G. D. Airey

Rheological properties of styrene butadiene styrene polymer modified road bitumens

Abstract The use of polymers for the modification of bitumen in road paving applications has been growing rapidly over the last decade as government authorities and paving contractors seek to improve road life in the face of increased traffic. Currently, the most commonly used polymer for bitumen modification is the elastomer styrene butadiene styrene (SBS) followed by other polymers such as styrene butadiene rubber, ethylene vinyl acetate and polyethylene. This paper describes the polymer modification of two penetration grade bitumens with SBS. Six polymer modified bitumens (PMBs) were produced by mixing the bitumens from two crude oil sources with a linear SBS copolymer at three polymer contents. The rheological characteristics of the SBS PMBs were analysed by means of conventional as well as 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, with the higher polymer concentrations in a high aromatic content bitumen producing a highly elastic network which increases the viscosity, complex modulus 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.

Rheological evaluation of ethylene vinyl acetate polymer modified bitumens

Abstract The morphological, thermal and fundamental rheological characteristics of ethylene vinyl acetate (EVA) copolymer modified bitumens are studied in this paper. Nine plastomeric EVA polymer modified bitumens (PMBs) have been produced by laboratory mixing bitumen from three sources with an EVA copolymer at three polymer contents. The morphology, thermal properties and rheological characteristics of the EVA PMBs have been analysed using fluorescent microscopy, differential scanning calorometry and dynamic mechanical analysis using a dynamic shear rheometer, respectively. The results of the investigation indicate that EVA polymer modification increases binder stiffness and elasticity at high service temperatures and low loading frequencies with the degree of modification being a function of bitumen source, bitumen–polymer compatibility and polymer concentration. Filler type modification is evident at low temperatures, temperatures above the melting temperature of the semi-crystalline EVA copolymer and for those modified binders that do not exhibit a dominant polymer network.

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.

STATE OF THE ART REPORT ON AGEING TEST METHODS FOR BITUMINOUS PAVEMENT MATERIALS

The findings of an extensive literature review on bitumen and asphalt mixture ageing test methods are presented in the paper. The primary factors affecting the durability of bituminous paving mixtures, assuming they are constructed correctly, are age hardening and moisture damage. Ageing of the bituminous binder is manifested as an increase in its stiffness (or viscosity). Water damage is generally manifested as a loss of cohesion in the mixture and/or loss of adhesion between the bitumen and aggregate interface (stripping). Short-term ageing is primarily due to volatilisation of the bitumen within the asphalt mixture during mixing and construction, while long-term ageing is due to oxidation and some steric hardening in the field. Of the tests used to simulate short-term ageing, the extended heating procedures of the thin film oven test (TFOT) and the rolling thin film oven test (RTFOT) are the most frequently used binder methods. In regard to long-term binder ageing, the oxidative pressure ageing vessel (PAV) test and the rotating cylinder ageing test (RCAT) have shown the greatest potential. Asphalt mixture ageing is primarily limited to extended heating methods for loose bituminous material prior to compaction and combinations of extended oven ageing, high and low pressure oxidation and ultraviolet and infrared light treatments.

Absorption of Bitumen into Crumb Rubber Using the Basket Drainage Method

This paper describes an evaluation of the absorption of different sources and grades of bitumen into particles of crumb rubber using a basket drainage method. The effect of the rubber–bitumen interaction has been investigated in terms of the absorption of the light fractions of the bitumen into the rubber and the chemical composition and rheological properties of the residual binder. Eight bitumens from two crude oil sources and four penetration grades ranging from 200 to 35 pen have been mixed with 2–8 mm sized granulated crumb rubber at three rubber to binder ratios of 1:4, 1:6 and 1:8 by mass. The increased mass of the crumb rubber was used to determine the loss of volatiles and light fractions absorbed from the different bitumens. The residual binders were then subjected to asphaltene content tests, high temperature viscosity and dynamic mechanical analysis using a dynamic shear rheometer to determine the chemical composition and rheological properties of the binders following their interaction with crumb rubber. The results show that the rate of adsorption is directly related to the penetration grade (viscosity) of the binders as well as to the chemical composition of the bitumen (crude source) but that the total amount of absorption is controlled by the nature of the crumb rubber. In terms of the rheological properties of the residual bitumen, all the binders showed an increase in viscosity, stiffness (complex modulus) as well as elastic response with these changes being consistent for both crude sources and all four penetration grades.

Use of Black Diagrams to Identify Inconsistencies in Rheological Data

ABSTRACT This paper describes the use of Black diagrams of complex modulus versus phase angle to detect the occurrence of inconsistencies in rheological data caused by testing irregularities and distinctive material properties. In general, conventional penetration grade bitumens can be classified as “thermo-rheologically simple” materials with their rheological properties being temperature and time equivalent provided that they are determined within the binders linear viscoelastic region and by suitable testing procedures. In the paper, Black diagrams have been successfully used to identify compliance (testing) errors in rheological data associated with the inappropriate use of various dynamic shear rheometer spindle geometries. The results indicate that using a 25 mm diameter testing geometry at complex modulus values greater than 105 Pa leads to an overestimation of elastic response and an underestimation of binder stiffness. As Black diagrams do not require any manipulation of rheological data prior to data presentation, they provide a convenient means of assessing the effect of polymer modification and oxidative ageing on the rheological properties of bituminous binders. In general, semi-crystalline EVA PMBs tend to show unique rheological characteristics at intermediate temperatures due to the occurrence of different crystalline structures at different temperatures. Elastomeric SBS PMBs tend to produce a distinctive elastic response at high temperatures/low frequencies as a result of their dominant polymer network. Finally, Black diagrams have been used to identify discrepancies in rheological data due to non-linear effects before attempts are made to shift the data to produce smooth, continuous master curves.

VISCOELASTIC LINEARITY LIMITS FOR BITUMINOUS MATERIALS

As bituminous materials are viscoelastic in nature, their performance must be characterised using test methods and analytical techniques that account for time (or rate) of loading and temperature. In addition, it is usually advisable to confine the characterisation of a bitumen to its linear viscoelastic response (small strains) to simplify the mathematical modelling of the material, as non-linear response, particularly for viscoelastic materials, is extremely difficult to characterise in the laboratory and model in practical engineering problems. This paper describes an investigation of the linearity limits of a range of unmodified and modified bituminous binders and mixtures using a dynamic shear rheometer and a purpose-built dynamic, direct tension-compression, servo-hydraulic testing apparatus. The results show that there are strain dependent linearity criteria for both binders and asphalt mixtures at high stiffness values (low temperatures for binders and low to intermediate temperatures for mixtures) as well as a high temperature strain dependent linearity criterion for elastomeric modified binders. The linearity strain criterion for the mixtures was found to be in the order of 100 microstrain with the criterion for the binders being at least 100 times greater at just over 10,000 microstrain and the polymer network strain criterion at 1,000,000 microstrain.RésuméÉtant donné que les matériaux bitumineux sont naturellement viscoélastiques, la caractérisation de leur tenue en service doit faire appel à des méthodes expérimentales et des techniques analytiques qui tiennent compte du temps (ou de la vitesse) de chargement et de la température. En outre, il est généralement recommandé de se baser sur la réponse viscoélastique linéaire (petites déformations) dans la caractérisation du bitume. Ceci permet de simplifier la modélisation mathématique du comportement matériel, vu que la réponse non linéaire des matériauxviscoélastiques est difficile à caractériser expérimentalement et à modéliser dans le cas des problèmes pratiques de l’ingénieur. Cet article décrit une étude des limites de linéarité concernant une gamme de liants et mélanges bitumineux non modifiés et modifiés, à l’aide d’un rhéomètre de cisaillement dynamique et d’une machine à commande hydraulique, conçue en vue d’effectuer des essais dynamiques de tension-compression directe. Les résultats montrent que des critères de linéarité dépendant de la déformation existent aussi bien pour les liants que pour les mélanges bitumineux, pour des valeurs élevées de la rigidité, à de basses températures pour les liants et à des températures basses ou intermédiaires pour les mélanges. Dans le cas des liants élastomères modifiés, un critère de linéarité dépendant de la déformation à haute température est également mis en évidence. Le critère de linéarité dépendant de la déformation pour les mélanges s’est avéré de l’ordre de 100 micro-déformation. Le critère correspondant aux liants étant au moins 100 fois supérieur et dépasse les 10000 micro-déformation et celui du réseau de polymère se situe à 1000000 micro-déformation.

A Dissipated Energy Approach to Fatigue Evaluation

ABSTRACT The fatigue behaviour of bituminous binders and/or bitumen-filler mastics has been postulated as having a strong correlation with the fatigue behaviour of asphalt mixtures. The binder is one of the major factors controlling fatigue of the asphalt mixture and is considered as the leading media of energy dissipation. It is verified in this paper that the application of the Ratio of Dissipated Energy Change (RDEC) approach in terms of the fatigue characteristics of bituminous binders and mastics produces a unique energy parameter, known as the Plateau Value (PV), similar to the PV previously identified for asphalt mixtures. The relationship between PV and fatigue life (Nf) is found to be unique for asphalt mixtures and binders (mastics). This suggests the RDEC approach is a fundamental approach for fatigue analysis of HMA. Furthermore, the two PV-Nf curves for asphalt mixtures and binders are strongly related, which provides a new way to explain mixture fatigue behaviour from a binders rheological characteristics.

Aggregate Orientation and Segregation in Laboratory-Compacted Asphalt Samples

Different laboratory compaction methods can produce volumetrically identical asphalt mixture specimens but with widely varying mechanical properties. Provided that the mixture design is constant, variations in mechanical properties are probably due to differences in the structure of the aggregate-bitumen matrix. The objective of this study is to investigate the structure of the internal aggregate-bitumen matrix created by different laboratory compaction methods and compare it with mechanical performance. Three types of laboratory compaction are considered: gyratory, vibratory, and slab. Image analysis techniques have been used to provide quantitative information on the orientation and distribution of aggregates on horizontal planes within asphalt mixture specimens, and the results indicate that circumferential alignment of aggregate particles occurs in gyratory and vibratory compacted specimens. This behavior is more pronounced for larger aggregate particles and in those with an aspect ratio (maximum length/maximum width) greater than two. Slab-compacted specimens display a more random particle orientation. The distribution and segregation of aggregates has been considered relative to the center of each horizontal asphalt-specimen cross section. While overall levels of aggregate particle density are similar across all compaction methods considered, greater segregation occurs in vibratory-and gyratory-compacted specimens. Repeated load axial testing was done on specimens compacted by each method. The results indicate higher resistance to deformation in the vibratory- and gyratory-compacted samples than in volumetrically identical slab-compacted samples.

Fundamental Binder and Practical Mixture Evaluation of Polymer Modified Bituminous Materials

Conventional bituminous materials have tended to perform satisfactorily in most highway pavement and airfield runway applications. However, in recent years, increased traffic levels, larger and heavier loads, new axle designs and increased tyre pressures have added to the already severe demands of load and environment on the pavement system. This has facilitated the need to enhance the properties of existing asphalt material with bitumen modification, particular polymer modification, offering one solution to overcome the limitations of bitumen and, thereby, improve the performance of these asphalt mixtures. This paper evaluates the relative performance of a series of ethylene vinyl acetate (EVA) and styrene butadiene styrene (SBS) polymer modified bitumens (PMBs) in terms of the two main distress modes associated with flexible asphalt pavements of permanent deformation and fatigue damage. The study makes use of fundamental rheological binder testing using a dynamic shear rheometer (DSR), pavement performance prediction by means of the Superpave binder parameters and the zero shear viscosity (ZSV) concept, and practical, mechanical asphalt mixture testing using the Nottingham Asphalt Tester (NAT). These binder and asphalt mixture procedures have been used to quantify the fatigue and permanent deformation performance of a series of polymer modified bituminous materials. The relative permanent deformation and fatigue cracking performance of the various PMBs and control penetration grade binders have then been ranked as a function of their binder rheological properties and actual asphalt mixture performance. The fundamental rheological data together with the permanent deformation and fatigue testing in the NAT all indicate an improved rutting and fatigue performance for the EVA and SBS PMBs compared to the unmodified penetration grade bitumens. However, based on the Superpave binder parameters and the ZSV, determined by means of the low frequency oscillation method, no unique correlation was found between actual mixture performance and predicted binder performance.