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Mix Design With Superplasticizers

Superplasticizers belongs to a class of water reducer chemically different from the normal water reducers and capable of reducing water content by about 30%. The Superplasticizers are broadly classified into four groups: sulfonated melamine formaldehyde condensate (SMF), sulphonated naphthalene formaldehyde condensate (SNF), modified lignosulphonate (MLS) and others including sulphonic acid ester, polyacrylates, polystryrene sulphonates, etc. The benefits obtained by Superplasticizers in the reduction of water in the concrete mixes are best illustrated by the following examples.

MIX DESIGN DETAILS

1Grad of Concrete:M-40
2Cement:Three mixes are to be designed
MIX-A

 

With PPC (Flyash based) conforming to IS:1489-part-I-1991. 7 days strength 38.5 N/mm2. Specific Gravity : 3.00

MIX-B

 

With OPC-43- Grade conforming to IS: 8112-1989. 7 days strength 40.7 n/mm2. Specific Gravity : 3.15

MIX-C

 

With OPC of Mix-B and Fly ash conforming to IS:3812 (Part-I)-2003 Specific Gravity : 2.25

Note: Requirements of all the three mixes are the same. Fine Aggregate, Coarse Aggregate and normal Super plasticizer are the same for all the three mixes.
3Fly ash replacement:30% Fly ash is required to be replaced with the total cementitious materials.
4Maximum nominal size of aggregates:20 mm Crushed aggregate
5Fine aggregate:River sand of Zone-II as per IS:383-1970
6Minimum cement content:360 kg/m3 including Fly ash
7Maximum free W/C Ratio:0.40
8Workability:50 mm slump
9Exposure condition:Extreme for RCC work
10Method of placing:Site mixing
11Degree of supervision:Good
12Maximum of cement content (Fly ash not included):450 kg/m3
13Chemical admixture:Super plasticizer conforming to IS:9103-1999. With the given requirements and materials, the manufacturer of Normal Super plasticizer recommends dosages of 20 gm per kg of OPC, which will reduce 28% of water without loss of workability. For fly ash included cement dosages will be required to be adjusted by experience/ trials.

TEST DATA FOR MATERIALS
1. The grading of fine aggregate, 10 and 20 mm aggregates are as given in Table. 1. Fine aggregate is of zone-II as per IS:383-1970. 10 and 20 mm crushed aggregate grading are single sized as per IS: 383-1970.

2. Properties of aggregates

Tests

Fine aggregate

10 mm aggregate

40 mm aggregate

Specific Gravity

2.65

2.65

2.65

Water Absorption %

0.8

0.5

0.5

3. Target strength for all A, B and C mixes
fck = fck + 1.65 x S
40 + 1.65 x 5
= 48.3 N/mm2 at 28 days age

4. For Mix A and B free W/C ratio with crushed aggregate and required target strength of 48.3 N/mm2 at 28 days from Fig. 1 Curve D found to be 0.4 Taking into the consideration of water in admixture,let it be 0.39. This is lower than specified maximum W/C ratio value of 0.4

Note:
In absence of cement strength, but cement conforming to IS Codes, assume from Fig. 1 and Fig. 2.
Curve A and B – OPC 33 Grade
Curve C and D – OPC 43 Grade
Curve E and F – OPC 53 Grade

Take curves C and D for PPC, as PPC is being manufactured in minimum of 43 Grade of strength.

5. Other data’s: The Mixes are to be designed on the basis of saturated and surface dry aggregates. At the time of concreting, moisture content of site aggregates are to be determine. If it carries surface moisture this is to be deducted from the mixing water and if it is dry add in mixing water the quantity of water required for absorption. The weight of aggregates are also adjusted accordingly.

DESIGN OF MIX-A WITH PPC
a) Free W/C ratio for the target strength of 48.3 N/mm2 as worked out is 0.39.

b) Free water for 50 mm slump from Table 2 for 20 mm maximum size of aggregate.
2/3*180 + 1/3*210
= 190 kg/m3
From trials also it is found that Normal Super plasticizer at a dosages of 21gm/kg of cement may reduce 28% water without loss of workability

Then water = 190 – (190 x 0.28) = 136.8 kg/m3
for trials say 137 kg/m3

c) PPC = 137/0.39 = 351 kg/m3 This is lower than minimum requirement of 360 kg/m3. Then take 360 kg/m3.
Then W/C = 137/360 = 0.38

d) Formula for calculation of fresh concrete weight in kg/m3
Um= 10 x Ga (100 – A) + CM(1 – Ga/Gc) – WM (Ga – 1)

Where,
Um = Wight of fresh concrete kg/m3
Ga = Weighted average specific gravity of combined fine
and coarse aggregate bulk, SSD
Gc = Specific gravity of cement. Determine actual value,
in absence assume 3.15 for OPC and 3.00 for PPC
(Fly ash based)
A = Air content, percent.
Assume entrapped air 1% for 40 mm maximum size of aggregate, 1.5% for 20 mm maximum size of aggregate and 2.5% for 10mm maximum size of aggregate.

There are always entrapped air in concrete. Therefore ignoring
entrapped air value as NIL will lead the calculation of higher value of density.
Wm = Mixing water required in kg/m3
Cm = Cement required, kg/m3
Note:- The exact density may be obtained by filling and fully compacting constant volume suitable metal container from the trial batches of calculated design mixes. The mix be altered with the actual obtained density of the mix.

Um =10 x Ga (100 – A) + Cm (1 – Ga/Gc) – Wm (Ga – 1)
=10 x 2.65 (100 – 1.5) + 360(1- 2.65/3.00) – 137 (2.65 -1)
2426 kg/m3

e)Aggregates = 2426 – 360 – 137 = 1929 kg/m3

f) Fine aggregate = From Table 3 for zone-II Fine aggregate and
20 mm maximum size of aggregate, W/C ratio = 0.39, 50 mm slump found to be for trial 33%.

Fine aggregate = 1929 x 0.33 = 637 kg/m3
Coarse aggregate = 1929 – 637 = 1292 kg/m3
10 and 20 mm aggregate are single sized as per IS: 383-1970. Let they be combined in the ratio of 1.2:1.8 to get 20 mm graded aggregate as per IS: 383-1970
10 mm aggregate = 517 kg/m3
20 mm aggregate = 775 kg/m3

g) Thus for M-40 Grade of concrete quantity of materials per cu.m.
of concrete on the basis of saturated and surface dry aggregates:

Water=137 kg/m3
PPC = 360 kg/m3
Fine Aggregate (sand) = 637 kg/m3
10 mm Aggregate = 517 kg/m3
20 mm Aggregate = 775 kg/m3
Normal Super Plasticizer = 7.560 kg/m3

MIX- B WITH OPC

a) Water = 190 – (190 x 0.28) = 136.8 kg/m3 say 137 kg/m3
b) OPC = 137/0.39 = 351 kg/m3
Minimum content specified = 360 kg/m3
Then take 360 kg/m3
c) Density:
10 x 2.65 (100 – 1.5) + 360 (1 – 2.65/3.15) – 137 (2.65 – 1)
= 2442 kg/m3

d) Total Aggregates = 2442 – 137 – 360 = 1945 kg/m3
Fine Aggregate = 1945 x 0.33 = 642 kg/m3
Coarse aggregate = 1945 – 642 = 1303 kg/m3
10 mm Aggregate = 1303×1.2/3 = 521 kg/m3
20 mm Aggregate = 1303×1.8/3 = 782 kg/m3

e) Thus for M-40 Grade of concrete quantity of materials per cu.m of concrete on the basis of SSD aggregates are given below:
Water = 137 kg/m3
PPC = 360 kg/m3
Fine Aggregate (sand) = 642 kg/m3
10 mm Aggregate = 521 kg/m3
20 mm Aggregate = 782 kg/m3
Normal Super Plasticizer = 7.2 kg/m3

MIX. C WITH OPC + FLYASH
With the given set of materials increase in cementitious materials = 12%
Total cementitious materials = 360 x 1.12 = 403 kg/m3

Materials

Weight (kg/m3)

Volume (m3)

OPC = 403 x 0.70

282/3150

0.0895

Flyash = 403 x 0.30

121/2250

0.0538

Free Water = 137 x 0.95

130/1000

0.13

Normal Super Plasticizer = 8.2kg

8.2/1150

0.0071

Air = 1.5%

0.015

Total

0.2954

Total Aggregates = 1 – 0.2954

0.7046

1.00

Coarse Aggregate

1303/2650

0.4917

Fine Aggregate = 0.7046 – 0.4917 = 0.2129
= 0.2129 x 2650 = 564 kg
Note:-
1. Specific gravity of Normal Superplasticizer = 1.15
2. Addition of Flyash reduces 5% of water demand.

M-40 Grade of concrete quantity of material per cu.m of concrete
on the basis of saturated and surface dry aggregates of
Mix ‘A’, ‘B’ and ‘c’ are given below:

Materials

MIX. ‘A’ with PPC

Mix. ‘B’ with OPC

Mix. ‘C’ with OPC+Flyash

Water kg/m3

137

137

130

PPC kg/m3

360

OPC kg/m3

360

282

Flyash kg/m3

121

Fine Agg. kg/m3

637

642

564

10mm Agg. kg/m3

517

521

521

20 mm Agg. kg/m3

775

782

782

Normal Super- plasticizer kg/m3

7.560

7.2

8.2

W/Cementations ratio

0.38

0.38

0.323

Note:-
1. For exact W/C ratio the water in admixture should also be taken into account.
2. The W/C ratio of PPC and OPC is taken the same assuming that the strength properties of both are the same. If it is found that the PPC is giving the low strength then W/C ratio of PPC have to be reduce, which will increase the cement content. For getting early strength and in cold climate the W/C ratio of PPC shall also be required to be reduced.
3. PPC reduces 5% water demand. If this is found by trial then take reduce water for calculation.
4. If the trial mixes does not gives the required properties of the mix, it is then required to be altered accordingly. However, when the experiences grows with the particular set of materials and site conditions very few trials will be required, and a expert of such site very rarely will be required a 2nd trial.
Table. 1: Grading of Aggregates

IS Sieve Designation

Percentage Passing

Fine Aggregate

Crushed Aggregate

10 mm

20 mm

40 mm

100

20 mm

100

12.5 mm

100

10 mm

100

85

4

4.75 mm

99

5

0

2.36 mm

88

0

1.18 mm

74

600 Micron

43

300 Micron

24

150 Micron

6

Table. 2: Approximate free-water content (kg/m3) required to give various levels of workability for non-air-entrained (with normal entrapped air) concrete.

Maximum size of aggregate (mm)Type of aggregateSlump (mm) Degree of workability

vary low

25-75

Low

50-100

Medium

100-180

High

10

Uncrushed Crushed

150

180

205

235

220

250

240

265

20

Uncrushed Crushed

140

170

180

210

195

225

210

245

40

Uncrushed Crushed

120

155

160

190

175

205

190

220

Note:- When coarse and fine aggregate of different types are used, the free water content is estimated by the expression.
2/3Wf+1/3Wc
Where,
Wf=Free water content appropriate to type of fine
Aggregate and Wc=Free water content appropriate to type of coarse aggregate.

Table. 3: Proportion of fine aggregate (percent) with 10mm and 20mm maximum sizes of aggregates and with different workability.
table -3 grading of coarse aggreagates
Table. 4: Proportion of fine aggregate (percent) with 40 mm maximum sizes of Aggregates and with different workability.

Grading Zone of F.A

W/C Ratio

40 mm aggregate Workability

VL

L

M

H

I

0.3

27-33

29-35

33-39

38-46

0.4

29-35

31-38

35-42

41-49

0.5

31-38

33-41

37-44

43-52

0.6

33-41

36-43

39-47

45-54

0.7

36-44

38-46

42-50

47-57

II

0.3

22-27

23-29

27-33

31-28

0.4

24-29

25-31

28-35

32-41

0.5

25-31

27-33

30-37

34-43

0.6

27-33

29-36

32-39

36-45

0.7

29-36

31-38

34-42

38-47

III

0.3

18-22

20-23

22-27

26-31

0.4

20-24

21-25

24-28

27-32

0.5

21-25

23-27

25-30

29-34

0.6

23-27

24-29

27-32

30-36

0.7

24-29

26-31

29-34

32-36

IV

0.3

16-18

18-20

19-22

22-26

0.4

17-20

19-21

20-24

24-27

0.5

18-21

20-23

22-25

25-29

0.6

20-23

22-24

23-27

26-30

0.7

21-24

23-26

25-29

28-32

VL = Very low workability.
L = Low workability – slump 25-75 mm
M = medium workability – slump 50-100 mm
H = High workability- slump 100-180 mm

Figures From Experimental Data
Click on the picture to zoom it.
relation between water cement ratio and compressive strength of concrete using crushed aggregates

relation between water cement ratio and compressive strength of concrete using uncrushed aggregates