Concrete Mix Design

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

11. 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

12. Ex 1 New Design

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

15. 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

16. Ex 2 New Design

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

18. Ex 3

19. 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

20. Ex 3 New Design

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

22. Ex 4

23. 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

24. Ex 4 New Design

25. Problem 1

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

27. P1 Pg 125

28. 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

29. P1 New Mix Design

30. Problem 2

31. 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

32. P2

33. 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

34. P2 New Mix Design

35. Problem 3

36. 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

37. P 3

38. 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

39. P 3 new mix design

40. Problem 4

41. 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

42. P 4

43. 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

44. P 4 new mix design

45. Problem 5

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

47. P 5

48. 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

49. P 5 new mix design

50. Problem 6