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Continuous mixing plants are advancing
02. November 2011
Asphalt Mixing Plant ContiMix

The asphalt world differentiates between two production methods. Continuous and batch-based production of the asphalt mix. The method used was often determined by tradition, formed over the years by the manufacturers in their regional markets. A few years ago Ammann began to incorporate continuous mixing plants in its product range and to develop them further. A successful move, as a glance at the two plants from the ContiMix range in France demonstrates.

 

The French market has always been open towards methods of continuous production. It is, however, also a very discerning market. And so it was a fortunate coincidence that Am- mann found a partner with whom to pursue the development of a continuous production plant. The prototype of the ContiMix II is located at SMC (Centre de traitement de Mâchefers de Blainville-sur-Orne), a Eurovia company situated in Normandy. Up to 100,000 tonnes of asphalt have been produced in Blainville-sur-Orne each year for the last 15 years and supplied to road construction sites in the municipalities of Bayeux and Falaise and the Pays d’Auge region.

 

You have to look carefully to find the plant on the industrial estate – the Renault Truck factory, just a stone’s throw away, is much more impressive. After all, the mixing plant is a mere 20 metres tall and fully enclosed to boot. Only the chimney is visible. A discontinuous plant would be 10 metres taller. This is because continuous production has one cycle less than discontinuous production: that of screening and weighing the granular aggregate at the upper end of the mixing tower. A simple, precise and direct method of feeding all the materials into the mixer has achieved a 20 % increase in output for the entire plant. The plant’s low height makes it easy to conceal in housing. This prevents dust, noise and odours from entering the outside environment. But that is not the only feature that makes the SMC plant particularly environmentally friendly. A new burner saves energy, whilst the ratio of reclaimed asphalt was raised from 10 to 40 %. Small wonder, then, that the plant will soon have a “sister” at Eurovia’s site in Brest.

 

Quality through components

Increasing the ratio of reclaimed asphalt is the order of the day. Continuous production plants score extra points in this regard. Despite having the same components, the mixing process in a continuous plant can handle up to 10 % more granular asphalt than a discontinuous plant. Consequently the cold feed ratio can reach 40 % and even 70 % if a parallel drum is in use.

 

The fact that both systems use the same components is down to Ammann’s strategic approach: whilst the world leader in batch mixing plants did not have to reinvent the wheel, its customers can rest assured that the components have been well and truly tested. Since close to 90 % of the components are the same, customers with existing plants can switch between the two methods without any complications.

 

Furthermore, these tried and tested components always assure a high mix quality. The twin-shaft paddle mixer used in the plants has a wide range of possible paddle arrangements that makes it easy to find the right weighting between material conveyance, shear action and displacement to quickly achieve the desired quality. The wet and dry mixing times on ContiMix plants are adjustable between exactly 24 and 48 seconds. This ensures that the granular aggregate is sufficiently coated with bitumen. The desired quality and homogeneity is maintained from the first to the last tonne of asphalt, produced with a particular recipe, to leave the mixing plant. That is by no means standard practice. It is generally believed that continuous production is only profitable for production runs exceeding 50 tonnes. Conti- Mix plants from Ammann achieve profitability from runs in excess of just 10 tonnes.

 

Everything is possible everywhere

A third plant situated in France proves that continuous production does not necessarily mean missing out on any of the possibilities that modern asphalt road construction has to offer. The companies Colas and SCREG (both subsidiaries of the Bouygues Group) have operated a new ContiMix plant in the harbour of Strasbourg since the beginning of June. The name SARM, which stands for Société alsacienne de recyclage de matériaux, says it all. It became apparent during the run-up to a motorway construction project that a great deal of granular asphalt would be produced; resurfacing the roads of Alsace also produces significant quantities of reclaimed asphalt. The plant was therefore equipped with the appropriate components. From cold asphalt with added emulsion to foamed bitumen technology (up to 120 °C), from 40 % warm reclaimed asphalt feed rates to hot asphalt feed rates of up to 70 % via parallel drum.

 

Production method conserves environment and resources

And there is more. The plant has a production output of 300 tonnes per hour and is equipped with accessories that allow the use of fibres as well as the production of coloured surface coatings. The plant operated by SARM is the only one in the greater Strasbourg area to offer such versatility – a real competitive advantage for the company. “This investment is our response to the challenges of our times. Our production method conserves the environment and resources, meets the demands of our market and has even increased our output by 35 %”, says René Studli, managing director at SARM.

 

Of course, ContiMix plants are not only sought after in France and by other leading construction companies throughout Europe. They are now producing asphalt in countries such as New Zealand, Australia and Great Britain. The indications are that other countries are set to follow suit. Among them are some countries where continuous plants are as yet unheard of. Whether or not a continuous plant is the right choice is more a question of technology than of culture.

 

 

 

At a glance: Benefits of ContiMix plants

  • Combination of both shaft types: Batch and continuous
  • Output increases by 20 % as the screening and weighing cycle in the mixing tower is not required
  • Omitting the screening and weighing unit reduces the installation height as well as the cost of production and investment
  • Compact design equals less space requirements
  • Twin-shaft paddle mixer produces a high-quality mix
  • No loss of material during arrivals to and departures from the plant
  • “Zero Waste System” is already patented
  • Maximum flexibility thanks to highly developed control system with recipe changes on-the-fly and extension options