Challenge

Project on Concrete Mix Design for various grades of Concrete

UUnik Kansara18 Jun 2022

AIM: - To calculate Concrete Mix Design proportion of M35 grade concrete with fly ash.

INTRODUCTION: - Concrete Mix Design is a process of determining the proportion of ingredients of concrete with better quality control. Economical concrete is achieved by this method. This method is used to determine mix proportion for concrete grade M30 onwards. For calculation of Concrete Mix Design in India, recommended guideline is IS10262:2009. This guideline explains the procedure for Concrete Mix Proportioning.

PROCEDURE: -

STIPULATION OF MIX PROPORTIONING

a) Grade designation	M35
b) Type of cement	OPC 43 grade conforming to IS 8112
c) Type of mineral admixtures	Fly Ash conforming to IS3812 (Part 1)
d) Maximum nominal size of aggregate	20mm
e) Minimum cement content	320 kg/m³
f) Maximum water-cement ratio	0.45
g) Workability	100 mm (slump)
h) Exposure condition	Severe (for reinforced concrete)
i) Method of concrete placing	Pumping
j) Degree of supervision	Good
k) Type of aggregate	Crushed angular aggregate
l) Maximum cement content	450 kg/m³
m) Chemical admixture type	Superplasticizer

TEST DATA FOR MATERIALS

a) Cement used	OPC 43 grade conforming to IS 8112
b) Specific gravity of cement	3.15
c) Fly ash	Conforming to IS 3812
d) Specific gravity of fly ash	2.2
c) Chemical admixture	Superplasticizer conforming to IS 9103
d) Specific gravity of:
1) Coarse aggregate	2.74
2) Fine aggregate	2.74
e) Water absorption:
1) Coarse aggregate	0.5 percent
2) Fine aggregate	1.0 percent
f) Free (surface) moisture:
1) Coarse aggregate	Nil (absorbed moisture also nil)
2) Fine aggregate	Nil
g) Sieve analysis:	Conforming to table 2 of IS 383
1) Coarse aggregate
2) Fine aggregate	Conforming to grading Zone I of Table 4 of IS 383

Target Mean Strength

To calculate Water- Cement Ratio we have to calculate the Target Mean Strength of concrete after 28 days.

fct = fck +1.65S

S = Standard deviation in N/mm²

For M30 Grade of concrete, S = 5 N/mm²

Therefore, fct = 30 + 1.65(5)

= 38.25 N/mm²

SELECTION OF WATER-CEMENT RATIO

From Table 5 of IS 456, maximum water-cement ratio = 0.45.

Based on experience, adopt water-cement ratio as 0.40.

0.40 < 0.45, hence O.K.

SELECTION OF WATER CONTENT

From Table 5 of IS10262:2009 maximum water content for 20mm aggregate = 186 litres (for 25mm to 50mm slump)

For 100mm slump

Water content = 186 + 186 X (3+3)/100 = 197 litres

As superplasticizers are used the water content can be reduced by 20 percent or above.

Based on trials reduction in water content achieved is 29% with superplasticizers.

Hence, Water content = 197 X 0.71 = 140 litres.

CALCULATION OF CEMENT CONTENT

Water cement ratio = 0.4

Cementitious material (Cement + Fly ash) = 140/0.4 = 350 kg/cum

From Table 5 of IS456:2000 minimum cement content for severe exposure condition = 320 kg/cum

Now to proportion a mix containing fly ash the following steps are suggested:

The percentage of fly ash used needs to be decided based on project requirement and quality of materials.
In some cases, increase in cementitious material can be warranted. Increase in cementitious material content and its percentage may be based on experience and trial (In this example we increase 12% of cementitious material).

Cementitious material content	350 X 1.12 = 392 kg/cum
Water content	140 kg/cum
Water cement ratio	140/392 = 0.357
Fly ash @ 30% total cementitious material content	392 X 30/100 = 117 kg/cum
Cement (OPC 43)	392 – 117 = 275 kg/cum
Saving of cement using fly ash	350 - 275 = 75 kg/cum
Fly ash being utilized	117 kg/cum

PROPORTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE

From table 3 of IS10262:2009, volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate (ZONE I) for water cement ratio of 0.5 = 0.6

In present case, water cement ratio = 0.40

Therefore. volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.10. the proportion of volume of coarse aggregate is increased by 0.02 (at the rate of -/+ 0.01 for every ± 0.05 change in water-cement ratio).

Therefore. corrected proportion of volume of coarse aggregate for the water-cement ratio of 0.40 = 0.62

For pumpable concrete these values are further reduced by 10%

Therefore, Volume of Coarse aggregate = 0.62 X 0.9 = 0.56

Volume of fine aggregates = 1-0.56 = 0.44

MIX CALCULATION

The mix calculation per unit volume of concrete shall be as follows:

a) Volume of concrete	1 cubic metre
b) Volume of cement	==`(Mass of cement)/(Specific gravity of cement) X 1/1000` = `275/3.15 X 1/1000` = 0.087 cubic metre
c) Volume of fly ash	= `117/2.2 X 1/1000` = 0.053 cubic metre
d) Volume of water	= `140/1 X 1/1000` = 0.140 cubic metre
e) Volume of chemical admixture	= `7.6/1.145 X 1/1000` = 0.006 cubic metre
f) Volume of aggregate (coarse aggregate and fine aggregate)	a-(b+c+d+e) = 0.714 cubic metre
g) Mass of coarse aggregate	= 0.714 X 2.74 X 1000 X 0.56 = 1095 kg/cum
h) Mass of fine aggregate	= 0.714 X 2.74 X 1000 X 0.44 = 860 kg/cum

MIX CALCULATIONS FOR TRIAL NO. 1

Cement	275 kg/cum
Fly ash	117 kg/cum
Water	140 kg/cum
Fine aggregate	860 kg/cum
Coarse aggregate	1095 kg/cum
Admixtures	7 kg/cum
Water cement ratio	0.357
Trial mix ratio	1 : 2.19 : 2.79

NOTE - Aggregates should be used in saturated surface dry condition. If otherwise when computing the requirement of mixing water allowance shall be made for the free (surface) moisture contributed by the fine and coarse aggregates. On the other hand, if the aggregates are dry, the amount of mixing water should he increased by an amount equal to the moisture likely to be absorbed by the aggregates. Necessary adjustments are also required to be made in mass of aggregate. The surface water and percent water absorption of aggregate shall be determined according to IS2386 (part 3).

The slump shall he measured and the water content and dosage of admixture shall be adjusted for achieving the required slump based on trial. if required, the mix proportions shall he reworked for the actual water content and checked for durability requirements.
Two more trials having variation of ± 10 percent of water-cement ratio in step 10 shall be carried out and a graph between three water-cement ratios and their corresponding strengths shall he plotted to work out the mix proportions for the given target strength for field trials. However, durability requirement shall he met.

RESULT: - The required concrete mix design proportion is then determined and expressed as the ratio of,

Cement : Fine Aggregate : Coarse Aggregate.

For the given trial, the trial mix ratio is = 1 : 2.19 : 2.79

AIM: - To calculate Concrete Mix Design proportion of M50 grade concrete.

PROCEDURE: -

STIPULATION OF MIX PROPORTIONING

a) Grade designation	M50
b) Type of cement	OPC 53 grade conforming to IS 8112
c) Maximum nominal size of aggregate	20mm
d) Minimum cement content	340 kg/m³
e) Maximum water-cement ratio	0.45
f) Workability	75 mm (slump)
g) Exposure condition	Very Severe (for reinforced concrete)
h) Method of concrete placing	Pumping
j) Degree of supervision	Good
k) Type of aggregate	Crushed angular aggregate
l) Maximum cement content	450 kg/m³
m) Chemical admixture type	Superplasticizer

TEST DATA FOR MATERIALS

a) Cement used	OPC 53 grade conforming to IS 8112
b) Specific gravity of cement	3.15
c) Chemical admixture	Superplasticizer conforming to IS 9103
d) Specific gravity of:
1) Coarse aggregate	2.74
2) Fine aggregate	2.74
e) Water absorption:
1) Coarse aggregate	0.5 percent
2) Fine aggregate	1.0 percent
f) Free (surface) moisture:
1) Coarse aggregate	Nil (absorbed moisture also nil)
2) Fine aggregate	Nil
g) Sieve analysis:
1) Coarse aggregate
2) Fine aggregate	Conforming to grading Zone I of Table 4 of IS 383

Target Mean Strength

To calculate Water- Cement Ratio we have to calculate the Target Mean Strength of concrete after 28 days.

fct = fck +1.65S

S = Standard deviation in N/mm²

For M30 Grade of concrete, S = 5 N/mm²

Therefore, fct = 50 + 1.65(5)

= 58.25 N/mm²

SELECTION OF WATER-CEMENT RATIO

From Table 5 of IS 456, maximum water-cement ratio = 0.45.

Based on experience, adopt water-cement ratio as 0.40.

0.40 < 0.45, hence O.K.

SELECTION OF WATER CONTENT

From Table 5 of IS10262:2009 maximum water content for 20mm aggregate = 186 litres (for 25mm to 50mm slump)

For 75mm slump

Water content = 186 + 186 X (3)/100 = 191 litres

As superplasticizers are used the water content can be reduced by 20 percent or above.

Based on trials reduction in water content achieved is 28% with superplasticizers.

Hence, Water content = 191 X 0.72 = 137 litres.

CALCULATION OF CEMENT CONTENT

Water cement ratio = 0.40

From Table 5 of IS456:2000 minimum cement content for Very Severe exposure condition = 340 kg/cum

Cement content = 137 / 0.40 = 342 kg/cum > 340 kg/cum HENCE O.K.

PROPORTION OF VOLUME OF COARSE AGGREGATE AND FINE AGGREGATE