BALTIMORE, MD (Nov. 2, 2006) – Structural Preservation Systems (SPS) -- the nation’s leading specialty-contracting firm focusing on the repair, protection and strengthening of structures -- recently received three project awards from the International Concrete Repair Institute (ICRI).
ICRI, in its 14th year, sponsors the annual awards program to recognize outstanding projects in the concrete repair industry. As the only organization dedicated to improving the quality of repair, restoration and protection of concrete and other structures, ICRI receives submittals for the competition from around the world. Winning projects are honored each year at the annual ICRI Awards Dinner and Reception held during the ICRI Fall Convention.
“The ICRI award winners continue to grow in complexity and diversity. It is our honor to be selected for these awards - a testimant to the advancements in today’s concrete repair techniques and tecnologies,” said Brian Gallagher, Vice President of Structural Preservation Systems.
Following are project descriptions for the three winning submittals:
Hyperbolic Cooling Tower Column and Lintel Beam Protection
Located at St. John's River Power Plant in Jacksonville, Fla., this project featured work on the No. 2 hyperbolic cooling tower. Used in large power generation plants, hyperbolic natural draft cooling towers are known for their distinct shape. Although eye-catching in form, the distinct shape serves a functional purpose in that it cools the water received from the steam condensers at a much lower operating cost than mechanical draft cooling towers.
This particular cast-in-place tower, in operation since 1987, is 450-feet tall and 360-feet in diameter. Constructed using traditional formwork for the columns and lintel beam and slip-form construction for the veil (shell), the structure's purpose is to cool hot water from the generator's steam condensers through a pipeline entering at ground level. Water is pumped upward to the tower interior, through four flumes and a series of pipes and is eventually discharged in spray form at about the forty-foot level. During the downward movement, the water is cooled by the air being drawn upward (by the natural draft) and undergoes evaporative cooling.
During the operation, practically all surfaces are subject to "immersion" conditions. The columns and lintels are subject to intermittent wet and dry conditions. As a result, these towers are extremely susceptible to corrosion-induced deterioration. Maintaining existing towers is crucial because construction of new hyperbolic natural draft cooling towers, represents a very large capital investment.
The owners, a joint venture between the Jacksonville Electric Authority (JEA) and Florida Power & Light Company (FPL), first noticed deterioration on the veil, perimeter columns and lintel beam in the form of severe corrosion of the reinforcing steel. Visual inspections noted concrete cracking, spalling, rust staining and delamination. Several factors were contributing to the deterioration. To begin, the cooling tower uses brackish water from the nearby St. John's River. This water contains a high volume of chlorides - a substance that is highly corrosive to steel embedded within the concrete. Additionally, airflow from the nearby Atlantic Ocean and St. John's River traveling though and around the cooling tower produces high oxygen and chloride levels at the columns and lintel beam. Once the brackish water and salty air start the corrosion process, the reinforcing steel begins to rust and expand - causing cracks to form in the concrete which become greater conduits for more chloride and oxygen intrusion. The result is delamination and spalling.
Repairing corrosion-induced deterioration typically involves removal of deteriorated concrete, undercutting around the reinforcing steel, cleaning and protection of the reinforcing steel, and re-establishing the original concrete section. However, one thing this project clearly recognized was the importance of installing a protection system.
The scope of Structural Preservation Systems' (SPS) repair included installation of 120 lintel beam jackets and 240 column jackets for a total of 34,000 sq ft of jacketing. Procedures included removing delaminated concrete with pneumatic chipping guns, profiling concrete surfaces to a minimum concrete surface and cleaning the corroded reinforcing bars utilizing 35,000 PSI ultra-high pressure water blasting equipment and pneumatically rotated handguns prior to placing and grouting the fiberglass jackets.
Gaining access to the repair areas was a significant challenge. Nearly all of the work on this project was done off of aerial lifts. A total of 16 articulating aerial lifts and two 4x4 scissor lifts were required to provide access. This type of activity was new to most of the crew, so the contractor arranged for instructors to come to the jobsite and perform onsite field and classroom training. In addition to giving the crews the opportunity to practice operating the lift, these sessions taught the crews the dangers involved in using this equipment and what needed to be checked daily before using the lift. The crews also engaged in safety courses highlighting communication and the safe use of such large equipment in tight quarters.
Years of experience working in a shut-down environment clearly made a difference to the successful outcome of what turned out to be the largest cathodic protection system installation for Structural Preservation Systems.
Strengthening and Restoration of the Resorts International Casino
The 100,000-square foot Resorts Casino in Atlantic City features action 24-hours-a-day. Originally constructed in the 1920s, a new hotel tower was constructed a few years ago. The final phase of the project was to connect the original hotel tower, lobby, check-in area and casino with the new lobby by creating a new promenade between them. However, because of differences in the slab elevations of the floors in the two towers, the new promenade needed to be inclined to compensate for the difference. Structural Preservation Systems (SPS) removed an existing intermediate slab at the old tower in order for the new concourse to pass through from the lower elevation at the old tower to the higher one at the new tower. The change of the structural condition resulted in columns that span two floors high.
Another challenge was the new walkway, designed to be held up by a series of supports resting on the original base slab below. The base slab was thought to be a slab-on-grade, but as construction progressed, an entrance hatch was discovered on the wall in the area adjacent to the original base slab. After further investigation, SPS determined that this part of the base slab was actually an elevated slab that had an old steam tunnel under it. The existing structural beams supporting the slab in this steam tunnel had never been maintained and had severely deteriorated over time to the point that they would not be able to carry the new loads. In many of the beams, slabs and columns, the steel rebar was fully exposed or completely deteriorated. Not only would these members require repair, they would also have to be strengthened to meet today's design codes. SPS immediately installed temporary shoring to support the slab until remediation and strengthening plans were established. To strengthen the beams, SPS employed an enlargement technique using a reinforced concrete jacket that bonds to each existing beam.
Repair of the below sea-level room that contained the grease recovery and processing system for all of the casino restaurants also proved to be a challenge. The concrete ceiling and three very large columns in the room had deteriorated to a point of structural concern due to a constant combination of high temperatures and humidity. Once the original ceiling structure was removed, formwork was placed and a new two-way slab and beam system was cast with new hangers and supports for the piping and the equipment. Then, reinforced enlarged sections were added to repair and strengthen the columns. These innovative repair and strengthening strategies allowed the casino to remain open during repairs and the project to be completed ahead of schedule.
Refurbishment of the Xerox Square Tower
Xerox Corporation's 33-story, Xerox Square Tower stands high amid the downtown Rochester skyline. The elegant facade is constructed of cast-in-place exposed garnet aggregate concrete - a mix that offers extremely high compressive strengths and a dramatically decorative finish.
On September 25, 1998, vibrations caused by a mild earthquake reached downtown Rochester and caused delaminated concrete to fall from the building's facade. A subsequent inspection revealed corrosion-induced delaminations and cracks in the concrete, as well as extensive interior honeycombs. Water was also penetrating the building through sealant joints at various locations. Recommendations were made for repairs to the building's structure, sealants, and curtain wall system. Structural Preservation Systems was asked to bid on, and, ultimately chosen for the project, has extensive experience in concrete and masonry restoration on high-rise structures.
Safety for the building occupants, the general public and the contracting team was paramount. It was also important to phase the project so that only one building elevation would be affected at a time - leaving the rest of the building accessible to the large flow of Xerox employees. The safest way to accomplish this task was to work over four construction seasons - from spring through fall of four consecutive years.
The project began in June 2002 and concluded in October 2005. Mobilization took place each spring and demobilization each fall for four consecutive years. During each phase, crews operated 24 hours per day, 5 days a week. In total, 1,638 cubic feet of concrete were replaced at 1,912 repair locations; 138,000 linear feet of sealants were replaced (34,500 linear feet per elevation); 2,445 linear feet (516 locations) of existing aluminum channel sections were replaced, and 100 percent of the lockstrip T-gasket system was inspected, and 36,000 linear feet were replaced.
In addition to the magnitude of the work, the difficulty in matching the exposed garnet aggregate, the extreme height of the work areas and the diligence required to protect the public and property presented challenges and learning opportunities.
Concrete repairs were necessary from the second floor entablature to the roof level - replacing portions of deteriorated cast-in-place columns and precast sections on all four elevations. Each repair site was sounded - the concrete with compressive strengths ranging from 12,000 to 15,000 psi - was chipped with 15 lb. pneumatic chipping guns (in many locations up to six inches of material was removed) and sounded again. The edges were sawcut and detailed before the exposed steel was sandblasted and coated with a protective coating. The Engineer then inspected and sounded each site to ensure that no loose or delaminated areas remained before each patch was formed and the concrete mix hand-poured. In total, 1,638 cubic feet of deteriorated/distressed concrete were replaced at 1,912 repair locations.
Because of the uniqueness of the repairs made to the concrete, the difficulty in matching the exposed garnet aggregate, the extreme height of the structure, the magnitude of the scope involved and the diligence required in protecting the public and property surrounding the area, the project presented numerous challenges.
As work commenced, access equipment used to reach the height of the repairs became a challenge. To perform concrete repairs to the building's facade, the Contractor needed access all around the column perimeters protruding four feet from the face of the windows. Additionally, to keep debris from falling, the Contractor needed a swing stage that conformed to the configuration of the columns and windows. Initial plans utilized the existing window washing swing stages. The system involved three rigs that covered one side of the elevation and measured 125 feet wide. The rigs had a tooth-like appearance with cantilevering platforms that fit into the gaps between the columns.
After securing a supply of the hard-to-find aggregate (garnet tailing is a by-product of garnet mining), the Contractor worked through numerous trials, tests, batches and field tests to establish a color and concrete mix consistent with the original construction. Preparation of the aggregate proved critical. This included washing and cleaning the aggregate and sifting it through a screen so only appropriately sized pieces remained. At the end of the testing, the final result was a field-placed concrete mix design that included a pre-packaged repair mortar, precisely measured water and the garnet aggregate.
A crucial step in ensuring the integrity of the mix was the process of pre-washing and drying the garnet tailing. Because garnet has a specific gravity of 3.01 and can absorb three to four percent of its own weight in water, it had to be pre-washed and soaked for 24 hours and dried so it was moist on the surface. Failure to do so would cause the garnet to absorb water from the concrete mixture. Such absorption would lead to a low slump and, ultimately, difficulty in placing the concrete. Prior to each placement cycle, the mixture was tested by the on-site Engineer. Once approved, batches were mixed on the platforms for use on individual patches. When the form was removed, the surface layer of the concrete could be removed with a combination of mechanical means and power washing. The result - a beautifully exposed garnet aggregate finish.
About ICRI
With roots dating back to a meeting held in conjunction with the World of Concrete in 1988, the original organizing members sought an organization dedicated to improving the quality of concrete restoration, repair and protection, through education of, and communication among, the members and those who use their services. The philosophy of the group was that if the quality of work improves, and purchasers of repair services feel that they are obtaining a durable product, the demand for their products and services would increase and the image of the concrete repair industry will be elevated. Initially it was to have been an organization for contractors, however, the immediate interest of engineers, manufacturers and others in its formation and success made it obvious that it should be open to all. Today, ICRI publishes a bimonthly magazine and technical guidelines for concrete repair, as well as cosponsors the World of Concrete. Local chapters provide regional networking opportunities.
About Structural Preservation Systems, a Member of Structural Group
Structural Group is a $300 million Baltimore-based specialty-contracting firm that delivers services, systems and technologies that build, repair, protect, strengthen and reinforce concrete, steel, masonry, timber and soils. As one of the nation’s leading specialty contractors, Structural Group is comprised of three dynamic and diversified companies. Structural Preservation Systems is the largest specialty contractor focusing on structural repair and strengthening. VSL is the technical leader in post-tensioning and specialty reinforcement. And, Pullman Power leads the industry in chimney, silo, and stack construction, maintenance, and repair. From 18 operating centers around the United States, Structural Group businesses perform a wide range of projects involving industrial facilities, commercial properties, public infrastructure and municipal buildings. For more information about Structural Group, please visit http://www.structural.net/.