Covering For Tank Heads On STW Gersthofen
The STW Gersthofen is sized for 45.000 PE and has two secondary clarifcation tanks. Both tanks have a diameter of 26 m and are equipped with a solid-wall bridge scraper running with a velocity of abt. 3 cm/sec. Permanent fulling by the scraper wheels and weather influence destroyed the concrete head in the course of time. Coating with aritficial resin mortar had brought only temporary success and became defective already some years later. To achieve a lasting solution, the municipality of Gersthofen decided to refurbish the concrete head completely and protect it with a stainless steel covering.
At first, the old damaged coating had to be removed with high pressure and sandblast machines to obtain a surface resistance of 1.5 N/mm.
During leveling after removal of the old coating it was noticed that their was a difference in height of ± 2 cm so that the concrete head needed to be reconstructed.
Auxiliary forms were at first fitted to the inside and outside wall and were leveled.
Prior to applying the coating, the heating strips were screwed onto the concrete head inside of copper ducts to allow for replacement of the heating strips.
The coating of artificial resin mortar was applied in two working steps.
Prior to hardening of the second layer a wet/wet method was applied to paste on the individual stainless steel segments, then they were flexibly mounted laterally.
By equalizing the differences in height the loads on the scraper's central bearing were reduced and thus its lifespan considerably increased. The new stainless steel covering with heating guarantees now trouble-free operation all year long.
by Stefan Wittl