Milling layers separately, recycling economically

While traffic continued to flow on one lane, the powerful 500kW large milling machine set to work removing the damaged sections. “Our machine is equipped with the Vacuum Cutting System (VCS),” explains Site Manager Mr Koji Yamada. Five years ago, the VCS vacuum cutting system developed by WIRTGEN was included in the New Technology Information System (NETIS) of the Japanese Ministry of Land, Infrastructure, Traffic and Tourism.

To repair cracks in the road pavement, the large milling machine in Mito was equipped with a standard milling drum. After removal of the 10cm-thick surface course, the W 210 cold milling machine milled the binder course to a depth of 15cm in a second pass. Because the different types of mix were separated, it was possible to return both layers to the material cycle for reuse in line with their technical suitability and qualitative characteristics. The selective reclaiming of the material alone delivers clear ecological and economic benefits. When intelligent milling technology is factored in, Wirtgen cold milling machines not only optimize the overall rehabilitation process, but also the cost-effective reuse of the RAP in the asphalt mixing plant.

Load-dependent water sprinkling plays a key role here. The water required for cooling the cutting tools is regulated in accordance with the engine load and milling speed. As the water system is automatically switched on when the milling drum is lowered into working position and automatically switched off when the milling work is stopped, water consumption can be cut considerably. Specifically, up to 20% of the water can be saved.

As a result, the service life of the cutting tools is extended, the cold milling machine requires less frequent refills and the downtimes are shorter. In addition – and this is decisive for materials processing – the residual moisture of the milled material is only 3–4% per ton. If Wirtgen milling technology is not employed, the residual moisture is generally 5%.

When producing new asphalt, a simple equation applies to the drying process in the asphalt mixing plant: 1% drier source material saves 1 liter of heating oil in the production of 1t of asphalt. On top of this comes a reduction in CO2 emissions due to the lower energy requirements. When processing the milled material on the Jōban Expressway, a total of some 400 liters of heating oil were saved – and in just two hours, as this was how fast Unite Co., Ltd. selectively and precisely removed the surface and binder courses with the powerful W 210. Site Manager Mr. Koji Yamada says: “The quality of the milled surface is flawless thanks to the Level Pro levelling system – it’s the perfect base for paving and compacting the new asphalt.”

The up to 20% lower water consumption with Wirtgen milling machines increases energy efficiency, as the following applies: −1% water in the source material = −1 liter heating oil per ton of asphalt during further processing into recycled mix, e.g. in Benninghoven asphalt mixing plants.

For the Jōban Expressway site, this means:

• 800m² are x 0.25m milling depth = 200m³ volume of RAP
• 200m³ volume of RAP x 2.47t/m³ density by volume of granulated RAP = 500 liters heating oil

Result: The potential quantity of heating oil that can be saved in the mixing plant as a result of using the Wirtgen cold milling machine is around 500 liters.