What Is Concrete Spalling?
The phenomenon in which the Concrete Surface undergoes flaking or peeling near the surface portion of the finished slab, which may further extend to the top layer of reinforcing steel is known as Concrete Spalling. Spalling occurs through freezing and thawing cycles of concrete which may be 150 mm in diameter and 25 mm in depth or more.
Concrete spalling repair methods involve addressing the deterioration of concrete surfaces where fragments or layers have broken off. One common approach is the use of patching materials, such as epoxy-based compounds, to fill and seal the damaged areas, restoring both the aesthetics and structural integrity of the concrete.
Concrete Spalling is greatly influenced by material parameters such as permeability of concrete, porosity, and moisture content, properties of aggregate, reinforcement, and presence of cracks. However, environmental factors influencing the concrete spalling include thermal restraint, heating rate, and profile, and temperature level.
Spalling can be categorized into 3 different types, which include aggregate spalling, corner spalling i.e. sloughing off, and explosive spalling. Each type of sapling affects concrete in different ways which include a broad variety of structures such as multi-story car parks, framed buildings, bridges, tanks, jetties, and bunds. Parapet wall Wood
Concrete Spalling Repair Methods
Even after taking measures to prevent Spalling, it is likely that still spalling may occur hence it becomes necessary to repair it using various methods.
The repairing process of Spalling Concrete is well dependent on how severe the damage is and its location of occurrence.
The process of concrete spalling repair methods is given below,
- Clean Spalled Concrete Area
- Remove Loose Concrete
- Clean and Coating Corroded Steel Bars
- Apply Repair Material Mixture
- Apply Pain or Coat on Repaired Surface
1. Clean Spalled Concrete Area
Proper cleaning of the damaged area to be repaired is ensured to eliminate bond breaker agents. Accumulation of dirt or strains creates a separating layer from concrete to the surface further reducing their bonding.
However, in case of heavy stains and dirt, a pressure washer is required for proper cleaning of the surface. Sometimes the surrounding area is also cleaned for proper application of Repair Material Mixture.
2. Remove Loose Concrete
Concrete Spalling leaves loose and broken concrete which are to be removed manually from the area is to be repaired. This is the simplest process and could be carried out using simple tools. However, in some cases grinding and shot blasting is required to prepare the surface.
The recommended depth for concrete to be removed is 3.81 cm to progress repair. While removing concrete it is also advised to thoroughly tap the surrounding area to check for possible deterioration. Tapping sound helps to find out the condition of the concrete.
That is, if it sounds hollow then it is a sign of deteriorated concrete and should be eliminated preventing any further repair.
Patching can be performed by simply cutting the rectangular portion of concrete. Cutting also gets concrete contained within a specified area and finally, dust and debris are removed using a vacuum.
3. Clean and Coating Corroded Steel Bars
After removal of Loose Concrete, the exposed reinforcement bars are cleaned if the corrosion has taken place i.e. the rust is removed using brushes. Bars are also cleaned to obtain a dust-free surface for further coating.
Corroded Steel Bars are the main reasons for the occurrence of spalling. After the cleaning, the bars are coated with a corrosion-resistant substance in order to prevent further Rusting.
4. Apply Repair Material Mixture
For applying Repair Material Mixture there are various products available depending on size and depth of repair required. Spalling depth lesser than one-third of its concrete thickness then we can simply apply a surface repair.
However, for conducting repairs on damage greater than 1/3 of the concrete depth, full depth restoration with or without installation of reinforcement bars may be required. In order to improve bonding on rough surfaces, necessary adhesion agents are applied.
Further Patching is done using suitable admixture generally using Epoxy or Portland cement-based material. Temperature emerges as the main factor to be looked out for during patching. To tackle such problems selection of patching material is done accordingly, where the material has thermal expansion closer to the working concrete.
Similarly, ambient temperature is considered (should be more than 4.50C) during patching as it can affect the patching material. Damage caused to horizontal surfaces such as driveways and walkways is repaired with cementitious overlay.
After Applying Repair Material the work we are left with is finishing which is followed by curing and applying the coat. Among which let’s first elaborate on the finishing work.
Before starting to finish, one needs to scrape off the excess product using a margin trowel and then apply the finishing. One must also ensure to level the surface evenly during Finishing.
The finished surface is left for curing, which is done based on the time required for the surface to gain adequate strength. Curing time varies from surface to surface depending on thickness, type, and quality.
Curing operation involves watering the surface constantly in order to maintain the hydration process for concrete.
Curing itself is of various types such as Wet Hessian or Gunny Bags Curing, Sealing Curing Compounds, Water Ponding, Chemical Curing, Membrane Curing, and steam curing.
7. Apply Paint or Coat on Repaired Surface
This application will reduce repetitive maintenance of any surface by a significant amount.
Spalling Concrete Causes
- The primary reason for concrete spalling is corrosion caused by embedded steel reinforcement.
- The formation pressure in concrete further leads to Concrete Spalling. (Boq)
- Spalling also occurs due to the freezing and thawing of concrete because of water present in concrete.
- The construction defects such as inadequate depth and low-quality concrete cover over reinforcement may also lead concrete to spill.
- Accumulations of rust due to corrosion occupy more volume causing expansion and inducing tensile stresses in the concrete which in turn can ultimately cause spalling and cracking.
- Another primary reason for spalling is exposure of RCC to chloride ions, in which the probability of spalling increases with the increase in the number of chlorine.
- Concrete constantly exposed to fire causes free water available in concrete change to vaporize hence creating internal expansive.
- The carbonation process is slow which occurs in concrete due to the entry of CO2, which eventually causes spalling in concrete.
- Alkali Silica Reaction causes expansion in concrete hence leading to spalling.
- Expansion caused in aggregate due to absorption of water above a certain limit.
- Improper-constructed joints may cause joint spalls.
- Bond failure is also a valid cause of spalling which occurs in two-course construction due to the differences in shrinkage between topping and base courses.
- Acids in the acidic rain, Sulphate Attacks, and Thaumasite are some of the chemical attacks the concrete can undergo in order to initiate its spalling.
Measures to Prevent Concrete Spalling
Concrete Spalling causes damage to many categories of structures which include multi-story car parking, tanks, components of bridges, framed buildings jetties, etc. The formation of This further causes patchy surfaces and pits.
Hence it becomes necessary to take measures in order to prevent concrete spalling responsible for distorting the aesthetic appearance of the structure. Such measures are listed below,
- Thermal barriers can be used to limit the temperature increase at the concrete surface which reduces the risk of spalling at a certain limit and also maintains the mechanical strength of concrete.
- Using air entrained concrete, water-repellent sealer,, and curing concrete wells prevents chemical-related spalling.
- Managing properly the pouring of concrete for obtaining adequate cover and placement of joints keeps checking on the occurrence of concrete spalling.
- Water is the main factor in concrete for occurrences of spalling hence it is mandatory to ensure a proper water cement ratio while preparing concrete.
- Excess of water in concrete encourages spalling after certain years due to tensile force occurrence.
- The application of a good water sealant to the finished surface prevents spalling by preventing water from entering the concrete.
- For keeping a check on spalling in the case of concrete floors, early entry of dry cuts is helpful.
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