Using cold recycling technology, seven machines from Wirtgen, Vögele and Hamm rehabilitate the damaged taxiway at Guglielmo Marconi Airport in Bologna/Italy in a minimum of time and with maximum precision.
Opened in 1931, the airport handled over 6.5 million passengersin 2014 and today ranks among the seven busiest airports in Italy. The current rehabilitation work is part of an extensive maintenance programthat is designed to further improve the complete infrastructure. The focus was initially on the taxiway section between junctions TN (Tango November) and TM (Tango Mike) – including rehabilitation of the drainage system and stabilizing and widening of the shoulders:the inner one (on the apron side) from its current 3.50 m to 9 m, and the outer one (on the runway side) to 7.5 m. The airport authority also called forthe stabilizationand asphalt resurfacing of a further 70 m of taxiway in the direction of junction TP (Tango Papa).
Following this, the service lane to the south of Apron 2 was also to be rehabilitated and – in a secondphase – four aircraft parking bays were to be resurfaced.
Wirtgen W 200 powerfully mills complete pavement structures
When selecting the machinery, the company commissioned with the construction work, Bindi S.p.A., once again put its trust in the mature technologiesof the Wirtgen Group. As usual, the project kicked off with a Wirtgen cold milling machine – in this case the W 200. Among other things, it is perfectly suited to the large-area, selective milling of surface courses athigh daily performance rates. On the badly worn taxiway with a length of 340 m and a width of 23 m,the large milling machine also proved equal to the task of milling out the entire surfacing to a total depth of 70 cm in three passes. Unmistakable signs of a reduced load-bearing capacity of the underlying base courses had prompted the responsible managers to take this decision.
To remove the pavement highly effectivelyyet economically, the machine operator brought one of the numerous, invaluable features of the W 200 into play: the three, selectable milling drum speeds. They can be conveniently set from the operator’s platformand ensure the ideal milling outputfor the prevailing requirements. In this case, the lowest milling drum speed was called for. Working at this speed, the W 200 with its 558 HPachieves the maximum milling outputwith reduced fuel consumption per cubic meterof milledmaterial. This setting also minimizes cutter wear.
Wirtgen cold recycling technologywith the WR 2400 and KMA 220
But before the taxiway could slip into its new asphalt garb, it was first essential to stabilize the base course, whose load-bearing capacity was no longer sufficient. That was just the job for Wirtgen recyclersand soil stabilizers, which increase the strength of the soil by adding binders, or re-use the milled material to rehabilitate roads in a resource-conserving, eco-friendly process. Indeed, they can even do both of these jobs at once– as the Wirtgen cold recycler and soil stabilizerWR 2400 did in this instance.
Since roughly half of the base course consisted of clayey soil, the other 50%being a mixture of sand and gravel, the recycler and soil stabilizer first mixed it with lime andthen, in a second step, with cement. Once the soil had been stabilized in this way,durably restoring its load-bearing capacity, 50cm of recycled material with a cement content of 6% were then laid. To produce the new base course, Bindichose a combination of in-situ and in-plant processes, this being the most efficient method under the prevailing local conditions. Once 25 cm of the material originally milled out had been replaced in the milled cut by an excavator, it was time for the Wirtgen recycler and soil stabilizer to get back to work. This time, the powerful milling and mixing rotor of the WR 2400 mixed the material into a homogeneous mass, adding water and cement.
At the same time and just a few meters beyondthe airport grounds, the Wirtgen mobile cold recycling mixing plant KMA 220saw to the mixing of the second pavement layer, which likewise had a thickness of 25 cm. This plant can be used to produce cold mix from a wide variety of new aggregate mixtures, reclaimed recycling materialsand binding agents. With its maximum mixing capacity of 220 t/h,the KMA 220sees to it that a full truckload of 20 t cold recycled mixcan be produced and immediately placed again every six minutes. A 20-tHamm 3520 compactor with 3-point swivel joint and vibratory smooth roller drum was used in Bologna for professional compaction of the final, 50-cm recycled layer.
Top-quality asphalt paving thanks to the Vögele SUPER 1803-3
Finally, the moment had arrived forthe SUPER 1803-3 paver from Vögele to fit out the taxiway in its new asphalt attire. Step by step, it paved a 10-cm base course, a 6-cm binder course and a 4-cm surface course. The surface course was paved instone mastic asphalt to maximize the service life and give aircraft a good grip on the new taxiway, even in bad weather. This material is not only more durable, but also allows optimum drainage of surface water owing to its open grain structure.
Niveltronic Plus®, Vögele’s proprietary automatic grade and slope control system installed on the SUPER 1803-3, came into play once again,ensuring that the paving work was true to line and level.In terms of ease of operation, qualityand reliability, it is the perfect solution for all grade and slope control tasks. Optimally coordinated with the machine technology, Niveltronic Plus®delivers high-quality paving results based on pre-defined reference values.The BigMultiPlexSki also employed by Bindi further enhanced the quality of the pavement. Equipped with a row of three sonic sensors, the BigMultiPlexSki simultaneously scans a reference atseveral separate points. These measurements can then be used to derive a virtual reference level with the help of the VögeleNiveltronic Plus®system. This is a decisive advantage, particularly on areas like the 23 m-wide taxiway, since lengthy surface irregularities, such as bumps, can easily be detected and evened out in this way.
Hamm’s DV 90 and GRW 18 add the finishing touch
Finishing was the job of asphalt rollers from Hamm. Here, too, building contractor Bindiwas able to rely on the leading technologiesof the Wirtgen Group. The DV 90 pivot-steered tandem roller with the time-proven Hammtronic electronic machinemanagement system set the ball rolling, achieving an impressive area output and compaction performance. Immediately after, as a classic part of the workflow,a rubber-wheeled roller added the final touch. Rubber-wheeled rollers like the GRW 18 from Hamm play an important role in final compaction since thekneading effect of the rubber wheels makes for perfect sealing of the surface – as at Guglielmo Marconi Airport, whose taxiway is now optimally equipped for the high dynamic stresses imposed by the aircraft rolling over it.
Stringentproject requirements met
Elena Sturlini, Technical Manager at Bindi S.p.A, is certainlypleased with the result, havingcarried out the rehabilitation work without disrupting normal airport operation. That requirement posed an additional challenge, on top of the already stringent requirements of the project.Sturlinisays: „In addition to punctual completion, we primarily had to ensure the qualityand durability of the construction work, despite all the logistical challenges involved in the project.”Being able to rely on the support of a strong partner was all the more important in this situation. „There’s no doubt that, thanks to the reliable operation of the Wirtgen Group technologies, we were optimally equipped to meet the performance parameters stipulatedby the airport authority while achieving maximum productivity,” says the Technical Manager.