advanced concrete technology 3

BUILDING TECHNOLOGY AND MANAGEMENT

CONCRETE MIX DESIGN

CONCRETE MAKING MATERIALS• Cement• Aggregates• Water• Admixtures

2CONCRETE MIX DESIGN

TYPES OF CONCRETE MIXES

1. NOMINAL MIXMixes of fixed proportions, IS:456-2000 permits nominal mixes for concretes of strength M20 or lower

2. DESIGN MIXDesigned on the basis of requirements of the concrete in fresh and hardened states.


TRIAL MIXESPrepared to verify whether the Design Mix would perform as per the assumptions. If appreciable variation exists, the available alternatives are:

1. directly employ the trial mix proportions at the site2. modify the trial mix proportions on the basis of intuition and employ

the revised proportions at the site3. prepare further trial mixes incorporating changes in the proportions

based on the feedback generated from the previous mix.


CONCRETE MIX DESIGNDEFINITION

“ Mix Design is the science of determining the relative proportions of

the ingredients of concrete to achieve the desired properties in the

most economical way.”

CONCRETE MIX DESIGN 5

PRINCIPLES OF MIX DESIGN1 The environment exposure condition for the structure

2 The grade of concrete, their characteristic strength’s and standard

deviations

3 The type of cement

4 The types and sizes of aggregates and their sources of supply

5 The nominal maximum sizes of aggregates

6 Maximum and minimum cement content in kg/m3

7 Water cement ratio

8 The degree of workability of concrete based on placing conditions


9 Air content inclusive of entrained air

10 The maximum/minimum density of concrete

11 The maximum/minimum temperature of fresh concrete

12 Type of water available for mixing and curing

13 The source of water and the impurities present in it.


CONCRETE MIX DESIGN 8IS 456:2000

FACTORS DEFINING THE CHOICE OF MIX PROPORTIONS

1. Compressive Strength2. Workability3. Durability4. Type, size and grading of aggregates5. Aggregate-cement ratio


COMPRESSIVE STRENGTHAbram’s Law

log F = log A1 – x log B1

where F is the compressive strength A1, B1 are constants and x is the w/c ratio by weight


WORKABILITY

“that property of freshly mixed concrete which determines the ease

and homogeneity with which it can be mixed, placed, consolidated and

finished.”

DURABILITY

“the resistance to weathering action due to environmental conditions

such as changes in temperature and humidity, chemical attack,

abrasion, frost and fire.”


METHODS OF CONCRETE MIX DESIGN1. American Concrete Institute Committee 211 method2. Bureau of Indian Standards Recommended method IS 10262-823. Road note No. 4 (Grading Curve) method4. Department Of Environment (DOE - British) method5. Trial and Adjustment Method6. Fineness modulus method7. Maximum density method8. Indian Road Congress, IRC 44 method


American Concrete Institute Method of Mix Design

(a) Data to be collected :(i ) Fineness modulus of selected F.A.(ii ) Unit weight of dry rodded coarse aggregate.(iii ) Sp. gravity of coarse and fine aggregates in SSD condition(iv ) Absorption characteristics of both coarse and fine aggregates.(v ) Specific gravity of cement.

(b) From the minimum strength specified, estimate the average design strength by using standard deviation.

(c) Find the water/cement ratio from the strength and durability points of view. Adopt the lower value.


(d) Decide the maximum size of aggregate to be used. Generally for RCC work 20 mm and pre-stressed concrete 10 mm size are used.

(e) Decide workability in terms of slump for the given job.

(f ) The total water in kg/m3 of concrete is determined, corresponding to the selected slump and selected maximum size of aggregate.

(g ) Cement content is computed by dividing the total water content by the water/cement ratio.

(h) Select the bulk volume of dry rodded coarse aggregate per unit volume of concrete, for the particular maximum size of coarse aggregate and fineness modulus of fine aggregate.


( j ) The weight of C.A. per cubic meter of concrete is calculated by multiplying the bulk volume with bulk density.

(k ) The solid volume of coarse aggregate in one cubic meter of concrete is calculated by knowing the specific gravity of C.A.

(l ) Similarly the solid volume of cement, water and volume of air is calculated in one cubic meter of concrete.

(m) The solid volume of FA is computed by subtracting from the total volume of concrete the solid volume of cement, CA, water and entrapped air.

(n) Weight of fine aggregate is calculated by multiplying the solid volume of fine aggregate by specific gravity of F.A.


ACI METHOD: DESIGN EXAMPLE

1 Design a concrete mix for the construction of an elevated water tank.

The specified design strength of concrete (characteristic strength) is 30

MPa at 28 days measured on standard cylinders. Standard deviation

can be taken as 4 MPa. The specific gravity of FA and C.A. are 2.65

and 2.7 respectively. The dry rodded bulk density of C.A. is 1600

kg/m3, and fineness modulus of FA is 2.80. Ordinary Portland cement

(Type I) will be used. A slump of 50 mm is necessary. C.A. is found to

be absorptive to the extent of 1% and free surface moisture in sand is

found to be 2 per cent. Assume any other essential data.


1 Mean Cylinder Compressive StrengthAssuming 5 per cent of results are allowed to fall below specified design strength,

The mean strength, fm= fmin + ks

= 30 + 1.64 x 4 = 36.5 MPa

2 Water/cement ratio Strength criteria Durability criteria



Strength Criteria


Durability Criteria


3 Mixing Water Content

Slump = 50 mm Maximum size of aggregate = 20 mm Concrete is non air-entrained


The mixing water content is 185 kg/m3 of concrete

The approximate entrapped air content is 2%.

The required cement content =185/0.47

= 394 kg/m3


4 Bulk Volume of C.A.

Maximum size of C.A = 20mm

Fineness Modulus of F.A. = 2.80

Find the dry rodded bulk volume of C.A.


The dry rodded bulk volume of C.A. = 0.62 per unit volume of concrete

The weight of C.A. = 0.62 x 1600

= 992 kg/m3


5 The first estimate of density of fresh concrete = 2355 kg/m3


The weight of all the known ingredients of

concrete

Weight of water = 185 kg/m3

Weight of cement = 394 kg/m3

Weight of C.A. = 992 kg/m3

Weight of F.A. = 2355 – (185 + 394 + 992)

= 784 kg/m3

6 Weight of FA


Alternatively, the weight of F.A. can be determined by the more

accurate absolute volume method

Absolute Volume = weight/(1000ρ) m3


Total absolute volume = 697 x 103 cm3

Absolute volume of F.A. = (1000 – 697) x 103

= 303 x 103

Weight of FA = 303 x 2.65

= 803 kg/m3


7 Estimated quantities of materials per cubic meter of concrete are:

Cement = 394 kg

F.A = 803 kg

C.A = 992 kg

Water = 185 kg


8 Proportions

C : F.A : C.A : water

394 : 803 : 992 : 185

1 : 2.04 : 2.52 : 0.47

Weight of materials for one bag mix

in kg = 50 : 102 : 126 : 23.5


9 The above quantities is on the basis that both F.A and C.A are in saturated and surface dry condition (SSD conditions).

FA has surface moisture of 2%

Total free surface moisture in FA = (2/100 x 803)

= 16.06 kg/m3

Weight of F.A in field condition = 803 + 16.06 = 819.06 kg/m3


Quantity of water absorbed by C.A. = (1/100 x 992) = 9.92 kg/m3

Weight of C.A in field condition = 992 – 9.92

= 982 kg/m3

C.A absorbs 1% water

Water contributed by F.A = 16.06 kg Water absorbed by C.A. = 9.92 kg Extra water contributed by aggs. = 16.06 – 9.92 = 6.14 kg Total water content = 185.00 – 6.14

= 179 kg/m3

Change in Water Content


Cement = 394 kg/m3

F.A. = 819 kg/m3

C.A. = 982 kg/m3

Water = 179 kg/m3

Field density of fresh concrete = 2374

kg/m3

Quantities of materials to be used in field, corrected for free surface moisture in F.A and absorption characteristic of C.A

2. A mix with a mean 28-day compressive strength of 35 MPa and a

slump of 50 mm is required, using OPC. The maximum size of well

shaped, angular aggregate is 20mm, its bulk density is 1600 kg/m3

and its specific gravity is 2.64. The available fine aggregate has a

fineness modulus of 2.60 and a specific gravity of 2.58. No air-

entrainment is required.


Water/Cement ratio

As durability criteria is not mentioned, consider strength alone


Strength Criteria

Water/cement ratio =0.48


Slump = 50 mm

Max size of aggregate = 20 mm

Determine water content

Composition of concrete (kg/m3)

Water = 185

Cement = 386

CA = 1020

FA = 738

Density of Concrete= 2329 (kg/m3)


ROAD NOTE No. 4 METHOD OF MIX DESIGNProposed by the Road Research Laboratory, UK (1950)

Procedure:

1. The average compressive strength of the mix to be designed is obtained by

applying control factors to the minimum compressive strength

2. Water/cement ratio is read from compressive strength v/s w/c ratio graph

3. Proportion of combined aggregates to cement is determined from tables,

for maximum size 40 mm and 20 mm

4. If the aggregate available differs from the standard gradings, combine FA

and CA so as to produce one of the standard gradings


5. The proportion of cement, water, FA and CA is determined from

knowing the water/cement ratio and the aggregate/cement ratio.

6. 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.


DRAWBACKS OF ROAD NOTE NO. 4 METHOD

1. Cannot be used directly for the design of air - entrained concrete

2. No recommendations for durability or strength, regarding the

water/cement ratio

3. The design tables refer to mixes in which the FA and CA are of the

same shape

4. In selecting aggregate/cement ratio, only 3 shapes of aggregates and 4

gradings are recommended.


DOE METHOD OF MIX DESIGN

Can be used for concrete containing fly ash.PROCEDURE1. Target mean strength is calculated2. Select water/cement ratio, from the type of cement and CA. Compare

this with the ratio from durability conditions.3. Decide the water content for required workability4. Compare the cement content with the minimum cement content value

and adopt the higher value5. Find out the total aggregate content6. Determine the proportion of FA using the appropriate FA% v/s CA

size graph, and find the weight of CA and FA7. Work out a trial mix.


BIS RECOMMENDED MIX DESIGN METHOD

The BIS recommended mix design procedure is covered in IS 10262-

82.

In line with IS 456-2000, the first revision IS 10262-2009 was

published, to accommodate some of the following changes:

• Increase in strength of cement

• Express workability in terms of slump, rather than the compacting

factor

• Extend the W/C ratio v/s compressive strength graph



Modifications in IS 10262-2009

MIX DESIGN BASED ON IS RECOMMENDATIONSBased on IS 10262:1982

Procedure:


1. Target mean strength for mix design:

fck* = fck + tS

where fck = characteristic compressive strength at 28 days

S = standard deviation t = a statistical value depending on the

risk factor.

2. Selection of Water/Cement ratio


3. Estimation of Entrapped Air


4. Selection of Water Content and Fine to Total Aggregate ratio


5. Calculation of Cement Content:

cement by mass = Water content/Water cement ratio

To be checked against the minimum cement content for the requirement of

durability and the greater of the two values to be adopted.


6. Calculation of aggregate content:


7. Actual quantities required for mix

Adjust the mix for deviations from assumed conditions


8. Check the calculated mix proportions

DESIGN EXAMPLE: BIS RECOMMENDED METHOD

Grade M20(a ) Design stipulations(i ) Characteristic compressive strengthrequired in the field at 28 days - 20 MPa(ii ) Maximum size of aggregate - 20 mm (angular)(iii ) Degree of workability - 0.90 compacting factor(iv ) Degree of quality control - Good(v ) Type of Exposure - Mild

(b) Test data for Materials(i ) Specific gravity of cement - 3.15(ii ) Compressive strength of cement at 7 days - Satisfies the requirement

of IS: 269–1989

(iii ) 1. Specific gravity of coarse aggregates - 2.60 2. Specific gravity of fine aggregates - 2.60

(iv ) Water absorption:1. Coarse aggregate - 0.50%2. Fine aggregate - 1.0%

(v ) Free (surface) moisture:1. Coarse aggregate - Nil2. Fine aggregate - 2.0%

Design Procedure

1. Target mean strength of concretefck* = fck + tS


fck = 20, t = 1.64 , S = 4

fck* = 26.6 MPa

2. Selection of Water/Cement Ratio


Durability Criteria: Mild Exposure Conditions


W/C ratio from strength considerations = 0.50

W/C ratio from durability considerations = 0.55

Adopt the lower value


3. Selection of water and sand content


Adjustments in Water and Sand Contents


4. Determination of cement content

Water-cement ratio = 0.50water = 191.6 kg/m3


Cement = 191.6/0.50 = 383 kg/m3

Is this satisfactory for ‘mild’ exposure condition?

5. Determination of coarse and fine aggregate contents

Specified max. size of aggregate = 20 mmCorresponding entrapped air = 2%


fa = 546 kg/m3,

Ca = 1188 kg/m3

Final Mix Proportions

Water Cement FA CA191.6 383 546 1188

0.50 1 1.425 3.10


CHARACTERISTICS OF MATERIALS

Cement – OPC – 43 grade

Fly Ash – Conforming to Part1 of IS 3812

GGBS – Conforming to Part1 of IS 12089

SILICA FUME – Conforming to Part1 of ACI 234R-06

Superplasticizer – Normal or retarding type (as required)

Satisfying the requirements of IS 9103

(approx. 1-2% by wt of cement)

FLY ASH

• Fly ash is finely divided residue resulting from the combustion of powdered coal and transported by the flue gases and collected by electrostatic precipitator.

• Fineness : 320 m2/kg.

• 10-25%

• Specific gravity : 1.9 to 2.55

GGBS

• is obtained by quenching molten iron slag (a by-product of iron and steel-making) from a blast furnace in water or steam, to produce a glassy, granular product that is then dried and ground into a fine powder.

• Fineness : 400 to 600 m2/kg.• 25-65%.• Specific gravity : 2.9

http://en.wikipedia.org/wiki/Slag

http://en.wikipedia.org/wiki/Blast_furnace

http://en.wikipedia.org/wiki/Glassy

Silica fume

• by-product of the silicon and ferrosilicon alloy production.• Specific gravity : 2.2• The size of cement particles may very from 0.5 to 100μ

and that of silica fume varies from 0.005 to 0.5μ• Silica fume is generally added from 5 to 25 %.• Fineness : 20,000 m2/kg.• Specific gravity : 2.2

AGGREGATES

Coarse Aggregate : 10 mm, 20 mm, 40 mm max. size

Fine Aggregate : Zone II Grading

(Natural or crushed stone)

Silt Content : 3% by weight, max. (natural sand)

Silt Content : 15% by weight, max. (crushed stone)

SUGGESTED STANDARD DEVIATION VALUES (As per IS 456) For Good Quality Control

Grade of Concrete Standard Deviation Value (N/mm2)

M 10M15 3.5M 20M 25 4.0M 30M 35M 40M 45M50M 55

5.0

WATER CEMENTITIOUS MATERIALS RATIO

W ratio to be estimated from Fig. 1, for the target 28-

C+F day compressive strength of concrete

53

47

42

37

33

2927

0

20

40

60

0.20 0.30 0.35 0.40 0.45 0.50 0.55 0.60

W/C+F (by wt.)

28-d

ay C

ompr

essi

ve s

treng

th o

f con

cret

e, M

Pa

TYPICAL RELATIONSHIP BEWTEEN W/C+F AND 28-DAY COMPRESSIVE STRENGTH OF

SUPERPLASTICISED FLYASH CONCRETE

Fig. 1

WORKABILITY OF CONCRETE

(i) Medium : 50 – 60 mm slump

(ii) High : 80 – 100 mm slump

ESTIMATION OF MIXING WATER AND SAND CONTENT (For sand grading: Zone II & crushed rock coarse aggregate**)

Slump, mm Max. size of aggregate

10 mm 20 mm 40 mm

50-60 200 190 180

80-100 210 200 190

Sand content*, % 40 35 30

* For sand of grading Zone I, (+) 1.5% sand

For grading Zone III, (-) 1.5% sand

** For rounded aggregate, the water requirement will be (-) 10 l/m3 of concrete

FINE AGGREGATE GRADINGS(% passing)

IS Sieve Designation

Grading Zone I

Grading Zone II

Grading Zone III

Grading Zone IV

10 mm 100 100 100 100

4.75 mm 90-100 90-100 90-100 95-100

2.36 mm 60-95 75-100 85-100 95-100

1.18 mm 30-70 55-90 75-100 90-100

600 micron 15-34 35-59 60-79 80-100

300 micron 5-20 8-30 12-40 15-50

150 micron 0-10 0-10 0-10 0-15

Note 1: For crushed stone sand, the permissible limit on 150 micron is increased to 20%.

Note 2: Fine aggregate conforming to Grading Zone IV should not be used in reinforced concrete, unless tests ascertain the suitability of proposed mix proportions.

FLY ASH CONTENT

Recommended replacement (% by wt.) : 15-25%

15-20% for good quality of fly ash:

i. Fineness : 320-400 m2/kg

ii. L.R. : 4.5-5.0 MPa

21-25% for very good quality of fly ash:

i. Fineness : > 400 m2/kg

ii. L.R. : > 5.0 MPa

TYPICAL GRADING OF CRUSHED SAND (CRUSHED STONE AGGREGATE)

IS Sieve Size

% passing (IS: 383)Grading Zone III

Grading Zone II

4.75 mm 99.2 90-100 90-100

2.36 mm 90.4 85-100 75-100

1.18 mm 66.2 75-100 55-90

600 micron 49.8 60-79 35-59

300 micron 31.8 12-40 8-30

150 micron 21.4* 0-10 0-10

75 micron 12.0

* IS: 383 permits upto 20% passing through 150 micron sieve

DURABILITY REQUIREMENT(As per IS 456) (For 20 mm MSA)

S. No.

Exposure Plain Concrete Reinforced ConcreteMinimum Cement Content

kg/m3

Minimum Free

Water Cement

Ratio

Minimum Grade of Concrete

Minimum Cement Content

kg/m3

Minimum Free

Water Cement

Ratio

Minimum Grade of Concrete

1 Mild 220 0.60 - 300 0.55 M 20

2 Moderate 240 0.60 M 15 300 0.50 M 253 Severe 250 0.50 M 20 320 0.45 M 30

4 Very severe

260 0.45 M 20 340 0.45 M 35

5 Extreme 280 0.40 M 25 360 0.40 M 40

For 10 mm MSA + 40 kg/m3

For 40 mm MSA - 30 kg/m3

AIR CONTENT OF CONCRETE

Max. size of aggregate (mm)

Entrapped Air (%)

40 1.0

20 2.0

10 3.0

ESTIMATION OF SAND CONTENT AND COARSE AGGREGATE CONTENT, KG PER CUBIC METER OF CONCRETE

V-Vol. of air = W + C + Quantity of Fly Ash + Quantity of Sand X 1

Sc Sp. Gr. of Fly Ash p x sp. gr. of sand 1000

V-Vol. of air = W + C + Quantity of Fly Ash + Quantity of coarse aggregate X 1

Sc Sp. Gr. of Fly Ash (1-p) x sp. gr. of c. aggregate 1000

V = 1 m3 concrete

W = Weight of water, kg/m3

C = Weight of cement, kg/m3

Sc = Sp. Gr. of OPC = 3.15

p = Proportion of sand (i.e. sand ratio)

Total aggregate

COARSE AGGREGATE GRADING (COMBINED) (As per IS 383)

IS sieve size (mm)

% passing for graded aggregate

40 mm MSA 20 mm MSA 10 mm MSA

40 95-100 100 -

20 30-70 95-100 100

10 10-35 25-55 95-100

4.75 0-5 0-10 27-36

2.36 - - 0-10

EXAMPLES ON COMBINED GRADING

EXAMPLE 1 (% passing)

Sieve size (mm)

Fraction I (20-10 mm)

Fraction II (Below 10 mm)

60% of Fraction I

+ 40% of

Fraction II

Desired grading

limit

40.0 100.0

20.0 93.0 100 55.8 + 40 = 95.8

95-100

10.0 3.4 80.12 2.0 + 32 = 32.2

25-55

4.75 0.12 2.60 0.07 + 1.04 = 1.1

0-10

EXAMPLE 2 (% passing)

Sieve size (mm)

Fraction I (20-10 mm)

Fraction II (Below 10 mm)

60% of Fraction I

+ 40% of

Fraction II

50% of Fraction I

+ 50% of

Fraction II

Desired grading

limit

40.0 100.0 - - - -

20.0 89.72 100 53.8 + 40 = 93.8

44.8 + 50 = 94.8

95-100

10.0 2.48 85.84 1.48 + 34.33 = 35.8

1.24 + 42.92 = 44.1

25-55

4.75 0.08 4.92 0.048 + 1.968= 2.01

0.04 + 2.46 = 2.5

0-10

DATA REQUIRED1. Grade of concrete

2. Desired workability of concrete (slump, mm)

3. Durability requirement – exposure condition

4. 28-day compressive strength of cement

5. Quality of superplasticiser (% water-reduction)

6. Data on Fly Ash:

• Fineness

• Lime reactivity

• Loss on ignition, %

7. Gradings of sand, coarse aggregate (different size fractions)

8. Sp. gr. of sand, coarse aggregate and fly ash

9. Water absorption (%) of sand and coarse aggregate

advanced concrete technology 3

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