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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