Concrete cracks. It’s a fact of life. Some cracks might not need attention while others could have serious structural consequences. But how can you tell the difference? Much of the time you can’t and expert advice is required.
“It is important to accurately assess structural cracks to determine what is significant and what is not,” says John Duntemann, a principal at consulting engineering firm Wiss, Janney, Elstner Associates Inc. (WJE), Northbrook, Ill. “You have to properly identify the extent and cause of cracking before you can implement the right repair solution.”
Cracks in concrete might be caused by a number of factors, such as thermal expansion and contraction, subgrade settlement, the loads being applied, and even earthquakes. This all adds up to internal and external stress that manifests as large and small cracks.
In many cases, however, there is uncertainty as to what to do about cracks. Pete Barlow, a principal at Contech Services Inc., Seattle—a company that repairs, strengthens, and waterproofs concrete structures—says his company constantly is being contacted by anxious building managers and owners. “Many times a week, people send us photos of cracking at their facilities asking for advice,” says Barlow.
There are various methods of classifying cracks in concrete. One primary way is to split them into two groups: structural and nonstructural. Structural cracking affects the integrity of the building. Cracking in support beams, columns, and load bearing areas is of particular concern.
Nonstructural cracks, on the other hand, are not detrimental to building integrity, though they may need to be addressed due to cosmetic reasons or to take proactive steps to prevent those cracks from growing over time and eventually reaching the structural stage. Tiny fractures also can lead to other challenges. “Small cracks in belowgrade foundation walls can allow water to migrate into the structure,” says Barlow.
The size of the gap is another consideration. Hairline cracks generally are not a problem, but it depends on where they are. A high frequency of them could indicate an underlying stress issue that needs to be addressed. But as the size of openings increases, so should the concern. “As a rule of thumb, cracks larger than 0.015 inch or larger,” says Barlow, should be investigated. “The larger the width, the greater the likelihood you have lost aggregate interlock. But repairs can be done on cracks down to 0.005 inch.”
A third issue is location and orientation. Cracks in random directions are of lower priority than those in beams, columns, or other load-bearing areas. “If one side of the fracture is offset from the other, that is often a bad sign,” says Barlow. “Other warning signs are closely spaced cracks or repetition of cracking at the same locations on each floor.”
Epoxy in concrete repair
In many cases, epoxy injection is used as the remedy for concrete cracks. Although there are many epoxy types and uses, high-performance epoxies manufactured for structural concrete bonding and crack repair are the focus here.
Duntemann gives the example of cracking that appeared in a cooling tower being constructed at a synthetic fuel plant. Cracking developed at the ends of prestressed concrete beams. Demolishing the structure and starting over was not considered an option. Management brought in WJE to find an alternative. “The beams were injected with epoxy and load tested to verify their structural capacity,” says Duntemann.
In another case, WJE was retained to investigate large cracks in the concrete caps on top of concrete pile foundations. “We developed a method of reinforcing the pile caps and injected an epoxy into the cracks to reconnect the fragmented caps,” says Duntemann.
Water, however, presented a further challenge—the epoxy had to deal with a saturated environment. WJE requested help from Redwood City, Calif.-based ChemCo Systems’ team of chemists. They formulated an epoxy that could fill 3/4-inch cracks and cure in the presence of water. ChemCo specializes in making two-component structural epoxies and application equipment designed for concrete structural repairs, including at industrial plants, bridges, stadiums, and parking decks, to name a few.
“You often run into challenging environments such as cracks full of water, cold temperatures, or exceedingly wide cracks that require a customized solution,” says Duntemann. “We typically identify potential products, and consult with the manufacturer for advice on the product application.”
Duntemann points out that while many different types of epoxy are available, one size does not fit all. It requires the right combination of materials, chemistry, and expertise. “We have found manufacturers to be very helpful when we are developing repair solutions,” says Duntemann.
Building owners noticing cracks are advised to contact a structural engineer to assess the extent of the damage. They can help determine whether or not it is a significant issue. “As building owners are typically not engineers, they are advised to retain a licensed structural engineer who can evaluate concrete cracking,” says Barlow. He also advises against a do-it-yourself approach for all but the most minor problems. In his view, there are too many factors involved in the engineering and chemical formulation side to leave anything to chance. “When a problem is identified, it is important to retain professionals with experience solving these problems,” says Duntemann. “The correct solution to a problem requires a good understanding of the cause of that problem.”
Drew Robb is a Los Angeles-based writer specializing in business, engineering, and technology.