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This paper analyses the effect of water on the durability of hot asphalt mixtures made with recycled aggregates from construction and demolition debris. Indirect tensile stress tests were carried out to evaluate stripping behaviour. The mixtures tested were fabricated with 0, 20, 40 and 60% recycled aggregates. Two types of natural aggregates were used: schist and calcite dolomite. An increase in the percentage of recycled aggregates was found to produce a decrease in the tensile stress ratio of the hot asphalt mixtures. To study this phenomenon, two and three factor analyses of variance (ANOVA) were performed with indirect tensile stress being used as the dependent variable. The factors studied were the percentage of recycled aggregates (0, 20, 40 and 60%), the moisture state (dry, wet) and the type of natural aggregate (schist, calcite). On the basis of the ANOVA results, it was found that the most important factor affecting resistance was the moisture state (dry, wet) of the specimens. The percentage of recycled aggregate also affected indirect tensile stress, especially in the dry state. The type of natural aggregate did not have a significant effect on indirect tensile stress. The hot asphalt mixture specimens made with different percentages of recycled aggregates from construction and demolition debris and of natural quarry aggregates showed poor stripping behaviour. This stripping behaviour can be related to both the poor adhesion of the recycled aggregates and the high absorption of the mortar of cement adhered to them.

This paper reports on research into the technical viability of the use of construction and demolition debris in hot mix asphalt. A semi-dense and a coarse asphalt mixture were studied, both containing 50% recycled aggregate from construction and demolition debris. Two control mixtures were also studied, similar in grading but not containing recycled aggregates.It was proven that the mixtures containing recycled aggregates were more open graded and had considerable potential for stripping, a characteristic that can be related to the high water absorption level of the mortar adhered to the recycled aggregates. It was also proven that the dynamic modulus is higher in the mixtures made with recycled aggregates, particularly in the semi-dense asphalts. Whereas a deterioration of the fatigue law was observed in the semi-dense mixtures, this property did not appear to worsen in the coarse mixtures. This meant it was possible to design structural sections for flexible pavements bearing medium or low volumes of traffic with a service life comparable to that of conventional materials.Nevertheless, further research is required as, for the time being, the lack of resistance to water action casts doubt on the use of asphalt mixtures incorporating these types of recycled aggregate.

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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® 1 , Asphaltan A® 1 , Asphaltan B® and Licomont BS 100 s ) 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.

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This study examines the potential of adding electric arc furnace slag to bituminous mixtures to be heated by microwaves. The susceptibility of bituminous mixtures to microwave energy is limited and so, in order to improve the energy performance of the heating process, it is necessary to incorporate additives or components to the mixture so as to improve the capacity for microwave heating. The article presents the results of adding various components, (steel wool, scrap tire wire, silicon carbide, iron filings) and an alternative aggregate: electric arc furnace slag. According to the results obtained in the laboratory, slag addition of at least 5% by weight of the bituminous mixture represents the best option for both technical and economic reasons. The results may promote the valorization of this steel industry residue in bituminous mixtures by improving microwave heating response. RESUMEN:Utilización de aditivos para mejorar la sensibilidad de las mezclas bituminosas al calentamiento con microondas. El presente trabajo examina el potencial de añadir escorias siderúrgicas de horno de arco eléc-trico en mezclas bituminosas cuando se calientan con energía de microondas. La susceptibilidad de las mezclas bituminosas a las microondas es limitada y con el objetivo de incrementarla es necesario incorporar aditivos o componentes que sí son susceptibles. El artículo presenta los resultados obtenidos con varios aditivos (lana de acero, alambre metálico reciclado de neumáticos fuera de uso, carburo de silíceo y limaduras de hierro) y un árido alternativo: escorias de horno de arco eléctrico. De acuerdo con los resultados obtenidos en el estudio, la incorporación de escorias en al menos un 5% en masa de la mezcla bituminosa representa la mejor opción por motivos técnicos y económicos. Este resultado puede potenciar la valorización de este residuo de la industria del acero en mezclas bituminosas para mejorar su respuesta al calentamiento con energía microondas.