M20 Grade Concrete Mix Design – IS10262 Latest Edition

M20 Grade Concrete Mix Design – IS10262 Latest Edition

This article covers the mix design of M20 Grade Concrete as per Indian standard codebook – CONCRETE MIX PROPORTIONING – GUIDELINES – IS10262 & IS456.

I. STIPULATIONS FOR PROPORTIONING

This section is about the condition or requirement that is specified or expected from the concrete. Change the values in this section as per your requirements to do the mix design of m20 grade concrete.

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A	Grade Designation	M20
B	Type of Cement	OPC 53
C	Maximum Nominal Size of Aggregate	20mm
D	Minimum Cement Content	300kg	Table 5-IS456
E	Maximum Cement Content	450kg	As per clause 8.2.4.2
F	Maximum W/C ratio	0.55	Table 5-IS456
G	Workability	75mm	For RCC As per code

Table 5 Minimum Cement Content, Maximum water-cement Ratio for Mix design of M20 grade concrete – IS456 codebook

II. TEST DATA FOR MATERIALS

Values in this section should be based on the laboratory tests as per the codebook. Here, standard values of different materials are assumed for the mix design of M20 grade concrete.

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 depends on other factors like mixing method, climate etc. Hence Target strength (F_ck) should be more than 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

Standard deviation (S) value for the M20 grade concrete is given in table 1 of IS10262.

Table 1 Standard Deviation for M20 grade Concrete – IS10262 Codebook

Fck	= fck.+1.65s	“S” from Table1-IS10262
Fck	= 20+(1.65 x 4)	S = 4
Fck	= 26.6 N/mm2

After 28 days of curing, concrete should have more than 26.6 N/mm2 of compressive strength when tested in the Direct Compressive Testing Machine (CTM).

IV. SELECTION OF WATER-CEMENT RATIO

The maximum water-cement ratio for M20 grade concrete can be found from Table 5-IS456 given above.

Maximum W/C ratio	=0.55	Table 5-IS456
Adopted W/C ratio	=0.55

You can reduce the water-cement ratio based on your requirements but remember that the Water-cement ratio directly affects the strength of the concrete.

V. SELECTION OF WATER CONTENT

Maximum water content for differing aggregates to get up to 50mm slump is given in Table 2 of IS10262.

Table 2 Maximum Water Content per cubic meter – IS10262

For aggregate = 20mm, Slump = 50mm

Maximum Water Content

= 186 L

But for our mix design, we need water content for 75mm slump. Clause 4.2 suggests an increase of 3% of water content for every extra 25mm slump from 50mm slump

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

VI. CALCULATION OF CEMENT

The weight of cement can be calculated from the water-cement ratio and the water content.

Adopted Water Cement Ratio	= 0.55
Cement required	= Water Content / W-C Ratio
	= 190/0.55
	= 345.45 kg
Adopted Cement Content	= 345 kg

VII COARSE AND FINE AGGREGATE

Coarse aggregate ratios for different Zones of Fine aggregates are given in Table 3 of IS10262. These are ratios are valid for the 0.5 Water-cement ratio.

Table 3 Volume of coarse aggregate to total aggregate ratio for Mix Design of M20 concrete – IS10262

For aggregate = 20mm, Fine aggregate= Zone II, Water-cement ratio = 0.50

Coarse Aggregate ratio (For W/C =0.5)

=0.62

Table3-IS10262

But for our mix design, we need C.A ratio for 0.55 water-cement ratio. In situations like this subtract 0.01 from the C.A ratio for every 0.05 additional change in water-cement ratio from 0.5. Hence we need to subtract 0.01 from the C.A ratio.

For aggregate = 20mm, Fine aggregate= Zone II, Water-cement ratio = 0.55

Coarse Aggregate ratio (For W/C =0.5)	=0.62	Table3-IS10262
Coarse Aggregate ratio (For W/C =0.55)	=0.61	(0.62-0.01 = 0.61)
Final Fine Aggregate ratio	= 0.39	(1-0.61) = 0.39

VIII MIX CALCULATIONS OF M20 GRADE CONCRETE

This section deals with calculating 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)
		= 345/(3.15*1000)
		= 0.110 cu.m
C	Volume of Water	= Water /(S.G*1000)
		= 190/(1*1000)
		= 0.190 cu.m
D	Total Aggregates requirement	= A – (B+C+D+E)
		= 1 – (0.110+0.190)
		= 0.7 cu.m
E	Coarse Aggregate (C.A)	= F * C.A ratio * S.G * 1000
		= 0.7*0.61*2.74 *1000
		= 1170 kg
F	Fine Aggregate (F.A)	= F * F.A ratio * S.G * 1000
		= 0.7*0.39*2.74 *1000
		= 748 kg

Cement Fine and Coarse Aggregate needed for M20 grade concrete

S.No.	MATERIALS	QUANTITY
1	Cement	345 kg
2	Fine Aggregate	750 kg
3	Coarse Aggregate (20mm)	1170 kg
4	WATER	190 L

To find the design mix ratio, divide the calculated value of all materials by the weight of cement. Therefore Mix Design Ratio of M20 Grade concrete by weight is Cement: F.A: C.A: Water = 1 : 2.17 : 3.4 : 0.55

Note: This is a Design mix ratio by weight which is different from the Nominal volumetric mix ratio. Read this post to understand the difference between Nominal Mix and Design Mix.

Workability Requirements for Different Concrete as per IS456 Codebook

Er.SP.ASWINPALANIAPPAN., M.E.,(Strut/.,)

Structural Engineer

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