Gonzalo Valdés

Fenix test: development of a new test procedure for evaluating cracking resistance in bituminous mixtures

This paper presents a new direct tensile test to evaluate cracking resistance of asphalt concrete mixtures: the Fénix test. First, the literature on cracking factors and mechanisms of bituminous mixtures, as well as current tests to measure cracking properties, is reviewed. Next, the Fénix test is described, and some initial experimental results of the influence of variables, such as binder type and content and test temperature, are provided. Additionally, test repeatability and sensitivity are statistically analyzed. Correlations between parameters obtained by the Fénix test and the three-point bending beam fatigue test are also shown. Finally, the main conclusions of this work are summarized. These conclusions confirm that the Fénix test is a practical and efficient method for characterizing cracking behavior of asphalt concrete mixtures as far as the studied variables are concerned.

Effect of Thermal Stresses on Fatigue Behavior in Bituminous Mixes

Fatigue cracking in asphalt mixtures—a common, widely studied mode of distress in flexible pavements—necessitates major investments in pavement maintenance and rehabilitation. To date, research has focused on the response of bituminous mixes subjected to cyclic loading until failure. Moreover, low-temperature thermal stresses in bituminous mixes have been investigated in isolation to determine the effect of thermal gradients on materials. However, decreased temperature leads to a combined effect of fatigue distress and thermal stress. To provide insight into this phenomenon, an experimental study based on a new test procedure developed by the Road Research Laboratory of the Technical University of Catalonia, Spain, is presented. This method allows the simultaneous evaluation of the effect of thermal stresses and the fatigue response of asphalt mixtures.

Assessment of cracking resistance of bituminous mixtures by means of Fenix test

This paper shows the application of a new direct tensile test developed at the Road Research Laboratory of the Department of Transport and Regional Planning of the Technical University of Catalonia. The test is called Fenix test and is aimed at the assessment of cracking resistance of different types of bituminous mixtures at different temperatures. Fenix test calculates the dissipated energy during the cracking process of the material and the softening phase in the load-displacement curve of the test. The test procedure consists of subjecting one half of a 63.5 mm thick cylindrical specimen of a 101.6 mm diameter prepared by Marshall or gyratory compaction to a tensile stress at a constant displacement velocity (1 mm/min) and specific temperature. A 6 mm-deep notch is made in the middle of its flat side where two steel plates are fixed. The specimen is glued to the steel plates with a thixotropic adhesive mortar containing epoxy resins. Both plates are attached to a loading platen so that they can rotate about fixing points. Different types of mixtures with different stiffness moduli, including very flexible mixtures like gap-graded and SMA mixes, as well as stiffer mixtures like high modulus mixtures, were tested. The results were compared with those obtained for the same mixtures from standard fatigue bending beam tests.

Propiedades Físicas y Mecánicas de Bloques de Hormigón Compuestos con Áridos Reciclados

The main objective of this paper is to show a technique for the construction of prefabricated concrete bricks utilizing recycled aggregates coming from demolitions of pavements and to check the degree of fulfillment of the current rules that are applied to the manufacture of these building elements. The physical and grain-size characteristics of the aggregates constituent of the mixture were analyzed, and the cement and aggregates were dozed according to the Faury-Joisel method. The analyzed aggregates showed differences in densities being lower the ones made of recycled material, but always within the established limits of the current norms. The compression tests were carried out on the concrete bricks manufactured with recycled material showed resistances of 15 % lower than those manufactured with natural aggregates. However, both elements fulfilled with the parameters established by the current norm for the mechanical resistance, the maximum water absorption and the humidity content.

Nuevo procedimiento para evaluar el comportamiento a fatiga en pavimentos asfálticos a través del ensayo Fénix

This article presents an experimental study and its application in a methodology to evaluate the fatigue behavior of asphalt mixtures in pavement structures. This methodology and its application are based on the correlations obtained between stiffness and deformation parameters of a simple new fracture test, named Fenix test, and those obtained by the fatigue laws determined by the three point bending beam fatigue test, which complies with the European standard UNE-EN 12697-24. Four different Spanish asphalt mixture gradations were used, named G-20, S-20, S-20R60 and S-12R40, respectively. Two were also based on standard gradations but had a different percentage of Recycled Asphalt Pavement, RAP (S-20R60 and S-12R40 with 60% and 40% of RAP, respectively). Two mixtures, G-20 and S-20, were manufactured with penetration binders B60/70 and B13/22. Test temperatures were 5 °C and 20 °C. The binders of S-20R60 and S-12R40 mixtures had penetrations of 250 and 200 dmm, respectively. Mixtures test temperature was 20 °C. The main conclusion obtained from this research was that the proposed methodology allows evaluating the fatigue life of a pavement structure through a simple procedure. At the same time, this study attempts to solve the problems presented by the fatigue testing of asphalt mixtures due to their complexity and the time required

Influencia de la Tipología del Ligante en las Propiedades Mecánicas de una Mezcla Asfáltica Densa

Resumen En el presente articulo se presentan los resultados del estudio destinado a analizar la influencia del tipo de ligante en las propiedades mecanicas de una mezcla asfaltica densa. Los ligantes asfalticos utilizados en el estudio fueron dos ligantes de penetracion, CA 60/80 y CA 80/100, y estireno-butadieno-estireno (SBS), un ligante modificado con polimeros. Las propiedades mecanicas analizadas para cada ligante evaluado en la mezcla fueron: cohesion, modulo resiliente, resistencia a la traccion indirecta y deformaciones plasticas. Los resultados permiten concluir la importancia de la utilizacion del ligante modificado en este tipo de mezclas, puesto que presentan un mejor comportamiento frente a las propiedades mecanicas evaluadas. Se establece tambien que la energia de compactacion y la temperatura de ensayo tienen una mayor influencia en las propiedades mecanicas de las mezclas fabricadas con ligantes de penetracion respecto a las fabricadas con el ligante modificado. Palabras clave: mezcla asfaltica, modulo resiliente, deformaciones platicas, propiedades mecanicas