CONCRETE CHIMNEY REPAIR WITH CARBON FIBER WRAP

A 250’-high concrete chimney was in need of extensive repairs to combat its structural deterioration which was causing safety concerns. Industrial Access proposed a comprehensive repair strategy that involved partial liner replacement and column reinforcement with a carbon fiber wrapping system. Services were provided to rehabilitate the structure to a safe and stable operating condition.

A 250’-high concrete chimney with brick liner in a cement plant had been determined to be in very poor condition. The uppermost 25’ was particularly structurally unsound with exposed rebar and bricks dislodging from the structure. Due to loose, unstable concrete and brickwork in upper elevations, the potential for falling object hazards was extremely high. The rest of the exterior column exhibited large cracking in certain areas with heavy oxidation on existing tension bands. Industrial Access (IA) was contracted to carry out a sophisticated rehabilitation strategy to restore the stack’s structural integrity, extend its lifespan, and ensure safety on site.

In order to make this scope of work possible, a motorized mast climbing work platform system was engineered and installed along the stack exterior. This access solution provided a full-height, 360-degree access to the stack column, allowing for a safe and efficient work performance. In some cases, like the liner interior washdown, expert rope access techniques were utilized instead.

IA mobilized during a pre-outage window on the site. Once set, IA started off by addressing the heavy deterioration of the very top of the chimney. The top six courses of liner brickwork were unstable and degraded beyond repair. Therefore, the crew carefully demolished the uppermost liner section, then rebuilt it anew to the structure’s designed height. The top section of the exterior column windscreen was also rebuilt to the designed height. The existing steel cap was reinstalled using new connection hardware.

IA crew continued to repair cracks on the exterior cement stack column. The top 25’ displayed the deepest cracks with exposed rebar and missing cement, so those had to be properly treated and filled with quality cementitious material. Smaller cracks were also cleaned and sealed using silicone caulk. It was important to thoroughly repair the top section to create a proper surface for the carbon fiber wrap installation. The carbon composite reinforcement system was then wrapped around the top 25’ of chimney exterior and sealed with protective coatings. This system is a single-layer, lightweight, flexible, corrosion-resistant reinforcement solution with low thermal expansion, providing strength reinforcement equivalent to 60 rebar at 12-inch spacing for hoop confinement. This is a great solution for improving the structural integrity of industrial structures.

To further strengthen the stability of the stack, nine new horizontal stainless steel tension bands were installed between the 230’ and 100’ el. levels. Each band was constructed using a 3”-wide stainless steel flat bar. The six existing bands were tool-cleaned and appropriately coated. In addition, the lower section of the brick liner had a broken missing band, which IA replaced and coated.

IA crew conducted a thorough washdown of the outer shell of the chimney as well as the liner interior. Hydro-blasting effectively removed dirt, dust, and loose debris from the surface, ensuring the stack would be ready for coating, while the accumulated fly ash in the interior was cleaned off and its accumulated debris removed from the ground floor of the liner.

A multi-step protective coating system was applied to the entire height of the stack exterior column. The chosen high-quality primer and paints will provide elastomeric protection against environmental factors. Lastly, to finish off the repairs, IA installed and coated a new platform and ladder with a fall protection system, while the top of the structure received a lightning protection system (LPS) replacement.

Stack repair and reinforcement services were completed successfully and on-time. This rehabilitation strategy was carried out to save the chimney from the risk of failure, ensure safety on site, return the stack to operation, and allow the client more time to develop further maintenance plans for this structure. The paramount benefit of IA’s work lies in the restoration of structural integrity and the long-term sustainability of the chimney, ensuring its continued safe and reliable performance.