common exam questions

Question 1

What are the common additions to concrete?

Answer 1

1. Fly ash
2. GGBS
3. Condensed silica fume
4. limestone
5. Metakaolin

Question 2

what does carbonation with respect to durability mean?

Answer 2

carbonation is the reaction of cement hydration products in concrete with co2 in atmosphere

Question 3

what does a loss in calcium hydroxide mean?

Answer 3

the pH will decrease, and there will be a loss in the passive oxide layer, and therefore vulnerable to corrosion

Question 4

what is constrictivity?

Answer 4

measure of how much diameter of pores change between large to small dimensions

Question 5

what are the other options available to reduce carbonation?

Answer 5

1. decrease w/c ratio
2. have a higher cement content - so more ca(oh)2 meaning slower process of carbonation
3. increase concrete layer over reinforcement
4. coat with a protective membrane that co2 cannot penetrate

Question 6

how is portland cement produced?

Answer 6

1. finely ground limestone and shale
2. heated in a clinker to 1400 degrees
3. clinker is then ground with 5% gypsum

Question 7

how is PFA produced?

Answer 7

it is residue ash from a pulverised coal fired power station- which is collected hydro statically from flue gases

Question 8

how is GGBS produced?

Answer 8

1. produced from blast furnace slag with forms on top of pig iron at the base of the furnace
2. then quenched to produce glassy material

Question 9

3 essential stages in planning an investigate insitu test for reinforced concrete?

Answer 9

1. planning- aims / requirements , visual inspection
2. non destructive testing- this can survey for areas of defectiveness
3. further testing- semi destructive tests

Question 10

pros and cons of using Ultrasonic pulse velocity?

Answer 10

pros: cheap, well established, quick, shows areas of lower strength really quickly
cons: for best results access to opposite faces is required

Question 11

pros and cons for rebound hammer tests?

Answer 11

pros: well established, simple, cheap
cons: results are affected by lots of factors, including where the hammer is positioned, local aggregate effects

Question 12

3 main causes of cracking in a material?

Answer 12

1. dimension changes due to moisture content
2. expansion of embedded materials
3. deformation due to external influences

Question 13

what role does aggregate play?

Answer 13

its a FILLER- cus its cheaper than concrete

Question 14

what characteristics influence type of aggregate you get?

Answer 14

1. grading 2. surface texture 3. physical properties

Question 15

larger, rounded smoother aggregate increases or decreases workability?

Answer 15

INCREASES

Question 16

Denser aggregates are more prone to…?

Answer 16

SEGREGAGTION

Question 17

an increases in fine aggregate content will..?

Answer 17

decrease workability

Question 18

quality of concrete is determined by?

Answer 18

1. testing
2. materials
3. production

Question 19

why will GGBS cause problems in carbonation environment?

Answer 19

will break down passive oxide layer

Question 20

how is aeration blocks produced?

Answer 20

fine divided Al powder in concrete mix,it reacts with h20 and lime to give h2 gas

Question 21

how do black bolts join sections together

Answer 21

when they are loaded in shear

Question 22

what type of tension is HSFB put under?

Answer 22

shank tension