What is Meant By Concrete Spalling ?
Concrete Spalling is breakaway of concrete surface which often extends to the top layers of reinforcing steel. Spalling maybe 150 mm or more in diameter and 25 mm or more in depth and the occurrence of smaller concrete spalls is also possible.
Spalling of concrete also affects a broad variety of structures including framed buildings, multi-storeyed car parks, bridges etc.
Spalling leaves the concrete surface patchy while exposing aggregate underneath. As soon as spalling is spotted it should be properly repaired otherwise it compromises concrete surface integrity and endangers ultimate capacity of the member. Moreover spalling can also distort aesthetic appearance of the structure.
Causes of Concrete Spalling
- Corrosion of embedded reinforcing steel because the corrosion products occupy more volume than the original steel and the resultant pressure spalls the concrete.
- Fire exposure due to which free water and concrete change to steam and create internal expansive pressure in concrete, consequently causes concrete spalling of concrete.
- Freeze and thaw cycling – If more than 90 % of the pores in the concrete are completely filled in water and if these pores freezes due to climatic change, there volume increases. These increased volume exerts stress on concrete which tends the concrete to crack and which can cause concrete spalling.
- Expansive effects of alkali silica reaction.
- Inadequate depth of cover over reinforcement.
- low quality concrete cover over reinforcing steel.
- Joint spalls are often caused by improper constructed joints lead to joint spalling.
- Bond failure and two course construction due to differences in shrinkage between topping and base courses, drying of the bonding ground before the topping concrete is placed etc.
Also Read : Segregation of Concrete & How to Prevent it
How to Prevent it ?
- In concrete floor slab, Early entry dry cut helps prevents Spalling.
- When the construction of concrete surface is finished, good quality water sealant should be applied on the top surface so that water should not enter into concrete
- At the time of pouring of concrete care should be taken that the adequate cover is still maintained and placement of joints are not dislocated.
- While mixing of concrete the quantity of water should be properly maintained. Excess water in concrete mixture leads to poor strength of concrete.
Also Read : Honeycombs in Concrete – Causes & Prevention