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Published byCandice Burdock Modified about 1 year ago

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Hardened Concrete Properties u Strength u compressive strength 2000-8000 psi u tensile strength 200-800 psi u flexural strength u compression >> tension since concrete is notch sensitivite

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Factors Affecting Strength u Curing conditions, humidity u temperature u w/c, (inversely related) Abram’s law u air content, (inversely related), short and long term u aggregate characteristics, roughness,grading, minerological. u cement type, composition, fineness, type I vs. type III u cement content (directly related) u Strength porosity relationship u mixing water

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Strength and Curing time in air entire time moist cured entire time in air after 3 days in air after 7 days Strength 28 100%

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Factors Affecting Concrete Strength

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Durability u Resistance to freezing and thawing u Cracking u Internal Problems u Rebar Corrosion

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Resistance to freezing and thawing-Major factors u Air Entrainment u w/c, low water -cement ratio/ water content u volume stability, stiff aggregates with low coefficient of thermal expansion

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Air Entrainment u Water gains 9% in volume upon freezing u nighttime freezing followed by daytime thawing, u approximately 40 cycles per year, average. max of 200 cycles per year. u fatigue loading of ice formation within pores u Air Entraining Admixture (AEA) Must provide: u Pore size u Pore spacing u Pore specific surface area

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Internal voids

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Durability-Cracking u path for harmful material to get into concrete u sulfates- soils u cause severe expansion, and deterioration u chlorides -deicing salts u initiate corrosion u Excessive shrinkage

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Durability-internal problems u Alkali-silica reaction u excessive sulfates

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Rebar corrosion NaCl + -

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Mechanism of corrosion

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Corrosion Protection u Proper cover of at least 2” u lower w/c u denser concrete u avoid using chlorides

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Review u Strength u Durability u Water Tightness u water cement ratio u Permeability u Volume Stability u shrinkage deformation with no load applied u creep deformation under sustained loading

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Load Induced Volume Changes u Instantaneous, 1D Secant modulus Tangent modulus

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Load Induced Volume Changes u Time dependant Creep deformation Deformation Time

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Creep in Concrete

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water Creep

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Consequences of creep u Loss in pre-stress u possibility of excessive deflection u stressing of non load bearing members

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Economy u Cement Content u 50-60$/ton u Aggregates u 5-6 $/ton u minimum cement required at the minimum water cement ratio, with the maximum strength and durability

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