Cold recycling of asphalt pavement - MIXING PLANT
In Sweden, a total of about 1 million tonnes of old pavement material is recycled each year.
Various techniques are used (cold, semi-hot and hot) of which cold plant recycling has become the most common method for flexible pavements on roads with low traffic volumes (ADTtotal <1500 vehicles/day). Cold recycling is an economical technique since the material does not need to be heated. The asphalt plants can easily be moved from place to place and are therefore suitable for small-scale production and for road construction in sparsely populated areas far from stationary plants. In cold recycling, up to 100% of the asphalt can be recovered, but for a good result it is important to crush and screen the old asphalt first. About 2.0–4.0% new bitumen emulsion is added, usually together with water and sometimes 10–20% virgin mineral aggregates. Various procedures have been developed to make the mix as homogeneous as possible and to ensure sufficiently good coverage with the emulsion. It is important that the quantities of new binder, water and mineral aggregate be determined through preliminary tests in the laboratory. A new test procedure for this type of mix has therefore been developed and is included in the new directives for cold recycling produced by the National Swedish Road Administration. The procedure comprises tests and specifications covering the following areas:
•sampling and evaluation of old asphalt material
•composition of the granulate (reclaimed asphalt pavement, RAP)
•guidelines for choosing a new binder and mixing water and mineral aggregate
•preparation and conditioning of test specimens
•mix design and quality assurance by testing mechanical properties and durability ofrecycled mix.