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Mandelholz Dam - Stabilizing Sealing Measures with Polyurethane Resins

The Mandelholz Dam is a barrage system located near Wernigerode in the Harz mountains of Germany. In the past, it was used for process water and today serves for flood protection and also for the environmentally friendly generation of power.

One barrage lock, the so-called Mandelholz reservoir, is closed off by a 28 m high earth-fill dam with an integrated concrete inspection walkway, perpendicular to the dam. This walkway was partly made from badly compressed concrete. In the course of time, large and small leaks formed and endangered the walkway's stability. An extensive reconstruction considering the following boundary conditions was necessary in order to maintain this function:

• Sealing of the structure against penetrating water
• Stabilization of the porous concrete at the same time
• Completion of the task by late fall before the next snowmelt

The structural condition analysis clearly showed what reconstruction measures where required: closing and bonding of moist to wet, partly pressurized water-bearing leaks obtaining structural strength and filling of cavities at temperatures of up to +1 °C by means of injection.

A glance at part 2, tables 6.2 to 6.4, of Concrete Repair Guideline Rili SIB 2001 shows the specific application ranges and conditions for crack filling materials. According to this guideline, the reconstruction objectives and the actual conditions on site are incompatible. A reconstruction is simply not possible in case of a strict interpretation of the regulations. In simple terms, either stabilization obtaining structural strength of a wet environment or "only" "flexible" sealing and closing of cracks if these are wet. And the weather conditions highly unfavorable for such tasks have not even been accounted for.

These regulations obviously do not cover our objectives and the actual conditions, which is why a special solution is called for.

The European Directive DIN EN 1504-5 offers a good starting point. Especially in part 5, supplemented by several tests from other countries, virtually the entire test scope of Rili SIB has been incorporated. The description of the applications is perfectly analogous to the guideline, but only the defined performance matters, whereas the material type selected to achieve this performance is optional. DIN EN 1504-5 is mentioned in part B1, section "crack filling materials" of the German List of Building Regulations with reference to conformity assessment process 2+.

In accordance with DIN EN 1504-5, it is no problem at all to carry out structurally bonding injections using PU resins. And as a matter of facet, materials providing this optional choice are already available on the market.

This is exactly what happened as far as the inspection walkway of the Mandelholz Dam is concerned: the performance of stabilizing PU resin exceeded all expectations. Irrespective of weather and moisture conditions, WEBAC® 1660 turned out to be the ideal solution for closing all leaks and cavities obtaining structural strength. The inspection walkway is now perfectly stable and the condition of the Mandelholz Dam can be inspected at all times without getting wet feet.