Concrete Technology Steel (CH10) Lecture 19 Eng: Eyad Haddad

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.

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

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.

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.

4. Protection from corrosion The 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.

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.

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.

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.

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.

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.

8. Physical properties of steels In 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

Stress Strain diagram:

The most common tests are tension test for ductile materials (steel) & compression test for brittle materials (concrete)