Jun 2019 THE CAUSES AND REPAIRS OF SPALLING CONCRETE
Much in the same as your skin may peel when over exposed to harsh conditions; Sephaku Cement describes the causes of spalling concrete and how to apply concrete repairs to unsightly damage. Spalling concrete sees the surface layers of the cement applications peel, chip and sheet off often exposing aggregate, joints or reinforced steel beneath the surface layers. Peeling between 15cm to 25cm in depth, spalling concrete can occur as a result of various reasons causing a flaky surface area across a broad range of cement based applications including concrete slabs, flooring or paving.
What causes Concrete Spalling?
While the most common culprit is attributed to the exposure of harsh weather conditions, there are a few different factors that can cause concrete spalling.
- Concrete Spalling can take place as a result of the corosion of the reinforcing steel set beneath the surface. As the steel rusts (as a result of the presence of moisture and oxygen inside the concrete), due to the increased volume of matter, pressure building from the “inside” of the concrete installation causes spalling to take place on the surface.
- An expansive effect of Alkali Silica Reaction, where the alkali’s present in cement reacts with the strained quarts in aggregates.
- Through exposure to fire or water the moisture present in the particles of concrete converts into steam, placing internal pressure on the construction which results in the consequential spalling of the concrete surface.
- Much in the same way as the effect of freeze thaw can cause cracks and fissures in concrete, the process is also linked to a leading cause of concrete spalling. Prolonged exposure to extreme heat as well as excessive cold conditions both compromises the surface of concrete.
- Concrete Spalling can also take place when steel reinforcements installed in concrete applications are not covered by an adequate volume (depth) of concrete.
- Joint spalls can also be caused as a result of construction joints that have not been correctly installed. Even the slightest error in installation can impact the overall integrity of the concrete
While this flaking condition of concrete caused by spalling can be effectively repaired; reversing the appearance of pitted and peeling concrete, if left untreated the area of concrete spalling will continue to expand, compromising the durability of the installation and requiring even more repair work. The key when it comes to repairing concrete spalling is to act fast and not compromise on quality.
As soon as you note concrete spalling taking place on any concrete installation follow these simple concrete repair steps to prevent irreversible damage.
- Step 1: Using a high pressure water washer, clean the spalled surface from dirt build up and debris that may later prevent a stable bond from forming on the area to be repaired.
- Step 2: Chip away broken concrete pieces still attached to the surface using a hammer and chisel. This step will ensure that repair work is able to attach to the original concrete application that has not yet been compromised by spalling. You may need to implement shot blasting or a grinder to adequately prepare the area to be repaired. You could also tap the surface of the original installation listening for hollow sounds that would indicate imminent spalling keeping in mind that every area of deterioration needs to be exposed for effective and lasting repair work. If reinforcement is exposed brush steel until free of dust and rust coat with a rust preventive sealcoat.
- Step 3: For spalling damage no more than 1/3 of the original concrete depth, now all that is required is to fill the spalled area with a repair material mixture making use of a good quality Portland cement such as Sephaku 42N. Once adequately cured, it’s recommended to seal the full surface area including the original application as well as your repair work with a quality concrete sealer, by doing so the lasting surface of the installation is maintained and future spalling avoided.