All the work on the stack of the power plant operated by E.ON was brought to a close a few weeks ago, with the concrete refurbishers of ThyssenKrupp Xervon finally abandoning their workplace at dizzy heights. During the project, a six- to eight-strong rehabilitation team with their materials and equipment had conducted a preliminary inspection at heights of up to 240 meters and carried out chronologically all the necessary rehabilitation work on the stack. Their workplace consisted of mobile work platforms that their scaffold erection colleagues had constructed specifically for this rehabilitation job.

Two-fold protective coating

To detect all the damage, the entire surface of the concrete and brick giant had to be inspected. It turned out that in places the 40 centimeter thick wall was damaged all the way through. These areas had to be shuttered and sealed with mortar. But first all the refurbishers treated the brickwork forming the top 30 meters of the stack, which was cleaned and then "hydrophobed", i.e. given a water-repellent coating. After this, they addressed themselves to the much more labor-intensive concrete refurbishment. First, all the damaged areas were chiseled out and the entire concrete surface was cleaned with high-pressure water (up to 1200 bar) for substrate pretreatment. All the exposed reinforcement bars were then blasted with an abrasive to an SA 2.5 finish. After the application of an adhesion promoter, the concrete surface was reprofiled with PCC mortar and a pure acrylate filler. Finally, the stack was given a two-fold acrylate-based protective coating.

Elevator system adapted to the structure

It was not only the men themselves who had to be lifted safely, but also their equipment consisting among other things of grouting pumps, hoses, worm pumps and airless spraying equipment. The chief challenge of the project was that the tower tapers upward, slimming down from a 64 meter circumference at the base to 34 meters at a height of 160 meters, beyond which the sides are parallel. For this purpose, the scaffold erectors had to create an efficient construction adapted to the structure's shape. The outcome was four separately running, electrically driven elevators, each with their own work platform. Each of the between 7 and 9 meter long aluminum platforms had angle sections at either end permitting perfect adaptation to the stack's curvature. The platforms were attached to a rope suspension system fastened to an existing ring-shaped platform at the top of the stack. The platforms were rehung from here so that the larger surface at the base of the stack could also be treated.

However straightforward this may sound in this summary, it called for disciplined teamwork between the scaffold erectors and their colleagues specializing in building maintenance. "Only with close coordination were we able to reconcile the needs of the refurbishers with scaffolding feasibility and arrive at a sensible and cost-effective solution," says a satisfied Project Manager Daniel Debbelt. "And as an industrial multi-trade service provider, we were able to deliver all the required work from a single source. This builds confidence and yields cost-effective solutions."