M40 Grade Concrete Mix Design as per ACI Method

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 + (1.65×5.6) = 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

8. Final M40 Grade Concrete Mix Proportion

Water – Cement ratio = 0.38

Water content = 180kg

Cement weight = 473kg

Sand weight (fine aggregate) = 645kg

Coarse aggregate weight = 1039kg

Final mix proportion = cement : sand : C.A = 474 : 646 : 1040 = 1 : 1.3 : 2.1