1. Hardened Concrete Properties
Strength
compressive strength psi
tensile strength 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. moist cured entire time
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 Volume Stability
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 Aggregates
50-60$/ton
Aggregates
5-6 $/ton
minimum cement required at the minimum water cement ratio, with the maximum strength and durability