Anas (The Italian National Road Company) has started the renovation works for the road surfaces of the State Road.

The University of Pisa has taken part to the project thanks to the great experience it has acquired in the study of road surfaces with low noise emissions also thanks to the Nereide project. Ecopneus has contributed to this project by offering technical assistance.

Anas (The Italian National Road Company) has started the renovation works for the road surfaces of the State Road, SS 73 Senese-Aretina at the beginning of July. It has put in place an experimentation of noise reduction on a stretch of road of about 2.6km with an investment of about 800 thousand Euros, there included the remaking of the lower levels of the road. The works have been carried out in the towns of Monterchi and Anghiari, in the Province of Arezzo. In particular, the stretches of road have been identified at km 175-176, in the village of “San Leo” for 1,600 metres and speed limit at 70 km/h, and near the neighbourhood of “Le Ville” at approximately km 168 of the State Road n 73, for a length of 700 metres and speed limit of 50 Km/h.

The works have seen the collaboration of the Departmental Area of Tuscany of ANAS, that has taken care of the management of the works. The Engineering and Testing Department has coordinated all the activities. It also shall take care of the measurements of the acoustic performances and the superficial quality of the surfaces made thanks to its Centre of Cesano. In particular, it shall verify the characteristics of grip of the experimental layers – a fundamental parameter for the aims of road safety.

The University of Pisa has also taken part to the project with its Department of Civil and Industrial Engineering. Indeed, it has gained considerable knowledge in the study of low sound emission road surfaces in the course of the projects Leopoldo (financed by Region Tuscany) and Nereide (currently ongoing and financed by the European Community as a LIFE project). In particular, the University has taken care of the definition of the specific compounds, studying the balancing of the requisites of minimum noise emissions and the ones of adequate characteristics of grip at the expected transiting speeds. 

The following have also taken part to the project: Ecopneus has given technical assistance for the definition and supply of the specific materials in collaboration with the companies Asphalt Rubber Italia, Valli Zabban, and Lucos - the company that has physically carried out the works on behalf of Anas.

The noise-reducing layers made are of three types:

•         Dense graded wearing course with optimised texture with hot bituminous conglomerate.

•         “Warm” dense graded wearing course with optimised texture made with highly-workability bitumen modified with SBR/NR polymers obtained from rubber powders deriving from End-of-Life Tyres following a “wet” process.

•         “Warm” dense graded wearing course with optimised texture made with highly-workability bitumen modified with SBR/NR polymers obtained from rubber powders deriving from End-of-Life Tyres following a “dry” process.

In simple terms, the three compounds of bituminous conglomerate are characterised by an “optimised” grain curve where the particular distribution of the dimension of the aggregates in the compound is able to move part of the noise emissions caused by the rolling of the tyre to frequencies that are dampened at short distance from the point of contact between tyre and surface. This guarantees low noise emissions. 

The use of rubber powder has been planned in the second and third compound. This rubber is the product of a specific shredding process of End-of-Life Tyres, which modifies the rheological characteristics of the bituminous binding agent and, as a consequence, the viscous-elastic properties of the bituminous mastic. Such modification allows to keep the texture of the surface more stable in time and, as a consequence, it preserves the acoustic performance. In the case of the “wet” process, the rubber powder is used in the liquid phase, for its melting into the bituminous compound. In the “dry” process, instead, it is added to the compound as a solid aggregate.

In both cases, the production process provides for relatively low temperatures upon laying phase, in order to avoid the breaking of sulphur bonds present in vulcanised rubber.

The objective is to minimise the production of fumes and unpleasant emissions during the laying process.  

Great care has been put in the characterisation of gaseous emissions upon bitumen laying. In the following photos, the tests made by ASL (the Local Health Body) of the city of Siena are shown. Measurements of gaseous pollutants were made on the workers at the site, on the vehicles, and by the means of a control unit placed at the margin of the building site. The fourth photo shows the temperature of the conglomerate upon its laying on the road.

In addition to the three experimental layers, other “standard” stretches of road have been made (the so-called “B-type” standard wearing course, present in the Anas technical specifications). This was made to be able to compare the performances of noise emissions of the special wearing courses with the ones produced by the “new” ordinary wearing courses in optimal conditions. The latter shall, then, be compared also with older or damaged wearing courses. 

Recent experimental results allow to expect a net gain of about 4-6 dB in the noise emissions of the optimised wearing courses compared to traditional surfaces. These data derive from the research carried out by the University of Pisa: the Leopoldo Project (that was concluded some years ago), the LIFE “Nereide” Project (still ongoing), and the European Project LIFE MONZA (http://www.lifemonza.eu/?q=it/node/27).

In practice, however, all those activities that will renovate also old or damaged road surfaces in the future, they will be able to produce even greater positive effects in the perception of the residents interested in the problem of noise emissions