Transcript Hardened Concrete Properties Strength

Hardened Concrete Properties
 Strength
 compressive
strength 2000-8000 psi
 tensile strength 200-800 psi
 flexural strength
 compression >> tension since concrete is notch
sensitivite
Factors Affecting Strength
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Curing conditions, humidity
temperature
w/c , (inversely related) Abram’s law
air content, (inversely related), short and long term
aggregate characteristics, roughness,grading,
minerological.
cement type, composition, fineness, type I vs. type III
cement content (directly related)
Strength porosity relationship
mixing water
Strength and Curing
moist cured entire time
Strength
in air after 7 days
100%
in air after 3 days
in air entire time
28
time
Factors Affecting Concrete Strength
Durability
 Resistance
to freezing and thawing
 Cracking
 Internal
Problems
 Rebar Corrosion
Resistance to freezing and thawing-Major
factors
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Air Entrainment
w/c, low water -cement ratio/ water content
volume stability, stiff aggregates with low coefficient of
thermal expansion
Air Entrainment
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Water gains 9% in volume upon freezing
nighttime freezing followed by daytime thawing,
approximately 40 cycles per year, average. max of 200
cycles per year.
fatigue loading of ice formation within pores
Air Entraining Admixture (AEA) Must provide:
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Pore size
Pore spacing
Pore specific surface area
Internal voids
Durability-Cracking
 path
for harmful material to get into
concrete
 sulfates- soils
 cause
severe expansion, and deterioration
 chlorides
 initiate
-deicing salts
corrosion
 Excessive
shrinkage
Durability-internal problems
 Alkali-silica
reaction
 excessive sulfates
Rebar corrosion
NaCl
+ -
Mechanism of corrosion
Corrosion Protection
 Proper
cover of at least 2”
 lower w/c
 denser concrete
 avoid using chlorides
Review
 Strength
 Durability
 Water
Tightness
 water
cement ratio
 Permeability
 Volume
Stability
 shrinkage
deformation with no load applied
 creep deformation under sustained loading
Load Induced Volume Changes
 Instantaneous,
1D
E 
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Tangent modulus
Secant modulus
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Econcrete  33
1.5
f 'c
  unit weight of concrete , lbs / cubic ft
f 'c  compressiv e strength , psi
Load Induced Volume Changes
 Time
dependant
Deformation
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Creep deformation
Time
Creep in Concrete
Creep in Concrete
water
Creep
Consequences of creep
 Loss
in pre-stress
 possibility of excessive deflection
 stressing of non load bearing members
Economy
 Cement
Content
 50-60$/ton
 Aggregates
 5-6
$/ton
 minimum
cement required at the minimum
water cement ratio, with the maximum
strength and durability