23 October 2015

Breakthrough in the use of reclaimed asphalt in Porous Asphalt mixtures

Percentage of raw material recycling triples to over 90 percent

Utrecht, 22 October 2015 - BAM has succeeded in producing industrial scale ZOAB (porous asphalt concrete) that comprises 93 percent recovered raw materials.

Compared to current ZOAB recycling percentages, which amount to 0% to 30%, this means a breakthrough in sustainable asphalt production. The successful trial involving approximately 60 tonnes of ZOAB took place on Thursday 22 October on the site of the Brabantse Asfalt Centrale (Brabant Asphalt Plant) in Helmond. BAM developed this innovative production method in the framework of the European Life+ demonstration project, LE2AP.

BAM’s innovative ZOAB mixture comprises old ZOAB, recovered stone and mastic. The recovered and subsequently enriched mastic is foamed so that the mixture can be produced at approximately 110˚C. As well as the high reuse value, this also delivers CO2 reductions of approximately 30% and an approximate 40% energy reduction.

The stone (PA Stone) has recently been certified by KIWA as new building material. PA Stone is already being successfully used in ZOAB in several BAM roads projects. 

The behaviour of the ZOAB layer and the recovered raw materials used in this has been tested using various methods on the scale of bitumen, mastic and mixture. On every scale the recovered raw materials and the asphalt produced with this were shown to have at least the same quality as traditionally-produced ZOAB and were often even of higher quality.

Replacement market

With LE2AP, BAM is taking a new route regarding asphalt recycling. LE2AP stands for Low Emission Asphalt Pavement, in which the 2 indicates that this concerns both sound emissions as well as materials that have environmental impact. The LE2AP project is partly financed by a European LIFE+ subsidy.

The basic idea behind LE2AP is that the accepted method for recycling asphalt is limited. These limits have been reached by industry and this restricts further increases in recycling percentages. As fewer and fewer roads are being constructed in the Netherlands, the importance of horizontal recycling is increasing. The asphalt market is now much more a replacement market than a greenfield market.

The basic idea behind LE2AP is to stop recycling asphalt and start recovering raw materials from old asphalt. New asphalt can then be produced from the recovered raw materials. This working method gives total control over building material quality and the recipe for newly-produced asphalt.

The LE2AP process generally follows the following steps:

  • Old asphalt is separated into stone and mastic. The bitumen in the old asphalt appears mainly in the recovered mastic - a mix of sand, filler and bitumen - which means that the recovered stone contains only a small amount of bitumen (often <1%).
  • The stone is then sieved in various fractions. The stone fractions do not need further treatment and are immediately available as high-quality building material (PA Stone) for the production of new asphalt.
  • The recovered mastic contains aged bitumen and therefore does require treatment. By heating the recovered mastic and enriching this with a fresh soft bitumen and a rejuvenator, a high-quality mastic is obtained with a consistent bitumen percentage and consistent quality. As the mastic is available as separate material fraction it can be mixed well during this upgrade. This optimises old and new bitumen mixing and also creates a very homogenous mastic. A building material of consistent high-quality is obtained by controlling the mastic properties and the bitumen percentage.
  • The development of its low-temperature asphalt, LEAB, has enabled BAM to gain considerable knowledge and experience in foaming bitumen. In LE2AP, this knowledge and experience are used to foam the enriched and homogenised recovered mastic.
  • By foaming the mastic, it can be mixed with the reclaimed stone at relatively low temperatures to create a high-quality new asphalt that is produced at low temperatures and that largely comprises recovered raw materials.

The LE2AP end goal is the construction in 2016 of 1 km wearing course with the following properties:

  • Initial noise reduction ≥ 7dB,
  • Reuse of materials ≥ 80%,
  • Produced at ≤ 80°C,
  • A significant reduction in harmful substance emissions.