concrete

Question 1

whats the composition of mortar

Answer 1

water+sand+cement``

Question 2

what occurs when too much water added

Answer 2

rapid evaporation

• plastic settlement
• segregation

Question 3

explain the effects of rapid evaporation

Answer 3

• plastic shrinkage cracking

- the cracks allow air to enter» rusting

Question 4

explain plastic settlement

Answer 4

coarser aggregates sink» cracks» rusting

Question 5

name the 4 binders apart from Portland cement

Answer 5

• alkali activated cements
• calcium aluminate
• magnesium oxide
• bitumen

Question 6

pros and cons of alkali-activated cements

Answer 6

+ve:60-90% less co2 emmisions than PC

-ve: the need for alkaline solution

Question 7

pros and cons to magneswium oxide

Answer 7

• sensitive to weather conditions-rain(indoor use
• v high early strength
• low carbon footprint

Question 8

pros and cons of calcium aluminate

Answer 8

catastrophic results if used in wrong conditions-rain

high early strength

Question 9

bitumen concretes

Answer 9

bind stones together to form a solid- used for roads

softens and flows under heat

Question 10

post tensioned concrete

Answer 10

concrete poured, hollow ducts to insert the steel, stretched and released and clamped to the ends

Question 11

anodic, cathodic reaction in rusting

Answer 11

Fe» e+ Fe2+
h20+02+e» OH0
Fe2+ +2OH-»> Fe(OH)2

Question 12

what happens in the presence of chlorine

Answer 12

-Cl- grabs fe from the anode
- dissolving the passive film
-reacts with OH- to form Fe(OH)2
releasing cl- for process to repeat

Question 13

passive film of steel breaks down when

Answer 13

Ph drops

cl is present

Question 14

concrete service life is defined as what

Answer 14

time take for the ci- to diffuse to the steel and initiate corrosion