London is known for its diverse architecture, from the striking curvature of the Gherkin to its quaint timber-built heritage pubs and taverns. Despite the renaissance of new construction techniques and materials, one ever-present material in the London skyline is concrete.
From its first documented use as a lime-based material in Roman constructions, to more modern Lytag constructions, concrete has seen a diverse use in construction for thousands of years. Concrete is known for its durability and resistance to the weather. However, resistance doesn’t mean complete protection, especially for aged or unreinforced concrete.
In this blog, we’ll discuss what causes concrete to fail, what the risks are with structural concrete damage, and what repair solutions are available to protect against further damage.
Why Does Concrete Fail in Commercial Structures?
Concrete is a hardy material, used in constructions from the Channel Tunnel to high-rise apartment blocks. However, there are several defects that can cause concrete to crumble, spall, or crack over time.
Water Ingress
Whether through an external defect or a plumbing leak, water ingress presents a real problem for any concrete it encounters. Concrete is porous and, over time, water can wear away the material.
Freezing and Thawing Moisture
For external-facing concrete, seasonal freezing and thawing can cause concrete to fail. This moisture expands as it freezes, causing the concrete around it to expand in turn, putting additional pressure on the surrounding material. This pressure eventually causes the concrete to crumble away, exposing the concrete underneath to the elements.
Carbonation
Another danger for porous concrete is carbon dioxide from vehicle emissions. This compound mixes with moisture in concrete, which then reacts with calcium hydroxide within the cement, forming calcium carbonate. This reduces the pH of the concrete, removing the protective layer around the steel rebar within.
Lack of Reinforcement
The addition of reinforcement to concrete only became a staple of modern construction in the late 19th century. Before then, it was unlikely for buildings to contain reinforcement at all. Older, unreinforced concrete is at a greater risk of weathering, carbonation, and urban vibrations caused by new infrastructure. Each of these risks can cause cracks to form more readily than in reinforced concrete.
Reinforcement Corrosion
This occurs when moisture penetrates enough to contact the steel rebar within reinforced concrete. When exposed to moisture, the steel corrodes, reducing its structural strength and rendering it prone to failure.
Unstable Foundations
London is built on a foundation of clay, especially in its Northern districts. If not compacted correctly during construction, this clay can give way to subsidence issues or moisture retention, creating more movement in the structural foundations of a building. This movement can cause cracks to form on the surface or within the concrete.
What are the Warning Signs of Concrete Structural Damage?
There are several warning signs that can alert you to an issue with your structural concrete.
- Spalling, where the freezing and thawing of water has caused the concrete to crumble away. This is most evident on external concrete that is exposed to the weather. Spalling may also show historic salts on the concrete’s surface, characterised by a white, dusty appearance.
- Rust staining, where the steel rebar within the concrete has become exposed to moisture, either from a defect in the concrete or a persistent leak around it. This moisture causes the steel rebar to corrode and rust, which may leech through the concrete and appear on the surface as copper brown stains.
- Structural cracking, where the concrete cracks due to increased stress upon it., creating noticeable defects on the surface. This can be caused by water ingress over time. However, it is often the result of structural pressure of materials pushing down on the concrete from above, especially if the concrete is a load-bearing component such as a lintel.
- Exposed reinforcement, where the internal steel rebar is revealed after the failure of the concrete around it. This steel rebar is then at a greater risk of corrosion without the protective concrete surrounding it.
How can I Repair Damaged Structural Concrete?
While concrete damage is serious and should be remediated at the earliest opportunity, there are several repair options available to restore the concrete’s structural rigidity. The availability of each option will depend on the environment surrounding the concrete, as well as the length of time the concrete has been left in an exposed state.
Request a Structural Repair Survey
The first step to repairing concrete damage is to have a professional structural repair survey conducted. This will not only assess the condition of any apparent concrete damage but will also highlight any potential risks in other areas of the building. Repairing one defect just to have another defect appear later is less cost-effective, and leads to further disruptions to any occupants of the building during these renovations.
Patch Repairs
Patch repairs consist of clearing any loose concrete from around a crack, either by hand or by using a chisel or sledgehammer. Once cleared, a suitable concrete repair mortar is applied to the area using the same materials as the original concrete. This is especially important in heritage buildings, as the materials used must be in keeping with any conservation concerns while restoring the property.
Resin Injection
An alternative to mortar repairs, resin can be injected into the capillaries of the concrete. These capillaries allow the resin to penetrate concrete, strengthening the same areas affected by the previous water ingress. Resin is versatile and can be used in anything from walls to driveways to floor slabs. However, it is less effective on extreme structural failures or areas of unstable soil beneath foundations. Many of London’s buildings are built on clay and may not be suitable for resin repairs.
Structural Strengthening
If the concrete is under a greater-than-expected load capacity, strengthening might be required for the structural concrete. This can involve several methods, such as jacketing (adding new concrete and reinforcement), steel bonding (installing external steel plates), or carbon fibre polymer bonding (installing a plate or fabric on the surface of the concrete). Repairs in this section aim to increase the load capacity of the concrete, reducing the likelihood of future defects forming.
Protective Coatings
These repairs involve applying a chemical coat (often epoxy or polyurethane) to the surface of the concrete to protect against carbonation and weathering. Once dry, these chemicals create a waterproof barrier that is ideal for use in infrastructure where there is an increased risk of moisture ingress, such as bridges or car parks. It can also be used as a tanking option in below ground structures. However, its use should be carefully considered prior to installation, as it can increase hydrostatic pressure behind a wall, leading to the creation of future defects.
Basement and Below-Ground Waterproofing
These repairs involve preventing water ingress around concrete structures. This is achieved by diverting water off waterproof membranes and through channels installed into the concrete at the base of the wall or within the floor slab. This prevents water ingress into the concrete itself and does not allow hydrostatic pressure to build behind a wall or under a floor slab.
Several structural waterproofing options are available, and you should consider each option carefully before choosing what system to install in your property. Our structural waterproofing page has more information on these options, and our surveyors will consult and design a waterproofing solution to your specification upon completion of a survey.
Why Does Early Intervention Save Money?
Early Intervention on a structural concrete repair often decreases the likelihood of expensive and extensive structural repairs. When caught early, concrete can often be repaired through previously described resin or mortar-based treatments. These repairs are often inexpensive and quick to implement, while also restoring the structural integrity of the concrete.
These repairs also don’t tend to disrupt the use of the building, and so occupants can continue to live and work in the building during remedial work. This makes them ideal in situations where the defect has not progressed significantly.
Conversely, the longer it takes to report a repair, the higher the likelihood of more repair work being required. A crack may start small, but can very easily leak to corrosion and other damage that can risk the integrity of the concrete. Once the integrity of the concrete is compromised, it’s very easy for the concrete to break away, especially if the concrete is load-bearing. In these cases, often the only remedial option available is structural strengthening, which can be time-consuming, expensive, and cause more disruption for any inhabitants of the building.
How do I Have My Structural Concrete Repaired?
You should book a structural repair survey prior to any remedial work to have your building assessed by one of our expert surveyors. This will help identify the correct solutions for your defects, as well as highlight any further defects that may require attention.
Upon receiving your survey, you might wish to contact our surveyor to discuss any concerns you might have. Doing so will provide peace of mind and will ensure that you are happy with any proposed remedial solutions prior to commencing work.
Post-survey, our team of technicians will conduct any required remedial work to the concrete to restore its structural integrity. Many of our structural repairs also include insurance-backed guarantees to ensure their success and longevity.
FAQs
How Much Does Concrete Repair Cost in London?
Concrete repairs can vary in costs depending on the severity of the damage and where in the building the damage is located. You should book a survey to have your property professionally assessed. Your survey will include a quotation for any recommended remedial work required to restore your property.
Is Spalling Concrete Dangerous?
Spalling concrete can pose a risk, as it often exposes the steel rebar supporting the concrete to corrosion if left untreated for long enough. This rebar provides structural strength to concrete, and damage to the rebar risks further structural weakening, either in the immediate area of spalling or further up the construction.
Can Reinforced Concrete be Restored?
Yes, it is often possible to restore reinforced concrete. Several methods are available to repair reinforced concrete, including mortar repairs, resin injections, or carbon fibre/steel plate installation on the surface of the concrete. The use of each method depends on the location and longevity of any defect, but each of these repairs aims to restore the structural strength of the concrete.
Do Concrete Repairs require Building Closure?
Often, many concrete repairs are minimally invasive and can be conducted without wider closures if caught and remedied early enough. However, it may be required to close a building in cases where a concrete repair is extensive or if the defect is in a location that provides structural strength to the remainder of the building. It may also be necessary to close a building if the repair is required in an area of high footfall to reduce the risk of injury to any occupants of the building.
