Concrete TechnologyConcrete Technology

Steel (CH10)

Lecture 19

Eng: Eyad HaddadEng: Eyad Haddad

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1. Introduction:

In general, metals are classified into two major groups:

(1) ferrous and (2) nonferrous

A ferrous metal is one in which the principal elements is iron as in

cast, wrought iron, and steel.

A nonferrous metal is one in which the principal is not iron, as in

copper, tin, lead, nickel, and aluminum.

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2. Ferrous Metal: Ferrous comprise three general classes of materials of construction of

construction :

1. Cast iron.

2. wrought iron.

3. Steel. Both cast iron and wrought iron have fallen in production with the

ardent

of steel, as steel tends to exhibit better engineering properties than do

cast and wrought iron.

The application of steel and steel alloys is so widespread it has been

estimated that there are over a million uses.

In construction, steel has three principal uses:

(1) structural steel. (2) Reinforcing steel. (3) Forms and pans.

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3.Corrosion and

wear: Each year millions of dollars worth of damage to iron and steel

structures is caused by corrosion.

Further, millions of dollars are to replace worn cut parts of machine

structures.

Corrosion and wear damage take place gradually. They seldom cause

sudden or dramatic structural disasters, as parts damaged by

corrosion or wear can be replaced or repaired before failure occurs.

Most metals associated with construction materials come in contact

with water which contains dissolved oxygen or with moist air and water

into solution readily.

The rate of solution is usually retarded by a film of hydrogen forming

on the metal or by coating the metal with a protective coating. However,

oxygen will combine with the hydrogen and over a period of time will

strip it away from the metal, and thus further corrosion will result.

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Four classifications of corrosion for metals exist:

1. Atmospheric: In atmospheric corrosion a large excess of oxygen is

available and the rate of corrosion is largely determined by the quality of

moisture in the air and the length of time on contact with the metal.

2. Water immersion: When metals are immersed in water containing

dissolved oxygen, they will corrode. If the water does not contain any

dissolved oxygen, the metal will not corrode. If the water is acidic, the

corrosion rate is increased, whereas water that is alkaline has very little

corrosion activity unless the solution is highly concentrated.

3. Soil: In soil corrosion, the most important item is the ingredient coming

in contact with the iron or steel.

4. Chemicals other than water: It is influenced by the type of chemicals

coming in contact with the iron or steel.

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4. Protection from

corrosionThe most common protective coating against corrosion for iron and steel

is paint.

The paint coating is usually mechanically weak and it cracks and wears

out. Thus, to do a satisfactory job, the paint must be reversed every 2 or

3 years.

Before the structure is painted, it should first be cleaned and the rust

removed. For asphalt coatings are used for protection. Metals under

stress especially those beyond their elastic strength, corrode more

rapidly than do unstressed metals.

Another way of protection is via encasing the iron or steel in concrete.

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5. Carbon steel:Carbon steel, also called plain carbon steel, is a metal alloy, a

combination of two elements, iron and carbon, where other elements are

present in quantities too small to affect the properties.

The only other alloying elements allowed in plain-carbon steel are

manganese (1.65% max), silicon (0.60% max), and copper (0.60% max).

Steel with a low carbon content has the same properties as iron, soft but

easily formed. As carbon content rises the metal becomes harder and

stronger but less ductile and more difficult to weld. Higher carbon

content lowers steel's melting point and its temperature resistance in

general.

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5. Carbon steel: (Cont.)

Carbon content influences the yield strength of steel because they fit

into the interstitial crystal lattice sites of the body-centered cubic

arrangement of the iron molecules.

The interstitial carbon reduces the mobility of dislocations, which in turn

has a hardening effect on the iron.

To get dislocations to move, a high enough stress level must be applied

in order for the dislocations to "break away". This is because the

interstitial carbon atoms cause some of the iron BCC lattice cells to

distort.

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Types of carbon steel:

Typical compositions of carbon:

Mild (low carbon) steel: approximately 0.05–0.29% carbon content.

Mild steel has a relatively low tensile strength, but it is cheap and

malleable. Medium carbon steel: approximately 0.30–0.59% carbon content.

Balances ductility and strength and has good wear resistance; used

for large parts, forging and automotive components. High carbon steel: approximately 0.6–0.99% carbon content. Very

strong, used for springs and high-strength wires.[4] Ultra-high carbon steel: approximately 1.0–2.0% carbon content.

Steels that can be tempered to great hardness. Used for special

purposes like (non-industrial-purpose) knives, axles or punches.

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6. Structural steel:Structural steel is steel construction material, a profile, formed with a

specific shape or cross section and certain standards of chemical

composition and strength.

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7. Reinforcing steel:Rebar or reinforcing steel in concrete is a great step for a lifetime of

beautiful walkways and driveways.

Reinforced concrete, also called ferroconcrete in some countries, is concrete in

which reinforcement bars ("rebars") or fibers have been incorporated to strengthen a

material that would otherwise be brittle. In industrialized countries, nearly all concrete

used in construction is reinforced concrete.

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8. Physical properties of

steelsIn general, three principal factors influence the strength, ductility and

elastic properties of steel.

1. the carbon content.

2. the percentages of silica, sulfur, phosphorous, manganese, and

other alloying elements.

3.The heat treatment and mechanical working.

Stress Strain diagram:

The relationship between loads and deflection/stress-strain in a structure

of a member can be obtained from experimental load deflection/ stress-

strain curves

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Stress Strain

diagram:

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The most common tests are tension test for ductile materials (steel)

& compression test for brittle materials (concrete)