Welcome to our new blog post! In this post, we will cover the topic ”Rebar corrosion in Concrete”.
Chloride induced corrosion to reinforcement is the leading cause of deterioration and degradation of concrete structures. Under conditions of wetting and drying concrete draws in and absorbs water, moisture and contained salts which affect reinforcement close to the surface and result in concrete spalling. To minimize effect of chloride ion ingress in concrete and consequent passivation of reinforcement concrete should have low permeability.
Benefits of SFRC
It is well known that addition of fiber in the concrete brings better control of cracking and enhances mechanical properties of concrete. Steel fiber improves performance of concrete section under direct tension, flexure, shear and torsion, increases toughness, fatigue endurance and impact resistance. The much smaller sensitivity to corrosion of the steel fiber in SFRC compared with reinforcing bars in concrete can be attributed to:
- lower tendency to cracking
- increased tendency for self-healing of cracks in fiber reinforced composites
- small diameter of fibre does not lead to the formation of sufficient rust for scaling of the concrete
- lack of electrical conductivity because of the discrete nature of the steel fibre, non-continuous and randomly dispersed in concrete mix fiber provide no mechanism for propagation of corrosion
- improved matrix microstructure and denser interfacial transition zone in the fiber compared with conventional steel
- enhanced structure composition considering that drawing operation for producing wires and fiber result in an alignment of ferrite grains which provide surface homogeneity and therefore corrosion resistance compared to reinforcing bars
Durability of SFRC
Steel fibers close to an exposed concrete surface can show signs of corrosion due to carbonation of the surrounding concrete. This is the natural process where the carbon dioxide in the air causes the concrete to gradually become less alkaline and the pH-value to drop. This process starts at the concrete surface and continues inward as long as there is sufficient carbon dioxide available but hardly more than 5mm for SFRC concretes. At first glance it would appear that steel fiber would be susceptible to severe corrosion, particularly near the surface of the concrete, where the cover is quite small. Great number of tests performed worldwide showed that even when some surface fiber corroded, there was no apparent adverse effect on the structural integrity of the concrete and the corrosion did not lead to surface spalling.
The risk of corrosion is much greater in traditional bar reinforced concrete as bar reinforcement will start to corrode when the weight of chloride salts exceed 0.4% by weight of the cement mix. In comparison, SFRC provides much higher capacity against corrosion and can tolerate chloride concentrations up to 3-4% without undue distress.
It is recommended that addition of steel fiber can, in many ways, improve the performance of reinforced concrete and should be considered for increasing the lifecycle of a concrete structure.
Thank you for reading.