A bit of history
Since its inception, the recycling of bituminous mixtures has been the focus of Pavimental‘s interest. In the 1980s of the 20th century, the use of new technologies began to be adopted for the recycling of materials from the demolition of road pavements.
In parallel with the first hot recycling at the asphalt plant, in the 1980s hot in-place recycling equipment for bituminous mixtures, called ART (Asphalt Recycling Train) developed in collaboration with Marini S.p.A., were used.
These mobile plants were able to rehabilitate the surface layers of the pavement directly on the road, reusing up to 95% of the existing material.
As the years went by, the widespread problems with the bearing capacity of the pavements caused by reaching the end of the service life of the asphalt layers made it necessary to develop technologies capable of carrying out deep rehabilitation of the carriageways. The idea was to reuse the existing material as much as possible and cold recycling with modified bitumen emulsions was identified as the most promising technology.
For this purpose, trains for on-site recycling were developed and put into operation:
This technology was used to restore the base and binder layers for overall thicknesses of up to approx. 30 cm. From 2004 to 2011, about 540,000 cubic meters of cold recycled material were produced, reusing over one million tons of RAP. About 40,000 articulated trucks would have been needed to transport all this material.
In parallel, hot in-place recycling trains were put into operation in the same years, using special heaters capable of softening the existing mix and removing it without altering the aggregate gradation.
Using this technology, around 900,000 square metres of on-site recycling was achieved by reusing 90% of the existing material.In particular, the whole Livorno – Cecina section of the A12 motorway was regenerated.
These “in situ” recycling technologies were based on the conviction that the transfer of the work directly onto the road was the winning choice, as it made the site extremely flexible, avoided the need to set up fixed settlements and reduced transport costs.
The changed operating conditions resulting from the increased attention to the mitigation of traffic interferences, and the environmental constraints in terms of reducing harmful pollutant emissions, have in fact made the mobile recycling trains unusable for pavement maintenance activities.
The evolution of pavement recycling technologies
Currently, with regard to the rehabilitation of pavement layers and the reuse of RAP, the prevailing orientation is to adopt cold technologies (with emulsion or foamed bitumen) for foundation and sub-base layers, whereas for hot bituminous mixtures tipically used for base, binder and wearing courses, the objective is to increase the percentage of RAP.
In recent years, as part of maintenance work on motorway pavements, Pavimental has repaired approximately 750 km of motorway lanes using in-situ stabilization technology with foamed bitumen.
As far as cold recycled bituminous mixturesfor base and sub-base layers are concerned, semi-mobile plants are currently used.
The transfer to the asphalt plant has made it possible to significantly improve the quality of the cold mix, in particular the possibility of selecting and sieving (fractioning) the RAP by optimising the gradation.
With this technology, in the years 2010-2011, the base layer was created as part of the extension works to the 3rd lane of the A1 North Branch (Fiano Romano – GRA section), reusing over 200,000 tons of milled material.
On this issue, the main problems to be solved are not so much the technical possibility of introducing high quantities of RAP into the mixture, but the achieving of proper performance, particularly in terms of service life, and the risk of exceeding harmful pollutant emissions into the atmosphere during production.
Pavimental financed the ERA project with the aim of finding confirmation on a scientific basis of the perception, the result of years of experience, that in order to obtain satisfactory results, the increase in the use of RAP in bituminous mixtures must be accompanied by greater control over the quality of the milled materials, the lowering of production and laying temperatures, and optimisation of binders and additives.
The first results obtained largely confirm the correctness of the strategy adopted. Overall, with current technologies and technical regulations, Pavimental reuses on average 20% of the total weight of the bituminous conglomerate produced, in the order of 200,000 tons / year. Thanks to the intuition that led to the development of the ERA project well in advance, Pavimental is ready to accept the increase targets that will be imposed by the next application of the Minimum Environmental Criteria (CAM).
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