Concrete cracks. It’s the reality of life. Certain cracks may not require attention, while others may have grave structural implications. How do you know the different?
“It is essential to correctly evaluate structural cracks in order to determine what’s important and what’s non-significant,” said John Duntemann an engineer in structural engineering at the consulting engineering firm Wiss, Janney, Elstner Associates (WJE). “You must be able to determine the severity and reason for cracks prior to implementing the best repair method.”
Cracks in concrete can result from a variety of reasons, such as temperature-related expansion or contraction subgrade settlement, the load being placed on the concrete or even earthquakes. All of these causes cause external and internal stress which manifests in large and tiny cracks.
In most cases however, there’s doubt about how to deal with cracks. Pete Barlow, a principal of Contech Services Inc., an organization that repair and strengthens concrete structures, said that his firm is always approached by concerned owners and managers of buildings. “Many times throughout the week, clients send us pictures of cracks in their properties, seeking guidance,” said Barlow.
Concrete Crack Classification
There are a variety of methods for categorizing cracks that occur in concrete. One method is to divide them into two categories which are Non-structural and structural. The structural cracks can compromise the integrity of the structure. Cracks in support beams columns, and load bearing zones is particularly problematic. Certain cracks in concrete structural permit the steel reinforcing the concrete to corrode. This further reduces strength of the building.
Non-structural cracks, on contrary, aren’t damaging to the integrity of the structure However, they might have to be repaired because of aesthetic reasons, in the event of leakage of water or proactive measures to stop those cracks from getting worse and eventually becoming structural in nature. Small fractures may result in other problems.
“Small cracks in foundation walls that are below grade allow water to move inside the structures,” said Barlow.
The width, length and the depth of cracks are other factors to be considered. Hairline cracks generally aren’t an issue, however it is dependent on the location they’re located. If they are frequent however, may be a sign of a stress issue which needs to be addressed. As the openings’ size increases as does the potential for concern. In general cracks that are 0.015 inches or greater,” said Barlow, “should be examined. The greater the width more likely that you’ve lost aggregate interlock. Repairs can be made on cracks that are less than 0.005 inches.”
A third issue is location/orientation. Cracks that occur in random directions are more important than those found in columns, beams or other areas bearing loads. “If you notice that one of your sides of the crack is in a different direction from the other it is usually an indication of a problem,” said Barlow. “Other indications of danger are tightly spaced cracks , or repeat cracks in the same places on the floor.”
Epoxy in Structural Concrete Repair
In many instances epoxy injection is used as the most effective method of crack repair in concrete. There are many kinds of epoxy and their uses the most high-performance epoxies that are made for concrete bonding in structural construction or crack repair is the primary focus on in this article.
Duntemann provides an example of cracking which occurred in a cooling system being built at the synthetic fuel plant. “Cracking occurred at the end of concrete beams that were pre-stressed. The structure was demolished and the idea of restarting it was not an alternative. Management called in WJE to help find a solution. The beams were then injected with epoxy, and then loaded to test the structural capacity,”said Duntemann.
In another instance, WJE was retained to examine large cracks in caps of concrete that were placed on the foundations of concrete piles. “We came up with a method for strengthening the caps of the pile and then injected an epoxy through the cracks in order to connect the caps that were split,” said Duntemann.
Water However, it caused a different problem “the epoxy was required to deal with a saturated atmosphere. WJE sought assistance by ChemCo Systems’ team of scientists and chemists. They created an epoxy that can fill cracks of three quarter inches and cure when exposed to water. ChemCo is a specialist in the production of two component structural epoxies , as well as the application equipment to repair concrete structures which can be found in bridges, industrial plants, parking decks and stadiums to mention several.”
“You frequently encounter challenging situations like cracks filled with water, cold temperatures or huge cracks, which need a bespoke solutions,” said Duntemann. “The ChemCo Systems staff is extremely familiar with epoxy in general as well as their products as well as the conditions where the products are used. We usually identify products that could be used and then consult with the company like ChemCo Systems for advice on the application of the product.”
Contech Services, too, has been working in conjunction with ChemCo Systems for more than 25 years. The field staff have been fully trained in the application and usage for ChemCo Systems epoxy resins and equipment used for structural repairs.
“Their Chemists are aware of their physical characteristics of various resins , and how to mix them in order to ensure that the job is done correctly,” said Barlow. “We would prefer ChemCo Systems as it acts as a single source for materials, equipment and knowledge for a wide range of resins. Major manufacturers typically have three or four resins, at the most. ChemCo Systems has about a dozen. If you encounter something that is unique they can tell which one or mix is the best for.”
