short fiber-reinforced thermoplastics at lower temperature the melt viscosity of polystyrene(PS)-sisal composites are lower than that at higher temperatures. At 180°C the viscosity of the composite is governed by wall-slip, which decreases the viscosity and at 190°C the viscosity is governed by fiber melt interaction that increases the viscosity. The morphology of the extrudate was studied using optical and electron microscopy.     

Effect of warm mix asphalt chemical additives on the mechanical performance of asphalt binders

Warm mix asphalt (WMA) has become very popular in asphalt pavement construction because it allows reducing both energy consumptions and carbon emissions. WMA can be obtained by using different types of additives and can be produced, applied, and compacted at temperatures 20–40 °C lower than hot mix asphalt. WMA additives allow reducing the working temperatures without compromising the final performance of the asphalt concrete. Many WMA additives are available on the worldwide market and some of them reduce the viscosity of asphalts binder (organic additives or foam) whereas others do not act on this sense (chemical additives). This study focuses on the effect of chemical additives on the performance of asphalt binders for WMA production. To this purpose, a neat bitumen, a polymer modified bitumen (PMB) and two different chemical additives were selected. All the binders were characterized through conventional tests, DSR, MSCR, FTIR and microscopic analysis. The result clearly showed that the influence of the chemical additives on the neat bitumen is negligible or non-existent. On the contrary, significant changes were observed in the modified bitumen properties. Specifically, chemical additives reduce the viscosity temperature susceptibility of PMBs in the temperature range between 80 and 140 °C, increase the rutting resistance potential and the elastic response of PMBs at high temperatures. Moreover, a morphological inspection supported the modifications observed in the rheological properties of PMBs.     

Rheological characterization of wax-modified asphalt binders at high service temperatures

The research reported herein focuses on the rheological characterization of wax-modified asphalt binders used in warm mix asphalt (WMA) technology. Wax-modified asphalt binders were produced by adding controlled quantities of different types of wax to a 50/70 unmodified bitumen. Five different kinds of wax were used, including synthetic hydrocarbons Fischer–Tropsch wax, Montan waxes and amidic-modified waxes. All the blends were subjected to different rheometric tests to assess their mechanical response at high service temperatures. The viscous deformation mechanism was analyzed with reference to static and repetitive creep loading; it was found that the viscous deformation is strongly affected by the presence of both hydrocarbons and amidic-modified waxes. Wax-modified binders exhibited an effective improvement in intrinsic resistance to non-reversible deformation, even in high applied stress and cyclic loading conditions. It was observed that the chemical composition and the consequent physical characteristics of the wax are the most important factors regulating the final behavior of wax-modified asphalt binders at high service temperatures. The final contribution of the experience performed is related to the technical evaluation of wax-modified asphalt binders and to the general development of WMA technologies for pavement applications.     

Effect of ageing on different modified bituminous binders: comparison between RTFOT and radiation ageing

Standard laboratory ageing methods of bitumen only take into account the effect of thermo-oxidation during the service life of a pavement but the effect of high energy cosmic radiation on site is not simulated in these procedures. The aim of the present work is to compare the laboratory simulated short term bitumen ageing (rolling thin film oven test) with ageing produced by short exposures of bitumen samples to Ultra Violet and gamma radiation. The influence of ageing agents on the thermal properties and rheological performance of the pristine and modified bitumen binders has been evaluated in this study. The thermal behavior of various aged bitumens is characterized by both isothermal as well as non-isothermal thermogravimetric analysis. The thermoanalytic investigations on bituminous samples are carried out to evaluate the thermal stabilities and activation energies of the binders and the life time prediction of the materials is made with the help of the kinetic information. It is found that modified bituminous binders are more resistant to heat and radiation. Different rheological tests are conducted by dynamic shear rheometer to examine the effect of ageing in terms of bitumen oxidation and polymer phase degradation which has a major consequence on high temperature rutting or low temperature cracking. Type of modifier is found to be of decisive importance. Creep and recovery tests show that the structure-time dependency of pristine aged bitumen is influenced much by stress and temperature than in the case of modified aged bitumens. The study has revealed that the elastomeric modifier protects the bituminous binder more than plastic modifier or nano filler. Finally, a fair correlation has been made between standard RTFO ageing and radiation aging.     

Numerical and experimental evaluation of the influence of the filler–bitumen interface in mastics

The successful use of additives in modified asphalt mixtures, such as warm mix asphalt, depends largely on the effect such modification has on the mastic. Previous research indicated that such modifiers do not simply change the bitumen properties, but can also change the interaction between the filler and the bitumen matrix. Understanding the effect of the properties of the fillers, the bitumen and their interaction is thus important for future asphalt mix design. In order to investigate this and to define the dominant relationships, this paper combines a numerical and experimental approach. In the experiments, the viscosities of modified and unmodified mastics with different filler concentrations and types were systematically investigated utilizing a novel testing protocol. In the numerical analyses, the Finite Element Method was utilized for a micro-mechanical analysis, in which the shape and size of the filler particles were varied in the bitumen matrix. Combining the experimental and numerical results allowed for a detailed investigation of the effect of the interface properties, with and without modifiers. The research further indicated that the effect of the shape and size of the fillers varied, depending on the interface properties. From the research relationships were established between the overall mastic viscosity and the influence of the filler–bitumen interface, considering shape and size. The conclusion of this paper can thus be useful for the effective development of modified asphalt mixtures and gives strong indications towards future research directions.     

An RVE-based micromechanical analysis of fiber-reinforced composites considering fiber size dependency

An RVE-based micromechanical elastic damage model considering fiber size dependency is presented to predict the effective elastic moduli and interfacial damage evolution in fiber-reinforced composites. To assess the validity of the present model, the predictions based on the proposed micromechanical elastic model are compared with Hashin’s theoretical bounds [Hashin Z. Analysis of properties of fiber composites with anisotropic constituents. J Appl Mech: Trans ASME 1979;46:543–50]. The proposed micromechanical elastic damage model is then exercised under uniaxial loading conditions to show the overall elastic damage behavior of the proposed micromechanical framework and to illustrate fiber size effect on the behavior of the composites. Moreover, comparisons between the present prediction and experimental data are made to further illustrate the capability of the proposed micromechanical framework for predicting the elastic damage behavior of fiber-reinforced composites.     

Influence of de-icing agents on the viscoelastic properties of asphalt mastics

A study using dynamic mechanical analysis (DMA) and stress rheometry was done on the viscoelastic properties of different bitumen-filler blends disposed to de-icing agents. The blends were mixtures of the same bitumen, B200 (B), and four different filler grades, limestone (L) filler, Oulu (O) stone (mica-gneiss with high biotite amount), Rovaniemi (R) stone (diabase) and Hietavaara (H) stone (diabase). The de-icing agents tested were water, formic acid, potassium acetate (KAc) and potassium formate (KFo). From the DMA measurements, the elastic modulus (stiffness) at −25 °C, the glass transition temperature (T _g) of the bitumen phase, and the softening temperature were measured. The stiffness data at −25 °C proposed that all agents seem to decrease the stiffness levels of the B-O blend with biotite to a larger extent. Formic acid and 50% potassium formates significantly decreased the stiffness level of the B-L blend. The stiffness of B-H blends was not affected by the chemical treatment. A plasticizing effect of water, formic acid, and 5% potassium acetate, was found for the B-L blend. From the changes in the softening temperatures in the temperature range 15–28 °C, it was concluded that chemical treatment may have an increasing effect on the softening temperatures of all blends, although the effect of hardening could not be omitted. Oscillatory flow measurements with a shear stress rheometer demonstrated that the viscosities of the blends increased significantly after the immersion in de-icing agents.