Project on Concrete Mix Design for various grades of Concrete
AIM
As concrete is a homogeneous material that has various ingredients like coarse aggregates, fine aggregates, water, admixtures etc.., for mixing. For concrete to achieve the desired strength these ingredients have to be included in the specific amount. This specific amount is decided based on the mix design ad per IS code 10262 : 2009. The specific amount is selected such that concrete gives desired workability in the plasyic state, desired durability in the given environmental state, desired strength hardened state, and economical concrete as possible.
Introduction :
This project contains two types of concrete mix design
1. Concrete mix design of M35
The concrete mix design of M35 is done by taking fly ash, superplasticizers and wet aggregates.
2. Concrete mix design of M50
The concrete mix design of M50 is done by taking superplasticizer and partially dry aggregates.
Concrete Mix Design of M35
DATA FOR CONCRETE MIX DESIGN OF M35 GRADE CONCRETE WITH FLY ASH
Grade of concrete : 35 N/mm^2
Maximum size of aggregates : 20 mm
Types of aggregates : Crushed angular aggregetes
Slump workability : 120 mm
Degree of quality control : good
exposure : severe ( for reinforced concrete )
method of concrete placing : pumping
Maximum cement content : As per IS 456:2000
chemical admixture ( confirmimg to IS 9103-1999 ) : super plasticizers - normal
zone of fine aggregates : zone III
types of mineral admixtures : fly ash confirming to IS 3812 ( part 1 )
Test data for material
Cement : OPC 53 N/mm^2
Specific gravity
cement : 3.15
coarse aggregate at surface saturated condition : 2.74
fine aggregate at surface saturated condition : 2.65
chemical admixtures : 1.145
fly ash : 2.2
Water absorpotion
coarse aggregate : 0.87
fine aggregate : 1.26
Moisture content of aggregate as per IS 2386 ( part 3 ) : 1967
coarse aggregate : 2.15 %
fine aggregate : 4.68 %
Free moisture content
free surface moisture of coarse aggregates = moisture content - water absorption
coarse aggragate : 1.28 %
free surface moisture of fine aggregates = moisture content - water absorption
fine aggregate : 3.42 %
fineness modulus : 2.41
aggregate impact value : 18.76 %
combined flakiness and elongation index : 28.56 %
Admixtures
super plasticizers : 1 percent by cement wt
water reduction by super plasticizers : 23 percent of water quantity
Pozzolanic material
Amount of fly ash material being used : 30 %
Increase in the cement content : 10 %
Pumpable concrete
Reduction for pumpable concrete : 10 %
Design mix
1. target strength for mix
Fck = fck + 1.65 *`sigma`
`sigma`= 5 as per Table 2 of IS 10262 : 2019
Also, as per table 1 of IS 10262 : 2019 , value of X ( =1.65 * `sigma`) for M35 = 6.5
Fck = 35 + 1.65 * 5
Target mean strength from standard deviation 43.25 MPa
Target mean strength from value of X 41.5 MPa
The higher value of adopted. therefore taking target mean strength 43.25 MPa
2. Air entrapped
( As per table 3 of IS 10262:2019 )
for 20 mm nominal maximum size of aggregates : 1 percent
3. Water cement ratio
As per table 5 of IS 456:2000
maximum water cement ratio for severe exposure : 0.45
minimum grade of concrete in severe exposure : M30
From fig 1 of IS 10262:2019, for target mean strength of 43.25 MPa and OPC cement of grade 53 MPa : 0.36
Therefore taking value of w/c ratio : 0.36
4. Water content calculation
from table 4 of IS 10232:2019, water content for 20 mm nominal maximum size of aggregates
water for 50 mm slump value as per table 4 : 186 kg/m^3
slump required at the site for workability : 120 mm
estimated water contentcfor site slump
( water for 50mm slump as per table 4 of 10262:2019 x 3 x ( required slump -50 ) )/ 25} * 3%
water content for 75mm slump 201.624 kg/m^3
The effect of superplasticizers is to reduce water content and increase workability. Generally superplasticizers giver reduction in water content by more than 20%
taking plasticizers by percentage weight of cement 1 %
amount of water reduced by super plasticizers 23 %
Hence water content is 155.25 kg/m^3
5. Calculation of cement
w/c ratio : 0.36
cement content calculation = ( w/c )/ water content
cement amount as calculated : 431.25 kg/m^3
As per IS 456 has recommended the value of cement for M35 grade concrete
minimum value of cement : 320 kg/m^3
maximum value of cement : 420 kg7m^3
Now a days as the economy is one of the main concern of the projects. Cement is one of the material that is costly and a small substitution of cement with fly ash also serves the structural purpose of the project. So , fly ash is being used as a substitute material which has a certain advantages over conventional advantages like permeability, less heat of hydration, reduction of cracks, bleeding etc..
Use of pozzolanic material sometimes a requirement of increment of the cement content is warrented. It is decided based on the trials and experience.
Talking the content of fly ash as 30% and increment of content as 10% .
Cement content after incrementing for fly ash : 474.38 kg/m^3
weight of fly ash : 142.31 kg/m^3
cement content taken : 332.06 kg/m^3
Finally cement taken : 332.06 kg/m^3
Finally taken cement must be more than 320 kg/m^3 for severe exposure
No of bags for cement ( assuming 1 bag = 50 kgs ) : 6.64 bags
correction for water content : 119.54 kg/m^3
Finally taken water content : 155.25 kg/m^3
total plasticizers required : 3.32 kg/m^3
6. Calculation of proportion of coarse aggregate to total aggregates
From table 5 of IS 10232:2019 for 20mm size of aggregate and zone 3 of sand . This table given value of ration of CA/TA for w/c ratio 0.5
for w/c ratio 0.5 proportion of CA/TA : 0.64
Required w/c ratio : 0.36
The proportion of volume of coarse aggregates that of total aggregates is increased at the rate of 0.01 for every decrease in the water cement ratio by 0.05 and decreased at the rate of 0.01 for every increase in water cement ratio 0.05
correction for water cement ratio as per clause 5.5.1 of IS 10232:2019
Assuming 1 unit as total aggregate then
For pumpable concrete general reduction of 10% of aggregate is done for ease of doing work.
The proportion of coarse aggregate : 0.6012
The proportion of fine aggregates = 1- proportion of coarse aggregates : 0.3988
7. Mix Calculation
Taking volume of concrete : 1.000 Cum ( assumption )
volume of air entrapped = As per table 3 of IS 10262 volume of air entrapped : 0.010 Cum
volume of cement = (mass of cement / specific gravity of cement )*1/1000 : 0.105 Cum
volume of water = ( mass of water / specific gravity of water ) * 1/1000 : 0.155 Cum
volume of chemical admixtures = ( mass of admixtures / specific gravity of admixtures )* 1/1000 : 0.003 Cum
volume of fly ash = (mass of fly ash /specific gravity of fly ash)*1/1000 : 0.065 Cum
volume of Aggregates= total volume of air entrapped - volume of cement - volume of water - volume of admixtures- volume of fly ash.
volume of aggregate in 1 Cum : 0.662 Cum
Quantity of coarse aggregate : 1090.084 kg/m^3
Quantity of coarse aggregate = volume of total aggregates x proportion of coarse aggregate x specific gravity of coarse aggregate x1000
quantity of fine aggregate : 699.345 kg/m^3
8. Correction for wet aggregate
As the above calculation is done for saturated surface dry condtion . If the condition is otherwiswe then while calculating the water content, we have to make allowance for either free surface or dry aggregates.
wet coarse aggregate = mass of coarse aggregate in SSD condition x ( 1+ free moisture/100) : 1104.372 kg/m^3
wet fine aggregate = mass of fine aggregate in SSD condition x ( 1 + free moisture /100) : 723.263 kg/m^3
Increase in water content
For Coarse aggregates
Increase in water due to coarse aggregates = mass of coarse aggregate in SSD condition - mass of coarse aggregate in wet condition : - 13.953 kg/m^3
Increase in water due to fine aggregate = mass of fine aggregate in SSD condition - mass of fine aggrgate in wet condition = : - 23.918 kg/m^3
increase in water cement content : - 37.871 kg/ m^3
9. Final Quantities :
For surface saturated dry condition ( only in kg/m^3 )
for 1Cum
cement : 332.064
water : 155.250
admixtures : 3.321
coarse aggregate : 1090.084
fine aggregate : 699.345
fly ash : 142.313
final w/c : 0.468
For surface saturated wet condition ( only in kg/m^3 )
for 1 cum
cement : 332.064
water : 117.380
admixture : 3.321
coarse : 1104.037
fine : 723.263
fly ash : 142.313
final w/c : 0.353
This decrease in w/c ratio is due to the wet aggregates as these aggregates also have free some water over and above required for absorption to saturated surface condition. This additional water supplements the w/c ratio water requirement.
Concrete mix Design of M50
DATA FOR CONCRETE MIX DESIGN OF M50 GRADE CONCRETE WITHOUT FLY ASH
Grade of concrete : 50N/mm^2
Maximum size of aggregates : 20mm
types of aggregates : crushed angular aggregates
slump workability : 75 mm
degree of quality control : good
exposure condition : severe
method of concrete placing : chute ( non pumpable )
maximum cement content without fly ash : 450 kg/ m^3
chemical admixtures : super plasticizers normal
zone of fine aggregate : zone III
Test data for material
cement : OPC 53 N/mm^2 ( confirming to IS 12269-2013 )
Specific Gravity
cement : 3.15 as per IS code
coarse aggregate at surface saturated condition : 2.74
fine aggregate at surface saturated condition : 2.65
chemical admixture ( super plasticizers) : 1.145
Water absorption :
coarse aggregate : 0.87
fine aggregate : 1.26
fineness modulus : 2.41
aggregate impact value : 18.76 %
Combined flakiness and Elongation index : 28.56 %
Admixtures
Super plasticizers : 1% of cement wt
Water reduction : 23 % of water quantity
Design mix
1. Target strength for mix
Fck = fck + 1.65* S
s= standard deviation
As per table 2 of IS 10626:2019
S = 5
Also, as per table of IS 10262:2019, value of X= ( 1.65*S ) for M50
6.5
Fck = 50+1.65*5
Target mean strength from the standard deviation : 58.25 MPa
target mean strength from value of X is : 56.5 MPa
The higher value of adopted. Therefore taking target mean strength : 58.25 MPa
2. Air Entrapped
As per table 3 of IS 10262:2019
For 20mm nominal maximum size of aggregates : 1 %
3. W/C Ratio
As per table 5 of IS 456:2000
Maximum water cement ratio for severe exposure : 0.45
minimum Grade of concrete in severe exposure : M30
From fig 1 of IS 10262:2019, for target mean strength of 58.25 MPa and OPC cement grade of 53 MPa : 0.33
Therefore taking value of W/C ratio : 0.33
4. Water content calculation
From table of IS 10262:2019, water content for 20mm nominal maximum size of aggregates
water for 50mm slump value as per table 4 : 186 kg/m^3
slump required at site for workability : 75 mm
Estimated water content for site slump =
[ water for 50mm slump as per table 4 of IS 102626 : 2019 X 3 X (required slump - 50) / 25 ] * 3 %
water content for 75 mm slump : 191.58 kg/m^3
The effect of superplasticizers is to reduce water content and increase workability. Generally superplasticizers giver reduction in water content by more than 20% .
Taking plasticizers by the percentage of the weight of cement : 1%
amount of water reduced by pasticizers : 23 %
Water content =
water content for site slump x [ 1- ( % of reduction in water by admixture / 100 ) ]
Hence water content : 147.52 kg/m^3
5. Calculation of cement
W/C ratio : 0.33
cement content calculation =
( w/c ratio ) / water content
Cement content is calculated as : 447.02 kg/m^3
As IS 456 has recommended the value of cement for M50 grade concrete
minimum value of cement : 320 kg/m^3
maximum value of cement : 450 kg/m^3
Finally taken cement content : 447.02 kg/m^3
No.of bags for cement : 8.94 bags
( Assuming 1 bag = 50 kg )
Correction for water content : 147.52 kg/m^3
Finally taken water content : 147.52 kg/m^3
Total plasticizer required : 4.47 kg/m^3
6. Calculation of proportion of coarse aggregate to total aggregate
From table 5 of IS 10262:2019, for 20mm size of aggregate and zone III of sand. This table gives the value of ratio of CA/TA for w/c ratio 0.5
For W/C ratio 0.5, the proportion of CA/TA : 0.64
Required W/C ratio : 0.33
Correction for W/C ratio as per clause 5.5.1 of IS 10262:2019 : 0.674
Assuming 1 unit as total aggregate then,
The proportion of coarse aggregates : 0.674
The proportion of fine aggregates : 0.326
6. Mix Calculation
Taking the volume of concrete : 1.000 Cum ( Assumption )
The volume of Air Entrapped ( as per table 3 of IS 10262 )
The volume of Air Entrapped : 0.010 Cum
The volume of cement =
( mass of cement / specific gravity of cement ) * 1/1000
volume of cement : 0.142 Cum
The volume of water =
( mass of water / specific gravity of water ) * 1/1000 : 0.148 Cum
The volume of Chemical admixture =
( mass 0f admixture / specific gravity of admixture )* 1/1000 : 0.004 Cum
The volume of aggregate = total volume - volume of air entrapped - volume of cement - volume of water - volume of admixture
The volume of aggregate in 1 Cum : 0.697 Cum
Quantiy of coarse aggregate : 1286.579 kg/m^3
Quantity of course aggregates = volume of total aggregates x proportion of coarse aggregates x specific gravity of coarse aggregates x 1000
Quantity of fine aggregates : 601.582 kg/m^3
Quantity of fine aggregate = volume of aggregates x proportion of fine aggregate x specific gravity of fine aggregates x 10000
8. Correction for water absorption by aggregate :
As the above calculation is done for the saturated surface dry condition. If the condition is otherwise then while calculating the water content, we have to make allowance for free surface moisture or dry aggregates
Partially satuarated coarse aggregates =
mass of coarse aggregate in saturated surface condition / 1+ ( water absorption / 100 )
partially satuarated coarse aggregates : 1275.482 kg/m^3
Partially saturated fine aggregates =
mass of fine aggregate in saturated surface condition / 1 + ( water absorption /100 )
partially saturated fine aggregats : 594.363 kg/m^3
This reduction in the value if aggregation is accounted for the increase in water quantity as excess water above w/c ratio is being absorbed by the aggregate to make surface saturated by
Increase in water content
For coarse aggregate
Increase in water due to coarse aggregates =
mass of coarse aggregate in SSD condition - mass of coarse aggregate in dry condition
= 11.097 kg/m^3
Increase in water due to fine aggregate =
mass of fine aggregate in SSD condition - mass of fine aggregate in dry condition
= 7.489 kg/m^3
Increase in water content : 18.586 kg/m^3
9.FINAL QUANTITIES
For surface saturated Dry condition ( only in kg/m^3 )
for 1 cum
cement : 447.020
water : 147.517
Admixture : 4.470
Coarse aggregate : 1286.579
Fine aggregate : 601.852
final W/C : 0.330
For Dry or partially Dry condition ( only in kg /m^3 )
for 1 cum
cement : 447.020
water : 166.102
admixture : 4.470
coarse aggregate : 1275.482
fine aggregate : 594.363
final W/C ratio : 0.372
This increasing in w/c ratio is due to the dry or partially saturated aggregates as these aggregates also absorb some water. This absorption of water decrease water required for proper chemicla reaction and leads to undeveloped strength due to a shortage of water.
RESULTS :
From both concrete mix designs, we got to know the all the concrete ingredients required to make concrete of required grade which gives desired properties as required in both plastic and hardened state of concrete. Concrete ingredients required for 1 cum of concrete and 1 bag ( 50 kg ) of cement are shown in final quantities.