Spalling concrete is a common problem, where part of the surface peels, breaks, or chips away, also known as scaling, as a result of a weakened surface that is susceptible to damage to the spalled concrete, it may be caused by a freeze-thaw cycle or de- icing salts.
Spalls might be 150 mm or more in diameter and 25 mm or more in-depth and the prevalence of small spalls can also be potentially based on ACI 302.1 R-4.
It affects a wide variety of structures including framed buildings, multi-story car parks, bridges, jetties, tanks, and bunds by leaving the surface of the concrete patchy and pitted while exposing the aggregate underneath.
As soon as spalling is observed, it must be properly cured otherwise it compromises the solid surface integrity and endangers the ultimate capacity of the member.
In addition, the aesthetic of the structure can spoil the appearance.
Repairing Process of Spalling of Concrete:
Concrete spalling repair varies relying on the severity of the damage, type, and location of the concrete construction, this should be done on the basis of recommendations of applicable codes like ACI Code and BS EN 1504.
1. Clean Spalled Concrete Area:
Clean the area to be repaired by any diet to eliminate bond breaker agents and if heavy stains and dirt build up, a pressure washer may be required to clean the surface properly.
2. Remove Loose Concrete:
Using a hammer and chisel, remove loose and broken concrete from the area.
Sometimes, proper surface preparation may require shot blasting or grinding and to make a successful repair it is recommended to remove the concrete about 3.81 cm deep.
It is advisable to tap the surrounding area firmly with a hammer to check for possible deterioration.
A hollow sound is a sign of corroded concrete and it should be eliminated as this prevents the need for future repair of concrete spalling.
It is recommended to cut the rectangular portion of the concrete, so that patching can take place and the concrete can be mixed within the designated area.
Finally, eliminate dust and debris using a vacuum.
3. Clean and Coating Corroded Steel Bars:
Clean the rebar from rust or different dirt using a wire brush then apply a protecting coating to keep away from rust as illustrated.
4. Apply Repair Material Mixture:
There are many types of products used depending on the size of the repair, if the spalling depth is less than 1/3 of the thickness of the concrete, the concrete can usually achieve the surface repair.
However, for losses greater than 1/3 of the concrete depth, a steel bar may need to be installed and a full depth restoration may be required.
Strengthening the affected surface and applying an appropriate adhesion agent to improve bonding, the most commonly recommended patching material is Portland cement-based or epoxy.
It is necessary to select patching materials with thermal expansion close to the existing concrete.
Consider the ambient temperature throughout patching because it impacts the patching materials, the ambient temperature will probably be above 4.5 °C.
Damage on the driveway, walkway, and other horizontal surfaces may be repaired with a cement overlay.
If the affected areas are contiguous to the joint concrete spalling, ensure that it is properly restored so that some allowance may be made for the expansion of the member.
Using a margin trowel, scrape off the surplus product and apply to complete the surface.
Ensure the fabric adequately that it acquires the required strength.
7. Apply Pain or Coat on Repaired Surface:
Once the material is fully set, then apply paint to the waterproofing membrane to avoid reorientation of spalling.
Causes of Concrete Spalling:
- Concrete spalling causes the corrosion of embedded reinforcing steel because of corrosion merchandise (rust) occurs in higher portions than the unique steel that resulting pressure spalls the concrete.
- As a result of fire exposure, free water within the concrete adjustments the stem and creates inside growth pressure within the concrete, resulting within the spalls off the concrete.
- It causes the freeze and thaw cycling.
- In-depth effects of the alkali-silica reaction.
- Insufficient depth of casing on reinforcement.
- Less high-quality concrete cover for reinforcing steel.
- Joint spalls are often caused by improperly formed joints that lead to joint spalling concrete.
- Bond failure in two-course construction is due to the difference in shrinkage between the top and base course, drying of the bonding grout earlier than the topping concrete.
Measures to Prevent Spalling Concrete:
- In concrete floor slabs, early penetration helps prevent dry cuts.
- Apply a good water sealant to the finished surface to prevent water from entering the concrete.
- Proper management of concrete to ensure adequate cover and placement of joints in correct condition.
- Prevent excess water in the concrete mixture as it leads to spalling of concrete.
Also read: Concrete Screed, Concrete forms & Concrete Canvas
Concrete spalling involves breaking the layers or pieces of concrete from the surface during thermal exposure whereas aggregate spalling is caused by an aggregate failure close to the surface with small pieces flying off the surface.