Properties ofPortland Cement Concrete
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Concrete Ingredients
Gravel
Sand
Water
Cement
Air
40%
20%
5%10%
25%Pa
ste
Mor
tar
Concrete Strength
1. Aggregate
2. Cement/Aggregate Bond
3. Cement Paste
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Water-Cement Ratio
0.2
Water-Cement Ratio (Volume)
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31 sack of cement 1ft bulk 94 lb
gallons of waterw/c gallons sacksacks of cement
Water-Cement Ratio
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mass of waterw/cm
mass of cement + SCMs
mass of waterw/c dimensionless
mass of cement
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Water-Cement Ratio
0.2
TYPICALRANGE
0.25 = Full Hydration
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Water-Cement Ratio
Rodded
Vibrated
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Water-Cement Ratio
WaterCement
0% Hydration
100% Hydration
Hydration Products WaterAir
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Cement Paste Strength
Air Content of Paste - percent
Freeze-Thaw Durability
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Freeze-Thaw Durability
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Air Entrainment
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Air Entrainment
(data from tests on mortar cubes)
Air Requirements
0
1
2
3
4
5
6
7
8
40 50 60 70 80
Tota
l Air
Con
tent
(%)
Mortar Content (%)
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3"1½"
¾"
⅜"
Optimum Air Content = 9% of Mortar Volume
NMAS =
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Properties Affected by Air Content
durability
consistency
strength
bleeding
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Air Entrainment
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Air Entrainment
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Important Properties
workabilityharshness
compressive strengthtensile / flexural strength
stiffnessdurability
permeabilityshrinkage / creep
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Workability
workability (n.) the ease with which theconcrete ingredients (gravel, sand, cement,water) can be mixed, transported, placed,consolidated, and finished with minimumloss of homogeneity.
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Workability
workability = consistency + cohesion
refers to the fluidity of the concrete and how easily it can be transported, placed, and
consolidated without inhomogeneity
refers to the stickiness of the concrete and how easily it can be placed and finished
without inhomogeneity
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Inhomogeneity
segregation (n.) the tendency for the gravel particles to separate from the rest of the ingredients.
bleeding (n.) the tendency for the mixing water to separate from the rest of the ingredients.
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Causes of Segregation
improper placement
too much mixing water
over-vibration
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Causes of Bleeding
too little cement
too much water
over-vibration
over-working
Concrete Strength
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28-day
7-day
3-day
1-day
28-day
7-day
3-day
1-day
Air-entrainedNon-air-entrained
Strength Gain Over Time
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w/c = 0.3
w/c = 0.4
w/c = 0.5w/c = 0.6w/c = 0.7
0 20 40 60 80 100Age (days)
90
80
70
60
50
40
30
20
10
0
Com
pres
sive
Str
engt
h (M
Pa)
Concrete Maturity
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Log function
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Tensile Strength
0.1t cf f
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Tensile Strength
6.7t cf f cf in psi
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Beam Flexure Test
3L
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Modulus of Rupture
2
PLMORbd
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Concrete Behavior
1
E
1
E
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Beam Flexure Test
2
PLMORbd
ft
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Flexural Strength
8.4 cMOR f cf in psi
6.7t cf f cf in psi
1.25 or 0.8t tMOR f f MOR
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Flexural Strength
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Stiffness and Strength
1
E
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Stiffness and StrengthSource: ACI Manual of Concrete Practice
1.5cE 33w f
2
3
2c
E elastic modulus in lb inw unit weight in lb ftf compressive strength in lb in
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Stiffness and Strength
cE 57,000 f
Typical test data
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Stiffness and Strength
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Durability
Sources ofDeterioration
Alkali-SilicaReaction
SulfateAttack
Freeze-ThawCycles
aggregate typecement type
air contentw/c ratio
cementtype
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Shrinkage / Creep
Sources ofVolume Change
TemperatureChanges
CreepStrains
DryingShrinkage
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Coefficient of Thermal Expansion
AggregateType
Coefficient(10-6 in/in/oF)
Quartz 6.6Sandstone 6.5
Gravel 6.0Granite 5.3Basalt 4.8
Limestone 3.8Average 5.5
Example
How much strain would develop in a graniticconcrete due to a 60°F temperature change?
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Example
1
E
43.6 10
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Drying Shrinkage Coefficient
TensileStrength
(psi)
ShrinkageCoefficient
(in/in)300 or less 0.0008
400 0.0006500 0.00045600 0.0003
700 or more 0.0002Typical 0.0006
Example
How much will a typical 14-ft pavement slabshrink during curing if it is unrestrained?
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Example
How much tensile stress will develop in theslab in the previous example if it is restrained?
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