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A true structural repair. The surface seal becomes an integral part of the crack injection process.


Understanding the movement of cracks will increase the success rate of repair. There are 6 ways in which a crack in a below-grade poured concrete wall generally moves:

  • Tensile/inward: due to lateral loading
  • Outward: due to shrinkage of soils
  • Opening: due to thermal changes
  • Closing: due to thermal changes, i.e. cold, wet, dry, etc.
  • Shear: due to differential loading
  • Combination: all of the above conditions, plus the added load of the structure

This system revolutionizes concrete crack repair by combining carbon fiber stitching embedded in a hardened epoxy with a structural polyurethane grout injection.

A true structural repair. The surface seal becomes an integral part of the crack injection process.

All other surface seals add nothing to the crack repair and need to be removed.
Can be used for vertical or horizontal crack repair.
Dual Surface seal carbon fiber stitching prevents cracking fatigue and distributes load to solid concrete.

Imagine one repair material and technique that addresses all 6 movements!


UNDERSTANDING CRACK MOVEMENT:

The first step is to understand the variables that can cause cracking. Cracking of concrete is a natural consequence of the concrete going from a plastic state to a solid state. This is due in part to stress caused by temperature change and restraint. This is often referred to as drying and shrinkage cracking. Depending on the moisture content, this process is over within a maximum of 3 years. In poured concrete, cracks are usually vertical in nature. The concrete will typically perform the way it was designed after chemically welding the crack back together.


STRUCTURAL CRACKS:

This cracking pattern will be larger in diameter than shrinkage cracks and usually appear more on a 45° angle. Understanding settlement vs. lateral loading allows for proper procedure of repair. If settlement exists, no method of repair will withstand the differential movement and loading resulting from the settling (whether it be grouting and sealing or epoxy /urethane injections) until the settlement issue is corrected.

Lateral loading may present the same cracking patterns as settling, with the exception of mapping out cracks into floor slab. Distinguish whether there are lateral load or settlement problems. Always check for proper sill plate anchorage (building staying put and foundation sliding inward). In either settlement or sill plate slide conditions, the problems need to be corrected or cracking will continue. In some cases the cracking will be elsewhere in foundation.

In drying and shrinkage crack repair, a standard epoxy injection or urethane grout technique is most commonly used. Stitching has proven to take the load away from the repair material glue line and increase long-term success. Time is the enemy of a successful concrete repair and the interaction between repair material and concrete substrate.


STRUCTURAL CRACKING IN POURED CONCRETE:

The goal is to return a given structure to its designed condition. You must diagnose and solve initial problem before addressing the cracking. Failure to address the cracks themselves will allow cracks to worsen with time. Cracks that are larger than 3/8-inch wide may require a gel epoxy rather than a low viscosity epoxy. By their nature, gels or pastes have less wetting or bonding capabilities than liquid materials. Stitching provides a superior upgrade to these types of repairs, when done in conjunction with crack injection.


HOW CRACKS MOVE:

Understanding the movement of cracks will increase the success rate of repair. There are 6 ways in which a crack in a below-grade poured concrete wall generally moves:

movement1movement2movement3-2movement4

  1. Tensile/inward: due to lateral loading
  2. Outward: due to shrinkage of soils
  3. Opening: due to thermal changes
  4. Closing: due to thermal changes, i.e. cold, wet, dry, etc.
  5. Shear: due to differential loading
  6. Combination: all of the above conditions, plus the added load of the structure

Stitching in surface seal: These are usually caused by settlement, lack of reinforcement, differential loading, inadequate concrete or improper anchorage at top. Once cracking occurs, lateral forces also contribute.

Note: These types of cracks experience all six loads. Carbon fiber and repair materials are not very good in shear loads, which may be the dominant movement. However, aligning the carbon tows at 30° to the expected shear loads will load the carbon in tension, allowing carbon to function in shear.

There are actually more than 6 factors, but these are the most common. Many of these six, if not all, are the same in masonry walls (although their behavior is somewhat different.)

Imagine one repair material and technique that addresses all 6 movements.

Carbon fiber reinforcement or steel has little benefit without making concrete one again. A poured wall with 2 cracks is actually 3 separate sections of concrete, susceptible to all 6 movements. In most cases the wall was not designed to be 3 individual moving sections, unless control joints were part of the original design. All control joints must be respected for their purpose. Understanding these principles are the difference between successful crack repairs or mind-boggling failures.


HOW CARBON FIBER SURFACE STITCHING OF CRACKS WORK

EPOXY INJECTION:

This is the best marriage because the two work in harmony. The epoxy does the work for #2 because it creates a wedge instead of a hinge point. It also does the work on #4; the crack cannot close due to its high compression. On numbers 1,3,5 and 6 it also performs well to a point. The carbon fiber excels in #1 and #3. It can also increase success in #5 and #6. In #1, the inward movement is a tensile force which carbon is tailor-made for. #3 is also a tensile force. In #5 and #6 you have a combination tensile force or pulling and shear forces. The carbon fiber can be aligned for tensile in a shear force.


POLYURETHANE INJECTION:

Carbon fiber stitching can increase long-term success of polyurethane injections. However, in some instances, they may fight each other over different goals. Urethane by design works by allowing for crack movement. Carbon’s purpose by design is to arrest crack movement. Interesting enough, movement alone is not the enemy of urethane, but rather too much movement. This is where stitching with carbon can aid polyurethane injections. By eliminating some of the 6 movements, stitches allow the urethane to function better for its designed movement capabilities. Urethane grout is very good in compression but has limited tensile properties. Carbon fiber will help urethane dramatically with #1 inward movement and #3 opening or crack, but very little with #2 outward and #4 closing of crack. A high compression material such as epoxy, or cement based grout, must be pushed into face of crack to eliminate #2 outward, #4 closing and #5 shear when using urethane foam as well as aligning carbon properly for shear movement with #5 and #6.

Such materials act as a wedge in these hinge conditions, thus allowing the urethane foam to perform to its primary strengths. NOTE: This is not easily done on small or tight cracks. Short of filling the crack with a high compression material, there is no way of knowing if the wedge is sufficient for arresting the conditions of hinging.

CARBON versus STEEL:
Have you ever seen rebar bend? Once it is bent, it will not bend back to original form. Carbon loads up much quicker, and will not move back. That is why it is important to understand outward movement, etc. Carbon can be used in tensile and in shear by placing and loading in tension or redirecting load.

This information is designed to be a simple guide to understanding crack movement and the function of carbon fiber in crack repair. It is not Technical Specification in nature.