CHAPTER 3

Question 1

What is the difference b/n concrete + asphalt and steel?

Answer 1

CONCRETE AND ASPHALT :
engineers and contractors directly influence strength, stability and durability

STEEL
civil engineer has less flexibility in specifying steel

Question 2

5 construction uses for steel

Answer 2

structural
cold formed
fastening products
reinforcing steel
miscellaneous

Question 3

3 steps from steel production

Answer 3

1. reduction of iron ore to pig iron (high carbon)
2. refining pig iron to steel
3. forming steel into products

Question 4

reduce of iron ore to pig iron : how does it work?

Answer 4

Blast furnace w/ carbon and limestone

• • limestone removes impurities from iron ore
• • slage (molten rock and impurities) is skimmed off the top
• • molten iron and carbon are collected at the bottom

Question 5

Refining pig iron and scrap to steel

Answer 5

remove excess carbon and other impurities by oxidation in another furnace.

BOF : basic oxygen furnace
EAF : electric arc furnace : electric arc melts steel

Question 6

forming steel into products :2 possibilities

Answer 6

• • cast into ingots (large blocks that must be re-melted and re-shaped)
• • continuous shapes

Question 7

Steel and carbon content : behaviour?

Answer 7

cast iron >2% carbon = brittle and hard

high carbon steel : 0.8 à 2% carbon = brittle

structural steel : low carbon (0.15 à 0.27%) = ductile

Question 8

how does the modulus of elasticity changes when the carbon content is changed?

Answer 8

modulus of elasticity does not change

Question 9

4 types of heat treatments

Answer 9

annealing
normalizing
hardening
tempering

Question 10

what does a heat treatment do?

Answer 10

refines grain structure, removes internal stresses, removes gases, changes eletrical and magnetic properties

Question 11

what is annealing?

Answer 11

heating above austenitic temperature then slowly cooling to room temperature

steel gets softer, more ductile, refines grain structure, removes stresses and increases toughness

Question 12

what is normalizing

Answer 12

similar to annealing but hotter and air cooled.

gives a uniform, fine-grained structure.

provides high fracture toughness

more corrective rather than strengthening or hardening

Question 13

what is hardenizing

Answer 13

higher heat, then rapide cooling by quenching in water/brine/oil

steel is harder and more brittle and must be following by tempering

Question 14

what is tempering?

Answer 14

reheating hardened steel to a lower temperature and quenching

increases ductility and toughness after hardening.

Question 15

what is a steel alloy?

Answer 15

steel + alloying metal that changes the properties

Question 16

properties of steel alloys

Answer 16

hardenability
corrosion resistance
machineability
ductility
strength

Question 17

types of steels used for structural applications (3)

Answer 17

• • carbon
• • high strength low-alloy
• • corrosion resistant high-strength low-alloy

Question 18

types of fastening products

Answer 18

• • conventional bolts
• • twist-off-type tension control bolt assemblies
• • nuts
• • washers
• • compressible washer type direct tension indicators
• • anchor rods
• • threaded rods
• • forged steel structural hardware

Question 19

4 things required for corrosion

Answer 19

1. anode : positive electrode where corrosion occurs
2. cathode : negative electrode needed for electric current
3. conductor : metallic pathway for electrons to flow b/n electrodes
4. electrolyte : liquid that can support the flow of electrons

Question 20

4 corrosion protection methods

Answer 20

1. active
2. passive
3. permanent
4. temporary

Question 21

3 types of coatings that can be used to prevent corrosion

Answer 21

1. barrier coatings (isolates steel from moisture)
2. inhibitive primer coating (pigments migrate to steel surface to passivate it)
3. sacrificial primers (cathodic protection : metal pigments such as zing become the anode, give up electrons to the steeel and corrode instead of the steel

Question 22

What is an anode

Answer 22

positive electrode where corrosion occurs

Question 23

What is a cathode

Answer 23

negative electrode needed for electric current

Question 24

What is the conductor?

Answer 24

Metallic pathway for electrons to flow between electrodes

Question 25

What is an electrolyte

Answer 25

Liquid that can support the flow of electrons