Building Pathology - Concrete Defects

Question 1

Concrete defects - What is High Alumina Cement ?

Answer 1

• Used between 1954-1974 originally in maritime applications to give high strength to concrete. Found in pre cast concrete beams.
• Mineralogical change reduces chemical resistance when water is present. When water and chemicals are present the concrete becomes friable and loses strength.

Question 2

How would you identify HAC

Answer 2

Concrete becomes friable and becomes a chocolate brown colour

Question 3

How would you remedy HAC?

Answer 3

There is no cure treatment. When identified its strength should be assessed and monitored.

Question 4

What is concrete Sulphate Attack? and how might you remedy it?

Answer 4

Its a chemical reaction caused by sulphates - affecting concrete causing it to expand and crack.

Remedy - often the case that concrete will need to be replaced with a sulphate resist concrete.

Question 5

Can you name some concrete defects?

Answer 5

• Crazing (caused by improper curing/ temp extremes)
• General cracking
• Voids and honeycombs (improper mixing/ compaction)
• Delamination (top layer separation)

Question 6

What is Carbonation?

Answer 6

• Carbonation occurs when CO2 reacts with the calcium in the cement
• This lowers the concretes alkalinity and breaks down the oxide layer of reinforcement causing it to corrode.
• This intern damages the surrounding concrete

Question 7

What is Alkiali Silica Reaction (ASR)?

Answer 7

• ASR often occurs in marina structures. It occurs when the silica reacts with the alkali cement and water creating a Gel.
• The gel absorbs and expands exerting pressure and cracking the concrete.