BASt-Forschungsvorhaben "EINFACH" gestartet

So far, road tunnels in Germany are typically constructed as a double-shell system comprising a temporary outer lining made of reinforced sprayed concrete and an inner lining of in-situ reinforced concrete. Sealing is usually provided either by a continuous plastic waterproofing membrane (KDB) or by designing the structure as water-retaining concrete (WU structure). While this construction method is fundamentally robust, it unfortunately has serious disadvantages: above all, the high consumption of raw materials and the poor CO₂ footprint make a significantly leaner construction method necessary in light of climate change. This is precisely what “EINFACH” aims to achieve.

The first step is to develop a CO₂-optimised sprayed concrete mix that combines clinker-reduced cements with suitable mineral additives. This sprayed concrete is intended to contain both steel fibres and polypropylene fibres to ensure load-bearing capacity and fire resistance.

A tricky challenge lies in ensuring sprayability, as steel fibre concretes – especially when PP fibres are added – exhibit increased stiffness at the same w/c ratio. Rheology, layer stability and early strength therefore need to be optimised in laboratory tests to guarantee reliable application.

The project partners also aim to demonstrate in large-scale trials that a single-shell lining constructed from this sprayed concrete can achieve the water tightness required for a WU structure without the need for an additional waterproofing membrane. Water tightness and bond behaviour between layers are tested in STUVA’s fully equipped experimental facilities.

The main objective of “EINFACH” is to demonstrate clear ecological and economic advantages of the single-shell fibre-sprayed concrete lining compared with conventional double-shell linings. To this end, a life cycle assessment (LCA) is being carried out, recording in particular the greenhouse gas emissions (GWP) and material flows over the entire life cycle. This will create the basis for establishing the new construction method as a regular, plannable and approvable alternative in tunnel construction shortly after the project ends.

“EINFACH” (FE No. 88.0241/2025/AV01) is funded under the “Innovationsprogramm Straße” support scheme by the Federal Highway Research Institute (BASt) on behalf of the Federal Ministry of Transport.