In the experimental study reported in this paper a creep-recovery shear test method was used to evaluate the anti-rutting potential of different polymer-modified bituminous binders. The effects of several factors related to modification were investigated, such as polymer type (SBS, styrene–butadiene–styrene vs. ethylene–vinyl–acetate), composition (styrene content), structure (linear vs. radial SBS) and dosage (3–6 % by weight of the base bitumen). The effect of short-term aging was also considered by comparing binder response before and after treatment with the rolling thin-film oven test. Following previous work on the development of the test protocol, experimental results were analyzed by referring to shear modulus curves G(t) and to permanent compliance (J _P), obtained by dividing residual strain at the end of the unloading phase by the stress applied during creep loading. Results indicated the effectiveness of the proposed method in discriminating between the behavior of the different polymer-modified binders and in capturing the effects caused by the factors considered in the investigation. Reliable rankings of the binders were established and were explained by referring to the specific behavior of employed modifiers.

The experimental investigation described in this paper refers to the performance-related characterization of cold-recycled bituminous mixtures employed for the construction and maintenance of road pavements. One of the most critical issues that have to be examined for these mixtures is their short term behaviour under loading, since in the early phases after laying they are more similar to unbound granular materials than to traditional hot bituminous mixtures. In such a context, the authors carried out triaxial tests on a reference cold-recycled mixtures by employing the equipment generally recommended for subgrade soils and foundation materials. Slender laboratory compacted specimens, prepared by means of a gyratory shear compactor, were subjected to triaxial tests for the determination of resilient modulus and of shear strength parameters at three different temperatures (20, 40 and 60°C) and in three different curing conditions (short term, intermediate and full curing). The obtained results were analyzed according to models already available in literature and were discussed by taking into account the internal structure and composition of the mixture.

A three-parameter fractional model, composed by a springpot in series with a dapshpot, was employed to describe the rheological behaviour of a set of polymer-modified bituminous binders obtained by combining a single-base bitumen with different types of syrene-butadiene-styrene copolymers at different concentrations. Experimental strain-time curves gathered from creep-recovery shear tests carried out by means of a dynamic shear rheometer at various temperatures were found to be in good agreement with model predictions. The fractional approach leads to a synthetic yet exhaustive description of the viscoelastic behavior of all materials. Variation of model parameters, each of which with a precise physical meaning, appears to be coherent with different binder compositions and testing conditions, reflecting the variations in terms of polymer concentration and temperature.

Great efforts have been made in recent years by the scientific community and the asphalt industry in developing sustainable technologies for the production of asphalt mixtures for road paving applications, pursuing the use of ever higher quantities of recycled materials. In this regard, the challenge is to define the optimal formulation of the mixture which allows the various component materials to be synergistically combined without compromising the performance and durability of the asphalt pavement. In such a context, the experimental study described in this paper aimed to provide a contribution to research by investigating sustainable asphalt mixtures containing 50% reclaimed asphalt pavement (RAP) and polymeric compound composed of 100% recycled plastics. A wide set of mixtures was prepared in a laboratory by employing different dosages of polymeric compound added via the hybrid method at various binder contents. For comparison purposes, an additional set of reference asphalt mixtures containing standard polymer-modified binder (PmB) and virgin aggregate without RAP was prepared and tested. The experimentation focused on the main engineering properties of the asphalt mixtures, including their workability, volumetric properties, and mechanical characteristics. The experimental study involved a preliminary trial phase to establish an appropriate laboratory mixing procedure. The results obtained from the experimentation indicated that recycled waste plastics have good potential for use in asphalt mixtures with high contents of RAP, provided that the quantity of added plastics is adequately balanced.