Warm Mix Asphalt: A Technique that’s on the Rise
Warm-mix asphalt accounts for 30% of production in North America and is now spreading at quite a pace through Europe after a ten-year observation period. Two main techniques are emerging, making use of either additives or foamed bitumen. FAYAT offers tried and tested industrial solutions for new or renovated equipment.
Warm-mix asphalt began to appear in some countries – particularly Holland and South Africa – in the late 1990s, before reaching France at the beginning of the new millennium. FAYAT’s first warm-mix asphalt project dates back to 1999, in Holland, with a foamed bitumen process installed in a batch-mix plant. Ten years later, its use worldwide is mixed.
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Progression in France has been slow, and the professionals explain this either by the red tape – which is gradually being eased – or the sheer amount of company processes available until recently. The same can be said about Italy and Germany, where there is a widespread drop in demand for traditional asphalt. In Italy, MARINI has just commissioned a TT 3000, with SAM SpA. Use of the sequential coating process LEA-CO is one of the first applications in this country and will be kept a close eye on, especially since in this application, the production temperature verges on 100°C, i.e. a temperature drop of 50 to 60°C.
The main advantages of warm-mix asphalt are as follows:
- Reduction in the asphalt temperature by at least 25°C
- Reduction in greenhouse gas emissions (including CO2)
- Fuel savings (15% with the foamed bitumen)
- Elimination of vapours and odours at the plant, during transportation and application
- Asphalt is easier to handle
- A higher recycling rate is possible
The European standards on hot-mix asphalt apply to technical specifications: NF EN 13108 -01, then 02 and07.
Two main techniques emerge after a period of clarification:
- Chemical addition of additives to the bitumen
- Foaming of the bitumen by injecting water
Other solutions, such as sequenced coating, mentioned above, are less common and certainly more technical.
Questions to be resolved by the manufacturer concern:
- Managing the gas temperature
- Managing the burner
- Optimising the drum flights
- Reducing unnecessary air intake
- Heat insulating the duct
- Additional burner for the gas leaving the drum
- Heat insulating the filters
- Introducing additives or foam
This is because reducing the material temperature brings about a local reduction in the gas temperature to below 100°C. Water can become liquid again, particularly in contact with walls. All of the aforementioned solutions limit loss effectively, and they are not all necessary. New equip- ment tends to be kitted out for this type of production, particularly as regards heat insulation; the additional burner heating the gas is recommended for large filters.
Additives can be solid or liquid, and in both cases the manufacturers offer industrial modules that are easy to connect and move about.
Foamed Bitumen, the AQUABlack foam gun
In the USA, the vast majority of warm-mix asphalt is produced using foamed bitumen. This trend is taking hold worldwide, probably thanks to the industrial use of well-suited high-pressure pumps. Depending on the technical choices (with or without high pressure), the use of additives is not compulsory.
FAYAT offers FOAM GUN, which is easy to install on new or existing continuous and batch-mix plants. After North America, where several hundred plants operate with AQUABLACK, ten installations are in operation in France. The launch in Asia, particularly China, has been effective since 2012.
Production is the first stage, followed by implementation after transportation.
Figure on this page shows that the lower the temperature, the more energy compaction requires. This is the main reason for the virtually universal reference of 150°C and above for traditional asphalt. As a result, compaction must be controlled and perfectly grasped. So-called “smart” compactors such as the BOMAG ASPHALT MANAGER achieve effective, uniform compaction and the settings are saved and therefore traced. In reality, the whole chain of equipment is concerned – “from the plant to the road” – including production, transportation, setup and compaction. The paver finisher plays a key role both during the pre-compaction stages and implementation of the smooth surface, and the set- tings depend to a large extent on how workable the asphalt is. Spreader boxes S500 and S600 of the paver-finishers BF 800, the heaviest on the market, go a long way to helping meet this objective.
FAYAT Road Building Equipment thus offers all of the equipment you need for high-quality work.