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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
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- 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)
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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
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Concrete of different types
- Normal concrete
- Slip formed
- Self compacting
- Shot crete
- Light weigh concrete
- High density concrete
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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
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Aggregates for concrete
- Reduce cost
- Stability
- Thermal capability between concrete and steel
- Technical reasons (abrasion and chemical resistance)
- Aesthetics
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Sand for concrete Less than 4.74mm
- Improves workability
- Sand must be well graded from fine to coarse sizes
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Stone for concrete
Use to provide dimensional stability and reduce cost
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Aggregate properties
- Grading (important for sand)
- Relative density and volume
- Particle shape and texture (interface)
- Aggregate strength
- Geological source (durability)
- Shrinkage
- Moisture content
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Grading of sand
Fineness modulus of sand
- FM <2.0 fine sand (too sticky)
- FM >3.0 coarse sand (too boney)
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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
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What is moisture content always measured by?
Mass
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Moisture content of Sand
High surface area may retain excess water when damp
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Moisture content of stone
Lower surface area and larger size makes material free draining
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Important to allow ____ in _____ when doing mix design
Important to allow for moisture in damp aggregate when doing mix design
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Oven dry
- Aggregate contains no moisture
- pores are empty
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Air dry
Agg contains some moisture but is not saturated, pores partially filled
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Saturated Surface Dry
Aggregate is saturated pores are filled but there is no free water on surface
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Damp or wet
Aggregate is saturated pores are filled and there is excess water on the surface
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Aggregate effect on water demand
More water is required to lubricate agg with angular shapes than well rounded and smooth particles
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Angular example and water demand
Kaitaia 190L/m^3
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Chunky example and water demand
Auckland - 175 L/m^3
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Elongated example and water demand
Christchurch - 165 L/m^3
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Rounded example and water demand
150 L/m^3
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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
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Water for concrete is require to:
- Make concrete sufficient workable
- React with cement to give strength
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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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