In most situations it is best to first carry out a program of surface cleaning works, usually working from top-down. That surface reparation will remove any lose or severely damaged concrete. This action may expose additional area of damage that will subsequently require treatment.
How Much To Remove
As a general rule concrete removal should be kept to a minimum, particularly any sound concrete. However, where actively corroding steel reinforcement is present, it must be fully exposed to beyond its corroding length and around its full circumference. To allow cleaning and preparation, a distance equivalent to the bar diameter and a minimum of 12.5 mm is normally required.
In marine environments where the concrete has previously been exposed and contaminated by chlorides (even when they are at some distance from the sea due to a combination of the structure’s height and prevailing winds), the concrete and the steel surfaces should be washed with clean water to remove the chloride deposits. The cleaned and prepared concrete surface should be free from dust and any other contaminants.
Cleaning Exposed Steel
Any exposed steel reinforcement should be cleaned to remove rust and corrosion products. EN 1504 Part 10 recommends the steel be prepared to Sa 2 1/2 (if barrier coating is applied) or to Sa 2 (if active coating is applied). Any method of steel surface preparation may be used, with grit blasting normally recommended as the best and the fastest, particularly with the larger areas of steel that can be exposed on cooling towers.