Concrete as a Building Material & Formwork

1. Concrete as a Building Material & Formwork Lesson 1 M. S .Martin – Sept 2009

2. Definition • Concrete is basically an artificial stone, that can be formed and molded into desired shapes in its plastic state. • Main Components (p. 3 concrete basics): • Cement • Fine aggregate • Course aggregate • Water

3. Cement • Cement, when combined with water acts like glue, or the binder. • Some textbooks refer to this as the paste. • What we know as Portland Cement, is derived from limestone and clay. • There are many other types of cement we use in concrete as well.

4. Types of Cement • Made to meet requirements of AS3972 Portland & Blended Cements • General purpose Type GP – general purpose Portland cement Type GB – general purpose blended cement Special purpose Type HE – high early strength cement Type LH – low heat concrete Type SR – sulphate resistant cement. Look at p. 3 basic concreting handout

5. Storage of Cement - p. 4 basic concreting • It will retain it’s quality indefinitely if • It doesn't come in contact with water • Therefore storage should be in facilities as air tight as possible • Should also have raised floor, above ground to avoid moisture • Tightly pack bags to reduce air circulation • “first in, first out” use of

6. Fine Aggregate - Sand • This is fine particles of stone, generally less than 5mm in size. • Sand for concrete must be of a clean washed regulated mixture. • Sand types: • Pit sand • River sand • Beach sand • Crusher fines P. 4 basic concreting

7. Coarse Aggregate • This consists of crushed rock. • A good coarse aggregate must be: • Dense & hard • Durable and chemically inert • Clean, no silt clay or salt • Rough and of various sizes over 5mm • Non-porous to help prevent water penetration of the finished concrete P. 4 basic concreting

9. Water – P. 4 basic concreting • When used for concrete should be free from problem causing substances – • Acids • Alkalis and oils • Water containing vegetable mater • Generally, water suitable to drink is a good guide.

10. Reinforcement in Concrete • This is used for its good tensile strength. • Also its shear properties. • Reinforcement is useful to counteract the various stresses put on concrete. • Look at BBCS P.227-229 and following slides to understand these stresses • Stresses BBCS p. 225

11. Shear

12. Tension

13. Compression

14. Torsion

15. Types of Reinforcement and accessories

16. Mesh

17. Bar Type

18. Stirrups

19. Reinforcement Chairs

20. Setting of Concrete • The hardening process of concrete (or setting) takes place through: - a chemical reaction - of the cement & water - this process is called “hydration” - Characterized by the release of heat

21. Setting of Concrete • Basic Concreting P. 6 • Setting is the initial stiffening of the cement paste • Where concrete loses it’s plasticity before it gains much strength • This is affected by water content and temperature • More water, slower set • Higher temp, faster set

22. Hardening of Concrete • Also P. 6 basic concreting • Hardening is the gain in strength that takes place after it has set • Effected by type of cement used • And temperature • High temp’s cause more rapid hardening

23. Workability of Concrete P. 7 BC • In it’s plastic state it is very workable • But depends on some governing factors • Water cement ratio, more water, more workable • Cement content, higher the cement content, the more workable it is • Grading of aggregates, produce more workable concrete • Particle shape & size, smooth / round are more workable

24. Vibration • Concrete is usually vibrated to achieve good Compaction • P. 23 BC • Three types of vibrators • Immersion vibrators • Form vibrators • Surface or screed vibrators

25. Curing • P. 28 BC • A critical part of the process • Can be achieved by • Ponding • Sprinkling • Wet coverings • Plastic sheets • Curing compounds

26. Testing of Concrete • Primarily two types of testing used for concrete in residential construction • Slump testing – measuring the consistency of the mix • Compression testing – where the strength of concrete is measured

27. Slump Testing • Done on site • With purpose made equipment • Should be done in stages during poor • If incorrect, poor should be stopped • Look over P. 11-12 BC

28. Compression Tests • Samples gathered on site • Left to next day • Taken back to laboratory • Crushed at pre determined intervals until they fail • Thus, determining strength of concrete • Look over P. 12 – 13 BC

29. Ordering Concrete • Name & Address for delivery • The use (driveway etc.) • Amount in cubic metres • Class (see p.14 BC) • Slump in mm • Maximum agg size • Time for first truck and / or space between • Any admixtures

30. Formwork

31. Simple Formwork