chapter 6 experimentation and methodology for the...

CHAPTER 6

EXPERIMENTATION AND METHODOLOGY FOR THE STUDY OF RHA

ON OPC- HYDRATION SYSTEM

6.1 INTRODUCTION

This chapter reports the effect of rice husk ash on OPC hydration mechanism.

Development of compressive strength with age has been chosen as the principal

parameter for comparing the effects of rice husk ash in mortar and concrete.

6.2 MATERIALS

6.2.1 Cement

Ordinary Portland Cement-53 grade confirming to IS: 12269-1989 was used for the

present study. The total quantity of cement required was approximately estimated,

brought, and stored in an air tight container. The physical properties of the cement

were tested in accordance with IS: 4031-1968 and are given in Table 6.1.

6.2.2 Aggregates

Locally available crushed granite aggregate of 20mm maximum size was used as

coarse aggregate. Locally available river sand with fineness modulus of 2.62 was used

as fine aggregate. The specific gravity of both coarse and fine aggregate was 2.70 and

2.63 respectively and the water absorption was 0.4 percent and 0.5 percent

respectively. Aggregates were tested as per IS: 2386-1963 and the results pertaining

to the properties and sieve analysis are presented in Table 6.2. Gradation curves for

fine and coarse aggregates are shown in Figs. 6.1(a) & (b) respectively.

6.2.3 Rice Husk Ash

Rice husk ash produced under optimum incineration/production condition (500°C -

120 minutes) was used for further studies. The grinding was done in a laboratory ball

mill for 30 minutes duration (Vide § 4.4). The sample retrieved from the furnace was

110

kept in air tight polythene bags and stored in a similar manner after grinding. The

standard Le-chatelier flask confirming to IS: 1727-1967 was used for the

determination of specific gravity of RHA samples. The fineness of RHA samples

were found out using Blaine’s air permeability apparatus as per IS: 1727-1967 and

BET nitrogen adsorption technique (vide § 4.6.3). The chemical composition of RHA

was found out by chemical analysis tests. The physical properties and chemical

composition of RHA are presented in Table 6.3.

a) Properties of RHA: The specific gravity of RHA sample studied was observed as

2.19. The range of specific gravity values reported by earlier researchers is 2.02 to

2.16 [Nehdi et al., 2003; Bui et al., 2005 and Ganesan et al., 2008]. It is to be noted

that the fineness of RHA sample used in the present study is higher than the values

reported by other studies [Zhang et al., 1996; Nehdi et al., 2003 and Ganesan et al.,

2008].

Loss on ignition (LOI) which represents the un-burnt carbon present in the sample is

one of the important parameters for assessing the quality of pozzolana. In the present

study, LOI of RHA sample is 2.27 percent. This value is much lower than the

maximum limit of 10 percent prescribed for Class N pozzolan [ASTM C 618]. It is

observed that the total oxide content, including silica, alumina, and iron, is 91 percent.

Sodium oxide is present in 2.09 percent. Alkalies in RHA are permanently bound in

the structure and therefore do not leach out and are not available for alkali silica

reaction [Mehta and Folliard, 1995 and Hwang and Chandra, 1997].

6.2.4 Chemical Admixture

Due to the porous nature of RHA, there will be a considerable reduction in the

workability of the mixes. Therefore, super-plasticizer was used as water reducing

111

agents to maintain required/comparable workability. Super-plasticizer based on

second generation of poly carboxylic ether polymers, developed using nano

technology was used for the mortar and concrete mixtures as high range water

reducing agents. It is a light brown free flowing liquid solution containing not less

than 30 percent solids by weight.

6.2.5 Mixing Water

Ordinary potable water available in Pondicherry Engineering College (PEC) campus

was used for the entire experimental investigation including curing of specimens.

6.3 RICE HUSK ASH MORTAR

6.3.1 Consistency and Setting Time of RHA- OPC Blends

Standard consistency of RHA blended cement samples was determined in accordance

with IS: 4031 (Part 4)-1995 with RHA content varied from 10 percent to 30 percent

by weight. Pastes having standard consistency were used to determine the initial

setting time and final setting time in accordance with IS: 4031 (Part 5) -1995. It was

observed that the consistency values of RHA blends varied from 31 percent to 42

percent. The initial and final setting times of RHA blends varied from 125 to 110

minutes and 185 to 162 minutes respectively. Fig.6.2 indicates that the increase in

RHA content causes the increase in water requirement for standard consistency. Due

to high specific surface area and hygroscopic nature of RHA, it absorbs more water

[Ganesan et al., 2008 and Hwang and Chandra, 1997].

Fig. 6.3 shows the setting time of cement paste with RHA in various percentage of

replacement. RHA addition tends to increase the initial setting time of cement. The

rate of increase in initial setting time varies depending upon the addition rate of RHA.

The rate of increase increases with RHA replacement up to 20 percent and then it

112

decreases. But, according to Ganesan et al. (2008), the decrease was beyond 15

percent RHA addition. Unlike other pozzolanic materials, RHA tends to shorten the

final setting time. The rate of retardation of final setting time decreases continuously

with increase in RHA content up to 30 percent. This may be due to the water

adsorption ability of the cellular form of rice husk ash and hence, the surrounding

water-to-cement ratio is reduced. Similar observations were made by Hwang and

Chandra (1997).

6.3.2 Hydration Mechanism of RHA Mortar

To study the hydration mechanism of RHA with cement, standard cement mortar

cubes and RHA-cement mortar cubes were prepared by partially replacing 10 percent

(mass) of cement by RHA. Water-binder ratio was maintained constant for all the

mixtures by introducing water reducing agents. Addition of RHA increased the water

demand of mortar and hence super-plasticizer (SP) was added. The dosage of super-

plasticizer was 0.75 percent by weight of cementitious materials.

Reference mortar cubes and OPC-RHA mortar cubes of specimen size 70.6mm were

prepared with 1:3 mix proportions using 53 grade OPC cement as per IS: 4031 part 6

(1998). Initially, RHA and standard sand were mixed thoroughly for 2 minutes and

then mixed with cement thoroughly till homogeneous mixture obtained. Totally 30

specimens were prepared to study the hydration mechanism of RHA in mortar. Soon

after the preparation of mortar specimens, they were covered by wet gunny bags in

order to avoid desiccation, for the initial period of 24 hours. After 24 hours, the

specimens are de-moulded and transferred to water for curing under laboratory

conditions. Compressive strength of the mortar cubes was determined at 1, 3, 7, 28

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and 60 days, using three test specimens per age. Lumps of crushed specimens were

examined at appropriate ages under SEM.

Variation of compressive strength with age has been presented in Fig.6.4. In attaining

strength levels, RHA mortar cubes shows higher compressive strength than that of

reference mix at all ages. Maximum percentage of increase in strength was about 24

percent at the age of 60 days.

Figs.6.5 & 6.6 shows SEM micrographs taken on fractured specimen of reference

mortar cubes and OPC-RHA blend cubes at various ages of hydration. Calcium

silicate hydrates crystals with fibrous morphology and poorly crystalline is clearly

identified from Fig.6.5 (a). Fig.6.5 (b) shows the presence of small fibrous crystals of

calcium silicate hydrates, thin hexagonal crystals of mono sulphate hydrate and needle

shaped crystals of calcium sulpho aluminate hydrate (ettringite) in the control mix.

Appearance of massive crystals of calcium hydroxide can be noticed from the Fig.6.5

(e). Even at 28 days of hydration, appearance of calcium hydroxide crystals in the

OPC hydration system is recognized from Fig. 6.5 (h). In RHA mortar, C-S-H gel

was in the form of dense sponge matrix (Fig.6.6 (a)). Close scrutiny reveals small

protuberances on the gel matrix. It looks like bundle of fibres interlocked and have

flower ends (Fig.6.6 (b). Large prismatic crystals of calcium hydroxide were seen.

Irregular particles of RHA were also seen (Fig.6.6 (c)). After three days of hydration,

fibers of CSH gel grow in size and occupy the voids (Fig.6.6 (e) & (f)). This is also

confirmed by SEM-EDXA analysis (Fig.6.7). Some hexagonal plates similar to mono

sulpho aluminate were also observed on three days of hydration. After 28 days of

hydration (Fig.6.6 (h)), small fibrous crystals of calcium silicate hydrates are seen

predominantly. The matrix becomes denser. The presence of calcium hydroxide

114

becomes unclear. SEM-EDXA analysis (Figs.6.8 & 6.9) specified the formation of

relatively denser hydrated products in the OPC-RHA system with probably a few

calcium hydroxide cubical crystals.

6.4 RHA BLENDED CONCRETE

6.4.1 General

Compressive strength is the most important mechanical property of concrete. In

general, for a given set of cement and aggregates and under the same mixing, curing,

and testing conditions, the compressive strength of a concrete primarily depends on

water binder (w/b) ratio, binder/aggregate ratio, mixture composition, degree of

consolidation, etc. However, it is the w/b ratio that chiefly controls the development

of compressive strength in concrete. The limits of w/b ratio to achieve a targeted

compressive strength in high-strength HPC are as follows: [Lessard et al., 1995]

50 MPa – 75 MPa, for 0.30≤ w/b≤ 0.40

75 MPa – 100 MPa, for 0.25 ≤ w/b ≤ 0.35

100 MPa – 125 MPa, for 0.20 ≤ w/b ≤ 0.30

125 MPa and above, for w/b ≤ 0.20

6.4.2 Mix Proportions Selected

Four concrete mixtures have been considered in the present study. They are

designated as C550, C500, C450, and C350. C550 indicates that the cement content in the

mixture is 550 kg/m3. The four mixtures were proportioned with suitable quantity of

fine and coarse aggregates and water cement ratio such that the slump of concrete was

aimed at 75 to 100 mm. RHA has been added to the concrete mixtures in partial

replacement of cement by 10, 15, 20 and 30 percentage on weight basis. The mixture

details are presented in Table 6.4. Totally 19 concrete mixtures including control

115

mixtures are considered in the work. The super-plasticizers dosage is tailored in each

mixture to achieve a slump of 75 to 100 mm. The slump details are also presented in

Table 6.4.

6.4.3 Casting of Specimens

A laboratory type concrete pan mixture of 55 litre capacity was employed to prepare

concrete mixtures. Initially the dry ingredients were mixed for 2 minutes to ensure

homogeneity and then mixed for 3 minutes after adding water. Slump of concrete was

determined immediately following the mixing. Cubes of 100 mm size were cast and

compacted in two layers using vibrating table. The moulds were covered, after casting

with wet gunny bags for 24 hours. Thereupon, the specimens were de-moulded and

cured in water at a temperature of 20°C until the day of testing. Totally 228 specimens

were prepared to study the compressive strength. Compressive strength of the

concrete specimens was determined at 3, 7, 28, and 60 days using three test specimens

per age.

6.5 TESTS CONDUCTED

6.5.1 Compatibility Test

Chemical admixtures, especially super-plasticizers have become essential components

of high performance and high strength concretes. There are guidelines available to use

chemical admixtures on concrete. However, these guidelines are for general purpose

applications only. When it becomes the need for maximum exploitation of a chemical,

it needs to be done carefully and cautiously without causing any adverse behavior on

concrete.

In this study, compatibility tests were conducted by means of a marsh cone with

dimensions as shown in Fig.6.10 (a) and Photo 6.10 (b). This is an approach similar to

116

the flow cone tests in the ASTM C 939 and a recent AFREM recommendation. It

consists of an inverted hollow metal cone with small opening of 12.5 mm at the

bottom. The test was conducted using the following procedure:

A marsh cone was attached to a wall using the clamp so that the small

orifice was pointing down and a graduated glass cylinder was placed

under the cone.

Closing the small orifice with the finger, 1000 ml of cement paste was

poured into the cone.

The orifice was opened and the stop watch was started.

The time taken for 200 ml to flow through it is determined.

The same procedure is repeated for various dosages of super

plasticizers level.

The fluidity and the saturation dosage for a particular cement-super plasticizer

combination are determined by generating a flow curve. The variation of time of flow

with SP dosage is shown in Fig. 6.11. The plot reflects the decrease in the flow time

(or the increase in fluidity) due to the incorporation of SP until the saturation dosage,

beyond which the fluidity does not increase significantly. Optimum dosage of super

plasticizer used in this study as determined by the flow curve is 2.5 percent.

6.5.2 Workability

It is the property of freshly mixed concrete that determines the ease with which it can

be properly mixed, placed, consolidated, and finished without segregation. Slump was

used as a measurement of workability. Slump was measured as per IS: 1199 (1989).

The slump was maintained between 75 to 100 mm by varying the dosage of the super

plasticizer for all mixes. The dosages of super plasticizer for different mixes to have

117

desired slump range are shown in Fig. 6.12. All investigated mixtures had targeted

slump values. Higher the RHA content, higher will be the SP dosage. The maximum

dosage of SP was 11.00 lit/m3 for mix C550-30. RHA being very fine material

demanded more SP dosage to maintain comparable workability. Increased surface

area necessitated the use of higher dosage of SP to achieve targeted range of

workability. This behaviour goes well with the findings of Bui et al, (2005).

6.5.3 Compressive Strength

Compressive strength was determined at the ages of 3, 7, 28, and 60 days. At the

appropriate ages the specimens were recovered from water curing. Surface water was

wiped off, and then tested for compressive strength in accordance with IS: 516 (1959)

using 3000 kN compressive testing machine. The compressive strength for various

mixes is presented in Tables 6.5 to 6.8 and Figs. 6.13 to 6.16.

RHA addition has contributed to strength improvement of concrete at all ages.

However, with the amount of cement replacement up to 20 percent with RHA,

strength gain goes up and beyond this level of RHA addition, the strength gain

decreases. Investigation has been carried out in the range of 0 to 30 percent of cement

replacement. At 30 percent RHA addition, compressive strength of RHA concrete

attains values equivalent to that of control concrete mixtures. From the results, it is

inferred that 20 percent RHA addition contributes to maximum strength in all the

mixtures. The above behaviour is independent of the age of curing and water binder

ratio. From the study, it is noticed that cement content of the concrete mixture has

some impact on the compressive strength of RHA-concrete. The maximum

compressive strength attained is 92MPa for the C550 concrete mix with 20 percent

118

RHA replacement. It appears that higher the cement content higher will be the

compressive strength, however it needs further investigation for confirmation.

Increase in compressive strength of RHA concrete mixtures for various cement

replacement levels at various ages are depicted in Figs.6.17 & 6.18. Percentage of

increase in compressive strength increases with increase in RHA content up to 20

percent and beyond this level of RHA addition; it gets decreased drastically for all

mixtures. C500 and C350 concrete mixes has the highest and the lowest percentage of

increase in compressive strength respectively. The corresponding values are 25

percent and 5 percent. It reveals that 20 percent RHA addition is the optimum for the

maximum contribution to the compressive strength of RHA concrete.

Variation of compressive strength of RHA concretes with respect to cement

replacement levels are shown in Figs.6.19 to 6.21. Rate of increase in compressive

strength remains fairly uniform up to 10 percent RHA addition level. Between 10 and

20 percent level, rate of increase in compressive strength increases with increase in

RHA content. The highest increase in compressive strength is found at 20 percent

RHA addition level for all investigated mixtures. Beyond 20 percent level, there is a

steep decrease in the rate of increase in compressive strength of RHA concrete

mixtures.

The relative strength of RHA blended concrete for various mixes is shown in Figs.

6.20 to 6.23. Relative strength is defined as the ratio of compressive strength of RHA

blended concrete to the strength of plain cement concrete with the same binder

content and cured to the same age. Relative strength is found to increase with the

amount of RHA addition up to 20 percent for all the mixes and is found to be more

than 100 percent. At 30 percent RHA addition level, relative strength decreases

119

drastically and it is almost equal to 100 percent. It is noticed that with respect to age,

the relative strength increases with increase up to 28 days and remains fairly uniform

or slightly increases at later age of 60 days. The maximum value of relative strength

attained is 125 percent. This is probably due to the fact that during this period

pozzolanic reaction is active.

It was reported that the compressive strength of concrete containing up to 30 percent

RHA was higher than that of control concrete [Zhang and Malhotra, 1996;

Bhanumathidas and Mehta, 2004]. The amorphous silica and high specific surface

area of RHA are the principle reasons for the excellent pozzolanic activity and

increase in compressive strength of concrete.

6.6 SUMMARY

In this chapter, comprehensive experimental investigations on the effect of RHA on

OPC hydration system were carried out. RHA addition tends to retard the initial

setting and accelerate the final setting. Compressive strength of mortar cubes blended

with RHA was higher than that of reference mix at all ages. Microscopic studies

confirm the formation of relatively denser hydrated products of C-S-H in OPC-RHA

hydration mechanism. The strength characteristics of RHA blended concretes were

also investigated. It was observed that RHA contribute much to the strength gain in

concrete. Compressive strength of reference concrete mixtures varies from 49 to 80

MPa. Whereas, compressive strength of RHA concrete mixtures varies from 55 to 92

MPa.

The results obtained have indicated that 20 percent RHA addition is optimum, since

the maximum strength is achieved at that level. The maximum percentage of relative

strength achieved in RHA concrete is 125 percent. However, at 30 percent

120

replacement, comparable/equivalent strength with respect to the reference mixture is

achieved. Though in the present study, RHA was not replaced beyond 30 percent,

from the overall behaviour and trend of strength gain, addition of RHA beyond 30

percent could not be beneficial. Further, the SP requirement beyond 30 percent RHA

addition may be increased significantly, which may result in high cost.

121

Table 6.1: Physical properties of cement

S.No Properties 53 Grade OPC Recommended as

per IS:12269

1 Standard consistency (%) 29.0 -

2 Initial setting time, minutes 105 30 (min)

3 Final setting time, minutes 145 600 (max)

4 Specific gravity 3.10 -

5

Compressive strength (MPa)

3days

7days

28days

28.03

40.65

56.75

27 (min)

37 (min)

53 (min

Table 6.2: Properties of aggregates

Sieve size(mm)

Cumulative percentage retained (%)

Coarse aggregate Fine aggregate

20 mm 54.1 -

16 mm 81.2 -

12.5 mm 96.6 -

10 mm 99.5 -

4.75 mm 99.99 0.5

2.36 mm - 1.6

1.18 mm - 22.5

600 µm - 63.3

300 µm - 77.5

150 µm - 98.4

Fineness modulus 9.31 2.62

Water absorption (%) 0.40 0.50

Specific gravity 2.74 2.63

Rodded density (g/cc) 1.74 1.62

122

Table 6.3: Physical properties and chemical composition of RHA

Properties RHA

Physical properties

Specific gravity

Fineness passing 45μm (%)

Blaine’s fineness (cm2/g)

BET surface area (m2/g)

Colour

Constituents by weight (%)

Silicon dioxide (SiO2)

Ferric oxide (Fe2O3)

Calcium oxide (CaO)

Aluminum oxide (Al2O3)

Magnesium oxide (MgO)

Sulphur oxide (SO3)

Sodium oxide (Na2O)

Potassium oxide (K2O)

Loss on ignition

2.19

99.50

22, 260

50.20

White

89.47

0.62

2.69

Traces

1.16

0.93

2.09

0.83

2.27

Table 6.4: Mix proportions and slump of the various concrete mixtures

Mix

designation

Cement

(kg/m3)

RHA

(kg/m3)

Sand

(kg/m3)

Coarse

aggregate

(kg/m3)

Water

(lit/m3)

SP*

(lit/m3)

w/b**

Slump

(mm)

C550-0

C550-10

C550-15

C550-20

C550-30

550

495

467

445

385

0

55

83

105

165

490

490

490

490

490

1200

1200

1200

1200

1200

165

165

165

165

165

2.75

4.12

5.50

8.25

11.00

0.30

0.30

0.30

0.30

0.30

100

80

90

85

80

C500-0

C500-10

C500-15

C500-20

C500-30

500

450

425

400

350

0

50

75

100

150

510

510

510

510

510

1240

1240

1240

1240

1240

165

165

165

165

165

1.75

2.25

3.50

6.75

9.75

0.33

0.33

0.33

0.33

0.33

75

100

80

90

85

C450-0

C450-10

C450-15

C450-20

C450-30

450

405

382

360

315

0

45

68

90

135

530

530

530

530

530

1280

1280

1280

1280

1280

162

162

162

162

162

1.35

1.80

2.70

5.40

8.10

0.36

0.36

0.36

0.36

0.36

100

90

100

80

85

123

C350-0

C350-10

C350-15

C350-20

350

315

297

280

0

35

53

70

560

560

560

560

1345

1345

1345

1345

154

154

154

154

0.87

1.22

1.75

3.15

0.44

0.44

0.44

0.44

90

100

75

75

SP* - Super-plasticizer

w/b**- Water-binder ratio

Table 6.5: Compressive strength and relative strength of concrete mix C350

Mix

designation

Compressive strength (MPa) at

various ages (days)

Relative strength (%) at various

ages (days)

3 7 28 60 3 7 28 60

C350-0 30.5 38.4 43.4 49.2 100 100 100 100

C350-10 31.4 39.6 45.5 51.8 103 103 105 106

C350-15 32.0 42.1 47.5 54.6 105 110 110 111

C350-20 34.0 43.5 49.3 55.4 111 113 114 112


Mix

designation


various ages (days)


ages (days)

3 7 28 60 3 7 28 60

C450-0 53.2 61.1 67.3 72.0 100 100 100 100

C450-10 53.5 61.5 73.8 78.3 100 104 109 109

C450-15 55.6 66.4 75.6 81.7 103 108 112 113

C450-20 60.3 71.2 79.5 87.0 113 116 118 120

C450-30 51.3 62.1 67.3 73.4 97 102 101 102

124


Mix

Designation


various ages (days)


ages (days)

3 7 28 60 3 7 28 60

C500-0 55.1 61.0 68.2 71.0 100 100 100 100

C500-10 57.4 63.8 72.0 78.0 104 105 106 108

C500-15 59.3 67.5 76.5 81.0 108 110 112 113

C500-20 61.7 72.0 85.0 88.6 113 116 125 122

C500-30 52.0 60.1 69.4 72.3 95 98 102 101


Mix

Designation


various ages (days)

Relative strength (%) at

various ages (days)

3 7 28 60 3 7 28 60

C550-0 48.1 64.0 76.0 80.0 100 100 100 100

C550-10 49.7 66.0 83.5 87.0 102 103 110 109

C550-15 51.0 69.0 85.0 90.1 106 108 112 113

C550-20 52.0 70.0 87.0 92.0 108 109 115 116

C550-30 47.1 64.5 76.4 81.0 98 101 100 101

125

Fig. 6.1 (a): Gradation curve for fine aggregate

Fig. 6.1(b): Gradation curve for coarse aggregate

0

20

40

60

80

100

120

0.1 1 10

Cu

mu

lati

ve p

assi

ng

(%)

IS sieve size (mm)

0

20

40

60

80

100

120

1 10 100

IS sieve size(mm)

Cu

mm

ula

tive

pa

ssin

g (

%)

126

Fig. 6.2: Standard consistency of RHA- OPC blends

Fig. 6.3: Initial and final setting time of RHA-OPC blends

0

5

10

15

20

25

30

35

40

45

0 5 10 15 20 25 30 35

Stan

dar

d c

on

sist

en

cy (

%)

Cement replacement level (%)

0

20

40

60

80

100

120

140

160

180

200

0 10 20 30

Sett

ing

tim

e (

min

ute

s)


initial setting time

Final setting time

127

Fig. 6.4: Compressive strength of reference and RHA blended mortar specimens

0

10

20

30

40

50

60

70

80

0 10 20 30 40 50 60

Co

mp

ress

ive

str

en

gth

(M

Pa)

Age (days)

Reference mortar

10% RHA

(a) 1 day (b) 1 day (c) 1 day (d) 1 day

(e) 3 days (f) 3 days (g) 28 days (h) 28 days

Fig. 6.5: SEM micrographs on fractured specimens of reference mortar cubes at various ages of hydration

128

(a) 1 day (b) 1 day (c) 1 day (d) 1 day

(e) 3 days (f) 3 days (g) 28 days (h) 28 days

Fig. 6.6: SEM micrographs on fractured specimens of OPC-RHA blend cubes at various ages of hydration

129

Fig. 6.7: SEM EDXA analysis on fractured specimens of OPC-RHA mortar cubes on 3 days of hydration

130

Fig. 6.8: SEM EDXA analysis on fractured specimens of reference mortar cubes on 28 days of hydration

131

Fig. 6.9: SEM EDXA analysis on fractured specimens of OPC-RHA mortar cubes on 28 days of hydration

132

133

Fig. 6.10: (a) Marsh cone details (b) Test set up photo

Fig.6.11: Marsh flow curve for various dosages of super plasticizer

0

2

4

6

8

10

12

0.5 1 1.5 2 2.5 3 3.5 4

Tim

e o

f fl

ow

(se

con

ds)

Dosage of SP (% wt of cement)

134

Fig.6.12:Super plasticizer dosage for various percentages of cement

replacement level

Fig. 6.13: Compressive strength of RHA blended concrete at various ages for

C550 concrete mix

0

0.5

1

1.5

2

2.5

0 10 20 30 40

SP

do

sag

e (%

)


C350

C450

C500

C550

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Co

mp

ress

ive

str

en

gth

(M

Pa)

Age (days)

Reference mix

10% RHA

15%RHA

20%RHA

30%RHA

135

Fig. 6.14: Compressive strength of RHA blended concrete at various ages for C500

concrete mix


concrete mix

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Co

mp

ress

ive

str

en

gth

(M

Pa)

Age (days)

Reference mix

10% RHA

15%RHA

20%RHA

30%RHA

0

10

20

30

40

50

60

70

80

90

100

0 10 20 30 40 50 60 70

Co

mp

ress

ive

str

en

gth

(M

Pa)

Age (days)

Reference mix

10% RHA

15%RHA

20%RHA

30%RHA

136


concrete mix

Fig. 6.17: Increase in the compressive strength of RHA blended concrete mixtures for

various cement replacement levels

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70

Co

mp

ress

ive

str

en

gth

(M

Pa)

Age (days)

Reference mix

10% RHA

15%RHA

20%RHA

0

5

10

15

20

25

30

0 5 10 15 20 25 30 35

Incr

eas

e in

str

en

gth

@2

8 d

ays

(%)


C550

C500

C450

C350

137

Fig. 6.18: Increase in the compressive strength of RHA blended concrete mixtures for

various cement replacement levels

Fig. 6.19: Compressive strength of C550 concrete mix at cement replacement levels

0

5

10

15

20

25

0 10 20 30 40

Incr

eas

e in

str

en

gth

@6

0 d

ays

(%)


C550

C500

C450

C350

0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35

Co

mp

ress

ive

str

en

gth

(M

Pa)

RHA content (%)

3 days 7 days

28 days 60 days

138



0

10

20

30

40

50

60

70

80

90

100

0 5 10 15 20 25 30 35

Co

mp

ress

ive

str

en

gth

(M

Pa)

RHA content (%)

3 days 7 days

28 days 60 days

40

45

50

55

60

65

70

75

80

85

90

0 5 10 15 20 25 30 35

Co

mp

ress

ive

str

en

gth

(M

Pa)

RHA content (%)

3 days 7 days

28 days 60 days

139

Fig. 6.22: Relative strength at various RHA replacement levels for C550 concrete mix


90

95

100

105

110

115

120

0 20 40 60 80

Re

lati

ve s

tre

ngt

h (

%)

Age (days)

10% RHA

15%RHA

20%RHA

30%RHA

90

95

100

105

110

115

120

125

130

0 20 40 60 80

Re

lati

ve s

tre

ngt

h (

%)

Age (days)

10% RHA

15%RHA

20%RHA

30%RHA

140



90

95

100

105

110

115

120

125

0 20 40 60 80

Re

lati

ve s

tre

ngt

h (

%)

Age (days)

10% RHA

15%RHA

20%RHA

30%RHA

100

102

104

106

108

110

112

114

116

0 20 40 60 80

Re

lati

ve s

tre

ngt

h (

%)

Age (days)

10% RHA

15%RHA

20%RHA

chapter 6 experimentation and methodology for the...

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