Staff Writer: Asphalt Technology & Recycling Innovations

Plants for mixing asphalt are becoming more sophisticated than ever as users look for ecological and technological benefits. Patrick Smith reports.

New demands from operators mean that asphalt plant manufacturers have had to come up with new solutions.

This has been brought about because of a greater emphasis on higher productivity with lower costs; warm asphalt mixes; an increasing awareness of environmental issues, and a rise in the use of recycled material. One innovative concept, Con Asphalt, is being put forward by Astec, which points out that whether a project involves work on an airport where the runway base is asphalt and the top paving surface is concrete or work on a project where the base is roller-compacted concrete and the driving surface is asphalt, a contractor has to produce more than one material to meet the project specifications.

Under conventional means, a contractor would need two different types of production plants to produce the two different materials needed for the project but the aim of Con Asphalt is to change that.

Where the jobsite is not in delivery range of a stationary facility such as an asphalt or concrete plant, being able to produce all the materials for a project would be advantageous for the contractor who would be able to bid for both parts of the contract and self-perform, realising a stronger financial outcome of the job.

In order to provide production of mixed materials, Astec took a closer look at the structural components of aggregate with a binder, such as asphalt cement for making hot-mix asphalt (HMA) or Portland cement for making concrete, and found that both materials have a similar constituent make-up: the variable is the addition of either asphalt cement or Portland cement (with water or other additives) to create the desired mix.

Most concrete for road building is produced in a plant with a mixer, either a tilt-drum mixer or a twin-shaft mixer. Every asphalt and concrete plant has components that help proportion the materials, including the sand.

Astec said, “The Con Asphalt plant would manage the production of both asphalt and concrete with the same group of aggregate bins. The contractor would then improve the profitability and consistency of the materials by using fractioned aggregates for concrete or asphalt in the multi-bin aggregate management system. The single plant would have the mechanical devices to make either product simply by engaging the right controls to move the aggregates to the appropriate mixer.”

Turkish company E-MAK, a division of the Simge Group, which recently agreed to export a complete asphalt production plant to a German company for the first time, is also offering innovation with its RATech system. It is designed to boost the efficiency of using recycled asphalt pavement (RAP) in asphalt production, and with no direct heating of the recycled materials, the binder is not damaged in the process thus improving the quality of the output material.

Another key feature of the system is the triangular profile dryer where the RAP is heated indirectly and which is conveyed cold in a vertical elevator to prevent sticking and build-ups. Hot material in the system flows from top to bottom, and heat loss is prevented because the RAP is stored in a heated bin.

The RATech can also be incorporated with conventional asphalt batching plants to produce the higher quality binder and wearing course grades of asphalt.

Another manufacturer, Bernardi Impianti International of Italy claims its Red Dryer system aids high quality output and makes major savings in running costs. Designed to deal with up to 40% RAP as well as fresh aggregates, the equipment features twin drives and twin geared motors, and in use the operator sets the mix levels and a feeder system then transfers the bitumen and aggregates with RAP to the mixer in the quantities required.

Mixing is carried out in the chamber at optimum temperatures to ensure a homogenous product. “The bitumen in the RAP does not burn as the flame does not touch the material,” explained the company.

The new dryer ensures an effective coating…