Cracking up not a laughing matter when it comes to concrete
by Drew Robb
 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 (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, 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., a company that repairs, strengthens, and waterproofs concrete structures, says his company is constantly being contacted by anxious facility managers at amusement parks, parking structures, stadiums, and any structure where concrete is critical to a structure’s integrity.
Crack Classification
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 loadbearing 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 prevent them 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,” Barlow says.
The 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 cracks could indicate an underlying stress issue that needs to be addressed. But as the size of openings increases, so should the concern. As a general rule, Barlow says cracks 0.015 inches or larger should be investigated.
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,” Barlow says. “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 pre-stressed concrete beams. Demolishing the structure and starting over was not considered an option, so 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 that sat 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,” he says.
Water, however, presented a further challenge—the epoxy had to deal with a saturated environment. WJE requested help from ChemCo Systems’ team of chemists and formulated an epoxy that could fill three-quarter-inch cracks and cure in the presence of water.
Duntemann pointed 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.
Building owners who notice 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. “The correct solution to a problem requires a good understanding of the cause of that problem,” says Duntemann.
Drew Robb is a Los Angeles-based writer specializing in business, engineering, and technology. Originally from Scotland, he has a degree in geology/geography from the University of Strath-clyde in Glasgow.
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