High pressure water jet technology for bridge renovation
There are 39,000 bridges on motorways and major roads in Germany. The majority of these are more than 40 years old. Apart from the type and age-related deficiencies, for the Federal Ministry of Transport and Digital Infrastructure (BMVI), the underlying problem is that the bridges are no longer able to cope with the sheer weight of traffic. For this reason, the focus is on bridge renovation.
In September 2015, the BMVI announced that it was increasing the budget for 2016 to two billion euros. The renovation challenge: 70% of all bridges are made of prestressed concrete, i.e. bridges of reinforced concrete with an additional longitudinal brace on the bridge girders. Once the steel reinforcement begins to corrode, it attacks the concrete. These areas must be exposed, derusted, protected against renewed corrosion and resealed. For local removal of concrete, it is important to work as precisely as possible to prevent vibrations liable to cause further damage to the surrounding structure. In such cases, high pressure water jet technology is the method of choice as it enables work to be carried out quickly and safely.
Whether extensive concrete removal, stripping of reinforced concrete or heavily reinforced concrete floors: high pressure water jetting today is the preferred working method for diverse applications in construction. In the meantime, high pressure water jetting is recommended or partly prescribed in virtually all relevant building regulations and guidelines. High pressure water jet technology is currently the preferred method also in bridge renovation. Since it is possible to work very precisely, components or joints cannot be damaged or loosened. In contrast to mechanical solutions, e.g. pneumatic hammer, no shocks and vibrations are produced, so that cracks in the remaining concrete are avoided. The steel reinforcement remains intact. high pressure water jetting is also safe to use as no gases, vapours or slurries are produced.
The work result largely depends on two factors. On the one hand, it is important for removal to know the main parameters of the concrete. This includes reinforcements in the surface, age, carbonisation, chloride corrosion and poor surface stability of the concrete. On the other hand, it is important to select the matching mechanical power. Decisive here are operating pressure and volume flow of the high-pressure unit as well as the water tool. Units with an operating pressure of 1000 to 3000 bar are used for concrete removal in bridge renovation. Residual coatings, cement slurries or concrete layers with low strength can be removed up to 1000 bar. From operating pressures of about 1500 bar, deep and extensive removal is possible.
Hand-held water tools have shown to be effective for necessary selective renovation measures. The operator must ensure that a recoil force of 150 Newton, respectively 250 Newton when working with body support, is not exceeded. As an alternative to hand-held solutions, automated variants are used to an increasing extent. This is interesting in particular for the exposure of large areas and/or where the permissible recoil force for the operator is exceeded The use of robots in combination with suitable water tools ensures safe and efficient working. Very good results are achieved at a relatively low operating pressure (about 1000 bar) in combination with high flow rates (200 l/min) using robots. These solutions offer tremendous time-saving potential: projects that hitherto took weeks are now completed in several days.
Further information on product and application solutions from WOMA are available here.
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