1. Concrete
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2. Concrete
Cement
Sand
Gravel
Water

3. Portland Cement
A dry powder made from limestone and is usually packaged in bags containing 1 cubic foot and weighs 94 pounds

4. Portland Cement
When mixed with water, it forms the “glue” to hold the aggregate together

5. Fine Aggregate
Sand
It should be clean of clay, silt, and organic matter

6. Course Aggregate
Gravel and rocks over ¼” in diameter

7. Water
Should be clean

8. Concrete Trucks
Most concrete is delivered by trucks to the construction site as ready-mixed concrete

9. Mortar
Does not contain coarse aggregates and is used to join bricks or blocks

10. Cement
Although many people call concrete “cement”, cement is the powdered material and concrete is the mixture of ingredients

11. Weight
lbs. per cubic foot

12. Slump Stronger concrete requires less slump
The consistency or wetness of the mixture

13. Slump
If concrete has too much slump (is too wet), adding aggregate such as sand and gravel will correct the problem

14. Uniformity
Is thoroughly mixing all ingredients so that the “glue” which is wet cement will be around all sand and gravel particles (aggregates)

15. Workability
Refers to the ease with which concrete can be placed and shaped

16. Ratio
Expressed as a three digit number
Example: 1,2,3

17. Ratio The first number is parts of cement
Second number is parts of fine aggregate (sand)

18. Ratio The third number is parts of large aggregate (gravel)
Parts may be shovels full, pounds, cubic feet, etc.

19. Ratio
Less sand, gravel, and water are used for the same amount of water to make concrete stronger

20. Hand Mixing
May be done in a wheelbarrow or mixing box (mortar box) by using a shovel or hoe
done

21. Hand Mixing Add sand and then cement and mix thoroughly
Then add and mix gravel

22. Hand Mixing
Last thing to add is water and mix well

23. Machine Mixing
Uses a concrete or mortar mixer

24. Machine Mixing
First, add about 10% of water needed so that ingredients will not stick to mixer

25. Demonstrate Concrete Skills

26. Form
A wood or metal structure that confines concrete to the desired shape until it hardens

27. Form
Trenches are dug in the ground for footings of buildings, and the soil walls are the forms

28. Form
Wood or metal can be used

29. Form
When wood is used, ” X 4”, 2” X 6”, 2” X 8” and other 2” size lumber is used because forms must not bend or warp and must be braced to prevent movement

30. Form
In warm weather, forms should stay in place 2 to 3 days and twice that long if weather is cold

31. Pour or Place
Concrete should be poured or placed as evenly as possible in the forms to prevent having to move it

32. Finishing
Bringing the surface of concrete to the proper grade and smoothness

33. Finishing
Screeding is using a straightedge such as a 2” X 4” board to level concrete with top of form

34. Finishing
Bull float is used to impact the concrete at the surface and to make it easier to finish

35. Finishing
Texture of the finishing tool will determine smoothness of concrete surface

36. Finishing
Wood float, stiff broom, or burlap will make a gritty, non-slip surface for floors, driveways, or walkways

37. Finishing
For a very smooth surface, a steel cement finishing trowel should be used

38. Reinforcement
Needed because concrete has low tensile strength and high compressive strength

39. Reinforcement
This means it has low stretch and high compaction

40. Reinforcement
Helps equalize and prevent cracking or breaking

41. Reinforcement
Clean steel rods or bars called rebar and clean welded wire are used in concrete for reinforcement

42. Estimating Materials
Cubic yards equal length in feet multiplied by width in feet multiplied by thickness in feet divided by 27, which is the number of cubic feet in a cubic yard

43. Estimating Materials
Note: thickness of concrete is usually in inches and will need to be changed to a fraction of a foot

44. Estimating Materials
Examples: 3’ = ¼ foot, 4” = 1/3 foot, 6” = ½ foot

45. Estimating Materials
Example: How many yards of concrete are needed to pour a driveway 100’ long, 8 feet wide, and 3” thick?

46. Estimating Materials
Formula:
Cu. yds. =
100X8X1/4= 200= 7.41

47. Estimating Materials Example:
If concrete is purchased in only whole yards and 10% should be allowed for waste and uneven ground level, how much ready mixed concrete should be ordered?

48. Estimating Materials
7.41 X 10% = To get the right amount, 9 cubic yards must be purchased

49. Treat With Oil
Wood and metal forms should be treated with oil and wet down with water before concrete is poured

50. Treat With Oil
Oil makes the forms easier to remove and water will prevent swelling

51. Bleeding
Water rising to the top surface of concrete poured in tall or deep forms is called bleeding

52. Bleeding
This problem can be corrected or reduced by pouring concrete slower and by using a stiffer or less watery mix