Acid Attack

• Concrete structures exposed to the atmosphere & swampy & peaty soils are often subject to acid attack , such as carbonic and sulphuric acids & other acidic fumes by dissolving & removing part of the set cement , leaving behind a soft area .
• In practice , acid attack occurs at values of PH 6.5 . For values of pH between 3 & 6 , the attack progresses at a rate approximately proportional to the square root of time .

Rate of acid attack depends on :

• The type & quantity of acid present .
• Whether the acids are likely to be continously renewed .
• The velocity & pressure of the flow of ground water against the concrete .
• The cement content & type of aggregates .

To minimise rate of acid attack :

• Use concrete with increased cement content & reduced water / cement ratio .
• Provide sufficient sacrificial thickness of same quality concrete .
• Protect concrete with coating of inert material such as epoxies , polyurethanes , polyesters or bituminous compounds .