Paving block used against nitrogen oxides in Stuttgart

On the site of the former freight train station in Bad Cannstatt, Germany, a new 25-hectare residential and industrial estate, NeckarPark, is currently under construction. The site was acquired in 2000, when the region of Stuttgart had planned to apply for the Olympic Games in 2012. This site at that time had been earmarked for the erection of the Olympic Village. This opened up the new perspective for developing a variably used town quarter with a high quality of life, oriented in exemplary manner to energy utilization and environmental sustainability.

The energy concept for this project provides for a maximum of supply with locally available regenerative energy sources such as solar energy, geothermal energy and wastewater heat. The enhanced structural thermal insulation of the buildings – in addition to wastewater utilization via a local heating network with solar installations for power generation – comprehensively reduce energy consumption as compared to energy consumption of new buildings built to current standards. Another aim was to prevent local emission of pollutants, along with exemplary all-around implementation of environmental protection.

Pioneering rainwater management

Furthermore, the key element of planning for the site is pioneering rainwater management. Dipl.-Ing. Alfred Diem from the engineering firm diem.baker in Ditzingen, Germany, explains the background: the specifications were to retain at least 90 % of the total precipitation on the site in order to use it there, or to let it evaporate on the site. Only residual and/or emergency drainage of rainwater was to take place away from the site. “This would maintain the natural water cycle to as great an extent as possible and would protect the development site from excessive heat islands,” says Diem.

Water-permeable execution of the concrete block pavement

To meet these requirements in the course of surface stabilization, the planners decided on the use of two block-paving systems from the concrete plant Betonwerk Adolf Blatt, in Kirchheim on the Neckar River in Germany. The Cityblock system measuring 30 x 20 x 14 cm was used for the roads subjected to heavier traffic. On the side roads and on sidewalks, the permeable “Stuttgarter Sickerstein,” 20 x 20 x 10 cm in size, was used.

Alfred Diem explains the construction method: “The Cityblock paver system is really an entirely normal paver: the roadways become water-permeable only by the special construction method used. The joints are designed with a width of 8 mm and are filled with 1/3 of hard stone without lime content. For the bedding, we use the same material in 2/5 mm. The permeable Stuttgarter Sickerstein used on the sidewalks is made of lightweight aggregate concrete with open structure. Precipitation here seeps directly through the block.

The water seeps in both cases into the basecourse, which then acts as a rainwater retention basin and ensures that water infiltrates farther into the subgrade soil only after time delay. To ensure that both block systems function, the entire upper pavement structure is executed to be permeable to water.

Degradation of nitrogen oxides by titanium dioxide

The second special characteristic of the blocks used is their function to degrade nitrogen oxides. On this, Richard Beck, Project Supervisor of the company Blatt: “All the paving blocks manufactured for the NeckarPark are provided with a facing layer over the constituent titanium dioxide used. When light hits the pavement surfaces, a photocatalytic reaction of the blocks take place. In this way, the nitrogen oxides in the ambient air are degraded. This reaction is repeated any number of times, since the titanium dioxide does not consume itself.” The aggregate used in the concrete is the innovative concrete admixture Photoment from partners at Powerment GmbH & Co. KG, in Ettlingen, Germany. Independent analysis by the Technical University of Berlin has confirmed the effect. According to these results, one of the areas the size of a soccer field paved with these special blocks is able to degrade around 17 g of nitrogen oxides in one hour. The photocatalytic reaction has the additional effect that adhered matter, such as general pollution or moss growth, is underwashed by the water present, and is thereby prevented from accumulating. This not only has a positive effect on the appearance, but also eliminates the need for any cleaning.