Project on Concrete Mix Design for various grades of Concrete

AIM:

To calculate the concrete mix design for M35 grade concrete with fly ash and M50 grade without fly ash.

Introduction to Concrete Mix Design:

Concrete mix design is the process of finding the right proportions of cement, sand, and aggregates for concrete to achieve target strength in structures. So, concrete mix design can be stated as Concrete Mix = Cement:Sand:Aggregates. The concrete mix design involves various steps, calculations, and laboratory testing to find the right mix proportions. This process is usually adopted for structures which require higher grades of concrete such as M25 and above and large construction projects where quantity of concrete consumption is huge. The benefits of concrete mix design is that it provides the right proportions of materials, thus making the concrete construction economical in achieving required strength of structural members. As, the quantity of concrete required for large constructions is huge, the economy in quantity of materials such as cement makes the project construction economical.

Procedure:

The procedure for concrete mix design for M35 grade concrete with fly ash as additive content and M50 without fly ash as additive content is as follows

Now let's first find out concrete mix design for M35 grade concrete with fly ash.

1) M35 grade concrete - By name itself one would understand the compressive strength of the concrete that attained by 28 days is 35 N/mm^2.

I. 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.

A	Grade Designation	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

II. 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	Confirming to IS8112
B	Specific Gravity of Cement	3.15	Test – IS: 2720
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		Test – IS 2386
	Coarse aggregate	0.5 %
	Fine aggregate	1 %
H	Sieve Analysis		Test – IS 2386
	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	“S” from Table 1-IS10262
Fck	= 35+1.65×5
Fck	= 43.25 N/mm2

IV. 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

V. SELECTION OF WATER CONTENT

Maximum Water Content

=186 L

Table 2-IS10262

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

VI. CALCULATION OF CEMENT AND FLY ASH CONTENT

Adopted Water Cement Ratio	=0.45
Total Cementitious (Cement +Fly ash) requirement	= Water Content / WaterCement 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	Table 3-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	Fly ash	118 kg
3	Fine Aggregate	720 kg
4	Coarse Aggregate (20mm)	1226 kg
5	WATER	160 L
6	PCE based Superplasticizer	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: Fly ash: F.A: C.A: Water = 1:0.4:2.6:4.46:0.58

2) M50 grade concrete - By name itself one would understand the compressive strength of the concrete that attained by 28 days is 50 N/mm^2.

I. STIPULATIONS FOR PROPORTIONING OF M50 GRADE CONCRETE

Detailed calculation for M50 Grade mix

The different design stipulations required for the desired mix are shown in the table below:

Stipulations for proportioning
Type of Concrete	RCC
Grade Designation	M50
Shape of Particle	Angular
Slump	50 mm
Water- Cement Ratio	0.45
Exposure Condition	Severe
Concrete Placement	Pump
Degree of Supervision	Good

The different experiemental data required for the desiered mix are shown in the table below:

Sieve analysis
Fine Aggregate	Zone 1
Coarse Aggregate	20 mm

Chemical Admixture
Volume (By mass of cement)	2%
Water Content Reduction	Zero

Test data for materials
Standard Deviation	5 MPa
Specific Gravity of Fine Aggregate	2.74
Specific Gravity of Coarse Aggregate	2.74
Specific Gravity of Cement	3.15
Specific Gravity of Admixture	1.145
Water absorption of Fine Aggregate	1.0 %
Water absorption of Coarse Aggregate	0.5%
Free Surface Moisture of Fine Aggregate	Zero
Free Surface Moisture of Coarse Aggregate	Zero

Step by step detailed procedure for concrete mix design of M50 grade as per IS – 10262:2009 and IS- 456:2000

Step 1: Calculate the target mean compressive strength at 28 days

target mean compressive strength	characteristic strength + 1.65 X Standard Deviation
target mean compressive strength	50 + 1.65 X 5 = 58.25 N/mm2

Where sufficient test results for a particular grade of concrete are not available, the value of standard deviation could be taken from Table 1 of IS-10262.

Step 2: Selection of maximum water/cement ratio

The maximum water-cement ratio should be selected as per Table 5 of IS – 456: 2000.

Maximum water-cement ratio	0.45
​ Adopted water-cement ratio	0.45

Step 3: Estimation of entrapped air

For the maximum size of aggregate used the air content is estimated.

tep 4: Selection of water content and fine to total aggregate ratio

The selection of water content is based on Table 2 of IS:10262:2009.

Maximum water content for 20 mm aggregate and a slump value of 25 to 50 mm = 186.00 l.

Estimated water content

186 litres

Step 5: Calculation of Cement content

The cement content per unit volume of concrete is computed sing Table 5 of IS:456:2000: