Mix Design Basics CIVL

Transcription

1 Mix Design Basics CIVL

2 Mix Design Goals adequate workability adequate strength adequate durability minimum cost CIVL

3 Cost of Materials CIVL Source: November 7, 2011 enr.com

4 Mix Design Goals adequate workability adequate strength adequate durability minimum cost CIVL

5 Minimizing Cost Cement minimize the void space between the aggregate particles minimize the surface area of the aggregate particles CIVL

6 Minimizing Void Space Void content = 48% Void content = 41% CIVL

7 Minimizing Surface Area 10" surface area = 11 ft 2 surface area = 22 ft 2 CIVL

8 Minimizing Surface Area surface area = 6.0 ft 2 /ft 3 surface area = 4.8 ft 2 /ft 3 CIVL

9 Obtaining Adequate Workability gravel Need enough mortar to keep all the gravel particles apart. mortar CIVL

10 Inside Concrete gravel sand mortar cement paste CIVL

11 Obtaining Adequate Workability sand Need enough cement paste to keep all the sand grains apart cement paste CIVL

12 Inside Concrete sand cement cement paste water CIVL

13 Obtaining Adequate Workability cement Need enough mixing water to lubricate all the cement grains water CIVL

14 Obtaining Adequate Workability cement Air entrainment adds lubrication without adding additional water air bubble water CIVL

15 Figure 7 14 CIVL

16 CIVL 3137 f c 4500 psi 20

17 CIVL 3137 f c 4500 psi 21

18 4500 psi 5700 psi CIVL 3137 f 22 c f cr

19 Overdesign Factors Table 7-12 Overdesign Necessary to Meet Strength Requirements A CIVL

20 Overdesign Factors Required Average Compressive Strength When Data Are Not Available to Establish a Standard Deviation Adapted from ASTM C94 CIVL

21 CIVL

22 Trial Mix Design CIVL

23 Mix Design Example CIVL

24 Step 1: Select the slump Equivalent to Table 7 13 CIVL 3137 Source: Design and Control of Concrete Mixtures (PCA, 2003) 29

25 Step 2: Select the NMAS NMAS narrowest dimension 5 NMAS depth of slab 3 NMAS 0.75 clear space CIVL

26 Step 3: Estimate the water and air Equivalent to Table 7 14 CIVL 3137 Source: Design and Control of Concrete Mixtures (PCA, 2003) 31

27 Air Content 40% Cement Paste Paste Air Content Assume 7% 60% Aggregate Smaller NMAS Concrete Air Content 0.4 7% = 2.8% CIVL

28 Air Content 30% Cement Paste Paste Air Content Assume 7% 70% Aggregate Larger NMAS Concrete Air Content 0.3 7% = 2.1% CIVL

29 Adjust for Aggregate Shape CIVL 3137 Source: Design and Control of Concrete Mixtures (PCA, 2003) 35

30 Step 4: Select the w/c ratio Equivalent to Table 7 15 f cr CIVL 3137 Source: Design and Control of Concrete Mixtures (PCA, 2003) 37

31 Overdesign Factors Required Average Compressive Strength When Data Are Not Available to Establish a Standard Deviation Adapted from ASTM C94 CIVL

32 Step 4: Select the w/c ratio Equivalent to Table 7 15 f cr CIVL 3137 Source: Design and Control of Concrete Mixtures (PCA, 2003) 39

33 Figure 7 14 CIVL

34 CIVL

35 Step 5: Calculate the cement weight W W = water cement w/c ratio CIVL

36 Step 6: Estimate coarse aggregate Equivalent to Table 7 17 b bo CIVL 3137 Source: Design and Control of Concrete Mixtures (PCA, 2003) 43

37 b/b o b o b CIVL

38 Step 6: Estimate coarse aggregate bulk bulk gravel o concrete V b b V bulk bulk gravel gravel gravel W V γ dry-rodded unit weight bulk bulk gravel o concrete gravel W b b V γ CIVL

39 Step 7: Estimate fine aggregate Estimated Weight Method (Section 7 8.1) NMAS First Estimate of Concrete Unit Mass (lb/ft 3 ) (in) Non Air Entrained Concrete Air Entrained Concrete ⅜ ½ ¾ ½ Equivalent to Table 7 18 CIVL

40 CIVL

41 CIVL

42 Step 7: Estimate fine aggregate Estimated Weight Method (Section 7 8.1) W W W W W total cement gravel sand water W W W W W sand total cement gravel water CIVL

43 Step 7: Estimate fine aggregate Absolute Volume Method (Section 7 8.2) V V V V V V total cement gravel sand water air V V V V V V sand total cement gravel water air CIVL

44 Step 7: Estimate fine aggregate Absolute Volume Method (Section 7 8.2) V V V V V V sand total cement gravel water air V V 1 W W W V cement gravel water sand total bulk air γw 3.15 Ggravel 1.00 sand sand G bulk sand W V γ w CIVL

45 Step 8: Adjust for Aggregate Moisture 1. Increase W water by an amount equal to the weight of water needed to saturate the fine and coarse aggregate. 2. Increase W sand and W gravel by an amount equal to the moisture contents of the aggregate stockpiles. 3. Decrease W water by the same amount you increased W sand and W gravel. CIVL