Project on Concrete Mix Design for various grades of Concrete
Introduction-Concrete mix design is required to have maximum w/c ration to gain adequate workability, maximum cement content to minimize shrinkage and ultimately have desired strength to resist loads.
Procedures- Procedure involves Proportioning, Test data for the materials being used, Target strength of the mix, Selection of water-cement ratio, Selection of water content, Calculation of cement content & fly ash, Proportion of volume of coarse and fine aggregate, Mix calculations and finally Mix proportion for the trial.
Proportioning
a. Grade Designation :- M35
b. Type of Cement :- OPC grade 43 as per IS 8112.
c. Type of mineral admixture :- Fly ash as per IS 3812 (part I)
d. Maximum Nominal size of aggregate :- 20 mm
e. Minimum cement content :- 320 kg/m3 (Table 5 of IS 456:2000, exposure condition)
f. Maximum water-cement ratio :- 0.45 (Table 5 of IS 456:2000, exposure condition)
g. Workability :- 100 mm (slump value for pumpable concrete)
h. Exposure condition :- Severe (for RCC)
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 :- Super Plasticizer
Test data for the materials being used
a.Cement used:- OPC 43 grade as per IS 8112
Specific Gravity = 3.15
b.Fly Ash:- As per IS 3812(part I)
Specific Gravity = 2.2
c.Chemical Admixture:- Super plasticizer as per IS 9103
Specific Gravity = 1.145
d.Aggregates
Specific Gravity of Coarse aggregate = 2.74
Specific Gravity of Fine aggregate = 2.74
e.Water Absorption
Coarse Aggregate = 0.5%, Fine Aggregate = 1.0%
f.Free surface moisture
Coarse aggregate = Nil, Fine aggregate = Nil
g.Sieve Analysis
Coarse aggregate = As per Table 2 of IS 383
Fine aggregate = As per Table 4 of IS 383, Grading Zone I
Target Mean Strength for Mix
f ’ck = f ck + 1.65 σ
= 35 + 1.65*5 = 43.25 N/mm2
f ’ck = Target average compressive strength at 28 days
f ck = Characteristic compressive strength at 28 days
σ = Standard Deviation
f ck = 35 N/mm2 , σ = 5N/mm2 (From Table 1 of IS 10262:2009 & Table 8 of IS 456)
Selection of water-cement ratio
From Table 5 of IS 456:2000, It can be taken as per the exposure condition
w/c = 0.45 & Minimum grade = M 30
Minimum Cement content = 320 kg/m3
Based on previous studies(which is experienced one) it is adopted to be, w/c = 0.40
{For accurate value of w/c Fig1 and Fig2 of IS 10262:1982 can also be referred on the basis of target strength of 43.25 N/mm2}
0.40 < 0.45, Hence OK.
Selection of water content
From Table 2 of IS 10262:2009, Maximum water content for 20 mm aggregate = 186 L (186 kg) {for Slump = 25-50 mm}
For additional slump 3% is added for every 25 mm increase in slump.
Here, Slump = 100 mm
So, water content = 186 + (6/100) *186 = 197 L {Since 50 mm increase in slump i.e. 25*2, So 6% increase in water content}
As super plasticizer is used which reduce the water content up to 20% and above.
Let us assume it 25%
Hence, new water content = 197*0.75 = 148 L
Calculation of cement content
w/c = 0.40
Cementitious Material (cement + fly ash)= 148/0.4 = 370 kg/m3 > 320 kg/m3 {Hence OK}
{From Table 5 of IS 456 minimum cement content for severe exposure condition = 320 kg/m3}
Now to proportion mix containing fly ash,
1. i) Percentage of fly ash is decided based on project requirement and quality of material.
2. ii) Increase in cementitious material content and its percentage based on experience and trial, let’s assume 10% cementitious material content increase
Cementitious Material content = 370 * 1.10 = 407 kg/m3
Water Content = 148 L
So, w/c ratio = 148/407 = 0.36
Fly ash @ 30% total cementitious material = 122 kg/m3
Cement (OPC) = 407 – 122 = 285 kg/m3
Saving of cement while using fly ash = 370-285 = 85 kg
Fly ash utilized = 122 kg/m3
Proportion of volume of coarse and fine aggregate
From Table3 of IS 10262:2009, Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone I) for w/c of 0.5 = 0.6 (Volume of coarse aggregate)
But w/c = 0.4 { Now coarse aggregate content is increased to reduce the fine aggregate content}
As w/c 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 w/c of 0.4 = 0.62
For pumpable concrete these values are reduced by 10%
Therefore, volume of coarse aggregate = 0.62*0.9 = 0.56
Volume of fine aggregate = 1 – 0.56 = 0.44
Mix Calculations
The mix calculation per m3 of concrete shall be as follows:
a.Volume of Concrete = 1 m3
b.Volume of cement = (Mass of cement / Specific Gravity) * (1/1000)
= (285/3.15)*(1/1000) = 0.0905 m3
c.Volume of fly ash = (Mass of fly ash / Specific Gravity) * (1/1000)
= (122/2.2)*(1/1000) = 0.05545 m3
d.Volume of water = (Mass of water / Specific Gravity) * (1/1000)
= (148/1)*(1/1000) = 0.148 m3
e.Volume of chemical admixture = (Mass of admixture / Specific Gravity) * (1/1000)
= (8.14/1.145)*(1/1000) = 0.009 m3 {2% of cementitious material}
f.Volume of aggregate {FA(fine aggregate) CA(coarse aggregate)} = a – (b + c + d + e)
= 1 - 0.30295
= 0.69705 m3
g.Mass of coarse aggregate = f * Volume of coarse aggregate * Specific gravity of coarse aggregate * 1000
= 0.69705 * 0.56 * 2.74 * 1000
= 1070 kg/ m3
h.Mass of fine aggregate = f * Volume of fine aggregate * Specific gravity of fine aggregate * 1000
= 0.69705 * 0.44 * 2.74 * 1000
= 840 kg/ m3
Mix Proportion for the trial
Cement = 285 kg/ m3
Fly Ash = 122 kg/ m3
Water = 148 kg/ m3
Fine aggregate = 840 kg/ m3
Coarse aggregate = 1070 kg/ m3
Chemical Admixture = 8.14 kg/ m3
Water-cement ratio = 0.36
Trial mix ratio = 1:2.06:2.63
Result:- From the above procedure it is found out that the trial mix ratio is 1: 2.06: 2.63 for M35 grade of concrete mix design using fly ash.
Concrete Mix Design for M50 grade
Introduction- Concrete mix design is required to have maximum w/c ration to gain adequate workability, maximum cement content to minimize shrinkage and ultimately have desired strength to resist loads.
Procedures- Procedure involves Proportioning, Test data for the materials being used, Target strength of the mix, Selection of water-cement ratio, Selection of water content, Calculation of cement content, Proportion of volume of coarse and fine aggregate, Mix calculations and finally Mix proportion for the trial.
Proportioning
a.Grade Designation :- M50
b.Type of Cement :- OPC grade 43 as per IS 8112.
c.Maximum Nominal size of aggregate :- 20 mm
d.Minimum cement content :- 320 kg/m3 (Table 5 of IS 456:2000, exposure condition)
e.Maximum water-cement ratio :- 0.45 (Table 5 of IS 456:2000, exposure condition)
f.Workability :- 100 mm (slump value for pumpable concrete)
g.Exposure condition :- Severe (for RCC)
h.Method of concrete placing :- Pumping
i.Degree of Supervision :- Good
j.Type of aggregate :- Crushed angular aggregate
k.Maximum cement content :- 450 kg/m3
l.Chemical admixture type :- Super Plasticizer
Test data for the materials being used
a.Cement used:- OPC 43 grade as per IS 8112
Specific Gravity = 3.15
b.Chemical Admixture:- Super plasticizer as per IS 9103
Specific Gravity = 1.145
c.Aggregates
Specific Gravity of Coarse aggregate = 2.74
Specific Gravity of Fine aggregate = 2.74
d.Water Absorption
Coarse Aggregate = 0.5%
Fine Aggregate = 1.0%
e.Free surface moisture
Coarse aggregate = Nil
Fine aggregate = Nil
f.Sieve Analysis
Coarse aggregate = As per Table 2 of IS 383
Fine aggregate = As per Table 4 of IS 383, Grading Zone I
Target Mean Strength for Mix
f ’ck = f ck + 1.65 σ
= 50 + 1.65*5 = 58.25 N/mm2
f ’ck = Target average compressive strength at 28 days
f ck = Characteristic compressive strength at 28 days
σ = Standard Deviation
f ck = 50 N/mm2 , σ = 5 N/mm2 (From Table 1 of IS 10262:2009 & Table 8 of IS 456)
4. Selection of water-cement ratio
From Table 5 of IS 456:2000, It can be taken as per the exposure condition
w/c = 0.45 & Minimum grade = M 30
Minimum Cement content = 320 kg/m3
Based on previous studies(which is experienced one) it is adopted to be, w/c = 0.32
{For accurate value of w/c Fig1 and Fig2 of IS 10262:1982 can also be referred for target strength of 58.25 N/mm2}
0.32 < 0.45, Hence OK.
Selection of water content
From Table 2 of IS 10262:2009, Maximum water content for 20 mm aggregate = 186 L (186 kg) {for Slump = 25-50 mm}
For additional slump 3% is added for every 25 mm increase in slump.
Here, Slump = 100 mm
So, water content = 186 + (6/100) *186 = 197 L {Since 50 mm increase in slump i.e. 25*2, So 6% increase in water content}
As super plasticizer is used which reduce the water content up to 20% and above.
Let us assume it 25%
Hence, new water content = 197*0.75 = 148 L
6. Calculation of cement content
w/c = 0.32
Cement Content = 148/0.36 = 411 kg/m3 > 320 kg/m3 {Hence OK}
{From Table 5 of IS 456 minimum cement content for severe exposure condition = 320 kg/m3}
Cement Content = 411 kg/m3
Water Content = 148 L
So, w/c ratio = 148/411 = 0.36
Proportion of volume of coarse and fine aggregate
From Table3 of IS 10262:2009, Volume of coarse aggregate corresponding to 20 mm size aggregate and fine aggregate (Zone I) for w/c of 0.5 = 0.6 (Volume of coarse aggregate)
But w/c = 0.32 { Now coarse aggregate content is increased to reduce the fine aggregate content}
As w/c 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 w/c of 0.4 = 0.69
For pumpable concrete these values are reduced by 10%
Therefore, volume of coarse aggregate = 0.69*0.9 = 0.62
Volume of fine aggregate = 1 – 0.62 = 0.38
Mix Calculations
The mix calculation per m3 of concrete shall be as follows:
a.Volume of Concrete = 1 m3
b.Volume of cement = (Mass of cement / Specific Gravity) * (1/1000)
= (411/3.15)*(1/1000) = 0.1305 m3
c.Volume of water = (Mass of water / Specific Gravity) * (1/1000)
= (148/1)*(1/1000) = 0.148 m3
d.Volume of chemical admixture = (Mass of admixture / Specific Gravity) * (1/1000)
= (8.22/1.145)*(1/1000) = 0.0072 m3 {2% of cementitious material}
e.Volume of aggregate {FA(fine aggregate) CA(coarse aggregate)} = a – (b + c + d + e)
= 1 - 0.2857
= 0.7143 m3
f.Mass of coarse aggregate = e * Volume of coarse aggregate * Specific gravity of coarse aggregate * 1000
= 0.7143 * 0.62 * 2.74 * 1000
= 1214 kg/ m3
g.Mass of fine aggregate = e * Volume of fine aggregate * Specific gravity of fine aggregate * 1000
= 0.7143 * 0.38 * 2.74 * 1000
= 744 kg/ m3
Mix Proportion for the trial
Cement = 411 kg/ m3
Water = 148 kg/ m3
Fine aggregate = 744 kg/ m3
Coarse aggregate = 1214 kg/ m3
Chemical Admixture = 8.22 kg/ m3
Water-cement ratio = 0.32
Trial mix ratio = 1:1.8:2.9