New Sealing System for Steel Bridges

In the past, STRABAG used the ESHA-ISOTEX 2000 plus sealing system to seal steel bridges. It consists of a bituminous primer and a bituminous adhesive layer. Since this sealing system could no longer be used due to the manufacturer, there was a need to develop a new system.

For this purpose, suitable products were examined in cooperation with a supplier and STRABAG Sonderbau Essen: The aim is to develop a sealing system for steel bridges that meets the requirements and which, after being assessed by the Federal Highway Research Institute (BASt), can be registered in the ZTV ING Part 7 Section 4 for use on structures and components on federal traffic routes.

First, several variants of the primer and the adhesive were tested and optimised.

The respective layers (bituminous primer and bituminous adhesive layer) of the waterproofing system were applied according to TP-BEL-ST under defined climatic conditions on special steel plates, which show the cover plate of the building, and tested for corrosion, adhesion, stability under heat etc.

After a few laboratory tests, a test area was realised. The support for the test area installation consisted of:

• Investigation of the tear strength of the adhesive layer on steel
• Layer thickness measurement of the primer and the adhesive layer
• Assembly of the system on the steel plates for the laboratory tests
• Determination of the ring and ball softening point according to Wilhelmi

AuFurther optimisations of the materials could be derived from the knowledge gained up to that point. The STRABATAN S sealing system can be used for all load classes in accordance with the RStO.

The new waterproofing system STRABATAN S corresponds to variant 1 of type 2 with bitumen sealing system according to the ZTV-ING. The structure is as follows:

• Steel sheet, Sa 2½
• bituminous primer PRIMEX (approx. 150-300 mm)
• Adhesive layer compound ISOTEX (approx. 3 mm)
• Grit 1/3 (approx. 2 kg / m²)
• Mastic asphalt protective layer
• Mastic asphalt surface

In 2017 and 2018, the basic examination of the sealing system was carried out by the Stuttgart materials testing institute. The results show that the developed system meets the requirements of TL and ZTV-BEL-ST. The sealing system has been listed as STRABATAN S at BASt since 2018 and is therefore approved for use on federal trunk roads. This makes STRABAG one of only three providers of sealing systems for steel bridges approved in Germany.

With the new system, additional test areas are to be created in order to gain further experience on the durability of the sealing system under various boundary conditions such as location, structure, traffic loads, etc.