Concrete delamination is the detachment of thin layers of concrete from the concrete surface. The peeled-out concrete surface then becomes prone to all kind of abraders in the atmosphere which consequently weaken the structure. It, therefore, becomes extremely essential to find the area to be remedied before it spreads any further. Generally, the emergence of a drummy sound on striking the surface of the concrete by a hammer is an indication of concrete delamination.
Here, the causes, effects, and precautions for delamination of concrete are explained in brief.
Causes of Delamination
The timing of final trowelling operations is the main factor that leads to delamination of the concrete surface. It is recommended that the finishing operations i.e. trowelling, is supposed to start only after the initial setting time of the concrete. Else, there could be chances to have delamination issues.
Conducting the trowelling operation before the initial setting time makes the bleeding water or air underneath to form blisters. When the surface is subjected to any sort of load action, these blisters would delaminate out.
Going with the finishing processes before the bleeding is completed traps the water or air-voids below the finishing layer. These, as a result, form subsurface voids which make that concrete zone weak. As time passes, these subsurface voids detach with loads.
Delamination can also occur due to :
- The use of a sticky mortar mix with a huge amount of fines.
- High rate of evaporation.
- Hastily performed finishing works.
When the finishing process is performed hastily, the delamination issue would be widespread over an entire area. This affects larger zones of the concrete surface.
This detachment layers may be in 3 to 6mm thick. Delamination is mainly observed in concrete slabs.
Effect of Delamination on Concrete Performance
Having delamination on a single spot is not an issue. But when this delamination begins to spread, the performance of the concrete surface is affected badly. Delamination also results in the separation of the flooring material from the top surface of the concrete.
Delamination splits up any top coat on the concrete surface which makes pathways to facilitate pathways for moisture intrusion. Moisture intrusion propagates cracks and the performance of the structure is affected.
Read More: Defects in Concrete Structure
Precautions for Concrete Delamination
The risk of delamination can be avoided by the control of following factors:
- The uniformity at which the concrete is placed
- The rate of bleeding
- The setting time of the concrete surface
- The rate of surface evaporation
- The process of finishing
As mentioned earlier, premature finishing process is the major cause of delamination. Giving enough time for the bleeding water to rise up and evaporate prior to finishing process helps in avoiding the issue of delamination. This time is mainly the initial setting time of the concrete.
Some of the dos and don’ts to avoid concrete delamination are :
- Sealing of the concrete surface before the completion of the bleeding process must be avoided. The concrete mix with high cement or high sand content tends to bleed more easily.
- If the concrete contains air-entrained admixtures i.e. air content greater than 3%, the finishing process must be carried out lightly with care. A dense hard troweled finishing is not necessary. It just requires a light steel trowelling.
- If the concrete surface is made over an impervious surface, it is recommended not to perform the finishing process too early. Because the only way for the bleeding water to evaporate is the top surface so time has to be given for that. Bleeding water and the bleeding time is higher for a concrete surface made over an impervious surface compared to a porous surface.
- If the temperature of the ground subgrade is less than 40 degree Celsius, it is recommended not to place the concrete. Placing concrete on such cold subgrades delays the setting and the time of finishing cannot be predicted. It is advised to keep the subgrade covered till the time of concrete placement.
- Accelerators can be used to obtain a uniform concrete setting. This helps in increasing the final setting time of the concrete.
- If the site has a rapid evaporation rate due to hot temperatures, lower humidity and huge wind rate, special ways are adopted to decrease the evaporating rate. The wind can be reduced by the use of windbreaks and an evaporative retardant can be used to reduce the rate of evaporation.
As a remedy for a concrete area affected by delamination, it is recommended to remove the defective concrete layer at a depth till sound concrete layer is observed. The unsound concrete can be removed by :
After the removal of the affected surface, a new layer is placed. The whole area can be ground and smoothened to obtain a final smooth and sealed finish.