Mix Design of Concrete

PROPERTIES OF CONCRETE

A good concrete should have three basic qualities : a) Strength b) Workability c) Durability

Table 1: Nominal Mixes As Per IS: 456-2000 (Fine Aggregate of Zone II As Per IS: 383- 1970) Grade of As per Mix ratio by wt concrete IS:383-1970 Cement Fine Coarse Max size of aggregat aggregat graded e e coarse aggregate M20 M20 M20

10 20 40

1 1 1

: : :

1.8 1.5 1.3

: : :

2.7 3.0 3.2

Max Max W/C cement ratio aggregate ratio by mass 0.60 0.60 0.60

Proportions by weight can be converted to proportions by volume, by dividing with the bulk density of the materials available for use at site. The bulk density of sand may be taken 1.44 Kg/lit

1:5 1:5 1:5

Table 2: Grades Of Concrete As Per IS:456-2000 Group

Grade Designation

Specified characteristic compressive strength of 150mm 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

DURABILITY OF CONCRETE •

A durable concrete is one that performs satisfactorily in the working environment under its anticipated exposure conditions during service.

•

Main characteristics influencing the durability of concrete is its permeability to ingress of water, oxygen, carbon dioxide, chloride, sulphate and other potentially deleterious materials.

•

Factors influencing durability include a) b) c) d) e) f)

The environment The cover to embedded steel The type and quality of constituent materials The cement content and water/cement ratio of the concrete Workmanship, to obtain full compaction and efficient curing The shape and size of the member

STATISTICAL PRINCIPLE For assessing the acceptance criteria of concrete on statistical principles a large number of cube test results are needed. At a given stage of construction, let the cube strength of ‘n’ samples be available. The strength of each sample is the average strength of 3 samples. The sampling is also done in a random manner. If the strength of ith sample Mean strength, fm Deviation of each sample from mean Standard deviation

= fi = Σ fi / n = (fm –fi ) = √Σ (fm –fi )2/(n-1)

The value of standard deviation will be low in case of good control and high in case of lax control. The acceptability of concrete depends upon achieving a desired mean strength and keeping the deviation small.

Acceptance criteria as per old code a)

b)

c)

The grade of concrete is specified. M25 concrete means concrete with a characteristic strength of 25 MPa at 28 days curing. A target mean strength is fixed. ft = fck + k x s ( The value of k for calculating ft is taken as 1.65, which gives a probability of not more than 5% of the samples tested will fall below fck) Each sample is checked for acceptability. Test strength of each sample will be the average of three specimen with individual variation being not more than ±15% of the average.

Clause 15.1 of IS: 456-1978 a) Accept all samples with fi ≥ fck b) For samples with strength less than fck two checks are applied. Both checks must be satisfied • First check : fi should not be less than the larger of two values. (i) fck – 1.35 x s (ii) 0.8 x fck

•

Second check : Average strength of all the samples is not less than fck + 1.65 [ 1-√(1/n)] s Clause 15.2 of IS: 456-1978 a) Reject the concrete if fi is less than the greater of (i) fck – 1.35 x s (ii) 0.8 x fck

b) Reject the concrete also if fi < fck + [1.65 – (3/√n)] s Note : concrete which does not meet the requirement of Clause 15.1 but has a strength greater than required by clause 15.2 can be accepted at the discretion of the designer.

Acceptance criteria as per new code The acceptance criteria as per new code is : a) fm ≥ fck + 0.825 x s or (fck +4) MPa , whichever is greater AND b) fi ≥ (fck – 4) MPa Where, fm = Mean of four results in a group fi = Strength of any individual sample s = Established standard deviation rounded off to nearest 0.5 MPa Note :- When sufficient number of samples have not accumulated, a standard deviation of 4.0 MPa is assumed for M20 & M25 concrete. While 5.0 MPa is taken for M30 to M50. The calculated value of ‘s’ is used as soon as 30 results are available.

( BASED ON IS:456 – 2000)

METHOD OF CONCRETE MIX DESIGN Step 1 :-

Work out the Target mean strength of concrete from the relation:

fck = fck +t x s Where,

fck = fck =

Target average compressive strength at 28 days characteristic compressive strength at 28 days

s

= Standard Deviation

t

= 1.65 (as per IS:456-2000 clause 9.2.2 )

Table 3: Assumed Standard Deviation For Three Strength Groups Grade of Concrete

Assumed standard deviation MPa

M10 M15

3.50

M20 M25

4.00

M30 M35 M40 M45 M50

5.00

The above values correspond to the site control having proper storage of cement; Weigh batching of all materials; controlled addition of water; regular checking of all materials, aggregate grading and moisture content; and periodic checking of workability and strength. Where there is deviation from the above, the values given in the above table shall be increased by 1 N/mm²

Step 2 :Find out the value of W/C ratio against the target mean strength from the curves available for the purpose. Select the appropriate curve for the type of coarse aggregate and the type of cement being used. Step 3 :For durability consideration check the obtained free watercement ratio from appropriate table of IS:456-2000. If required use lower value of water cement ratio. Step 4 :As per clause 7 page 17 of IS:456-2000 find out the degree of workability required for the job. Step 5 :From table 4, find out the quantity of free water in Kg/m³ for the type and maximum size of aggregate being used and for the required workability and normal- air entrained concrete.

Step 6 :Find out the cement content in Kg/m³ from the information of step 2 and step 5. Cement content =

Free water content Water cement ratio

For durability consideration, check the minimum cement content , if required take higher value. Step 7 :Find out the density of concrete in Kg/m³ for different maximum sizes of coarse aggregate corresponding to particular value of combined specific gravity of aggregates from the given tables 5,6 &7. Step 8 :Find out the aggregates content per cum of concrete. Total aggre = conc density – Free water – cement content (Kg/m³ )

(Kg/m³ )

(Kg/m³ )

(Kg/m³ )

Step 9 :Find out the proportions of sand (percent) of the total aggregate from table 8 for particular maximum size of coarse aggregate, required workability, zone of sand and water- cement ratio. Find out the quantity of fine aggregates in Kg/m³ from total aggregate calculated in step 8 above. Step 10 :Find out the quantity of coarse aggregate in Kg/m³ by subtracting the quantity of fine aggregate from total aggregates. Step 11 :If the coarse aggregates are in more than one fraction , they shall be combined in a suitable proportion to get a graded coarse aggregate as per IS: 383-1970. In general, if the coarse aggregates are in single size as per IS: 383-1970, they shall be combined as follows for obtaining a combined graded aggregate. (a) 10 & 20 mm aggregate in ratio 1:2 (b) 10, 20 & 40 mm aggregate in ratio 1:1.5:3

IMPORTANT NOTE THE CALCULATED MIX PROPORTIONS MUST BE CHECKED BY TRIAL MIXES FOR REQUIRED SPECIFICATIONS, AND AS PER REQUIREMENTS SUITABLE ADJUSTMENT IN THE MIX PROPORTION SHOULD BE DONE.

COMPRESSIVE STR VS W/C RATIO (Uncrushed coarse aggregate) 80.0

A=21.6 – 25.0 N/mm² B=25.0 – 29.8 N/mm² C=29.8 – 35.0 N/mm² D=35.0 – 41.5 N/mm²

70.0 28 – DAY COMPR STR OF CONCRETE (N/mm²)

E=41.5 – 48.0 N/mm² F=48.0 – 53.4 N/mm²

60.0 50.0 40.0

F E

(Values given above correspond to the 7- day strength of cement tested according to IS: 4031-1968)

D C B A

30.0 20.0 10.0 0.0 0.30

0.35

0.40

0.45

0.50

WATER – CEMENT RATIO

0.55

0.60

0.65

0.70

COMPRESSIVE STR VS W/C RATIO (Crushed coarse aggregate) 80.0

28 – DAY COMPR STR OF CONCRETE (N/mm²)

70.0 60.0 50.0 40.0

A=21.6 – 25.0 N/mm² B=25.0 – 29.8 N/mm²

F

C=29.8 – 35.0 N/mm² D=35.0 – 41.5 N/mm² E

E=41.5 – 48.0 N/mm² F=48.0 – 53.4 N/mm²

D

(Values given above correspond to the 7- day strength of cement tested according to

C

IS: 4031-1968)

B A

30.0 20.0 10.0 0.0 0.30

0.35

0.40

0.45

0.50

WATER – CEMENT RATIO

0.55

0.60

0.65

0.70

Water cement ratio & cement contents for Durability Type of Exposure

Plain Cement Concrete

Reinforced Cement Concrete

Min cement Kg/m³

Max Free W/C

Min grade of concrete

Min cement Kg/m³

Max Free W/C

Min grade of concrete

Mild

220

0.6

-

300

0.55

M20

Moderate

240

0.6

M15

300

0.5

M25

Severe

250

0.5

M20

320

0.45

M30

Very Severe

260

0.45

M20

340

0.45

M35

Extremely Severe

280

0.40

M25

360

0.4

M40

Note :- Min cement content value applies to 20mm max size of agg

Adjustments to minimum cement content for aggregates (other than 20mm max size of agg) Sl No.

Nominal max aggregate size

Adjustments to minimum cement content

1.

10

+40

2.

20

0

3.

40

-30

Note :a) b)

Cement content prescribed in the table is irrespective of the grades of cement and is inclusive of mineral admixtures like fly ash, silica fume etc. The additions such as fly ash or ground granulated blast furnace slag may be taken into account in the concrete composition with respect to the cement content and water cement ratio if the suitability is established and as long as the maximum amounts taken into account do not exceed the limit of pozzolona and slag specified in IS 1489(Part I) and IS 455 respectively.

Table 4:Approx Free water content(kg/m³) With non air- entrained concrete (Normal entrapped air) Maximum size of aggregate (mm)

10

20

40

Type of aggregate

Slump (mm)

-

25-75

50-100

100-180

Compacting factor

0.75-0.80

-

-

-

Degree of workability

Very low

Low

Medium

High

Uncrushed

150

205

220

240

Crushed

180

235

250

265

Uncrushed

140

180

195

210

Crushed

170

210

225

245

Uncrushed

120

160

175

190

Crushed

155

190

205

220

When coarse and fine aggregates of different types are used, the free water content is estimated by the expression : 2 W f + 1 W c , where, 3

3

Wf = Free water content appropriate to type of fine aggregate Wc = Free water content appropriate to type of coarse aggregate

Table 5:Estimated wet density of fully compacted concrete(kg/m³) (Max size of saturated & surface dry aggregate 10 mm for first trial) Free water content (Kg/m³)

Specific gravity for combined aggregates 2.4

2.5

2.6

2.7

2.8

2.9

130

2250

2320

2390

2460

2530

2600

140

2235

2305

2375

2445

2515

2585

150

2220

2290

2360

2430

2500

2570

160

2205

2275

2345

2415

2485

2555

170

2190

2260

2330

2400

2470

2540

180

2175

2245

2315

2385

2455

2525

190

2160

2230

2300

2370

2440

2510

200

2145

2215

2285

2355

2425

2495

210

2130

2200

2270

2340

2410

2480

220

2115

2185

2255

2325

2395

2465

230

2100

2170

2240

2310

2380

2450

240

2085

2155

2225

2295

2365

2435

250

2070

2140

2210

2280

2350

2420

The table is worked out for cement content 330 kg/m³. For each 20 Kg difference in cement content from 330 Kg correct the weight per m³, 3 Kg in the same direction.

Table 6:Estimated wet density of fully compacted concrete(kg/m³) (Max size of saturated & surface dry aggregate 20 mm for first trial) Free water content (Kg/m³)

Specific gravity for combined aggregates 2.4

2.5

2.6

2.7

2.8

2.9

120

2285

2355

2425

2495

2565

2635

130

2270

2340

2410

2480

2550

2620

140

2255

2325

2395

2465

2535

2605

150

2240

2310

2380

2450

2520

2590

160

2225

2295

2365

2435

2505

2525

170

2210

2280

2350

2420

2490

2560

180

2195

2265

2335

2405

2475

2545

190

2180

2250

2320

2390

2460

2530

200

2165

2235

2305

2375

2445

2515

210

2150

2220

2290

2360

2430

2500

220

2135

2205

2275

2345

2415

2485

230

2120

2190

2260

2330

2400

2470

The table is worked out for cement content 330 kg/m³. For each 20 Kg difference in cement content from 330 Kg correct the weight per m³, 3 Kg in the same direction.

Table 7:Estimated wet density of fully compacted concrete(kg/m³) (Max size of saturated & surface dry aggregate 40 mm for first trial) Free water content (Kg/m³)

Specific gravity for combined aggregates 2.4

2.5

2.6

2.7

2.8

2.9

100

2335

2405

2475

2545

2615

2685

110

2320

2390

2460

2530

2600

2670

120

2305

2325

2445

2515

2585

2655

130

2290

2360

2430

2500

2570

2640

140

2275

2315

2415

2485

2555

2625

150

2260

2330

2400

2470

2540

2610

160

2245

2315

2385

2455

2525

2595

170

2230

2300

2370

2440

2510

2580

180

2215

2285

2355

2425

2495

2565

190

2200

2270

2340

2410

2480

2550

200

2185

2255

2325

2395

2465

2535

210

2170

2240

2310

2380

2450

2520

The table is worked out for cement content 330 kg/m³. For each 20 Kg difference in cement content from 330 Kg correct the weight per m³, 3 Kg in the same direction.

Table 8: Proportion of fine aggregate with different workability Zone of FA

I

II

III

IV

W/C ratio

10mm aggregate

20 mm aggregate

40 mm aggregate

VL

L

M

H

VL

L

M

H

VL

L

M

H

0.3

43-53

46-56

49-60

54-67

32-39

35-42

39-47

44-53

27-33

29-35

33-39

38-46

0.4

46-56

48-58

51-62

57-69

34-42

37-45

41-49

46-56

29-35

31-38

35-42

41-49

0.5

48-58

50-61

53-65

59-72

37-45

39-47

43-52

48-59

31-38

33-41

37-44

43-52

0.6

50-61

52-63

56-68

62-75

39-47

41-50

45-54

50-61

33-41

36-43

39-47

45-54

0.7

52-64

55-66

58-70

64-77

41-50

44-53

47-57

53-64

36-44

38-46

42-50

47-57

0.3

36-43

37-46

40-49

44-54

27-32

28-35

32-39

35-44

22-27

23-29

27-33

31-38

0.4

37-46

39-48

42-51

46-57

28-34

30-37

33-41

37-46

24-29

25-31

28-35

32-41

0.5

39-48

41-50

44-53

47-59

30-37

32-39

35-43

39-48

25-31

27-33

30-37

34-43

0.6

41-50

42-52

45-56

49-62

32-39

34-41

36-45

41-50

27-33

29-36

32-39

36-45

0.7

42-52

44-55

47-58

51-64

34-41

36-44

38-47

43-53

29-36

31-38

34-42

38-47

0.3

29-36

32-37

33-40

37-44

23-27

24-28

27-32

30-35

18-22

20-23

22-27

26-31

0.4

31-37

33-39

35-42

38-46

24-28

26-30

28-33

31-37

20-24

21-25

24-28

27-32

0.5

32-39

34-41

36-44

40-47

25-30

27-32

29-35

33-39

21-25

23-27

25-30

29-34

0.6

34-41

36-42

38-45

42-49

27-32

29-34

31-36

35-41

23-27

24-29

27-32

30-36

0.7

35-42

37-44

39-47

43-51

28-34

30-36

32-38

36-43

24-29

26-31

29-34

32-38

0.3

26-29

27-32

29-33

32-37

19-23

21-24

23-27

26-30

16-18

18-20

19-22

22-26

0.4

27-31

29-33

30-35

34-38

21-24

22-26

24-28

28-31

17-20

19-21

20-24

24-27

0.5

28-32

30-34

32-36

35-40

22-25

24-27

26-29

29-33

18-21

20-23

22-25

25-29

0.6

30-34

31-36

33-38

36-42

23-27

25-29

27-31

30-35

20-23

22-24

23-27

26-30

0.7

31-35

32-37

35-39

37-43

25-28

26-30

28-32

32-36

21-24

23-26

25-29

28-32

Table 9: Grading requirements of Coarse aggregates (IS:383-1970) IS Sieve Designation

Percentage passing for Single Sized Aggregate of Nominal Size

Percentage passing for Graded Aggregate of Nominal Size

63mm

40mm

20mm

16mm

12.5mm

10mm

40mm

20mm

16mm

12.5mm

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9)

(10)

(11)

80mm

100

-

-

-

-

-

100

-

-

-

63mm

85-100

100

-

-

-

-

-

-

-

-

40mm

0-30

85-100

100

-

-

-

95-100

100

-

-

20mm

0-5

0-20

85-100

100

-

-

30-70

100

-

-

16mm

-

-

-

85-100

100

-

-

-

90-100

-

12.5mm

-

-

-

-

85-100

100

-

-

-

90-100

0-5

0-5

0-20

0-30

0-15

85-100

10-35

25-55

30-70

40-85

4.75mm

-

-

0-5

0-5

0-10

0-20

0-5

0-10

0-10

0-10

2.36mm

-

-

-

-

-

0-5

-

-

-

-

(1)

10mm

Table 10 : Grading Requirements For Fine Aggregates (IS :383-1970) IS Sieve Designation

I

II

III

IV

100

100

100

100

4.75 mm

90-100

90-100

90-100

90-100

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

05-20

08-30

12-40

15-50

150 micron

00-10

00-10

00-10

00-15

10 mm







Percentage Passing For Grading Zone

For crushed stone sands, the permissible limit on 150 micron IS sieve is increased by 20 %. Fine aggregate complying with the requirements of any of the grading zone in this table is suitable for concrete. It is recommended not to use the fine aggregate conforming to the grading zone IV in reinforced concrete unless tests prove it suitable for the purpose. Where concrete of high strength and good durability is required, fine aggregate conforming to any of the four zones can be used, but the concrete mix should be properly designed. As the fine aggregate grading becomes progressively finer, the ratio of fine aggregate to coarse aggregate should be progressively reduced.

Exposure Conditions Sl Exposure No. condition

Description

1.

Mild

Concrete surfaces protected against weather or aggressive conditions, except those situated in coastal areas.

2.

Moderate

Concrete surfaces sheltered from severe rain or freezing whilst wet Concrete exposed to condensation and rain Concrete continuously under water Concrete in contact or buried under non aggressive soil / ground water Concrete surfaces sheltered from saturated salt air in coastal area

Sl Exposure No. condition

Description

3.

Severe

Concrete surfaces exposed to severe rain, alternate wetting and drying or occasional freezing whilst wet or severe condensation Concrete completely immersed in sea water Concrete exposed to coastal environment

4.

Very Severe

Concrete surfaces exposed to sea water spray, corrosive fumes or severe freezing conditions whilst wet Concrete in contact with or buried under aggressive sub- soil/ ground water

5.

Extreme

Surface of members in tidal zone Members in direct contact with liquid/ solid aggressive chemicals

Workability of Concrete Sl No.

Placing conditions

Degree of workability

Slump (mm)

1.

Blinding Concrete Shallow Sections Pavements using pavers

Very low

0.75-0.80 (CF)

2.

Mass Concrete Lightly reinforced sections in slabs, beams, walls, columns Floors Hand placed pavements Canal linings Strip footings

Low

25-75

3.

Heavily reinforced sections in slabs, beams, walls, columns Slipform work Pumped concrete

Medium

50-100 to 75- 100

4.

Trench fill In-situ piling

High

100- 150

5.

Tremie Concrete

Very High

By flow determination

Example 1:A mix is required to be designed for M20 grade of concrete which is to used in lightly reinforced slab. Other details are as given below : Standard deviation from previous relevant work Required workability Exposure Maximum free W/C ratio Minimum cement content Maximum size of aggregate Type of sand Cement Other Details

: 4.0 N/mm² : (low) slump (25-75 mm) : mild : 0.55 : 300 Kg/ m³ : 20mm (uncrushed) : River sand : OPC 43 Grade : The sand and aggregate has been used in the construction since the last 40 years and they are found to be quite good.

Test results of materials : Cement 7 days compressive strength

: 39.5 N/mm²

Sand grading

: Zone II

Aggregate grading

: 20- 05 mm graded

Specific Gravity of Sand

: 2.7

Specific Gravity of Aggregate

: 2.7

Water absorption of sand

: 1.4%

Water absorption of aggregate

: 0.9%

Bulk density of room dry sand

: 1.52 Kg/lit

Bulk density of room dry aggregate

: 1.47 Kg/lit

Solution :Step 1 :Target mean strength of concrete, _

f

ck

=

f ck + 1 . 65 s

= 20 + 1.65 x 4.0 = 26.6 N/mm² Step 2 :- Selection of free w/c ratio 7- day compressive strength of cement = 39.5 N/mm² Type of aggregate = Uncrushed (River gravel) Therefore, from the appropriate curve, the w/c ratio for target strength of 26.6 N/mm² is 0.51. The value is selected as the same is less than specified max w/c ratio of 0.55

Step 3 :- Selection of free water content From table, for 20mm uncrushed aggregate and river sand, for required workability of 25-75 mm slump, free water content is found to be 180 kg/m³ Step 4 :- Determination of cement content w/c ratio = 0.51 Water = 180 kg/m³ Cement = 180/0.51 = 353 kg/m³ The value of cement content is higher than the specified minimum cement content of 300 kg/m³, hence accepted Step 5 :- Determination of concrete density Specific gravity of combined aggregates Maximum size of aggregate Free water content Density of concrete ( from table )

= 2.7 = 20mm = 180 kg/m³ = 2408 kg/m³

Step 6 :- Determination of aggregate quantity Concrete density = 2408 kg/m³ Cement content = 353 kg/m³ Water content = 180 kg/m³ Total aggregates = (2408 – 353 – 180) kg/m³ = 1875 kg/m³ Step 7 :- Determination of sand content Workability = Low Max size of aggregate = 20mm Zone of sand = II w/c ratio = 0.51 From table the proportion of sand = 33- 39% = 36% (say) Sand = 1875x0.36 = 675 kg/m³ Step 8 :- Determination of coarse aggregate Coarse aggregate = (1875- 675) kg/m³ = 1200 kg/m³

FINAL PROPORTIONS : Thus the quantity of materials per cum of concrete on the basis of saturated and surface dry aggregates: Water = 180 kg/m³ Cement = 353 kg/m³ Sand = 675 kg/m³ Coarse agg = 1200 kg/m³ Mix ratio by weight on the basis of saturated and surface dry aggregates: Cement : Sand : C/aggregate = 1 : 1.91 : 3.40 Water cement rati0 = 0.51

CONVERSION OF PROPORTION BY WEIGHT TO PROPORTION BY VOLUME Proportion by weight can be converted into proportion by volume, by dividing it with the bulk density of site aggregates. Bulk density of cement = 1.44 x 103 kg/m³ Bulk density of sand = 1.52 x 103 kg/m³ Bulk density of c/ aggregate = 1.47 x 103 kg/m³ Therefore, mix ratio by volume = 1 : 1.81 : 3.33 Free water cement ratio = 0.51 Working out volume of aggregate for one bag of cement Cement = 50 kg = 35000cc Dry sand = 1.81x35000 = 2x(33cm x 33cm x 29cm) Room dry agg = 3.33x35000 = 4x(32cm x 32cm x 28.5cm) Free water = 25.5 liter NOTE : The bulking of sand and adjustment in mixing water should be taken into consideration as per actual moisture content of site aggregates.

MIX DESIGN WITH USE OF PLASTICIZER In Example 1 above , it is proposed to use superplasticizer for reduction in mixing water. It is found that 3cc/kg of superplasticizer reduces 10% of water. Accordingly, water reqmt = (180-18) Kg/ m³ = 162 Kg/ m³ Cement reqmt = (162/0.51) Kg/ m³ = 318 Kg/ m³ Density of wet concrete = 2430 Kg/ m³ Total aggregate = (2430 – 162 – 318) Kg = 1950 Kg/ m³ Therefore, Sand = 1950x0.36 = 683 Kg/ m³ C/ aggregate = 1950 – 683 = 1267 Kg/ m³ Superplasticizer = 318x3 = 954 cc/ m³

Quantity of material by volume per bag of cement Cement = One bag (50 Kg) Dry sand = 2x( 33cm x 33cm x 32.6cm) Dry aggregate = 4x( 32cm x 32cm x 33.3cm) Water = 25.5 lit Superplasticizer = 150 cc Saving in cost/cum of concrete Saving in cement = 353 – 318 = 35 Kg cost of cement saved = 35x3 = Rs.105 Cost of superplast = Rs. 50 (One liter)

Overall saving

= Rs.(105-50)

= Rs. 55

(Per cum of concrete)

Thus use of superplasticizer results in saving in cost and other benefits such as reduction in mixing water & well compacted better finished concrete.