Der Streuer ist am Fertiger direkt hinter der Einbaubohle angebracht.

A Street with a New Function

Sustainable transportation infrastructures at STRABAG begin with the pavement recipe. The company has developed a unique system in asphalt construction that makes cleaner air and less noise on the road.

Martin Muschalla

Project Manager, TPA GmbH

Recipe for a road with a new, additional function. The ingredients:

Quartz powder and quartz sand

Both aggregates are used to increase the strength of concrete. Quartz sand forms the bulk of the concrete, while quartz powder acts as a filler. The substances are among the main components of the granulate.

Titanium dioxide

Under UV light, TiO₂ acts as a catalyst to accelerate the conversion of nitrogen oxides into harmless, water-soluble nitrates. The TiO₂ particles are not consumed during the reaction.

Cement

Cement serves as a binder and is the main component of the innovative asphalt. It produces strength-forming CSH phases through the hydration of cement clinker (e.g., C3S, C2S) with tempering water.

The sustainable high-tech ClAir® asphalt has a pollutant- and noise-reducing function. The synthetic material is made of crushed ultra-high-performance concrete (UHPC) mixed with titanium dioxide. The titanium dioxide is used for photocatalysis.

Different batches of the innovative granulate are provided for testing by the manufacturer FC Nüdling. The material is stored in plastic bags.

In five years of research, many material studies were conducted with various granulates and asphalt surfaces. The samples are stored in the laboratory at FC Nüdling.

The laboratory also investigates how the material reacts under UV light. Titanium dioxide acts as a catalyst and accelerates the conversion of air pollutants such as nitrogen oxide into harmless nitrates.

The results of measurements under UV radiation are evaluated in the laboratory.

The aggregate is incorporated directly into the asphalt, giving it a lighter surface.

Titanium dioxide is an important component of the synthetic aggregate. It is a naturally occurring material that is mined or produced by chemical processes. With its ultra-white colour, the ability to diffuse light and its UV resistance, TiO2 is a common ingredient in paints, foods and cosmetics.

Quartz sand forms the bulk of the concrete in the granulate.

Cement is an important binder in the aggregate and produces strength-forming CSH phases through the hydration of cement clinker with tempering water. It is a main component of the material.

Quartz powder and quartz sand are strength-forming aggregates. The quartz powder shown here is a filler. Like quartz sand, the substance is a main component of the granulate.

The new road surface being tested: the ClAir® asphalt is exposed to air pollutants while the conversion of nitrogen oxides into harmless nitrates is measured. The results of two stretches of road were compared, one with and one without ClAir® asphalt.

The synthetic aggregate for ClAir^® Asphalt consists of crushed ultra-high-performance concrete (UHPC) mixed with titanium dioxide and other materials. The raw UHPC has a TiO₂ content of about five percent. For the aggregate, the UHPC is crushed to a 1/3 mm grain size (TiO₂ content <1%). It can be used for all load classes. In the road paving process, about one kilogramme of the granulate is sprinkled directly into the hot asphalt per one square metre of road. Under UV light, the material accelerates the conversion of air pollutants such as nitrogen oxides into harmless nitrates. It also reduces the rolling noise of vehicles travelling on the road.

In this project, STRABAG not only developed the recipe and the installation process, but also optimised the machine and processing technology as well as the sensors for monitoring the temperature and distribution of the mix. The project was managed by PSS in Bad Hersfeld.

Here you can see how the new building material and the paving technique are tested in a construction project (and on a test stretch) on the Federal Highway 1 in Geltow near Potsdam.

Facts and figures

Up to 26 %

reduction of nitrogen oxide concentrations in the air as shown by field trials.

6,500 m² ClAir^® Asphalt

were installed during the field trial in Geltow on a single day.

ClAir® (Clean Air) Asphalt

was developed as part of the NaHiTAs sustainable high-tech asphalt research project funded by the German federal government with participation from the STRABAG competence centre TPA together with renowned partners from science and industry.

As part of the renovation work on the federal highway B1, ClAir® Asphalt will be installed in Geltow, Brandenburg. On the demonstration track, the reduction of nitrogen oxide is tested by the photocatalytic properties of the asphalt. The residents will later benefit from the noise-reducing effect of the pavement.

The aggregate is ready and waiting in big white sacks on the roadside. Since the TiO2 layer is only activated in contact with UV radiation, the paving material must be brought directly onto the road surface.

Martin Muschalla, Project Manager at TPA, explains the installation of the sustainable ClAir® asphalt to the visitors in attendance.

Martin Muschalla describes the innovative installation method with the specially developed “innovation bunker“.

Sebastian Czaja (right) follows the installation of the demonstration track in Geltow. The Project Engineer has accompanied the research and implementation process right from the start.

Asphalt paving on the B1 in Geltow near Potsdam: a team of Road Builders, Engineers and Project Managers is bringing the innovative asphalt onto the road.

The “innovation bunker“ consists of two components: the asphalt bunker is filled with hot asphalt, after which the asphalt feed is briefly interrupted and the bunker is loaded with aggregate.

The paver-mounted spreader allows the direct incorporation of the aggregate into the asphalt surface course and ensures a uniform and needs-oriented spreading pattern.

The Dynapac DF 145 – the research paver is used for the development projects. The machine was slightly modified for the installation of the paver-mounted spreader, the innovation bunker, the conveyor belt and the electronic coupling between paver and spreader.

The spreader is mounted to the paver directly behind the screed. Through an electrical coupling, the spreader adapts to the speed of the paver. As a result, the spread rate is kept even throughout the installation process.

The innovaton bunker consists of an asphalt and an aggregate bunker and is equipped with sensors for monitoring the temperature and distribution of the mix.

Road rollers are used to compact the asphalt and aggregate.

Only a small amount of the aggregate is needed for full-surface coverage – about 1.3 kg/m².

The sensors in the innovation bunker measure the level and temperature of the asphalt and aggregate. If a value shows irregularities, it can react quickly.

Installation of the road surface

1. The paver-mounted spreader

The spreader is mounted to the paver directly behind the screed. Through an electrical coupling, the spreader adapts to the speed of the paver, keeping the spread rate even during installation. Only a small amount of the aggregate is necessary for full-surface coverage – about 1.3 kg/m².

The spreading width is between 2.5 and 5 m; with attachments, the paver-mounted spreader can be extended up to 8 m. The spread rate is 300 to 3,000 grams per square metre.

2. The innovation bunker

The charging concept fills the paver-mounted spreader continuously with the aggregate. The innovation hopper consists of an asphalt bunker and an aggregate bunker. It is also equipped with temperature and level sensors. A hydraulic flap on the aggregate bunker allows for a separate filling of asphalt mix and aggregate. The aggregate is transported by means of a conveyor belt to the spreader behind the screed. The asphalt bunker holds about 27 tonnes of material. The capacity of the aggregate bunker is up to 2 tonnes.