This project was born with the objective of contributing to the resolution of the environmental problems linked to the phenomena of disturbance created by the noise of passing vehicles.

 

Life Nereide is coming to the finish line: the latest development of the project 

The Life Nereide Project (noise efficiently reduced by recycled pavements) is coordinated by the Department of Civil and Industrial Engineering of the University of Pisa and it is currently coming to its end phase.

This project was born with the objective of contributing to the resolution of the environmental problems linked to the phenomena of disturbance created by the noise of passing vehicles. This disturbance is particularly felt in urban areas and it is strictly linked to the superficial characteristics of the wearing course. This project aims at drafting some Guidelines for the designing, building, and monitoring of road surfaces with high environmental sustainability.

Picture 1 – Example of warm technology: the laying of the compounds without smoke

 

The project has been developed based on investigations carried out on two experimental sites, where 12 compounds of bituminous conglomerate for wearing courses have been laid, of which: 7 conglomerates with low noise emissions (they work on the reduction of the generation of the noise created by the rolling of tyres on the surface) and 5 are sound-absorbing bituminous conglomerates.

Such conglomerates have been produced at lower temperatures compared with the ones of the traditional hot conglomerates. The so-called “warm” technologies have been used to achieve this goal. They are composed of virgin raw aggregates and bitumen, but also of millings coming from the resurfacing of existing surfaces as well as rubber powder deriving from End-of-Life Tyres (ELTs). The key eco-objectives the NEREIDE aimed at were:

•  noise pollution mitigation;
• reduction of CO₂ emissions into the atmosphere. This has been made possible thanks to the lowering of the production temperatures and the reuse of waste material that would otherwise be destined to the landfill.

The project has provided for the construction of 12 experimental stretches of road: one per each compound. Each stretch of road was about 400 m long. They are located in two precise points, identified on the urban roads of Region Tuscany. These stretches of road have been appropriately chosen among those that needed improvement activities aimed at noise pollution reduction within the scope of the Regional Plans. In particular, six experimental wearing courses were made on the “SRT 439 Sarzanese-Valdera” in the town on Massarosa (LU) at the end of 2018. The remaining 6 stretches of road were made on the “SRT 71 Umbro-Casentinese” in the cities of Arezzo and Castiglion Fiorentino (AR) between April and May 2019.

 

THE PROJECT OF COMPOUNDS

The design of ths undoubtedly represented the hardest task of the project. An in-depth knowledge of the constituting materials, of the volumetric composition, and of the mechanical characteristics of the thickened compound is fundamental to envisage its behaviour once put in place. The design of the compounds has been carried out in two phases in the course of over a year. In the first phase the compounds containing the rubber powders for site I were studied. In the second phase, the compounds containing rubber powders and millings for site II were developed. The first step was to define the maximum quantities of rubber powder and millings that could be added to the compounds in order to guarantee the reaching of the sound and functional performances requested without compromising their mechanical performances by the means of specific laboratory tests carried out on the binding agents and the mastics (compounds made with raw bitumen + part of RAP passing at 0.15 mm).

Picture 2 – Example of road surface with low sound emission: the noise mitigation is realized restricting the rolling noise production	Picture 3 – Example of sound-adsorbing road surface: the noise mitigation is realized with the absorption of acoustic energy

The rubber from ELTs used in the production of bituminous conglomerates can be obtained from automobile or truck tyres. The most used material for the composition of the automobile tyre compound is the Styrene-Butadiene-Rubber (SBR) polymer. This is a copolymer of synthetic rubber made with styrene and butadiene. The compound for truck tyres, instead, is mainly composed of natural rubber (NR). Generally, rubber powder coming from both tyre typologies is used (50% each) and, thus, the deriving powder is known as SBR/NR.

As it is well-known, the methodology that provides for the addition of powder directly to the aggregates and the bitumen upon the mixing of the bituminous conglomerate is known as “dry” technology. Instead, the one that provides for the addition of rubber to bitumen within a specific mixing plant is known as “wet” technology. In the latter, bitumen and SBR/NR are mixed and allowed to react at a temperature that allows rubber particles to inflate. The quantity of rubber to add to the bitumen varies from 15 to 22% in weight. The quality of the obtained binding agent strongly depends on a number of factors, such as: temperature, the mixing time, the type and intensity of the imposed mechanical mixing energy, the morphology and grain size of the powder, the eventual presence of aromatic groups in the bitumen.

All the compounds created within the scope of the NEREiDE project have been made introducing powder both through a dry and a wet process - to the exception of the traditional ones of reference. For what concerns the content of RAP to be used for each typology of compound, the maximum percentage of reuse has been identified by assuring the contemporary respect of two fundamental requisites:

• definition of a compound grain size suitable for guaranteeing the reaching of a specific superficial texture of the finished layer necessary for the reduction of noise generation;
• adequate resistance to fatigue of the mastics produced with the maximum percentage of RAP that do not affect the service life of the surface.

A further step was the identification of the additives necessary for the reduction of the mixing and laying temperatures both thanks to rheological measurements on the bitumen with rotational rheometer, and by the means of workability measurements carried out on the compounds during their thickening with a Gyratory Pressure Distribution Analyzer (GPDA).

THE EXPERIMENTAL SITES

The stretches or road object of intervention were chosen based on a priority index linked to the contemporary presence of several schools and over 800 people exposed to daily noise levels higher than rses was preceded by the removal of the previous surface for a thickness of 4 cm. The most damaged parts of the road were also renovated through the reconstruction of the binding layer. The areas to be renovated were identified by the means of the monitoring of the structural characteristics of the existing surface with a Falling Weight Deflectometer (FWD) and the constant recording of the layers with the Ground Penetrating Radar (GPR).

The first experimental site is 2,400 metres long. It was identified on the “SRT 439 Sarzanese-Valdera” in the town of Massarosa (LU), in the neighbourhoods of Quiesa and Pian del Quercione. The second stretch of road is about 3,000 m long and is located along the SRT 71 “Umbro-Casentinese” in the cities of Arezzo (in the neighbourhoods of Rigutino, Policiano, and Il Matto), and Castiglion Fiorentino (AR). 

Picture 4 – The realization of experimental site: the removal of the existing surface and lay of the new wearing course

The typologies of compounds laid on Site I were:

 

•         2 control hot “traditional” compounds, of which:

➢ a 0-12 draining compound;

➢  a 0-12 Splittmastix Asphalt (SMA) compound;

•         4 innovative “warm” compounds containing rubber powder with uneven grain sizes, of which:

➢ two with “open graded” grain size (dry and wet process);

➢ two with “gap graded” grain size (dry and wet process);

The typologies of compounds laid on Site II were 6 innovative “warm” compounds containing rubber powder and millings (RAP); in particular:

 

•         4 with uneven grain sizes of which:

➢ two with “open graded” grain size (dry and wet process);

➢ two with “gap graded” grain size (dry and wet process);

➢ two with “dense graded” grain size (dry and wet process).

 

THE RECORDING OF THE SUPERFICIAL CHARACTERISTICS: ANTE AND POST OPERAM MONITORING

 

Monitoring campaigns have been carried out on the sites object of intervention. They were made to record the sound, structural, and functional indicators in order to quantify the benefits obtained following a before-after approach. Moreover, the monitoring of such indicators has allowed to record their evolution in time as a consequence of the passing of traffic. The evaluation of the superficial characteristics has been carried out with reference to macro texture, regularity and adherence. The profiles for the calculation of the macrotexture and regularity indexes have been obtained thanks to a laser profilometer. The macro texture has been evaluated with reference to ETD, whilst the regularity in terms of IRI.

 

The adherence measurements were carried out with a BV11 skiddometer. They have been expressed with reference to BPN, CAT, and F60 (according to the IFI model). Such indicators fall within the Life Performance Indicators – LPI – which represent some monitoring indexes of the impacts of the project. Three monitoring sessions have already been carried out for texture, adherence, and regularity on Site I of Massarosa (LU) and 1 monitoring session for Site II in Arezzo and Castiglion Fiorentino (AR). The results are fully satisfying.

 

 Picture 5 – The temperature control during the laying of the compounds. The temperature is at least 40°C less than the traditional warm compounds

 

THE ANALYSIS OF BENEFITS

To quantify the consumption of material energy, as well as the release of CO₂ and Aromatic Polycyclic Hydrocarbons (APH) in the environment associated with this intervention, a quantitative analysis of the benefits obtained from the implementation of the project has been carried out. The results have shown that the production of compounds with warm technology and the use of recycled materials allow an important reduction of the environmental impact associated with the building of they represent a valid alternative to the traditional technologies and are able to fully comply with the expected “eco-environmental” results. In particular, the use of recycled materials reduces waste disposal in landfills and, in particular for what concerns millings, it allows important savings with reference to virgin raw materials such as bitumen and aggregates. Moreover, the reduction of the production and laying temperatures (Photo 5) allows the improvement of the workers’ health conditions.

  

FUTURE ACTIVITIES

Post-operam noise and functional monitoring campaigns are planned on Site II in the next months. The new noise protocols for the measurement of noise from tyre rolling will be experimented there. The drafting of Guidelines containing indications useful for the identification of technologies, materials, and typologies of intervention to use without affecting the mechanical performances and the functional characteristics of the new road surfaces will be the final task of the project.