Cracks in concrete are common 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. They 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 – if any.
Non-structural cracks do not impact on the integrity and strength of the concrete structure, but affect the aesthetics of the structure. 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, water and chemicals into the concrete structure.
Cracks that are identified as small and fine (less than 0.3 mm in width), are generally deemed acceptable as part of minor settlement. However, if you are unsure of a crack’s status, we recommend having it inspected and diagnosed to classify the severity of the crack, the cause of the crack, if it is a dormant or a live crack in order to determine if a repair is needed and if so what the most effective repair method would be.
Cracks that are 0.3 mm or greater can pose an issue for durability and watertightness. This can eventuate into concrete deterioration, affecting its strength and durability.
Successful long-term repair procedures must address the causes of the cracks as well as the cracks themselves. Repairs to concrete structures should be undertaken with the advice of a qualified and licenced professional. Inappropriate repair techniques may result in greater damage later. Repair of mass concrete structures will depend on the crack width, depth, if it is dormant or live (active) and the service conditions of the structure.
Once the cause and significance of the concrete cracking has been diagnosed by a qualified and licenced inspector, it is important that accurate repair methods are followed. The selected repair methods are based on an evaluation of the crack and the repair’s objective(s).
Concrete crack repair objectives:
The key to successful crack repairs is having an understanding of the causes of the cracking and also whether the cracks are dormant or active.
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 sealing 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 width or greater.
Low viscosity epoxy resin is mainly used for structural crack repair when future movements are not anticipated (dormant cracks). If a crack is subject to subsequent movement, a repair with an epoxy resin may not be suitable.
Another thing to consider is that epoxy resins can have difficulties in setting and developing into the desired strength if there is presence of water, 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. The benefit of polyurethane crack injection is that it is strong and it provides some flexibility for crack movement.
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