Andrea Grilli

Compactability and thermal sensitivity of cement–bitumen-treated materials

Full-depth reclamation is one of the most used rehabilitation methods for subbase courses in high-traffic roads. The use of both cement and bituminous binders as binding agents for reclaimed pavement materials can lead to mixtures having high bearing capacity and resistance to permanent deformation, avoiding premature cracking due to shrinkage. This article focuses on two main topics: compactability and thermal sensitivity of cement–bitumen-treated materials (CBTMs). The dosage of liquids in CBTMs is a key parameter in order to obtain an effective compaction. The volumetric characteristics and the optimum liquid content of CBTMs were studied by means of two compaction methods: Proctor and Shear Gyratory Compactor. The temperature susceptibility of CBTMs can be a valuable factor in both design and construction quality control. The influence of temperature on the stiffness modulus of CBTMs was investigated using two testing methods: indirect tensile stiffness modulus and ultrasonic pulse velocity (UPV). While ITSM provided reference modulus values at strain levels and rates typical of traffic loads, UPV was used to estimate Youngs modulus at very low strain levels and high frequencies.

Full-depth reclamation for the rehabilitation of local roads: a case study

Full-depth reclamation (FDR) techniques for pavement construction and rehabilitation have gained general recognition because of their technical, economical and environmental advantages. The use of cement–bitumen-treated material (CBTM) has rapidly increased over the last 10 years mainly in motorways. Public administrations have recognised the advantages of FDR, and this technique has also begun to be applied for the rehabilitation of local and/or rural roads. This paper shows the results from a trial section built to verify the suitability of FDR for the rehabilitation of local roads. The design planned the in situ stabilisation with styrene-butadiene-styrene (SBS)-modified bituminous emulsion and cement of hot mix asphalt and foundation course. The mechanical characteristics of CBTM were evaluated by means of stiffness modulus tests at different temperatures and fatigue tests. The obtained results offer good prospects for the application of FDR in the maintenance project of local roads.

Synthesis of standards and procedures for specimen preparation and in-field evaluation of cold-recycled asphalt mixtures

The use of recycled asphalt (RA) materials in pavement rehabilitation processes is continuously increasing as recycling techniques, such as cold recycling (CR), are being utilised in increasing magnitude and greater awareness for use of recycled materials and consideration of sustainable practices is becoming common in the construction industry. The focus of this paper is on developing a state of the art and state of the practice summary of processes used for classification of RA as well as the curing and specimen preparation practices for cold-recycled asphalt mixtures. A variety of topics were explored through an exhaustive literature search, these include RA production methods, definition of RA materials, stockpiling practices, industrial operations, specimen curing and preparation practices and in-field evaluation of cold-recycled rehabilitation. This paper was developed through efforts of CR task group (TG6) of RILEM Technical Committee on Testing and Characterization of Sustainable Innovative Bituminous Materials and Systems (TC-237 SIB).

Curing and temperature sensitivity of cement–bitumen treated materials

In the present study, the curing process of cement–bitumen treated materials (CBTM) was investigated by analysing the influence of cement dosage and curing temperature on moisture loss and evolution of complex modulus. Moreover, the study aimed to characterise the thermo-rheological behaviour of cured CBTM. Results showed that moisture loss by evaporation controls the increase in stiffness of the mixtures. However, excessive evaporation can hinder the full potential of the cement hydration process. Results also showed that the quantitative effects of curing time and loading frequency on stiffness can be superposed. Similar to hot-mix asphalt, CBTM showed a viscoelastic and thermo-dependent response. In particular, results suggested that at higher frequencies, the iso-thermal viscoelastic response is mainly affected by the aged binder whereas, at lower frequencies, the response of the mixtures depended mainly on the behaviour of the fresh binder.

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.

Evaluation of mechanical performance of cement–bitumen-treated materials through laboratory and in-situ testing

Nowadays, cold recycling is considered as a common road construction/maintenance technique and no longer as an alternative technique to the traditional ones. The difficulties in simulating the production and construction processes in laboratory have led researchers to practise full-scale testing of mixtures. This paper presents a comprehensive evaluation of the mechanical performance of a cement–bitumen-treated materials (CBTMs) containing 80% of reclaimed asphalt. After a preliminary mix design, the mixture was produced in a mix plant and laid down on two trial sections with different layer thicknesses (15 and 20 cm) over a homogeneous subgrade. The mixture was sampled before laying, compacted and characterised through indirect tensile test and indirect tensile stiffness modulus test. The same tests were carried out on cores taken from the trial sections. Light weight deflectometer and falling weight deflectometer surveys were performed on the trial sections to evaluate the performances of the CBTMs.

Runway Pavement Reconstruction with Full Material Recycling: The Case of the Airport of Treviso

This technical paper shows the innovative approach used in the rehabilitation of the runway of the airport of Treviso. Treviso is located in North Italy and lies about 40 km far from Venice. For this reason, the airport of Treviso may be considered the second airport of Venice and receives the low-cost companies. In order to minimize the environmental impact of the rehabilitation project, the materials coming from the demolition of the old runway pavement were completely recycled in the new runway pavement. Several recycling techniques were used such as the cement stabilization of soil, cement treatment of milled cement concrete and cement-bitumen treatment of reclaimed asphalt. This paper shows the technical application of scientific knowledge on pavement recycling developed in Italy in the last decade.

Cold Recycling of Reclaimed Asphalt Pavements

Pavement engineers have in front of them multiple challenges linked to addressing issues related to social development and society’s expanding needs. One of the most substantial of these issues is perhaps how to effectively rehabilitate and/or maintain the existing road network while preserving and sustaining limited natural resources. The re-usage of existing pavement materials to reconstruct/rehabilitate our future pavements is the solution that is now more and more selected by the different road administrations around the world. However, upon closer inspection, one can find many areas and details, not negligible issues, that are simply extensions of HMA technology (i.e. mix design process in cold recycling) or empirical arrangements; in particular RAP still does not have an internationally recognized classification. So SIB – TG6 decided to develop a classification protocol of RAP, depending on its intended application. The objective has been followed by considering the procedures generally utilized to classify the natural aggregates: tests able to identify the main components (i.e. the geometrical and mechanical properties of aggregates and the characterization of recovered bitumen for RAP) and provide information on their behaviour under specific conditions, near to real life usage (e.g. the Los Angeles test for aggregates gives an idea of the potential behaviour of aggregates under the action of a roller compactor). The following sections illustrate and explain the actions of the TG in order to achieve the goals outlined above: the review of current standards, the protocol designed to classify RAP and the round robin tests carried out to validate the protocol.

Tests Campaign Analysis to Evaluate the Capability of Fragmentation Test to Characterize Recycled Asphalt Pavement (RAP) Material

Cold and hot recycling of reclaimed asphalt pavement (RAP) is increasingly gaining in popularity worldwide due to the need to increase the sustainability of asphalt pavement, both from environmental and economic perspectives. Despite the increasing of use of these techniques, we are still faced with the problem of correctly characterizing RAP. In the framework of the RILEM TC 237-SIB TG6, a Round Robin Test (RRT) was performed in order to evaluate the capacity of the fragmentation test to characterize RAP materials. A total of 5 laboratories located in 4 different countries were involved in the testing program. This paper focuses on the presentation of the fragmentation test method and the results of the RRT performed on different sources of RAP. To differentiate RAP materials in terms of size alteration vulnerability, fragmentation tests were performed at three different temperatures (5, 20 and 40 °C) on different sources of RAP. Fragmentation testing consists in evaluating the amount of materials passing through a control sieve of a coarse uniform RAP material after a fixed series of strokes carried out with a normalized falling mass. Results show that fragmentation is reduced when the testing temperature increases. Fragmentation tests performed on natural aggregates indicate that they do not vary with the testing temperature, and such test results are a function of the amount of foreign matter in the RAP. The results also show that the test is suitable for differentiating RAP materials from different sources.

Effect of bio-based additives on bitumen properties

In the last years, the constant shift in bituminous binder sources and qualities have increased interest in identifying new products that can enhance the properties of bitumen. This study is a broad testing overview on the effect of five chemistries, derivate from the pine-trees, on a selected paving grade bitumen. The experimental programme was based on empirical properties, such as penetration value and softening point temperature, and fundamental properties such as dynamic viscosity and rheology-based behaviour. The cross over temperature were used to determine the transition between a more predominantly elastic behaviour and a more predominantly viscous behaviour. It has been noticed that different chemistries can either harden, soften or change the temperature susceptibility of bitumen. Further investigation will include the ageing process effect on these chemistries, to develop products addressed to enhance bitumen quality.