What is spalling of concrete?
Spalling of concrete refers to the deterioration of the surface of concrete, resulting in flaking and peeling off the surface layer of concrete.
It occurs in various structures such as buildings, bridge decks, multistorey frames, water tanks, etc.
Various factors such as environmental conditions, depth of concrete cover, and reinforcement corrosion causes a part of the concrete structure to deteriorate eventually.
It is important to address the concrete spalling as soon as spotted, to prevent further damage and integrity of the structure.
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Causes of spalling of concrete
There are several causes for the spalling of concrete. Some of the major ones are listed below.
a) Free-thaw cycle of concrete
Concrete is essentially vulnerable in the areas of fluctuating water levels or water spraying conditions. In these conditions, the water can easily seep into the concrete pores.
When the temperature becomes too low during cold weather, the water in the pores begins to start freezing. When water freezes, it expands in volume and creates internal pressure within the pores of the concrete.
As the ice thaws, the pressure is released, thus weakening the concrete pores. The repeated cycles of freezing and thawing have a cumulative effect on the durability of concrete structures, resulting in cracks and harmful effects.
b) Corrosion of reinforcement
Concrete is a high-alkalinity material. The pH of newly produced concrete is usually in the range of 12 and 13. In this range of high alkalinity, reinforcement steel is usually protected from corrosion.
Due to the penetration of water, when the reinforcement steel within the concrete starts to corrode, it converts iron to rust. The rust is usually larger in volume. This voluminous expansion exerts pressure on the surrounding concrete.
At first, the concrete starts to develop cracks. These cracks generally run in straight, parallel lines to the reinforcement. As deterioration continues, spalling of concrete will occur and the reinforcing bars become visible.
c) Chemical attacks
Exposure to aggressive chemicals such as chlorides and sulfates may initiate a chemical reaction with the products of hydration in concrete. This causes the weakening of the concrete matrix and results in ultimate deterioration and spalling.
These attacks widely happen in places where the environment is so much aggressive such as sea shore, industrial places, etc.
d) Poor construction practices
Sometimes poor construction practices are also a major cause of the deterioration of concrete. Most of these errors do not lead directly to the failure of concrete. Instead, they enhance the adverse impacts of other mechanisms.
Some of the poor construction practices are mentioned below,
- Improper alignment of formwork
- Improper consolidation
- Improper curing of concrete
- Improper location of reinforcing steel
- Inadequate depth of concrete cover
- Early removal of formwork etc.
e) Fire damages
A fire in a concrete structure can cause some serious damage. The extent of which depends upon the intensity and duration of the fire.
In the case of reinforced concrete, the fire introduces a high-temperature gradient and as a result of it, the surface layers tend to separate and fall off from the cooler interior.
Effects of spalling of concrete
Spalling of concrete can produce several severe safety hazards and also affects the structural integrity and aesthetics of the structure. Some of the important effects of spalling of concrete are mentioned below.
1) Reduced load-bearing capacity
Concrete spalling reduces the depth of the concrete structure thus reducing its ability to carry the designated design load. This weakens the concrete and can lead to structural instability and safety hazards.
2) Exposed reinforcement steel
The spalling of concrete results in exposing reinforcement to the environment, making it more susceptible to corrosion. This can further accelerate the deterioration of the structure.
3) Affect the aesthetics
The unsightly appearance of the spalled concrete structure not only diminishes its value but also adversely impacts the overall aesthetics of the building.
Moreover, it can instill a sense of danger and unease among the users, influencing their psychology and perception of safety.
4) Safety hazards
Cracked Drywall on the Ceiling can also be a concern within buildings. If you notice any signs of cracked drywall on the ceiling, it’s essential to investigate further to determine the underlying causes and take preventive measures to ensure the safety of the building’s occupants.
Sometimes, the spalling can happen outside of the building structure and pose a serious threat to pedestrians, especially in high-traffic areas.
How to prevent the spalling of concrete?
Preventing spalling of concrete requires a combination of proper design, good construction practices, and maintenance. Here are some of the major preventive measures:
1) Make sure you use a proper mix ratio with desired compressive strength and proper admixtures to increase the durability of the concrete.
2) Make sure to properly cure the concrete. Curing allows concrete to gain sufficient strength and resist surface cracking.
3) In colder regions, where the freeze-and-thaw effect is possible, use admixtures like air-entrained agents to minimize the effect of the freeze-thaw cycle.
4) As we see before, most of the problems in the concrete arise due to the penetration of water. Hence it is necessary to apply suitable waterproofing coatings to protect the concrete from water and chemical ingress.
5) During concrete pouring, necessary guidelines and proper construction practices should be followed.
For example, According to IS 456:2000,
- The concrete should be mixed in a mechanical mixer for at least 2 mins.
- The maximum height, at which the concrete is allowed to free fall is 1.5m.
- The pH value of water used for concrete should be in the range of 6-9.
6) In case of areas prone to fires, use fire-resistant concrete or use additional fire protection measures.
How to repair the spalling of concrete?
Before we get into the repairing process, it is important to assess the damage caused to the concrete structure.
If the severity of the spalling is too low, then it can be repaired by following normal procedures.
However, if the severity of the spalling is too severe or if the spalling is caused by fire accidents, then the strength of the structure should be assessed and should employ proper strengthening techniques like shotcreting or retrofitting.
The repair process involves the following steps:
a) Surface Preparation
Remove loose and damaged concrete from the surface with the help of chisels, hammers, or any other mechanical methods.
While removing the damaged loose concrete, it is also recommended to check the surrounding area for possible deterioration.
A hollow sound is a sign of deteriorated concrete, those concrete should be removed.
b) Clean the surface
Thoroughly clean the area to be repaired from any dirt, debris, and contaminants that could interfere with the bonding agents.
If there is a heavy build-up of nice dust, then the usage of a pressure washer should be recommended.
c) Clean the corroded steel rebars
The rust deposited on the surface of the reinforcing steel bar should be scrapped off with the help of a wire brush.
After removing the rust, apply a coat of protective film to prevent any future corrosion.
d) Application of repair products
Several repair products are available based on the severity of the damage.
For small and moderate spalling, use either a normal cement mortar mix (or) polymer-modified mortars.
For large-sized spalling, employ techniques like shotcrete to regain the lost strength.
e) Finishing
After the repair material has been properly applied and compacted, ensure a smooth and uniform finish to match the surrounding concrete surface.
f) Curing
Properly cure the repaired area for the recommended curing period to achieve maximum strength and durability.
g) Apply a protective coat
After the recommended curing period, the surface should be coated with paint or any waterproof coat to avoid the penetration of moisture and the reoccurrence of spalling.
Regular maintenance and inspection are essential to identify the early signs of spalling and other concrete defects. Timely repairs can prevent further deterioration and extend the lifespan of the structure.
Hope you understand everything you need to know about the spalling of concrete. If you found this article helpful, let us know in the comment section.
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