In recent times, recycling using cold bituminous mixtures has become one of the most interesting techniques in pavement engineering from sustainability aspect. This study focuses on the clarification of the steps concerned with the cold mixture mix design to determine the initial aggregate gradation of the mixture. The study has been developed involving procedures followed in Canada and Italy. In both the cases, three different gradations, normally employed in the production of traditional bituminous mixtures, were compared. The effect conferred by the gradation type has been studied in terms of workability, compactability and mechanical properties. Results show that in both the procedures the gradation influenced the workability and the compaction behaviour of the mixtures studied. At the same time, in terms of mechanical properties, the gradation influenced the strength of the final mixture in only one of the procedures applied.

Cold Recycled Mixtures (CRM) are composed of high amounts of Reclaimed Asphalt Pavement (RAP) together with bitumen emulsion. As additional binder, some ordinary cement is normally employed. Since RAP aggregates represents almost the entire solid structure, it is important to fully characterise Cement-Bitumen Treated Materials (CBTM) produced with different RAP materials. This work focuses the characterisation at small strain level, investigating the stiffness modulus at three testing temperatures; at the failure point, measuring the Indirect Tensile Strength; and studying the fracture behaviour, in Semi-Circular Bending Test configuration. From the results, it is possible to confirm the influence of different RAP materials, also characterised by different aggregates Nominal Maximum Size. As a consequence, a reliable RAP classification can allow a better prediction of the final CBTM mechanical properties.

Cold recycled materials (CRMs) are products of modern recycling techniques that are used in maintenance and rehabilitation of pavement structures with significant economical and environmental benefits. CRM mixes are produced at ambient temperature using bitumen emulsion or foamed bitumen as a binding agent, and the aggregate phase is composed mainly of reclaimed asphalt pavement (RAP). This paper investigated the compactability of two RAP sources and their effects on the behavior of CRM mixtures tested in the small strain domain. The compactability was studied using experimental results and the compressible packing model (CPM). Complex modulus tests of CRM mixtures were conducted, and the results were modeled using the Di Benedetto–Neifar (DBN) model. Findings showed that in CRM mixtures with the same gradation and formulation, one RAP source required almost half of the compaction energy of the other source to reach the design air voids content. The rheological analysis results highlighted the impact of the RAP source on the behavior of the CRM mixes in the small strain domain.

In the last decades, recycling of hot mix asphalt (HMA) materials became one of the major issue concerning the world of pavement engineering. As required by Italian technical specifications, pavements surface layers must be produced using high-quality aggregates, in order to meet performance in terms of mechanical and anti-skid properties. Inevitably, the extraction of virgin mineral aggregates and their decreasing availability encourage the use of recycled alternatives, such as electric arc furnace steel slag and municipal solid waste. This study evaluates the possibility to implement recycled aggregates, and others sustainable solutions, in the production of HMA surface layers. In particular, eleven mixtures were produced combining the use of recycled aggregates to polymers obtained from plastic waste recycling and basalt fibres obtained from mineral deposit productions. Laboratory and field results confirmed the validity of the ecological solutions proposed in terms of fundamental properties for surface layers, such as fatigue resistance, rutting and skid resistance.