Edoardo Bocci

Influence of reclaimed asphalt content on the mechanical behaviour of cement-treated mixtures

For the rehabilitation of asphalt pavements the upper distressed layers are usually milled before overlaying to eliminate reflection cracking–related problems and to preserve the pavement geometry. This maintenance technique generates a large amount of reclaimed asphalt (RA) as a product of the milling operation. The recycling of RA in cement-treated base and subbase courses represents a valuable solution in terms of technical, economic and environmental benefits. However, the influence of RA on the mechanical properties of cement-treated materials (CTMs) is still not completely understood. As a consequence, CTMs using a high content of RA have not yet been widely applied. The present paper shows the findings of an experimental analysis on CTMs including 50% and 80% RA in comparison with the reference CTM consisting of 100% mineral aggregates. In particular, indirect tensile tests and unconfined compressive tests were conducted to evaluate the resistance characteristics of the CTMs. In addition, complex modulus tests and ultrasonic pulse velocity tests were performed to investigate the stiffness properties of CTMs. The investigation shows promising results as regards the use of high percentages of RA in CTMs and offers a substantial contribution for the understanding of the mechanical behaviour of CTMs.

Analysis of Structural Compatibility at Interface Between Asphalt Concrete Pavements and Orthotropic Steel Deck Surfaces

Orthotropic steel deck is the most suitable solution for long-span bridges by virtue of its low weight and good mechanical properties. However, this deck shows a lack of adhesion with ordinary paving materials; for this reason special bonding coats are usually applied on the steel surface. Polymer-modified bitumen, asphalt-based mastic, epoxy asphalt, and reinforced asphalt membrane have been used at the interface between the hot-mix asphalt (HMA) course and steel bridge decks. A description of these materials and their construction process is provided. In some extreme situations mechanical reinforcement is necessary to provide adequate bonding between the steel deck and the asphalt pavement. The aim of this study was the laboratory evaluation of the shear properties of smooth and reinforced steel interfaces, which were coated with a polymer-modified bitumen and placed between the steel deck and conventional HMA. A suitable specimen preparation procedure was first defined. Shear resistance was evaluated with the ASTRA shear test device to investigate the effects of temperature and normal stress on different types of HMA–steel interfaces. The results showed that reinforced steel interfaces guaranteed higher performance than did smooth interfaces, especially with increasing temperature. Reinforced steel interfaces can be considered as a reliable solution in cases of high-shear traffic-induced stresses.

Experimental Evaluation of Shear Resistance of Improved Steel-Asphalt Interfaces

Although steel orthotropic deck is currently the most widely adopted solution for long-span bridges, the poor adhesion to the upper asphalt layers still represents a serious problem without a clear solution. In recent decades many techniques that involve the use of special bituminous bonding coats, reinforced asphalt membranes, net-reinforced steel deck surfaces, or epoxy asphalt binders have been applied, with varying results, to improve the level of adhesion of the asphalt pavement to the steel surface. In this experimental study, two such techniques were adopted to investigate the shear resistance of steel–asphalt pavement systems. The first technique used epoxy asphalt both as a bonding coat and as a binder of the upper asphalt layer, while the second technique involved the use of a reinforced asphalt membrane that was applied on the steel deck before overlaying with conventional hot-mix asphalt (HMA). The Ancona Shear Testing Research and Analysis shear test device was used to evaluate the shear resistance of different types of HMA–steel interfaces and to investigate the effects of temperature and normal stress. The results have been compared with the shear properties of bitumen-coated interfaces, studied in previous research. The results showed that epoxy asphalt guaranteed high performance regardless of the test temperature. However, the shear resistance of the system with the asphalt membrane was lower than with the epoxy asphalt, although it was higher than the resistance of bitumen-coated interfaces at high temperatures.

The evolution of the mechanical behaviour of cold recycled mixtures stabilised with cement and bitumen: field and laboratory study

Road construction and maintenance involve huge amounts of materials that can include wastes from the demolition of old asphalt pavements. Recycling allows environmental and economic benefits to be achieved, by reducing the consumption of natural resources. These advantages are maximised with cold-recycling, in particular when full depth reclamation (FDR) is adopted as road rehabilitation technique. The aim of this research was to compare different FDR techniques, which produce cement-treated material and cement–bitumen treated material (CBTM) combining the use of cement and bitumen emulsion or foamed bitumen. The FDR was applied in a trial section built along an in-service highway and monitored with annual falling weight deflectometer (FWD) surveys in order to evaluate the performance evolution. Results highlighted that, because of the effect of temperature, the FWD deflections were not suitable to accurately evaluate the evolution of the mechanical behaviour of the cold recycled mixture (CRM) layers. However, the temperature-corrected FWD moduli allowed to conclude that the performance of the CRM layers was similar.

Mechanical Behaviour of Asphalt Concrete Containing C&D Recycled Materials

Recycling of waste materials is actually one of the main targets in civil engineering, because of economic and environmental features. To this aim, the field of road engineering offers many technical solutions, including the use of recycled materials from construction and demolition of civil works (C&D) in pavement layers. These materials have been investigated to be used as aggregate in asphalt concrete base layers for flexible road pavements. Different percentages (0, 15, 30 and 50 %) of C&D materials were used in order to determine the most suitable solution. The scope was to evaluate both static and dynamic mechanical properties of the mixtures. In particular, a servo-hydraulic control static press was used to run indirect tensile tests and a Nottingham Asphalt Tester was used to determine indirect tensile stiffness modulus and fatigue strength. Specimens were manufactured by mixing the aggregate with 5 % of bitumen and compacted with a shear gyratory compactor to a fixed height, in order to have a constant air voids content equal to 5 %. Experimental results showed that C&D materials can conveniently be used in asphalt concrete for base layers (up to maximum 30 %) without penalizing the mechanical performance of the mixture.

Mechanical behaviour of cement-bitumen treated materials containing different amounts of reclaimed asphalt

Cold recycling techniques have become one of the main sustainable solutions in road construction and maintenance. The use of reclaimed asphalt (RA) as a constituent material for bound mixtures offers two main advantages: it eliminates problems concerning disposal and it allows natural resources to be preserved. Among the most widespread recycled mixtures, the use of cement–bitumen-treated materials (CBTM) for subbase courses has rapidly increased over the last 10 years. This paper deals with the influence of RA content on the mechanical characteristics of CBTM. Several mixtures were produced by combining different dosages of binders (cement and bituminous emulsion) and RA contents. The behaviour of recycled mixtures was evaluated and compared in terms of indirect tensile strength, water sensitivity and stiffness modulus. In addition, the effects of temperature on the stiffness properties were investigated. Experimental results showed that the RA content did not significantly affect the compactability and the strength properties of CBTM. The presence of RA determined an increase in mix deformability and thermodependence, but the effect can be inhibited by increasing cement dosage. The findings offer good prospects for increasing the use of RA and encourage administrations to employ this material as an effective construction solution.

Hot Recycling of Reclaimed Asphalt Using a Bio-based Additive

Hot recycling of reclaimed asphalt (RA) has increasing interest worldwide due to economical and environmental benefits. In particular, the use of RA in place of virgin aggregates reduces of aggregate supply and disposal of RA. Moreover, the hot recycling process allows reusing the aged bitumen from the RA, implying a reduction of the required amount of new bitumen. However, the ageing process, which occurs from the production throughout the service life of the pavement, affects physical and chemical properties of bitumen, determining its hardening. For this reason, when high amounts of RA has to be reused (more than 20 % by aggregate weight), the use of specific additives is strongly recommended in order to reach the desired bitumen properties and consequently to produce an asphalt concrete (AC) with high performance. This experimental project focused on the use of a bio-based additive (A) for the production of an AC for binder course with a high amount of RA. The experimental program consisted of two main phases: the first phase dealt with the mix design of three mixtures containing respectively no RA, 40 % of RA, 40 % of RA treated with A; the second phase aimed at producing and laying down in a trial section selected mixtures for the validation of the full-scale hot recycling process.