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