By Daniel Green
In Part One we discussed common issues with concrete and some questions remedial experts will face and need an answer to it prior to beginning work. In this article, we’ll go into more depth about the repair methods themselves.
Concrete repairs generally occur in three primary ways.
- Demolition and rebuilding. The first way of concrete repairing is Demolition and rebuilding. Mechanical means removing the offending material and rebuilding the area with fresh concrete or polymer concrete-like materials.
- Crack injection. The second way of concrete repairing is Crack injection. Access is made for the injection ‘needle’ and epoxies [two stages] or urethanes [single stage] are injected. Upon curing these products can maintain properties equal to or better than the surrounding concrete.
- Cathodic protection. The third way of concrete repairing is Cathodic protection. Sacrificial anodes are installed into the slab that is of a lesser material than steel reinforcement, corrosively speaking. The anodes sacrifice themselves by corroding first, leaving the rebar intact.
Chemical damage. There are many different repair methods because there are scores of possible scenarios. It is impossible to list them all.
One common situation is acid damage. You can frequently see mild deterioration like vinegar and red wine on bottle shop floors. Also, you can find heavy damage such as battery acid, alkaline liquids such as coolant, and some industrial oils on workshop floors.
In this and many other chemical damage scenarios, wet diamond grinding using a rotary grinder will remove the lighter damage. There still may be discolouration but it should be significantly reduced. Heavier damage, however, may require a deeper penetration such as mechanical removal coupled with a polymer repair product, self-leveling flooring, or fresh concrete. Again, this depends on the surrounding finish and the needs of the client.
The cause will almost fully dictate the repair.
Ground settlement is expected after large civil works and/or deep excavation. If construction is swift or there is unexpected ground movement then concrete structures can crack and ultimately – collapse. Similarly with tectonic movement, although naturally, this can be on a much wider scale.
Extreme temperatures can see the concrete contract and expand significantly even in normal weather conditions. An environment with lows of 20ºC and highs of 35ºC will see concrete expand and contract by 12mm every 30m. When that variance is greater than 15ºC the movement increases significantly. Regular concrete is built to withstand what is considered a ‘normal’ operating range – from both annually and daily cycles. However there are many places on earth that regularly see a 50ºC variance in the same day, and, due to weather patterns, 50ºC variances within a matter of hours.
Lacklustre deshuttering can cause issues with the concrete. For example, if it is stripped when the slab is too green or if the form workers are careless – or both.
In all of the above cases, there is no one repair to fit all. Traditionally, demolition and rebuilding was the only available action. But with the advent of technology, concrete repair in the form of crack injection is a superb, non-invasive solution. This is where epoxies or urethanes are injected into cracks that once cured, maintain properties equal to or greater than the concrete itself. However, if the damage is significant enough it will almost certainly call for demolition and reporting.
During the extreme heat caused by fire, trapped air inside masonry products becomes superheated. Because the surrounding material envelops it, the pressure grows until it explodes. The Great Fire of London in 1666 saw St. Paul’s Cathedral almost totally destroyed by exploding air pockets in its stone walls. The remedy for this is totally dependent on the type of damage, how much there is, and the physiological environment around the concrete.
Repairing expansion joints on floor slabs are often straightforward, though it depends on the depth of the damage. If the damage is superficial then the repair needn’t be as invasive as if the damage has broached the entire slab. In either case, all loose concrete, rebar, and dust need to be removed, with a focus on stepping the edges so as little feathering can occur as possible. The best scenario is to vertically cut at least 75mm deep with a concrete saw, ensuring the new pour is thick enough to retain strength.
This depends entirely on the location of the leak[s]. In some scenarios, the repair is easily accessible whereas in others it will require partial deconstruction.
Concrete cancer. Cathodic Protection and demolition are the only real options. Remember that CP will not fix cancer, it will merely stop or slow it down. A true back-to-base repair will involve mechanical deconstruction and rebuilding.
Rendering. Most issues that arise from render are poor workmanship, substandard products, or improper use of those products. Thankfully, the render is not structural so repairs are less costly. Depending on the issue the render may need a full replacement or just it is enough to patch the damaged areas. One footnote: cracked render can be a precursor to deeper underlying issues. A thorough site visit is required.
Human error. If the engineer hasn’t allowed for enough concrete material in webbings; or his design has put steel reinforcing too close to the surface or not enough; or a feature tapers out too thinly; no matter how good the mix, concreters, farmworkers, and materials are – it will fail. The scope of this scenario is so broad that the concrete repair can only be determined case by case after a thorough site inspection, though obvious repairs are partial demolition or crack injection.
Correcting some issues with concrete is very straightforward. However, some repairs can be quite complex and will need the expertise of a professional.
Concrete Remediation. We Get It Done.
For more information on our services, take a look at our webpage or request a free quote.contact us today