Project on Concrete Mix Design for various grades of Concrete

The calculation of Concrete Mix Design for M35 grade concrete with fly ash

1. STIPULATIONS FOR PROPORTIONING OF M35 GRADE CONCRETE

This section contains specifications for the materials and requirements for the concrete to be manufactured. The specific gravity of Fly ash is 2.1 to 3, while the specific gravity of GGBS is 2.85. Use the appropriate specific gravity value based on the type of admixture used.

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A	Grade Concrete	M35
B	Type of Cement	OPC 53
C	Type of Admixture	Fly ash
D	Maximum Nominal Size of Aggregate	20mm
E	Minimum Cement Content	340kg	Table 5-IS456
F	Maximum Cement Content	450kg	As per code
G	Partial replacement of cement by Fly ash	30%	as per requirement
H	Maximum W/C ratio	0.45	Table 5-IS456
I	Workability	100mm
J	Chemical Admixture	PCS Type

1. TEST DATA FOR MATERIALS

Materials must be tested to find its below physicals and chemical properties. Standard values are considered below.

A	Cement Used	OPC 53
B	Specific Gravity of Cement	3.15
C	Mineral Admixture	Fly ash	Confirming to IS12089
D	Specific Gravity of Fly ash	2.90
E	Chemical Admixture	@0.6%	IS9103
F	Specific Gravity of		Test – IS 2386
	Coarse Aggregate	2.74
	Fine Aggregate	2.74
	Admixture PCE based	1.12
G	Water Absorption
	Coarse aggregate	0.5 %
	Fine aggregate	1 %
H	Sieve Analysis
	Coarse aggregate		Confirming to Table 2-IS383
	Fine aggregate	Zone II	Confirming to Table 4-IS383

III. TARGET STRENGTH FOR MIX PROPORTIONS OF M35 GRADE CONCRETE

The strength of concrete may vary depending on the quality of the material, the mixing method and the construction procedures. Therefore the target strength (Fck) must be greater than the required strength of the concrete (fck).

Table 1 of IS456 gives the standard deviation value (s) for different grade concretes.

Fck	= fck+1.65s
Fck	= 35+1.65×5
Fck	= 43.25 N/mm2

1. SELECTION OF WATER-CEMENT RATIO

The maximum water-cement ratios for different grades of concrete are given in Table 5-IS456. You can reduce the water-cement ratio based on your needs.

The water-cement ratio directly affects the strength of the concrete.

Maximum W/C ratio	=0.45	Table 5-IS456
Adopted W/C ratio	=0.45

1. SELECTION OF WATER CONTENT

Maximum Water Content

=186 L

Table 2-IS1026

The water content above is for a slump of 25 to 50 mm, but according to the specification our concrete requires a slump of 100 mm. Therefore, to get the desired slump, the water content must be increased. Clause 4.2 of IS1026 recommends increasing the water content by 3% to obtain an additional 25 mm slump. Therefore, to obtain a slump of 50 mm in addition to our concrete, the water content must be increased by 6%.

Water-content for 100mm Slump	=186+(0.06*186)
	=197.16 L

As we use super plasticizers we can reduce the water content to gain strength in the concrete. The amount of water-content to be reduced depends on the type of super plasticizer.

Percentage of Reduction in water content	=20%
Water content requirement after SP	=198 – (0.20*198)
	=157.73
Adopted Water Content	=160 L

1. CALCULATION OF CEMENT AND FLY ASH CONTENT

Adopted Water Cement Ratio	=0.45
Total Cementitious (Cement +Fly ash) requirement	= Water Content / Water/Cement ratio
	=160/0.45
	=355.55 kg

Since flying ash is used, the amount of cementitious content (cement + fly ash) should be increased to get good performance and strength. The percentage of increasing cementitious content depends on experience and research. Here we have increased the cementitious content by 10%.

Final Cementitious Content (Cement+Fly ash)	= 356*1.10
	=391.6 kg
Minimum Cement Content required for ‘severe’ exposure	=340kg	Table 5-IS456
Adopted Cementious content	=391.6 kg	> 340kg

Fly ash content requirement	= 391.6 * 0.30	30% replacement
	= 117.48 ~ 118 kg
Cement Content requirement	=Cementious content – Fly ash
	=391.6-117.48
	= 274.12

Calculation of Super Plasticiers @ 0.6 percent to the mass of cementitious content = = 391.6*(0.6/100) = 2.35 kg

VII COARSE AND FINE AGGREGATE

Coarse Aggregate ratio	= 0.62	Table3-IS10262 (For W/C =0.5)
Coarse Aggregate ratio for 0.45 w/c ratio	= 0.63	(adding 0.01 for every decrease .05 and vice versa)
Final Fine Aggregate ratio	= 0.37	(1-0.63) = 0.37

VIII MIX CALCULATIONS OF M35 GRADE CONCRETE

A	Volume of Concrete	= 1 cu.m
B	Total Volume of Cement	= Cement/(S.G*1000)
		= 275/(3.15*1000)
		= 0.087 cu.m
C	Total Volume of Fly ash	= Flyash/(S.G*1000)
		= 118/(2.5*1000)
		= 0.041 cu.m
D	Volume of Water	=Water /(S.G*1000)
		= 160/(1*1000)
		= 0.160 cu.m
E	Volume of Superplasticizers	= Superplasticizers /(S.G*1000)
		= 2.35/(1.12*1000)
		= 0.002 cu.m
F	Total Aggregates requirement	= A – (B+C+D+E)
		=1 -(0.087 +0.041+0.160+0.002)
		=0.71 cu.m
G	Coarse Aggregate (C.A)	= F * C.A ratio * S.G * 1000
		= 0.71*0.63 *2.74 *1000
		= 1225.6 kg
I	Fine Aggregate (F.A)	= F * F.A ratio * S.G * 1000
		= 0.71*0.37*2.74 *1000
		=719.8 kg

Cement Flyash Sand Aggregate Water and Superplasticizer needed for M35 grade concrete

S.No.	MATERIALS	QUANTITY
1	Cement	275 kg
2	Flyash	118 kg
3	Fine Aggregate	720 kg
4	Coarse Aggregate (20mm)	1226 kg
5	WATER	160 L
6	PCE based Super Plasticizer	2 L

To find the design mix ratio, divide the calculated value of all materials by the weight of cement. Therefore Mix Ratio of M35 Grade concrete by weight is

Cement : Flyash: F.A : C.A : Water = 1:0.4:2.6:4.46:0.58

Mix design for M50 grade of concrete

1. STIPULATIONS FOR PROPORTIONING

This section deals with different specifications and conditions that are expected to be fulfilled by the concrete. You can change the values in this section to meet different requirements for Mix Design of M50 grade concrete.

A	Grade Designation	M50
B	Type of Cement	OPC 53	As per requirement
C	Maximum Nominal Size of Aggregate	20mm
D	Maximum W/C ratio	0.35	Table 5-IS456
E	Workability	75mm	For RCC As per code

1. TEST DATA FOR MATERIALS

Cement, sand and aggregate must be tested in a laboratory to determine their various physical properties. The standard values given here are the different physical properties of the building materials commonly used in India.

A	Cement Used	OPC 53	Confirming to IS8112
B	Specific Gravity of Cement	3.15	Test – IS: 2720
C	Specific Gravity of		Test – IS 2386
	Coarse Aggregate	2.74
	Fine Aggregate	2.74
D	Water Absorption		Test – IS 2386
	Coarse aggregate	0.5 %
	Fine aggregate	1 %
E	Sieve Analysis		Test – IS 2386
	Coarse aggregate		Confirming to Table 2-IS383
	Fine aggregate	Zone II	Confirming to Table 4-IS383

III. TARGET STRENGTH

Apart from mix design, the strength of the concrete is influenced by other factors like mixing method, climate, curing etc. Therefore the Target strength (F_ck) of the concrete should be greater than the designed characteristic strength (f_ck).

Target strength for m20 grade concrete can be found from the formula given in the codebook.

F_ck = = f_ck.+1.65s

The Standard deviation (S) value for M50 grade concrete is given in table 8 of IS456.

After curing in water for 28 days, the concrete should have compressive strength greater than 58.25 N/mm² when tested in a Direct Compressive Testing Machine.

1. SELECTION OF WATER-CEMENT RATIO

The maximum water-cement ratio required for M50 grade concrete can be found in Table 5-IS456 given above.

Maximum W/C ratio	=0.35	Table 5-IS456
Adopted W/C ratio	=0.35

1. SELECTION OF WATER CONTENT

Maximum water content for 20mm aggregate to get 50mm slump is given in Table 2 of IS10262.

For aggregate = 20mm and Slump = 50mm.

Maximum water content (50mm slump) = 186L

186 L of water is required to get a slump of 50mm but we need slump of 75mm as per our specifications. Clause 4.2 recommends increasing the water content by 3% to obtain an additional slope of 25 mm from the 50 mm slope

Therefore as per clause 4.2 For aggregate = 20mm, Slump = 75mm

Water-content for 75mm Slump	= 186+(0.03*186)	As per Clause 4.2
	= 191.58 L
Adopted Water Content	= 190 L

1. CALCULATION OF CEMENT

The weight of cement for the mix design of M50 grade concrete can be calculated from the water-cement ratio and the water content.

Adopted Water Cement Ratio	= 0.35
Cement required	= Water Content / W-C Ratio
	= 190/0.35
	= 542.85 kg
Adopted Cement Content	= 543 kg

VII COARSE AND FINE AGGREGATE

Coarse aggregate ratios for different Zones of Fine aggregates are given in Table 3 of IS10262.

From the table 3, For aggregate = 20mm, Fine aggregate= Zone II and Water-cement ratio = 0.50

Coarse Aggregate ratio (For W/C =0.5)

=0.62

Table3-IS10262

But we need C.A ratio for 0.35 water-cement ratio. In such cases, a value of 0.01 should be added to the C.A ratio for every 0.05 point decrease in the water-cement ratio from 0.50. So since our water cement ratio is 0.35 we need to add the value 0.01 to our C.A ratio

Therefore For aggregate = 20mm, Fine aggregate= Zone II and Water-cement ratio = 0.45

Coarse Aggregate ratio (For W/C =0.5)	=0.62	Table3-IS10262
Coarse Aggregate ratio (For W/C =0.35)	=0.65	(0.62+0.03 = 0.65)
Final Fine Aggregate ratio	= 0.35	(1-0.65) = 0.35

VIII MIX CALCULATIONS OF M30 GRADE CONCRETE

This section deals with the calculation of the weight of fine aggregate and coarse aggregate from the aggregate ratio, cement and water.

A	Volume of Concrete	= 1 cu.m
B	Total Volume of Cement	= Cement/(S.G*1000)
		= 543/(3.15*1000)
		= 0.172 cu.m
C	Volume of Water	= Water /(S.G*1000)
		= 190/(1*1000)
		= 0.190 cu.m
D	Total Aggregates requirement	= A – (B+C)
		= 1 -(0.172+0.190)
		= 0.638 cu.m
E	Coarse Aggregate (C.A)	= D * C.A ratio * S.G * 1000
		= 0.638*0.63*2.74 *1000
		= 1101.32 kg
F	Fine Aggregate (F.A)	= D * F.A ratio * S.G * 1000
		= 0.638*0.37*2.74 *1000
		= 646.8 kg

Cement Fine and Coarse Aggregate needed for M50 grade concrete

S.No.	MATERIALS	QUANTITY
1	Cement	543 kg
2	Fine Aggregate	647 kg
3	Coarse Aggregate (20mm)	1101 kg
4	WATER	190 L

To find the design mix ratio, divide the calculated value of all materials by the weight of the cement. Therefore Mix Ratio of M50 Grade concrete by weight is Cement : F.A : C.A : Water = 1 :1.19 : 2.03 : 0.35