Loading on Concrete

Question 1

What happens when concrete is first loaded

Answer 1

When first loaded, a reinforced component will deform as it takes the strain.
 The concrete may crack as the re-bars take up any tensile or shear stresses.
 This is common & is known as Settlement Cracking.
 Re-bar is protected from corrosion due to the high pH.
 This stimulates the formation of a passive skin of Fe2O3.
 The passivation must be maintained & no water is allowed to seep in.

Question 2

What is the minimum cover over steel reinforcement

Answer 2

60mm

Question 3

What happens when water enters the concrete

Answer 3

 If passivation is lost by water ingress causing Chloride attack, or by Carbonation, then the Fe2O3 skin will be lost & replaced by Fe2+.
 This form of Ferrous Oxide expands as it forms, creating an increase in volume of the oxide layer around the re-bar.
 This pushes the concrete apart in the local area.