Chapter 6 PROPOSED MIX DESIGN METHOD FOR HPC …shodhganga.inflibnet.ac.in/bitstream/10603/23542/16/16_chapter_06.pdf · Chapter 6 Proposed Mix Design Method for HPC and Validity

Chapter 6 Proposed Mix Design Method for HPC and Validity

Mix Proportioning of High Performance Concrete for Indian Environment 229

Chapter 6

PROPOSED MIX DESIGN METHOD FOR HPC AND VALIDITY

6.1 INTRODUCTION

Concrete mix design is a process of proportioning the ingredients in right

proportions. Though it is based on sound technical principles and heuristics, the entire

process is not in the realm of science and precise mathematical calculations. This is

because of impreciseness, vagueness, approximations and tolerances involved.

The objective of any mix design method is to determine an appropriate and

economical combination of concrete ingredients that can be used for a first trial batch

to produce a certain concrete which is close to that can achieve a good balance

between various desired properties of concrete at the minimum cost. A mixture

proportioning only provides a starting mix design that will have to be more or less

modified to meet the desired concrete characteristics. In spite of the fact that mix

design is still something of an art, it is unquestionable that some essential scientific

principles can be used as a basis for calculations. Mix design of high performance

concrete (HPC) is different from that of usual concrete because of the following

reasons (Laskar and S. Talukdar, 2008):

• Water-binder ratio is very low.

• Concrete quite often contains cement replacement materials that drastically

change the properties of fresh and hardened concrete.

• Slump or compaction factor can be adjusted using high range water reducing

admixture (HRWRA) without altering water content.

Concrete is required to exhibit performance in the given environment.

However, there has been no established method whereby the mixture proportions of

concrete can be optimized according to the required performance. The conventional

mix design methods are no longer capable of meeting the stringent multiple

requirements of HPC (Wong and Kwan, 2005). These methods are not directly

applicable to HPC mixes. Several methods have been proposed over the years for the

proportioning of mineral admixture – based HPC mixes. The methods proposed by



ACI, modified ACI, Mehta and Aitcin, DOE among other methods are popular and

are found to be suitable for designing HPC mixes especially in cold countries where

temperature hardly goes beyond 25oC (Kumbhar and Murnal,2011). These methods

have been in use successfully by the engineers over the years. However, the British or

American methods will not be applicable for our country, as the specific relationships

constituting figures and tables are based on their materials. Also the climatic

conditions of our country are different from the climates of these countries.

India, being a tropical country has different environment in its different parts.

Tropical countries usually receive significant rainfall during only some part of the

year leading to substantial variation in the level of humidity in many parts of the

tropics. High temperatures, low humidity and wind cause rapid evaporation of water

from the concrete mix during summer. This drying of concrete leads to cracking and

crazing of the surface (Gambhir, 2005). The variation in temperature and humidity

has profound effect on the properties of HPC such as strength and durability since the

mix proportions are usually decided at laboratory conditions. Therefore, a new

modified method of mix design procedure has been proposed and is discussed in

subsequent sections for design of HPC mixes taking into account the effect of

environmental conditions such as varying humidity and temperatures on the properties

of HPC mixes.

6.2 GENERAL INFORMATION

Based on the results of experimentation it is stated that the following material

specifications must meet to develop HPC mixes of desired workability and target

compressive strengths.

6.2.1 Cement:

The ordinary Portland cement (OPC) of 53 grade satisfying the IS

Specifications. The cement content obtained from the existing IS Code method of mix

design (IS10262-1982) works out to be more than the maximum specified limit of

450kg/m3 for mixes with low water-cement ratios. Hence, the quantity of cement

needs to be altered and should be used in combination with suitable mineral



admixture such as micro silica. The total quantity of materials (called as binders) thus

will include both cement and desired quantity of mineral admixture (micro silica).

6.2.2 Fine Aggregates:

From the investigations carried out to study the effect of sand zones on various

properties of HPC mixes, it is recommended to use fine aggregates conforming to

Zone-I for obtaining better strength properties.

6.2.3 Coarse Aggregates:

The cubical shaped coarse aggregates of two fractions are recommended for

use in developing HPC mixes of grades M50-M90.

Fraction: I – passing through 20mm IS sieve and retained on 12.5mm IS sieve (60%)

Fraction: I – passing through 12.5mm IS sieve and retained on 10mm IS sieve (40%)

6.2.4 Mineral Admixtures:

Several mineral admixtures such as fly ash, micro silica, GGBS etc are being used in

making HPC mixes of different grades. However, micro silica is a highly pozzolanic

mineral admixtures and the addition it in concrete will start contributing to strength in

about 3 days (Bagade and Puttaswamy, 2007). A micro silica content of 5% to15 %

leads to an increase of concrete strength. However, the desirable content of micro

silica needed from point of view of workability and 28 day compressive strength is to

be determined by trials.

6.2.5 Chemical Admixtures:

The research and the experience indicate that the admixtures based on the poly

carboxylic ethers (PCE) are the best suited as they have a water reducing capacity of

18%-40% in reference to the control concrete. These admixtures assist in achieving

higher slump at much lesser w/c ratios (< 0.30).

6.3 PROPOSED MIX DESIGN METHOD FOR HPC

The proposed mix design method for HPC mixes is based on the principles of

existing IS Code method of mix design (IS 10262-1982 and IS 10262-2009). In the

development of this proposed method, the basic mix proportions were obtained for



making HPC mixes using w/c ratio’s worked out by extrapolating the established

relationships between free water cement ratio and concrete strength for different

cement strengths as shown in figure 6.1 (IS:10262-1982). Different curves indicating

28 day strength range of cement, when tested according to IS 4031-1968 is given

Table 6.1. The curves indicating relationship between free water-cement ratio and 28

days compressive strength for different cement strengths were extrapolated and

modified to generate smooth curves (figure 6.2). The equations used in developing

the smooth curves are given in Table 6.2. The quantities of fine aggregate and coarse

aggregate were determined using the equation given in IS Code method (IS: 10262-

1982). The basic mix proportions thus obtained by following the guidelines of

existing IS Code method were used in making trial HPC mixes by incorporating

desirable contents of micro silica and superplasticizer in view of achieving the desired

workability and strength properties.

Figure 6.1: Relation between free Water-Cement Ratio and Concrete

strength for different cement strengths (Extrapolated curves-original)

Table 6.1: 28 days strength of cement, tested according to IS: 4031-1968

A=31.9-36.8 N/mm2 D=46.6-51.5 N/mm

2

B=36.7 – 41.7 N/mm2 E=51.5 -56.4 N/mm

2

C=41.7 – 46.6 F=56.4-61.3 N/mm2

10

20

30

40

50

60

70

80

90

100

0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

28 D

ays

Com

p S

t.,

MP

a

Water-Cement Ratio

F-Curve

E-Curve

D-Curve

C-Curve

B-Curve

A-Curve



Figure 6.2: Relation between free W/C Ratio and Concrete St. for

different cement strengths (Modified Extrapolated-smooth curves)

Table 6.2: Equations used in developing smooth curves for relationship

between free water-cement ratio and concrete strength

Curve Exponential Equation of curve

A y = 92.85e-3.05x

B y = 107.6e-3.09x

C y = 119.5e-3.07x

D y = 131.8e-3.06x

E y = 145.0e-3.02x

F y = 159.1e-3.06x

Where, y= Comp. St., in MPa and x= w/c ratio

Further, based on experimental observations and the results of compressive

strengths of various grades of HPC mixes, the curves given in IS Code method are

modified so as to arrive at water-binder ratios best suited to different grades of HPC

mixes (Figure 6.3 to 6.5). The curve indicating generalized relationship between free

water cement ratio and compressive strength of concrete is also extrapolated and

modified so as to arrive at water-binder ratios best suited to different grades of HPC

mixes (Figure 6.6 to 6.8). The equations used to develop smooth curves for the

relationship between free water-binder ratio and compressive strength of concrete and

10

20

30

40

50

60

70

80

90

100

0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.55 0.6

28

Day

Co

mp

St.

, MP

a

Water-Cement Ratio

F-Curve

E-Curve

D-CurveC-Curve

B-Curve

A-Curve



also to arrive at water-binder ratios best suited for different grades of HPC mixes are

given in Table 6.3 and Table 6.4 respectively.

Figure 6.3: Relationship between free W/C Ratio and Concrete St. for

different Cement Strengths (Extrapolated to suit HPC)


different Cement Strengths (Extrapolated-Smooth Curves)

10

20

30

40

50

60

70

80

90

100

0.2 0.25 0.3 0.35 0.4 0.45 0.5

28

da

ys

Co

mp

St.

, M

Pa

Water- Cement Ratio

F-Curve

E-Curve

D-Curve

C-Curve

B-CurveA-Curve

(y = 235.4e-4.15x)

10

20

30

40

50

60

70

80

90

100

110

120

0.2 0.225 0.25 0.275 0.3 0.325 0.35 0.375 0.4 0.425 0.45 0.475 0.5

28 D

ay C

om

p S

t., M

Pa

Water-Binder Ratio

F-CURVE E-CURVED-CURVE C-CURVEB-CURVE A-CURVE

F-Curve

E-Curve

D-Curve

C-Curve

A-Curve

B-Curve



Table 6.3: Equations used in developing smooth curves for relationship

between free water-cement ratio and concrete strength


A y = 156.8e-4.28x

B y = 176.5e-4.26x

C y = 195.0e-4.22x

D y = 216.1e-4.19x

E y = 235.4e-4.15x

F y = 267.4e-4.25x



different Cement Strengths (Extrapolated Modified Curves to Suit HPC)

Table 6.4: Equations used in developing curves for relationship between

free w/b ratio and concrete St. best suited to HPC


A y=156.8e-4.28x

B y=176.5e-4.26x

C y =195e-4.22x

D y =216.1e-4.19x

E y = 235.4e-3.85x

F y = 267.4e-4.025x


(y = 235.4e-3.85x)

102030405060708090

100110120130

0.2 0.225 0.25 0.275 0.3 0.325 0.35 0.375 0.4 0.425 0.45 0.475 0.5

28

Day

s C

om

p S

t.,

MP

a

Water-Binder RatioF-CURVE E-CURVED-CURVE C-CURVEB-CURVE A-CURVE

F-Curve

E-Curve

D-CurveC-Curve

A-CurveB-Curve



Figure 6.6: Extrapolated Generalized Relation between free W/C ratio

and Comp. St. of Concrete (Original Curve as per IS: 10262-1982)

Figure 6.7: Extrapolated Modified (1st) generalized relation between free

W/C ratio and Comp. St. of Concrete to suit HPC mixes

y = 146.3e-3.46x

10

20

30

40

50

60

70

80

0.2 0.225 0.25 0.275 0.3 0.325 0.35 0.375 0.4 0.425 0.45 0.475 0.5

28

Da

ys

Co

mp

St.

, M

Pa

Water-Cement Ratio

y = 297e-4.84x

10

30

50

70

90

110

130

0.2 0.225 0.25 0.275 0.3 0.325 0.35 0.375 0.4 0.425 0.45 0.475 0.5

28 d

ays

Com

p S

t., M

Pa

Water-Binder Ratio



Figure 6.8: Extrapolated Generalized relation between free W/C ratio and

Comp St. of Concrete to suit HPC Mixes (Original & Modified)

From the experimental observations, the basic mix proportions adopted for

making trial HPC mixes were modified by altering coarse aggregate to fine aggregate

ratio and incorporating appropriate micro silica and superplasticizer contents so as to

get desired workability and compressive strengths for different combinations of

humidity and temperature. The proposed mix design method for HPC thus provides

the final mix proportions taking into account the parameters or variables necessary to

be incorporated in achieving the desired workability and strength properties for

different grades of HPC mixes. The various variables or parameters considered in the

proposed mix design method for HPC mixes are as given below:

1. Grade of the HPC mix under consideration

2. Desired workability for the mix

3. Prevailing Relative Humidity in the atmosphere

4. Prevailing Temperature in the atmosphere

5. Total binder content

6. Total cement content

7. Desired micro silica content

8. Desired water-binder ratio

9. Desired coarse aggregate to fine aggregate ratio

10. Desired superplasticizer dose (by weight of cement)

y = 146.3e-3.46x

y = 297e-4.84x

10

20

30

40

50

60

70

80

90

100

110

120

0.2 0.225 0.25 0.275 0.3 0.325 0.35 0.375 0.4 0.425 0.45 0.475 0.5

28

da

ys

Co

mp

St.

, M

Pa

Water-Binder Ratio



The stepwise procedure for the proposed method of mix design is outlined in

the following sections.

6.3.1 Stepwise Procedure of Proposed Mix Design Method for HPC

The mix design procedure consists of a series of steps, which when completed

provide a mixture meeting strength and workability requirements based on the

properties of selected and proportioned ingredients. Following are the necessary steps.

6.3.1.1 Step I: Test data for Materials

The test data of ingredients of HPC mixes namely specific gravity, fineness

modulus; water absorption, moisture content etc. should be obtained.

6.3.1.2 Step II: Target Mean Compressive Strength of HPC

The target mean compressive strength at 28 days curing period for HPC mix is

determined using the relationship given below:

where,

f'’ck = target mean compressive strength ,

fck = characteristic strength of concrete (grade of concrete) and

S = standard deviation (as per IS 456-2000)

As the strict quality control is necessary in making HPC mixes, the standard

deviation (SD) is not likely to exceed 5 MPa (Mullick, 2006). Hence, a standard

deviation value of 5MPa (as per IS 456 code) is assumed for arriving at target mean

strength.

6.3.1.3 Step III: Determination of Water-Binder Ratio

The determination of water-binder ratio is done by referring to the plotted

relationships between the 28 day compressive strength of concrete and water-binder

ratios for different humidity and temperature conditions as given in the figure 6.9 to

6.11. The w/b ratios for specific compressive strengths (grades of HPC mixes) and for

different humidity levels at 30oC, 35

oC, 40

oC temperature along with the equations

used for development of curves indicating relationship between w/b ratio and

corresponding compressive strengths are given in Table 6.5 to 6.10.



Figure 6.9: Relation between 28 day Comp St and Water-Binder for different humidity at 30O

C Temp

45

55

65

75

85

95

105

115

0.15 0.2 0.25 0.3 0.35 0.4 0.45

28 D

ay C

om

p S

t, M

Pa

W/B Ratio

RH-30%

RH-40%

RH-50%

RH-60%

RH-70%

RH-80%

RH-90%



Table 6.5: Comp St. and W/B ratio for different RH at 30O

C Temp

28 Day Comp

St., MPa

Humidity Levels,% (Temp-30oC)

30 40 50 60 70 80 90

58.25 0.382 0.374 0.365 0.365 0.357 0.354 0.350

68.25 0.338 0.331 0.324 0.318 0.311 0.306 0.302

78.25 0.300 0.294 0.289 0.278 0.271 0.264 0.261

88.25 0.267 0.261 0.258 0.242 0.236 0.227 0.225

98.25 0.237 0.232 0.230 0.211 0.204 0.195 0.193

Table 6.6: Equations used for development of curves for relationship

between Comp St. and W/B ratio for different RH at 30O

C Temp

Rh Exponential Equations (Temp 30oc)

30 y = 230.7e-3.6x

40 y = 230.1e-3.67x

50 y = 239.8e-3.88x

60 y = 201.2e-3.4x

70 y = 198e-3.43x

80 y = 186.5e-3.29x

90 y = 186.3e-3.32x

Where,

y =Compressive Strength in MPa,

x = w/b ratio and

e =exponent, the approximate value of e is 2.718282




C Temp

55

65

75

85

95

105

115

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

28 D

ay C

om

p S

t. M

Pa

W/B Ratio

RH-30%

RH-40%

RH-50%

RH-60%

RH-70%

RH-80%

RH-90%




C Temp

28 Day Comp

St., MPa


30 40 50 60 70 80 90

58.25 0.404 0.404 0.403 0.402 0.393 0.391 0.390

68.25 0.347 0.342 0.336 0.334 0.327 0.321 0.316

78.25 0.298 0.289 0.277 0.275 0.270 0.262 0.253

88.25 0.254 0.243 0.226 0.224 0.220 0.209 0.197

98.25 0.216 0.201 0.181 0.178 0.175 0.162 0.147

Table 6.8: Equations used in development of curves indicating relationship

between Comp St. and W/B ratio for different RH at 35O

C Temp

Rh Exponential Equations (Temp 35oC)

30 y = 179e-2.78x

40 y = 165.1e-2.58x

50 y = 150.2e-2.35x

60 y = 148.8e-2.335x

70 y = 149.5e-2.40x

80 y = 142.5e-2.29x

90 y = 134.7e-2.15x




C Temp

45

65

85

105

125

145

0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45

28 D

ay C

om

p S

t., M

Pa

W/B Ratio

RH-30

RH-40

RH-50

RH-60

RH-70

RH-80

RH-90




C Temp

28 Day Comp

St., MPa


30 40 50 60 70 80 90

58.25 0.378 0.371 0.372 0.369 0.369 0.363 0.348

68.25 0.339 0.331 0.323 0.312 0.310 0.302 0.290

78.25 0.305 0.297 0.281 0.262 0.258 0.249 0.240

88.25 0.275 0.267 0.244 0.218 0.213 0.203 0.196

98.25 0.249 0.240 0.210 0.179 0.172 0.162 0.156

Table 6.10: Equations used in development of curves for relationships

between Comp. St. and W/B ratio for different RH at 40O

C Temp

Rh Exponential Equations (Temp 40 O

C)

30 y = 269.9e-4.06x

40 y = 256.8e-4.00x

50 y = 193.8e-3.23x

60 y =160.9e-2.75x

70 y =155e-2.65x

80 y =149.6e-2.6x

90 y = 150.6e-2.73x

i. Selection of Water-Binder Ratio

The maximum w/b ratio for different exposure conditions from view point of

durability is to be adopted as per IS 456-2000. The values of w/b ratio obtained from

the developed relationships taking into account the ambient RH and Temperature is

compared with the values specified in IS 456-2000 for different exposure conditions

and the value whichever is smaller is selected for designing the HPC mixes.

6.3.1.4 Step IV: Determination of Binder Content

From the w/b ratio obtained for the target mean compressive strength and for

the specified humidity and temperature condition, the required binder content is

determined based on the proposed relationship between binder content (cement +

micro silica) and w/b ratio (Figure 6.12).



Figure 6.12: Proposed Relationship between Binder Content and W/B ratio

(Linear equation: y = -1665x + 1078, where y=binder content and x =w/b ratio)

From the selected w/b ratio and the obtained binder content, the total water content is

calculated using the following relationship:

Figure 6.13: Proposed variation of Micro Silica content with 28 days

Comp. St. of HPC

6.3.1.5 Step V: Determination of Desirable Contents of Mineral Admixture (Micro

Silica) and Cement Content

The desirable contents of micro silica required for making different grades of

HPC mixes can be obtained from the established relationship of micro silica content

y = -1665x + 1078

400

450

500

550

600

650

700

750

800

850

0.15 0.2 0.25 0.3 0.35 0.4

Bin

der

Co

nte

nt,

Kg

/m3

W/B Ratio

y = 1.146x - 33.80

20

30

40

50

60

70

80

90

100

50 55 60 65 70 75 80 85 90 95 100 105

Mic

ro S

ilic

a C

on

ten

t, K

g/m

3

28 Days Comp. St. of HPC, MPa



and compressive strength of HPC (Figure 6.13). Thus, knowing the micro silica

content, the required quantity of cement can be worked out by subtracting the micro

silica content from the total binder content.

6.3.1.6 Step VI: Determination of Desirable Contents of Superplasticizer (SP)

The type and desired dosage of superplasticizer needs to be decided by trials

to produce and maintain reasonable workability and enhance the strength of concrete

when micro silica is used as a mineral admixture. Though, in market different

varieties or brands of superplasticizers are available, the research and experience have

indicated that the admixtures based on the poly carboxylic ethers (PCE) are the best

suited as they have a water reducing capacity of 18%-40% in reference to the control

concrete.

In the present research work, HPC mixes have been developed using PCE

based superplasticizers. The dosage of superplasticizer was determined by weight of

the cement used for the HPC mix. In the proposed mix design method the

approximate superplasticizer dosages for different grades of HPC mixes (M50-M90)

corresponding to different water-binder ratios can be obtained using the plotted

relationship between superplasticizer content and the cement content required for the

specified grade of HPC mix (Figure 6.14).

Figure 6.14: Proposed variation of SP for different Cement contents

y = 0.012x - 2.83

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

400 425 450 475 500 525 550 575 600

SP

Con

ten

t, K

g/m

3

Cement Content, Kg/m3



6.3.1.7 Step VII: Determination of Coarse and Fine Aggregate Contents

Taking into account the adopted volume of coarse aggregate in the total

aggregate volume during the experimentation, a relationship between ratio of volume

of coarse aggregate to the volume of total aggregate per unit volume of concrete

(figure 6.15) is established for corresponding 28 days compressive strengths obtained.

From the established relationship the ratio of volume of coarse aggregate to the

volume of total aggregate is determined for the specified 28 days compressive

strength of the concrete.

Figure 6.15: Ratio of Volume of Coarse to Total Aggregate and 28 days

Compressive Strength (Exponential Eq.)

Thus, the following variables required for mix design process are determined:

1) Water-Binder Ratio

2) Binder content = ( Cement + Micro silica) content, Kg/m3

3) Water Content = (water-binder ratio x total binder content), kg/m3

4) Superplasticizer (by weight of cement)

5) Total Aggregate Content

= Volume of Concrete – (water + binder + superplasticizer) content

6) CA / FA Ratio

7) Volume of Fine and Coarse aggregate

y = 0.433e0.004x

0.45

0.5

0.55

0.6

0.65

0.7

0.75

0.8

50 55 60 65 70 75 80 85 90 95 100

Rati

o o

f V

ol

of

Co

ars

e A

ggt

to

Vol.

of

Tota

l A

ggt,

m3

28 Days Comp St, MPa



6.4 ILLSUTRATIVE EXAMPLE FOR MIX DESIGN OF M50 GRADE

HPC MIX

An illustrative example for mix proportioning of M50 grade HPC mix using

the Proposed Mix Design Method is presented below.

6.4.1 STIPULATIONS FOR MIX PROPORTIONING

Characteristic comp. strength : 50 N/mm2

Maximum size of aggregate : 20mm (angular)

Degree of workability – (slump) : 50-100

Degree of quality control : Good

Type of Exposure : Severe

Temperature : 30oC

Relative humidity : 50%

6.4.2 TEST DATA OF MATERIALS

Cement : OPC – 53 Grade

Specific gravity of cement : 3.15

Specific gravity of coarse aggt : 2.90

Specific gravity of fine aggt : 2.80

Water absorption,%

Coarse aggregate : 2.03

Fine aggregate : 1.48

Free (surface) moisture,%

Coarse aggregate : 1.98

Fine aggregate : 1.33 (Confirming to grading zone I of table 4

of IS: 383-1970)

6.4.3 TARGET STRENGTH FOR MIX PROPORTIONING

Where,

=target average compressive strength at 28 days

= characteristic compressive strength at 28 days,



= Standard deviation (Table 8 of IS456-2000)

= 5 N/mm2,

Therefore, target strength,

= 50 + 1.65 x 5 = 58.25 N/mm2

6.4.4 SELECTION OF WATER-BINDER RATIO

Referring to the plotted relationship between the 28 day compressive strength

of concrete and water-binder ratio (Figure 6.9), for a target mean compressive

strength of 58.25MPa and for specified humidity level of 50% and 30oC temperature a

water–binder ratio of 0.371 is obtained.

6.4.5 DETERMINATION OF BINDER CONTENT, MICRO SILICA AND

CEMENT

From the proposed relationship between binder content and w/b ratio (Figure

6.12), for a compressive strength of 58.25 MPa binder content (cement + micro silica)

of 460.28 Kg/m3

is obtained. Also, referring to the established relationship between

micro silica and 28 days compressive strength of HPC mixes (Figure 6.13), a micro

silica content of 32.94 kg/m3 (7.71%) is obtained. Thus, knowing the total binder

content and the amount of micro silica in it, the quantity of cement required can be

calculated by subtracting the micro silica content from the total binder content. Thus,

the quantity of cement is calculated as given below:

6.4.6 DETERMINATION OF DESIRABLE CONTENTS OF

SUPERPLASTICIZER (SP)

The desirable content of superplasticizer required for the desired workability is

determined by weight of cement. The superplasticizer dosage is obtained from the

established relationship between superplasticizer dosage and the cement content

required to attain the specified compressive strength under given humidity and

temperature conditions (Figure 6.14). Thus, from the calculated quantity of cement a



superplasticizer dose of 0.54% is determined. The quantity of superplasticizer per m3

of concrete is obtained as given below:

6.4.7 DETERMINATION OF WATER CONTENT

From the obtained w/b ratio and binder content, the required water content is

calculated as given below:

6.4.8 PROPORTION OF VOLUME OF COARSE AGGREGATE AND FINE

AGGREGATE CONTENT

The estimation of volume of coarse aggregate in the volume of total

aggregates is determined using the established relationship between 28 days

compressive strength and ratio of volume of coarse aggregate to the volume of total

aggregate per unit volume of concrete (Figure 6.15). Thus, for M50 grade HPC the

ratio of volume of coarse aggregate to the volume of total aggregate per unit volume

of concrete as obtained from the established relation is 0.55m3. Hence the volume of

fine aggregate is obtained as given below:

Volume of fine aggregate = (1- 0.55) = 0.45m3

6.4.9 MIX CALCULATION

Mix Calculations per unit volume of concrete shall be as follows:



6.4.9.2 Final Quantities of Ingredients and Mix Proportion

Cement = 427.34 kg/m3

Micro Silica = 32.94kg/m3

Water = 170.76 kg/m3

Fine Aggregate = 856.80 kg/m3

Coarse Aggregate =1084.60 kg/m3

Superplasticizer = 2.56 kg/m3



Figure 6.16: Workability of Trial HPC Mix (M50)

Figure (a): Slump Test

Figure (b: Flow Test

mixture

Mix Proportion obtained is : 0.37:1 (0.93: 07):1.86:2.36

The mix proportions so obtained are adjusted for field conditions as per usual

procedure before preparing trial mix.

6.5 EXPERIMENTAL VALIDATION OF PROPOSED MIX

PROPORTIONING METHOD FOR HPC

The mix proportions for different grades of HPC mixes are obtained by using

the established relationships (curves) developed through experimental studies. The

proposed method of mix proportioning of HPC mixes provides the mix proportions

for different levels of humidity and temperature combinations for the grades of M50

to M90 HPC mixes. To verify the validity of the proposed mix design method, a trial

HPC mix of M50 grade was prepared using the mix proportion obtained by the

proposed method. The mix was designed for a slump range of 75-100mm considering

a humidity of 80% with a temperature of 30oC. The mix proportion, expressed as parts

of water : binder content (cement+micro silica) : fine aggregate : coarse aggregate,

adopted for making the HPC mix was 0.36:1(0.93:0.07):1.81:2.29. A superplasticizer

content of 0.56% by weight of cement was used as obtained from the mix design.

The trial mix produced using the above proportion showed a very good quality

with a slump of 90mm and a flow value of 23.67% and a compressive strength of

54.07MPa at 28 days curing. The slump test and the flow test conducted on the trial

mix are shown in figures 6.17(a) and 6.17(b) respectively. Since the trial HPC mix

prepared was found to give satisfactory workability with good flow property and also

in a single trial for the mix proportion obtained by the proposed method, it can be

stated that the proposed method of mix design is valid for proportioning HPC mixes

for specified humidity and temperature conditions.



The Software based on the Artificial Neural Network (ANN) approach is also

developed to get the mix proportions for the given grade of HPC and any given

humidity and temperature conditions. In order to check the validity of the software, a

trial mix of M50 grade of HPC was prepared for the ambient humidity (80%) and

temperature (30OC) conditions by adopting the mix proportion provided by the

developed software (ANN). The prepared trial HPC mix showed good results in

respect of workability (slump & flow values) and compressive strength. The results of

the slump (210mm) and compressive strength test (56.70MPa) were found to be close

to the expected results for the mix. The figure 6.18 shows the various stages during

slump test. The flow of the trial mix concrete indicating the spread on the table is

shown in figure 6.19.

Figure 6.18: Flow Test on Trial HPC mix

Figure 6.17: Stages in the Slump Test on Trial Mix of HPC

(a) (b) (c) (d)

Documents

Chapter 6 PROPOSED MIX DESIGN METHOD FOR HPC …shodhganga.inflibnet.ac.in/bitstream/10603/23542/16/16_chapter_06.pdf · Chapter 6 Proposed Mix Design Method for HPC and Validity