Concrete, Ceramic & Bitumen

Question 1

Durability definition

Answer 1

Ability to maintain structural integrity, protective capacity and aesthetic qualities over a prolonged period of time

Question 2

Examples of deteriorative effects of concrete (6)

Answer 2

1) Wetting & drying
2) Freezing & thawing
3) Heating
4) Erosion
5) Abrasion
6) Chemical attack

Question 3

Key factors associated with freeze / thaw resistance (2)

Answer 3

1) Presence of water

2) Low temperature

Question 4

Freeze / Thaw cycle (7)

Answer 4

1) Concrete saturated with water and temp at freezing
2) Phase transition - water to ice
3) Internal expansion causing cracking
4) Temperature increase causes thaw
5) Phase transition - ice to water
6) Reduction of volume (ice volume > water volume
7) More water able to enter concrete

Question 5

Two solutions to freeze / thaw concrete issues (2)

Answer 5

1) High strength concrete

2) Air entrained concrete

Question 6

High strength concrete (in relation to being a solution to freeze / thaw issues)…

Answer 6

May be able to resist pressure without cracking due to sufficiently high strength (I.e. no initial cracking = no damage)

Question 7

Detail how air entrained concrete will prevent freeze / thaw problems (4 points)

Answer 7

1) Air bubbles act as reservoirs for ice expansion
2) Bubbles dont fill up with water
3) Bubbles reduce internal pressure and prevent cracking
4) Loss in strength - 1% air = 5% loss

Question 8

Typical signs of freeze / thaw problems are (6)

Answer 8

1) Spalling and scaling of the surface
2) Large chunks coming away
3) Exposing of aggregate
4) Usually exposed aggregate is in-cracked
5) Parallel surface cracking
6) Gaps around aggregate form

Question 9

Two type of sulphate attack

Answer 9

1) Internal - Delayed Ettringite Formation (DEF)

2) External - Ettringite and Thaumasite attack

Question 10

3 Factors which influence the potential for DEF are;

Answer 10

1) Concrete composition
2) Curing conditions
3) Exposure conditions

Question 11

DEF is believed to be a result of…

Answer 11

Improper heat curing of the concrete where the normal Ettringite formation is suppressed

Question 12

3 stages of DEF

Answer 12

1) Sulphate concentration in the pore liquid is high for unusually long period of time in the hardened concrete
2) Eventually the sulphate reacts with calcium and aluminium containing phases of cement paste and the cement paste expands (Ettringite formation)
3) Empty cracks (gaps) are formed around aggregates. These remain empty of later are partly or even completely filled with ettringite