Rutting prediction of a granular material for base layers of low-traffic roads

[Abstract:] This paper analyses the permanent deformation performance of an unbound granular material for base layers of low-traffic roads. The material has been subjected to repeated triaxial loads. The shakedown theory was used to classify the structural response of the unbound granular material to the applications of load cycles. Three models were fitted to express the cumulative permanent strain as a function of the number of load cycles. In general, the predictions of two models previously studied by other researchers proved to be good but in the long-term, they tended to underestimate the measured values. In contrast, a third new model – the sum of two well known models – offered excellent predictions, which in the long-term did not tend to either underestimate or overestimate the measured values

Quality control of manufacturing and hot storage of crumb rubber modified binders

The ultimate performance of crumb rubber modified (CRM) binders is linked to the accurate control of the properties during manufacturing and hot storage. However, due to their complexity, asphalt technologists find the characterisation of these materials still challenging. In this study, the adoption of a Dual Helical Ribbon (DHR), a novel mixing/measuring device for rotational viscometers, is proposed for the real-time monitoring of CRM binders during manufacturing and hot storage. According to the laboratory results, manufacturing periods of 45-60 min at 195 degrees, as well as storage temperatures not exceeding 150 degrees C, are recommended for this type of modified binders. (C) 2019 Elsevier Ltd. All rights reserved

Study of the effect of four warm mix asphalt additives on bitumen modified with 15% crumb rubber

Due to a growing concern over global warming, the bituminous mixture industry is making a constant effort to diminish its emissions by reducing manufacturing and installation temperatures without compromising the mechanical properties of the bituminous mixtures. The use of mixtures with tyre rubber has demonstrated that these mixtures can be economical and ecological and that they improve the behaviour of the pavements. However, bituminous mixtures with a high rubber content present one major drawback: they require higher mixing and installation temperatures due to the elevated viscosity caused by the high rubber content and thus they produce larger amounts of greenhouse gas emissions than conventional bituminous mixtures. This article presents a study of the effect of four viscosity-reducing additives (Sasobit®, Asphaltan A®, Asphaltan B® and Licomont BS 100®) on a bitumen modified with 15% rubber. The results of this study indicate that these additives successfully reduce viscosity, increase the softening temperature and reduce penetration. However, they do not have a clear effect on the test for elastic recovery and ductility at 25 °C

Mechanical properties of hot mix asphalt made with recycled aggregates from reclaimed construction and demolition debris

[Resumen:] En este trabajo se dosificaron mezclas bituminosas fabricadas con áridos reciclados de residuos de construcción y demolición. Se realizaron una serie de ensayos que permitieron caracterizar el comportamiento mecánico de estas mezclas. Los parámetros mecánicos de las mezclas con áridos reciclados son similares a los de las mezclas fabricadas únicamente con áridos naturales de cantera. Sin embargo, las mezclas bituminosas con áridos reciclados tuvieron un mal comportamiento frente a la disminución de la resistencia por pérdida de cohesión por la acción del agua. No obstante, mediante la selección de materiales de mejor calidad y corrección de este mal comportamiento, existen posibilidades de utilizar áridos reciclados en mezclas bituminosas. Para ello será necesario ampliar la primera aproximación realizada en este artículo.[Abstract:] The mix design for asphalt mixtures containing recycled aggregates from construction and demolition debris was evaluated. The tests conducted to characterize the mechanical behaviour of these mixtures showed that the mechanical properties of mixtures with recycled and virgin aggregate are similar. The asphalt mixtures containing recycled aggregate proved to have lower resistance to water action. Nonetheless, recycled aggregate was found to be potentially usable in asphalt mixtures if higher quality materials are selected and such low resistance is corrected. This will call for expanding upon the preliminary work described in the present article

Development of new laboratory equipment for measuring the accelerated polishing of asphalt mixes

The skid resistance of pavements tends to decrease over time, resulting in greater risks for drivers. Currently, skid resistance and macrotexture values can only be determined for existing pavements. It would be of interest to be able to predict the evolution of the skid resistance of an asphalt mixture before its installation as a highway wearing course. This paper summarizes the experience gained and the results obtained during the development of a test procedure which has been applied in the laboratory to measure the evolution of the skid resistance of hot mix asphalts through a modified version of an accelerated polishing machine which is normally used to determine the polished stone value of aggregates

Estudio de los parámetros que influyen en el fallo estructural de mezclas asfálticas dosificadas con áridos reciclados

Este congreso tivo lugar do 19 ao 21 de setembro de 2007, en Valladolid[Resumen:] En este trabajo se determina la resistencia a la deformación plástica y a la fisuración de dos mezclas asfálticas bituminosas en caliente (MBC) fabricadas con áridos reciclados procedentes de residuos de construcción y demolición (RCD). Las mezclas fabricadas son las S-20 y G-20, denominadas semidensa y gruesa, respectivamente. De este estudio se deduce que las muestras dosificadas con áridos reciclados son más resistentes a las deformaciones plásticas, son más rígidas. Desde el punto de vista del comportamiento a fatiga, son las que presentan menor vida a fatiga para una amplitud de deformación dada. Finalmente, mediante un modelo multicapa elástico-lineal se determinó la variación de la vida útil de una sección de firme destinada a carreteras de bajo tráfico, cuando se incorporan capas que contienen áridos reciclados. Como resultado, se comprueba que el número de ciclos que la sección resiste es superior al número de ciclos previstos

Caracterización del comportamiento a fatiga de mezclas bituminosas en caliente fabricadas con áridos reciclados

[Resumen:] En este trabajo se estudia la resistencia a la fisuración por fatiga de mezclas bituminosas en caliente fabricadas con áridos procedentes de residuos de construcción y demolición (RCD). Las mezclas se dosificaron con un 50% de árido reciclado (AR) para ser utilizadas como capas de base o intermedia en carreteras de bajo tráfico. Los ensayos de fatiga se hicieron en flexión en tres puntos para generar tensiones de tracción que dan lugar a la formación de fisuras. Para cada una de las mezclas estudiadas se determinó las constantes de la ley de fatiga en deformación. También se obtuvieron otros parámetros de fatiga como el módulo dinámico y ángulo de desfase. Con estos datos y considerando un comportamiento del medio elástico lineal se obtuvo la vida del firme. Los resultados se compararon con los datos obtenidos para mezclas fabricadas únicamente con áridos de cantera (AC). Se ha constatado que a pesar de encontrar debilidades en las mezclas con áridos reciclados, los parámetros obtenidos en este caso, son similares a los que se obtienen con las mezclas que contienen áridos naturales.[Abstract:] This work evaluates the resistance to crack from fatigue of hot asphalt mixtures made with aggregates from construction and demolition debris. The mixtures were elaborated with a 50% of recycled aggregates in order to use them as road bases and binder courses in low traffic roads. The fatigue tests were carried out under flexural test to generate tensile stresses at the bottom of the bituminous surface layer, which are manifested as microcracks (crack initiation phase). Later microcracks propagate, densify and coalesce to form macrocracks. For each mixture studied the fatigue laws constants in deformation were obtained, as well as, the dynamic modulus. By means of this information and taking into consideration an elastic lineal behaviour the service lives were estimated. These results were compared to those obtained in hot asphalt mixtures elaborated with only virgin aggregates from quarries. Although they were found some shortcomings in the mixtures elaborated with a 50% of recycled aggregates, it was confirmed that the parameters are very similar to those obtained in the case of mixtures made with only virgin aggregates