Bituminous mixtures with low percentage of natural aggregates and rubber modified bitumen with wax

Abstract

The three mixtures included in the Spanish specifications (asphalt concrete, porous asphalt and very thin asphalt concrete) were designed replacing more than 80% of the natural aggregates by black slag of electric arc furnace and recycled asphalt pavement. Besides, a rubber modified bitumen was used as binder, analyzing the performance of a fatty acid amide wax as additive to decrease its viscosity at mixing temperature, and avoid the higher manufacturing temperature of this type of bitumen. Three stages were carried out to design the mixtures: first, the viscosity analysis of the rubber modified bitumen when the wax is added. Second, the experimental design of the mixtures with the alternative aggregates at conventional temperature, using the rubber modified bitumen without wax. Finally, the study of the behaviour of the three mixes with the same dosage of the previous phase, but manufactured at reduced temperature, that is including the fatty acid amide wax to the binder.

The tests of the Spanish specifications have been performed to design the mixtures and compare their performance in both conditions (with and without wax): void characteristics, water sensitivity test, wheel tracking test, and Cantabro loss particle test in dry and wet conditions. The results have shown that it is feasible to design mixtures in which practically the whole mineral skeleton comes from black slag and recycled asphalt, manufacturing them with a rubber modified bitumen but at the same range of temperatures than conventional 50/70 penetration grade binder, and fulfilling the standards for any climatic zone and heavy traffic level.