Assess and Repair Concrete Cracks in Building
After the beating your building probably took this winter, you may notice cracks beginning to form in your façade or at other points in your building. 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 (WJE). “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, sub-grade settlement, and the loads being applied. 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., a company that repairs, strengthens, and waterproofs concrete structures, says his company is constantly being contacted by anxious building managers and owners. “Many times a week, people send us photos of cracking in their buildings asking for advice,” he says.
The number-one thing owners should do upon noticing cracks is to contact a professional to assess the extent of the damage. They can help determine whether or not it's 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.
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 can also lead to other challenges.
“Small cracks in below-grade foundation walls can allow water to migrate into the structure,” says Barlow.
Size of the gap is another consideration. Hairline cracks are generally not a problem, but it depends on where they are. A high frequency of them, though, 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 inches, says Barlow, should be investigated.
“The larger the width, the greater the likelihood you have lost aggregate interlock,” Barlow says. “But repairs can be done on cracks down to 0.005 inches.”
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.”
Concrete Repair with Epoxy
After consulting with the engineer and if the engineer deems your building's cracks to be a problem, your engineer can recommend a course of action. “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.”
In many cases, epoxy injection is used as the remedy for concrete cracks, he says. There are high performance epoxies manufactured for structural concrete bonding and crack repair. 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 pre-stressed concrete beams. Demolishing the structure and starting over was not considered an option. Management brought in his firm to find an alternative.
“The beams were injected with epoxy and load-tested to verify their structural capacity,” says Duntemann. In another case, his firm was retained to investigate large cracks in the concrete caps that sat on top of concrete pile foundations for a building. “We developed a method of reinforcing the 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. His firm requested help from ChemCo Systems, an epoxy manufacturer, and their team of chemists formulated an epoxy that could fill three-quarter-inch cracks and cure in the presence of water.
“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. When it comes to concrete cracks, a do-it-yourself approach may be fine for 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, and a reputable epoxy manufacturer is vital.
He points out that while many different types of epoxy are available, one size does not fit all. Concrete cracks require the right combination of materials, chemistry, and expertise. If your engineer recommends epoxy repair, the right epoxy manufacturer can provide advice on the product application. Also, “their chemists should understand the physical properties of the various resins and how to blend them to ensure the job is done right,” says Barlow.
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