The bond strength between asphalt and aggregate plays a fundamental role in evaluating the moisture sensitivity of HMA Mixtures. In this study the effect of water on adhesive and cohesive properties of asphalt-aggregate systems was investigated using a modified version of the PATTI. The device was used to measure the pull-off strength on different asphalt-aggregate combinations and to evaluate the influence of water immersion at two different temperatures. In particular, six asphalt binders were employed in combination with two aggregate types, having different asphalt affinity. The effect of the aggregate surface temperature during specimen preparation was also tested. In the first phase of the study the within-laboratory repeatability of the test procedure was investigated. The results showed the PATTI test is able to evaluate with good precision the pull-off strength and that its repeatability depends on the failure type (adhesive or cohesive). In the second phase of the study a full factorial experiment was employed to verify the reliability of the test for routine use in determining the adhesive and cohesive properties of asphalt-aggregate combinations and the effects of moisture damage. The results showed that, in the dry condition, the test was able to measure the internal cohesion of the asphalt binders. The results also showed the effects of water damage on the pull-off strength and the decisive role of asphalt-aggregate affinity was clearly highlighted. Using wet conditioning of the PATTI samples it was proven that water affects the adhesive bond between asphalt and aggregate much more than the asphalt cohesion. Moreover, the results indicate that aggregate temperature during sample preparation has only a limited effect on the adhesive strength.

Nowadays, the growing energy costs and pressing worldwide demand for petroleum-based products create a strong need to develop alternative binders deriving from green and renewable sources. Bio-binders (or bitumen added to bio-based materials) can potentially be a viable alternative for the production of bituminous mixture, promoting the circular economy as well as environmental sustainability principles without reducing the overall performance of the mixture. In this context, the current study focuses on evaluation of the effects of a bio-binder on the mechanical response of asphalt concrete (AC) produced with it. In particular, a 10% bio-oil deriving from a by-product of the paper industry has been blended with a conventional 50/70 penetration grade bitumen to obtain the bio-binder. Moreover, plain bitumen having the same consistency was chosen to produce a reference AC. Two dense-graded AC wearing courses were prepared in the laboratory according to Italian technical specifications. A mechanical characterization in terms of indirect tensile strength, indirect tensile stiffness modulus, fatigue response and permanent deformation resistance was performed on gyratory compacted specimens using both conventional and performance tests. In addition, aging and water sensitivity of the AC specimens were evaluated. Overall results highlight that the AC produced with the bio-binder did not show reduced mechanical properties and it was comparable to the reference AC regardless of aging and water conditioning. This highly encourages the use of bio-binder as a viable alternative in asphalt technology.

Cold bitumen emulsion mixtures are eco-friendly materials for road pavement construction. Portland cement and other supplementary cementitious materials are added to the mixtures to improve their...

The present paper reports the results of a laboratory investigation aimed to investigate the resilient behaviour of unbound granular materials (UGMs) for pavement unbound layers under repeated triaxial loading. The first part of research was focused on the effects of stress history, in terms of loading conditioning phase and stress paths, on the resilient response of the investigated UGM. The obtained results highlighted that the samples that experienced several stress paths after an initial stress conditioning showed reduced resilient moduli as well as higher stress dependency of the resilient properties as compared with samples not subjected to any specific stress history. The second part of research aimed to evaluate the influence of the conditioning stress level on the resilient modulus. The results showed poorer resilient characteristics along the several stress paths as the selected conditioning stress increases. Whereas, a sort of “loading memory effect”, resulting in a similar mechanical behaviour, can be recognised as a similar stress state between conditioning phase and subsequent stress path is considered. The study confirms the high dependency of the resilient response of UGM on the stress condition and in particular, the main role of conditioning confining pressure on the stable mechanical behaviour of these materials is highlighted. Finally, a simplified approach that would allow the intrinsic resilient properties of UGM to be predicted for a specific combination of conditioning stresses and stress paths is proposed.