The effect of Cryogenic Crumb Rubber in cold recycled mixes for road pavements

• Including Cryogenic Crumb Rubber in 100% Reclaimed Asphalt Pavement (RAP) cold mixes.
• The percentage of CCR substitution is a basic variable to be controlled during the mix-design.
• The presence of CCR affects and reduces the mixture tensile strength.
• The rubber does not modify the thermo-dependence of the mix or its curing in terms of ITSM.
• CCR can positively improve the crack initiation resistance, while it negatively affects the fracture toughness.

Over recent years, the necessity of reducing the environmental impact of building new infrastructures has increasingly directed research toward developing innovative manufacturing methods and materials that can satisfy these objectives. Cold recycling, widely used in renovating road pavements in Italy, is also moving in this direction, lowering the manufacturing temperatures of bituminous mixes and reducing or ultimately eliminating the use of virgin raw materials. Currently, a wide range of materials are used and, consequently, the number of variables to be considered in the mix-design process of cold recycled mixes for road bases is considerable. Furthermore, new products are continuously being introduced or developed for recycling purposes. The objective of this research project was to test the effects, both mechanically and environmentally, of crumb rubber included in 100% Reclaimed Asphalt Pavement cold mixes for road bases, bound with bitumen emulsion and cement. The crumb rubber is produced cryogenically with granulometric selection, which together with the bitumen, the cement and the fine fractions of the mix forms a resilient mastic capable of imparting significant fatigue resistance properties to the conglomerate.