Bacteria makes concrete of Rijen tunnel ‘self-healing’

Self-healing concrete has been installed in the 25-meter-long wall of the tunnel (Photo: ProRail)

July 16, 2024 – The Vijf Eikentunnel in Rijen has a very special wall: it repairs itself. Or actually, it contains a bacterium that fills cracks as soon as they occur. This makes the railway underpass the first infrastructural project in which self-healing concrete has been combined with the reduction of horizontal reinforcement. The tunnel is produced more sustainably and is expected to last longer.

Contractor Heijmans Infra has installed self-healing concrete in the 25-meter-long wall of the tunnel. This concrete can heal itself when cracks appear. A special additive has been added, consisting of a combination of bacterial spores and nutrients. This acts, as it were, like a “concrete medicine.” For the tunnel wall, a mix of six kilos of bacterial spores and nutrients was added to each cubic meter of concrete.
When it comes into contact with moisture and oxygen through a crack, the bacteria in the concrete become active. The bacteria fill the cracks with a sealing limestone layer.
Self-healing concrete is expected to be more durable than traditional concrete because the bacterial spores biologically repair cracks. Heijmans and TU Delft expect this application to have a beneficial effect on the sustainability and lifespan of the tunnel. Self-healing concrete also requires approximately half as much horizontal reinforcing steel. That steel makes the concrete stronger, but also contributes significantly to the CO2 emissions of concrete: approximately 25 percent. Less reinforcing steel therefore means less CO2 emissions.
The railway underpass in Rijen is a pilot project in which ProRail, the province of North Brabant, and Heijmans Infra are working together to test the waterproofness of self-healing concrete in practice.

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