Concrete repair in industrial environments

Non-destructive testing and evaluation of a support column exposed to a hydrocarbon-fueled fire

One key factor that can have a large impact on an industrial environment is the deterioration of concrete structures. Caused by embedded metal corrosion; disintegration of the concrete matrix; the effects of moisture, thermal factors or varying loads; as well as faulty workmanship and/or inadequate or flawed design, concrete deterioration is a serious problem in an industrial setting. With the exception of faulty workmanship or design, these causes of deterioration have a consistent theme involving volume changes and/or alteration of the cement paste matrix within the concrete mass. The deterioration reduces the concrete’s integrity with losses in section and composite action with embedded reinforcing steel components. This is particularly a problem for in-service concrete that is unprotected and then exposed to acids, caustics, steam and refractory and cryogenic temperatures.

Load effects have been identified in many situations where an owner has implemented a change-of-use for a particular structure to upgrade or completely change the process equipment loadings. The need to improve process operations and reduce production costs have driven owners constantly to review and change their manufacturing processes with bigger, faster, better and more dependable equipment—which frequently means heavier equipment. It is not unusual for detected deterioration to have manifested into the secondary effects of embedded metal corrosion with the primary effect caused by cracking due to overloading. Essentially, the cracks provide conduits that allow moisture and atmospheric oxygen to contact the embedded reinforcing steel, initiating the corrosion process. 4Also, with many facilities located near seismically active areas of the country, earthquake loadings on older structures require upgrading to current seismic codes to resist such events, prevent further cracking and maintain process operations.

Failed floor slab repair and continued deterioration caused by embedded steel reinforcing bar corrosion

In contrast, faulty workmanship and construction defects are particularly insidious because the effects may not be seen until much later in the structures’ service life, when it needs the reserve structural capacity (i.e., absence or misplacement of embedded reinforcing steel) and/or durability (i.e., porous, low strength or lack of protective concrete cover) to maintain functionality.5 Inadequate or flawed design can mean many things, but the majority of problems observed in the industrial market relate to reinforcing steel density in very stout reinforced-concrete structures. Specifically, these structures support very large loads in small footprints requiring designs where large diameter reinforcing steel bars lap together and are designed in close proximity to formwork faces. During placement, excessive rebar density operates as a sieve and prevents concrete mixture constituents from encapsulating the steel bars, forming internal and external voids (i.e., honeycomb) in the finished construction.

Organization and extensive preplanning provide superior results in difficult environments – note debris chutes extending into dumpsters, hydraulic pump truck with articulated placement boom ready for repair material placement

Further complicating the maintenance and repair scenario are codes and standards. Industrial owners, not unlike their counterparts in other market sectors, follow codes, standards and guidelines established by ruling governmental and best-practices agencies regarding design of new construction and restoration of existing structures. These agencies include the American Concrete Institute (ACI), Portland Cement Association (PCA), Concrete Reinforcing Steel Institute (CRSI), Naval Facilities Command (NAVFAC), U.S. Army Corps of Engineers, American Society of Civil Engineers (ASCE), International Concrete Repair Institute (ICRI), American Association of State Highway and Transportation Officials (AASHTO), American Institute of Steel Constructors (AISC), American Welding Society (AWS), American Society of Mechanical Engineers (ASME), American Railway Engineering and Maintenance-of-Way Association (AREMA), American Institute of Timber Construction (AITC), National Concrete Masonry Association (NCMA), Brick Institute of America (BIA), American Society for Testing and Materials (ASTM), National Fire Protection Association (NFPA) and the American Petroleum Institute (API). In addition, many facilities and corporations maintain technical divisions with developed standards that in many cases are more stringent than the associations and agencies noted above. For a new design or restoration to proceed, it’s always prudent for the construction or repair team to investigate specific requirements regarding fire and environmental protection.  

Occasionally, especially in process fluid containment and clarifier water tanks, designers have been known to err and strictly follow ACI 318 (Building Code Requirements for Structural Concrete: Reported by ACI Committee 318) and not incorporate ACI 350 (Environmental Engineering Concrete Structures: Reported by ACI Committee 350) environmental provisions. Attention to detail is critical in such instances, as insufficient reinforcing steel will be incorporated into wall sections when strictly following ACI 318. Without the additional steel stipulated in ACI 350, conditions will be conducive for excessive cracking under load with contained process fluids wanting to egress through newly formed crack fissures, creating not only a structural issue but also affecting the structure’s long-term durability.

Tight tolerances require consistent QA/QC during construction and prior to repair Material placement

Inspection and Evaluation

The first step to ensuring the health of a structure is an inspection process. Industrial facilities operate using risk-based-inspection (RBI) methodologies in accordance with the various industries’ best practices. The philosophy behind the RBI is to spot problems before they occur, based on statistical probabilities and historical experience profiles with specific processes and/or equipment. Risk matrices have been developed throughout various industries to identify the severity of potential incident (or consequence) versus priority of repair (immediate to delayed action items). The matrix may indicate, based on input data, that negligible risk exists and no further action is required. However, if the data indicates significant to very high risk, action may be called for and repairs implemented immediately.

RBI philosophies addressing maintenance have been in place for many years regarding electrical, mechanical and chemical processes. However, only until recently and after numerous catastrophic events, have facility owners been alerted to the fact that civil infrastructure assets require the same scrutiny as their process systems. Although civil assets in an industrial setting don’t directly contribute to profitability, upon failure, they certainly can cost the owner a significant amount of money and directly affect a company’s profit/loss statement.

Many documents exist from various agencies, both governmental (e.g., Department of Transportation, U.S. Army Corps of Engineers, etc.) and non-governmental (e.g., ACI, ICRI, ASCE, etc.) that stipulate means-and-methods for conducting condition assessments and surveys of structures in service. However, no one document can cover all the different environmental scenarios possible within an industrial plant and the specific needs of each facility owner. Therefore, each industrial project should be treated as a unique opportunity with modifications made, as needed, to design/repair options so the owner achieves the desired work product.

Housekeeping is critical at an industrial facility – repair material mixing station prior to placement activities

There are many investigative approaches that can be mixed and matched with the techniques within your own evaluation toolbox. In the field of forensics, many believe the formulation of an investigative program is part art and part science. A process known as the LQQ method -- locate, qualify and quantify -- is a prudent and frequently selected approach in industrial situations with numerous unknowns. Investigators try to ascertain deterioration affecting a structure and provide a global perspective as to the location of the distress relative to individual member components. Once located, concrete professionals can qualify the distress to determine the type of deterioration mechanism, the extent of penetration and the overall effect on the structure. When qualifications are made regarding different deterioration types, prospective repair opportunities and repair priority, the repairs are quantified to develop an accurate repair estimate. The quality of an estimate cannot be over-stressed in an industrial environment. A facility owner typically budgets money to perform the repairs over a period of time and, if possible, at indicated priority intervals. Priorities can be broken into multiple categories and time frames ranging from immediate action to repairs required after six months, one year, three years, etc. This process allows the owner to address serious defects that, if not repaired, may become significant safety or structural integrity items.

Industrial environments also provide opportunities to apply non-destructive testing (NDT) and semi-destructive testing (SDT) techniques for gathering information regarding the physical and chemical properties of building construction materials. Currently, these techniques involve the transmission of energy, impose a load, or require the extraction/collection/submission of samples to an accredited analytical laboratory. When it comes to evaluating numerous structures and/or various structural types that are present in an industrial facility, a different approach is required due to the amount of time and data required with conventional evaluative techniques. Generally, the process involves an initial site reconnaissance and scope definition (Phase 1), a walkthrough evaluation and prioritization (Phase 2), and subsequent turnkey repairs (Phase 3).

Specialty repair materials matched to existing concrete substrates charged on-site into a transit-mix truck for large placements

Phase 1 consists of a cursory, short-duration site reconnaissance walk-through to define the scope of the condition evaluation. Phase 2 determines areas of concern highlighting safety, structural and durability issues revealed during the evaluation phase. Causes of distress, if readily apparent, also are evaluated in Phase 2 to establish repair work priorities and to provide conceptual repair recommendations with associated repair costs. Phase 3 represents the culmination of the evaluative effort with the implementation of the repair recommendations outlined in Phase 2.

Although an industrial environment promotes creative and innovative approaches regarding condition assessment for all of the different kinds of civil infrastructure, it is not necessarily investigator “friendly” (i.e., elevated safety measures when compared to commercial projects) and requires a modified thought process involving relationship/team building with all interested parties when working toward a desired product. Much of the investigative work done in an industrial environment needs to be performed around operating processes that may be sensitive to radio, mechanical, electrical or radioactive energy sources. Typically, these investigative programs require more time and therefore are more expensive to implement. Overall, however, the cost impact to the owner in most cases is minimal when compared to the effect an outage would have on the income-generating, process operation.

Unique Challenges Presented for Working Conditions & Safety

Industrial owners are fully committed to programs that sustain responsible business practices. Typically, management personnel and employees focus on fulfilling this commitment to ensure loss control systems are in place. These loss control systems provide the resources and training to maintain a safe and healthful work environment as required by industry standards, owner policies and legislative requirements. As a rule, all company employees and contractors are essential team players in a team effort requiring safe and responsible conduct. Every individual working in an industrial environment has the responsibility to follow established procedures, programs and standards to ensure compliance with owner requirements and applicable laws and regulations. It’s not uncommon for owners to request contractor personnel to report on practices and conditions, or on information that’s contrary to the aforementioned commitment to supervisory personnel. Contractors should continue up the line until a response is received and acknowledged. The purpose behind this philosophy is to protect people, property, the environment, neighbors in the community and the continued success of the business.

The “business-end” of the repair material placement – note formwork portal and radio communication during placement

Manufacturing firms and industrial concerns are required by law to perform workplace hazard assessments to identify potential sources of accidental releases. During this process, companies must complete a compilation of process safety information in written form. They must also conduct a process hazard analysis as part of their Process Safety Management (PSM) program. Literally, creating a safe work environment for company employees and contractors is mandated by law. However, jobsites are extremely complex with essentially hundreds of variables affecting, and in some cases in direct conflict with, the successful outcome of the job. It’s important to recognize the critical areas on a specific job that will require competent supervision to ensure there are employees with the training and experience necessary to recognize and change unsafe conditions.

Working in industrial environments requires civil contractors to rethink their work habits in another manner - recognizing that they are small cogs in larger machines. Bigger scenarios exist within a facility whose primary function is to refine, alter, or otherwise produce an intermediate or finished product without interruption and without compromising safety or product quality. Many times civil contractors, whose primary focus may be in commercial, public or transportation, face significant cultural challenges when performing work in industrial environments. Typically contractors’ worksite behaviors are inconsistent with plant policies, as contractors often forget they’re in another’s house. Most often, it makes sense for companies to set up industrial divisions to train their industrial employees differently from those that service other market sectors -- focusing on performing the job safely, rather than strictly on production. 

Each individual is responsible for his own safety in an industrial environment. Critical safety methodologies include the process of heightened awareness regarding your personal extremities (i.e., body parts), your place within the facility, your proximity to safe havens, your understanding of instructions as to evacuation contingency plans in the event of an emergency and making sure you go home each and every day as you arrived. Fortunately, employee education through public agencies (i.e., safety councils) and programs administered by facility owners provide valuable education tools and information to cope with the potential hazards an industrial environment can present.

Formwork designed to be mortar-tight – note foam sealed top-surfaces and heavy-duty bracing to resist hydraulic pressures associated with form & pump repair material placement

Logistics and Scheduling

It goes without saying that logistics are increasingly complex for a construction project – new or retrofit – in an industrial setting. Plants and manufacturing facilities create products by integrating numerous technologies that ultimately produce a marketable product at a profit. These technologies can involve electrical, mechanical, chemical, hydraulic, thermal, and nuclear energy powered equipment and/or processes. The inherently complex components of such process equipment require periodic maintenance, not unlike their civil infrastructure counterparts. Planning for scheduled outages or shutdowns (turnarounds, TARs, T/As) occurs years in advance to adequately address equipment/process needs and market trends. Obviously, unplanned outages due to problems caused by fire, explosions, or equipment or process failure also provide opportunities to perform maintenance to equipment/processes, albeit via unfortunate circumstances. Many industrial owners, in lieu of managing a scheduled outage themselves, will outsource and contract with specialty firms. Literally, businesses have evolved to address these industry needs with a proliferation of project management firms handling general and specific industry needs (e.g., petrochemical, automotive, energy, pulp and paper, etc.).

Consistent with performing work off-line in industrial environments is the frequent effect of trades or contractor interference that occurs when work takes place at the same time in the same location or proximity. Typically, a repair concurrent with plant activity involves the same civil asset (e.g., foundation, column, beam, slab, etc.) or process equipment attached to the asset. If the work is in the general proximity and safety dictates working conditions (i.e., welding, sandblasting, crane lifts, etc.), a decision and rules-of-protocol are determined from the outset by the owner as to the most critical aspect of the work. Then a computer model is developed for the project’s critical path in order to streamline the progress and maintain control of the project’s duration. As a rule, civil contractors aren’t generally put on the critical path, as the process will always take precedence. The owner always has the option to place a unit on-line early, should it be required due to plant or market conditions. It’s important to note that time is money, and time extensions to outages cost an owner money that is typically unrecoverable. Many projects offer incentives to reward turnaround participants for early completion or dictate penalties that must be paid for time extensions to the schedule. 

On-line repair opportunities occur in industrial environments on a regular basis, but evaluation and repair techniques become more complex, requiring specialized expertise and familiarity with the subject equipment and/or processes. Generally, repair construction costs increase with performing work on-line versus off-line. Special precautions such as dust suppression, hot work, noise and vibration suppression are but a few of the necessary containment strategies that require implementation during an on-line repair. The costs associated with these precautions, however, may be insignificant when compared to a plant production outage. The owner typically employs analysts to evaluate the cost-to-benefit regarding an on-line versus off-line civil asset repair program. On many occasions, due to safety and/or ambient working conditions, only off-line repair programs are considered, such as in the case of cryogenic or refractory support members (extremely cold and hot surface conditions, respectively) or vibratory or oscillating equipment foundations (high-speed reciprocating or rotating equipment sensitive to movement).

Regardless of on-line or off-line repair approaches, important consideration should be given to the anticipated project duration. Repair construction time duration and time to anticipated in-service use are critical to the long-term success of a concrete repair program. Besides the cured material properties associated with the repair, uncured material properties (e.g., sensitivity to temperature gradients, vibration, moisture, etc.) must be examined closely along with the identification and subsequent implementation of plant-friendly demolition, surface preparation, placement and curing activities that are consistent with providing a long-lasting, enduring repair product.

In addition to tough logistics, many contractors also view industrial concrete repairs as tough to access due to requirements for employee safety training, security background checks, drug-testing, entry into the gated plant facility, the process unit and ultimately securing a work permit to begin work. A substantial part of the workday may be spent on just accessing the worksite. Consistent with industry best-work practices, safety and security are prime considerations, with the work deemed secondary. Once at the site, not unlike other repair environments, elevation, confinement, proximity to embedded or mounted utilities or processes, and atmospheric conditions affect accessibility to the area of work. In addition, as discussed earlier, another contractor concurrently operating in the work area can become an accessibility nightmare without open communication and direction from the owner.

Access for elevation is mainly accomplished by system or site-built scaffolding with 100-percent fall arrest (i.e., full-body harness and double lanyard), articulated man-lifts, crane baskets or motorized swing-stages.  Hole-watch attendants with extractors and stand-by rescue teams are the typical means and methods for confined-space (i.e., space not intended for human habitation) access, including vessels, tanks and open excavations. By employing competent persons (i.e., those who are capable of identifying existing and predictable hazards in the surroundings or working conditions and who have the authorization to take prompt corrective measures to eliminate them) and qualified persons (i.e., those in possession of a recognized degree, extensive knowledge, certificate or professional standing and who have successfully demonstrated the ability to solve or resolve problems relating to the subject matter, work or project) accessibility can be accomplished safely and in a manner consistent with maintaining productivity.8

Typical Repairs

Although each restoration project is unique in character, many of the repairs performed in commercial, public, transportation and residential sectors are similarly performed in industrial work environments. However, the aggressive nature of service associated with industrial processes requires that repairs perform compositely under load and maintain durable characteristics, even in the most aggressive operating environment. Essentially, industrial repairs require:

• closer tolerances in repair cavity geometry, reinforcing steel augmentation and corrosion mitigation;
• resistance to impact and mechanical abrasion;
• resistance to atmospheric contact with deleterious process fluids and gases; and
• rapid return to service involving less curing than standard construction materials and quick achievement of mechanical and chemical properties.

The primary concern industrial owners have with concrete repairs made in their facilities is with the dust, dirt and debris generated during the course of work activities. Experienced contractors realize the containment and housekeeping practiced during the performance of the work is every bit as important as the finished product if the contractor wants to do further work for the owner. Concrete repair professionals should realize they are guests in another’s house and their conduct will be evaluated. If they want to be invited again to work for an industrial owner, all phases of the repair process must be performed in accordance with industry best practices.9

Demolition and concrete-substrate surface preparation practices vary depending on an industrial owner’s rules and regulations. However, the resultant concrete substrate must be uncontaminated, have an undulating surface profile with exposed coarse aggregate, achieve a clean pore structure and be capable of bonding with the newly applied repair materials. Many different types of demolition and surface preparation techniques can result in a bondable surface. Often, though, there are compromises made based on site conditions involving environmentally friendly technology, equipment costs, availability, repair technician expertise and project production.  In some instances, multiple techniques are required in lieu of a single demolition or surface preparation procedure (e.g., jackhammers followed by an abrasive grit-blasting of demolished surfaces versus hydrodemolition).

Containment is the engineering control process of separating the work from the surrounding industrial environment by the means of one or more barriers. Generally, if successfully accomplished with appropriate safeguards, the means-and-methods of construction within the containment can be similar to those employed in the commercial, public and transportation sectors of the concrete repair industry. The types of containment vary and can range from simple dust suppression and containment to full mechanical impact shielding of process equipment and utilities. Containment materials of construction are typically flame retardant and include polymer sheeting, wood paneling and/or sheet metal stock.

Often multiple and redundant containment systems are required, as in the case of food processing and precious metal refining. Serious consideration regarding ventilation and ambient temperature control must be given to these enclosures to ensure adequate air exchange and worker comfort. It’s becoming more prevalent for concrete repair contractors to employ the services of mechanical contractors for ventilation and temperature control in sophisticated applications. Obviously, containment criteria change according to on-line versus off-line working conditions with the more stringent criteria necessary when the plant is on-line.

It is recommended that repairing “like with like” modulus of elasticity, coefficient of thermal expansion and low material drying shrinkage be the goal of every concrete repair material that strives to be durable, long lasting and able to achieve composite behavior with the existing concrete substrate under load. Having selected an appropriate repair material, the installation of the material should undergo a rigorous analysis to achieve the most cost-effective yet highest quality installation possible. Industrial repair material application techniques include:

• trowel application for small and/or shallow repairs;
• shotcrete (pneumatically applied concrete materials);
• form and pump (installation of concrete within a mortar-tight formed cavity under hydraulic pressure pump conditions);
• form and pour (installation of concrete within a formed cavity placed under standard gravity fed conditions);
• crack injection (stabilization and waterstop applications); and
• protective coatings, membranes or linings installed on the surface of existing concrete or overtop of a repaired concrete member to protect against aggressive chemical attack.

Of the techniques noted, form and pump and form and pour are by far the most widely used, with trowel-on and shotcrete repairs used to a lesser extent. Although shotcrete is the least expensive of the repair applications listed above for deep repairs (i.e., greater than two inches in depth), requirements for industrial process protection, material rebound losses, tight process utilities placement and equipment proximity makes the resultant installed product suspect, unless performed after significant utility relocation or process shielding and installed under close quality assurance/quality control (QA/QC) scrutiny. Crack injection of cementitious or resinous products to repair cracks are commonly used in industrial environments, much like in commercial, public and transportation markets. Protective coatings, membranes or linings are used in localized areas (e.g., aisles, secondary containment for hazardous material storage, waterproofing, etc.) where specific protective qualities are required to contain process fluids and/or protect the concrete from aggressive chemical attack and resultant degradation.

Modifications to both form and pump and form and pour methods to adjust for the industrial environment include the incorporation of fire-retardant materials into the construction of formwork panels as well as corrosion resistant form-tie assemblies. Formwork design usually requires the formwork be stouter to address tight clearances in and around existing utilities/process streams and the need to attach external form vibrators to assist in concrete consolidation. Also, the formwork is typically tighter to protect prepared concrete substrate surfaces against airborne contaminants or incidental process fluid contact prior to placement.

Final Steps for Success

After the condition assessment and any necessary repairs, it is important to establish a long-term maintenance program. A key component of such a plan is consulting with an experienced and reputable concrete repair professional. Those with the right experience can develop a plan that will add years of life to your existing structure and help you achieve the greatest return on investment. 

Tom Kline is the Engineering Services Division Manager in Structural Preservation Systems, Inc.’s Houston office. He is a graduate construction engineer with more than 25 years of experience in concrete distress and failure investigations. Kline is a member of American Concrete Institute (ACI), American Society of Civil Engineers (ASCE), American Society for Testing and Materials (ASTM) and the International Concrete Repair Institute (ICRI). He serves on the Technical Activities Committee and is chairman of an ICRI task group on Monolithic Bonding of Concrete Repairs.