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Hardened Concrete Properties

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. Curing conditions, humidity temperature w/c , (inversely related) Abram’s law

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Hardened Concrete Properties

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

  2. Factors 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

  3. 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

  4. Factors Affecting Concrete Strength

  5. Durability • Resistance to freezing and thawing • Cracking • Internal Problems • Rebar Corrosion

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

  7. Air 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

  8. Internal voids

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

  10. Durability-internal problems • Alkali-silica reaction • excessive sulfates

  11. Rebar corrosion NaCl - +

  12. Mechanism of corrosion

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

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

  15. Load Induced Volume Changes Tangent modulus • Instantaneous, 1D Secant modulus

  16. Load Induced Volume Changes • Time dependant Deformation Creep deformation Time

  17. Creep in Concrete

  18. Creep in Concrete water Creep

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

  20. 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

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