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 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

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

Factors Affecting Concrete Strength

Durability Resistance to freezing and thawing Cracking Internal Problems Rebar Corrosion

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

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

Internal voids

Durability-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 problems Alkali-silica reaction excessive sulfates

Rebar corrosion NaCl + -

Mechanism of corrosion

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

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

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

Load Induced Volume Changes Time dependant Deformation Creep deformation Time

Creep in Concrete

Creep in Concrete water Creep

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

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