Concrete is the most commonly used building material because of its durability, aesthetic appeal, ease of application, and low material cost. Due to the rigid nature of concrete, slab cracks are unavoidable. Uneven drying, shrinkage, and temperature changes can all cause fractures in your slab. In some applications, a slab crack only affects the aesthetics but in many applications, even a small crack can cause water intrusion, structural deficiencies, or other major problems.
Crack Classification
Cracks are classified as structural and non-structural.
Structural cracks may endanger the safety and durability of a building or structure. Structural cracks can form when the control joints were not designed correctly, during faulty construction, when a building is overloaded, or through aging.
Non-structural cracks are often caused by stress in building materials and don’t endanger the building structure. However, when left untreated, they can lead to corrosion of reinforcement material and facilitate the ingress of moisture and other destructive environmental substances degrading the structural integrity of the concrete.
In order to properly diagnose a crack and determine the best course of action, a qualified professional should be consulted. Only by an accurate diagnosis of the cause of cracking can you be assured that the crack repair will be durable and prevent further settlement and structural deterioration. Simply pouring hydraulic cement into foundation cracks may hide the problem from view, but it does nothing to repair cracks or prevent further deterioration.
Common Causes of Slab Cracks
Poor concrete mix
The quality of concrete depends on the quality of the materials that go into it. Inferior concrete is known to have a shorter life span, and it may present with visible cracks on its surface. Poor-quality concrete is also characterized by lower tensile strengths than high-quality concrete, which means that these structures give in to the pressure exerted on them at relatively low amounts of stress. Excess water or the wrong ratio of concrete to aggregate can significantly affect the quality of the concrete mix. Low-quality concrete will often form drying shrinkage cracks as the concrete cures.
Concrete not thick enough
A concrete floor or slab must be poured to the correct thickness according to the design of a certified engineer. Slabs that are poured too thin may experience rapid drying which inhibits the proper curing process and weakens the concrete. When concrete dries improperly smaller cracks will often occur and the slab is prone to further damage as it ages.
Settlement
Slab settlement is the downward movement of a concrete slab due to soil subsidence, which occurs when the soil supporting it can no longer bear its weight. Ground subsidence may result from the settlement of native low-density soils, or the caving in of natural or man-made underground voids.
Ground movement
Careful consideration of the ground under a slab should be taken during planning and construction to ensure long-term stability and prevent slab movement. The way that it is done can include: appropriate drainage, sloping the ground away from the building, paved areas to minimize water retention, careful thinning of plants in order to avoid root growth which could damage foundations of buildings, and preventing unnecessary watering of garden beds and lawns during rainy seasons to minimize soil displacement.
Shrinkage
During the mixing stages, excess moisture is often added since it helps to place and work with the concrete. The extra water is not part of the hydration process and evaporates from the concrete over time. As the water leaves, it creates a change in volume, known as drying shrinkage. If the concrete is not strong enough during the curing process to withstand the tensile forces of this volume change, the new concrete will crack
Expansion
Expansion joints are a crucial part of concrete construction — they allow the concrete to expand and contract as the temperature changes. They form a break between a slab and the surrounding concrete, allowing movement with reduced stress. The permanent joints should provide space for movement on all four sides of the slab. An improperly installed expansion joint can cause concrete cracks even in newly poured concrete slabs.
Traditional Repair Methods for Concrete Cracks
Sealant
A sealant or penetrating primer is applied to the concrete surface to soak into the pores of the portland cement, reducing or eliminating the ability of water to penetrate the surface. This common technique will strengthen the concrete, help adhere loose concrete and reduce the damage by freeze/thaw cycles. This is a common technique for concrete floors although an aggregate is generally required to provide a non-slip finish. A sealant is not really a repair material to fix cracks but it does serve to reduce future cracking and protect the concrete.
Coatings
An epoxy coating is a popular product to resurface a garage floor or any concrete floor. They will cover existing cracks in concrete, even penetrating into the crack somewhat, but they cannot penetrate the entire crack and are generally considered a temporary crack repair solution prone to re-cracking in time. Even when applied with a backer rod, further movement of the concrete or uneven settlement will cause cracks to reform in time.
Concrete
Some contractors repair concrete by adding more concrete, but this method only fills the crack and does not provide any tensile strength. Concrete has very poor adhesion to pre-existing concrete so this is not a long-term crack repair technique.
Caulking materials
Polyurethane and silicone caulk are popular choices for sealing a concrete crack or crevice because of their easy application with a caulking gun. They have very low permeability and can often be painted when dry. Using a flexible caulking material is a better solution than a more rigid coating system but the caulks do not add tensile strength to the concrete and are only used for superficial and non-structural cracks.
Epoxy and urethane injections
In order to fix cracks that are deeper in a concrete structure you can use an epoxy injection or a hydrophilic urethane injection. These are excellent solutions for wider cracks and provide a longer leak-free service life than other repair options. They will not strengthen the concrete to prevent future cracks so they are usually combined with another repair technology for optimal, long-term performance.
A New Approach – Crack Repairs with Carbon Fiber
Carbon fiber composites have been used for structural strengthening for almost three decades. As more FRP composites are used to reinforce structures, design engineers are finding that this innovative technology is far more effective than conventional methods of structural strengthening, including crack repairs.
Carbon fiber composites are a versatile tool for repairing cracks in concrete. The composite system provides outstanding adhesion and can actually increase the tensile strength of a damaged concrete section. Carbon fiber can be used to arrest the expansion of existing cracks or to bridge cracks in concrete to ensure a water-tight surface.
Application of Carbon Fiber Composite for Crack Repair
Carbon fiber composites can be applied over expansion joints or stress cracks in concrete, after the application of a bond-breaker, to create a long-term water-tight seal. This is especially popular in industrial settings, like secondary containment structures that are subsequently coated.
The installation process of carbon fiber crack repair
A penetrating primer is applied to the concrete to strengthen the surface and increase the bond strength of the repair.
Epoxy putty or elastomer is applied into the crack to create a smooth surface.
A bond-breaker, life Teflon tape, is applied over the crack to allow for movement.
A saturated Carbon fiber composite is applied over the crack. If multiple layers are used, they are tapered to relieve stress at the edge of the repair.
A protective coating can be applied if required to protect the remaining concrete.
Corrosion from severe MIC or aggressive materials, as well as isolated pipe corrosion, can be fixed with an internal carbon fiber system,
Internal pipe repair with carbon fiber composite provides a long-term life extension of your assets. With more than 10 times the strength to weight ratio of steel, internal composite carbon fiber repair can repair and structurally rehabilitate even the most badly corroded pipes.
Internal pipe repair can be done on pipes above 32 inches in diameter because it does take a technician in the pipe to install.
The biggest benefit of internal pipe repair is that it is a permanent solution, no matter what state of degradation your pipe has. Engineered solutions are available that provide more than 50 years of additional service life.
The surface preparation is critical for a successful bond between the carbon fiber composite and the existing concrete. Any existing deterioration or corrosion of internal reinforcement must be resolved prior to the installation of the FRP reinforcement.
Uses of Carbon Fiber in Concrete Repair
Carbon Fiber Composite is a very practical tool for strengthening and retrofit of concrete structures outside of simple crack repairs. It is appropriate for
Flexural strengthening,
Shear strengthening, and
Column confinement and ductility improvement.
Carbon fiber composite systems are also an attractive option to stabilize concrete structures in seismic zones. These systems have been used to mitigate a range of concrete problems, including brittle failure mechanisms such as shear failure of unconfined beam-column joints, shear failure of beams and columns, and lap splice failure.
Need Help with Fixing a Cracked Concrete? Contact us.
Advanced FRP Systems offers innovative, customized structural repair and reinforcement solutions using high-quality materials compliant with many pertinent ISO, DOT, ASME, and API code requirements.
If you struggle with cracks in your concrete structures,contact us and we’ll find the right composite solution for you.
Concrete Slab Crack Repair: Best Methods for Walls & Floors
Concrete is the most commonly used building material because of its durability, aesthetic appeal, ease of application, and low material cost. Due to the rigid nature of concrete, slab cracks are unavoidable. Uneven drying, shrinkage, and temperature changes can all cause fractures in your slab. In some applications, a slab crack only affects the aesthetics but in many applications, even a small crack can cause water intrusion, structural deficiencies, or other major problems.
Crack Classification
Cracks are classified as structural and non-structural.
Structural cracks may endanger the safety and durability of a building or structure. Structural cracks can form when the control joints were not designed correctly, during faulty construction, when a building is overloaded, or through aging.
Non-structural cracks are often caused by stress in building materials and don’t endanger the building structure. However, when left untreated, they can lead to corrosion of reinforcement material and facilitate the ingress of moisture and other destructive environmental substances degrading the structural integrity of the concrete.
In order to properly diagnose a crack and determine the best course of action, a qualified professional should be consulted. Only by an accurate diagnosis of the cause of cracking can you be assured that the crack repair will be durable and prevent further settlement and structural deterioration. Simply pouring hydraulic cement into foundation cracks may hide the problem from view, but it does nothing to repair cracks or prevent further deterioration.
Common Causes of Slab Cracks
Poor concrete mix
The quality of concrete depends on the quality of the materials that go into it. Inferior concrete is known to have a shorter life span, and it may present with visible cracks on its surface. Poor-quality concrete is also characterized by lower tensile strengths than high-quality concrete, which means that these structures give in to the pressure exerted on them at relatively low amounts of stress. Excess water or the wrong ratio of concrete to aggregate can significantly affect the quality of the concrete mix. Low-quality concrete will often form drying shrinkage cracks as the concrete cures.
Concrete not thick enough
A concrete floor or slab must be poured to the correct thickness according to the design of a certified engineer. Slabs that are poured too thin may experience rapid drying which inhibits the proper curing process and weakens the concrete. When concrete dries improperly smaller cracks will often occur and the slab is prone to further damage as it ages.
Settlement
Slab settlement is the downward movement of a concrete slab due to soil subsidence, which occurs when the soil supporting it can no longer bear its weight. Ground subsidence may result from the settlement of native low-density soils, or the caving in of natural or man-made underground voids.
Ground movement
Careful consideration of the ground under a slab should be taken during planning and construction to ensure long-term stability and prevent slab movement. The way that it is done can include: appropriate drainage, sloping the ground away from the building, paved areas to minimize water retention, careful thinning of plants in order to avoid root growth which could damage foundations of buildings, and preventing unnecessary watering of garden beds and lawns during rainy seasons to minimize soil displacement.
Shrinkage
During the mixing stages, excess moisture is often added since it helps to place and work with the concrete. The extra water is not part of the hydration process and evaporates from the concrete over time. As the water leaves, it creates a change in volume, known as drying shrinkage. If the concrete is not strong enough during the curing process to withstand the tensile forces of this volume change, the new concrete will crack
Expansion
Expansion joints are a crucial part of concrete construction — they allow the concrete to expand and contract as the temperature changes. They form a break between a slab and the surrounding concrete, allowing movement with reduced stress. The permanent joints should provide space for movement on all four sides of the slab. An improperly installed expansion joint can cause concrete cracks even in newly poured concrete slabs.
Traditional Repair Methods for Concrete Cracks
Sealant
A sealant or penetrating primer is applied to the concrete surface to soak into the pores of the portland cement, reducing or eliminating the ability of water to penetrate the surface. This common technique will strengthen the concrete, help adhere loose concrete and reduce the damage by freeze/thaw cycles. This is a common technique for concrete floors although an aggregate is generally required to provide a non-slip finish. A sealant is not really a repair material to fix cracks but it does serve to reduce future cracking and protect the concrete.
Coatings
An epoxy coating is a popular product to resurface a garage floor or any concrete floor. They will cover existing cracks in concrete, even penetrating into the crack somewhat, but they cannot penetrate the entire crack and are generally considered a temporary crack repair solution prone to re-cracking in time. Even when applied with a backer rod, further movement of the concrete or uneven settlement will cause cracks to reform in time.
Concrete
Some contractors repair concrete by adding more concrete, but this method only fills the crack and does not provide any tensile strength. Concrete has very poor adhesion to pre-existing concrete so this is not a long-term crack repair technique.
Caulking materials
Polyurethane and silicone caulk are popular choices for sealing a concrete crack or crevice because of their easy application with a caulking gun. They have very low permeability and can often be painted when dry. Using a flexible caulking material is a better solution than a more rigid coating system but the caulks do not add tensile strength to the concrete and are only used for superficial and non-structural cracks.
Epoxy and urethane injections
In order to fix cracks that are deeper in a concrete structure you can use an epoxy injection or a hydrophilic urethane injection. These are excellent solutions for wider cracks and provide a longer leak-free service life than other repair options. They will not strengthen the concrete to prevent future cracks so they are usually combined with another repair technology for optimal, long-term performance.
A New Approach – Crack Repairs with Carbon Fiber
Carbon fiber composites have been used for structural strengthening for almost three decades. As more FRP composites are used to reinforce structures, design engineers are finding that this innovative technology is far more effective than conventional methods of structural strengthening, including crack repairs.
Carbon fiber composites are a versatile tool for repairing cracks in concrete. The composite system provides outstanding adhesion and can actually increase the tensile strength of a damaged concrete section. Carbon fiber can be used to arrest the expansion of existing cracks or to bridge cracks in concrete to ensure a water-tight surface.
Application of Carbon Fiber Composite for Crack Repair
Carbon fiber composites can be applied over expansion joints or stress cracks in concrete, after the application of a bond-breaker, to create a long-term water-tight seal. This is especially popular in industrial settings, like secondary containment structures that are subsequently coated.
The installation process of carbon fiber crack repair
Corrosion from severe MIC or aggressive materials, as well as isolated pipe corrosion, can be fixed with an internal carbon fiber system,
Internal pipe repair with carbon fiber composite provides a long-term life extension of your assets. With more than 10 times the strength to weight ratio of steel, internal composite carbon fiber repair can repair and structurally rehabilitate even the most badly corroded pipes.
Internal pipe repair can be done on pipes above 32 inches in diameter because it does take a technician in the pipe to install.
The biggest benefit of internal pipe repair is that it is a permanent solution, no matter what state of degradation your pipe has. Engineered solutions are available that provide more than 50 years of additional service life.
The surface preparation is critical for a successful bond between the carbon fiber composite and the existing concrete. Any existing deterioration or corrosion of internal reinforcement must be resolved prior to the installation of the FRP reinforcement.
Uses of Carbon Fiber in Concrete Repair
Carbon Fiber Composite is a very practical tool for strengthening and retrofit of concrete structures outside of simple crack repairs. It is appropriate for
Carbon fiber composite systems are also an attractive option to stabilize concrete structures in seismic zones. These systems have been used to mitigate a range of concrete problems, including brittle failure mechanisms such as shear failure of unconfined beam-column joints, shear failure of beams and columns, and lap splice failure.
Need Help with Fixing a Cracked Concrete? Contact us.
Advanced FRP Systems offers innovative, customized structural repair and reinforcement solutions using high-quality materials compliant with many pertinent ISO, DOT, ASME, and API code requirements.
If you struggle with cracks in your concrete structures, contact us and we’ll find the right composite solution for you.