Increased use of recycled asphalt pavement technology

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The use of reclaimed asphalt has increased over the past 30 years, and it is set to grow even more. Patrick Smith reports

In the USA, asphalt from roads is said to be the most recycled material. Figures show that up to 80% of that removed during widening or resurfacing projects is remixed to be used in new roads, sub-base, shoulders and embankments.

And in many European countries the use of reclaimed asphalt pavements (RAP) is common practice, having started more than 30 years ago. It is big business, with over 4,000 asphalt production sites and over 10,000 companies involved in the production or laying of asphalt.

Europe now produces some 25% of the world’s asphalt total (300million tonnes of hot mix asphalt and 5million tonnes of cold mixtures annually), and it is estimated that well over 50million tonnes of RAP is produced each year with, in some instances, over 70% of it being reused for road surfaces.

The goal should be to achieve 100%, says 2947 European Asphalt Pavement Association (EAPA), which points out that RAP is 100% recyclable; it can be reused to produce new asphalt (in plant and in situ) and it can be recycled by using emulsions, foamed bitumen and by adding cement (in plant and in situ).

Equipment manufacturers now incorporate or offer options on plant that make it capable of recycling old asphalt. 383 Ammann Group says that it has a number of solutions at its disposal that will contribute towards achieving the global goals relating to CO2 reduction: lower operating temperatures and the use of as much recycled asphalt as possible.

It has industrialised a low-temperature asphalt technology in cooperation with 3774 Shell and Kolo 3687 Veidekke, WAM Foam asphalt, that has a production temperature of is 115°C, and it also claims to have produced the first asphalt mixing plant capable of producing quality aggregate from 100% reclaimed asphalt using a special parallel drum. Originally seen in north Germany, the unit had an improved drying and heating process that Amman claims increases efficiency in comparison to conventional parallel drums and enabled fuel savings of around 10%.

“The waste product of yesterday is increasingly becoming a valuable base material that is meanwhile used in many quality asphalt recipes,” says Ammann.

Professor André-Gilles Dumont, head of 2948 Lavoc (the traffic and transport laboratory) at ETH Lausanne, Switzerland, says in a report in the Ammann company magazine: “Using large quantities of reclaimed asphalt is a different topic to low-temperature asphalts. We will soon be faced with a mountain of asphalt chunks that we will have to recycle, sooner or later. We have no choice but to improve aggregate mixes with a proportion of reclaimed asphalt, and we also have to be willing to recycle our layers more than once. Let’s not forget that the largest, albeit aged, current source of bitumen lies in the roads themselves.”

In the UK, construction company FM 2949 Conway’s €11.5 million investment in its asphalt production facilities near London is said to be paying dividends.

The core of the operation is a new Benninghoven BA5000 asphalt plant featuring an innovative layout with a sophisticated parallel drum design that allows it to mix RAP along with fresh material to deliver a range of output grades. It is one of a few asphalt plants in the UK capable of using RAP, a development that has allowed the company to pursue its policy of boosting recycling and lowering its carbon footprint. The RAP is provided by FM Conway’s contracting arm.

“We have got five mills and we plane off the roadway ourselves. We screen it and make sure it has the right properties. We test it to make sure we have got a homogenous material,” says the site’s general manager, Tim Metcalf.

The dryer system for the fresh materials can handle up to 320tonnes/hour while the RAP is elevated through the plant at up to 240tonnes/hour. The quantities of RAP used in the mix vary, depending on factors such as available feed, throughput and the output specifications.

“In some materials we can go as high as 80%,” says Metcalf. While employing RAP as feed achieves important sustainability targets, Metcalf points out that the key driver for FM Conway using this in asphalt production is that it provides a highly cost-effective source of good quality material that helps boost the company’s profitability.

In the UK, there are only a few asphalt plants capable of handling RAP while in the Netherlands up to 30% of feed materials for asphalt production are from recycling processes, which makes sense for a country that has to import construction materials.
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