Introduction to Construction industry

1. Introduction to Construction industry Eng. Eyad Haddad Second Semester 2009 Lec. 8+9

2. Reinforced Concrete

3. Concrete History: - 1850s, reinforced concrete invented; - 1920s, pre-stressed concrete invented. Selecting a Building’s Structure: Major factors involved: a) Cost b) Typical bay sizes c) Expected lateral loads from wind and seismic d) Desired design flexibility e) Story heights (different for office versus residential, etc) f) Durability g) Exterior details.

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

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

6. Concrete Mixing and Proportioning • Qualityof 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.

7. 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)

9. Concrete Mixing and Proportioning • Workabilityof 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.

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

13. Concrete Mixing and Proportioning • Economicaltakes 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.

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

15. 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.

16. Fly ash is a very fine powder, essentially the waste product of thermal plants, Fly ash decreases the permeability of a concrete, increases its strength, reduces the need for water and improves the permeability. • Coloring agents are used for architectural needs.

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. Type I - Normal

20. Type I - Normal

21. Type III - High Early

22. Type IV - Low Heat of Hydration

23. Failure Mechanism of Concrete • Shrinkage Microcracksare the initial shrinkage cracks due to • carbonation shrinkage, • hydration shrinkage, • and drying shrinkage.

24. Failure Mechanism of Concrete carbonation shrinkage.

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

26. Failure Mechanism of Concrete • Matrix Microcracks : • are microcracks that occur in the matrix. • The propagate from 20% fc. • Occur up to 30-45 % ultimate strength of concrete. • Matrix microcracks start bridge one another تظهر مرة ثانيةat 75%. • Aggregate microcracks occur just before failure (90%).

27. Creep يتغير شكله(زحف الخرسانة) • 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, • the second which is time dependent, is called creep

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

29. The placement of concrete. • Concrete is not a liquid, but rather, an unstable mixture that will segregate if handled improperly. • Concrete is deposited in formworks directly from the truck, through buckets or pumps. • The mix may be vibrated to consolidate the mix. Then finishes are applied, like finishing its surface for a sidewalk or a stamped driveway, etc.

30. Concrete being placed in 1929. Note the buggy that brings the concrete from an on-site concrete mixing machine.

31. Concrete placement today, direct from the truck.

32. Buckets are used for sites away from the truck.

33. Tower crane and bucket.

34. Pumps can now reach 150 m high.

35. Concrete Segregation • Segregation takes placebecause the heavy aggregates in the mix separate and settle. • The results are a non-uniform mix with reduced strength and weaker surfaces. • The most common causes are: • Excessive vibration of the mix • 2) Dropping the concrete from • excessive heights • 3) Trying to move the concrete horizontally using a vibrator; this is commonly seen when casting a wall.

41. Curing in extreme temperatures

42. The top of the slab is being protected during cold weather.

43. ConcreteFormwork • Formwork is a temporary structure that will provide the shapes and supports the wet concrete. • It is designed to support the concrete and the steel reinforcing, plus the construction loading without excessive deflection. • Forms must also be easily stripped once the concrete is cured. • The quality of the finished concrete surface is a function of the quality of the form material and its structural strength (including the form ties and the framing spacing).

46. Steel Reinforcement 1. General • Standard Reinforcing Bar Markings

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

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

50. Properties of reinforcing bars