M40 grade stands for it’s a mix of concrete with a characteristic compressive strength of 40 N/mm2. The mix design procedure for M40 grade concrete as per ACI Method is discussed.
M40 Grade Concrete Mix Design Procedure
1. Required Data
Grade of concrete = M40
Specific gravity of cement = 3.15
Specific gravity of Fine aggregate = 2.65
Specific gravity of coarse aggregate = 2.7
Bulk density of coarse aggregate = 1600kg/m3
Fineness modulus of fine aggregate = 3.0
Maximum size of aggregate = 25mm
Degree of super vision = Very good
Non-Air entrained concrete type
2. Mean Design Strength
For very good degree of super vision standard deviation value for required grade of concrete is as follows.
Grade of concrete
Standard deviation for different degree of supervisions (N/mm2)
Very Good
Good
Fair
M10
2.0
2.3
3.3
M15
2.5
3.5
4.5
M20
3.6
4.6
5.6
M25
4.3
5.3
6.3
M30
5.0
6.0
7.0
M35
5.3
6.3
7.3
M40
5.6
6.6
7.6
M45
6.0
7.0
8.0
M50
6.4
7.4
8.4
M55
6.7
7.7
8.7
M60
6.8
7.8
8.8
Therefore, from the above table, s =5.6
Mean design strength fm = fmin + K.S
= 40 + (1.65x5.6) = 49.24N/mm2.
3. Water-Cement Ratio
Effective water cement ration for the design strength of 49.24mpa is not in the below table. So, consider minimum water cement ratio and that is 0.38.
Mean design strength after 28 days (MPa)
Effective water cement ratio
Air entrained concrete
Non-air entrained concrete
15
0.71
0.8
20
0.61
0.7
25
0.53
0.62
30
0.46
0.55
35
0.40
0.48
40
-
0.43
45
-
0.38
4. Water Content and Air Content
For the slump of 35mm and 25mm maximum size of aggregate, water and air contents are selected from the following table and they are
Water content = 180 kg/m3
Air content = 1.5%
Slump/air content
Water content, kg/m3 of concrete for max size of aggregate
10mm
12.5mm
20mm
25mm
40mm
50mm
70mm
150mm
30-50mm
205
200
185
180
160
155
145
125
80-100mm
225
215
200
195
175
170
160
140
150-180mm
240
230
210
205
185
180
170
-
Air content %
3
2.5
2
1.5
1
1
0.3
0.2
5. Cement Content
Cement content is calculated from the water cement ratio.
W/C = 0.38
180/C =0.38
Cement content C = 180/0.38 = 473kg per cu.m of concrete.
6. Coarse Aggregate Content
Fineness modulus of fine aggregate = 3.0
Bulk density of coarse aggregate =1600kg/m3
Maximum size of aggregate = 25mm
Therefore bulk volume of dry rodded coarse aggregate from below table = 0.65
Maximum size of aggregate (mm)
Bulk volume of dry rodded coarse aggregate w.r.to fineness modulus
2.4
2.6
2.8
3.0
10
0.5
0.48
0.46
0.44
12.5
0.59
0.57
0.55
0.53
20
0.66
0.64
0.62
0.6
25
0.71
0.69
0.67
0.65
40
0.75
0.73
0.71
0.69
50
0.78
0.76
0.74
0.72
70
0.82
0.80
0.78
0.76
150
0.87
0.85
0.83
0.81
Then, coarse aggregate weight = 0.65 x 1600 = 1039kg per cu.m of concrete.
7. Fine Aggregate
Fine aggregate quantity is decided by knowing the unit weight of fresh concrete from below table.
Fresh concrete density for 25mm size aggregate = 2375kg/m3
Maximum size of aggregate (mm)
Density of fresh concrete (kg/m3)
Air entrained
Non air-entrained
10
2190
2285
12.5
2235
2315
20
2280
2355
25
2315
2375
40
2355
2420
50
2375
2445
70
2400
2465
150
2435
2505
Approx. Air content =1.5%
Therefore, fine aggregate weight= 0.985(2375) – (180+473+1039) = 646kg per cu.m of concrete
