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Rubberised asphalts for sustainability of road pavements

Università degli Studi of Palermo and Ecopneus investigating the recyclability of rubberised asphalt mixtures for road pavements in Italy

Compactor roller

  Per la versione in Italiano:

In modern years, the use of recycled materials in road construction is becoming increasingly important, certainly as ameans of reducing waste but more often asphalt technologists are discovering means of taking advantage of specific end-of-life products [1] to even enhance properties of conventional asphalt mixtures. This is the case of Rubberised Asphalt Mixtures (RAM).

In fact, RAM have shown to be a more sustainable solution for road pavement construction providing more silent and longer-lasting pavement [2 and 3]. In a limited extent, considering the length of the whole road network, this is true also in Italy where, so far, more than 670 km/lane of roads with modified asphalt containing recycled tyre rubber have been made [4].

Test at Santa Ninfa
1. The first test took place in Santa Ninfa, in the province of Trapani (photo credit: Flavio Leone of SSILAB)

Along these lines, the Rubberap project (, developed by the University of Palermo and Ecopneus (, the non-profit company for the tracking, collection, processing and final destination of end-of-life tyres (ELTs) in Italy, in collaboration with the University Gustave Eiffel, SMACOM Srl and SicilBitumi Srl, aims at developing and transferring knowledge from academia to local and national industries, with two main objectives: promoting the consistent implementation of rubberised asphalt mixtures of local and national roads and investigating their recyclability by engineering asphalt mixtures with high content of 50% Reclaimed Rubberized Asphalt Mixtures (RRAM) for wearing courses.

Validating the use of RRAM for Italian road pavements would offer many benefits, such as the possibility of re-using rubberised asphalt mixture beyond their end-of-life, however also some challenges are associated with engineering this technology, for instance to list few: the mechanical and functional properties of the resulting mixtures could be an issue, as well as their final performance; the quality of the recycled material can be affected by several agents such as the presece of contaminants; different types of rubberised asphalt technologies can provide different results.

Furthermore, available literature documenting experience relating RRAMs was found to be limited to few recent studies [5, 6, 7 and 8].

Structure of the investigation
2. Structure of the investigation

With this in mind, there is therefore a need to understand how, and ultimately if, RAM can be recycled to produce RRAM, and to identify any barriers which may prevent this technology from being effective also complying with requirements of Italian road authorities. In this sense, Rubberap project aims to be an important step towards assess the recyclability of RRAMs through a bespoken experimental programme including:

  1. laboratory production of RRAM by means of artificial aging of several types of plant-produced RAMs (Dry process and Hybrid);
  2. the design of asphalt mixtures composed by 50% RRAM and 50% virgin materials;
  3. their mechanical and performance-related characterisation.

The aim of this specific paper is to provide stakeholders with the results of the design and mechanical characterisation, as required by the major Italian road authority [8], of two plant-produced controls, a conventional asphalt concrete mixture (AC10) and a rubberised asphalt concrete mixture made with a dry process (AC8-RAM), and an asphalt concrete mixture engineered in laoratory with 50% RRAM and 50% virgin materials (AC10-RRAM).

Furthermore, the authors provide a glance on possible future steps towards higher technology readiness levels.

Grading distribution
3. Grading distribution

Materials and methods

The bituminous mixtures considered in the research were produced in plant for rehabilitation paving of wearing courses on secondary highways (medium-low traffic) and urban roads (low traffic) in Italy (Figure 2).

Two mixture compositions were considered: “AC10” and “AC8-RAM”. The AC10 mixture is a conventional AC10 with 4.5% of 50/70 bitumen and is designed to be used on both low and medium traffic roads. On the other hand, the AC8-RAM mixture is produced using 6% of 50/70 bitumen and 0.6% of Engineered Crumb Rubber (ECR) through a dry process [9 and 10].

The AC8-RAM has a finer grading distribution and is designed for urban roads with low traffic. The ECR rubber used in the study is an innovative rubber that is chemically treated to prevent swelling during laying and compaction operations but also it apparently allows reducing the processing temperatures as a warm mix technology. Figure 3 depicts their grading distribution.

Voids comparison
4. Voids comparison at different compaction energies

The procedure here introduced aims to provide scientific evidence regarding the feasibility of effectively use RRAM within asphalt mixtures by evaluating their mechanical properties according to the Italian road authority requirements [8]. These requirements mainly consider the compactability, strength properties and moisture sensitivity of the mixtures.

Compliance with road Authority requirements

The compactability of the mixtures was assessed against EN 12697-8 (Figure 4). As a result, all the mixtures complied to the guidelines, except for the AC10, which slightly exceeded the maximum limit at 120 gyrations The presence of ECR in AC8-RAM and AC10-RRAM contributed to their superior compactability compared to the conventional AC10.

To evaluate the mechanical performance in terms of strength and water sensitivity, specimens were compacted to achieve a target voids content of 5%. The indirect tensile strength (ITS) was assessed according to EN 12697-23, and the moisture susceptibility (ITSR) was evaluated according to EN 12697-12. Results indicated that all mixture are comparable.

Compliance with Road Authority requirements
5. The compliance with Road Authority requirements (left), where Min indicates the Anas limits (right)

Conclusions, next and future steps

Findings suggest that RRAMs can be a promising solution for road pavement construction, as they offer comparable and, in some scenario, improved performance compared to traditional asphalt mixtures.

Overall, this study highlighted that with appropriate engineering design, incorporating RRAM in road pavement construction in Italy seems to be possible, according to the requirements of the major Italian road authority for wearing courses.

It is forecasted that at the end of the Rubberap project, these technologies, currently with a technology readiness level of 4-5 (TRL 4-5) (Figure 6), will be ready for a next advancement into demonstration projects, hence leading to future steps such as:

  • implementing a full-scale scenario (plant and field);
  • monitoring filed performance of material and paving technology during construction and use;
  • investigating the multi-recyclability of RRAM;
  • increasing the recycling content.
6. Level of technological advancement of the project RUBBERAP


[1]. W. Buttlar, J. Meister, B. Jahangiri, H. Majidifard, P. Rath – “Performance characteristics of modern recycled asphalt mixes in Missouri, including ground tire rubber, recycled roofing shingles and rejuvenators, MoDOT,, 2019.

[2]. D. Lo Presti – “Recycled tyre rubber modified bitumens for road asphalt mixtures: a literature review”, Constr. Build. Mater. 49, 863-881,, 2013.

[3]. Sabita, Guidelines for the design, manufacture and construction of bitumen-rubber asphalt wearing courses, 2016.

[4]. F.J. Navarro, P. Partal, F. Martínez-Boza, C. Gallegos – “Thermorheological behaviour and storage stability of ground tire rubbermodified bitumens”, Fuel. 83, 2041-2049,, 2004.

[5]. Z. Rice, S. Halligan – “The use of reclaimed asphalt pavement from crumb rubber modified asphalt”, 2020.

[6]. Z. Rice, Y. Choi, L. Latter – “Investigation of the use of reclaimed asphalt pavement from crumb rubber modified asphalt”, Stage 1 Interim Report,–-Stage-1-Final.pdf, 2019.

[7]. W.W. Crockford, D. Makunike, R.R. Davison, T. Scullion, T.C. Billiter, T.T. Institute, T.D. of Transportation, F.H. Administration – “Recycling crumb rubber modified asphalt pavements”, Final Report,, 1995.

[8]. ANAS, Capitolato speciale di appalto – Pavimentazioni stradali, Norme tecniche per l’esecuzione del contratto, 1-5, 2020.

[9]. T.M. Letcher, S. Amirkhanian, V.L. Shulman – “Tire waste and recycling”, Tire Waste Recycl., 1-630,, 2021.

[10]. L.D. Poulikakos, W. Buttlar, N. Schüwer, D. Lo Presti, T. Balmer, M. Bueno – “Can crumb rubber modifier effectively replace the use of polymer- modified bitumen in asphalt mixture?”, Sustain. Resilient Infrastruct. 7, 515-530, 28, 2022.

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