Challenge

Project on Concrete Mix Design for various grades of Concrete

PPallavi Harish27 Aug 2022

Explain in detail the concrete mix design for M35 grade concrete with fly ash.

Concrete Mix Proportioning:

Aim: Mix design for M 35 grade concrete with fly ash

Procedure:

Stipulations for proportioning:

Grade of Concrete = M35
Type of cement = OPC 43 grade confirming to IS 8112
Type of mineral admixture: Fly ash confirming to IS 3812 (Part 1)
Maximum nominal size of aggregate = 20mm
Minimum cement content = 320 kg/m³ (from table 5 of IS 456:2000, based on the exposure condition)
Maximum water-cement ratio = 0.45 (from table 5 of IS 456:2000, based on the exposure condition)
Workability = 100mm (slump value for pumpable concrete)
Exposure condition = severe (for reinforced concrete)
Method of concrete placing = Pumping
Degree of supervision = Good
Type of aggregate = Crushed angular aggregate
Maximum cement content = 450 kg/m³
Chemical plasticizer = superplasticizer

Test data for materials

Cement used = OPC 43 grade confirming to IS 8112
Specific gravity of cement = 3.15
Fly ash: Conforming to IS 3812 part 1
Specific gravity of fly ash: 2.2
Chemical plasticizer = superplasticizer confirming to IS 9103
Specific gravity of:
Coarse aggregate = 2.74
Fine aggregate = 2.74
Water absorption:
Coarse aggregate = 0.5%
Fine aggregate = 1.0%
Free surface moisture:
Coarse aggregate = Nil
Fine aggregate = Nil
Sieve analysis
Coarse aggregate = Confirming to table 2 of IS 383

IS sieve size (mm)	Analysis of coarse aggregate fraction		% of different fraction			Remarks
	I	II	I	II	Combined	Confirming to Table 2 of IS 383
20	100	100	60	40	100
10	0	71.2	0	28.5	28.5
4.75		9.4		3.7	3.7
2.36		0

Fine aggregate = Confirming to grading zone I of table 4 of IS 383

Target mean strength of concrete, ft = fck + 1.65 S

Where, fck = compressive strength of concrete = 35 N/mm²

S = standard deviation obtained from table 1 of

IS 10262:2009 = 5 N/mm²

Target mean strength of concrete, ft = fck + 1.65 S

= 35 + (1.65 X 5)

Target mean strength of concrete, ft = 43.25 N/mm²

Selection of water-cement ratio

The w/c ratio from the maximum free w/c ratio for severe exposure condition as per Table-5 of IS 456:2000

For severe weather condition, for Reinforced concrete,

Maximum water-cement ratio = 0.45

Based on experience, adopted w/c ratio = 0.40

0.40 < 0.45, hence ok.

Selection of water-content:

From Table 2 of IS 10262:2009, maximum water-content for 20mm aggregate = 186 litre (for 25mm to 50mm slump range)

Estimated water content for 100mm slump = 186 +

= 197 Litre.

As superplasticizer is used, the water content can be reduced up 20% and above.

Based on trials with superplasticizer water content reduction of 29% has been achieved.

Hence the arrived water content = 197 x (1- 0.29) = 197 x 0.71 = 140 litre.

Calculation of cement content

Water/cement ratio = 0.40

Cement content = = 350 kg/m³

From table 5 of IS 456:2000, minimum cement content for ‘severe’ exposure condition = 320 kg/m³

350 kg/m³ > 320 kg/m³, hence, Ok.

To proportion the mix containing fly ash, following steps are suggested:

The percentage of fly ash need to be decided based on project requirement and quality of materials.
In some cases, increase in cementitious materials can be warned. Increase in cementitious material content and its percentage may be based on experience and trial.

In this increase of 10% cementitious material content is considered.

Cementitious material content = 350 x 1.1 =385 kg/m³

Water content = 140 kg/m³

So, water- cement ratio = 140/385 =0.364

Fly ash at 30% total cementitious material content =

= 385 X 30% = 115 kg/m³

Cement (OPC) =385-115 =270 kg/m³

Saving of cement while using fly ash = 350-270=80 kg/m³

Fly ash being utilized = 115 kg/m³

Proportion of volume of coarse aggregate and fine aggregate content

From Table 3 of IS 10262:2009, volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate

(Zone I) for water-cement ratio of 0.50 = 0.60.

In the present case w/c ratio is 0.40. Therefore, the volume of coarse aggregate needs to be increased to decrease the fine aggregate content.

As the w/c 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 volume of coarse aggregate for water-cement ratio of 0.40 = 0.64.

(If coarse aggregate is not of angular type, then also the volume of coarse aggregate may be required to be increased suitably, based on experience)

For pumpable concrete these values should be reduced by 10%.

Therefore, volume of coarse aggregate = 0.64 x 0.9 = 0.576

Volume of fine aggregate = 1 – 0.576 = 0.424

Mix calculations:

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

Volume of concrete = 1m³
Volume of cement = (Mass of cement / Specific gravity of cement ) *1/1000 = (270/3.15 )*1/1000 = 0.085 m³
Volume of water = ( Mass of water / Specific gravity of water)*1/1000= (140/1)*1/1000 = 0.140 m³
Volume of fly ash = (Mass of flyash / Specific gravity of flyash )*1/1000 = (115/2.2) *1/1000= 0.052 m³
Volume of chemical admixture: (superplasticizer @ 2% by mass of cementitious material) = for 2 % of cementitious material, mass of chemical admixture = 7 kg/m³=( Mass of admixture / specific gravity of admixture)*1/1000= ( 7/1.145)*1/1000=0.006 m³
Volume of all in aggregate (FA & CA) = [a – (b + c + d + e )]= [ 1 – (0.085 + 0.140 + 0.052 + 0.006)] = 0.717 m
Mass of coarse aggregate = [e x volume of coarse aggregate x specific gravity of coarse aggregate x 1000] = 0.717 x 0.576 x 2.74 x 1000= 1131 kg/m³
Mass of fine aggregate = [e x volume of fine aggregate x specific gravity of fine aggregate x 1000] = 0.717 x 0.424 x 2.74 x 1000= 832 kg/m³

Mix proportions for Trial Number 1:

Cement = 270 kg/m³

Fly ash = 115 kg/m³

Water = 140 kg/m³

Fine aggregate = 832 kg/m³

Coarse aggregate = 1131 kg/m³

Chemical admixture = 7 kg/m³

Water-cement ratio = 0.40

Trial mix ratio = 1: 2.16: 2.93

The slump shall be measured and the water content and dosage of admixture shall be adjusted for achieving the required slump on trial. The mix proportion shall be reworked for the actual water content and checked for durability requirements.
Two or more trials having variation of 10 % of water-cement ratio in Clause 10(Step 10) shall be carried out and a graph between three water-cement ratios and corresponding strengths shall be plotted to work out the mix proportions for the given target strength for field trials. However durability shall be met.

Result: The mix design for M 35 grade of concrete with fly ash is 1: 2.16:2.93

Explain in detail the concrete mix design for M50 grade concrete.