When we carry out remedial repairs on concrete structures, our repair’s object is to improve the durability and wear characteristics of the concrete surface, providing watertightness and preventing the development of a corrosive environment for the reinforcement steel.
With that, our goal is to ensure that the long-term integrity of the concrete elements is not compromised.
We repair everything from basic hairline fractures in concrete, right through to more serious structural damage.
Concrete elements with visible cracks can be repaired and renewed with long-term results, provided the structure has not been wholly deformed and the original cause of cracking has been eliminated.
Cracks in concrete are of common occurrence and they develop when stresses in the concrete exceed its strength. Cracks are often caused by normal shrinkage of the concrete when hardening and drying. Concrete cracks can range from being a non-structural and unsightly crack to being detrimental to the structural integrity and safety of a building.
Generally speaking, while most types of cracks do not affect the structural stability or durability, a crack’s status identification is critically important. Identifying what type of crack it is, and how it occurred, will help determine what repairs that are required.
Non-structural cracks, do not impact on the integrity and strength of the concrete structure, but affect the aesthetics of the structure and with time. Nevertheless, if left untreated, they have the potential to develop into a problem as they can act as a passageway for the penetration of materials into the concrete structure.
Cracks that are 0.3 mm or greater pose an issue for durability and watertightness. This can eventuate into concrete deterioration, affecting its strength and durability.
Repair of Dormant cracks – Dormant cracks are stable and future movements are not anticipated or in other words, unlikely to open, close or extend further. Cracking caused by drying shrinkage and thermal shrinkage will be active cracks at the beginning but may eventually stabilise and become dormant.
Fine hairline cracks may not need any repairs however, these cracks may prove to be a future durability problem. We recommend sealing them by installing a bonded overlay or surface treatment as a protective coating. (If the fine crack is non-dormant, we would recommend v-cutting it and seal it with appropriate sealant material to accommodate for the potential movement). These treatments will aid in protecting the concrete from water ingress and other destructive environmental influences.
Wider cracks may be sealed by epoxy, polyurethane or acrylic resins followed by a protective coating or membrane.
Repair of Active/Non-dormant cracks: – Active/dynamic/live concrete cracks are expected to experience further movement and growth. The cracks may be resulting from continuous foundation settlement or the cracks are acting as contraction and expansion joints.
These cracks should be treated as if they are the moving joints and the repair should cater for the anticipated potential movement. V-cutting along the line of the crack and then seal it with appropriate sealant material will allow movement and protect against further expansion of the crack and possible water ingress.
Active/dynamic/live cracks can effectively be repaired with high-pressure polyurethane injection, which may be followed by installation of a joint-seal and protective coating or membrane.
When to use Epoxy
Depending on the specific requirements of the job, crack repair by epoxy injection can restore structural integrity and reduce water penetration through concrete cracks that measure 0.05 mm in with or greater.
When future movement cannot be anticipated (dormant cracks), low viscosity epoxy resin is used. It may not be possible to repair the crack with epoxy resin if the crack is subject to subsequent movement.
Another consideration is that epoxy resins can have difficulty setting and developing their desired strength if there is water present unless the epoxy resin is designed to tolerate water during the curing process.
When to use Polyurethane
Polyurethane resins are excellent to seal wet and leaking cracks and cracks that are non-dormant/active cracks. This repair option is used to stop water leaks and consists of injecting a highly water reactive resin into cracks under pressure. The product reacts rapidly with the water, chasing the water present in the crack and begins to foam and expand, filling the entire crack resulting in a strong bond with the concrete and a flexible waterproof seal preventing future water leaks. This repair is a permanent repair and works with either active or dormant cracks. One of the benefits of polyurethane crack injection is that it both strong as well as providing some flexibility for crack movement.
INJECTING REPAIRABLE CRACKS IN CONCRETE WILL:
✔️ Restore structural and/or design strength to the cracked concrete structure (usually repaired with Epoxy injection). Depending on the type of crack, we normally use either Polyurethane for flexible crack repair or Epoxy for structural repair.
✔️ Eliminate serious spalling of concrete initiated by cracking and aggravated by thermal changes and ground movement.
✔️ Prevent corrosion of reinforcing steel and pre-stress tendons by encapsulating them against moisture or water contact.
✔️ Stop the leakage of water and fluids through concrete structures.
✔️ Repair concrete architecturally without any of the unsightly surface marks caused by standard surface crack repairs.
THREE MAIN INJECTION TECHNIQUES THAT WE USE:
Syringe or gravity injection – Low pressure
Paste on injection packers – Medium pressure
Packer injection – High pressure
Photos below show concrete crack injection repair carried out with high-pressure injection of polyurethane resin into a cracked concrete slab in an underground car park on the Gold Coast, Queensland:
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