For industrial plants, concrete repair activities pose challenges that are quite different from those encountered in new concrete construction. For a concrete repair project to be successful, it must integrate new materials with existing materials, to form a composite structure that is able to withstand environmental conditions and process use, while also providing extended service life.

Like it or not, over the course of the next few years, plant managers will need to spend millions of dollars on plant infrastructure that generates no revenue per se. Concrete is a prime example: it carries piping, holds equipment, and provides foundations and flooring. Yet, since it produces no product - or revenues - focusing on its repair can easily be dismissed as being of little value.

That view may be shortsighted. Concrete needs routine preventive maintenance, just like machinery and equipment. Although the process of deterioration or damage may take years to manifest itself, once the "fuse is lit" it is irreversible. The longer the deterioration is ignored, the more extensive (and expensive) the repairs will be. It's a classic "pay now... or pay a lot more later" situation for plant managers, who need to keep an eye on both short-term and long-term expenditures.

In Part 1 of this series, we outlined the variety of factors that can shorten the service life of concrete construction within plant operations. These factors can relate to the initial design, quality control or construction practices. Man-made forces such as impact, overloading, and attack by aggressive surface-applied chemicals are also potential contributing factors, not to mention the impact of natural forces such as freeze-thaw cycling, wind and water flow.

Where do we go from here?

Once the decision is made to undertake a concrete repair project, the critical question becomes how best to examine repair strategies, and choose the best course of action. Repair technologies have advanced far beyond the simple concrete patch. In fact, there is currently a wide range of strategies that can be considered for implementing concrete repairs plant operations. They fall into five groupings:

• Surface repair
  
  
• Stabilization
  
  
• Strengthening
  
  
• Waterproofing
  
  
• Protection

And each of these categories can be broken down even further into subcategories

• Surface Repair
  
  
• Stabilization
  
  
• Strengthening
  
  
• Waterproofing
  
  
• Protection

With so many possible strategies available to the repair designer, solutions from more than one category will often be implemented concurrently in order to achieve the best results. This typically allows the repairs to be completed more cost-effectively within a plant's repair budget constraints. But at the same time, it creates greater complexities, because the repair options involve a variety of materials to select from - as well as several different repair practices or techniques.

Determining the most appropriate repairs for the particular conditions under which a facility operates is best accomplished by involving all parties associated with the repair. These include the engineer, contractor, plant processing manager, plus the facility owner.

The engineer must understand the behavior of the materials. This includes physically cured properties and the chemical uncured behavior, in order to specify a successful repair material. The materials manufacturer must understand the engineering aspects of how its repair material will interact with an existing substrate under expected load-carrying conditions.

The contractor must understand concrete deterioration mechanisms in order to be knowledgeable about surface preparation requirements. And while the building owner cannot be expected to master the technical details of concrete repair, he or she should be a well-informed generalist - familiar with the many diverse aspects of concrete problems, as well as possible solutions.

Choosing the Right Ingredients

Often, deciding on the most appropriate concrete repair materials is an exercise in compromise. Even the most seasoned repair technicians find it difficult to select one product that meets all of a project's needs. At a minimum, the materials chosen should fill the repair cavity completely, avoid shrinking during the curing cycle, and behave in a similar manner as the existing substrate when subjected to loads, temperature fluctuations, or changes in moisture content.

During the material selection process, the repair designers should consider each of the following questions:

• What are the performance requirements?
  
  
• ... the service and exposure conditions?
  
  
• ... the load-carrying requirements?
  
  
• What will be the operating conditions during placement and cure?
  
  
• Has the original cause of the deterioration been addressed?
  
  
• What placement techniques have been selected, and what characteristics are required for placement?
  
  
• What properties are necessary to meet the conditions and requirements?
  
  
• What materials or systems will provide the required properties?

When selecting repair materials, the ultimate decision should be based on the relationship between cost, extended performance, and the acceptable level of risk. Whatever course of action is chosen, the degree of success a repair project achieves will depend on properly balancing the needs and risk of the building owner, plus ensuring close coordination among all parties involved in designing and implementing an enduring repair solution.

Upping the Ante

At some sites, plant and facility engineers may find themselves "outside their element" when confronted with infrastructure issues such as deterioration of structural concrete. In industries such as food processing and pharmaceutical plants, federal, state or local regulations mandate significant funds to be allocated for civil structure repairs. Not so in some other industries. Facility maintenance budgets are typically well funded for repair of equipment and process systems, but civil structure repair budgets are given a much lower priority - until some problematic structural condition deteriorates to the point where the plant process is jeopardized, thus threatening plant profitability! Of course, most plant operations fall in between these two extremes.

In concept, perceived "value-added" services relating to concrete repair should be no different than those provided by equipment suppliers. Education of plant personnel concerning concrete material basics, deterioration mechanisms, repair strategies and construction techniques will enable repair teams to make better repair strategy decisions.

As in any decision-making process, knowledge is power... and in this case, the knowledge should be available to all - from the owner to the plant personnel, from the contractor to the repair material supplier. The end result will be more successful, enduring repair projects - and far better control over infrastructure costs, thereby improving the facility's operating and financial performance. Early intervention is key... for what may appear to be only cosmetic issues could actually end up costing hundreds of thousands of dollars.

Case Study: Bouncing Back from a Refinery Fire

An extensive fire occurred at a large refining facility that processes petroleum crude oil. The fire, which initiated from ruptured feedstock tubes within a catalytic furnace, soon engulfed the furnace, and required four hours to extinguish. As a result, severe damage was done to the furnace and the concrete column support elements. Because the furnace was a critical component in the refining process stream, the unit would remain offline until the problem was solved. And that meant $500,000 per day in lost revenues, so time was of the essence!

Structural Preservation Systems was brought in to assess the situation, recommend and carry out action steps to restore normal operation at the facility. Recognizing the need for quick action and a turnkey repair, a crew was mobilized from SPS's Engineering Services Division. A Condition Survey was conducted, involving nondestructive and destructive testing including mechanical sounding, ultrasonic testing, surface hardness testing, concrete sample extraction, plus physical and chemical laboratory testing. The result of these efforts was to locate, qualify and quantify the root cause and extent of the distress - also known as the LOQ method.

Several concrete repair scenarios were discussed and considered. Upon review of these options, comparisons between cost, effect on work space, and fast-track installation opportunities were evaluated. The program that was finally agreed upon was an ambitious one. The existing columns were not to be removed in their entirety. Instead, new repair materials were integrated with existing, sound "parent" concrete materials, with each restored column functioning as one member. It was important to avoid "passive" structural repairs (a "patch" solution), in favor of "active" repairs, wherein the load is removed by shoring and jacking prior to repair. This would provide extended service life.

The following repair program was recommended and implemented by SPS:

• Temporary shoring and structural support of the catalytic furnace by engaging the furnace's structural steel framing.
  
  
• Saw-cutting in rectilinear configurations the perimeter of deteriorated concrete areas identified in the Condition Survey report.
  
  
• Excavating and removing deteriorated concrete materials within the perimeter saw-cut.
  
  
• Undercutting exposed reinforcing steel bars to allow access for reinforcement cleaning, concrete substrate surface preparation, and coating encapsulation of exposed reinforcing steel bars.
  
  
• Inspecting existing reinforcing and anchor bolts for consistency with original design specifications. Then, installing and/or augmenting existing reinforcing in those areas not in compliance with original design details and ACI guidelines.
  
  
• Installing expansion anchors with double-nutted plates into the concrete excavation cavity to mechanically fasten new concrete materials to the existing prepared concrete substrate. Also, installing new welded wire fabric to the expansion anchor bolt grid, fastening the fabric to the double-nutted plates.
  
  
• Preparing concrete and steel surfaces using abrasive grit and/or high-pressure water-blasting techniques.
  
  
• Applying corrosion-inhibiting technology to repair concrete substrate interfaces and exposed reinforcing steel bars.
  
  
• Assembling and installing mortar-tight concrete column formwork at the concrete repair locations that were designed to accept hydraulic pressures associated with form-and-pump placement techniques.
  
  
• Installing ball-type check valves with pressure gauges to regulate pumping pressures, as well as installing vent ports in preparation for form-and-pump activities.
  
  
• Reestablishing the structural section to concrete columns by placing very rapid-setting, dense cementitious repair material within the formed cavity areas, using form-and-pump techniques. Repairs to concrete elements did not involve significant volumetric quantities, but consistent material characteristics and properties were required. The repair materials were conveyed using hydraulic pumps. Once the form cavities were full and vented, the formwork was pressurized and the valves closed. Subsequent to the initial repair material "set", valves were removed and the repair material cured.
  
  
• Removing mortar-tight formwork after the recommended curing period, along with surface ground concrete repairs to match existing concrete column surface contours.
  
  
• Removing temporary shoring and structural support of the catalytic furnace.

It was important that SPS's portion of the repair not impede the mechanical and electrical work segments. The refinery owner wished to keep the various contractors from interfering with one another. In order to achieve this, SPS recommended that the work be performed around the clock - with the shoring designed and assembled to accommodate work activities around the columns, yet also provide structural support so that work within the furnace box above the column repairs could be performed safely and efficiently.

During the repair procedure, the high-capacity shoring resulting in close working spaces required SPS to use small chipping hammers to execute "dental work" around the embedded reinforcing steel bars, to ensure that the existing bars would be integrated into the new repair material. Care had to be taken in the choice of repair materials so they would closely match the physical and chemical characteristics of the original material. This would guard against new corrosion cells developing around the repair, and would also ensure that the all-new and existing concrete materials would be of similar rigidity in sharing the load.

The methodical, step-by-step repair approach taken by SPS was successfully accomplished on a fast-track schedule. Repairs to all six columns were completed in only five days - two full days ahead of the refinery owner's schedule.

Part I: Is Concrete Really All It's Cracked Up To Be?
CONCRETE DEGRADATION IN REFINERY OPERATIONS, Part I