Time savings key to the success of cold in-place recycling process
Time is another factor in the success of cold in-place recycling, as this application is called. Shortening the duration of the project from 12 weeks to 4 days was only possible because almost no material had to be transported. The actual construction site planning had envisaged that both lanes would be excavated to a depth of 54 centimetres and rehabilitated from scratch. This would have resulted in 7,500 m³ of material that would have had to be transported away from the construction site and replaced with new material. Replacing the material, including all the associated work, resulted in the planned construction duration of 12 weeks. Cold in-place recycling eliminates the need to replace existing material, as it can be reused right on the construction site. By adding lime and foamed bitumen as binding agents and using all the existing materials, a new, high-quality construction material is produced on the spot. The new bitumen-stabilised material (BSM) serves as the new ‘backbone’ of the busy road, and is immediately fit for traffic again after completion of a construction section.
Flexibility thanks to adjustable working widths
The width of the lane varied between 2.75 metres and 3.25 metres on the construction site. The W 380 CR cold recycler was thus equipped with a milling drum unit with a working width of 3.2 metres instead of its standard unit with a working width of 3.8 metres. The innovative MCS system even made it possible to switch the units on the construction site.
The University of Minho was responsible for designing the mix for the new BSM layer and collecting samples of the existing road structure. In the process, they determined that the road bed still had enough bearing capacity that a BSM layer plus a new asphalt surface layer represented a long-lasting alternative to the conventional, cost-intensive process of building a new road. To produce the new BSM layer, 7 kg of lime per square metre needed to be added to the mix. The lime was applied directly to the old road surface before the mixing process. With its extremely precise spreading unit, a Streumaster SW 5 RC mounted to a John Deere tractor ensured that the lime was evenly distributed. The maximum spreading width of 2.5 metres required the spreader to make two passes to cover the CR’s working width of 3.2 metres. By carefully discharging the material at the right spreading width, the crew achieved a high degree of spreading accuracy, which kept costs as low as possible.