Challenge

Project on Concrete Mix Design for various grades of Concrete

LLavina Ruzario18 Jul 2022

Concrete Mix Design for M35 grade concrete with fly ash

Aim: To calculate the mix design for M35 grade concrete with fly ash

Introduction: Concrete Mix Design is a systematic process of choosing economical relative proportion of various ingredients from available material that gives the concrete the desired workability. The process of selecting suitable ingridients for producing concrete of required strength, durability and workability as economical as possible is known as concrete mix design. The compressive strength of the concrete depends on the quality and quantity of cement, water & aggregate. So it is very important to calculate the concrete mix design carefully and properly.

This project covers the calculation of the mix design for M35 grade concrete with fly ash & The Calculation for M50 grade concrete without fly ash.

Objectives: To achieve pre-determined minimum strength and durability of M35 grade concrete in most economical manner.

Equations used:

Target mean strength : f’ck= fck +1.65 s
Where,
f’ck = target mean strength

fck= compressive strength at 28 days of concrete

s = standard deviation
Volume of concrete= 1 m^3
Volume of cement = (mass of cement /specfic gravity of cement )x1 /1000
Volume of fly ash = (mass of fly ash/specific gravity of fly ash )x 1/1000
Volume of water = ( mass of water /specific gravity of water ) x1 /1000
Volume of chemical admixtures = ( mass of chemical admixture / specific gravity of chemical admixture )x 1/1000
Volume of aggregates =( volume of concrete -( volume of cement +volume of fly ash + volume of water + volume of admixture )
Mass of coarse aggregates= volume of aggregate x volume of coarse aggregate x specific gravity of coarse aggregate x1000
Mass of fine aggregate = volume of aggregate x volume of fine aggregate x specific gravity of fine aggregate x1000

Procedure:

Step 1:-Stipulations for proportioning:-

Grade designation : M35
Type of cement : OPC 43 grade conforming to IS 8112
Type of mineral admixture: Fly ash confirming to IS 3812 ( Part 1)
Maximum nominal size of aggregates : 20mm
Minimum cement content : 320 kg/m^3 (Table :5 IS 456-2000,based on exposure condition)
Maximum water-cement ratio : 0.45 (Table :5 IS 456-2000,based on exposure condition)
Workability :100mm slump value of 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/m^3.
Chemical admixture type : Superplaticizer.

Step 2:-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 flyash : 2.2
Chemical admixture : Superplaticizer conforming to IS 9103
Specific gravity of : Coarse aggregate : 2.74 Fine aggregate : 2.74
Water absorption : Coarse aggregate : 0.5% Fine aggregate : 1%
Free surface moisture: Coarse aggregate : Nil Fine aggregate : Nil
Seive analysis: Conforming to Table 2 & 3 of IS 383

Step 3:-Target strength for mix proportioning:-

Target mean strength : f’ck= fck +1.65 s

Where,
f’ck = target mean strength

fck= compressive strength at 28 days of concrete

s = standard deviation

From Table 1- IS 10262:2009,

S = 5 N/mm^2

f’ck=35 +1.65 × 5

f’ck= 43.25 N/mm^2

Step 4:-Selection of water/cement ratio:-

From Table 5 of IS 456:2000, for severe exposure maximum water/cement ratio is 0.45

Based on experience, adopted water/cement ratio is 0.41

0.41 < 0.45, hence OK

Step 5:- Selection of water content:-

From table 2 of IS 10262:2009,

Maximum water content for 20mm aggregate =186 litres (for 25mm to 50mm slump range)

For 100 mm slump ,= 186+(6/100)×186 =197 litres

As superplaticizer is used, the water content is reduced upto 20%

Hence arrived water content = 197-(197×20/100)

water content = 158 litres

Step 6:- Calculation of cementatious material (Cement + Fly ash):-

Water cement ratio = w/c= 0.41

Water content = W = 158 kg

Cementitious content = c=158/0.41 = 385.3 = 385 kg/m^3

Minimum cement content = 360 kg/m^3

360< 385 kg/m^3 ( hence okay )

The cementitious content has to be increased by 10% in order to attain good workability and strength.

385 x 0.10 + 385 = 424 kg/m^3

W= 158 kg

Water cement ratio = 158/424= 0.372

Fly ash at 30 % total cementitious material content= 424 x 30/100 = 127 kg/m^3

Cement (OPC ) = 424-127 = 297 kg/m^3

Saving of cement while using fly ash = 385 – 297 = 88 kg/ m^3

Fly ash = 127kg/m^3

Step 7:-Proportion of volume of coarse aggregate and fine aggregate:-

From table 3 of IS 1026:2009, volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone 1) for water- cement ratio =0.6

In present case the water/cement ratio is 0.41

Therefore the volume of coarse aggregate needs to be increased to decrease the fine aggregate content. (at the rate of +/- 0.01 for every +/- 0.05 change in water- cement ratio)

Therefore the corrected value ofcoarse aggregate for the water-cemnt ratio = 0.62

For pumpable concrete, these are reduced by 10 %

Volume of coarse aggregate = 0.62×0.9 = 0.56

Volume of fine aggregate = 1-0.56 =0.44

Step 8:- Mix calculations:-

Volume of concrete= 1 m^3
Volume of cement = (297/ 3.15) x1/1000= 0.094 m^3
Volume of fly ash = ( 127/2.2) x1/1000=0.057 m^3
Volume of water = ( 158/1)x 1/1000=0.158 m^3
Volume of chemical admixtures = ( 7.6/ 1.145)x1/1000=0.006 m^3
Volume of coarse aggregate and fine aggregate = a – ( b + c + d+e)
= 1-( 0.094 + 0.057 +0.158+ 0.006)= 0.685 m^3
Mass of coarse aggregate = 0.685 x 0.56 x 2.74 x1000 = 1051.06 kg/m^3
Mass of fine aggregate = 0.685 x 0.44 x 2.74 x1000 = 825.83 kg/m^3

Result:-

Step9:-Mix proportion for trial :-

Cement = 297 kg/m^3
Fly ash = 127 kg/m^3
Water = 158 kg
Fine aggregate = 825.83 kg/m^3
Coarse aggregate = 1051.06 kg/m^3
Chemical admixture = 0.006 kg/m^3
Water- cement ratio = 0.372 kg/m^3

Trial mix ratio : 297 :825.83 : 1051.06 = 1: 2.78 : 3.53 ( C: FA: CA)

Step 10:-

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.

Step :11

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 feild trials .However durability shall be met.

Concrete mix design for M50 grade concrete without Fly ash

Aim: To calculate the mix design for M50 grade concrete without fly ash

Objectives: To achieve pre-determined minimum strength and durability of M50 grade concrete in most economical manner.