What is concrete

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What is concrete?

• Cement
• Water
• Aggregates Fine (0 - 5 mm)
• Coarse (gt 5mm)
• (Admixtures)
• Concrete should be
• cohesive to be transported and placed without
  segregation
• able to be compacted by means available
• satisfactory compressive strength when hardended
• Properties related to compressive strength
• Density
• Permeability
• Durability
• Resistance to abrasion
• Resistance to impact
• Resistance to sulphates

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Portland Cement

• Raw materials
• limestone
• Kleins point, Rapid Bay, Angaston
• silica, alumina in clay or shale near Angaston
• ironstone

1400oC
Clinker
Grind with gypsum
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Main compounds of Portland cement

• Tricalcium silicate 3CaO.SiO2 C3S
• Dicalcium silicate 2CaO.SiO2 C2S
• Tricalcium aluminate 3CaO.Al2O3 C3A
• Tetracalcium aluminoferrite 4CaO.Al2O3.Fe2O3 C4AF
  
• C3S and C2S
• are responsible for the strength of hydrated
  cement paste
• C3A is undesirable
• is present in small quantities. Reacts very
  rapidly with water (flash set)
• gypsum retards this
• provides early strength
• prone to sulphate attack
• C4AF
• dark in color with little cementing value
• forms due to iron oxide, a useful flux during the
  burning process.

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Properties of the major constituents
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Types of cement

• General purpose Portland cement (GP)
• General purpose blended cement (GB)
• GP slag / fly ash / silica fume
• High early strength cement (HE)
• early stripping of formwork, very cold weather,
  repairs
• Low heat cement (LH)
• mass concrete, hot weather
• Sulphate resisting cement (SR)
• marine construction, sulphate bearing soils
• Off white / white Portland cement
• Coloured cements
• Masonry cement
• unsuitable for concrete
• High alumina cement (HAC)
• high early strength, resistance to very high
  temperatures and sulphates
• loss of strength in warm, humid conditions

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Composition of cement
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Properties of cement

• Heat of hydration
• Strength development
• blended cements gain strength slowly over a
  longer period.

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Properties of cement

• Setting times of cement
• initial set gt 45min
• final set lt 10 hrs
• Shrinkage
• neat cement, 13 mortar, concrete

Setting time of concrete
900
800
Initial set 6.5 hrs Final set 8.7 hrs
700
600
?3.5 MPa
500
Penetration resistance (psi)
400
300
200
?0.5 MPa
100
0
4
5
6
7
8
9
10
Age (hours)
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Properties of cement

• Permeability
• Alkalinity
• hydrated cement paste pH 12.5
• protects steel from corrosion
• Resistance to chemical attack
• increased by decreasing the permeability
• most acids attack hardened cement
• resistance to sulphates can be increased by
  lowering C3A content
• chlorides increases corrosion of steel

Moist curing required for capillary discontinuity
W/C ratio
Duration of curing
0.4
3 days
7 days
0.45
0.5
14 days
0.6
6 months
0.7
1 year
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Properties of cement

• Resistance to freezing and thawing
• ? with ? permeability , air entrainment
• Resistance to heat
• strength unaffected up to 200ºC
• progressive loss from 300ºC - 600ºC
• complete loss of strength over 600ºC