When ultraviolet light hits titanium dioxide, a cleaning effect of the air occurs through photocatalysis. The process has been known for the last 30 years. The ultraviolet light activates the titanium dioxide physically, and oxygen and water vapour in the air are transformed to free radicals. These molecules are very reactive and attach to air pollutions, especially nitrogen oxides (NOx) and organic particles, and convert or decompose them.
In recent years the RISE institute The Swedish Cement and Concrete Research Institute (CBI) together with Cementa and Finnish company Kemira have investigated the possibilities to use titanium dioxide in concrete. Tests also have been conducted to study the mixture’s effect on the concrete’s normal characteristics, such as durability and frost.
Today, there are several products on the market that use photocatalytical concrete with titanium dioxide. One example is bright façade elements made of white concrete, were the cleaning principle of photocatalytical concrete is applied. In pavers, the principle of reducing air pollutions is used.
With 21,500 vehicles passing by every day, Amiralsgatan has the highest content of NOx in Malmö. In 2009, 80 metres of one side of the street was remade, using pavement slabs prepared with titanium dioxide. The goal was to find out if it was possible to improve the air quality.
The results showed a decrease of the nitrogen oxides of more than 5 per cent on a daily basis, corresponding to 2,000 vehicles per day. The arrangements were not sufficient to reach the environmental quality norm. In addition to NOx, high traffic intensity also involves other harmful effects: noise, climate gases and small particles.
Two years ago, Cementa launched the company’s first product based on titanium dioxide, TiOmix. During 2010, CBI studied how the special mixture affects the concrete’s physical properties. The results showed that the mixture does not change the concrete’s physical attributes.
"The study is included in a project with the goal to plan and conduct new field studies in order to further investigate the technique’s effect on air pollution in cities", says Lars Kraft at CBI.