Corrosion – Leading cause of defect issues in concrete

25 Jun Corrosion – Leading cause of defect issues in concrete

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Remedial waterproofing and concrete repairs are a fact of life for any organisation whose assets include sizeable concrete structures. Car parks in both residential and commercial buildings often require maintenance and repair. Undercover or underground/basement car parks are especially prone to water seepage and concrete deterioration.

The cause of steel-enforced concrete deterioration can often be linked back to moisture-borne contamination. In other words; penetration of water or water-borne compounds (chlorides, sulphates, carbonates, etc.)

A coastal climate with high humidity, salinity in the soil, salts in rainfall and a high level of airborne salts can accelerate the deterioration of unprotected concrete structures. Reinforced concrete structures degrade and corrode as the concrete’s alkalinity is reduced either by carbonation or by the ingress of chlorides (salts).

The build-up of corrosion causes tensile stresses as it grows in thickness. The pressure causes the concrete to form cracks near the steel that will with time lead to more extensive cracking as the rust builds up until the concrete starts to break away from the reinforcing steel bars (spalling of concrete) and expose the corroded reinforcing steel rods.

The corrosion of reinforcing steel leads to reduced resistance of the steel bars, which depending on severity, may negatively affect the load-bearing capacity and service life of the concrete.

What are the risk factors that can contribute to concrete cancer and spalling?

Several factors predetermine the risk of concrete cancer, including proximity to the coastline and a built-up environment; the degree of concrete cover to the reinforcing steel; the presence of differential metals; the quality and density of coating systems; inadequate waterproofing; building defects such as concrete cracking; insufficient joint and penetration detailing and the level of preventative maintenance.

The high pH (alkalinity) of concrete forms a passive film on the surface of the embedded reinforcing steel rods and acts as a protective shield that prevents or minimises corrosion. Reduction of the concrete’s pH by carbonation or the ingress of chlorides (salt), which are the most common causes of concrete corrosion, causes the steel’s passive film to degrade. Rust begins to form on the unprotected reinforcing steel.

Reduction of the concrete’s alkalinity either by carbonation or by the ingress of chlorides (salts) are the most common causes of concrete corrosion.

Three conditions must exist for reinforcing steel to corrode:

• The passivation of the steel must have been destroyed by chlorides or by carbonation
• The presence of moisture as an electrolyte
• The presence of oxygen

Reinforced concrete structures degrade with time and exposure to the environment, particularly if that environment contains salts. Corroding reinforcement is also commonly found in older precast concrete where excess calcium chloride has been added to the concrete mix to accelerate the hardening of the concrete.

One of the most common locations one can find corrosion of reinforcement steel are in columns and beams with the primary cause being a lack of concrete cover to protect the steel and/or poor-quality concrete. Other common areas of water-driven concrete cancer are basements, underground car parks, flat concrete rooftops and balconies.

Corrosion of the reinforcing steel or other embedded metals is by far the leading cause of premature ageing, deterioration and durability issues in concrete. Concrete cancer can happen in many areas of a concrete structure, so it is a good idea to regularly look out for tell-tale signs so that it can be remedied before it gets severe and becomes a serious problem and starts affecting the strength and structural integrity of the building.

To help prevent spalling from occurring, cracks and holes should be adequately sealed as soon as possible. A qualified and licenced professional should be consulted to classify the severity of the crack and appropriately investigate the cause of the crack and determine the most effective repair method if required.

Depending on the depth and/or width of the crack, certain concrete cracks may be v-cut with a concrete crack chaser and filled with suitable material, or by targeted injection of appropriate material tailored to the individual crack’s diagnosis, followed by a suitable concrete protection application.  A protective coating, a penetrative concrete sealer or a waterproof membrane will provide a barrier against moisture, salts and chemical attacks.

Signs to look out for in concrete and cement render:

• Flaking, crumbling, spalling, expanding concrete
• Rust Stains leaking out of the concrete
• Bubbling, blistering, plating of concrete render
• Leaks in overhead concrete surfaces
• Rusting and exposed reinforcement pushing concrete so that it cracks and becomes loose

Unfortunately, the problem is likely to be much more extensive than symptoms on the concrete surface suggest. As steel rusts, it can expand up to eight times its original size, causing the surrounding concrete to break away. Once established, the rusting will spread along the reinforcing in each direction. It is impossible to know the full extent of the damage until the concrete is chiselled away.

How to fix concrete cancer

Waterstop Solutions is an industry leader in concrete repair and protection of concrete structures.

Our extensive experience on major civil projects has afforded Waterstop Solutions opportunities to design with industry-leading engineers and tackle some of the most complex concrete repair challenges imaginable in the built environment. Using this knowledge, we can provide you with a range of options to best meet your project criteria.

With extensive training both locally and internationally our team stays up to date with the latest local and international standards to ensure our repair work is of the highest quality available. Waterstop Solutions also works closely with external specialist remedial engineers as required to ensure the best outcome for our clients.

Having earnt our reputation based on countless repair projects, Waterstop Solutions adds value to our clients’ assets and ensures the assets’ durability for the years to come.

The typical method of concrete cancer repair follows a process of:

1. Break out unsound concrete and expose reinforcing steel until sound concrete and clean non-corroded steel reinforcing are found.
2. Saw cut repair zone perimeter to eliminate feather edges.
3. The concrete around the reinforcing steel is chiselled away. Prepare substrates including removing any corrosion. Reinstate steel and/or add more as deemed necessary.
4. After completion of material removal, concrete primers and rust inhibitor to the steel are applied prior to reinstating with a high build shrinkage compensated repair mortar. Formwork may be erected to close the cavity prior to installing the repair products.
5. For further long-term protection, we also recommend a membrane coating system. Install a heavy-duty modified acrylic membrane in multiple layers as a moisture barrier primer system. The primer system will assist in preventing bubbling or blistering, which is highly likely if the remedial waterproofing application is not performed, which could otherwise affect the durability of the system.
6. Our recommendation is that treatment of concrete cancer should incorporate proper weather/waterproofing membrane or protective coating or the repair risks being a temporary solution. Install correct waterproofing or protective coatings that are designed to protect surfaces that are exposed to rainfall, wind and/or sea spray. Ensure that the waterproof membrane or the protective coating system is detailed to all penetrations and junctions.

Once the concrete cancer has been repaired, it is important to take preventative steps to ward off a recurrence. We recommend implementing a maintenance program tailored to the environment the building is subjected to including dedicated inspections. Regular maintenance checks will help identify any problems in the early stages for repairs, which again will help enhance the service life and reduce the life cycle cost of concrete structures.

With access to the latest proven products we are able to produce high-quality concrete repairs in the following fields:

• Concrete Cancer
• Crack Repairs
• High-pressure Leak Sealing Injections
• Joint repairs
• Void Injection and Chemical Grouting
• Cathodic Protection
• Protective Coatings

Waterstop Solutions teams are available for all your concrete repair and remedial waterproofing needs in Brisbane, Gold Coast, Sunshine Coast and Sydney.

If you have cracked or damaged concrete and/or moisture/seepage problems in your building, we welcome you to arrange a booking with one of our experienced inspectors to carry out an onsite assessment and provide you with their recommendations and a quotation for remedial repairs.  Contact us

Give us a call to discuss the best protective treatment application for your vertical and horizontal surfaces to help you choose the appropriate product and methods to protect them and how to best prepare the surface before installation for best performance.

If you have any issues with water ingress, rooftop leaks, leaking balcony, leaking basement, wet lift pit, cracking concrete slabs, structural cracks, concrete deterioration, spalling concrete, concrete cancer, deteriorated joints, moisture, seepage, efflorescence, rising damp and/or high-flow active leaks in concrete structures, we would be happy to assist you. You are welcome to contact us with any questions that you may have.

Brisbane office: (07) 3205 1899   

Email: [email protected]

Sydney office: (02) 9346 8308   

Email: [email protected]

Are you interested in finding out more about the various remedial building services we are providing?

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Waterstop Solutions Capability Statement is now available to download as PDF. (The image is clickable and opens up a link to our Capability Statement). 

Good maintenance begins with a proactive approach to maintain, keep, preserve and protect a building.