Metodología para la caracterización de ligantes asfálticos mediante el empleo del ensayo cántabro

La caracterización de los ligantes bituminosos se ha venido realizando mediante una serie de ensayos físicos: penetración, punto de reblandecimiento, punto de fragilidad, ductilidad, etc., que tienen por objeto identificar el producto y comprobar que satisface las especificaciones fijadas. Sin embargo, esta caracterización es compleja e incompleta: hay que acudir a un gran número de ensayos que sólo evalúan parcialmente y de forma indirecta alguna de sus propiedades, y que en la mayoría de los casos no gozan de la sensibilidad necesaria para diferenciar a los distintos betunes asfálticos de modo satisfactorio; propiedades tan importantes como la cohesión, la susceptibilidad térmica o la adhesividad no quedan suficientemente caracterizadas. Si esta afirmación es válida para los betunes puros, lo es más para los modificados, que ya constituyen de por sí un nuevo material de propiedades notablemente distintas de los betunes originales.Se plantea, pues, el problema de seleccionar los métodos de ensayo que aseguren la bondad de un determinado ligante para una mezcla asfáltica y garanticen la durabilidad del betún en servicio. Ha sido precisamente la poca idoneidad de estos ensayos para la caracterización de ligantes asfálticos lo que ha llevado a desarrollar un nuevo procedimiento: el método Universal de Caracterización de Ligantes (método UCL), basado en la aplicación del ensayo cántabro de pérdida por desgaste, que de manera fiable y sencilla permite definir con amplitud y precisión las propiedades de los ligantes asfálticos, tanto de los obtenidos directamente de la destilación del petróleo y de la hulla, como de los modificados mediante la incorporación de aditivos.El ensayo cántabro de pérdida por desgaste se ha mostrado como un ensayo rápido, sencillo y suficientemente sensible, que permite evaluar las propiedades fundamentales de los ligantes: cohesión, susceptibilidad térmica, adhesividad y envejecimiento, así como las características del mástico fíller-betún.To date, characterization of asphalt binders has been based on physical tests: penetration, softening point, fragility, ductility, etc. The objective of such tests is to identify the product and make sure that it meets the established specifications.Nevertheless, such a characterization is complex and incomplete: many tests have to be performed to partially and indirectly evaluate some of the binders' properties; very few cases have enough sensitivity to satisfactorily differentiate asphalt binders: properties as important as cohesion, thermal sensitivity or adhesivity are not sufficiently characterized. This problem is magnified for modified binders.We therefore seek a new test method that ensures the suitability of a binder for an asphalt mix and guarantees the binder durability when it is in service.The lack of suitability of the existing tests for the characterization of asphalt binders encouraged the development of a new procedure: the Universal Method of Binders Characterization ("UCL" method), which is based on the application of the cántabro test of abrasion loss, which, in a reliable and simple way, allows us to define the properties of asphalt binders (those directly obtained from petroleum distillation and also those modified through additive incorporation) thoroughly and accurately.The cántabro test of abrasion loss has proven to be a quick and easy to perform test, holding enough sensitivity to assess the essential characteristics of binders: cohesion, thermal sensitivity, adhesivity and ageing, as well as the filler/bitumen mastic characteristics.Postprint (published version

Asphalt toughness effect on bituminous mixture fatigue behavior

One of the most important parameters to define bituminous mixture behavior in service is the toughness that the bitumen provides when binding the aggregate particles; that is; the dissipated energy during the materials fracture process. The greater the dissipated energy in fracture, the better the bituminous mixture quality is. Hence, a relationship will have to exist if the toughness is removed during one load cycle (direct tension) or during many cycles along time (fatigue). The purpose of this study is to determinate relationships between the toughness of different bitumens and the fatigue behavior of their corresponding bituminous mixtures, for which, the toughness has been obtained by means of direct tension test and has been compared with the value of the fatigue law and dissipated energy obtained by fatigue bending test. Results showed that, this study expect to give important means for further research to predict fatigue life from a static test.Peer ReviewedPostprint (published version

Ageing and temperature effect on the fatigue performance of bituminous mixtures

The ageing of asphalt mixes, together with their exposure to low temperatures, causes a progressive increase of cracking. In this paper, the effect of ageing and temperature on the fatigue of asphalt concretes made with two types of binders, conventional (50/70) and polymer modified bitumen (PMB), is studied. For this purpose, specimens previously subjected to an accelerated laboratory ageing process were tested by a strain sweep test at different temperatures (-5°C, 5°C and 20°C). Results were compared with the obtained from the unaged specimens showing the relative importance of ageing, temperature and type of bitumen on the parameters that determine the fatigue life of the mixture. The mixtures behaviour becomes more brittle with ageing and the decrease of temperature. However, ageing hardly has an effect on fatigue at lower temperatures. In general, mixtures made with polymer modified bitumen have a better fatigue performance to ageing and temperature.Peer ReviewedPostprint (published version

Labeling strategy for evaluating the performance of thin asphalt wearing courses

Traditional design procedures of asphalt mixtures are based on volumetric parameters and the compliance with the mechanical performance, while functional properties receive less attention. Additionally, even though the potential of sustainable technologies is proven, this is not sufficiently reflected in the technical specifications and their use is not widely spread. In order to face these challenges, the development of a useful tool that allows infrastructure managers an easy evaluation of the mechanical, functional, and environmental performance and the pursuit of balance between properties will encourage the optimization of road surfaces. The aim of this research is to develop a multi-labeling scheme for asphalt mixtures for thin wearing courses according to their mechanical, functional, and environmental attributes. In particular, the study focuses on the Spanish case, because all the collected data belong to the Spanish road network; however, the approached methodology is flexible enough to be adjusted to the requirements of individual countries. The findings in this research show promise because the developed labeling scheme allows not only the assignation of performance labels to any asphalt mixture based on its properties, but also the comparison of features between different asphalt mixtures.Peer ReviewedPostprint (published version

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

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

Effect of the use of Marpol waste as a partial replacement of the binder for the manufacture of more sustainable bituminous mixtures

This is an Accepted Manuscript of an article published by Taylor & Francis Group in International Journal of Pavement Engineering on 2022, available online at: http://www.tandfonline.com/10.1080/10298436.2022.2046275Society must move towards an economy in which sustainability is its main driving force. A sustainable solution to avoid sending waste to landfill, the consumption of raw materials and, therefore, the depletion of natural resources, is the reuse or recycling of waste. Here, pavement engineering has great potential, as waste can be used for the manufacture of bituminous mixes. In particular, one of these residues is Marpol, which is generated during shipping, maintenance and cleaning operations, including wastewater and waste other than cargo waste. There are few studies on the analysis of its use in mixtures. Thus, in this work, the effect of partially replacing the binder of bituminous mixtures for another obtained from the treatment of Marpol oily waste was studied in order to contribute to environmental sustainability and circular economy. For this, water sensitivity, deformation and cracking resistance were analysed of two asphalt mixtures whose binder was partially replaced by Marpol binder. Furthermore, the binder ageing resistance was studied. The results obtained from the laboratory, plant and test section mixture were very close to those obtained for the reference. These results have demonstrated the feasibility of partially replacing the conventional binder by one obtained from Marpol waste.This research was funded by the Centre for Industrial Technological Development (CDTI) of the Spanish Ministry of Economy and Competitiveness within the framework of the project “Nuevo ligante bituminoso para firmes de carreteras a partir de técnicas de recuperación de residuos oleosos derivados del Marpol” (IDI-20180889).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