Marking a first in Italy: Wirtgen Cold Recycler and Soil Stabilizer WR 250 rehabilitating A4

The A4 Autostrada is a highway linking Turin to Trieste via Milan and Venice. Cutting across northern Italy from west to east, it runs for a total of 522 km. The A4 is divided into five segments, the Turin-Milan, Milan-Brescia, Brescia-Padua, Padua-Venice and Venice-Trieste, and is managed by different companies. Stretching across the entire Po River Valley, one of the most densely populated and industrialized areas of Europe, the A4 is also one of the most highly trafficked highways on the continent with transit of over 115 million vehicles in 2013. Local, national and international transport all account for the high rate of traffic, since the A4 is the fastest and most direct route for vehicles travelling from Portugal, Spain and France in the direction of Austria, Slovenia and other European countries beyond Italy's eastern border.

Like all Italian highways under concession, the Autostrada Brescia-Verona-Vicenza-Padova SpA operates under the supervision of the SVCA (highway concessions authority) which is the supervisory agency of the Ministry of Infrastructure and Transport. Due to the heavy volume of traffic (in 2013 the Brescia-Padua segment alone saw the transit of 95.6 million vehicles), the concessionaire performs monitoring of the pavement and its condition, and according to the degree of wear, decides the type of maintenance to be performed in order to maintain sufficient grip and uniformity of the pavement. Some types of maintenance operations (including milling and upgrading of the surface layers) are performed directly by Serenissima Costruzioni, the operations branch of the concessionaire assigned with planning and scheduled maintenance. Other operations, such as cold recycling of deep layers to restore the bearing capacity are contracted out to specialized companies like Ecovie, who successfully utilizes Wirtgen stabilizers.

Ecovie was the first Italian company that purchased one of the new WR 250 cold recyclers sold in the world, and the absolute first sold to Italy. The decision was made after Ecovie technicians performed a broad set of evaluations and actual stabilization and cold recycling with foamed bitumen using a pre-production trial model from Wirtgen Macchine, the Italian branch of Wirtgen Group. The machine consistently demonstrated improved manoeuvrability and productivity compared to the WR 2500 S, the model now out of production but that Ecovie still operates successfully in many applications, as do many other users around the world. The choice was hence a logical one for the company, who is well aware that cold recycling is the application sphere where Wirtgen has traditionally exhibited a clear advantage over the competition when it comes to technology and productivity.

Recently Ecovie has been busy with a series of maintenance jobs on the Brescia-Verona-Vicenza-Padua segments where, in different lots, the company has performed cold recycling of over 20 km of highway in the slow lane heading east towards Padua, i.e., the lane most subject to greater dynamic stresses due to the constant passage of trucks.

The first lot started at the Sirmione exit and proceeded east for about 2 km. Once the pavement's various layers were pre-milled 13 cm, an additional 20 cm were cold recycled in order to reach a total layer of recycled material with foamed bitumen of 30 cm (20+13cm); in fact the pre-milling depth was increased because it was calculated that the material would raise by about 3 cm due to the effect of mixing. From analyses performed on the existing pavement it was also established that in order to reach an optimum mix, it would be necessary to add a percentage of bitumen of 2.9% and 2.6% of cement.

The operation was carried out using two recycling trains in order to cover 4 meters of the lane; the WR 250 in the first train milled the material 2.40 meters, i.e. the entire span of the milling drum, while the second train following where a WR 2500 S was operating, performed the remaining 1.60 meters. This operating scheme had the dual advantage of avoiding one machine having to perform two passages to cover the width of the lane (and thus keeping within the stringent timeframes imposed by Serenissima Costruzioni), and at the same time make the most of the two recyclers. The WR 250, featuring high power and productivity, was left with the harder task of mixing for the whole width of the drum (2.40 m), whereas the WR 2500 S, with less power, had the job of milling a smaller width, thus using only a part of the drum (1.60 m). As a result, the system made it possible to compensate for the lower productivity of the WR 2500 S, which advanced at an average of 3.5-4 meters a minute versus the 5 or 6 meters of the WR 250.

The material produced by the train of the WR 250 was compacted with the new Hamm H 20i vibratory compactor, whereas that of the WR 2500 S with a Hamm 3520 vibratory compactor, both having a roller weight of 28.48 metric tons. Afterwards, the material was profiled using a grader, then compacted again with vibratory rollers. Finally, a GRW 280 rubber-wheel roller ensured the perfect "sealing" of the surface. This procedure ensured that the recycled layer passed the plate load tests, which yielded values of 1,500 kg per square cm, and dynamic tests with the falling weight system, which indicated EV2 values of 100 MN per square meter.

When the procedure was terminated, 8 cm of binder and 4 cm of a layer of permeable and noise-reducing wearing course were laid to ensure grip and visibility also in hard rain.

Technical director Fabrizio Furlan sums up his impressions of the new WR 250: "It was important for us to verify the productivity of the WR 250, and I imagine that it will be the same for others who've used the WR 25000 S with success. The previous model was noted for a legendary work capacity and reliability, and I think it was responsible for winning Wirtgen a reputation as an undisputed leader in this product segment, especially cold recycling. But the WR 250 is a definite step ahead when it comes to productivity, consumption and control. That's the conclusion we came to after a set of comprehensive tests whose results convinced us to buy the machine. The different architecture of the WR 250 offers advantages in terms of transportability because of the machine height reduction. The new configuration also enables improved handling and manoeuvrability, especially when steering around tight spaces. The cab is definitely improved and the operator has told us that the joystick system and the graphical interface of the on-board computer, together with overall comfort and climate control, have a positive impact on working conditions and productivity."