When the pulping process at a paper company that manufactures 345,000 metric tons of newsprint paper yearly for the United States and Europe encounters problems, an immediate solution must be found. For Resolute Forest Products, Inc. of Clermont, Quebec, Canada, that meant fixing their 50,000 square foot (4,645 m²) concrete clarifier, which had been damaged by mild chemical attack and abrasion from their pulping process. They needed to find a solution that would rehabilitate and protect their clarifier, so they contacted MBI Corexcel, a local corrosion-resistant specialized contractor, for assistance.
An added challenge: The solution required coordination of the facility, contractor, and coatings manufacturer so that project completion would not disrupt operation and result in minimum downtime during construction.
An Engineered Solution
To start, MBI Corexcel used a 20-person team that worked over two10-hour shifts. Upon arriving at the jobsite, the crew started in on 100 square foot (9 m²) areas of both the wall and floor. They prepared each area’s surface, applied the epoxy mortar repair system, and sprayed on the fiber reinforced system.
Working in small test sections permitted the contractor’s employees to familiarize themselves with the materials and any idiosyncrasies particular to spraying fiber-filled material through a 65:1 airless pump. Also, it would enable the coatings manufacturer, Sauereisen, to approve acceptable surface preparation methods and make recommendations for any improvements they thought would assist in making the project more successful. Furthermore, once the 10-by-10-foot areas (3 m by 3 m) were completed, all stakeholders were able to agree upon how the final product would appear throughout the entire 50,000 square feet (4,645 m²) of surface area. And finally, the test gave the crew a comparison to use as a reference when the coatings experts departed from the jobsite.
Walls and Weirs
On all vertical surfaces, MBI Corexcel’s five-person coatings crew used high-pressure water blasting for the surface preparation. Wearing dust masks, protective face shields, and protective clothing, they worked in two shifts while others prepared the floors and adjacent areas to be coated over the next two days.
Since Resolute Forest Products had concerns about contamination of the manufacturing process, the crew was recommended to use water blasting instead of sand blasting as the means of surface preparation. They left the vertical wall areas to dry overnight and then came in the next day to repair any pitted areas with a 100-percent solids epoxy mortar by Solhydroc called Solhydweld Thixo. The epoxy repair mortar is specifically formulated to bond to rough concrete surfaces with the ability to fill imperfections and bug holes without sagging or outgassing. The crew applied it anywhere from 1/32" to ½" (0.08–1.3 cm) thickness depending upon the condition of the concrete; greater surface imperfections required greater amounts of material.
The crew used a rubber squeegee to hand-trowel the mortar. This step not only refinished the concrete surface to an acceptable surface for application of the lining, but it also repaired the concrete, offering a 72-hour recoat time for coordination of the lining and eliminating the need for a primer. Thus, by using this epoxy mortar, both time and materials were reduced without affecting product performance.
The 72 hour re-coat time permitted Sauereisen and the crew the required time to mobilize and conduct training with the airless spray equipment. The 10-by-10-foot (3 m by 3 m) wall area was sprayed with the specified 40-mil (1,016 microns) thickness of Sauereisen Fibercrete Epoxy Novolak 218. This liner is a 100-percent solids system that incorporates an inter-locking fiber matrix to provide outstanding flexural and tensile strengths. The resin/hardener system also enhances the material to protect against sliding abrasion from particulate solids in gaseous or liquid environments, such as at Resolute Forest Products. To get the correct thickness of the liner, the crew used a standard mil thickness painter’s gauge to measure areas during application and calculate material usage needed to cover the area.
Laying the Ground Work
While one team attacked the clarifier wall, another team worked on the floors, which provided even more of a unique challenge than the vertical surfaces. Not only was there deteriorated concrete, but also, prior to coating, laitance had to be removed on the floors. There were also many deep gouges and depressions in the concrete floor that were caused by abrasions from solids and damage from a sludge-removal clarifier rake arm that had to be repaired.
Unfortunately, for the floor portion of this job, the crew could not utilize high pressure water blast due to ongoing work on the walls and complete work in the allotted construction period. That meant that the floor areas would have to be prepared with a scabbler machine followed by a walk-behind sandblaster. This process, which would not interfere with or contaminate other procedures that were ongoing in the clarifier at the time, enabled surface preparation on both the walls and the floor areas to be done concurrently. This in turn enabled the crew to meet project demands and complete other ongoing scheduled work. Working in 10-hour shifts per day in 2 shifts on a 7-day schedule enabled the crew to complete the total 50,000-square-foot (4,645 m²) rehabilitation in the allotted time.
Once the floor was prepped, the crew needed to start applying the basecoat. Due to the expanse of the floor area, the degree of established slopes, and the amount of damage in some areas deeper than ½-to-1 inch (1–3 cm), a pour and spread epoxy repair material was selected to rehabilitate and resurface the floors. The Sauereisen Epoxy Monolithic Pour and Spread broadcast repair system provided a more durable basecoat and a sandpaper-like surface profile that was recommended by the manufacturer to ensure both adhesion and minimal outgassing of the epoxy lining system that would follow.
Working on one side of the clarifier at a time, the crew squeegeed the epoxy system and then broadcast sand to excess. This layer cured overnight, and then the crew swept and collected the excess sand from the surface, which was recycled and used on the adjacent area on the other side of the rake arms.
Rotating the clarifier allowed for continuous application and access to the entire surface area, and it also offered a place to rest the rake arms once the coating had dried. Using a Graco 65:1 Airless sprayer, the crew applied 40 mils (1,016 microns) to the entire floor with the same fiber-reinforced lining that was used on the walls.
At the end of the project, with newly coated walls and floors, Resolute Forest Products can go back to its full production of manufacturing newspaper print. For MBI Corexcel, which serves the pulp and paper companies, completing a project like this is an everyday occurrence, but for the folks at Resolute Forest Products, having a fully operational facility makes their day-to-day duties much easier to handle.
About The Author:
Gregory M. Severyn is a 27-year veteran of Sauereisen. He has been instrumental in collaborating on corrosion control projects throughout the world as well as expanding Sauereisen’s market share of sulfur and specialty ceramic cements. For more information, contact: firstname.lastname@example.org, (412) 963-0303 ext. 229.