Evaluating the role of aggregate gradation on cracking performance of asphalt concrete for thin overlays

Thin asphalt concrete overlays are a maintenance technique that mainly restore the functional properties of pavements. One of the main issues in thin overlays is reflective cracking that can cause early deterioration and reduce their service life. For this reason, the purpose of this investigation is to evaluate the effect of material selection on cracking performance of asphalt concrete mixtures for thin overlays. In particular, this paper evaluates the role of aggregate skeleton gradation. The study of the effect of aggregate gradation was divided into two stages: (1) fine fraction content and (2) maximum nominal aggregate size. Based on this, up to seven asphalt mixture gradations were designed and evaluated through the Fénix test at different test temperatures. The results showed a significant correlation between the fine fraction content, and maximum nominal aggregate size, and the cracking performance of the asphalt concrete mixtures. Mixtures manufactured with a low content of fine aggregates, as well as small nominal maximum size, experienced a further improvement of their toughness. These results reflected the importance of considering not only the effect of asphalt binder and environmental conditions but also aggregate gradation in the design of asphalt concrete mixtures in order to achieve a desirable cracking performance.Peer ReviewedPostprint (published version

Obtaining the fatigue laws of bituminous mixtures from a strain sweep test: effect of temperature and aging

Fatigue is associated with the deterioration caused by applying repeated loads, and is affected by temperature or aging. Generally, time sweep tests are used to simulate fatigue, in order to obtain the fatigue laws. However, this requires too much time, often preventing its use. A method to estimate the fatigue laws from a strain sweep test is presented. The test was performed on a semi-dense mixture with different types of binder (unconditioned or aged) tested at different temperatures. This test is able to estimate fatigue laws more quickly, allowing the effect of different factors on the mixtures' fatigue life to be studied.Peer ReviewedPostprint (author's final draft

Estimating the fatigue law of asphalt mixtures using a strain sweep test (EBADE test)

Fatigue characterization of asphalt mixtures is a very important issue. However, existing techniques to that end are expensive and time consuming. For that reason the asphalt technicians have been studying several different methods to reduce the testing time needed. Such is the case of the Visco-Elastic Continuum Damage models. In that regard, this paper presents the efforts carried out by the Road Research Laboratory at the UPC-BarcelonaTech to reduce that testing time, by implementing a strain sweep test and approximating the fatigue law of the material from the data obtained. The EBADE test was applied to four mixtures for which the conventional fatigue laws were obtained using time sweep tests. The data collected was used to fit a fatigue model based on two strain values that can be directly computed from the EBADE test, namely Failure strain and No Damage strain. A good correlation was found between the model proposed and the experimental data.Postprint (published version

Effect of the recycling process and binder type on bituminous mixtures with 100% reclaimed asphalt pavement

There is a great interest in increasing the amount of recycled material used in asphalt mixes because of the beneficial impact on the environment. This is leading to the development of different recycling procedures, from cold in-situ to hot in-plant recycling. The objective of the study presented in this paper is to evaluate cracking resistance of recycled mixes manufactured by three types of processes, i.e., cold with emulsion, hot with high penetration bitumens and hot with emulsion (half-warm mixture), using 100% of reclaimed asphalt pavement (RAP) at different temperatures. Differences in their workability and ease of use are also analysed by gyratory compaction.Peer ReviewedPostprint (author's final draft

New approach to characterize cracking resistance of asphalt binders

Asphalt binder characterization is a complex and difficult task due to its rheological behaviour. Indeed it has been traditionally realized by means of simple tests at an established temperature. An added challenge is that low temperatures, as well as binder aging, lead to significant changes in the viscoelastic behaviour of binders. This study aimed to characterize asphalt binders, not through the traditional procedures, but through the ductility and tenacity that they provide to a mixture, being these two properties directly related to the cracking response of the binder. To this end, a new approach for asphalt binder characterization was proposed based on the application of the Fénix test on a standard mixture with a defined aggregate gradation and composition, without fines or filler, manufactured with different types of binders and tested at different temperatures, as well as subjected to accelerated aging in laboratory. The obtained results showed the thermal susceptibility of binders, which evidence the need to characterize binder performance at different temperatures to obtain a reliable cracking response. In addition, binder aging results in a more brittle cracking fracture, being the aging effects more pronounced in high penetration binders.Peer ReviewedPostprint (author's final draft

Nuevos ensayos para la caracterización de ligantes y mezclas asfálticas

El ensayo y caracterización de mezclas y ligantes bituminosos siempre ha presentado cierta dificultad, principalmente debido a la complejidad de los productos ensayados. El comportamiento mecánico de una mezcla o de un ligante bituminoso se puede asimilar en unos casos al de un sólido elástico, en otros al de un cuerpo viscoso, y en otros al de un material plástico. No es extraño, por tanto, que cuando nos refiramos a las mezclas bituminosas las definamos como un material elasto-visco-plástico. Esto es debido a que la respuesta de las mezclas y de los ligantes bituminosos varía con la temperatura a que se realicen los ensayos y con la duración de la carga aplicada. A temperaturas bajas y tiempos muy cortos de aplicación de carga, las mezclas se comportan elásticamente. Por el contrario, a temperaturas altas y largos periodos de aplicación de cargas, la respuesta de las mezclas es visco-plástica

Evaluation of the effect of heat-adhesive emulsions for tack coats with shear test from the road research laboratory of Barcelona

The use of conventional emulsions for tack coats can cause problems as they frequently stick to the tires of construction vehicles. Consequently the bond between the asphalt layers is inadequate. The importance of tack coats in the performance of the pavement means that bituminous emulsions are constantly being improved. Recently, new types of emulsions have been developed from very low penetration bitumen that contains no flux. They are known as “heat-adhesive” emulsions and they are resistant to construction vehicles. The purpose of this study is to analyze the effect of different heat-adhesive emulsions and to verify their performance in service, in comparison with the response of a conventional emulsion. For this reason a new shear test –the LCB test- has been developed in the Road Research Laboratory of the Technical University of Catalonia. This test is carried out at different temperatures, both on laboratory specimens and on cores extracted from recently constructed pavements, where the same emulsions and dosages have been used. The application of the LCB test has shown that the performance of the different heat-adhesive emulsions mainly depends on the characteristics of the base bitumen and the kind of modifier used. At low temperatures, heat-adhesive emulsions reach, in general terms, lower shear resistances than conventional emulsions; however, at intermediate temperatures there are heatadhesives emulsions with both higher and lower strengths than those of the conventional emulsions.Peer Reviewe

Spanish experience with the application of gyratory compactor and indirect tensile test in design and control of cold recycled asphalt pavement

This paper summarizes the Spanish experience in the design and control of cold in-place recycling (CIR) of asphalt pavements. First, the results obtained in laboratory after the mixture design process are compared with the densities encountered in the field. Second, the application of the Superpave Gyratory Compactor (SGC) for specimen manufacture during the design stage is analyzed by varying the standard conditions of gyration angle and vertical pressure. Finally, a new design method based on the indirect tensile test is proposed.Peer Reviewe

Effect of filler nature and content on the bituminous mastic behaviour under cyclic loads

The role of the filler in asphalt mixtures is particularly important because of its influence on mastic behaviour. The filler improves the resistance properties of bitumen against the action of traffic loads and temperature. However, the filler can also adversely affect bitumen in mastics excessively brittle and stiff due to inappropriate design. For these reasons, it is interesting to investigate the effect of filler type and content on mastic composition. This paper presents results from a strain sweep test applied to bituminous mastics prepared with different filler types and contents at several temperatures. The obtained stiffness modulus and failure strain results provide information to assess the fatigue behaviour of the analysed mastics.Peer ReviewedPostprint (author's final draft

Complexity of the behaviour of asphalt materials in cyclic testing

This paper compares the results obtained in two types of cyclic tension-compression tests, a time sweep test, constant strain amplitude, and a strain sweep test, increasing strain amplitude every 5000 cycles, called EBADE (standing for the Spanish words for strain sweep test). This comparison has shown that the rapid loss of stiffness during the initial part of cyclic testing is recoverable in bituminous materials. It has been found that reversible phenomena dominate in asphalt binders, while in mixtures are as important as damage. A damage equation has been proposed to describe the evolution of the material distress during the phase II in time sweep tests. In addition, a new methodology to estimate the fatigue law of bituminous mixtures is proposed.Peer ReviewedPostprint (author's final draft