Reasons for Epoxy Crack Injection Concrete Repair
Despite the fact that cracks don’t always adversely affect structural performance, they can adversely affect structural durability.
Concrete cracks are most commonly caused by post cure and drying shrinkage, thermal stress, alkali-reactive silica and sulfates, freezing and thawing cycles due to water expansion, corrosion of steel rebar, settlement, load stresses, and design and construction errors.
The addition of steel reinforcement to structural concrete can cause elements to work both in compression and in tension, often resulting in tension cracking of concrete.
Concrete corrosion in parking garages, bridges, industrial facilities and more is caused by water. Chloride, water, and carbon dioxide can corrode reinforcement structures deep within a structure.
A leaky roof can lead to water leaks that contain corrosive substances and chlorides that breakdown concrete and cause corrosion in steel reinforcements and rebar. Many structures that show signs of these problems can be repaired with epoxy concrete crack injection. A complete tear down can often be avoided with the right concrete crack injection team.
Epoxy Concrete Crack Injection Systems
Injection Resin can mitigate problems of cracked concrete with larger and fine cracks. ACI specifies cracks widths that are acceptable in structures under defined conditions. ACI 224R-012 provides a guideline for crack widths for reinforced concrete under service loads for new construction. Crack widths deemed acceptable may range from 0.004 in. (0.1 mm) to 0.016 in. (0.41 mm), and even smaller widths for concrete in wet or aggressive environments. These crack dimensions would be considered fine and hairline cracks.
The epoxy crack injection resins conform to ASTM C881 specifications and have the appropriate viscosities for the crack widths. epoxy bonds to concrete cleaners more strongly than concrete itself can withstand tensile forces.
If the crack is wider, it may require a higher viscosity epoxy, while if it is smaller, it may require a lower viscosity injection resin. The viscosities at room temperature may vary between approximately 150 and 600 cps depending on the requirements.
Repairs of cracks in concrete can be performed with Epoxy Cartridge Systems or epoxy bulk resins using air guns, hand-operated delivery systems, or dual-component injection pumps.
It is imperative to examine the structure carefully before determining whether epoxy crack injection is the correct method to regain structural integrity. You must determine what caused the cracks in the first place. It is necessary to identify cracks and establish the allowable crack width. Crack gauge cards are used to determine the crack width. An expansion and contraction cycle measurement may be recommended in some cases. A petrographic and chemical examination of core samples can be used to determine the depth and cause of cracking. Ultrasonic pulse velocity can also be used to measure crack depth in nondestructive testing (NDT).
Surface-mounted injection ports are typically adequate for injecting most cracks. However, badly deteriorated concrete or higher injection pressures may require the use of drill-in or hammer-in plastic ports or even mechanical packers. Surface ports, aka plastic tubing ports, are glued on the surface over the open cracks using epoxy paste adhesive. The injection ports are typically installed at a spacing that is equal to or slightly narrower than the depth of the crack. Hairline cracks require closer spacing than wider cracks.
Wire brushing and vacuuming the crack surface along the crack is often sufficient for surface preparation. In areas of badly deteriorated concrete, pressure washing, grinding, and V-grooving may be specified.
Injecting epoxy continues from the next port once the epoxy appears at the next higher port. Multiple ports can be used for most epoxy injection applications. Typically, injection pressures are between 50 and 100 psi (3 to 6 bars), with very fine cracks requiring pressures of over 200 psi (12 bars).
Temperature is an important factor when it comes to epoxy resins. The resin viscosity decreases at higher temperatures, but the reaction time increases. When injecting the resin, it is best to keep it at room temperature or a little above.
The epoxy paste adhesive is removed from the concrete surface after the injection resin has cured.
Inspection of the injection process and product consumption, testing the injection equipment for mix ratio, taking core samples and testing repaired cracks using nondestructive testing methods are all examples of quality assurance and control measures.
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