Project on Concrete Mix Design for various grades of Concrete

Aim: - To Calculate the Concrete Mix Design for M35 grade concrete with fly ash & M50 grade concrete without Fly ash.

Introduction: -

Concrete mix design is the method of finding the precise proportion of cement, sand and aggregates for concrete to achieve the target strength in structures, therefore concrete mix design can be stated as concrete mix in terms of cement: sand: aggregates. The design is done according to the requirements of concrete strength. So, we can achieve the desirable properties of concrete either it is in fresh stage or in hardened stage. The fresh concrete properties like workability, setting time and hardened concrete properties like compressive strength, durability etc. are attained surely by this method. Use of additives like admixtures, retarders etc. other than basic ingredients are used to improve the properties of mix.

This project consists of two parts, the first part deals with the design of M35 grade cement with fly ash as a part of it and second part is the design of M50 grade concrete without fly ash.

Objective: -

The objective of this project is to produce a mix design for M35 grade concrete containing fly ash and M50 grade concrete. The mix will be prepared as per IS METHOD: Concrete mix proportioning guidelines from IS 10262:2009 and recommend guide lines from IS 10262:1982.

Used formulas: -

• Target mean strength

f’ck = fck + 1.65s,

where,

f’ck = target average compressive strength at 28 days

fck = characteristics compressive strength at 28 days

s = standard deviation satisfying IS 10262:2009

• Cement content = water content/water-cement ratio
• Volume calculations: -

1. Volume of concrete
2. Volume of cement = (mass of cement)/(specific gravity of cement)*(1/1000)

• Volume of chemical admixture = (mass of admixture) / (specific gravity of admixture) *(1/1000)

1. Volume of all in aggregate = (a-(b+c+d))
2. Mass of course aggregate = e*volume of course aggregate*specific gravity of fine aggregate*100
3. Mass of fine aggregate = e*volume of fine aggregate*specific gravity of fine aggregate*100

Part 1: - For concrete mix deign of M35 grade concrete with fly ash.

• Details for the mix design: -

Grade designation ------------- M35

Type of cement---------------- OPC 43 grade confining to IS 8112

Type of mineral admixture------------- Fly ash confining to IS 3812 part 1

Maximum nominal size of aggregate------------- 20mm

Minimum water content------------------- 320 kg/m^3, as per IS 456:2000

Maximum water cement ratio------------- 0.45 as per IS 456:2000

Workability---------------- 100mm

Exposure condition--------------- Severe

Methods of concrete placing--------------- Pumping

Degree of supervision-----------------Good

Type of aggregate--------------------- Crushed angular

Maximum cement content------------ 450 kg/m^3

Chemical admixture type--------------- Super plasticizer confining to IS 9103

• Test data of materials

Specific gravity of cement----------- 3.15

Specific gravity of fly ash------------- 2.2

Specific gravity of coarse aggregate-------------- 2.74

Specific gravity of fine aggregate---------------- 2.74

Water absorption of coarse aggregate----------------- 0.5%

Water absorption of fine aggregate--------------- 1%

Sieve analysis for coarse aggregate confining to IS 383

Sieve analysis for fine aggregate confining to IS 383

• Target strength for mix proportioning

f’ck = fck + 1.65 s

s= 5 N/mm^2

hence, f’ck = 35+1.65*5 = 43.25 N/mm^2

from this we get target mean strength as 43.25 N/mm^2

• Water cement ratio

As per Table 5 of IS 456:2000, the maximum water-cement ratio to design M50 grade concrete = 0.45

We take adopted water cement ratio as 0.44

0.44<0.45 hence ok

Adopt w/c ratio = 0.44

• Water content

From table 2 of IS 1026:2009 we get the maximum water content for 2omm aggregate as 186 litres.

Increasing water content for every extra 25mm slump from 50 mm slump as per clause 4.2, so a 6% is to be added, hence we get 186+(6% of 186) = 197 litre

Water content reduction of about 20% has been achieved based on the trials with super plasticizer, hence the final water content is 197*0.8(reduction factor) = 158 litre

Water required is 158 litre.

• Cement and fly ash required

Adopted water cement ratio ----------------------- .44

Cement + fly ash requirement------------- 158/0.44 = 359 kg/m^3

The quantity can be increased in order to attain god workability and strength. Based on experiments and experience, let us increase by 10%

So final quantity --------------------- 359*1.10 = 395 kg

From IS 456, for severe exposure conditions, minimum cement content------------ 320kg

395>320 hence ok

Cementitious material content------------- 395

New water cement ratio----------------- 158/395 = 0.4

Fly ash content taken as 30% of the total------------- 395*0.3 = 118.5 kg/m^3

Cement required--------------- 395 – 118 = 277 kb/m^3

Quantity of cement replaced by fly ash-----------------350-277 = 73kg/m^3

Finally, cementitious material, cement and fly ash required is 395 kg/m^3, 277 kg/m^3 and 118 kg/m^3 respectively with new water cement ratio as 0.4

• Calculations for coarse and fin aggregate quantity

As per IS 10262:2009, volume of coarse aggregate corresponding to 20mm size aggregate and fine aggregate for w/c ratio of 0.50 is 0.62.

In the present case water-cement ratio is 0.44. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.06. 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 0.44 is 0.632

Values of pumpable concrete should be reduced up to 10%, hence volume of coarse aggregate becomes 0.632*0.9 = 00.568

Volume of fine aggregate = 1- 0.568 = 0.431

Volume of fine aggregate---------------0.431

Volume of coarse aggregate------------0.568

• Mix calculations

1. Volume of concrete--------/---1m^3
2. Volume of cement---------- 277/3.15)*(1/1000) = 0.087m^3

• Volume of fly ash---------(118/2.2)*(1/1000) = 0.053

1. Volume of water-------------- (158/1)*(1/1000) = 0.158m^3
2. Volume of chemical admixture-------------- (7.6/1.145)*(1/1000) = 0.006m^3
3. Volume of all(i,ii,iii,iv,v) in aggregate---------- [1-(0.087+0.053+0.158+0.006)] = 0.0696m^3

• Mass of coarse aggregate------------------------ 0.696*0.568*2.74*1000 = 1077 kg/m^3
• Mass of fine aggregate-------------- 0.696*0.431*2.74*1000 = 822kg/m^3

• Mix proportions

Cement-------------------- 277 kg/m^3

Fly ash-------------- 118 kg/m^3

Water---------------- 158 l/m^3

Fine aggregate-------------- 822 kg/m^3

Coarse aggregate 20mm---------------- 1077 kg/m^3

Chemical admixture--------------- 7.18 kg/m^3

Water cement ratio -------------------- 0.4

Mix proportions by weight------------ 1:2.08:2.72

• The slump shall be measured, 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 more trials having variation of 10% of water-cement ratio 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 for field trials.

Part 2: - For concrete mix deign of M50 grade concrete without fly ash.

• Requirements

Grade designation------------ M50

Type of cement----------- OPC 53 grade confining to IS 12269-1989

Maximum nominal size of aggregate------------20mm

Minimum cement content-------------320kg/m^3 as per IS 456:2000

Maximum water cement ratio--------------- 0.45 for exposure conditions as per IS 456:2000

Workability---------- 100mm

Exposure condition----------------Severe

Method of concreting-------------pumping

Degree of supervision-------------Good

Type of aggregate----------------- Crushed angular aggregates

Maximum cement content------------ 450 kg/m^3

Chemical admixture type-------Super plasticizer

• Test data for materials

Specific gravity of OPC 53 grade cement---------------- 3.15

Specific gravity of coarse aggregate-------------- 2.74

Specific gravity of fine aggregate---------------- 2.64

Water absorption of coarse aggregate----------------- 0.5%

Water absorption of fine aggregate--------------- 1%

Sieve analysis for coarse aggregate confining to IS 383 table 2

Sieve analysis for fine aggregate confining to IS 383 grading zone II

• Target strength

f’ck = fck + 1.65s

s= 5N/mm^2 as per Table 1 of IS 10262:2009

f’ck = 50 + 1.65*5 = 58.25 N*/mm^2

Target mean strength = 58.25N/mm^2

• Water cement ratio (w/c ratio)

The maximum water-cement ratio to design M50 grade concrete can be found from Table 5 of IS 456-2000 for severe exposure as 0.45

Based on experience adopt as .44<0.45 hence ok

Adopted w/c ratio = 0.44

• Water content

From Table 2 of IS 10262:2009, maximum water content for 20 mm aggregate is 186 litres.

Clause 4.2 suggests increasing of 3% of water content for every extra 25mm slump from 50mm slump. So a 6% is to be added to it, hence we get 186+(6%of 186) = 197 litres.

Based on trials and experience with super plasticizer, water content can be reduced by 20%, hence arrived water content is 197*0.8 = 158 litres

Water required is 158 litres.

• Cement required

w/c ratio------------- 0.44

cement content---------- 158/0.44 = 359 kg/m^3

for severe conditions as per IS 456, cement content = 320 kg/m^3 < 350 kg/m^3 hence ok

Required cement is 359 kg/m^3

• Quantity of coarse and fine aggregate

From Table 3 of (IS 10262:2009) Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone II) for water-cement ratio of 0.50 is-------------------- 0.62

In the present case water-cement ratio is 0.44. Therefore, volume of coarse aggregate is required to be increased to decrease the fine aggregate content. As the water-cement ratio is lower by 0.06. 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 0.44------------------------------0.632

For pumpable concrete these values should be reduced up to 10%. Therefore, volume of coarse aggregate-------------------- 0.632*0.9 = 0.568

Volume of fine aggregate content---------------- 1-0.576 = 0.431

Volume of fine aggregate------------0.431

Volume of coarse aggregate-----------0.568

• Mix calculations

Volume of concrete--------------- 1m^3

Volume of cement---------------- (359/3.15)*(1/1000) = 0.114 m^3

Volume of water------------------ (158/1)*(1/1000) = 0.158m^3

Volume of chemical admixture----------------- (7.6/1.145)*(1/1000) = 0.006m^3

Volume of all in aggregate------------ [1-(0.114+0.158+0.0060] = 0.722 m^3

Mass of coarse aggregate-------------- 0.722*0.568*2.74*1000 = 1123kg/m^3

Mass of fine aggregate--------------- 0.722*0.431*2.64*1000 = 821kg/m^3

• Mix proportions

Cement----------------- 359kg/m^3

Water-----------------158 l/m^3

Fine aggregate--------------- 821 kg/m^3

Coarse aggregate 20mm -------------- 1123kg/m^3

Chemical admixture---------------- 7.18kg/m^3

w/c ratio------- 0.44

Mix proportion by weight -------------- 1:2.28:3.12

• The slump shall be measured, 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 more trials having variation of 10% of water-cement ratio 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 for field trials.

• Results

Mix proportion by weight of M35 grade concrete with fly ash is 1:2.08:2.72 and its w/c ratio is 0.4.

Mix proportion by weight of M50 grade concrete without fly ash is 1:2.28:3.12 and its w/c ratio is 0.44.