What is the difference b/n concrete + asphalt and steel?
CONCRETE AND ASPHALT :
engineers and contractors directly influence strength, stability and durability
STEEL
civil engineer has less flexibility in specifying steel
5 construction uses for steel
structural cold formed fastening products reinforcing steel miscellaneous
3 steps from steel production
- reduction of iron ore to pig iron (high carbon)
- refining pig iron to steel
- forming steel into products
reduce of iron ore to pig iron : how does it work?
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
Refining pig iron and scrap to steel
remove excess carbon and other impurities by oxidation in another furnace.
BOF : basic oxygen furnace
EAF : electric arc furnace : electric arc melts steel
forming steel into products :2 possibilities
- cast into ingots (large blocks that must be re-melted and re-shaped)
- continuous shapes
Steel and carbon content : behaviour?
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
how does the modulus of elasticity changes when the carbon content is changed?
modulus of elasticity does not change
4 types of heat treatments
annealing
normalizing
hardening
tempering
what does a heat treatment do?
refines grain structure, removes internal stresses, removes gases, changes eletrical and magnetic properties
what is annealing?
heating above austenitic temperature then slowly cooling to room temperature
steel gets softer, more ductile, refines grain structure, removes stresses and increases toughness
what is normalizing
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
what is hardenizing
higher heat, then rapide cooling by quenching in water/brine/oil
steel is harder and more brittle and must be following by tempering
what is tempering?
reheating hardened steel to a lower temperature and quenching
increases ductility and toughness after hardening.
what is a steel alloy?
steel + alloying metal that changes the properties
properties of steel alloys
hardenability corrosion resistance machineability ductility strength
types of steels used for structural applications (3)
- carbon
- high strength low-alloy
- corrosion resistant high-strength low-alloy
types of fastening products
- 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
4 things required for corrosion
- anode : positive electrode where corrosion occurs
- cathode : negative electrode needed for electric current
- conductor : metallic pathway for electrons to flow b/n electrodes
- electrolyte : liquid that can support the flow of electrons
4 corrosion protection methods
- active
- passive
- permanent
- temporary
3 types of coatings that can be used to prevent corrosion
- barrier coatings (isolates steel from moisture)
- inhibitive primer coating (pigments migrate to steel surface to passivate it)
- sacrificial primers (cathodic protection : metal pigments such as zing become the anode, give up electrons to the steeel and corrode instead of the steel
What is an anode
positive electrode where corrosion occurs
What is a cathode
negative electrode needed for electric current
What is the conductor?
Metallic pathway for electrons to flow between electrodes
