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# Concrete Mix Design

Concrete Mix Design. ACI Variation. 5% Variation for Adjusting Mixes. Pg 116. Determine what is to be added or reduced If it is sand, stone, or cement compute it’s absolute volume by dividing it’s weight by the product of it’s specific gravity and 62.4

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## Concrete Mix Design

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1. Concrete Mix Design ACI Variation

2. 5% Variation for Adjusting Mixes Pg 116 • Determine what is to be added or reduced • If it is sand, stone, or cement compute it’s absolute volume by dividing it’s weight by the product of it’s specific gravity and 62.4 • If it is water then compute it’s absolute volume by dividing gallons by 7.5

3. 5% Variation Pg 116 • An equal volume of another component must be added or subtracted to account for the changed weight of the initial component. • Multiply the absolute volume of the component to be added or subtracted by it’s specific gravity and 62.4 (7.5 for water in gallons).

4. 5% Variation • Compute the new design quantities by adding to and subtracting from the original design quantities. • The following criteria are recommended for adjusting mix designs.

5. 5% Variation Pg 115 • A workable slump cannot be obtained with design water less than the maximum allowable water by specifications. • Add water as necessary up to the maximum allowed and subtract an equal volume of fine aggregate.

6. 5% Variation • A workable slump cannot be obtained using the maximum allowable water. • Reduce the surface area of aggregates by reducing the quantity of fine aggregate by 5% of it’s weight and replace it with an equal volume of coarse aggregate.

7. 5% Variation • A mix is to harsh ( to much coarse aggregate). • Add fine aggregate in the amount of 5% of it’s weight and reduce the coarse aggregate by an equal volume.

8. Examples

9. Example 1 Pg 117 • Mix gives a 2 ½ in slump. Increase the water by 1.5 gal/cu yd and adjust the mix appropriately. • One Cubic Yd Class B Non vib • Cement 545 Lbs

10. Ex 1 Solution • Increase the water by 1.5 gals. Must reduce the sand by an equal volume. • Abs vol of water = 1.5/7.5 = .20 cu ft • Wt of sand removed=.20 x 2.67 x 62.4 =33Lbs • 35.1 gals + 1.5 gals = 36.6 gals • 1307 Lbs sand – 33 Lbs = 1274 Lbs

11. Ex 1 New Design

12. Example 2 Pg 118 • Mix design with the max allowable water does not give the desirable slump. • One Cubic Yard Class A-vib

13. Ex 2 Solution • To increase slump, decrease surface area by reducing FA 5% and replacing with an equal amount of CA • 5% x 1154 Lbs of sand = 58 Lbs • 58 / (2.63 x 62.4) = .35 cu ft • Stone = .35 x 2.81 x 62.4 = 61 Lbs • 1154 Lbs sand – 58 = 1096 Lbs Sand • 1872 Lbs stone + 61 = 1933 Lbs Stone

14. Ex 2 New Design

15. Example 3 • Adjust the cement content to a Class AA with 715 Lbs of cement • One Cubic Yd Class A vib

16. Ex 3

17. Ex 3 Solution • Difference in Cem = 715 -564 = 151 Lbs • 151 / (3.15 x 62.4) = .77 cu ft • Sand = .77 x 2.66 x 62.4 = 128 Lbs • Sand = 1257 – 128 = 1129 Lbs

18. Ex 3 New Design

19. Example 4 Pg 120 • Harsh Mix. Adjust by the 5% ACI variation method. • One Cubic Yard Class AA vib

20. Ex 4

21. Ex 4 Solution • Add sand and reduce stone by equal volume • 5% x 890 Lbs sand = 45 Lbs • Sand added=45/(2.61 x 62.4) = .28 cu ft • Stone removed = .28 cf x 2.79 x 62.4 = 49 Lbs • 890 Lbs sand + 45 Lbs = 935 Lbs sand • 1996 Lbs stone – 49 Lbs = 1947 Lbs stone

22. Ex 4 New Design

23. Problem 1

24. P 1 • Mix did not give desired slump. Increase water to the maximum and adjust mix accordingly. • One Cubic Yard Class A vib

25. P1 Pg 125

26. P1 Solution • Increase water, Decrease Sand • Table 1000-1 = .532 x 564 = 300 /8.33 = 36.0 gal max water • 36.0 -34.0 = 2.0 gals increase • 2.0 / 7.5 = .27 cu ft • Sand removed = .27 x 2.73 x 62.4 = 46 Lbs • Sand = 1276 – 46 = 1230 Lbs

27. P1 New Mix Design

28. Problem 2

29. P 2 • The mix does not give the desired slump using the maximum water permitted. Adjust the mix using the 5% variation method. • One Cubic Yard Class A Vib AE

30. P2

31. P2 Solution • Decrease sand to reduce surface area, Increase stone • Sand removed = 1210 x .05 = 61 Lbs • 1210 – 61 = 1149 Lbs Sand • 61 / (2.63 x 62.4) = .37 cu ft • Stone added = .37 x 2.97 x 62.4 = 69 Lbs • Stone = 1916 + 69 + 1985 Lbs

32. P2 New Mix Design

33. Problem 3

34. P 3 • Change the Class B mix so that it contains 7 sacks per yard of cement. Adjust other components as necessary. • One Cubic Yard Class B non vib

35. P 3

36. P3 Solution • The Cement will increase, and the Sand will decrease. • Cement = 94 x 7 = 658 Lbs • 658 – 545 = 113 Lbs increase in cement • 113/(3.15 x 62.4) = .57 cu ft • Sand deducted = .57 x 2.63 x 62.4 = 94 Lbs • Sand = 1329 – 94 = 1235 Lbs

37. P 3 new mix design

38. Problem 4

39. P 4 • Change the Class A mix to a AA mix with 7.6 sacks of cement per yard. Adjust the other components as necessary. • One Cubic Yard Class A Vib

40. P 4

41. P 4 Solution • Cement amount increases, Sand amount decreases. • 7.6 x 94 = 714 Lbs of Cement • 714 – 564 = 150 Lb increase in cement • 150 / (3.15 x 62.4) = .76 • Decrease in Sand = .76 x 2.63 x 62.4 = 125 Lbs • Sand = 1105 – 125 = 980 Lbs

42. P 4 new mix design

43. Problem 5

44. P 5 • The mix is to harsh. Adjust by using the 5% ACI variation method. • One Cubic Yard Class AA vib

45. P 5

46. P 5 Solution • Sand will increase and Stone will decrease. • Sand increase = 975 x .05 = 49 Lbs • Sand = 975 + 49 = 1024 Lbs • 49 / (2.63 x 62.4) = 0.30 cu ft • Stone decrease = .30 x 2.93 x 62.4 = 55 Lbs • Stone = 2037 -55 = 1982 Lbs

47. P 5 new mix design

48. Problem 6

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