Reinforcements

Question 1

Compare how good concrete and steel are in tension and compression.

Answer 1

Concrete is strong in compression but weak in tension, steel is very good in tension

Question 2

What kind of steel is used for reinforcements and why?

Answer 2

Usually mild (but not stainless) steel, as they tend to not only be cheaper but can be chemically altered to be corrosion resistant, they are often ribbed which creates a stronger bond to the concrete

Question 3

What are pre-tensioned cables?

Answer 3

Cables are installed, so when concrete is poured over the tension is released - this relies on interfacial bonding to steel

Question 4

What are post-tensioned cables?

Answer 4

Concrete is poured and then the cables are inserted and tensioned - this can have severe problems is the steel corrodes and the stress application is lost

Question 5

What is the equation for rusting?

Answer 5

Fe2+ + 2OH- => Fe(OH)2

Question 6

What causes iron corrosion?

Answer 6

Iron oxides form a passive film on the steel inside the concrete, which breaks down and leads to corrosion

Question 7

How can corrosion be prevented?

Answer 7

Reduce permeability of concrete

Question 8

How do you reduce the permeability of concrete?

Answer 8

Reduce the water/cement ratio, by using superplasticisers