Concrete as a Building Material

Concrete as a Building Material

1. Components of Concrete (1m3 / 2.5 tonnes)

   • Cement
     • 6-16% limestone/chalk/clay
     • 350kg
   • water
     • 12-20%
     • 200kg
   • fine aggregate
     • 20-30%
     • 650kg
   • coarse aggregate
     • 40-55%
     • 1250kg

2. What is cement

   • binding agent
   • binds aggregates

3. Oxides

   • limestone CaCO3
     • Calcium carbonate
   • Alumina Al2O3
     • Aluminium oxide
   • Iron Ore Fe2O3
     • Iron-ferric oxide
   • Silica SiO2
     • Silicone Oxide

4. Making Portland Cement

   • limestone and caly are burnt in a rotary kiln
     • Forms a clinker which is rich in calcium silicates
       • Clinker is ground into a fine powder
         • Gypsum ius added (calciukm sulfate) regulates rate of setting when mixed with water

5. Chemical compsition of OPC

   • 20% Dicalcium Silicate C2S
     • Slow strength gain
   • 12% Tricaclium aluminate C3S
     • quick setting
   • 50% Tricalcium silicate C3S
     • Hydrate quickly , rapid strength
   • 8% Tetracalcium aluminoferrite C4AF
     • Grey colour and resistance to rusting

6. Phases of concrete

   • cement + water = hydration
   • hydration = setting and hardening of concrete
     • setting
       • denotes the change from workable to a solid
     • hardening
       • describes the gain of strength of the solid
   • Hydration forms a feathery crystal which results in early strength gain
   • Strength is a byproduct of the exothermic reation which produces heat

7. Taxonomy of Concrete

   • Type 1
     • CEM 1
       • General purpose
   • Type 2
     • CEM 2
       • Moderate heat of hydration / Moderate sulfate resistance
   • Type 3
     • CEM 3
       • High early strength
   • Type 4
     • CEM 4
       • Pozzolanic cement / low heat of hydration
   • Type 5
     • SRPC
       • High sulfate resisting portland cement

8. Sulfates in the ground

   • chemical reaction between the sulfate and C3Q in the cement produces expansive compound limited to 3.5% in SPRC

9. Admixtures

   • material, added to concrete to modify the properties of the concrete
   • Reduce free water content

10. Properties of Fresh Concrete

    • S0 10-40mm
    • S1 50-90mm
    • S2 100-150mm
    • S3 160-210 mm

11. Properties of hardened concrete

    • high compressive strength
    • low tensile strength
    • Free WCR 0.3-1.O
      • Strength ^ as WCR decreases
    • Crushed aggregates
      • result in increased strength
    • 50-60% in 7 days
    • 80-85% in 28 days

12. Concrete Mixes

    • ST3 - Domestic
      • GEN 2
        • S2 - House floor finsih
    • ST2 - Extremely versatile
      • GEN 1
        • S2 - House footings
        • S3 - Strip footings
        • S4 Trench fill

13. Compaction of concrete

    • reduce entrapped air
    • Large air voids
      • reduce strength
      • increase permeability
      • reduce bond between concrete and reinforcement
      • visual blemishes appear
    • Methods
      • hand vibration
        • traditional
        • use of a flat edge
        • lifting and dropping
      • Mechanical
        • pokers
        • vibrating screeds

Images and files in the map