Albtal dam

Repair of the Alb dam in St. Blasien with sprayed concrete for the existing concrete class A2*)
The small river Alb, which gives the romantic valley its name, has its source on the Feldberg, the highest point in the Black Forest, and flows into the Rhine at Albbruck.

In the valley of the Alb south-east of St. Blasien, the Alb Dam dams up the Alb reservoir. The Alb dam is part of the Häusern upper stage of the Schluchseewerk AG pumped storage network. The concrete structure was completed in 1941 and is a 28 metre high gravity dam with a crown length of 152 metres.

The crown of the dam is suitable for foot traffic and is also used by the operator.

At the beginning of the 1980s, the crown of the structure was renovated as part of major work, with a concrete repair and then a fine mineral levelling with a final coating.
Regular inspections of the structure revealed cracks with widths of up to 0.5 millimetres, localised and extensive cavities and spalling. A continuous horizontal crack in the area of the parapet at the transition from the old concrete to the concrete renewed in the 1980s was visible in a strip around 20 centimetres wide on the inside and outside.

For the work now being carried out on the wall and its crown, it was important to examine the existing existing concrete classes*) in detail and to select suitable products specifically for the existing concrete classes*) found in accordance with the test results of the substrate.

The concrete wall from 1941 was categorised as existing concrete class A2*). The concrete used for the renovation work in the 1980s corresponded to existing concrete class A4*). The client and application team opted for StoCrete TS 126 dry shotcrete and StoCrete TG 203, which can be applied by hand.

StoCrete TS 126 is a product specially developed for the repair of substrate concretes in existing concrete class A2*). StoCrete TG 203 is ideally suited for substrate concretes of the existing concrete class A4*).

During application, the old repair materials are first professionally removed from the surface and the substrate concrete is prepared on the vertical wall surfaces and the top view of the wall crown. StoCrete TS 126 was then applied to the vertical parapet surfaces using the thin-phase conveying method. The "repair principle W" was fully implemented with the subsequent flat bridging of cracks coating.

The top of the wall was reprofiling with the suitable concrete replacement system StoCrete TG 203, followed by coating with a special surface protection system for permanent wet loading. The subsequent coating with a special surface protection system for permanent wet loading also fully implemented the W repair principle here.

Following substrate preparation, a highly resistant, slip-resistant and bridging-of-cracks coating system from the StoCretec product range was applied to the floor area of the dam crest that was walked and driven on. No concrete repair was required here.

Now nature lovers can once again safely enjoy their hiking routes around the Albstausee reservoir. The Alb and the Alb valley - a dream landscape for young and old.





*)Existing concrete: In its Technical Rule on the repair of concrete structures (German original: Technische Regel „Instandhaltung von Betonbauwerken“, version: May 2020), the Deutsches Institut für Bautechnik (German institute for structural engineering) has defined 5 categories of existing concrete (A1 to A5). The term ‘existing concrete’ refers to concrete that has already been installed in buildings and structures as opposed to concrete material yet to be installed. In German, these categories are called ‘Altbetonklassen’ which translates to ‘classes of existing concrete’. Existing concrete is categorised according to its compressive strength and surface tensile strength. Before repairing existing concrete, its ‘Altbetonklasse’ needs to be determined in order to select a suitable mortar or concrete.