The spalling of concrete is a deterioration seen in structures as a result of advanced corrosion of reinforcement. The stages of spalling of concrete will start with the growth of rust, then cracks and finally push off the part of the concrete cover.
Spalling of Concrete
The stages of spalling of concrete will start with the growth of rust, then cracks and finally push off the part of the concrete cover.
Delamination of concrete is a deterioration preceding the spalling activity. This phenomenon will result in hollowness below the surface. Mostly the reinforcement placed in series rust first. The concrete splitting hence will be happening neatly along the plane of the reinforcement. With time, the rust will grow and develop resulting in the detachment of concrete cover in large sheets.
|Fig.1. Development of Spalling Over the Rusting Reinforcement|
Before the occurrence of spalling, the delamination cannot be observed. But this presence can be understood by sound, by tapping the concrete with a small hammer. If we obtain a hollow sound, we will be able to locate the delamination.
Examination of Concrete Spalling
Spalling of the concrete will make the concrete reinforcement to be exposed. A Proper examination of the surface of the concrete will help in identifying whether the concrete is corroded by chloride penetration or carbonation.
The carbonation induced corrosion of reinforcement will remain fewer stains over the concrete. This is not same in the case of chloride penetration, as stains appear mainly in wet conditions. In wet conditions, the chloride penetration tends to be pitting corrosion which starts the reaction as a soluble product which will later spread into the concrete. This movement will remain stains.
How to Prevent Spalling of Concrete???
The cost of fixing the spalling problems can be minimised by taking adequate precautions. These include:
The painting procedure helps in preventing the carbonation which is the main problem with corrosion leading to spalling. Painting at an interval of 3 to 5 years will help in preventing the spalling issues to some extent. Use of anti-carbonation or the good quality paint can be helpful to a large extent.
2. Sealing the Cracks or the Holes
The presence of any holes or cracks has to be investigated and filled. This will resist the penetration of moisture or carbon di oxide from entering the concrete. Those holes that are not in use have to be sealed.
3. Provide Sufficient Ventilation
Carbonation or corrosion environment is speed up by the presence of humid environment. Reduction of humidity in areas of residential buildings, proper drainage for bridge structures, vents and roofs will help keep away corrosion to large extent.
How to Fix Spalling in Concrete?
Based on the severity of the condition, the problem of spalling of concrete might require large or smaller repair works.Some measures to fix spalling of concrete are mentioned below:
- If the damage to the concrete is shallower than one-third of the thickness, then it will require a repair. If the depth of damage is greater than one-third of the thickness, then full restoration must be required, involving the installation of steel bars.
- If the problem faced having the rebars exposed or corroded, then the treatment has to be conducted only after proper cleaning of the surface. A wire brush can be used to clean the corrosion debris properly. Later a protective coating must be provided in order to prevent this to happen further.
- If the issue of spalling is over a driveway or on a horizontal surface like sidewalks, overlay made of concrete must be applied. After the overlay is dried, a waterproof membrane is laid over it to prevent spalling.
- The effective concrete spalling repair will require the concrete removal to a depth of 1.5 inches and cleaning before starting the treatment.
- Patching of concrete will be done before treatment at a depth of 4 inches over the spalling area. For better result, a rectangular section of the area is saw cut so that patching can be done properly.
- Before patching, the area must be cleaned and water must be removed with the help of a sponge. Application of any compound or patching works has to be done only after the area is dried.
- The old surface must be made rough to have a good bond with the new bonding surface. Best patching material that can be used is Portland cement or epoxy based materials.
- The patching materials are compounds that react fast once mixed. So it should be taken take of mixing it if we are planning to use within 15minutes.
- The application must be conducted in an environment with a temperature of 40 degrees Fahrenheit. Else the patching material may not work.
- Use materials that have an expansion coefficient similar to that of concrete.
- Repairing of a joint must require the proper restoration of the joints so that the expansion of the concrete structure is permitted.
Make sure the air temperature is over 40 degrees Fahrenheit, otherwise, the patching material might not work.
Use only materials with an expansion coefficient similar to that of the concrete
If a joint needs to be repaired, it must be restored properly to allow for expansion of the concrete slab.