Hardened Concrete Hardened Concrete Properties Properties Strength compressive strength 2000-8000 psi tensile strength 200-800 psi flexural strength compression >> tension since concrete is notch sensitivite
Feb 25, 2016
Hardened Concrete Hardened Concrete PropertiesProperties
Strength compressive strength 2000-8000 psi tensile strength 200-800 psi flexural strength compression >> tension since concrete is notch
sensitivite
Factors Affecting StrengthFactors Affecting Strength 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 CuringStrength and Curing
time
in air entire time
moist cured entire time
in air after 3 days
in air after 7 daysStrength
28
100%
Factors Affecting Concrete StrengthFactors Affecting Concrete Strength
DurabilityDurability Resistance to freezing and thawing Cracking Internal Problems Rebar Corrosion
Resistance to freezing and thawing-Major Resistance to freezing and thawing-Major factorsfactors
Air Entrainment w/c, low water -cement ratio/ water content volume stability, stiff aggregates with low coefficient of
thermal expansion
Air EntrainmentAir Entrainment 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:
Pore size Pore spacing Pore specific surface area
Internal voidsInternal voids
Durability-CrackingDurability-Cracking path for harmful material to get into
concrete sulfates- soils
cause severe expansion, and deterioration chlorides -deicing salts
initiate corrosion Excessive shrinkage
Durability-internal problemsDurability-internal problems Alkali-silica reaction excessive sulfates
Rebar corrosionRebar corrosion
NaCl
+ -
Mechanism of corrosionMechanism of corrosion
Corrosion ProtectionCorrosion Protection Proper cover of at least 2” lower w/c denser concrete avoid using chlorides
ReviewReview Strength Durability Water Tightness
water cement ratio Permeability
Volume Stability shrinkage deformation with no load applied creep deformation under sustained loading
Load Induced Volume ChangesLoad Induced Volume Changes
Instantaneous, 1D
E
Secant modulus
Tangent modulus
c.
concrete 'fE 5133ftcubic/lbs,concreteofweightunit
psi,strengthecompressiv'f c
Load Induced Volume ChangesLoad Induced Volume Changes
Time dependant Creep deformation
Deformation
Time
Creep in ConcreteCreep in Concrete
Creep in ConcreteCreep in Concrete
water
Creep
Consequences of creepConsequences of creep
Loss in pre-stress possibility of excessive deflection stressing of non load bearing members
EconomyEconomy Cement Content
50-60$/ton Aggregates
5-6 $/ton minimum cement required at the minimum
water cement ratio, with the maximum strength and durability