REINFORCEMENT

Question 1

Define reinforcement and spacer blocks

Answer 1

Reinforcement : steel bars, meshes, or fibers embedded in concrete to enhance its tensile strength and compressie.

Spacer blocks: Small, often plastic or concrete, devices used to maintain the correct position and cover of the reinforcement within the concrete formwork.

Question 2

List the different types of reinforcement used in concrete

Answer 2

1. Hot Rolled Mild Steel, Plain Surface
   250 MPa
   Suitable for most jobs
   Easily cut, bent, welded
   8- 40mm diameter
   16mm: foundations, retaining walls, beams , heavy sections of work.
   8-16mm: floors. roof slabs, walls , smaller structural members
   10/12mm : column links, beam stirrups
2. Hot Rolled High Yield Stress, Deformed surface
   450 MPa
   Ribbed surface increases bond to concrete
   Saving in steel
   Improved bond
   Fewer end anchorages because of better bond.
3. Welded Fabric
   Hars drawn plain steel wire,welded
   Mainly for floors, flat roofs, roads

Question 3

Discuss the bond between concrete and steel reinforcement

Answer 3

Similar thermal movements
Cement paste has high pH which protects steel from rusting.
Concrete shrinkage improves grip on steel
Steel is fairly cheap
Concrete is fire resistant so protects steel.

Question 4

Discuss methods in which reinforcement can be used

Answer 4

1.Working drawings ( info provided)
2.Bending schedules (more info provided like steel type etc.)
3.Cutting bending and labelling (in accordance with bending schedule)
4.Storage on site (stack off ground, protect from weather, remove dirt and loose rust, hose down to wash off salt in marine environment)
5.Fixing (tying, support, splicing)
6.Checking (inspect before concrete is placed: bar diameter, spacing, position, length, no. of bars, clean surface)

Question 5

Discuss how to protect reinforcement in concrete

Answer 5

Low w:c
Properly compacted
Properly cured
Cover adequately
Spacers must be impermeable

Question 6

Describe reinforcement corrosion mechanisms

Answer 6

1. Carbonation
   CO2 from air reacts with concrete (calcium hydroxide) to form calcium carbonate. This lowers pH of concrete thus reducing passivation layer around steel.
2. Chloride ingress
   Chlorides from seawater or contaminated aggregates penetrate the concrete through breaking down passivation layer thus leading to corrosion.

Question 7

Identify corrosion of steel reinforcement and problems with spacer blocks

Answer 7

Occurs when the protective passivation layer on the steel is compromised, allowing moisture and oxygen to react with the steel. Leads to the formation of rust.

Problems with spacer blocks
(Used to maintain correct cover between steel reinforcemnt and concrete surface)
* Incorrect placement
*Material degradation
* Movement during pouring

Question 8

Discuss methods to repair spalled concrete