# Concrete Mix Design

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Concrete Mix Design
Concrete Mix Design
Unit-III
Syllabus
Concrete Mix Design
Mix Design for compressive strength by I.S. Method, Road Note Method, British method, Mix Design for flexural Strength
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Concrete Mix Design
Concrete mix design may be defines as the art of selecting suitable ingredients of concrete and determining their relative proportions with the object of producing concrete of certain minimum strength & durability as economically as possible.
Objectives of Mix Design
The purpose of concrete mix design is to ensure the most optimum proportions of the constituent materials to fulfill the requirement of the structure being built. Mix design should ensure following objectives.
To achieve the designed/ desired workability in the plastic stage
To achieve the desired minimum strength in the hardened stage
To achieve the desired durability in the given environment conditions
To produce concrete as economically as possible.
Basic Considerations
The following point must be considered while designing concrete mixes
Cost
Specification
Workability
Strength and Durability
Basic Considerations
Cost
The cost of concrete is made up of
Material Cost
Equipment Cost
Labour Cost
The variation in the cost of materials arises from the fact that cement is several times costlier than aggregates. So it is natural in mix design to aim at as lean a mix as possible. Therefore, all possible steps should be taken to reduce the cement content of a concrete mixtures without sacrificing the desirable properties of concrete such as strength and durability.
Basic Considerations
Specifications
The following point may be kept in mind while designing concrete mixes
Minimum Compressive Strength required
Minimum water/ cement ratio
Maximum cement content to avoid shrinkage cracks
Maximum aggregate / cement ratio
Maximum density of concrete in case of gravity dams
Basic Considerations
Basic Considerations
Workability
The following points related to workability shall be kept in mind while designing concrete mixes.
The consistency of concrete should no more than that necessary for placing, compacting and finishing.
For concrete mixes required high consistency at the time of placing, the use of water-reducing and set-retarding admixtures should be used rather than the addition of more water
Wherever possible, the cohesiveness and finishibility of concrete should be improved by increasing sand/ aggregate ratio than by increasing the proportion of the fine particles in the sand.
Workability
Strength and Durability
Strength and durability
Strength and durability require lower w/c ratio. It is usually achieved not by increasing the cement content, but by lowering the water at given cement content. Water demand can by lowered by throughout control of the aggregate grading and by using water reducing admixtures.
Strength and Durability
Grade of Concrete
The concrete shall be in grades designated
Group Grade designation Characteristics compressive strength of 150 mm cube at 28 days, N/mm2
Ordinary Concrete M10
M15
M20 10
15
20
Standard Concrete M25
M30
M35
M40
M45
M50
M55 25
30
35
40
45
50
55
High Strength Concrete M60
M65
M70
M75
M80 60
65
70
75
80
What is M 20 ?
M refers to Mix
20 refers to characteristic compressive strength of 150 mm cube at 28 days in N/mm2
The minimum Grade of Plain Concrete (PCC) shall be 15 N/mm2
The minimum grade of reinforced Concrete ( RCC) shall be 20 N/mm2
Nominal Concrete Mixes
and
Design mix concrete
Nominal Mix Concrete
The wide use of concrete as construction materials has led to the use of mixes of fixed proportion, which ensures adequate strength. These mixes are called nominal mixes.
They offer simplicity and Under normal circumstances, has margin of strength above that specified.
Nominal mix concrete may be used for concrete of grades M5, M 7.5, M10, M15 and M20.
Nominal Concrete Mixes
and
Design mix concrete
Proportions of Ingredients in Nominal Mixes
The proportions of materials for nominal mix shall be in accordance
Grade Proportions
C: FA: CA
M5 1: 5:10
M 7.5 1:4:8
M 10 1:3:6
M 15 1:2:4
M 20 1:1.5:3
Design Mix Concrete
The concrete mix produced under quality control keeping in view the strength, durability, and workability is called the design Mix.
Others factors like compaction equipment's available, curing method adopted, type of cement, quality of fine and coarse aggregate etc. have to be kept in mind before arriving at the mix proportion.
The design mix or controlled mix is being used more and more in variety of important structures, because of better strength, reduced variability, leaner mixed with consequent economy, as well as greater assurance of the resultant quality.
Design Mix Concrete
Factors Influencing Choice of Mix Design
According to IS 456:2000 and IS 1343:1980 the important influencing the design of concrete mix are
Grade of Concrete
Type of Cement
Maximum nominal Size of Aggregate
Grading of Combined aggregate
Maximum Water/ Cement Ratio
Workability
Durability
Quality Control.
Factors Influencing Choice of Mix Design
Grade of Concrete
The grade of concrete gives characteristic compressive strength of concrete. It is one of the important factor influencing the mix design
The grade M 20 denotes characteristic compressive strength fck of 20 N/mm2. Depending upon the degree of control available at site, the concrete mix is to be designed for a target mean compressive strength (fck) applying suitable standard deviation.
Factors Influencing Choice of Mix Design
Factors Influencing Choice of Mix Design
Type of Cement
The rate of development of strength of concrete is influenced by the type of cement.
The higher the strength of cement used in concrete, lesser will be the cement content. The use of 43 grade and 53 grade of cement, gives saving in cement consumption as much as 15 % and 25 % respectively, as compared to 33 grade of cement. For concrete of grade M25 it is advisable to use 43 and 53 grade of cement.
Types of Cement
Factors Influencing Choice of Mix Design
Maximum Nominal Size of Aggregates
The maximum size of C.A is determined by sieve analysis. It is designated by the sieve size higher than larger size on which 15 % or more of the aggregate is retained. The maximum nominal size of C.A. should not be more than one-forth of minimum thickness of the member.
For heavily reinforced concrete members as in the case of ribs of main beams, the nominal maximum size of the aggregate should usually be restricted to sum less than the minimum clear distance between the main bars or 5 mm less the minimum cover to the reinforcement, whoever is smaller.
The workability of concrete increases with an increase in the maximum size of aggregate. But the smaller size of aggregates provide larger surface area for bonding with the mortar matrix which gives higher strength.
Factors Influencing Choice of Mix Design
Grading of Combined Aggregates
The relative proportions of the fine and coarse aggregate in a concrete mix is one of the important factors affecting the strength of concrete.
For dense concrete, it is essential that the fine and coarse aggregate be well graded. In the case when the aggregate available from natural sources do not confirm to the specified grading, the proportioning of two or more aggregate become essential
Grading of Combined Aggregates
Factors Influencing Choice of Mix Design
Maximum Water/ Cement Ratio
Abramâs water/Cement ratio states that for any given condition of test, the strength of a workability concrete mix is dependent only on water/cement ratio. The lower the water/Cement ratio, the greater is the compressive strength
Workability
Workability of fresh concrete determines the case with which a concrete mixture can be mixed, transported, placed, compacted and finished without harmful segregation and bleeding.
Factors Influencing Choice of Mix Design
Durability
Durability require low water/Cement ratio. It is usually achieved not by increasing the cement content, but by lowering the water demand at a given cement content.
Water demand can be lowered by through control of the aggregate grading and by using water reducing admixtures
Method of Concrete Mix Design
Some of the commonly used mix design methods are
I.S. Method
A.C.I method
Road Note 4 method ( U.K. Method)
IRC 44 method
Arbitrary method
Maximum Density method
Fineness modulus method
Surface area Method
Nix design for high strength Concrete
Mix design for pumpable Concrete
DOE (British) Mix design method
IS Method of Mix Design
The Bureau of Indian Standards, recommended a set of procedure for design of concrete mix. The procedure is based on the research work carried out at national laboratories.
Data for mix design
The following basic data are required to be specified for design a concrete mix
Characteristic Compressive strength only a few specified proportions of test results are expected to fall of concrete at 28 days (fck)
Degree of workability desired
Limitation on water/Cement Ratio with the minimum cement to ensure adequate durability
Type and maximum size of aggregate to be used.
Standard deviations of compressive strength of concrete.
IS Method of Mix Design
Target Strength for Mix Design
The target average compressive strength (fck) of concrete at 28 days is given by
Fck= f ck + t.s
Where,
Fck= target average compressive strength at 28 days
F ck= characteristics compressive strength at 28 days
s= Standard deviation
t= a stastical value, depending upon the accepted proportion of low results and the number of tests.
IS Method of Mix Design
According to Is 456: 2000 and IS 1343:1980 te characteristic strength is defined as the value below which not more than 5 percent of results are expected to fall. In such cases the above equation reduced to
Fck= fck + 1.65 s
The value of standard deviation is obtained from the table
IS Method of Mix Design
IS Method of Mix Design
Step-II
Selection of Water âCement Ratio
Since different cements and aggregates of different maximum sizes, grading, surface texture shape and other characteristics may produce concrete of different compressive strength for the same free water cement ratio, the relationship between strength and free water cement ratio should preferable be established for the material actually to be used. In the absence of such data, the preliminary free water-cement ratio corresponding to the target strength at 28 days may be selected from the relationship shown below
IS Method of Mix Design
IS Method of Mix Design
Alternatively, the preliminary free water cement ratio by mass corresponding to the average strength may be selected from the relationship shown below using the curve corresponding to the 28 days cement strength to be used for the purpose. However, this will need 28 days for testing of cement.
IS Method of Mix Design
IS Method of Mix Design
The free water-cement ratio thus selected should be checked against limiting water-cement ratio for the requirements of durability as per table 5.4 and the lower of the two values should be adopted.
IS Method of Mix Design
IS Method of Mix Design
Step 3 Estimation of Air Content
Approximate amount of entrapped air to be expected in normal concrete is given in table 9.6
Nominal Maximum Size of Aggregates Entrapped Air, as percentage of volume of concrete
10 3 %
20 2 %
40 1 %
IS Method of Mix Design
Selection of Water Content and fine to total aggregate ratio
For the desired workability the quantity of mixing water per unit volume of concrete and the ratio of fine aggregate (sand) to total aggregate by absolute volume are to be estimated from table below as applicable. Depending upon the nominal maximum size and type of aggregate.
IS Method of Mix Design
Approximate Sand and water Content per Cubic Metre of Concrete for Grades up to M 35 W/C = 0.6 Workability= 0.8 C.F
Nominal Maximum size of aggregate (mm) Water Content per cubic metre of concrete (kg) Sand as percentage of total aggregate by absolute volume
10 208 40
20 186 35
40 165 30
IS Method of Mix Design
Approximate Sand and Water Content per cubic metre of concrete for grades above M 35 W/C = 0.35 Workability= 0.8 C.F.
Nominal Maximum size of Aggregates Water Content per cubic metre of concrete (kg) Sand as percentage total aggregate by absolute volume of (%)
10 200 28
20 180 25
IS Method of Mix Design
Adjustment of values in water content and sand percentage for other conditions
Change in Condition Adjustment Required
Water Content Percentage sand in total aggregate
For sand confirming to grading Zones I , III and IV 0 + 1.5 percent for zone I
-1.5 percent for zone III
-3.0 for zone IV
Increase or decrease in values of compacting factor by 0.1 Â± 3 % 0
Each 0.05 increase or decrease in free water cement ratio 0 Â± 1 %
-15 kg/m 3 -7 %
For rounded aggregates
Calculation of Cement Content
The cement content per unit volume of concrete may be calculated from the free water-cement ratio obtained in step- 2, and the quantity of water per unit volume of concrete obtained in step-4
The cement content so obtained should be checked against the minimum cement content for the requirement of durability as per table 5 IS 456:2000 and the greater of the two value is adopted.
Step -6 Calculation of Aggregate Content
With the quantities of water and cement per unit volume of concrete and the ratio of fine to total aggregate already determined, the total aggregate content per unit volume of concrete may be calculated from the following equations
V= [ W + C + 1 x fa ] x 1 for fine aggregate â¦â¦â¦â¦â¦â¦â¦â¦â¦â¦1
Sc p Sfa 1000
And
V = [ W + C + 1 x Ca ] x 1 for coarse aggregate â¦â¦â¦â¦..2
Sc (1-p) Sca 1000
Step -6 Calculation of Aggregate Content
Where,
V= Absolute volume of fresh concrete (m3)
W= Mass of Water (kg) per m3 of concrete
C= Mass of Cement (Kg) per m3 of concrete
Sc= Specific gravity of cement say 3.15
P= ratio of fine aggregate to total aggregate by absolute volume
Fa and Ca = Total masses of fine aggregate and coarse aggregate (kg) / m3 of concrete mass respectively
Sfa, Sca= Specific gravities of saturated surface dry fine aggregate and coarse aggregate respectively
Normally Sfa= 2.6 and Sca= 2.7
Trial Mixes
The Calculated mix proportions shall be checked by means of trial batches. The quantity of material should be sufficient for at least three 150 mm size cube concrete specimens
Example
Using I.S Method design a concrete mix for reinforced concrete structure for the following requirement.
Design data
Characteristic compressive strength= 20 N/mm 2
Maximum size of aggregates= 20 mm (angular)
Degree of workability= 0.9 CF
Degree of quality Control= Good
Type of exposure= Mild
Example
Test data for Material
Cement used= Ordinary Portland cement of grade 43 with 28 days strength 51 N/mm2
SG= 3.15
Bulk Density = 1450 kg/m3
Aggregate Fine Aggregate Coarse Aggregate
SG 2.66 2.75
Bulk Density 1700 1800
Water absorption 1 0.5
Free Moisture 2 Nil
Example
Step-I Target Mean Strength
Fck= fck + ts
fck= 20 N/mm2
T= 1.65
S= 4 from table 9.5 for M 20
Therefore
Fck= 20 + 1.65 x 4
= 26.6 N/mm2 (Mpa)
Example
Step-II
Selection of Water Cement Ratio
From the fig the free water cement ratio required for the target mean strength of 26.6 N/ mm2 is 0.5
From fig, for 28 days strength of cement 51 N/mm2, for curve D the free water cement ratio is 0.52
From table the maximum free water cement ratio for mild exposure is 0.55
Hence the free water cement ratio is taken as the minimum of above three values i.e. w/c = 0.5
Example
Step âIII
Estimation of Air Content
For maximum Size of aggregate of 20 mm, the air content is taken as 2 %
Example
Step-4 Selection of water and Sand Content
From table 9.7 for 20 mm nominal maximum size aggregate and sand confirming to grading zone âII water content per cubic metre of concrete = 186 kg and sand content as percentage of total aggregate by absolute volume= 35 %
Water= 186 kg/m3 of concrete
Sand= 35 % of total aggregate by absolute volume
Example
For change in values in water cement ratio, compaction factor and sand belonging to zone III the following adjustments required.
Change in Condition Water Content Percentage Sand in total aggregate
For Decrease in water cement ratio
(0.6-0.5) that is 0.1
0.1 x 1 = 2.0
0.05 0 -2.0
For increase in compacting factor (0.9 -0.8) = 0.1
0.1 x 3 = 3
0.1 + 3 0
For Sand conforming to Zone III 0 -1.5
+3 -3.5
Example
Required Water Content = 186 + ( 186 x 3 / 100)
= 186 + 5.58
= 191.6 lit /m3
= required sand content as percentage of total aggregate by absolute volume= 35 â 3.5
= 31.5 %
Example
Determination of Cement Content
Water Cement ratio= 0.5
Water = 191.6 lit= 191.6 kg
Therefore W/c = 0.5
191.6 = 0.5
C
C=383.4 kg/m3
= 383kg/m3 > 300 kg / m3 therefore O.K.
Example
Determination of fine and coarse Aggregates
Consider volume of Concrete= 1 m3
But entrapped air in wet concrete = 2 %
Therefore volume of fresh concrete= 1 â 2
100
1- 0.02
V= 0.98 m3
Example
With the quantities of water and cement per unit volume of concrete and the ratio of fine to total aggregate already determined, the total aggregate content per unit volume of concrete may be calculated from the following equations
V= [ W + C + 1 x fa ] x 1 for fine aggregate â¦â¦â¦â¦â¦â¦1
Sc p Sfa 1000
0.98 = [ 191.6 + 383 + 1 + fa ] x 1
3.15 0.315 2.66 1000
980 = 313.187 + 1.19 fa
fa= 558.75 kg mass of F.A
Example
And
V = [ W + C + 1 x Ca ] x 1 for coarse aggregate â¦â¦â¦â¦..2
Sc (1-p) Sca 1000
0.98 = [ 191.6 + 383 x 1 x Ca ] x 1
3.15 (1-0.315) 2.75 1000
980 = 313.187 + 0.5308 Ca
Ca= 1256.24 kg mass of C.A
Example
Water Cement F.A C.A
191.6 li 383 kg 558.75 kg 1256.24 kg
0.5 1 1.46 3.28
Water Cement F.A C.A
383 = 0.264 m 3
1450 558.75 = 0.328 m 3
1700 1256.24 = 0.698 m 3
1800
0.5 1.0 1.242 2.644
Example
Water Cement F.A C.A
25 li 50 kg 73 kg 164 kg
Example
Design a Concrete mix for M 25 grade as per IS 10262 for the following data:
Characteristic Compressive Strength in the field at 28 days 25 N/mm2
Maximum Size of Aggregate= 20 mm
Degree of Workability 0.9 CF
Degree of Quality Control= Good
Type of Exposure = Moderate
Example
Test data for Material
Cement Used : Ordinary Portland Cement of Grade 33 satisfying the requirement of IS: 269-1989
Specific Gravity of Cement: 3.15
Specific Gravity;
Coarse Aggregate=2.65
Fine Aggregate= 2.6
Water absorption
Coarse Aggregate 0.6 %
Fine aggregate= 1.2 %
Free moisture
Coarse aggregate Nil
Fine aggregate 2 %
CA conform to table 2 of IS 383-1970 FA is natural river Sand Confirming to Zone I of Table 383-1970
Example
Step-I
Target mean Strength of Concrete
Fck= fck + ts
fck= 25 N/mm2
T= 1.65 from table 9.4
S= 4.0 from table 9.5 for M 25 grade of concrete
Fck= 25 + 1.65 x 4
= 31.6 N/mm2
Example
Step-2
Selection of Water-Cement Ratio
From fig 9.1 the free water cement ratio required for the target mean strength of 31.6 N/mm 2 is 0.44
Now, from table 5.4 the maximum free water cement ratio for moderate exposure is 0.5
Hence, the free water cement ratio is taken as the minimum of above two value i.e
W= 0.44
C
Example
Step III Estimation of air Content
For maximum Size of Aggregate of 20 mm, the air content is taken as 2.0 %
Example
Step-4
Selection of Water and Sand Content
From table 9.7 for 20 mm nominal maximum size aggregates and sand confirming to grading Zone-II, water content per cubic metre of concrete = 186 kg and sand content as percentage of total aggregate by absolute volume = 35 % i.e.
Water = 186 kg/m3
Sand = 35 % of total aggregate by absolute Volume.
Example
For Change in values in water-Cement ratio, compaction factor and sand belonging to zone I the following adjustments are required.
Change in Condition Adjustment Required
Water Content Percentage Sand in total Aggregate
For Decrease in Water-Cement ratio (0.6 â 0.44) that is 0.16
Therefore 0.16 x 1 = 3.2
0.05 0 -3.2
(ii) For Increase in Compacting factor (0.9 -0.8)= 0.1
Therefore 0.1 x 3 = 3.0
0.1 +3 0
(iii) For Sand Conforming to Zone-I of table 4 of IS 383-1970 0 +1.5
Example
Required water Content = 186 + ( 186 x 3 )
100
= 191.6 lit / m3
Required Sand Content as Percentage of Total aggregate by absoluter Volume
p= 35 â 1.7
= 33.3 %
Example
Step- V Determination of Cement Content
Water Cement Ratio = 0.44
Water = 191.6 lit = 191.6 kg
Therefore,
W= 0.44
C
191.6 = 0.44
C
C= 435.45 kg/m3 > 300 kg /m3
This cement content is adequate for âModerate Exposureâ condition, according to table 5 IS 456-2000)
Example
Determination of fine and Coarse content:
Consider volume of concrete = 1 m3
But, entrapped air in wet concrete= 2 %
Therefore, absolute volume of fresh concrete= 1 â 2
100
= 1 â 0.02
V= 0.98 m3
Therefore,
Example
V= [ W + C + 1 x fa ] x 1 for fine aggregateâ¦1
Sc p Sfa 1000
And
0.98= [ 191.6 + 436 + 1 + fa ] x 1
3.15 0.33 2.6 1000
980 = 191.6 + 138.41 + 1.15 fa
fa= 562.76 kg
= 563 kg mass of F.A.
Example
Similarly,
V = [ W + C + 1 x Ca ] x 1 for coarse aggregateâ¦â¦..2
Sc (1-p) Sca 1000
0.98 = [ 191.6 + 436 x 1 x Ca ] x 1
3.15 (1-0.333) 2.65 1000
980 = 191.6 + 138.41 + 0.5657 Ca
Ca= 1149 kg/m3 mass of C.A.
Example
Mix Proportions (By Mass)
Water Cement F.A. C.A
191.6 li 436 kg 563 kg 1149 kg
0.44 1 1.29 2.64
Example
Water Cement F.A. C.A
22 li 50 kg 64.5 kg 132 kg
Example
Step 8 Adjustment for water absorption and free surface moisture in F.A. and C.A
For water Cement ratio of 0.44 quantity of water required = 22 lit
C.A absorbs 0.6 % of water by mass
Therefore extra quantity of water to be added
0.6 x 132 = 0.792 lit (+)
100
F.A contains 2 % free moisture by mass
Quantity of water to be deducted
= 2 x 64.5 = 1.29 (-)
100
Actual quantity of water to be added
= 22 + 0.792 â 1.29
= 21.5 lit
Example
Actual quantity of sand (FA) required after allowing for mass of free water
= 64.5 + 1.29 = 65.79 kg
Actual quantity of C.A required
= 132 - 0.792
= 131.21 kg
Water Cement F.A. C.A
21.50 li 50 kg 65.79 kg 131.21 kg
Example
Design a concrete mix from the following data by I.S. method
Target mean Strength= 35 N/mm2
Maximum Size of Aggregate = 20 mm
W/C ratio = 0.43
Water required per m3 of concrete= 190 kg
Sand as percentage of total aggregate by absolute Volume = 35 %
Entrapped air in concrete= 2 %
Sp gravity of Cement= 3.15
Sp gravity of fine aggregate= 2.6
Sp gravity of Coarse aggregate.= 2.7
Example
Step-I Target mean Strength
Fck=35 N/mm2
Step-II Selection of Water-Cement Ratio:
W/C ratio = 0.43
Step-III Estimation of air Content
Entrapped air = 2 %
Step-IV
Selection of water and sand Content
Quantity of water per m3 of concrete = 190 kg
Sand Content = 35 % of total aggregate by absolute Volume
Example
Step-V
Cement Content
Water-Cement Ratio = 0.43
Water = 190 kg
W = 0.43
c
190 = 0.43
C
C= 441 .86 kg/m3
Example
Determination of F.A and C.A Content
Consider Volume of Concrete = 1 m 3
But, entrapped air = 2 %
Therefore Absolute Volume of press Concrete
V= 1 â 2
100
V= 0.98 m3
Example
V= [ W + C + 1 x fa ] x 1 for fine aggregate â¦â¦â¦â¦â¦â¦1
Sc p Sfa 1000
0.98 = [ 190 + 442 + 1 + fa ] x 1
3.15 0.35 2.6 1000
0.98 = [ 190 + 140.32 + 1.098 fa] x 1
1000
fa= 591.69 kg/m3
fa= 592 kg/m3 Mass of FA
Example
Similarly,
V = [ W + C + 1 x Ca ] x 1 for coarse aggregateâ¦â¦..2
Sc (1-p) Sca 1000
0.98 = [ 190 + 442 x 1 x Ca ] x 1
3.14 (1-0.35) 2.7 1000
980 = 190 + 140.32 + 0.569 Ca
Ca= 1142 kg/m3 Mass of CA
Example
Mix Proportion (by mass)
Quantity for 1 bag of Cement
Water Cement F.A C.A
190 442 592 1142
0.43 1 1.34 2.58
Water Cement F.A C.A
21.5 50 67 129
The ACI Method of Mix Design
In the USA the method suggested by ACI is widely used. It has the advantages of simplicity in that it applies equally well, and with more or less identical procedure to rounded or angular aggregate, to normal or lightweight aggregate and to air-entrained or non-air-entrained concretes.
The ACI method is based on the fact that for a given size of well graded aggregates water content is largely independent of mix proportions, i.e. Water content regardless of variation in water/cement ratio and cement content.
The ACI Method of Mix Design
This method assumes that the optimum ratio of the bulk volume of coarse aggregates and on the grading of fineness aggregates regardless of shape of particles. This method also assumes that even after complete compaction is done, a definite percentage of air remains which is inversely proportional to the maximum size of aggregate.
The ACI Method of Mix Design
The steps by steps operation in the ACI method are
Step-1 Data to be collected
Fineness modulus of FA
Unit weight of dry CA
Specific gravity of FA and CA saturated surface dry condition.
Specific gravity of Cement
Absorptions characteristics of both CA and FA
The ACI Method of Mix Design
Step-2
Calculation mean design Strength, from the minimum strength specified, using standard deviation:
fm= fmin + K.S
Where,
F m= Specified minimum strength (Characteristic Strength)
K= Constant dependency upon the probability of certain no of results likely to fall fck= taken from table 9.4
S= Standard Deviation from table 9.5
IS Method of Mix Design
The ACI Method of Mix Design
Step-3 Estimation of Water-Cement Ratio
Water Cement ratio is estimated from table 9.10 for the mean design Strength.
The ACI Method of Mix Design
Average Compressive Strength at 28 days Effective Water-Cement Ratio (By Mass)
Non-Air Entrained Concrete
Air-entrained Concrete
45 0.38 -
40 0.43 -
35 0.48 0.4
30 0.55 0.46
25 0.62 0.53
20 0.7 0.61
15 0.8 0.71
The ACI Method of Mix Design
The water Cement ratio obtained from Strength point of view is to be checked against maximum W/C Ratio given for special exposure condition given in table 9.11 and minimum of the two is to be adopted.
The ACI Method of Mix Design
Requirement of ACI for W/C Ratio and Strength for Special Exposure Condition
Exposure Condition Maximum W/C ratio, normal density aggregate concrete Minimum Design Strength, low Density aggregate Concrete, MPA
Concrete Intended to be Watertight
Exposed to fresh Water
Exposed to brackish or sea Water 0.5
0.45 25
30
Concrete Exposed to freezing and Thawing in a moist Condition:
(a) Kerbs, gutters, guard rails or thin sections 0.45 30
Other elements 0.5 25
In presence of de-icing chemicals 0.45 30
For corrosion protection of reinforced concrete exposed to de-icing salts, brackish water, sea water or spray from the sources. 0.4 30
The ACI Method of Mix Design
Decide maximum size of aggregate to be Used. Generally RCC work 20 mm and Pre-stressed Concrete 10 mm Size are Used
Decide Workability in terms of slump for the type of job in hand. General guidance can be taken from table 9.12.
The ACI Method of Mix Design
Type of Construction Range of slump mm
Reinforced foundation walls and footings 20-80
Plain footing, cassions and substructure wall 20-80
Beams and Reinforced Wall 20-100
Building Column 20-100
Pavement and Slabs 20-80
Mass Concrete 20-80
The ACI Method of Mix Design
Step-4 Minimum Water Content and entrapped air content:
Decide maximum size of aggregate to be used. Generally for RCC work 20 mm and for pre-stressed concrete 10 mm size are used.
Decide workability in terms of slump for the type of job in hand. Recommended value of slump for various types of construction as given in table 9.12
The ACI Method of Mix Design
Step-5 Cement Content
Cement Content is computed by dividing the water content by the water/ Cement Ratio
Step-6
Bulk Volume of Dry Rodded Coarse Aggregate per Unit Volume of Concrete
Table 9.13 for a decided value of slump and maximum size of aggregate, decide the mixing water content and entrapped air content.
Table 9.13
Workability Water Content, kg/m 3 of Concrete for indicated maximum aggregate Size
Non- air entrained Concrete
Workability 10 mm 12.5 mm 20mm 25 mm 40 mm 50 m 70 mm 150 mm
Slump 30-50 mm 205 200 185 180 160 155 145 125
80-100 mm 225 215 200 195 175 170 160 140
150-180 mm 240 230 210 205 185 180 170 -
Approx entrapped air content 3 2.5 2 1.5 1 0.5 0.3 0,2
Table 9.13
Workability Water Content, kg/m 3 of Concrete for indicated maximum aggregate Size
Air entrained Concrete
Workability 10 mm 12.5 mm 20mm 25 mm 40 mm 50 m 70 mm 150 mm
Slump 30-50 mm 180 175 165 160 145 140 135 120
80-100 mm 200 190 180 175 160 155 150 135
150-180 mm 215 205 190 185 170 165 160 -
Table 9.13
Workability Water Content, kg/m 3 of Concrete for indicated maximum aggregate Size
Air entrained Concrete
Workability Water Content, kg/m 3 of Concrete for indicated maximum aggregate Size
Air entrained Concrete
10 mm 12.5 mm 20mm 25 mm 40 mm 50 m 70 mm 150 mm
Slump 30-50 mm 180 175 165 160 145 140 135 120
80-100 mm 200 190 180 175 160 155 150 135
150-180 mm 215 205 190 185 170 165 160 -
Recommended air Content
Mild Exposure 4.5 4 3.5 3.0 2.5 2.0 1.5 1.0
Moderate Exposure 6.0 5.5 5.0 4.5 4.5 4.0 3.5 3.0
Extreme Exposure 7.5 7.0 6.0 6.0 5.5 5.0 4.5 4.0
The ACI Method of Mix Design
Knowing the values of maximum size of coarse aggregates and fineness modulus (FM) of fine aggregate, bulk volume of dry rodded aggregate per unit volume of concrete is selected from table 9.14
Dry Bulk of Coarse Aggregate per unit Volume of Concrete as Given by ACI
Maximum Size of Aggregate Bulk Volume of Dry Rodded Coarse Aggregate per unit volume of concrete for fineness modulus of sand
FM 2.4 2.6 2.8 3.0
10 0.5 0.48 0.46 0.44
12.5 0.59 0.57 0.55 0.53
20 0.66 0.64 0.62 0.6
25 0.71 0.69 0.67 0.65
40 0.75 0.73 0.71 0.69
50 0.78 0.76 0.74 0.72
70 0.82 0.8 0.78 0.76
150 0.87 0.85 0.83 0.81
The value given will produce a mix that is suitable for reinforced concrete construction. For less workable concrete the value may be increased by 10 percent for workable concrete such as pumpable concrete the value may be reduced by upto 10 percent
From the minimum strength specified estimate the average design strength either by using coefficient of variation
Find the water/cement ratio from the table 9.14
The ACI Method of Mix Design
Step-7
The weight of CA per cubic metre of Concrete is Calculated by multiplying the bulk Volume with bulk density of CA
Step-8 Estimate of Density of fresh Concrete
Knowing the maximum Size of Coarse Aggregates, the density of fresh Concrete is estimated as
The ACI Method of Mix Design
First Estimate of Density of Fresh Concrete as Given by ACI
Maximum Size of Aggregates Non air-entrained air kg/m3 Airentrained kg/m3
10 2285 2190
12.5 2315 2235
20 2355 2280
25 2375 2315
40 2420 2355
50 2445 2375
70 2465 2400
The ACI Method of Mix Design
Step-9
Absolute volumes of ingredients per cubic metre of concrete are obtained by knowing the specific gravity of cement, water CA and FA
Step- 10
Trial mix proportions are calculated and adjustments for field conditions like free moisture and water absorption by aggregates are made.
Step-11
A trial mix is then made to study the properties of concrete in respect of workability, cohesiveness, finishing quality and 28 days compressive strength. The proportion of CA and FA may be changed to get desired properties.
Example-I
Design a Concrete mix Using ACI method for a multi-Storied building for the following data
28 days characteristic Compressive Strength= 30 Mpa
Type of Cement Available= Ordinary Portland Cement
Desired Slump= 80-100 mm
Maximum Size of aggregate = 20 mm
Standard Deviation from past Records = 4.5 Mpa
Specific Gravities for FA= 2.65
Specific Gravity for CA= 2.7
For Cement= 3.15
Bulk density of CA= 1600 kg/m3
Fineness modulus of FA= 2.8
CA absorbed 1 % moisture and sand
Contains 1.5 % free surface moisture
Assume any other data
Example-I
Solution
Step-I
Mean Design Strength
fm= fmin + K.S
= 30 + 1.65 x 4.5
= 37.425 Mpa
From table 9.4
Assume 5 % of test results are expected fall
K= 1.65
Example-I
Step-II
Estimation of Water-Cement Ratio
From table 9.1 for mean design strength of 37.425 Mpa, the estimated W/C ratio is 0.45
From table 9.11, for exposure condition âconcrete intended to be watertight and exposed to fresh waterâ, the maximum
w/C ratio is 0.5
Hence adopt a water cement ratio of 0.45
The ACI Method of Mix Design
Average Compressive Strength at 28 days Effective Water-Cement Ratio (By Mass)
Non-Air Entrained Concrete
Air-entrained Concrete
45 0.38 -
40 0.43 -
35 0.48 0.4
30 0.55 0.46
25 0.62 0.53
20 0.7 0.61
15 0.8 0.71
Exposure Condition Maximum W/C ratio, normal density aggregate concrete Minimum Design Strength, low Density aggregate Concrete, MPA
Concrete Intended to be Watertight
Exposed to fresh Water
Exposed to brackish or sea Water 0.5
0.45 25
30
Concrete Exposed to freezing and Thawing in a moist Condition:
(a) Kerbs, gutters, guard rails or thin sections 0.45 30
Other elements 0.5 25
In presence of de-icing chemicals 0.45 30
For corrosion protection of reinforced concrete exposed to de-icing salts, brackish water, sea water or spray from the sources. 0.4 30
Example-I
Mixing water content and entrapped air content
Maximum size of aggregates = 20 mm
Desired Slump= 80-100
Therefore from table 9.13
Mixing water Content = 200 kg/m3 of Concrete
Entrapped air Content = 2 %
Table 9.13
Workability Water Content, kg/m 3 of Concrete for indicated maximum aggregate Size
Non- air entrained Concrete
Workability 10 mm 12.5 mm 20mm 25 mm 40 mm 50 m 70 mm 150 mm
Slump 30-50 mm 205 200 185 180 160 155 145 125
80-100 mm 225 215 200 195 175 170 160 140
150-180 mm 240 230 210 205 185 180 170 -
Approx entrapped air content 3 2.5 2 1.5 1 0.5 0.3 0,2
Table 9.13
Workability Water Content, kg/m 3 of Concrete for indicated maximum aggregate Size
Air entrained Concrete
Workability 10 mm 12.5 mm 20mm 25 mm 40 mm 50 m 70 mm 150 mm
Slump 30-50 mm 180 175 165 160 145 140 135 120
80-100 mm 200 190 180 175 160 155 150 135
150-180 mm 215 205 190 185 170 165 160 -
Table 9.13
Recommended air Content
Mild Exposure 4.5 4 3.5 3.0 2.5 2.0 1.5 1.0
Moderate Exposure 6.0 5.5 5.0 4.5 4.5 4.0 3.5 3.0
Extreme Exposure 7.5 7.0 6.0 6.0 5.5 5.0 4.5 4.0
Example-I
Step-4
Cement Content
W/C ratio = 0.45
200 = 0.45
C
C= 445 kg/m3
Water = 200 kg/m3 of concrete
Example-I
Step-5
Bulk Volume of Dry Rodded CA:
Maximum Size of CA= 20 mm
Fineness modulus of FA= 2.8
Therefore table 9.14
The bulk volume of dry rodded CA is 0.62 per unit volume of Concrete
Maximum Size of Aggregate Bulk Volume of Dry Rodded Coarse Aggregate per unit volume of concrete for fineness modulus of sand
FM 2.4 2.6 2.8 3.0
10 0.5 0.48 0.46 0.44
12.5 0.59 0.57 0.55 0.53
20 0.66 0.64 0.62 0.6
25 0.71 0.69 0.67 0.65
40 0.75 0.73 0.71 0.69
50 0.78 0.76 0.74 0.72
70 0.82 0.8 0.78 0.76
150 0.87 0.85 0.83 0.81
The value given will produce a mix that is suitable for reinforced concrete construction. For less workable concrete the value may be increased by 10 percent for workable concrete such as pumpable concrete the value may be reduced by upto 10 percent
From the minimum strength specified estimate the average design strength either by using coefficient of variation
Find the water/cement ratio from the table 9.14
Example-I
Step-6
Weight of CA = 0.62 x 1600
= 992 kg/m3
Therefore density of CA is 1600 kg/m3
Example-I
Step-7
Dry density of fresh Concrete
For maximum Size of CA = 200 mm and non air entrained Concrete,
From table 9.15 dry density of fresh Concrete
= 2355 kg/m3
Example-I
Step-8
Mass of all the known Ingredient of Concrete
Mass of water= 200 kg/m3
Mass of Cement= 445 kg/m3
Mass of CA= 992 kg/m3
Mass of FA = 2355-[ 200 + 445 + 992]
= 718 kg/m3
Example-I
Sr.no Ingredient Mass, kg/m3 Absolute Volume m3
1 Cement 445 445 = 0.141 m3
3.15 x 1000
2 Water 200 200= 0.2 m3
1 x 1000
3 CA 992 992 = 0.367 m3
2.7 x 1000
4 Entrapped Air 2 % 2 x 1 = 0.02 %
100
Total Absolute Volume 0.728 m3
Hence, Volume of FA required = 1-0.728
= 0.272 m 3
Mass of FA = 0.272 x 2.65 x 1000
= 720.8 kg/m 3
Adopt mass of FA = 720.8 kg/m 3
= 721 kg/m 3
Estimated quantities of material per cubic metre of concrete are
Cement= 445 kg
FA= 721 kg
CA= 992 kg
Water= 200 kg
Total 2358 kg/m3 of Concrete
Example-I
Density of fresh Concrete is 2358 kg/m3 as against 2355
Water Cement F.A C.A
200 445 kg 721 kg 992 kg
0.45 1 1.62 2.23
Water Cement F.A C.A
22.5 kg 50 kg 81 kg 111.5
Example-I
Adjustment for water absorption and free surface moisture
F.A Contains 1.5 % free surface moisture
Total surface moisture of FA = 1.5 x 721
100
= 10.82 kg (-)
Mass of FA in field condition = 721 + 10.82
= 731.83 kg/m3
Say 732 kg/m3
CA absorbs 1 % of moisture,
Quantity of water absorbed by CA = 1 x 992
100
= 9.92 kg (+)
Therefore mass of CA in field Condition = 992 â 9.92
= 982 kg/m3
Example-I
Net Quantity of Mix Water = 200 -10.82+ 9.92
= 199.10 kg
Final mix proportions (for 1 m3 of concrete)
Water Cement F.A. C.A.
199.10 kg 445 kg 732 kg 982 kg
The British Method
The traditional British method has been replaced by the department of the environment for normal mixes, known as DOE(British) mix design method.
The following steps are Involved in DOE Method
Step-I
Find the target mean strength from the specified Characteristic Strength
ft= fck + k.S
Where,
ft= target mean strength
fck= characteristic Strength
S= Standard Deviation
K= risk factor or probability factor
CONCRETE MIX DESIGN
Step-II
Determination of free water cement ratio
From the given type of cement and aggregate, obtain the compressive strength of concrete corresponding to free w/c ratio of 0.5
Type of Cement Type of Coarse Aggregate 3 7 28 91
Ordinary or Sulphate Resisting Cement Uncrushed
Crushed
22
27 30
36 42
49 49
56
Rapid Hardening Portland Cement Uncrushed
Crushed 29
34 37
43 48
55 54
61
CONCRETE MIX DESIGN
Now adopt the pair of data i.e. compressive strength read from table 9.16 and w/c ratio mark point âPâ. Through this point draw a dotted curve parallel to neighbouring curve. Using this new curve we read the w/c ratio as against target strength ft calculated in step 1
Check this w/c ratio for durability considerations and adopt the lower value
Minimum grade 30 35 40 45 50
Maximum w/c ratio 0.65 0.6 0.55 0.5 0.45
Maximum cement content 275 300 325 350 400
CONCRETE MIX DESIGN
Fig.1 Relation between compressive strength and free water cement ratio
mark a point corresponding to strength f1, at water cement ratio 0.5.
draw a curve parallel to the nearest curve, through this point
Using the new curve,
Read off ( abscissa) the water cement ratio
corresponding to the target mean strength (ordinate)
Free water-cement ratio
CONCRETE MIX DESIGN
Step-3
Determination of water Content
Depending upon the type and maximum nominal size of aggregate and workability the water content is estimated as
W= 2 W fa + 1 W ca
3 3
Where,
W fa= free water content appropriate to the type of fine aggregate
W ca= free water content appropriate to the type of coarse aggregate
CONCRETE MIX DESIGN
Level of Workability Very Low Low Medium High
Description Slump 0-10 10-30 30-60 60-180
Vee-bee >12 12-6 6-3 3-0
Compaction Factor 0.75- 0.85 0.85-0.9 0.9- 0.93 >0.93
Maximum Size of Agg Type of aggregate Water Content
10 mm Uncrushed 150 180 205 225
Crushed 180 205 230 250
20 Uncrushed 135 160 180 195
Crushed 170 190 210 225
40 Uncrushed 115 140 160 175
Crushed 155 175 190 205
CONCRETE MIX DESIGN
Reduction in water content when fly ash is Used
% of fly ash Reduction in Water content Kg/m3
10 5 5 5 10
20 10 10 10 15
30 15 15 20 20
40 20 20 25 25
50 25 25 30 30
CONCRETE MIX DESIGN
Step 4 - Determination of Cement Content
The Cement Content if the mix is calculated from the selected w/c ratio
Cement Content = water content
W/C ratio
CONCRETE MIX DESIGN
Step-5
Determination of aggregate Cement Ratio
Absolute volume occupied by the aggregate
= 1- Cement Content (kg) â Water Content (kg)
1000 x Sc 1000 x Sw
Where, Sc= Specific gravity of cement particles
Therefore Total aggregate content (kg/m3)
= absolute volume occupied by the aggregate x 1000x Sa
Where Sa= Specific gravity of aggregate
CONCRETE MIX DESIGN
Step-6 Determination of FA and CA
Depending on the free water cement ratio, the nominal maximum size of coarse aggregate, the workability and grading zone of fine aggregate is determined from fig 9.5 (a), 9.5 (b) and 9.5 (c)
Once the proportion of FA is obtained, multiplying by the weight of total aggregate gives the weight of fine aggregate. Then coarse aggregate is calculated as
Fine aggregate content = total aggregate content x proportion of fine aggregate
Coarse aggregate content = Total aggregate content â fine aggregate content
CONCRETE MIX DESIGN
Determination of FA and CA
Determination of FA and CA
FIG 3- Recommended proportion of fine aggregate as a function of free water âcement ratio
Proportion of Different sizes of CA
Aggregate 4.75- 10 mm 10-20 mm 20-40 mm
Type-I 33 67 -
Type-II 18 27 55
CONCRETE MIX DESIGN
Step-7
Determination of final Proportion
The proportion so worked out should be tried for their specified strength and suitable adjustment are made to obtain the proportion.
CONCRETE MIX DESIGN
Example
Design a Concrete mix Using, DOE Method for a reinforced Concrete Work for the following data:
Required Characteristic Compressive Strength= 35 Mpa at 28 days
Type of Cement Used= Sulphate Resisting Portland Cement
Desired Slump= 50 mm
Maximum Size of Aggregate= 20 mm
Type of Aggregate= Uncrushed
Specific Gravity = 2.65
Fine aggregate conforms to grade Zone III with percent passing 600 micron sieve being 70 %
Exposure Condition = Moderate
Standard Deviation= 5.0 Defective Rate= 5 %
CONCRETE MIX DESIGN
Example
Mix Design Without fly ash:
Target Mean Strength:
Ft= fck+ kS
fck= 35 N/mm 2
Standard Deviation= 5.0
K= 1.65
ft= 35 + 1.65 x 5
= 43.25 N/mm 2
CONCRETE MIX DESIGN
Example
Determination of free Water-Cement Ratio
For type of Cement Sulphate resisting Portland cement and uncrushed aggregate 28 days compressive strength from table 9.16 is 42 MPA
For Compressive Strength equal to 42 MPA and w/c ratio 0.5, mark âPâ in fig and draw a dotted curve parallel to the neighbouring curve Using this new curve again ft= 43.25 N/mm2 the W/C ratio is read as 0.48
From table 9.17 from durability point of view the maximum w/c ratio is 0.6
Hence Adopt the minimum w/c ratio as 0.48
CONCRETE MIX DESIGN
Example
Step-3
Determination of Water Content:
For Desired slump = 50 mm
Maximum size of CA= 20 mm
From table 9.18 water content is 180 kg/m3
CONCRETE MIX DESIGN
Example
Step-4 Determination of Cement Content:
W/C ratio obtained from step 2 is 0.48 and water is 180 kg/m3
W/C = 0.48
180 = 0.48
C
Therefore C= 375 kg/m3 of Concrete
This is satisfactory as it is greater than minimum Cement Content of 300 kg/m3
CONCRETE MIX DESIGN
Example
Step: 5
Aggregate Cement Ratio
Specific gravity of aggregate is 2.65
Therefore fig 9.4 wet density of concrete is 2400 kg/m3
Therefore mass of total aggregate
= 2400 â 180- 375
= 1845 kg/m3
Alternatively Volume occupied by aggregate
= 1- 375 â 180 = 0.7009 m3
100x 3.15 1000 x 1
Therefore total Aggregate Content
= 0.7009 x 1000 x 2.65
= 1875 kg/m3
CONCRETE MIX DESIGN
Example
Step-6 Determination of FA and CA Content
For, Maximum size of aggregate = 20 mm
Slump= 50 mm
Free W/C ratio = 0.48
Percent aggregate Passing
600 micron sieve = 70 %
From fig 9.5 (b) the proportion of fine aggregate i.s 30 %
Mass of FA = 30 x 1875 = 557 kg/m3
100
Mass of CA = 1875 â 557.1
= 1299.9 kg/m3
= 1300 kg/m3
CONCRETE MIX DESIGN
Example
Step 7
The estimated Quantity are:
Water Cement F.A C.A
180 kg 375 kg 557 kg 1300 kg
0.48 1 1.485 3.46
CONCRETE MIX DESIGN
Road Note No. 4
Method Of Mix Design
CONCRETE MIX DESIGN
By
Alok Damare
Anand Paul
Pushpender Biwal
155
ROAD NOTE No. 4 METHOD OF MIX DESIGN
Proposed by the Road Research Laboratory, UK (1950)
Introduction
In this method, the aggregate to cement ratios are worked out on the basis of type of aggregate, max size of aggregate and different levels of workability.
The relative proportion of aggregates is worked on basis of combined grading curves. This method facilitates use of different types of fine and coarse aggregates in the same mix.
The relative proportion of these can be easily calculated from combined grading curves.
The values of aggregate to cement ratio are available for angular rounded or irregular coarse aggregate.
CONCRETE MIX DESIGN
156
Procedure
The average compressive strength of the mix to be designed is obtained by applying control factors to the minimum compressive strength.
w/c ratio is read from compressive strength v/s w/c ratio graph.
Proportion of combined aggregates to cement is determined from tables, for maximum size 40 mm and 20 mm.
If the aggregate available differs from the standard grading, combine FA and CA so as to produce one of the standard grading.
The proportion of cement, water, FA and CA is determined from knowing the water/cement ratio and the aggregate/cement ratio.
Calculate the quantities of ingredients required to produce 1 m3 of concrete, by the absolute volume method, using the specific gravities of cement and aggregates.
CONCRETE MIX DESIGN
157
CONCRETE MIX DESIGN
158
Method In Detail
Find The Target Mean Strength
Concrete is designed for strength higher than characteristic strength
as a margin for statistical variation in results and variation in degree of
control exercised at site. This higher strength is defined as the target mean
strength.
Target mean strength = Characteristic strength + K * s
Method In Detail
158
Determine water/cement ratio
The relation between Target Mean Strength and water cement ratio
for different cement curves is given in IS 10262
CONCRETE MIX DESIGN
159
CONCRETE MIX DESIGN
160
Finding cement content
CONCRETE MIX DESIGN
161
The Relative Proportion Are Worked Out
A trial proportion is taken and combined gradation is worked out for e.g.
35% fine aggregate 20% 10mm down aggregate, 45% 20mm down aggregate.
CONCRETE MIX DESIGN
162
Combined gradation is plotted and pushed towards Ideal curve by increasing or decreasing the sand content
CONCRETE MIX DESIGN
163
Calculation Of Cement Content
Cement Content (Kg/m3) = Plastic density /(1+a/c ratio + w/c ratio)
If weight of cement is âCâ the total weight per m3 will be
C +1.45C + 0.75C +1.6C + 0.46C=5.26C
Drawbacks Of Road Note No. 4 Method
This method leads to very high cement contents and thus is becoming obsolete.
In many cases use of gap graded aggregate becomes unavoidable. In many parts of the country the practice is to use 20mm coarse aggregates without 10mm aggregates. This is because of quality of 10mm aggregates produced from jaw crusher is very poor .Gap grading does not fit in to the standard combined grading curves of RRL method.
Sand available in some parts of country is graded that it is high on coarse fraction (1.18mm and above) and low on fines (600micron and below). It is difficult to adjust the sand content to match any of the standard combined grading curves .The combined grading curve often cuts across more than one standard curves in such cases
CONCRETE MIX DESIGN
164
Different aggregate to cement ratios are given for different levels of workability ranging from low to high. But these levels of workability are not defined in terms of slump, compaction factor or Vee Bee time as in case of other methods.
The fine aggregate content cannot be adjusted for different cement contents. Hence the richer mixes and leaner mixes may have same sand proportion, for a given set of materials.
CONCRETE MIX DESIGN
165
References
Concrete Technology by: R.P. Rethaliya
Concrete Technology by . M.S. Shetty
Internet websites
http://www.foundationsakc.org/
166
Thanksâ¦
CONCRETE MIX DESIGN

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