BOMAG sets the standard in compact tandem rollers up to 5 t operating weight. The machines offer outstanding compaction performance, maximum visibility and the highest levels of operator comfort. A lightweight BOMAG tandem roller was also used in the reconstruction of the A 61 motorway—a BW 120. However, at the customer's request, the machine was optimised in advance for the challenge of “rolling chip onto mastic asphalt”.
The A 61 motorway is a central arterial road of national significance. It runs from the Dutch border near Venlo to the Hockenheim motorway junction. For the most part, the route runs parallel to the Rhine, which is why it is also known as the “left-hand Rhine motorway”. Since 2016, the busy trunk road has been widened from four to six lanes between the Rheinböllen junction and the Hunsrück service area. New constructions are also replacing the two large bridges spanning the Pfädchensgraben and Tiefenbachtal valleys.
At the Rheinböllen junction, Bickhardt Bau AG used a BOMAG BW 120 tandem roller, optimised for rolling chip onto mastic asphalt at the customer’s request. This enabled the company to increase surface coverage by 11%, further optimise work processes and, above all, raise the quality of the mastic asphalt surface course to a new level. The extremely gentle roller finishing of the top layer also significantly impacts the life cycle costs for mastic asphalt.
Bickhardt Bau has been successfully involved in road construction since 1971 and thus contributing to the sustainable development of economic areas. With an annual construction output of around 500 million euros and 2,500 qualified employees, the sought-after full-service provider for major road construction projects is now Hesse's largest medium-sized construction company.
High deformation resistance and good grip: these are the special qualities of mastic asphalt wearing courses. They have outstanding acoustic properties: because fine-grained chip reduces rolling noise effectively. Mastic asphalt is particularly resistant to abrasion and wear, and at the end of its life cycle, it can be reused in an eco-friendly way as it is 100% recyclable.
The success story of mastic asphalt began back in the 1960s. And for good reasons: The mixture of aggregates and road paving bitumen as a binder is applied at a temperature of 210 °C to 230 °C, and the top layer can be driven on again after a minimum period of just 24 hours. The mastic asphalt is applied once and forms a water-impermeable top layer without additional compaction, onto which chip is applied in a single pass.
To ensure the asphalt surface course is hard-wearing and has above-average abrasion resistance, it is important in the final work step that the chip is pressed on particularly gently and that the hot asphalt, which still has a core temperature of 80 °C, is not deformed. Every road contractor fears the notorious formation of “elephant skin” or other damage to the chip pattern. Because in the worst case, this means the top layer has to be milled out again, resulting in high costs and lost time.
It was good that Bickhardt Bau had a competent technology partner in BOMAG. The result is a BOMAG BW 120 tandem roller optimised for asphalt mastic finishing and gentle chip pressing. To reduce the static linear load to approx. 10 kg/cm (standard: 11.25 kg/cm), BOMAG widened the drum to 135 cm for the customer and reduced the shell thickness from 13 to 10 mm. With a chip quantity of 12 kg/m2, the roller produced an excellent surface texture with a surface coverage 11% higher than that of a conventional 2.5 t tandem roller. The road was passable again after only a few hours.
In this case, water sprayers were not used with the special tandem roller because mastic asphalt reacts extremely sensitively to rapid temperature changes.
“We needed a high-performance roller for optimal results at the joints and edge areas of the new top layer. BOMAG’s design engineers exceeded our expectations,” says Sebastian Reschka, foreman at Bickhardt Bau. “Mastic asphalt is a versatile construction material used primarily for sealing road and bridge surfaces. In addition to state-of-the-art screeds and mastic asphalt pavers, our fledgling mastic asphalt department now also has a customised tandem roller in its portfolio that meets our high-quality standards.”
“We want to help our customers achieve their goals. That starts with listening. What is actually needed? What must the machine be able to do?” explains Sebastian Kölzer, product manager for lightweight tandem rollers at BOMAG. “In this case, the result is a tandem roller that is impressively light when rolling mastic asphalt and ensures a high-quality chip pattern.