Low-temperature mechanics of hot recycled mixtures through Asphalt Thermal Cracking Analyzer (ATCA)

Thermal cracking is recognized as a critical failure mode for bituminous mixtures and good fracture properties are a key factor to obtain long lasting asphalt pavements in cold climate. Investigating this aspect in hot recycled mixtures with high amount of Reclaimed Asphalt Pavement (RAP) is fundamental due to the stiffening effect of aged bitumen that can emphasize the cracking aptitude of the mixture when subjected to thermal stresses. An innovative tool for characterizing the low-temperature cracking behavior of asphalt mixtures is the new developed Asphalt Thermal Cracking Analyzer (ATCA). It allows the evaluation of several parameters (e.g. glass transition temperature, coefficients of contraction, cracking temperature) directly related to the mechanics of low-temperature performance. In this study, four recycled asphalt mixtures were produced in laboratory with 40% of RAP using the Bailey Method as tool to optimize the aggregate structure. Different binder contents and modified bitumens (with various level of polymer modification) were employed. An additional mixture with 25% of RAP was used as control mixture. All the mixes were tested using the ATCA device. Moreover, an original image analysis was performed to assess at a microscale level the effects of compaction properties and aggregate structure on thermal cracking response. Results show that mixtures with 40% of RAP can behave better than the control mixture at low temperature if an accurate mix design is performed. Careful selection of RAP material and type and quantity of virgin bitumen can enhance low temperature performance and aggregate packing although high amount of RAP aggregates

Modified PATTI test for the characterization of adhesion and cohesion properties of asphalt binders

It is well known that aggregate-asphalt bond is of fundamental importance for mechanical response and moisture susceptibility of asphalt mixtures. Many researchers have studied moisture effects on the binder adhesion-disbonding properties and their role in defining asphalt mixture performance, but a suitable system to measure binder adhesive properties to aggregates directly is not available yet. This paper includes a study to modify the Pneumatic Adhesion Tensile Testing Instrument (PATTI), which is a standard method used for paints or coatings. The modification is aimed at developing a reliable and practical test protocol for directly evaluating the adhesion/cohesion properties of asphalt binders. To achieve this goal, different asphalt binders and several test variables were varied to study their influence on pulloff strength. The analysis of the results collected indicates that the modified PATTI test protocol show high promise for evaluating adhesive bond strength and moisture susceptibility of asphalt binders. Moreover, the test appears to be simple and practical to allow discriminating different asphalt binders with different adhesion characteristics

Rheological Properties of Bituminous Binders with Synthetic Wax

Warm Mix Asphalt (WMA) has been introduced to reduce the environmental impact and improve energy efficiency of bituminous mixtures production and lay down. With this purpose, synthetic waxes are effectively used to allow reduction of temperature during mixing and compaction. Given these advantages, the basic WMA challenge is the production of a pavement mixture having, at least, the same performance as traditional HMA. This study describes the effect of a synthetic wax additive on the rheological properties of a paving grade bitumen in a wide range of temperatures. The effect of wax at mixing and compaction temperatures (T > 100°C) was evaluated using viscosity tests. A Dynamic Shear Rheometer (DSR) and a Bending Beam Rheometer (BBR) were used to investigate the rheological properties of the base and the WMA binder at midrange and low service temperatures (from 18°C to 37°C). The time-temperature superposition principle was applied to analyze the complex shear modulus and the creep stiffness modulus, through the construction of master curves. Particular attention was devoted to the study of wax effect on low temperature physical hardening

Influence of Physical Hardening on the Low-Temperature Properties of Bitumen and Asphalt Mixtures

A laboratory study was carried on the effects of physical hardening on the low-temperature performance of bitumen and corresponding asphalt mixtures. Bitumen testing involved measurements of glass transition temperature and creep stiffness at various isothermal storage times. Mixture testing included evaluation of glass transition temperature, thermal stress build-up in restrained conditions and thermal strains in non-restrained conditions. A physical hardening rate was introduced both for bitumen and mixtures (PHRB and PHRM). Results indicated that glass transition temperatures can be reduced passing from bitumen to mixtures and a correlation can be found between the hardening rates PHRB and PHR

Testing and Characterization of Compacted Asphalt Pavement Materials

ABSTRACT. This paper summarizes some key achievements and findings by the RILEM TC 206 ATB “advanced testing and characterization of bituminous materials” taking into account new developments in the field of bituminous road materials and test methods. These developments were triggered not only by an increasing variety of materials and requirements on the performance of bituminous pavement systems but also by environmentally driven innovations in terms of recycling and low temperature asphalt and new types of binders. Work on compacted asphalt pavement materials included interlaboratory wheel tracking tests on material from real motorways well as interlayer shear bond testing on material taken from specially constructed test sections. New developments in asphalt mixture testing, such as the application of image analysis techniques, were also taken into consideration. Results show that performance of bituminous mixtures must be considered also with respect to the whole pavement system. This is particularly true, e.g., in case of rutting tests, compaction and specimen preparation evaluation as well as interlayer bond properties. It was also found that test methods developed for one type of bituminous materials do not a priory apply to another type of bituminous materials and may even lead to completely misleading conclusions as compared to real life pavement performance