Concrete (1)

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  1. Concrete Making materials (6)
    1. Portland cement, water, stone and sand

    • 2. SCMS (supplementary Cementitous Materials      
    •     e.g fly ash, silica fume and natural pozzolans

    • 3. Other non-portland cements -
    •       Calcium aluminate, magnesium phosphate, and many others
    •  4. Chemical admixtures
    •     Air entrainment, water reducers, viscosity modifying, set modifiers and many others

    • 5. Fiber Reinforcement
    •    Organic, natural and metallic : macro and micro
    • 6. Conventional Reinforcement
    •    Plain, coated, stainless, non ferrous and others(mainly steel)
  2. Strength range for different uses of concrete
    • <2 MPa controlled low-strength materia
    • 15-20 MPa Residential concrete
    • 20-25 MPa Commercial buildings
    • 25-35 MPa Pavements
    • 45-60 MPa bridges
    • >70 High Rise buildings
    • >100 Special applications
  3. Concrete of different types
    • Normal concrete
    • Slip formed
    • Self compacting
    • Shot crete
    • Light weigh concrete
    • High density concrete
  4. Factors influencing concrete performance
    • Improper Reinforcement placement
    • Wet burlap and plastic
    • Curing Membrane
    • Re bar located to low to carry tensile loads in negative moment area
    • Salt corrosion
  5. Aggregates for concrete
    • Reduce cost
    • Stability
    • Thermal capability between concrete and steel
    • Technical reasons (abrasion and chemical resistance)
    • Aesthetics
  6. Sand for concrete Less than 4.74mm
    • Improves workability 
    • Sand must be well graded from fine to coarse sizes
  7. Stone for concrete
    Use to provide dimensional stability and reduce cost
  8. Aggregate properties
    • Grading (important for sand)
    • Relative density and volume
    • Particle shape and texture (interface)
    • Aggregate strength
    • Geological source (durability)
    • Shrinkage
    • Moisture content
  9. Grading of sand
    Fineness modulus of sand
    • FM <2.0 fine sand (too sticky)
    • FM >3.0 coarse sand (too boney)
  10. Moisture content of aggregates. Ideal condition?
    Saturated Surface Dry (SSD) is the ideal moisture condition for aggregates since no extra water is added r removed from concrete during mixing and fresh concrete state
  11. What is moisture content always measured by?
  12. Moisture content of Sand
    High surface area may retain excess water when damp
  13. Moisture content of stone
    Lower surface area and larger size makes material free draining
  14. Important to allow ____ in _____ when doing mix design
    Important to allow for moisture in damp aggregate when doing mix design
  15. Oven dry
    • Aggregate contains no moisture
    • pores are empty
  16. Air dry
    Agg contains some moisture but is not saturated, pores partially filled
  17. Saturated Surface Dry
    Aggregate is saturated pores are filled but there is no free water on surface
  18. Damp or wet
    Aggregate is saturated pores are filled and there is excess water on the surface
  19. Aggregate effect on water demand
    More water is required to lubricate agg with angular shapes than well rounded and smooth particles
  20. Angular example and water demand
    Kaitaia 190L/m^3
  21. Chunky example and water demand
    Auckland - 175 L/m^3
  22. Elongated example and water demand
    Christchurch - 165 L/m^3
  23. Rounded example and water demand
    150 L/m^3
  24. Water demand of concrete affected by: (4)
    • Shape and texture of aggregates
    • Grading of aggregates (esp sand) 
    • Amount of fine material (high surface area)
    • Temperature of concrete
  25. Water for concrete is require to:
    • Make concrete sufficient workable
    • React with cement to give strength
  26. Impurities in water and their action 
    What is preffered? 
    Check for what when testing water
    • Potable (drinking or town) water is preferable where possible
    • 1. Chlorides = corrosion of steel
    • 2. Sulphates = setting and strength
    • 3. Carbonates = accelerate setting
    • 4. Organic matter i.e = prevents setting
    • 5. Silts in clays = setting and strength
    • 6. Organic acids =delay setting 

    pH, softness, Cl- , So4 , Co3 and organics
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Concrete (1)
2014-04-08 09:32:50
Concrete (1)
Concrete (1)
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