Mixing technology

Whatever the output needs, manufacturers of mixing plants are focussed improving efficiency, from consumption to more options for mixing temperature and recipes, new control systems and other environmental considerations such as noise and fumes.

For instance, recycling old asphalt – also known as reclaimed or recycled asphalt pavement (RAP) – is an absolute must in the industry, according to Ammann. In fact, Ammann claims to be the only manufacturer that can offer plant technology to produce new asphalt from 100% RAP, and offers a variety of technologies, depending on how much RAP is added to the mix.

It recommends adding cold RAP directly to the mix for quantities of up to 30%, but offers a range of specially designed drums for higher RAP rates up to 100%. The RAH 100 drum, for instance, can handle up to 100% RAP.

Meanwhile, Ammann has also introduced a new asphalt mixing plant, the Universal HRT, with increased use of recycled materials in mind. Designed to cope with up to 60% RAP, the plant features a fully integrated parallel drum directly above the mixer for optimal material flow, and boasts an output capacity of between 320 and 500 tonnes/hour.

Fayat-owned mixing plant manufacturer Marini is also developing new mixing towers focussed on coping with higher quantities of RAP. The company has introduced the new eTower family of asphalt plants, which currently consists of two models – the eTower 2000 (150 tonnes per hour) and eTower 2500 (200 tonnes per hour).

The towers feature two systems for introducing RAP – a recycling ring, and direct introduction in the mixer via an elevator. Recycling rates of nearly 50% can be achieved, while even higher recycling rates can be achieved by equipping the plant with an additional parallel dryer drum for RAP.

The eTower range has also been designed to be able to gain from recent developments in warm-mix asphalt production – a process which allows asphalt to be produced at a lower temperature of around 90°C to 150°C, instead of traditional hot mix temperatures of 140°C to 180°C.

Additives such as foam bitumen need to be added to the mix to achieve quality warm mix asphalt, and the eTower 2500 is fitted with Marini’s AQUABlack foam bitumen production system, so the final asphalt temperature can be cut by more than 30°C, according to the company.

Warm mix production has the obvious benefits of cutting fuel consumption and decreasing emissions. In addition, engineering benefits include better compaction on the road, the ability to haul material for longer distances, and extending the paving season by being able to pave at lower temperatures. Indeed, Marini claims that warm-mix asphalt will soon account for 30% of production in North America.

Transportability

Mobility is another important consideration for contractors looking to invest in a new plant, and Ammann has been working to make life easier in this respect, too. It has developed two new asphalt mixing plants – the Prime 140 and the EasyBatch 140 – with transportability firmly in mind.

Both plants boast outputs of 140 tonnes/hour, but the Prime 140 has a transport length of 23 m and width of 3.2 m, while the EasyBatch 140 comes pre-assembled on two trailers and can be set up without a crane. Its transport dimensions are 21 m long for the first trailer and 15.5 m long for the second, while both are 4.25 m high.

Mobility was also the key consideration for Astec when it was developing its new Nomad line of hot-mix asphalt plants, which have production ratings of 72 tonnes per hour, 117 tonnes per hour and 158 tonnes per hour. Astec claims that, with an experienced crew, Nomad plants can be erected in less than a day.

Astec has also introduced new technology in the form of a diagnostic tool known as The Source. This is a hand-held device that simulates most of the electrical signals coming into an asphalt plant control system. It is said to help simplify plant setup and troubleshooting.

Once asphalt is produced, storage can then become an issue. Asphalt Drum Mixers (ADM) has tried to offer as much flexibility as it can in this respect by introducing new stationary and self-erect asphalt storage silos that are compatible with both its own and competitor models of asphalt plants.

The storage silos receive freshly mixed asphalt from a conveyor and keep it at a constant temperature until it is discharged. The stationary and self-erect designs allow them to be used in various asphalt plant configurations, and multiple capacity options are available.

The capacity of ADM’s self-erect silos ranges from 30 to 75 tonnes, and stationary silo models hold between 100 and 300 tonnes of asphalt mix. All models are equipped with alarms to alert operators when asphalt levels are high, and they feature a fiberglass blanket insulation to provide heat retention while the mixture is stored. Optional oil or electric heating systems are available to ensure asphalt is kept at the desired temperature.

All silos can be equipped with low material alarms and LC1000 loadout computers, which work together with truck scales, weight batchers or reverse (negative) weigh systems. The LC1000 allows operators to access truck loading data, job files, silo inventory and more.

Concrete

On the concrete side there are new developments focussed on increasing the efficiency of mixing technology, and recycling is also a key issue affecting developments in this sector.
SBM, for instance, has concentrated on bespoke solutions for its customers, and developed a mobile concrete batching plant, the Euromix 400C, for Dutch contractor Van Gansewinkel.

The plant and has been designed to process waste materials into concrete – the contractor then stores this concrete mix on landfill sites. Due to local regulations, certain loose waste material cannot be deposited directly into landfill as it contains substances that could leach into ground water.

By mixing the waste material with cement and producing concrete, it binds the substance for long-term storage as landfill. The plant is required to work continuously with an output of over 400 tonnes per hour and comes with an independent generator.

SBM said the demands made on the control system could not be met by conventional devices, so it developed a microprocessor control system to control the plant by laptop and WLAN. This system meant that all data from the plant was immediately available for further electronic data processing, and allowed the concrete mixing plant to be supervised online.

To reduce service and maintenance works, a specially designed high-pressure cleaning system was also installed – reducing running operation costs, according to SBM.

Meanwhile, the new Rapidmix 400CW from Rapid International aims to offer higher production rates. It incorporates a 1200 mm belt conveyor between the aggregates hopper and the continuous mixing chamber, and offers full weighing options for all materials as well as automated record keeping.

The first customer for the Rapidmix 400CW in the US was Texas-based Rollcon. The new machine has been put to work on the latest phase of the Port of Houston development project, producing up to 400 tonnes of material per hour.

Rapid International is also reporting interest in its cement treated base (CTB) mixing technology – a strong, frost-resistant road base.
CTB is comprised of native soils, gravels or manufactured aggregates mixed with cement and water in either a continuous flow or batch-type mixing plant. The resulting material is said to provide a weather resistant base which gains strength with age.

Rapid International said CTB can also distribute loads over a wider area, reducing the stresses on the subgrade. It is typically used as a pavement base for roads, streets, car parks, airports, materials handling and storage areas.

Increasing the use of recycled pavement, and reducing the amount of energy needed to produce high quality asphalt and concrete will continue to be key focusses for manufacturers of mixing technology. It will be interesting to see how the latest materials shape equipment developments in the future.