Utilización de técnicas petrográficas para evaluar los efectos inducidos del NaCl, condiciones climáticas extremas y el paso del tráfico en las superficies de las carreteras españolas

Abstract

ABSTRACT:The asphalt surface layer is the most exposed to weather and traffic conditions on roads, especially those subjected to winter maintenance. Therefore, a deep knowledge of the mechanisms which can damage this layer is necessary to improve its design, construction and long-term use. With this purpose, two types of asphalt mixtures used on roads from NW Spain were subjected to durability tests (freezing-thaw and thermal-stress) with a saturated NaCl solution. After the durability tests, a wheel tracking test was performed on the samples, and the resultant material was analyzed by optical polarized light and fluorescence microscopy. This analysis showed that the binder-aggregate low adhesion was the main responsible of the asphalt mixture damage. This damage was concentrated in the aggregates because the binder acted as an impermeable wall. Consequently, the NaCl solution penetrated and degraded the aggregates quickly and strongly. RESUMEN: Utilización de técnicas petrográficas para evaluar los efectos inducidos del NaCl, condiciones climáti-cas extremas y el paso del tráfico en las superficies de las carreteras españolas.Las capas de rodadura son las más expuestas al clima y al efecto del tráfico, especialmente en carreteras sometidas a mantenimiento invernal. Por este motivo, es importante conocer mejor los mecanismos de deterioro de dichas capas a la hora de mejorar su diseño, construcción y uso a largo plazo. Con este fin, dos tipos de mezclas asfálticas utilizadas en el NO de España fueron expuestas a ensayos de durabilidad (heladicidad y choque térmico) con una solución saturada de NaCl. Después, se realizó el ensayo de pista y el material deteriorado y deformado resultante fue analizado mediante microscopia óptica de luz polarizada y de fluorescencia. Dicho análisis mostró que el principal responsable de la degradación de la mezcla fue la baja adhesión árido-betún. Esta degradación se concentró en el árido debido a que el ligante actuó como una pared impermeable. En consecuencia, la solución de NaCl pudo penetrar y degradar rápida e intensamente el árido.

Long-term behavior of the micro-texture of aggregates used on roads subjected to extreme climate conditions and winter maintenance operations

“…This rock has a fine-very fine crystal size [27]. The schist aggregate has a porous and micro-cracked surface especially related to the laminated micro-structure of mica minerals (biotite and muscovite, Fig.…”

“…The effect of extreme climate conditions on the micro-texture of the aggregates in the laboratory were measured by durability tests: resistance to freezing and thawing (winter [32]) and thermal stress (summer [33]). In both tests, a solution of 23.3 wt % of NaCl was applied to rapidly analyze the presence of the NaCl spread as a deicer during winter maintenance operations and which remained on the roads in summer [27].…”

“…Therefore, in this paper, the long-term behavior of the micro-texture of two types of aggregates has been studied in a laboratory, taking into consideration the effect of traffic, some relevant environmental variables, and both factors together. Due to the humid oceanic and mountainous climate where the aggregates are used [1], deforestation, and global warming, which are causing more and more cold and heat waves in this area [27], the environmental conditions chosen were those related to extreme climate conditions. Additionally, these aggregates are located in roads that are subjected to winter maintenance operations, such as the airport runways of Santiago de Compostela or the highway which connects Santiago de Compostela with La Coruña in the Northwest region of Spain.…”