1. Design of Concrete Structure I Dr. Ali Tayeh First Semester 2009 Dr. Ali Tayeh First Semester 2009

2. Lecture 2 Concrete Property

3. Concrete  Concrete is a mixture of cement, fine and coarse aggregates, and water.  Water is the key ingredient for chemical reaction for curing.

4. Concrete Mixing and Proportioning Quality Workability Economical In the design of concrete mixes, three principal requirements for concrete are of importance:

5. Concrete Mixing and Proportioning Quality of concrete is measured by its strength and durability. Durability of concrete is the ability of the concrete to resist disintegration due to freezing and thawing and chemical attack.

6. Concrete Mixing and Proportioning The compressive strength of concrete is mainly affected by the water/cement ratio, degree of compaction, age, and temperature. It is determined through testing standard cylinders 15 cm in diameter and 30 cm in length in uniaxial compression at 28 days (ASTM C470-93a)

8. Concrete Mixing and Proportioning Workability of concrete may be defined as a composite characteristic indicative of the ease with which the mass of plastic material may deposited in its final place without segregation during placement, and its ability to conform to fine forming detail.

9. Workability Workability measured by slump test 1.Layer 1: Fill 1/3 full. 25 stokes 2.Layer 2: Fill 2/3 full. 25 stokes 3.Layer 3: Fill full. 25 stokes 4.Lift cone and measure slump (typically 2-6 in.) 1 2 3 4 12” slump

14. Concrete Mixing and Proportioning Economical takes into account effective use of materials, effective operation, and ease of handling. The cost of producing good quality concrete is an important consideration in the overall cost of the construction project.

15. –Applications: Improve workability Accelerate or retard setting and hardening Aid in curing Improve durability Admixtures

16. Admixtures –Air-Entrainment: Add air voids with bubbles Help with freeze/thaw cycles, workability, etc. Decreases density: reduces strength, but also decreases W/C –Superplasticizers: increase workability by chemically releasing water from fine aggregates.

17. Types of Cement  Type I: General Purpose  Type II: Lower heat of hydration than Type I  Type III: High Early Strength Higher heat of hydration quicker strength (7 days vs. 28 days for Type I)

18.  Type IV: Low Heat of Hydration Gradually heats up, less distortion (massive structures).  Type V: Sulfate Resisting For footings, basements, sewers, etc. exposed to soils with sulfates.

19. Failure Mechanism of Concrete Shrinkage Microcracks are the initial shrinkage cracks due to carbonation shrinkage, hydration shrinkage, and drying shrinkage.

20. Bond Microcracks are extensions of shrinkage microcracks, as the compression stress field increases, the shrinkage microcracks widen but do not propagates into the matrix. Occur at 15- 20 % ultimate strength of concrete. Failure Mechanism of Concrete

21. Matrix Microcracks - are microcracks that occur in the matrix. The propagate from 20% f c. Occur up to 30-45 % ultimate strength of concrete. Matrix microcracks start bridge one another at 75%. Aggregate microcracks occur just before failure (90%). Failure Mechanism of Concrete

22. Concrete Properties –Compressive Strength, Normally use 28-day strength for design strength –Poisson’s Ratio, n n = 0.15 to 0.20 Usually use n = 0.17

23. Concrete Properties Modulus of Elasticity, E c Modulus of Elasticity, E c Corresponds to secant modulus at 0.45 ACI 318-05 (Sec. 8.5.1) for normal concrete: normal weight concrete (density  2400 kg/m3)

24. Concrete Properties  Maximum useable strain, ACI Code: = 0.003 Used for flexural and axial compression For normal strength concrete, ~ 0.002

25. Concrete Properties Typical Concrete Stress-Strain Curves in Compression

26. Concrete Properties Types of compression failure There are three modes of failure. [a] Under axial compression concrete fails in shear. [b] the separation of the specimen into columnar pieces by what is known as splitting or columnar fracture. [c] Combination of shear and splitting failure.

27. Concrete Properties Tensile Strength –Tensile strength ~ 8% to 15% of –Modulus of Rupture, f r For deflection calculations, use : –Test: ACI Eq. 9-10 P frfr unreinforced concrete beam

28. Concrete Properties Tensile Strength (cont.) –Splitting Tensile Strength, f ct –Split Cylinder Test P Concrete Cylinder Poisson’s Effect

29. Creep Creep is defined as the long-term deformation caused by the application of loads for long periods of time, usually years. The total deformation is divided into two parts; the first is called instantaneous deformation occurring right after the application of loads, and the second which is time dependent, is called creep

30. Shrinkage Shrinkage of concrete is defined as the reduction in volume of concrete due to loss of moisture

31. Steel Reinforcement 1. General –Standard Reinforcing Bar Markings

32. Steel Reinforcement 2. Stress versus Strain –Stress-Strain curve for various types of steel reinforcement bar.

33. Steel Reinforcement E s = Initial tangent modulus = 2.04(10) 5 Mpa (all grades) Note: GR40 has a longer yield

34. W Kg/m Number of bars mm12345678910 60.220.280.570.851.131.411.71.982.262.542.83 80.390.501.011.512.012.513.023.524.024.525.03 100.620.791.572.363.143.934.715.56.287.077.85 120.891.132.263.394.525.656.797.929.0510.211.3 141.211.543.084.626.167.79.2410.812.313.915.4 161.582.014.026.038.0410.112.114.116.118.120.1 181.992.545.097.6310.212.715.317.820.422.925.4 202.473.146.289.4212.615.718.822.025.128.331.4 222.983.807.6011.415.219.022.826.630.434.238.0 243.554.529.0513.618.122.627.131.736.240.745.2 253.854.919.8214.719.624.529.534.439.344.249.1 264.175.3110.615.921.226.531.937.242.547.853.1 284.546.1612.318.524.630.836.943.149.355.461.6 305.547.0714.121.228.335.342.449.556.563.670.7 326.318.0416.124.132.240.248.356.364.372.480.4 Properties of reinforcing bars