Civil Engineering Materials

• Non-Destructive Testing


  Testing methods that do not damage the object being tested
• 1. ray Testing


  1. X-rays passed through object

  2. Expose photographic film on opposite side

  3. Darker patch on film indicates cavity in material
• Dye Penetrant Testing


  1. Surface preparation to remove oil/contaminants

  2. Suspect area heated

  3. Dye placed over surface, excess wiped off

  4. Developer sprinkled over object, then cooled

  5. Dye squeezed out of crack exposes it
• Ultrasonic Testing


  1. Transmitter sends ultrasonic waves through component

  2. Waves normally pass through and are reflected back to sender

  3. Display shows lower reading if cavity encountered as waves reflected early
• Slump Test


  Used to check concrete fluidity for casting
• Crack Formation and Growth


  Brittle failure method where materials undergo immediate brittle failure
• Glass and ceramics have poor tensile performance due to micro-cracks, micro gas bubbles and minute crystallites on surface that concentrate stress
• When a crack forms

  Strain energy released from the crack is concentrated at the bottom of the crack, increasing the strain energy at the tip
• Cracking is a common damage caused by stress in a material that can be exaggerated by factors like corrosion, fatigue, high pressure, and material of construction
• Critical Crack Length


  The length a crack must get to before it proceeds through a material until failure occurs
• Failure Due to Cracking

  Brittle fracture mechanism where a material's critical crack length is proportional to its propensity to crack
• Elimination of Failure Due to Cracking

  1. Design items without sharp corners to concentrate stress

  2. Place interfaces within a material which run perpendicularly to the expected growth of cracks blocking cracks from passing
• Repair of Cracking


  1. Metallic: Welding, may need heat treatment

  2. Polymeric: Polymer welding, adhesive technology
• Stone


  • Weak in tension, strong in compression, low in toughness, brittle
  • Igneous and metamorphic rocks tend to be very dense
• Glass


  • Amorphous solid, does not have regular crystalline pattern
  • Amorphous structure makes glass unfavorable to shaping at force as slip of atoms cannot occur
  • Shaping must be done at delegated temperatures where viscosity is reduced
  • Can be crystalized to produce tougher, less brittle material with less optical clarity
• Glass


  • Low toughness, brittle, weak in tension
• Toughened Glass


  1. Glass pane heated then outer surface cooled quickly by cold air (tempered)

  2. Outer surface placed in compression as interior cools and contracts
• Portland Cement


  75% limestone, 25% clay ground together and heated in a rotary kiln to form lumps of clinker
• Hydraulic Cement


  Can set under water e.g. portland cement, pozzolana cement
• Non-Hydraulic Cement


  Set and harden in air, cannot be used under water
• Bricks


  • Hard, durable, high water absorption, high compressive strength
• Brick Manufacturing


  1. Pressing: used for solid bricks and pavers, clay stamped down and compacted into mold

  2. Extrusion: used for bricks with holes, clay mixed with water for plasticity then extruded through die
• Composite


  A material made up of at least two constituent materials
• Timber


  • High specific strength to mass ratio, regenerative, easily handled and joined, can be laminated
  • Combustible and can decay, strength varies with species, weak in compression, expands and contracts with atmospheric moisture
• Concrete


  Particle-reinforced composite of aggregate, sand, cement and water
• Concrete Reinforcement


  1. Steel bars, mesh, or fibres can be added to improve tensile strength

  2. Reinforcements positioned in area sustaining tensile load, or at neutral axis for fluctuating loads

  3. Polymer fibres can be added to prevent expansion, cracking and spalling in fire
• Prestressed Concrete


  • Large compressive force applied through stretch and release of high-strength metal bars
  • Residual compressive force must be exceeded before tensile failure occurs
  • Can be pre-tensioned or post-tensioned