ARC1414: Building Technology 1, Module 2, Division 5: Metals

Metals

Aluminum

• Types of aluminum:
  • Aluminum sheet and strip: used for roofing, flashing, and gutters
  • Aluminum foil: used for thermal insulation and vapor barriers, rolled to a thickness of 0.005”
  • Corrugated aluminum: rigidized sheet fabricated from special aluminum alloys
  • Structural aluminum: used as a structural material, considering factors such as corrosion resistance, extrudability, and lightweight
  • Aluminum doors and windows: fabricated from extrusions and rolled shapes
  • Aluminum panels and sandwich panels: pre-fabricated units with aluminum exterior facing and cellular core
  • Ornamental aluminum: rods, bars, pipes, railings, fittings, and special shapes for ornamental design

Finishes of Aluminum

• Mechanical finishes: obtained by grinding, polishing, scratching, sandblasting, embossing, or other surface treatment
• Chemical finishes: based on chemical reactions with the aluminum surface, used for etching, cleaning, or polishing
• Electrolytic finishes (anodized finishes): used for protective and decorative coatings, colored finishes are porous and can be sealed
• Electroplating: covering aluminum with a protective or decorative film of another metal, usually by electrodeposition
• Porcelain or Vitreous Enamel: forming a hard, resistant surface with a broad color range
• Paint: applied to aluminum surfaces with a suitable chemical treatment finish

Iron

• Pure iron: tough, malleable, silvery-white metal, soft and ductile, easily magnetized, and oxidizes rapidly in air
• Characteristics: can be hardened by heating and sudden cooling, and made more pliable by heating and slow cooling

Types of Iron

• Cast iron: iron-carbon alloy with more than 1.7% carbon, hard and brittle, used for piping, ornamental ironwork, hardware, and porcelain enameled plumbing fixtures
• Wrought iron: almost pure iron with less than 0.1% carbon, soft, malleable, tough, and resistant to progressive corrosion, used for genuine wrought iron pipe, chain, sheet, and ornamental ironwork

Steel

• Plain carbon steels: alloys of iron and carbon, not containing more than 2% carbon, made in malleable or ingot form
• Characteristics: iron is always in excess of 95%, phosphorus, sulfur, oxygen, and nitrogen are present, manganese, silicon, aluminum, copper, and nickel may be present as residual impurities or elements deliberately added

Types of Steel

• Structural steel: medium carbon steel with controlled carbon content, available in angles, channels, I-beams, H columns, T shapes, Z shapes, plates, round pipe columns, sheet piling, open web joists, and light steel framing shapes

• Wrought carbon steels:

  • Reinforcement of concrete: deformed bars of varying grades and diameters
  • Sheet and strip: used for fabricated form as decking, galvanized sheet, expanded metal, panels, and sandwich panels, and as a base metal for porcelain enamel

• Alloy steels: added elements increase properties such as strength, hardness, electrical conductivity, and resistance to corrosion and wear### Types of Metals

• Steel:

  • High-strength low-alloy steels: improved mechanical properties, resistance to atmospheric corrosion, and used in pre-stressed concrete, high-strength bolts, cables for elevators, etc.
  • Stainless steels: contain >10% chromium, resistant to heat, oxidation, and corrosion, used in exterior and interior wall finishes, doors, windows, etc.

• Copper:

  • Ductile, malleable, nonmagnetic metal with high electrical and thermal conductivity
  • Resistant to corrosion by air and saltwater, but attacked by alkalis and common acids
  • Forms a protective green patina on exposure
  • Used in minor structural work, alloys, and electrical applications

• Tin:

  • Soft, ductile, malleable, bluish-white metal
  • Resists corrosion by air, moisture, sulfur dioxide, and hydrogen sulfide due to a thin film of stannic oxide
  • Takes a highly reflective polish
  • Used in protective coatings, alloys, and solders

• Zinc:

  • Medium hard, bluish-white metal
  • Characterized by brittleness and low strength
  • Readily attacked by acids and alkalis
  • Resistant to corrosion by water, forms a protective film of zinc carbonate or oxide on exposure
  • Used in galvanizing, die-casting, and alloys

• Brass:

  • An alloy of copper and zinc
  • Less hard and strong than steels but superior in workability and resistance to corrosion
  • Used in various architectural applications

• Bronze:

  • An alloy of copper and tin
  • Rich golden-brown metal
  • Can refer to alloys of copper with other elements, such as silicon, manganese, or aluminum
  • Used in various architectural applications

• Chromium:

  • Steel-white metal that takes a brilliant polish
  • Harder than cobalt or nickel
  • Nonmagnetic at ordinary temperatures but becomes magnetic at 13°F
  • Resists oxidation and corrosion
  • Used in ferrous and nonferrous metallurgy, and in chromium plating

• Nickel:

  • Inert silvery metal
  • Resistant to strong alkalis and most acids
  • Takes a high polish
  • Used in alloys to impart strength, hardness, toughness, and corrosion resistance
  • Used as a protective or decorative coating for other metals

• Lead:

  • Blue-gray, soft, very heavy metal
  • Extremely workable
  • Has good corrosion resistance
  • Relatively impenetrable to radiation
  • Used in various applications, including radiation shielding

Methods of Joining Metals

• Soldering:
  • Joining metals using a lower melting metal or alloy
  • Used to make electrical connections, seal joints, and join metals
  • Soldered joints have little tensile, shear, or impact strength
• Welding:
  • Process of joining two metals by creating an actual union of interatomic bonds
  • Can be done by close contact, heating, pressure, or adding molten metal
  • Resulting joints are as strong or stronger than the metals joined
• Rivets:
  • Devices used to join or fasten metals
  • Rivet is inserted through holes in the materials being joined and then flattened to tie the pieces together

Metals for Concrete Reinforcement

• Steel Bars:
  • Mostly used for concrete reinforcement
  • Can be plain or deformed (with lugs or projections for better bonding to the concrete)
  • Can be billet-steel or rail-steel bars
• Wire Fabric:
  • Made of cold-drawn steel wire
  • Widely used for reinforcing concrete slabs and floors, as well as stuccoed work
• Expanded Mesh:
  • Manufactured from solid steel sheets
  • Sheets are cut or pierced in staggered slots or patterns and then stretched to form an open mesh
  • Forms can include diamond, crimp, herringbone, and Z-rib
  • Used in various applications, including STEELCRETE
• Laths:
  • Permanent centering or self-centering laths
  • Produced in various forms, including flat or segmental sheets
  • Can be furnished painted or galvanized, and in open-hearth mild steel or special copper-bearing or alloy steels

Storage and Care for Metal Reinforcement

• Storage:
  • Metal reinforcement should be stored in racks above the ground and away from moisture and vegetation
  • If stored for an extended period, it's recommended to build a shed over the storage racks
• Care:
  • Bright-red rust on reinforcement is not detrimental
  • Actual rust scales can indicate a reduction in the effective cross section of the bar
  • Deep scaling should be considered a reason for condemning the use of reinforcement
  • All reinforcement should be kept free from oil to maintain a good bond between concrete and steel