Jonas Ekblad

Influence of polymer modification on low temperature behaviour of bituminous binders and mixtures

Effects of polymer modification on low-temperature properties of bituminous binders and mixtures were studied. Three bitumens were blended with 6% SBS, SEBS, EVA or EBA. Dense graded asphalt mixtures were prepared using a gyratory compactor. The low-temperature properties of the binders were characterised using dynamic shear rheometer and bending beam rheometer, and the low-temperature cracking of the mixtures evaluated by tensile stress restrained specimen test. The results indicated that low-temperature parameters were greatly dependent on the base bitumen, and in most cases, polymer modification did not show significant benefits as compared to the corresponding base bitumen. The mixture cracking temperature was found to correlate with the limiting temperatures (in bending beam rheometer) of the binders, weakly with Fraass breaking point, but not with parameters obtained using dynamic shear rheometer. Upon isothermal storage at low temperatures, the bitumens displayed physical hardening, and effect of polymer modification was small. However, physical hardening as measured by TSRST (tensile stress restrained specimen test) was not observed for the mixtures studied.RésuméLes effets de l’ajout de polymères sur les propriétés à basses températures ont été étudiés sur des liants bitumineux tel quel ou en enrobés. Trois bitumes ont été mélangés avec 6% SBS, SEBS, EVA ou EBA. Les enrobés denses ont été préparés avec une presse à cisaillement giratoire. Les propriétés à basses températures ont été caractérisées sur les liants à l’aide d’un rhéomètre dynamique à cisaillement et de l’essai de flexion sur barreau (BBR) et sur les enrobés à l’aide d’un essai de retrait empêché (TSRST). Les résultats indiquent que les propriétés à basses températures dépendent essentiellement du bitume de base et que, dans la plupart des cas, l’ajout de polymère n’améliore pas de façon significative ses propriétés. La température de fissuration des enrobés a pu être corrélée avec les températures limites BBR du liant, faiblement avec le point de fragilité Fraass mais pas avec les paramètres obtenus en utilisant le rhéomètre dynamique à cisaillement. Lors d’un stockage à une température basse donnée, les bitumes présentent un durchissement physique qui est peu influencé par les polymères. Néanmoins, ce durcissement physique n’a pas été observé sur les enrobés lors des essais de TSRST.

Rheological Properties of SEBS, EVA and EBA Polymer Modified Bitumens

The rheological properties of various polymer modified bitumens were studied. Three bitumens from two different sources were mixed with styrene-ethylenbutylene-styrene (SEBS), ethylene vinyl acetate (EVA) and ethylene butyl acrylate (EBA) copolymers at different polymer contents. The rheological properties of the modified binders were investigated by means of dynamic mechanical analysis and creep test (bending beam rheometer). The results indicated that polymer modification increased binder elastic responses and dynamic moduli at intermediate and high temperatures, and reduced binder complex and stiffness moduli at low temperatures. Polymer modification also reduced temperature susceptibility, glass transition temperature as well as limiting stiffness temperature. The degree of the improvement generally increased with polymer content, but varied with bitumen source/grade and polymer type.RésuméLes propriété rhéologiques de divers bitumes modifiés ont été étudiées. Trois bitumes de deux origines différentes ont été mélangés avec les copolymères styrène-éthylènebutylène-styrène (SEBS), éthylène-vinyl-acétate (EVA) et éthylène-butyl-acrylate (EBA), en utilisant différents pourcentages de polymère. Les propriétés rhéologiques des différents liants modifiés ont été examinées au moyen d’essais dynamiques et d’essais de fluage (bending beam rheometer). Les résultats montrent que l’ajout de polymère augmente la réponse élastique du liant et le module dynamique aux températures moyennes et hautes, et diminue le module complexe et le module de rigidité à basse température. L’ajout de polymère diminue la susceptibilité thermique, la température de transition vitreuse et la température de «rigidité limite». Le degré d’amélioration augmente généralement avec le pourcentage de polymère, mais il varie avec l’origine et la nature du bitume, et le type de polymère.

LOW-TEMPERATURE PROPERTIES OF STYRENE-BUTADIENE-STYRENE POLYMER MODIFIED BITUMENS

Abstract Low-temperature properties of the modified bitumens containing styrene–butadiene–styrene (SBS) polymers were investigated using conventional methods, dynamic mechanical analysis (DMA) and bending beam rheometer (BBR). Effects of the characteristics of base bitumens and polymers and the proportion of the components on these properties were studied. The results indicated that SBS polymers improved low-temperature properties of bitumens. The degree of improvement generally increased with SBS content and were influenced slightly by SBS structure. The study also showed a statistically linear relationships between different low-temperature parameters.

Time-domain reflectometry measurements and soil-water characteristic curves of coarse granular materials used in road pavements

Coarse granular materials are used extensively in road construction. Bearing capacity can be affected by the water content in the layers of these materials. The ability to estimate water content an ...

Influence of water and mica content on resilient properties of coarse granular materials

Elevated amounts of free mica particles in unbound granular materials used in road construction are believed to detrimentally influence bearing capacity. The objective of presented work was to investigate the influence of mica content on resilient properties of coarse granular material (maximum particle size 63 mm) under varying water contents. The test scheme comprised triaxial tests, using constant confining pressures, at incrementally raised water contents up to practically full saturation. Increased mica content was achieved by replacing a part of the base material grading smaller than 4 mm, with an equal amount of pure muscovite mica of similar grading, hence keeping the overall particle size distribution unchanged. Generally, resilient modulus decreased with increased mica content and elevated water contents caused reduction in stiffness. In relative terms, the reduction in resilient modulus caused by water decreased with increased mica content.

Influence of Hysteretic Heating on Asphalt Fatigue Characterization

This paper presents a study focusing on the influence of hysteretic heating on asphalt samples during laboratory fatigue testing. The experimental test setup for material characterization and temperature measurements, including its effect on fatigue test results, as well as theoretical aspects on hysteretic heating, are described. The experimental part of the investigation concerns linear viscoelastic and cyclic fatigue characterization of six asphalt concrete mixtures using uniaxial testing. All the mixtures show nominally identical volumetric properties (aggregate size distribution, binder and air void content) but different binder properties. Three base bitumens and three polymer modified binders were used. The cyclic fatigue tests were carried out at 0, 10, and 20°C using controlled strain and stress modes and different excitation amplitudes. In order to acquire knowledge regarding temperature changes during fatigue testing, several experimental techniques were used. The main thermal study was performed using thermocouples attached to the midheight envelope surface of each sample. The sample surface temperature distribution and its evolution during fatigue testing were investigated using an infrared thermal camera. Furthermore, a limited study of the magnitude of difference between surface and maximum temperature inside the sample was carried out using thermocouples embedded during gyratory compaction. When compared, each method shows advantages and disadvantages regarding simplicity and reliability. In principle, the three methods provide similar results, but the type of information obtained differs among the methods. The use of thermocouples attached to the envelope surface during fatigue testing provides accurate and consistent results of global temperature that can be used to investigate the influence of heating on asphalt fatigue characteristics. By use of thermal measurements and a continuum damage model, it was possible to show a pronounced effect of heating on fatigue behavior. The influence of heating was especially obvious at high excitation amplitudes and elevated temperatures, i.e., conditions where the material produces high amounts of viscoelastic dissipated energy as well as temperature sensitive material behavior.

Fatigue Modeling as Related to Flexible Pavement Design

ABSTRACT A literature study of rheological and fatigue modeling of asphalt mixtures is presented. Theoretical aspects on structural modeling, rheological behavior and the fatigue integration in design procedures are reviewed. In principle, pavement design methods can be categorized in three broad groups: empirical, semi-mechanistic and fully mechanistic methods. Pavement design is generally performed using semi-mechanistic methods comprising analytical or numerical structural response models and deterioration modeling based on transfer functions and shift factors. In the case of fatigue deterioration, several approaches have been elaborated e.g. classical models, fracture mechanics and damage mechanics. The approaches differ regarding theoretical foundation and evaluation methods used. Recognizing significant limitations concerning theoretical basis as well as lack of empirical support for current design methods, a shift in paradigm from semi-empirical methods towards more advanced fully mechanistic methods have been initiated. According to this approach, improved pavements are achieved by appropriate design methods which are capable of predicting fatigue resistance in the actual pavement environment, and thus taking into account complex stress conditions, influence of temperature and material characteristics, such as aging and healing.

Influence of Mica Content on Time Domain Reflectometry and Soil Water Characteristic Curve of Coarse Granular Materials

Elevated fractions of free mica particles in unbound granular materials, used in road constructions, are believed to reduce bearing capacity and influence the hydraulic behavior of the road structure. The objective of this investigation was to study the influence of mica content on the soil water characteristic curve and the dielectric response measured by time domain reflectometry, for coarse granular (maximum particle size 63 mm) materials. Increased fraction of mica was achieved by partly replacing the base crushed rock material smaller than 4 mm, by pure muscovite mica of similar grading, thereby keeping the overall particle size distribution unchanged. Acquired results indicated that, given equal matric suction, the water retention capacity increased with increased amount of mica. Concerning the time domain reflectometry measurements, no influence of mica content could be detected. Determined water contents required adjustment because of the nonlinear distribution of water in the sample.

Causes of rutting in flexible and semi-rigid test sections after 14 years of service

Rutting is a major distress and is commonly targeted in design-build contracts as a key requirement, but at the same time, contemporary design methods usually provide scarce information on evolution in absolute terms. The objective of this paper is to investigate and analyse rutting results from a large full-scale road test. The analyses concerned magnitudes and the causes of rutting with a main focus on flexible and semi-rigid structures: one Reference, one high-performance asphalt (HPA) and one asphalt on a lean concrete (LC) base. Field measurements and sampling for the current study comprised acquiring transversal profiles and coring pavement samples. The results suggest that for the HPA and the LC base pavements, rutting is mainly caused by studded tyre wear and densification of the asphalt layers. For the conventional reference pavement additional rutting, most likely in the lower layers, was noted.