What is cheap asphalt or concrete

Concrete would be an alternative to asphalt

Vienna - Concrete is a constant in road construction. However, this applies mainly to the high-level road network, i.e. motorways and expressways, as well as to heavily used areas such as intersections or roundabouts.

The material has what experts call high resistance to deformation, there is little rolling resistance, and old concrete is recyclable. On country roads and secondary roads, however, asphalt is usually paved, which, although it cannot keep up with the performance characteristics of concrete, is cheaper.

Viennese researchers from Smart Minerals have now tested a process that could make concrete interesting for this road network as well. Smart Minerals is a subsidiary of the Association of the Austrian Cement Industry (VÖZ) and the Vienna University of Technology.

The project was carried out in cooperation with the research company Eco Roads, whose goal is the development of sustainable technologies in road construction.

"Earth-moist" material

The suitability of so-called rolled concrete was tested on a test track. It is very dry with a maximum of 40 percent water content, experts call it "earth-moist". Rolled concrete is often used in the USA, but it is still exotic in Central Europe.

"It's not as closed as you would otherwise know from concrete," says Martin Peyerl, head of research at Smart Minerals. "It almost trickles like sand, and you need a lot of compression energy to bring it into a closed structure."

The paving is not done with conventional concrete pavers, which are designed for fixed street widths, but with a special vehicle. The Volvo company provided a tracked paver for the project.

This is actually an asphalt paver equipped with a double tamper screed, a high-performance compactor that "tampers" the concrete 1,600 times per minute, bringing it into position. The paving speed is 1.8 meters per minute. This already creates a closed structure.

The 20 centimeter thick concrete is already so strong that it can be subsequently compacted with a conventional road roller. Immediately afterwards, the rolled concrete ceiling can be walked on, after a day it can be driven on.

Testing under real conditions

The test route was a 500-meter-long private road in southern Styria, which serves as an access to a recycling plant. Since there is often heavy traffic here, the load-bearing capacity of the concrete ceiling could be tested under real conditions.

The incline of up to seven percent and frequent bends also simulate typical country road conditions. The researchers are currently regularly taking drill cores from the route in order to check the behavior of the new road surface under load.

Rapid usability, flexible installation technology, but also the longevity of rolled concrete speak for the building material also on country roads, according to Smart Minerals.

Concrete ceilings do not tend to form ruts, and the low rolling resistance also reduces fuel consumption. Since concrete is lighter than asphalt, it also heats up less in summer.

However, whether the installation costs of rolled concrete can compete with those of asphalt is not so easy to answer, says Peyerl: "The costs always depend on the quantity. But with rolled concrete we are not very far from asphalt." In any case, there are already concrete plans to build a test route in the public road network. (Raimund Lang, 11.11.2019)