3.0 development of m 25 grade of self compacting...

63

3.0 DEVELOPMENT OF M 25 GRADE OF

SELF COMPACTING CONCRETE

This investigation is mainly focused on the development of cost-effective

normal strength M 25 grade of SCC with moderate fines for the use of normal

building constructions. This chapter describes the constituent materials used to make

SCC, the test methods that are used for testing fresh mortar, fresh, hardened

mechanical, drying shrinkage and microlevel properties of SCC. In this study, a

simple tool has been developed for SCC mix design on the basis of key proportions of

the constituents of SCC.

This chapter investigated the use of mini slump cone test along with the

graduated glass plate to obtain the optimization of superplasticiser (SP) and viscosity

modifying agent (VMA) in self compacting mortar (SCM). The effect of coarse

aggregate blending on fresh properties of SCC has been studied and thereby

optimization of coarse aggregate blending in a given coarse aggregate content of SCC

was determined. The effect of coarse aggregate blending on mechanical properties of

SCC has been studied. The mechanical properties of M 25 grade of SCC and CC were

compared at different curing periods. Drying shrinkage of M 25 grade of SCC and CC

was measured at different drying periods. The effect of class F fly ash on the

microlevel properties of SCC was investigated and the correlation of micro and

macrolevel (mechanical) properties of concrete (SCC and CC) was also studied.

3.1 MATERIALS AND METHODS

This section describes the materials used to make SCC and test methods for

testing the fresh mortar and SCC fresh and hardened properties.

64

3.1.1 Materials

Constituent materials used to make SCC can have a significant influence on

the fresh and hardened characteristics of the SCC. The following sections discuss

constituent materials used for manufacturing SCC. Chemical and physical properties

of the constituent materials are presented in this section.

3.1.1.1 Cement

Ordinary Portland Cement 53 grade (Dalmia) was used corresponding to

IS 12269 (1987)86. The chemical properties of the cement as obtained by the

manufacturer are presented in the Table 3.1.

Table 3.1. Chemical composition of cement

ParticularsTest

result

Requirement as per

IS:12269-1987

Chemical Composition

% Silica(SiO2) 19.79

% Alumina(Al2O3) 5.67

% Iron Oxide(Fe2O3) 4.68

% Lime(CaO) 61.81

% Magnesia(MgO) 0.84 Not more Than 6.0%

% Sulphuric Anhydride (SO3) 2.48Max. 3.0% when C3A>5.0

Max. 2.5% when C3A<5.0

% Chloride content 0.003 Max. 0.1%

Lime Saturation Factor

CaO-

0.7SO3/2.8SiO2+1.2Al2O3+0.65Fe2O3

0.92 0.80 to 1.02

Ratio of Alumina/Iron Oxide 1.21 Min. 0.66

Summary of physical properties and various tests conducted on cement as per

IS 4031(1988)80, 81, 82, 83 are presented in the Table 3.2.

65

Table 3.2 Physical Properties of Cement

Physical propertiesTest

resultTest method/ Remarks

Requirement as

per IS 12269

(1987)

Specific gravity 3.15 IS 4031(1988) – part 11 -

Fineness (m2/Kg) 311.5 Manufacturer data Min.225 m2/kg

Normal consistency 30% IS 4031 (1988)- part 4 -

Initial setting time (min) 90 IS 4031 (1988)- part 5 Min. 30 min

Final setting time (min) 220 IS 4031 (1988)- part 5 Max. 600 min

Soundness

Lechatelier Expansion

(mm)

Autoclave Expansion (%)

0.8

0.01

Manufacturer data Max. 10 mm

Max. 0.8%

Compressive strength

(MPa)

3 days

7 days

28 days

25

39

57

IS 4031 (1988)- part 627 MPa

37 MPa

53 MPa

3.1.1.2 Additive or Mineral Admixture – Fly Ash

Class F fly ash produced from Rayalaseema Thermal Power Plant (RTPP),

Muddanur, A.P is used as an additive according to ASTM C 618( 2003)11. As per

IS 456 (2000)76, cement is replaced by 35% of fly ash by weight of cementitious

material. The properties of fly ash as obtained by RTPP are presented in the Table 3.3.

66

Table 3.3 Chemical and physical properties of class F fly ash

ParticularsClass F

fly ash

ASTM C 618 class F

Fly ash

Chemical composition

% Silica(SiO2) 65.6

% Alumina(Al2O3) 28.0

% Iron Oxide(Fe2O3) 3.0 SiO2+ Al2O3+ Fe2O3>70

% Lime(CaO) 1.0

% Magnesia(MgO) 1.0

% Titanium Oxide (TiO2) 0.5

% Sulphur Trioxide (SO3) 0.2 Max. 5.0

Loss on Ignition 0.29 Max. 6.0

Physical properties

Specific gravity 2.12

Fineness (m2/Kg) 360 Min.225 m2/kg

3.1.1.3 Chemical Admixtures

Sika Viscocrete 10R is used as high range water reducer (HRWR) SP and

Sika Stabilizer 4R is used as VMA. The properties of the chemical admixtures as

obtained from the manufacturer are presented in the Table 3.4.

Table 3.4 Properties of chemical admixtures

Chemical

Admixture

Specific

gravitypH

Solid

content (%)

Quantity (%)

by

cementitious

weight

Main component

Sika Viscocrete

10R1.10 5.0 40 0.6-2.0

Sika Stabilizer

4R1.09 7.0 40 0.2-1.0

Polycarboxylate

Ether

67

3.1.1.4 Coarse Aggregate

Crushed granite stones of size 20 mm and 10 mm are used as coarse

aggregate. The bulk specific gravity in oven dry condition (OD) and water absorption

of the coarse aggregate 20 mm and 10mm as per IS 2386 (Part III, 1963)79 are 2.6 and

0.3% respectively. The gradation of the coarse aggregate was determined by sieve

analysis as per IS 383 (1970)75 and presented in the Tables 3.5 and 3.6. The grading

curves of the coarse aggregates as per IS 383 (1970)75 are shown in Figs. 3.1 and 3.2.

Fineness modulus of coarse aggregate 20 mm and 10 mm are 6.95 and 5.89

respectively.

Table 3.5. Sieve analysis of 20 mm coarse aggregate

Cumulative percent passingSieve size

20 mm IS 383 (1970) limits

20 mm 100 85-100

16 mm 56.17 N/A

12.5 mm 22.32 N/A

10 mm 5.29 0-20

4.75 mm 0 0-5

Table 3.6. Sieve analysis of 10 mm coarse aggregate

Cumulative percent passingSieve size

10 mm IS 383 (1970) limits

10 mm 99.68 85-100

4.75 mm 8.76 0-20

2.36 mm 2.4 0-5

68

0

20

40

60

80

100

0.01 0.1 1 10 100

IS Sieve Size (mm)

Perc

enta

ge P

assi

ng20mm

Lower Limit (IS 383:1970)

Upper Limit (IS 383:1970)

Fig. 3.1 Grading curve of 20 mm coarse aggregate

0

20

40

60

80

100

0.01 0.1 1 10 100

IS Sieve Size (mm)

Perc

enta

ge P

assi

ng

10mm

Lower Limit (IS 383:1970)


Fig. 3.2 Grading curve of 10 mm coarse aggregate

69

Dry-rodded unit weight (DRUW) and void ratio of coarse aggregate with

relative blending by percentage weight as per IS 2386 (Part III, 1963)79 is shown in

Table 3.7 and Fig. 3.3.

Table 3.7 Dry-rodded unit weight and void Ratio of a given

coarse aggregate blending

Coarse aggregate blending

by percentage weight

( 20 mm and 10 mm)

DRUW

(kg/m3)Void ratio

100:0 1596 0.386

80:20 1642 0.368

70:30 1647 0.366

67:33 1659 0.362

60:40 1646 0.367

40:60 1631 0.373

20:80 1559 0.4

0:100 1533 0.41

1500

1550

1600

1650

1700

0% 20% 40% 60% 80% 100%

10mm aggregate to total gravel (by wt.)

Dry

-rodd

ed b

ulk

dens

ity, k

g/m

3

0.35

0.36

0.37

0.38

0.39

0.4

0.41

0.42

Voi

d

Bulk densityVoid

Fig. 3.3 Dry-rodded unit weight and void ratio of a given coarse aggregate blending

70

The DRUW of coarse aggregate 20 mm and 10 mm with relative blending

70:30, 67:33, 60:40 and 40:60 by percentage weight are 1647 kg/m3, 1659 kg/m3,

1646 kg/m3 and 1631 kg/m3 respectively. In this investigation, these four coarse

aggregate blending 70:30, 67:33, 60:40 and 40:60 were used to study the effect of

coarse aggregate blending on fresh properties of SCC.

3.1.1.5 Fine Aggregate

Natural river sand is used as fine aggregate. The bulk specific gravity in

oven dry condition (OD) and water absorption of the sand as per IS 2386 (Part III,

1963)79 are 2.6 and 1% respectively. The gradation of the sand was determined by

sieve analysis as per IS 383 (1970)75 and presented in the Table 3.8. The grading

curve of the fine aggregate as per IS 383 (1970)75 is shown in Fig. 3.4. Fineness

modulus of sand is 2.26.

Table 3.8. Sieve analysis of fine aggregate

Cumulative percent passing

Sieve No.Fine aggregate

IS: 383-1970 – Zone III

requirement

3/8” (10mm) 100 100

No.4 (4.75mm) 100 90-100

No.8 (2.36mm) 100 85-100

No.16 (1.18mm) 99.25 75-100

No.30 (600μm) 65.08 60-79

No.50 (300μm) 7.4 12-40

No.100 (150μm) 1.9 0-10

71

0

20

40

60

80

100

0.01 0.1 1 10

IS Sieve Size (mm)

Perc

enta

ge P

assi

ng

Fine AggregateLower Limit (IS 383:1970)


Fig. 3.4 Grading curve of fine aggregate

3.1.1.6 Water

Generally, drinking water is used in concrete. Water from industrial plants,

sewage and other contaminated areas should not be used in concrete. If the quality of

water is suspected, then that water should be tested before its usage in concrete.

3.1.2 TEST METHODS

This section describes the test methods that are used for testing fresh mortar

and SCC properties, hardened, drying shrinkage and microlevel properties of SCC

and CC.

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3.1.2.1 Tests on Fresh Mortar

This section describes various tests involved in mortar tests to determine the

optimum w/cm and optimum dosage of SP and VMA in mortar.

3.1.2.1.1 Mini Slump Cone and Graduated Glass Plate

The test apparatus for measuring the spread and viscosity of mortar comprises

a mini frustum (slump) cone and a graduated glass plate. Mini slump cone has top and

bottom diameters of 7 cm and 10 cm respectively with a height of 6 cm.

The graduated glass plate contains two circular graduations of 10 cm and

20 cm in diameter marked at its center as shown in Fig. 3.5. With this test apparatus,

both spread and viscosity of the mortar can be measured from a single test.

Fig. 3.5 Mini slump cone and graduated glass plate

73

Here in our study, mini slump cone is used to measure the spread of the mortar

as described in EFNARC (2002)49. To indicate the rate of flow or viscosity of the

mortar spread, T20 method (Shekarchi et al., 2008)179 is adopted instead of mini

V-funnel test.

As T20 indicates the intended viscosity of mortar during this test, it is

concluded that it is the best replacement of mini V-funnel test. Practically, it is very

much feasible to have a single test apparatus to measure both spread and viscosity of

mortar so that rigorous mortar tests can be reduced.

Determination of spread of mortar

In this test, the truncated cone mould is placed exactly on the 10 cm diameter

graduated circle marked on the glass plate, filled with mortar (o.56 litre) and lifted

upwards. The subsequent diameter of the mortar is measured in two perpendicular

directions and the average of the diameters is reported as the spread of the mortar.

Determination of T20 (sec)

T20 is the time measured in seconds from lifting the cone to the mortar

reaching a diameter of 20 cm. The measured T20 indicates the deformation rate or

viscosity of the mortar. So, during this test, T20 can be measured first and average of

the spread can be measured subsequently. This procedure is similar to slump cone test

conducted on SCC.

Consistence retention

Along with the spread and T20, consistence retention is also an important fresh

property of self compacting mortar (SCM). It refers to the period of duration during

which SCM or SCC retains its properties, which is important for transportation and

placing.

74

Consistence retention was evaluated by measuring the spread and T20 of

successful SCM at 45 and 60 minutes after adding water. Between measurements, the

mortar was stored in the mixing bowl and covered the top to avoid moisture loss. The

mortar was remixed for one minute before each test.

3.1.2.2 Tests on Fresh Properties of SCC

This section describes various tests involved in SCC tests to determine filling

ability, passing ability, segregation resistance and consistence retention of SCC.

3.1.2.2.1 Slump Flow Test

Slump flow test apparatus is shown in Fig. 3.6. Slump cone has 20 cm bottom

diameter, 10 cm top diameter and 30 cm in height. In this test, the slump cone mould

is placed exactly on the 20 cm diameter graduated circle marked on the glass plate,

filled with concrete (6 litre) and lifted upwards. The subsequent diameter of the

concrete spread is measured in two perpendicular directions and the average of the

diameters is reported as the spread of the concrete.

T50cm is the time measured from lifting the cone to the concrete reaching a

diameter of 50 cm. The measured T50cm indicates the deformation rate or viscosity of

the concrete.

3.1.2.2.2 V-funnel Test

V-funnel test apparatus dimensions are shown in Fig. 3.7. In this test, trap

door is closed at the bottom of V-funnel and V-funnel is completely filled with fresh

concrete (12 litre). V-funnel time is the time measured from opening the trap door and

complete emptying the funnel.

Again, the V-funnel is filled with concrete, kept for 5 minutes and trap door is

opened. V-funnel time is measured again and this indicates V-funnel time at T5min.

75

3.1.2.2.3 L-box Test

L-box test apparatus dimensions are shown in Fig. 3.8. In this test, fresh

concrete (14 litre) is filled in the vertical section of L-box without any compaction

and then the gate is lifted up to allow the concrete to flow into the horizontal section

of L-box. The height of the concrete at the end of vertical section represents h1 (mm)

and at the horizontal section represents h2 (mm). The ratio h2/h1 represents blocking

ratio.

3.1.2.2.4 Segregation Resistance

The segregation resistance of SCC was assessed by visual stability index

(VSI) from the slump flow test (Daczko and Kurtz, 2001)40. A VSI number of 0, 1, 2

and 3 is given to the spread to characterize the stability of the mixture (refer 2.2.3.3).

Segregation was considered to be present when a halo of mortar and an uneven

distribution or clustering of the aggregates was observed in slump flow. The stability

of SCC can easily be examined by evaluating the distribution of the coarse aggregate

visually within the concrete mass after the spreading of the concrete has stopped.

3.1.2.2.5 Determination of Consistence Retention

Consistence retention is also an important fresh property of SCC in view of

workability. It refers to the period of duration during which SCC retains its properties,

which is important for transportation and placing. Consistence retention was

evaluated by measuring the slump flow spread and T50cm of successful SCC mixes at

60 minutes after adding water. The SCC mix was remixed for one minute before each

test.

76

Fig. 3.6 Slump flow test

77

Fig. 3.7 V-funnel test

Fig. 3.8 L-box test

78

3.1.2.3 Tests on Hardened Properties of SCC and CC

This section describes the procedure to determine the mechanical properties of

SCC and conventional concrete (CC) and these include compressive strength,

modulus of elasticity (MOE) and splitting tensile strength (STS). These properties

were tested on cylinder specimens of size 150 mm x 300 mm for all the mixes.

3.1.2.3.1 Compressive Strength Test

Compressive strength test was conducted on the cylindrical specimens for all

the mixes at different curing periods as per IS 516 (1959)77. Three cylindrical

specimens of size 150 mm x 300 mm were cast and tested for each age and each mix.

The compressive strength (f’c) of the specimen was calculated by dividing the

maximum load applied to the specimen by the cross-sectional area of the specimen.

3.1.2.3.2 Modulus of Elasticity Test

Modulus of elasticity (MOE) test was conducted on the specimens for all the

mixes at different curing periods as per IS 516 (1959)77. Three cylindrical specimens

of size 150 mm x 300 mm were cast and tested for each age and each mix. Each

specimen was loaded until an average stress of (C+5) kg/cm2 is reached. Here, C is

the one-third of the average equivalent cube compressive strength. The equivalent

cube strength has been determined by multiplying the cylinder strength by 5/4.

Strains at regular interval of loads till the proportional limit, have been measured.

Stress-strain curve has been plotted. The secant modulus is calculated from the slope

of the straight line drawn from the origin of axes to the stress-strain curve

(IS 516, 1959)77 and this secant modulus is the required modulus of elasticity of the

concrete (Ec).

79

3.1.2.3.3 Splitting Tensile Strength Test

Splitting tensile strength (STS) test was conducted on the specimens for all the

mixes at different curing periods as per IS 5816 (1999)84. Three cylindrical specimens

of size 150 mm x 300 mm were cast and tested for each age and each mix. The load

was applied gradually till the failure of the specimen occurs. The maximum load

applied was then noted. Length and cross-section of the specimen was measured. The

splitting tensile strength (fct) was calculated as follows:

fct = 2P/ (Π l d)

Where, fct = Splitting tensile strength of concrete (N/mm2)

P = Maximum load applied to the specimen (in Newton)

l = Length of the specimen (in mm)

d = cross-sectional diameter of the specimen (in mm)

3.1.2.4 Drying Shrinkage Test

This section describes the procedure to determine the drying shrinkage strain

of SCC and CC. Drying shrinkage tests were performed in accordance with

ASTM C 157 (2008)10. For each concrete mixture, three 150 mm x 300 mm concrete

cylinders were cast for drying shrinkage test. These cylinders were cured for 7 days.

Initial shrinkage measurements were taken as soon as the cylinders were brought out

of the curing. All specimens were kept drying in a controlled environment at 23° ±

2°C and 50% ± 4% relative humidity. The length change of all the specimens was

measured by a length comparator having a digital extensometer (0-25 cm x 0.001

mm) as shown in Fig. 3.9 after 1, 7, 14, 28, 56 and 112 days of drying after 7 days of

curing. The average value of the measured shrinkage strains of the three specimens

for each mix was taken as the drying shrinkage of the concrete.

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Drying shrinkage of concrete at any drying period has been calculated as

follows:

Drying shrinkage =L

RR ti

Where:

Ri = Initial dial gauge reading of the specimen after 7 days of curing

Rt = Dial gauge reading of the specimen after t days of drying

L = Length of the specimen after 7 days of curing

Fig. 3.9 Length comparator

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3.1.2.5 Microlevel Properties

This section describes the procedure to determine the microlevel properties

of SCC and CC after 28, 56 and 112 days of curing. The microlevel properties that

were determined are microcrack widths between aggregate and paste by Scanning

electron microscope (SEM) analysis; the chemical elements and atomic

Calcium-Silica (Ca/Si) ratio of the paste matrix near the ITZ at different ages by

Energy dispersive X-ray (EDAX) analysis.

To carry out SEM and EDAX, the samples of approximate size

10 mm x 10 mm x 5 mm were collected from the tested cylindrical specimens after

the compressive strength tests as per IS 516 (1959)77 on SCC and CC at different

ages. All samples chosen for the SEM and EDAX were uncoated and unpolished.

The microlevel properties were studied on the samples using the instrument

JSM-6390 which is equipped with both SEM and EDAX. The SEM scans a focused

beam of electrons across the sample and measures any of several signals resulting

from the electron beam interaction with the sample (Stutzman, 2000)190.

The microcracking width images of all samples were acquired by SEM in secondary

electron (SE) mode at a magnification setting of X1300 and 10μm field width (micron

marker). EDAX provided the spectrum of chemical elements with the peaks and

quantitative chemical analysis with the relative intensities for all the samples.

82

3.2 A SIMPLE TOOL FOR SCC MIX DESIGN

This section includes the selection of mix proportions for SCC from the

relevant literature, design of SCC mix design tool, calculation of key proportions of

constituents for a given SCC scenario. A user-friendly and simple tool has been

developed for SCC mix design (“JGJ_SCCMixDesign.xls”) based on the key

proportions of the constituent materials of SCC with or without blended cement and

with or without coarse aggregate blending. This tool has been used for SCC mix

design through out this study.

3.2.1 Selection of SCC Mix Proportions

SCC can be made from any of the constituents that are generally used for

structural concrete. In the SCC mix design, it is most common to consider the relative

proportions of the key components or constituents by volume rather than by mass

(weight) (EFNARC, 2002)49. The following key proportions for the mixes listed

below (Okamura and Ozawa, 1995; EFNARC, 2002; Khayat, 1998; Domone

2006b)147, 49, 97, 47:

1. Air content (by volume)

2. Coarse aggregate content (by volume)

3. Paste content (by volume)

4. Binder (cementitious) content (by weight)

5. Replacement of mineral admixture by percentage binder weight

6. Water/ binder ratio (by weight)

7. Volume of fine aggregate/ volume of mortar

8. SP dosage by percentage cementitious (binder) weight

9. VMA dosage by percentage cementitious (binder) weight

83

3.2.2 Design of SCC Mix Design Tool

This section describes the material properties required for SCC mix design

tool, detailed steps for mix design and output constituent materials for SCC.

3.2.2.1 Material Properties for SCC Mix Design Tool

The following material properties for the SCC mix design tool are to be

determined as shown in Table 3.9 and Table 3.11.

1. Specific gravity of cement, fly ash, coarse aggregate and fine aggregate.

2. Percentage of water absorption of coarse and fine aggregates.

3. Percentage of moisture content in coarse and fine aggregates.

4. Dry-rodded unit weight (DRUW) of coarse aggregate for the particular

coarse aggregate blending.

5. Percentage of dry material in SP and VMA.

Table 3.9 Material properties

Material Data

Material Specific Gravity % Absorption % Moisture

Cement 3.15 N/A N/A

Additive – Fly Ash 2.12 N/A N/A

Coarse aggregate (CA1 20mm) 2.6 0.3 0

Coarse aggregate (CA2 10mm) 2.6 0.3 0

Fine aggregate (Sand) 2.6 1.0 0

84

3.2.2.2 Detailed Steps for SCC Mix Design Tool

The detailed steps for mix design are described as follows:

1. Assume air content by percentage of concrete volume.

2. Input the coarse aggregate blending by percentage weight of total coarse

aggregate.

3. Input the percentage of coarse aggregate in DRUW to calculate the coarse

aggregate volume in the concrete volume.

4. Adjust the percentage of fine aggregate volume in mortar volume.

5. Obtain the required paste volume.

6. Adopt suitable water/ binder ratio by weight.

7. Input the percentage replacement of fly ash by weight of cementitious

material.

8. Input the dosage of SP and VMA (if required) by percentage weight of

binder.

9. Adjust the binder (cementitious material) content by weight to obtain the

required paste.

The coarse aggregate optimization is shown in Table 3.10. The input parameters

section is shown in Table 3.11.

Table 3.10 Coarse aggregate optimization or blending

Coarse aggregate optimization

Material % by weight

CA1 20mm 60

CA2 10mm 40

85

Table 3.11 Input parameters section

Input parameters

Dry Rodded Unit Weight(kg/m3) 1646

% of CA in DRUW 44.3

% of Sand in Mortar 46.1

% of Fly ash 35

Wt. Water/Binder 0.36

Binder (kg/m3) 495

SP (% wt.of binder) 0.9

VMA (% wt. of binder) 0.2

% of Air 2

% of dry material in SP 40

% of dry material in VMA 40

3.2.2.3 Output Constituent Materials for SCC

Once the necessary input data is given, this tool automatically calculates and

shows the required output data. Concrete mix proportions by volume and total

aggregate by weight are shown in Table 3.12.

Table 3.12 Concrete mix proportions by volume

Coarse aggregate (kg/m3) 729.178

% of CA in concrete volume 28.045

Concrete Mix proportions by volume (lit/m3)

CA Mortar Sand Paste

280.453 719.545 331.711 387.836

Sand (kg/m3) 862.449

Total aggregates (kg/m3) 1591.627

86

Paste composition is shown in Table 3.13. Constituent materials for SCC are

shown in Table 3.14. Constituent materials for self compacting mortar (SCM) are

shown in Table 3.15. This tool also displays the constituent materials for the required

volume of SCC or SCM as shown in Table 3.14 and Table 3.15. Aggregate

proportions by volume and by weight are shown in Table 3.16.

Table 3.13 Paste composition

Vol. Water/Powder 0.969

Paste composition

Kg/m3 lit/m3

Cement Fly ash Water SP VMA Paste

321.75 173.25 178.2 4.455 0.99 387.509

Table 3.14 Constituent materials for SCC

Constituent Materials for Concrete

Required (m3)Material

(kg/m3)Initial Adjusted

0.0062g/ml

Cement 321.75 321.75 1.99485 1994.85

Fly Ash 173.25 173.25 1.07415 1074.15

Water 178.2 185.745 1.151619 1151.619

CA1 20mm 437.507 437.507 2.712542 2712.542

CA2 10mm 291.6712 291.6712 1.808361 1808.361

Sand 862.4489 862.4489 5.347183 5347.183

SP (lit) 4.455 4.455 0.027621 27.621

VMA (lit) 0.99 0.99 0.006138 6.138

Unit Weight 2270.272 Total (kg) 14.12247 14122.47

Litres 6.121

87

Table 3.15 Constituent materials for SCM

Constituent Materials for Mortar

Required (m3)Material

(kg/m3)Initial Adjusted

0.0008g/ml

Cement 321.75 321.75 0.2574 257.4

Fly Ash 173.25 173.25 0.1386 138.6

Water 178.2 183.5575 0.146846 146.846

Sand 862.445 862.445 0.6899592 689.9592

SP (lit) 4.455 4.455 0.003564 3.564

VMA (lit) 0.99 0.99 0.000792 0.792

Unit Weight 1541.094 Total (kg) 1.237161 1237.161

Litres 0.564

Table 3.16 Aggregate proportions by volume and by weight

Aggregate Proportions

Material % by Vol % by Weight

CA1 20mm 27.488 27.488

CA2 10mm 18.325 18.325

Sand 54.187 54.187

Total 100 100

3.2.2.4 Calculation of Key Proportions

The detailed steps for calculation of key proportions are presented in Appendix B

with an example.

88

3.3 OPTIMIZATION OF SUPERPLASTICISER AND VISCOSITY

MODIFYING AGENT IN SELF COMPACTING MORTAR

This section investigated the use of mini slump cone test along with the

graduated glass plate to obtain the optimization of superplasticiser (SP) and viscosity

modifying agent (VMA) in self compacting mortar (SCM). As SCC contains lower

content of coarse aggregate, mortar employs more effects on the SCC fresh

properties than conventional concrete (CC). Mortar not only provides lubrication

by wrapping coarse aggregates, it also predominantly influences the fresh

properties of SCC with a low yield stress and adequate viscosity so as to ensure

the required filling and passing ability without blocking and segregation. Mortar

is, thus an intrinsic part of SCC mix design and it has also formed a central part of

Jin’s research (Jin, 2002; Jin and Domone, 2002)88, 89. Hence, self compacting

mortar (SCM) is a precondition of the successful production of SCC. Thus,

optimization of SP and VMA in SCM must be done to ensure a stable SCC having

low yield stress and adequate viscosity for the given w/cm and mix proportion. And

this is best done by self compacting mortar tests.

3.3.1 Experimental Study

Our objective was to determine the optimum dosage of SP and VMA

in SCM with the available materials. In this respect, 53 grade ordinary Portland

cement (OPC 53), class F fly ash as an additive, river sand, SP and VMA were used in

preparing SCMs having w/cm 0.32 and 0.36. The SCM mixes had 35% replacement

of cement with class F fly ash by cementitious weight and 40% and 45% of sand in

mortar by volume. The fresh properties that were determined are the mortar spread,

T20 and consistence retention.

89

3.3.2 Experimental Procedure

3.3.2.1 Specimen Preparation

Mortars were prepared manually in a container in order to observe its

behaviour. Mortar volume of 0.0008 m3 (8 x 10-4 m3) (0.56 litre) is sufficient for each

mortar test using mini slump cone. It is known that mixing procedures have a

significant influence on the fresh properties of SCM. Modified Jin’s mixing procedure

(2002)88 was carried out throughout this work to achieve maximum efficiency of SP

and VMA. The mixing procedures for SCM with SP only shown in Fig. 3.10 and both

with SP and VMA shown in Fig. 3.11 are described as follows.

Mixing procedure for mortar with SP only:

Minutes

W2+SP Stop Mixing Rest 3 min Remix 1 min before testFly Ash+Sand

0 2 4 6 9 10

Cement+W1

W1 = 80% mixing water W2 = 20% mixing water SP = Superplasticiser

Fig. 3.10 Mixing procedure for mortar with SP only

1. Cement and 1st part (80%) of water was mixed for two minutes.

2. SP along with the 2nd part (20%) of water was added and mixed for two

minutes.

3. Fly Ash and sand was added to the mix and mixed thoroughly for two minutes.

4. The mix was stopped and kept rest for 3 minutes.

5. The mix was remixed for one minute and discharged for mortar test.

90

Mixing procedure for mortar with SP and VMA:

Minutes

W2+SP Stop Mixing Rest 2 min Remix 1 min before testFly Ash+Sand

0 2 4 5 7 9 10

Cement+W1 W3+VMA

W1 = 70% mixing water W2 = 15% mixing water W3 = 15% mixing water

SP = Superplasticiser VMA= Viscosity Modifying Agent

Fig. 3.11 Mixing procedure for mortar with SP and VMA

1. Cement and 1st part (70%) of water was mixed for two minutes.

2. SP along with the 2nd part (15%) of water was added and mixed for two

minutes.

3. VMA along with the 3rd part (15%) of water was added and mixed for one

minute.

4. Fly Ash and sand was added to the mix and mixed thoroughly for two minutes.


6. The mix was remixed for one minute and discharged for mortar test.

3.3.2.2 Tests on Fresh Mortar

The test apparatus comprising the mini slump cone and graduated glass plate

was used for determining mortar spread, viscosity (T20) and consistence retention

(refer 3.2.1.1).

3.3.3 Mortar Mix Design

This research investigated the effect of SP and VMA dosage on the three SCM

mixes (Mix 1, Mix 2 and Mix 3) which had 35% replacement of cement with class F fly

ash and water/cementitious ratios by weight (w/cm) 0.32 and 0.36 as shown in Tables

3.17 and 3.18. In other words, the cementitious proportion is kept same for all the mixes.

The volume of paste content was kept at 359 litre/m3 for the two mixes Mix 1 and Mix 2

and 388 litre/m3 for the Mix 3.

91

Table 3.17 Mortar Mix Proportions per 0.0008 m3 for 40% of Sand in Mortar

%SP %VMAw/cm by cementitious

weight

Cement(g)

Fly ash(g)

Water(ml)

Sand(g)

SP(ml)

VMA(ml)

0.6 0 253 136 128 498 2.3 0

0.7 0 253 136 128 498 2.7 0

0.8 0 252 136 127 498 3.1 0

0.9 0 252 136 127 498 3.5 0

1 0 251 135 126 498 3.9 0

1.1 0 251 135 126 498 4.3 0

1.2 0 251 135 126 498 4.6 0

1.3 0 250 135 125 498 5.0 0

1.4 0 250 135 125 498 5.4 0

0.32Mix 1

1.5 0 250 134 124 498 5.8 0

0.7 0 239 129 136 498 2.6 0

0.8 0 239 129 135 498 2.9 0

0.8 0.2 238 128 134 498 2.9 0.7

0.9 0.2 238 128 134 498 3.3 0.7

1.0 0.2 237 128 134 498 3.6 0.7

0.36Mix 2

1.1 0.2 237 128 134 498 4.0 0.7

As per the general purpose mix design method developed by Okamura et al.

(1993)142, sand content in mortar is kept at 40% of mortar volume in the first two

mixes (Mix 1 and Mix 2) as shown in Table 3.17. For the third mix (Mix 3), sand is

kept at 45% of mortar volume in order to evaluate the optimization of SP and VMA as

shown in Table 3.18. These mortar tests conducted to study the interactions among

cement, mineral and chemical admixtures and to determine optimum dosages of SP

and VMA for the given w/cm.

92

Table 3.18 Mortar Mix Proportions per 0.0008 m3 for 45% of Sand in Mortar

%SP %VMAw/cm by cementitious

weight

Cement(g)

Fly ash(g)

Water(ml)

Sand(g)

SP(ml)

VMA(ml)

0.7 0 274 148 156 567 3.0 0

0.8 0 274 147 155 567 3.4 0

0.8 0.2 273 147 154 567 3.4 0.80.36

Mix 3

0.9 0.2 273 147 154 567 3.8 0.8

Mortar tests started with minimum dosage of SP by percentage weight of

cementitious and increased the dosage of SP till the maximum spread of the mortar

has reached. When the mortar spread shows halo, minimum dosage of VMA by

percentage weight of cementitious was used to avoid the bleeding. For each dosage of

SP and VMA, fresh mortars were prepared and tested.

3.3.4 Results and Discussion

3.3.4.1 Effect of SP and VMA on Spread and T20 for the Mix 1

The influence of SP on mortar spread and T20 (viscosity) for the Mix 1 is

shown in Table 3.19. It is observed that as the SP dosage increases, the spread of

mortar increases and T20 decreases. Spread reaches the maximum value and T20

reduces to the minimum at a specific SP dosage. This point is referred as saturation

point. For this mix, maximum spread 301 mm was arrived at 0.9% SP dosage as

shown in Fig. 3.12. So, it is the optimum dosage of SP for this mix.

93

Table 3.19 Spread and T20 for the Mix 1

Time after water mixing (min)

Initialw/cm %SPSpread(mm) T20 (sec) Spread + Halo (mm)

0.6 271 9.67 -

0.7 287 6.62 -

0.8 298 5.94 -

0.9 301 4.68 -

1.0 300 4.70 -

1.1 297 4.77 -

1.2 296 5.6 -

1.3 296 5.85 305

1.4 295 6.27 301

0.32Mix 1

1.5 282 6.9 285

Fig. 3.12 Maximum spread of the Mix 1 at 0.9% SP

Beyond this saturation point, adding SP causes decrease in mortar spread and

increase in T20. Adding even more SP leads to segregation of mortar. So, it is

practically seen that before reaching the saturation point, the addition of SP increases

94

the spread and decreases T20. After the saturation point, the addition of SP leads to

decrease in the spread and increase in T20. The use of VMA dosage was not used in

this mortar Mix 1 as no segregation or bleeding (halo) was observed in the mortar

before the saturation point.

3.3.4.2 Effect of SP and VMA on Spread and T20 for the Mix 2

But for the Mix 2 with w/cm 0.36, it is seen that bleeding (halo) was observed

at the SP dosage of 0.7% by cementitious weight itself i.e., before the saturation point

as shown in Table 3.20 and Fig. 3.13. As we know that increase of water reduces the

yield stress and viscosity and some times leads to segregation. This behaviour is

clearly seen in the mixes Mix 1 and Mix 2 when w/cm is increased from 0.32 to 0.36.

T20 value of Mix 2 is significantly low i.e., rate of flow has been increased as

compared to that of Mix 1.



Initialw/cm %SP %VMA

Spread

(mm)T20 (sec)

Spread + Halo

(mm)

0.7 0 295 3.25 300

0.8 0 295 3.03 304.5

0.8 0.2 237 6 -

0.9 0.2 296 3.15 -

1.0 0.2 231 5.78 -

0.36

Mix 2

1.1 0.2 290 3.03 -

95

Fig. 3.13 Spread with halo of the Mix 2 at 0.7% SP

At 0.8% SP dosage, spread does not change, but T20 is decreased from 3.25 sec

to 3.03 sec and the thickness of halo is increased as shown in Fig. 3.14(a). It clearly

indicates the requirement of VMA in order to resist segregation.

Then, fresh mortar mix was prepared both with 0.8% SP dosage and minimum

VMA dosage of 0.2% by cementitious weight and mortar test was conducted. It is

observed that the minimum dosage of VMA stopped the bleeding, but the spread has

decreased from 295 mm to 237 mm as shown in Fig. 3.14(b) and T20 increased from

3.03 sec to 6 sec i.e., viscosity is increased. The reason being that VMA can imbibe

some free water and increases the viscosity and thus reduces the risk of segregation or

bleeding (Khayat, 1998)97. From the result, it indicates that maximum spread has not

been arrived at 0.8% SP dosage and 0.2% VMA dosage. It leads to increase in SP

dosage.

96

(a) Spread with halo without VMA

(b) Spread without halo with 0.2% VMA

Fig. 3.14 Spread of the Mix 2 at 0.8% SP

97

Hereafter, 0.2% VMA dosage was maintained for all the mixes of Mix 2

category. Now, fresh mortar mix was prepared with 0.9% SP dosage and 0.2% VMA

dosage and tested. It is seen that spread was increased from 237 mm to 296 mm

without any bleeding as shown in Fig. 3.15 and T20 decreased from 6 sec to 3.15 sec

i.e., rate of flow has been increased satisfactorily.

Fig. 3.15 Maximum spread of the Mix 2 at 0.9% SP and 0.2% VMA

After this point, mix prepared with 1% SP and 0.2% VMA dosage and tested.

Mortar spread again decreased from 296 mm to 231 mm which is less than the spread

237 mm that has been arrived at 0.8% SP dosage and 0.2% VMA dosage. At this

stage, T20 increased from 3.15 sec to 5.78 sec. This result was not satisfactory.

Again, a fresh mix with 1.1% SP and 0.2% VMA was prepared and tested.

Spread has increased from 231 mm to 290 mm, but it is less than 296 mm which was

maximum spread at 0.9% SP dosage. When comparing the mixes with 0.9% and 1%

SP dosage, maximum spread 296 mm was observed for the mix with 0.9% SP dosage.

98

So, it is referred as the saturation point. Thereby, it is noted that for the Mix 2

having w/cm 0.36, the optimum dosages of SP and VMA were 0.9% and 0.2%

respectively. Interestingly, it is observed that VMA dosage didn’t affect the saturation

point of SP dosage which is 0.9%. In our study, saturation point is arrived at the same

SP dosage of 0.9% by cementitious weight for the two mixes Mix 1 and Mix 2 with

w/cm 0.32 and 0.36 respectively. It is inline with the statement that for mortars with

the same powder (binder) proportions, the dosage of SP expressed in terms of

percentage by cementitious weight, doesn’t change significantly with the variation of

w/cm (Nepomuceno et al., 2008)134.

3.3.4.3 Effect of SP and VMA on spread and T20 for the Mix 3

The influence of SP and VMA on mortar spread and T20 (viscosity) for the

Mix 3 is shown in Table 3.21. This mix has 45% of sand in mortar volume. As it can

be seen from the Table 3.21, spread has decreased and T20 has increased when

compared to that of Mix 2. This is because of increase in percentage of sand in mortar

from 40% (Mix 2) to 45% (Mix 3).



Initialw/cm %SP %VMA

Spread (mm) T20 (sec) Spread + Halo(mm)

0.7 0 285 5.56 290

0.8 0 290 4.12 301

0.8 0.2 245 5.78 -

0.9 0.2 293 3.31 -

1.0 0.2 243 5.66 -

0.36Mix 3

1.1 0.2 290 3.23 -

99

But, the behaviour of the Mix 3 is almost similar to that of the Mix 2.

Interestingly, maximum spread 293mm was observed at 0.9% SP dosage which was

saturation point.

It is to be noted that irrespective of sand content in mortar volume, if

cementitious proportions are kept the same for the mixes, the dosage of SP

(i.e., saturation point) tends to be the same for those mixes.

3.3.4.4 Consistence Retention

As it can be seen from Table 3.22, all these three mixes attained good

consistence retention in the spread and T20 at 45 and 60 minutes after adding water.

So, it can be stated that the used chemical admixtures had good compatibility with the

cement and mineral admixture.

Thus, polycarboxylate-type superplasticiser can provide higher consistence

retention (Hanehara and Yamada, 1999)65. Hence after mixing, SCC should maintain

the fresh properties during transportation and placing, generally for 60 to 90 minutes

(Kasemchaisiri and Tangermsirikul, 2008; RILEM TC 174 SCC, 2000; Sonebi and

Bartos, 2000)95, 165, 186.

Table 3.22 Spread and T20 at 45 and 60 minutes after adding water


Initial 45 min 60 minw/cm %SP %VMA

Spread(mm)

T20(sec)

Spread(mm)

T20(sec)

Spread(mm)

T20(sec)

0.32Mix 1 0.9 0 301 4.68 301 4.76 292 5.24

0.36Mix 2 0.9 0.2 296 3.15 285 4.78 284 6.25

0.36Mix 3 0.9 0.2 293 3.31 283 4.92 282 6.31

100

3.4 DESIGN OF M 25 GRADE OF SCC

As there is no availability of SCC mix design standards for a particular

strength of concrete, this investigation is focused on the design of M 25 grade of SCC

satisfying both SCC performance and the desired strength.


Our objective was to develop M 25 grade of SCC with moderate fines for the

use of normal building constructions. To make use of the SCC for normal buildings

and to have adequate bond between aggregates and reinforcement in concrete

structures, crushed granite stones of size 20 mm and 10 mm were used in this study.

In this respect, 53 grade ordinary Portland cement (OPC 53), class F fly ash as an

additive, crushed granite stones of size 20 mm and 10 mm, river sand, SP and VMA

were used in preparing SCC mixes.

The fresh properties that were determined are filling ability, passing ability

and segregation resistance and consistence retention. The hardened properties that

were determined are compressive strength, modulus of elasticity (MOE) and splitting

tensile strength (STS) at different curing periods.

3.4.2 SCC Mix Design

Several methods exist for the mix design of SCC. The general purpose mix

design method was first developed by Okamura and Ozawa (1995)147. In this study,

the key proportions for the mixes are done by volume as per EFNARC (2002)49.

As already known that the increased content of powder (fines) and admixture leads to

higher sensitivity and cost, combination-type of SCC has been chosen in this study in

the SCC mix design so as to use moderate powder and reasonable quantity of

chemical admixtures. Three mixes were prepared with different paste contents

(36.0%, 37.7% and 38.8%) in order to evaluate the SCC fresh properties.

101

Keeping in view of the moderate fines, robustness and all SCC properties,

w/cm was chosen as 0.36 (by weight of cementitious) for all mixes. As per EFNARC

(2002)49, minimum coarse aggregate content of 28% was maintained for all the mixes.

Keeping in view of the savings in cost and land fill, greenhouse gas emissions, fresh,

mechanical and durability properties of SCC, the replacement level of class F fly ash

was kept at 35% as per IS 456 (2000)76 for all mixes. In this study, only cementitious

material was used as fines and fines (<0.125 mm) from the aggregates was not

included. 20 mm and 10 mm coarse aggregate particles were blended in 60:40

proportion by percentage weight of total aggregate.

The detailed steps for mix design are described as follows:

1. Assume air content as 2% (20 litres) of concrete volume.

2. Determine the dry-rodded unit weight (DRUW) of coarse aggregate for a

given coarse aggregate blending.

3. Using DRUW, calculate the coarse aggregate content by volume (28%) of mix

volume.

4. Adopt fine aggregate volume of 40 to 50% of the mortar volume.

5. Adopt the required paste volume (litre/m3) in the concrete volume.

6. Keep water/ cementitious ratio by weight (w/cm) as 0.36.

7. Calculate the binder (cementitious material) content by weight.

8. Replace cement with 35% class fly ash by weight of cementitious material.

9. Optimize the dosages of superplasticiser (SP) and viscosity modifying agent

for the given w/cm (0.36) using mortar tests by mini slump cone test.

10. Perform SCC tests.

102

3.4.3 SCC Mix Target

Typical acceptance criteria and target for SCC are shown in Table 3.23.

Table 3.23 Typical acceptance criteria and target for SCC

SCC mix targetProperty Test method Unit

Minimum Maximum

Slump Flow Mm 650 750

T50cm Sec 2 5Filling ability

V-funnel Sec 6 12

Passing ability L-box h2/h1 (mm/mm) 0.8 1.0

Segregation

resistance

V-funnel at

T5minSec 6 15

3.4.4 Mixing Procedure for SCC

It is known that mixing procedures have a significant influence on the fresh

properties of SCC. Liu’s (2010)118 mixing procedure was carried out throughout this

work to achieve maximum efficiency of SP and VMA as shown in Fig. 3.16.

Fig. 3.16 Mixing procedure for SCC with SP and VMA

103

Mixing procedure for SCC shown in Fig. 3.16 is described as follows:

1. Binder and aggregate are mixed for one minute.

2. The 1st part (70%) of water was added and mixed for two minutes.

3. SP along with the 2nd part (15%) of water was added and mixed for two minutes.

4. VMA along with the 3rd part (15%) of water was added and mixed for two

minutes.


6. The mix was remixed for one minute and discharged for SCC tests.

3.4.5 Testing Fresh Properties of SCC

The test procedures for slump flow, V-funnel and L-box tests are described in

the section 3.2.2 to determine slump flow, T50cm, V-funnel time at initial and after

5 minutes (T5min), blocking ratio (h2/h1), segregation resistance and consistence

retention.

3.4.6 Testing Hardened Properties of Concrete

The test procedures for compressive strength, modulus of elasticity and

splitting tensile strength tests are described in the section 3.2.3. These properties were

tested on cylinder specimens of size 150 mm x 300 mm for all the mixes.

3.4.7 Conventional Concrete Mix Design

M 25 grade of conventional concrete (CC) has been designed (refer

Appendix C) as per IS 10262 (2009)85 and IS 456 (2000)76 for comparative study.

3.4.8 Mix Proportions

Mix types with percentage relative proportions and mix proportions of

constituent materials are shown in Table 3.24 and Table 3.25. SCC mix design tool

(“JGJ_SCCMixDesign.xls”) is used to obtain the SCC mix proportions.

104

Table 3.24 Percentage relative proportions of trial mixes

Cementitious material – OPC+35% fly ash w/cm – 0.36 for SCC

Percentage

of

coarse

aggregate

Percentage

of

Mortar

Percentage

of

sand in

mortar

Percentage

of

pasteMix type

Coarse aggregate

blending percentage

by weight

(20 mm and 10 mm)

By volume

28_60:40Aa 60 40 28.05 71.95 50 36.0

28_60:40Bb 60 40 28.05 71.95 47.6 37.7

28_60:40c 60 40 28.05 71.95 46.1 38.8

M 25 60 40 43.81 56.19 43.5 31.7

a, b 28_60:40A & 28_60:40B mixes with a paste content of 36.0% and 37.7% respectively.

c 28_60:40: where 28 is the percentage of coarse aggregate volume in a concrete mix and

60:40 is the coarse aggregate blending by percentage weight of 20 mm and 10 mm resp.

Table 3.25 Mix proportions of constituent materials of trial mixes

Mix typeBinder

Kg/m3

Cement

kg/m3

Fly ash

kg/m3

Water

l/m3

20mm

Kg/m3

10mm

kg/m3

Sand

kg/m3

SP

l/m3

VMA

l/m3

28_60:40A 458 297.7 160.3 164.88 437.51 291.67 935.41 4.12 0.92

28_60:40B 481 312.65 168.35 173.16 437.51 291.67 890.51 4.33 0.96

28_60:40 495 321.75 173.25 178.2 437.51 291.67 862.45 4.46 0.99

M 25 384 384 - 192 683.4 455.6 636 - -

105


3.4.9.1 SCC Fresh Properties

SCC fresh properties i.e., the average values of slump flow, T50cm at initial and

at 60 minutes, V-funnel time, V-funnel time at 5 minutes (T5min) and L-box ratio

(h2/h1) are presented in the Table 3.26 for all the mixes.

Table 3.26 Fresh properties of trial mixes

Slump flow

(mm)T50cm (sec) V-funnel time (sec)

Mix type

InitialAt

60 minInitial

At

60 minInitial T5min

L-box ratio

(h2/h1)

28_60:40A 657 NDa 5.21 ND Blocked Blocked Blocked

28_60:40B 671 632 4.36 6.29 9.83 14.12 0.70

28_60:40 696 657 3.12 4.28 6.23 7.59 0.81

aND: Not done

From the Table 3.26, it is seen that though the mix 28_60:40A got the slump

flow spread of 657 mm in 5.21 sec, this mix was failed in V-funnel and L-box tests.

The blocking was due to insufficient amount of fines (458 kg/m3) and paste content

(36.0%). Whereas, it is seen from the Table 3.26 that the two mixes 28_60:40B and

28_60:40 have met the SCC acceptance criteria. It is clearly observed that the increase

in fines (481 kg/m3) and paste content (37.7%) as in the case of 28_60:40B and the

increase in fines (495 kg/m3) and paste content (38.8%) as in the case of 28_60:40

resulted in the improvement of SCC fresh properties in these two mixes. Though all

the three mixes have the same coarse content (28%) and coarse aggregate blending

(60:40), adequate fines and paste content played a key role to achieve successful SCC

106

mixes. When comparing the two mixes 28_60:40B and 28_60:40, the mix 28_60:40

performed excellent SCC fresh properties than that of the mix 28_60:40B. This is

particularly due to 495 kg/m3 of fines content and 38.8% of paste content of the mix

28_60:40 that resulted in the improvement of the fresh properties. Hence, it is to be

concluded that for a given coarse aggregate content and coarse aggregate blending,

mixes should have adequate fines and paste content to attain SCC acceptance criteria.

It is evidently revealed that for a given coarse aggregate content and its

blending, the decrease in fines content decreases the paste content and hence

decreases the performance of SCC. From the above results, it is concluded that for the

given coarse aggregate content of 28% with the coarse aggregate blending 60:40

(20 mm and 10 mm), the fines content of 495 kg/m3 can be considered as moderate

fines and the paste content of 38.8% can be considered as an adequate paste content

for a given w/cm (0.36).

3.4.9.2 Compressive Strength of CC and SCC

From the results obtained in the fresh properties of SCC as shown in

Table 3.26, the mixes 28_60:40B and 28_60:40 were considered as successful SCC

mixes. Compressive strength results of M 25 and SCC mixes 28_60:40B and

28_60:40 after 7 and 28 days of curing are presented in the Table 3.27.

Table 3.27 Compressive strength of CC and SCC

Mix typeMechanical property Age (days)

M 25 28_60:40B 28_60:40

7 23.20 13.02 17.98Compressive strength, f’c

(MPa) 28 31.12 27.16 32.26

107

From the Table 3.27, it is clearly seen that the mix 28_60:40 has attained a

compressive strength of 32 MPa after 28 days of curing which was equivalent to

28-day compressive strength of M 25 grade of CC. But the mix 28_60:40B has

attained only a compressive strength of 27.16 MPa after 28 days of curing and was

not meeting the requirement of M 25 grade of concrete. This is particularly due to

less amount of binder (481 kg/m3) as compared to that (495 kg/m3) of the mix

28_60:40 for a given w/cm (0.36) as shown in Table 3.27. It clearly indicates that for

a given w/cm, reduction in fines decreases the paste content and hence decreases the

compressive strength of the mix. Moreover, the mix 28_60:40B was compliance with

M 20 grade of concrete as per IS 456 (2000)76 and IS 10262(2009)85. So, for a given

w/cm (0.36) and 35% replacement level of class F fly ash, the total binder

(cementitious) content of 495 kg/m3 i.e., cement of 321.75 kg/m3 and class F fly ash

of 173.25 kg/m3 has been observed to be the adequate binder content for the mix

28_60:40 to attain 32 MPa.

From the results, it is concluded that for a given w/cm and replacement level

of class F fly ash, the reduction in the binder content decreases the cement content, fly

ash content and paste content and hence decreases the compressive strength of the

mix. From the compressive strength results, the mix 28_60:40 has been considered as

M 25 grade of SCC.

3.4.9.3 Mechanical Properties of CC and SCC

Table 3.28 shows the mechanical properties of CC (M 25) and SCC

(28_60:40) after 7, 28, 56 and 112 days of curing. As it is seen from the Table 3.28,

SCC has attained a lower compressive strength of 17.98 MPa as compared to that of

(23.20 MPa) CC after 7 days of curing due to slower pozzolanic action of class F fly

ash at early ages (Siddique, 2003)182.

108

Table 3.28 Mechanical properties of CC and SCC (28_60:40)


M 25 28_60:40

7 23.20 17.98

28 31.12 32.26

56 35.84 38.86

Compressive strength, f’c

(MPa)

112 39.05 48.10

7 24.40 18.19

28 28.91 27.12

56 31.48 30.10

Modulus of elasticity, Ec

(GPa)

112 33.11 34.38

7 2.97 2.33

28 3.68 3.02

56 3.96 3.68

Splitting tensile strength, fct

(MPa)

112 4.24 4.39

0

10

20

30

40

50

Age (Days)

Com

pres

sive

str

engt

h (M

Pa)

CC

SCC

Fig. 3.17 Compressive strength versus Age

7 28 56 112

109

After 28 days of curing, SCC and CC have attained a similar compressive

strength of 32 MPa. SCC has attained compressive strength of 38.86 MPa and

48.1 MPa at 56 and 112 days respectively, whereas CC has attained compressive

strength of 35.84 MPa and 39.05 MPa at 56 and 112 days respectively. So, it is clearly

seen that the gain of compressive strength was significant in SCC after 28 days as

compared to that of CC as shown in Fig. 3.17. This is particularly due to continuous

pozzolanic action of class F fly ash at later ages (Siddique, 2003)182.

For a given compressive strength of 32 MPa at 28 days, MOE of SCC and CC

were 27.12 GPa and 28.91 GPa respectively as shown in Table 3.28. It is observed

that for a given compressive strength after 28 days of curing, SCC has attained lower

MOE than that of CC. It is mainly due to lower coarse aggregate in SCC than that of

CC. It is already known that for a given strength higher coarse aggregate content leads

to higher unit weight and hence higher MOE of concrete (AASHTO, 2006; ACI 318,

1995; Noguchi et al., 2009; Tomosawa et al., 1990)3, 7, 140, 198. But there was

significant improvement observed in the MOE of SCC after 28 days as shown in

Fig.3.18. After 112 days of curing, SCC has attained higher value of MOE than that

of CC as shown in Table 3.28 and Fig. 3.18. This is due to continuous improvement in

the compressive strength of fly ash blended SCC at later ages due to pozzolanic action

of class F fly ash (Siddique, 2003)182.

For a given compressive strength at 28 days, SCC has attained lower splitting

tensile strength (STS) than that of CC as shown Table 3.28. It is mainly due to the use

of 35% of class F fly ash replacement in the cement and attributed to the slower

pozzolanic action of fly ash that decreases the STS at early ages (Liu, 2010)118. But

there was significant improvement observed in the STS of SCC after 28 days as

shown in Fig. 3.19.

110

0

5

10

15

20

25

30

35

Age (Days)

Mod

ulus

of e

last

icity

(GPa

)

CC

SCC

Fig. 3.18 Modulus of elasticity versus Age

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

Age (Days)

Split

ting

tens

ile s

tren

gth

(MPa

)

CC

SCC

Fig. 3.19 Splitting tensile strength versus Age

7 28 56 112

7 28 56 112

111

After 112 days of curing, SCC has attained higher value of STS (4.39 MPa)

than that of (4.24 MPa) CC as shown in Table 3.28 and Fig. 3.19. Studies already

revealed that mechanical properties of fly ash concrete continued to increase with age

(Siddique, 2003; Siddique, 2011; Liu, 2010)182, 183, 118.

From the above results, it is to be noted that the designed M 25 grade of SCC

was performing enhanced mechanical properties at later ages as compared to those

M 25 grade of CC. So, the adequate binder content (495 kg/m3) and 35% replacement

level of class F fly ash in the mix 28_60:40 was resulting enhanced fresh and

mechanical properties of SCC.

3.5 EFFECT OF COARSE AGGREGATE BLENDING ON

FRESH PROPERTIES OF SCC

This section is mainly focused on the effect of coarse aggregate blending on

fresh properties of SCC and thereby finding the optimization of coarse aggregate

blending or proportion in a given coarse aggregate volume of self compacting

concrete (SCC). To ensure its high filling ability, flow without blockage and to

maintain homogeneity, SCC requires a reduction in coarse aggregate content, high

cement content, superplasticiser (SP) and viscosity modifying agent (VMA)

(Okamura and Ouchi, 1999)143. According to Okamura (1997)141, blocking depends

on the size, shape and content of coarse aggregate.

A reduction in the coarse aggregate content and lowering the size are both

effective in inhibiting blocking, but it leads to higher drying shrinkage of SCC.

According to ACI 237R-07 (2007)6, the blending of different sizes of coarse

aggregate can often be beneficial to improve the overall properties of the mixture.

As a guideline to minimize blocking of SCC, if coarse aggregate size is greater than

112

12.5mm (1/2 in.), then the coarse aggregate content should be chosen between 28%

and 32% of the volume of the mix (ACI 237R-07, 2007)6.

Keeping in view of the drying shrinkage of SCC, attempts have been done in

this study to increase the volume of maximum size aggregate and coarse aggregate

content. As such, there is no data or specification available to specify the coarse

aggregate content that can be suitable for a particular coarse aggregate blending made

with 20 mm and 10 mm to make successful SCC. This leads to this research work to

determine the suitable (optimum) coarse aggregate blending with 20 mm and 10 mm

for the particular coarse aggregate content to obtain successful SCC.


Our objective was to determine the optimum blending of coarse aggregate

with 20 mm and 10 mm for a given coarse aggregate content to make successful SCC.

Keeping in view of the M 25 grade of SCC (refer section 6.1), w/cm and paste content

was kept at 0.36 (by weight) and 388 litre/m3 respectively for all mixes.

To study the effect of coarse aggregate blending on SCC, 20 mm and 10 mm

size aggregates are blended in 70:30, 67:33, 60:40 and 40:60 proportions by

percentage of weight of total coarse aggregate. The fresh properties that were

determined are filling ability, passing ability and segregation resistance and

consistence retention.

3.5.2 SCC Mix Design

SCC mix design procedure was described in the section 6.1.2. Coarse

aggregate content was chosen between 28 and 35% of concrete volume. The key

proportions of constituents of SCC mixes were obtained by using the SCC mix design

tool (JGJ_SCCMixDesign.xls).

113


Mix types with percentage relative proportions and mix proportions of

constituent materials are shown in Table 3.29 and Table 3.30.

Table 3.29 Percentage relative proportions of mixes

Cementitious Material – OPC+35% fly ash w/cm – 0.36Percentage

of

coarse

aggregate

Percentage

of

mortar

Percentage

of

sand in

mortar

Percentage

of

pasteMix type

Coarse aggregate

blending percentage

by weight

(20 mm and 10 mm)By volume

35_70:30 70 30 35.03 64.97 40.3 38.8

34_70:30 70 30 34.02 65.98 41.2 38.8

33_70:30 70 30 33.03 66.97 42.1 38.8

32_70:30 70 30 32.05 67.95 42.9 38.8

30_70:30 70 30 30.03 69.97 44.5 38.8

28_70:30 70 30 28.06 71.94 46.1 38.8

35_67:33 67 33 35.03 64.97 40.3 38.8

32_67:33 67 33 32.03 67.97 42.9 38.8

30_67:33 67 33 30.05 69.95 44.5 38.8

28_67:33 67 33 28.08 71.92 46.1 38.8

35_60:40 60 40 35.09 64.91 40.3 38.8

32_60:40 60 40 32.03 67.97 42.9 38.8

30_60:40 60 40 30.01 69.99 44.6 38.8

28_60:40 60 40 28.05 71.95 46.1 38.8

34_40:60 40 60 34.00 66.00 41.2 38.8

32_40:60 40 60 31.99 68.01 43.0 38.8

28_40:60 40 60 28.04 71.96 46.1 38.8

114

Table 3.30 Mix proportions of constituent materials

Mix typeBinder

Kg/m3

Cement

Kg/m3

Fly Ash

Kg/m3

Water

l/m3

20mm

kg/m3

10mm

Kg/m3

Sand

kg/m3

SP

l/m3

VMA

l/m3

35_70:30 495 321.75 173.25 178.2 637.55 273.24 680.75 4.46 0.99

34_70:30 495 321.75 173.25 178.2 619.11 265.33 706.81 4.46 0.99

33_70:30 495 321.75 173.25 178.2 600.66 257.43 733.35 4.46 0.99

32_70:30 495 321.75 173.25 178.2 583.37 250.01 757.88 4.46 0.99

30_70:30 495 321.75 173.25 178.2 546.47 234.20 809.60 4.46 0.99

28_70:30 495 321.75 173.25 178.2 510.73 218.89 862.24 4.46 0.99

35_67:33 495 321.75 173.25 178.2 610.23 300.56 680.75 4.46 0.99

32_67:33 495 321.75 173.25 178.2 557.99 274.83 758.12 4.46 0.99

30_67:33 495 321.75 173.25 178.2 523.53 257.86 809.28 4.46 0.99

28_67:33 495 321.75 173.25 178.2 489.07 240.89 862.09 4.46 0.99

35_60:40 495 321.75 173.25 178.2 546.14 364.09 680.97 4.46 0.99

32_60:40 495 321.75 173.25 178.2 499.73 333.15 758.09 4.46 0.99

30_60:40 495 321.75 173.25 178.2 468.12 312.08 811.63 4.46 0.99

28_60:40 495 321.75 173.25 178.2 437.51 291.67 862.45 4.46 0.99

34_40:60 495 321.75 173.25 178.2 353.60 530.40 706.99 4.46 0.99

32_40:60 495 321.75 173.25 178.2 332.72 499.09 760.32 4.46 0.99

28_40:60 495 321.75 173.25 178.2 291.62 437.43 862.50 4.46 0.99

115


3.5.4.1 SCC Fresh Properties

SCC fresh properties i.e., the average values of slump flow, T50cm at initial and

at 60 minutes, V-funnel time, V-funnel time at 5 minutes (T5min) and L-box ratio

(h2/h1) are presented in the Table 3.31 for all the mixes.

Table 3.31 Fresh properties of SCC

Slump flow

(mm)T50cm (sec) V-funnel time (sec)

Mix type

InitialAt

60 minInitial

At

60 minInitial T5min

L-box ratio

(h2/h1)

35_70:30 632 NDa 8.67 ND Blocked ND Blocked

34_70:30 637 ND 8.53 ND Blocked ND Blocked








28_67:33 685 ND 4.51 ND 10.21 13.23 Blocked



30_60:40 687 ND 4.06 ND 11.13 14.41 Blocked

28_60:40 696 657 3.12 4.28 6.23 7.59 0.81

34_40:60 688 ND 5.06 ND 11.69 14.31 Blocked

32_40:60 695 649 3.24 4.34 6.35 8.12 0.82

28_40:60 710 651 2.76 3.76 4.32 6.41 1.0

aND: Not done

116

From the Table 3.31, it is seen that though the mix 35_70:30 got the slump

flow spread of 632 mm in 8.67 sec, this mix was failed in V-funnel and L-box tests.

For the given blending 70:30, the reduction in coarse aggregate content from 35% to

28% increased the slump flow spread and the rate of flow, but all these mixes have

failed in V-funnel and L-box tests. The blocking was due to 70% of 20 mm aggregate

in a coarse aggregate content of 28-35% in the mix that leads to more collision and

internal friction within the coarse aggregate particles. As the minimum coarse

aggregate content was taken as 28% in this study, effect of the blending 70:30 was not

tried for the coarse aggregate content less than 28%.

Then, the coarse aggregate blending has been changed from 70:30 to 67:33

and performed the SCC tests on the mixes 35_67:33, 32_67:33, 30_67:33 and

28_67:33. From the results, it is seen that though the mix 35_67:33 got the slump

flow spread of 640 mm in 8.2 sec as shown in Fig. 3.20, this mix was failed in

V-funnel and L-box tests. The blocking was due to 67% of 20 mm aggregate in 35%

of coarse aggregate volume in the mix that leads to more collision and internal friction

within the coarse aggregate particles. Similarly, though the mixes 32_67:33 and

30_67:33 got the slump flow spread of 651 mm in 7.92 sec and 672 mm in 6.23 sec

respectively, these mixes were also failed in V-funnel and L-box tests due to more

internal friction within the coarse aggregate particles. The mix 28_67:33 was

successful both in slump flow and V-funnel tests, but this mix was failed in L-box

test. Though the coarse aggregate volume was reduced to 28%, the influence of 67%

of 20 mm aggregate in the coarse aggregate content also caused the blocking. So, for

the coarse aggregate blending 67:33, the mixes 35_67:33, 32_67:33, 30_67:33 and

28_67:33 have not met the SCC acceptance criteria.

117

Then, the coarse aggregate blending has been changed from 67:33 to 60:40

and performed the SCC tests on the mixes 35_60:40, 32_60:40, 30_60:40 and

28_60:40. The mixes 35_60:40 and 32_60:40 got the slump flow spread of 647 mm in

7.64 sec and 662 mm in 6.86 sec respectively, but these mixes were failed in V-funnel

and L-box tests. From the results, it is observed that the mix 30_60:40 was failed in

L-box test as shown in Fig. 3.23, though it was successful in slump flow and V-funnel

tests. Among the four mixes 35_60:40, 32_60:40, 30_60:40 and 28_60:40, it is

observed that only the mix 28_60:40 was successful and met the SCC acceptance

criteria as shown in Table 3.31 and Figs. 3.21 and 3.22. The reason was that for the

given blending 60:40, the increase of coarse aggregate content increased the volume

of 20 mm aggregate and leads to blocking of the aggregates. This is inline with the

statement that the filling ability and passing ability decreases with an increase in the

coarse aggregate content in concrete (Okamura and Ouchi, 2003b)145.

As compared to the mixes 28_70:30 and 28_67:33, the blocking of coarse

aggregate was not observed in L-box test in the mix 28_60:40 as shown in Fig. 3.22.

It is to be noted that the 60:40 blending reduced the yield stress or internal friction and

increased the deformation rate. Then, the coarse aggregate blending has been changed

from 60:40 to 40:60 and performed the SCC tests on the mixes 34_40:60, 32_40:60

and 28_40:60. It is clearly seen from the results, the mix 34_40:60 was failed in

L-box test, though it was successful in slump flow and V-funnel tests. From the

results, it is observed that for coarse aggregate blending 40:60, both the mixes

28_40:60 and 32_40:60 were met the SCC acceptance criteria. It is practically seen

that the influence of 40:60 (20 mm and 10 mm) blending didn’t significantly affect

the fresh properties of the mix 32_40:60. It can be stated that lower volume of

maximum size aggregate (i.e., 20 mm) can lead to increase the coarse aggregate

118

content to some reasonable extent. But the increase of coarse aggregate content from

32% to 34% for the same blending 40:60 caused the mix 34_40:60 blocking in L-box

test. This is due to more coarse aggregate content as compared to that of the mix

32_40:60. So, it is practically observed from the results that both coarse aggregate

maximum size and coarse aggregate volume are influential in obtaining the passing

ability of SCC and the same is confirming to ACI 237R-07 (2007)6.

Interestingly it is seen that both mixes 28_60:40 and 32_40:60 were almost

similarly performed the fresh properties. So, it is to be mentioned that if higher

volume of maximum size (20 mm) aggregate has to be used, the coarse aggregate

content has to be adjusted. Similarly, if the coarse aggregate content has to be

increased, the volume of maximum size (20 mm) aggregate has to be adjusted. So,

either volume of maximum size (20 mm) aggregate or coarse aggregate volume has to

be adjusted for a particular coarse aggregate blending to obtain successful SCC mixes.

For the failure mixes, the consistence retention measurements i.e., slump flow and

T50cm at 60 minutes were not performed. Segregation resistance of all successful SCC

mixes has been assessed by visual stability index (VSI) from the slump flow test. All

successful SCC mixes have been considered as stable mixes (VSI – 1) as described in

Table 2.1.

The typical range of coarse aggregate content suitable for a particular coarse

aggregate blending is represented as shown in Table 3.32.

Table 3.32 Coarse aggregate content for a particular coarse aggregate blending

Coarse aggregate blending (20 mm & 10 mm) Coarse aggregate content

70:30, 67:33 <28%

60:40 28%

40:60 28% to 32%

119

Fig. 3.20 Slump flow of 35_67:33 mix

Fig. 3.21 Slump flow of 28_60:40 mix

120

Fig. 3.22 L-box test of 28_60:40 mix

Fig. 3.23 L-box test of 30_60:40 mix

121

3.6 EFFECT OF COARSE AGGREGATE BLENDING ON

MECHANICAL PROPERTIES OF SCC

This section is mainly focused on the effect of coarse aggregate blending on

mechanical properties of SCC and these properties were compared to a conventional

concrete (CC) of a given compressive strength. The typical mix proportions of SCC

are different as compared to those of CC. These could influence the mechanical

properties of SCC include unit weight, compressive strength, modulus of elasticity

(MOE) and splitting tensile strength (STS). These mechanical properties are crucial to

the design and performance of concrete structures.

3.6.1 Unit Weight

As per ACI 237R-07 (2007)5, MOE of concrete is related to its compressive

strength, aggregate type and content, and unit weight of concrete. AASHTO LRFD

(2006)3 or ACI 318 (ACI, 1995)7 proposed MOE of concrete as a function of its

compressive strength and unit weight. Noguchi et al. (2009)140 expressed a

conventional equation for MOE of concrete as a function of its compressive strength

and unit weight of concrete made with light weight, normal weight and heavy weight

aggregates. It is revealed from many conventional equations that coarse aggregate

affect the value of MOE of concrete through the value of its unit weight (AASHTO,

2006; Tomosawa at al., 1990)3, 198. Tomosawa (1990)198 considered unit weight of

concrete at the time of compression test.


From the literature, it is revealed that the maximum size of coarse aggregate

and coarse aggregate content affects both the fresh and hardened properties of SCC.

The objective of this research work is to determine the effect of coarse aggregate

blending with 20 mm and 10 mm in a particular coarse aggregate content on

122

mechanical properties (unit weight, compressive strength, MOE and STS) of SCC at

different curing periods. And these properties were compared to a M 25 grade of CC.

From the results of SCC fresh properties shown in Table 3.31, the three successful

SCC mixes 28_60:40, 28_40:60 and 32_40:60 were selected for this study.

A new parameter called coarse aggregate points (CAP) has been introduced to

study the effect of coarse aggregate blending on mechanical properties of SCC. Our

objective was to determine the effect coarse aggregate blending (60:40 and 40:60) in a

coarse aggregate content (28% and 32%) on mechanical properties of SCC.

The hardened properties that were determined are unit weight, compressive

strength, modulus of elasticity and splitting tensile strength after 7, 28, 56 and 112

days of curing.

The measured MOE of all mixes were compared with ACI 363R

(ACI, 1992)8 and AASHTO LRFD (2006)3/ ACI 318 (ACI, 1995)7 predicted

equations. The measured STS of all mixes were compared with ACI 363R

(ACI, 1992)8 and CEB-FIP (1990)26 predicted equations.

3.6.3 Testing Hardened Properties of SCC and CC

The test procedures for compressive strength, modulus of elasticity and

splitting tensile strength tests are described in 3.2.3. These properties were tested on

cylinder specimens of size 150 mm x 300 mm for all the mixes. Unit weight or

density of hardened concrete (γc) was determined after 7, 28, 56 and 112 days of

curing prior to compression test. Weight of cylindrical specimen was measured prior

to compression testing and there by unit weight has been calculated by measuring the

volume of cylindrical specimen.

123

3.6.4 Coarse Aggregate Points

A new parameter, coarse aggregate points (CAP) has been introduced in this

study to evaluate the effect of coarse aggregate blending in a particular coarse

aggregate content on the mechanical properties of SCC. CAP represents a numerical

value based on the size of coarse aggregate, coarse aggregate blending in a given

coarse aggregate content. Size of coarse aggregate, coarse aggregate blending and

volume of coarse aggregate are used in the calculation of CAP. CAP will be

calculated for any size of coarse aggregate, coarse aggregate with or without blending

in any coarse aggregate content of SCC mix.

CAP can be calculated as below:

Let us consider a SCC mix with coarse aggregate content of 28% of concrete

volume. Coarse aggregate of sizes 20 mm and 10 mm with coarse aggregate blending

60:40 by percentage weight of total aggregate are used in this mix.

Coarse aggregate volume : 28% or 280 litre/m3

20 mm contribution : 60%

10 mm contribution : 40%

CAP (coarse aggregate points) : [280*(60/100)*20]+[280*(40/100)*10] = 4480


Mix types with percentage relative proportions along with CAP and mix

proportions of constituent materials of SCC and CC are shown in Table 3.33 and

Table 3.34.

124

Table 3.33 Percentage relative proportions of SCC and CC

Cementitious material – OPC+35% fly ash w/cm – 0.36 for SCC

Percentage

of

coarse

aggregate

Percentage

of

Mortar

Percentage

of

sand in

mortar

Percentage

of

PasteMix type

Coarse aggregate

blending percentage

by weight

(20 mm and 10 mm)

By volume

CAP

28_60:40 60 40 28.05 71.95 46.1 38.8 4480

28_40:60 40 60 28.04 71.96 46.1 38.8 3920

32_40:60 40 60 31.99 68.01 43.0 38.8 4480

M 25 60 40 43.81 56.19 43.5 31.7 7010

Table 3.34 Mix proportions of constituent materials of SCC and CC

Mix typeBinder

kg/m3

Cement

kg/m3

Fly ash

Kg/m3

Water

l/m3

20mm

Kg/m3

10mm

kg/m3

Sand

kg/m3

SP

l/m3

VMA

l/m3

28_60:40 495 321.75 173.25 178.2 437.51 291.67 862.45 4.46 0.99

28_40:60 495 321.75 173.25 178.2 291.62 437.43 862.50 4.46 0.99

32_40:60 495 321.75 173.25 178.2 332.72 499.09 760.32 4.46 0.99

M 25 384 384 - 192 683.4 455.6 636 - -

125


Hardened mechanical properties of M 25 grade of CC and SCC mixes are

presented in the Table 3.35.

Table 3.35 Mechanical properties of CC and SCC


M 25 28_60:40 28_40:60 32_40:60

7 2415.09 2160.38 2150.94 2160.38

28 2452.83 2320.75 2188.68 2301.89

56 2471.70 2339.60 2207.55 2320.75Unit weight, γc (kg/m3)

112 2490.57 2377.36 2245.28 2358.49

7 23.20 17.98 17.68 17.83

28 31.12 32.26 31.50 31.79

56 35.84 38.86 38.10 38.29

Compressive strength, f’c

(MPa)

112 39.05 48.10 47.89 47.94

7 24.40 18.19 17.92 18.11

28 28.91 27.12 24.78 26.61

56 31.48 30.10 27.48 29.69

Modulus of elasticity, Ec

(GPa)

112 33.11 34.38 31.40 33.82

7 2.97 2.33 2.05 2.26

28 3.68 3.02 2.71 2.92

56 3.96 3.68 3.30 3.61

Splitting tensile strength,

fct (MPa)

112 4.24 4.39 3.95 4.29

126

3.6.6.1 Unit Weight or Density of Hardened Concrete

As it can be seen from the Table 3.35, all SCC mixes have attained lower unit

weight than that of M 25 (CC) after 7, 28, 56 and 112 days of curing. Because, CC

has more coarse aggregate volume (i.e., 43.81%) as compared to that of SCC mixes.

Hence for a given concrete strength, higher the coarse aggregate content, higher is the

unit weight of concrete.

For a given coarse aggregate content (28%), the mix 28_60:40 has got more

unit weight than that of the mix 28_40:60 at all ages. It is mainly due to the higher

content of 20 mm (60%) in the mix 28_60:40 as compared to that of the mix

28_40:60. So, it is practically seen that for a given coarse aggregate content and

concrete strength, higher the maximum size aggregate volume in a coarse aggregate

blending, higher is the unit weight of concrete. It is concluded that the change in

coarse aggregate blending in a given coarse aggregate content, certainly affects the

unit weight of concrete.

For a given coarse aggregate blending (40:60), the mix 32_40:60 has got more

unit weight than that of the mix 28_40:60 at all ages. It is mainly due to the increase

in coarse aggregate content from 28% to 32%. Hence, for a given coarse aggregate

blending and concrete strength, higher the coarse aggregate content, higher is the unit

weight of concrete.

The effect of coarse aggregate blending can also be discussed in the CAP

point of view. When comparing the mixes 28_60:40 and 28_40:60, the mix 28_60:40

with a high CAP value (4480) attained high unit weight of concrete as compared to

that of the mix 28_40:60 having a low CAP value (3920). In other words, for a given

coarse aggregate content and concrete strength, higher the CAP value, higher is the

unit weight of concrete. Similarly, if we compare the mixes 28_40:60 and 32_40:60,

127

the mix 32_40:60 with a high CAP value (4480) attained high unit weight of concrete

as compared to that of the mix 28_40:60 having a low CAP value (3920). Hence, for a

given coarse aggregate blending and concrete strength, higher the CAP value, higher

is the unit weight of concrete.

Interestingly, the mixes 28_60:40 and 32_40:60 with the same CAP value

(4480) have got almost the same value of unit weight of concrete at all ages. This

trend can be easily assessed by knowing the CAP value of these two mixes.

Hence, it is concluded that for a given concrete strength irrespective of coarse

aggregate blending and coarse aggregate content, the mixes with the same CAP value

can exhibit almost similar values of unit weight of concrete at all ages.

So, the effect of coarse aggregate blending and coarse aggregate content on

unit weight of concrete for the given strength can be easily assessed by knowing the

CAP value of the mix.

3.6.6.2 Compressive Strength

All SCC mixes have attained almost the same value of compressive strength at

all ages. It is seen that the effect of coarse aggregate blending has not been observed

on the compressive strength of SCC mixes at all ages. So, it is agreed that the

compressive strength of SCC is mainly controlled by the composition of the binder

and w/cm (Domone, 2006b)47.

After 56 days of curing, all SCC mixes have attained significantly more

compressive strength than that of CC. This is mainly due to the influence of class F

fly ash in SCC mixes. Hence, it is agreed that fly ash blended concrete mixes attains

significantly more compressive strength than that of plain concrete at later ages i.e.,

after 28 days (Siddique, 2003)182.

128

3.6.6.3 Modulus of Elasticity

It is observed that for the given concrete strength after 28 days of curing, all

SCC mixes have attained lower MOE than that of CC. It is mainly due to more coarse

aggregate content in CC than that of SCC mixes. As it is already seen, higher coarse

aggregate content leads to higher unit weight of concrete for the same strength. Due to

higher unit weight of concrete, CC has attained high value of MOE as compared to

SCC mixes. Hence, it is agreed that the coarse aggregate affects the value of MOE of

concrete through its unit weight (AASHTO, 2006; Tomosawa et al., 1990)3, 198.

So it is concluded that, for a given concrete strength, higher the coarse aggregate

content, higher the unit weight of concrete and hence higher is the MOE of concrete.

After 56 days of curing, though MOE of SCC mixes were less than that of CC,

a significant improvement in MOE has been observed in SCC mixes as shown in

Fig. 3.24. This is particularly due to increase in strength of all SCC mixes. So, it is

well accepted that fly ash blended SCC mixes will continue to increase in strength

with age that tends to increase MOE of SCC mixes (Siddique, 2003)182.

For a given coarse aggregate content (28%), the mix 28_60:40 has attained

high MOE than that of the mix 28_40:60 at all ages. It is mainly due to higher value

of unit weight of the mix 28_60:40 as compared to that of the mix 28_40:60.

The effect coarse aggregate blending has been observed clearly in these two mixes

with respect to MOE. So, it is concluded that for a given coarse aggregate content and

concrete strength, higher the maximum size aggregate volume in coarse aggregate

blending, higher the unit weight and hence higher is the MOE of concrete.

For a given coarse aggregate blending (40:60), the mix 32_40:60 has attained

high MOE than that of the mix 28_40:60. It is mainly attributed to the higher unit

weight of the mix 32_40:60. So, it is concluded that for a given coarse aggregate

129

blending and concrete strength, higher the coarse aggregate content, higher the unit

weight and hence higher is the MOE of concrete.

The effect of coarse aggregate blending and coarse aggregate content can also

be discussed in CAP point of view. As we compare the mixes 28_60:40 and

28_40:60, the mix 28_60:40 with a high CAP value (4480) attained high unit weight

that leads to high MOE of concrete as compared to the mix 28_40:60 having a low

CAP value (3920). So, it is concluded that for a given coarse aggregate content and

concrete strength, higher the CAP value, higher the unit weight and hence higher is

the MOE of concrete. Similarly, when we compare the mixes 28_40:60 and 32_40:60,

the mix 32_40:60 with a high CAP value (4480) attained high unit weight that leads

to high MOE of concrete as compared to the mix 28_40:60 having a low CAP value

(3920). So, it is to be said that for a given coarse aggregate blending and concrete

strength, higher the CAP value, higher the unit weight and hence higher is the MOE

of concrete.

Also, it is observed that both the mixes 28_60:40 and 32_40:60 with the same

CAP value (4480) attained almost the same value of MOE of concrete at all ages

irrespective of coarse aggregate blending and coarse aggregate content as shown in

Fig. 3.24. So, it can be concluded that for a given concrete strength irrespective of

coarse aggregate blending and coarse aggregate content, the mixes with the same

CAP value attains almost the same value of unit weight and MOE of concrete. So, by

knowing the CAP value of the mix, the trend of MOE of concrete can be easily

assessed for the given concrete strength.

130

0

5

10

15

20

25

30

35

40

Age (days)

Mod

ulus

of E

last

icity

(GPa

)

M2528_60:4028_40:6032_40:60

28 56 112

CA

P 44

80

CA

P 70

10

CA

P 39

20

CA

P 44

80

CA

P 44

80

CA

P 70

10

CA

P 39

20

CA

P 44

80

CA

P 44

80

CA

P 70

10

CA

P 39

20

CA

P 44

80Fig. 3.24 MOE versus age

The ACI 363R (ACI, 1992)8 and AASHTO LRFD (2006)3 or ACI 318

(ACI, 1995)7 predicted equations for MOE of concrete are presented in the

Table 3.36.

Table 3.36 Expressions for MOE

Code of practice Expression for Ec (MPa) Range of concrete strength

ACI 363R (ACI 1992) 3320 'cf + 6900

No specified maximum

strength

AASHTO LRFD/ ACI 318 0.043 (γc)1. 5 + 'cf 21 MPa < f’c < 83 MPa

131

The measured MOE of all mixes after 28, 56 and 112 days of curing have been

compared with the ACI 363R (ACI, 1992)8 and AASHTO LRFD (2006)3 or

ACI 318 (ACI, 1995)7 predicted equations and presented in the Table 3.37.

Table 3.37 Comparison of measured and predicted MOE of all mixes

Modulus of elasticity, Ec (GPa)Mix type Age (days)

Experiment ACI 363R ACI 318

M25 (CC) 28.91 25.4 29.14

28_60:40 27.12 25.76 27.31

28_40:60 24.78 25.53 25.03

32_40:60

28

26.61 25.62 26.78

M25 (CC) 31.48 26.78 31.63

28_60:40 30.10 27.60 30.33

28_40:60 27.48 27.39 27.53

32_40:60

56

29.69 27.44 29.75

M25 (CC) 33.11 27.65 33.40

28_60:40 34.38 29.93 34.57

28_40:60 31.40 29.88 31.66

32_40:60

112

33.82 29.89 34.10

From the Table 3.37, it is seen that ACI 363R8 equation predicted the lower

values of Ec as compared to those of experimental values for all the mixes at 28, 56

and 112 days. Because, ACI 363R8 is not considering the unit weight of concrete in

its equation. Whereas, AASHTO LRFD3 or ACI 3187 predicted almost the same

values of Ec as compared to those of the experimental values for all the mixes at 28,

56 and 112 days.

132

As ACI 3187 included the unit weight of concrete, it is predicting the

appropriate values of Ec when compared to ACI 363R8 as shown in Fig. 3.25. Hence,

it is more reliable to use Ec predicted models which include both compressive strength

and unit weight of concrete.

20

22

24

26

28

30

32

34

36

30 35 40 45 50

Compressive Strength (MPa)

Mod

ulus

of E

last

icity

(GPa

)

Experiment

ACI363R

ACI318

Fig. 3.25 MOE versus compressive strength of SCC mixes

3.6.6.4 Splitting Tensile Strength

It is observed from the results that for a given concrete strength, all SCC

mixes have attained lower values of STS as compared to those of CC at 28 days. This

is primarily due to the use of 35% of fly ash replacement in the cement in SCC mixes

that tends to affect the aggregate-paste bond or interfacial transition zone (ITZ)

between the aggregate and cement paste at early ages. This is mainly attributed to the

slower pozzolanic action of fly ash that decreases the STS at early ages

(Liu, 2010)118.

133

Studies already revealed that though the STS is related to compressive

strength, several factors affect the STS such as aggregate type, particle size

distribution and mix design (Neville, 1988)136. Parra et al. (2011)155 revealed that the

use of higher fines or different superplasticisers affect the aggregate-paste bond,

which thus have a higher influence on tensile strength than compressive strength. The

interfacial transition zone characteristics tend to affect the tensile and flexural strength

to a greater degree than compressive strength (Mehta and Monterio, 2006)125.

The second reason being the lower coarse aggregate content and proportion of SCC as

compared to CC. Hence, it can be pointed out that for a given concrete strength, STS

primarily depends on the paste composition of the mix and secondarily on the coarse

aggregate content and its blending.

At 56 days, though the values of STS of all SCC mixes were lower than that of

CC, a significant improvement has been observed in the values of STS of all SCC

mixes as shown in Fig. 3.26. This is mainly attributed to the use of fly ash in SCC

mixes due to which SCC mixes have attained more compressive strength than that of

CC at 56 days. This increase in compressive strength caused the increase in STS of

SCC mixes. Hence, it is agreed that fly ash blended SCC mixes continued to increase

in compressive strength with age and there by increase in splitting tensile strength

(Siddique, 2003)182. At later ages i.e., after 112 days of curing, both SCC mixes

28_60:40 and 32_40:60 have attained higher values of STS as compared to those of

CC.

Results shown that for a given coarse aggregate content (28%), the mix

28_60:40 has attained higher STS as compared to that of 28_40:60 for the given

strength at all ages as shown in Fig. 3.26.

134

Hence, it is pointed out that for the coarse aggregate content and concrete

strength, higher the maximum size coarse aggregate volume in coarse aggregate

blending, higher is the CAP value and hence higher is the value of STS.

If we compare the mixes 28_40:60 and 32_40:60, the mix 32_40:60 exhibited

higher value of STS due to more coarse aggregate content as compared to that of the

mix 28_40:60. Hence for a given coarse aggregate blending and concrete strength,

higher the coarse aggregate content, higher is the CAP value and hence higher is the

value of STS as shown in Fig. 3.26. It is agreed that concrete with higher coarse

aggregate ratio (content) exhibits slightly higher STS as compared to that of concrete

with lower aggregate ratio (content) (Mahdy et al., 2002)121. So, it is concluded that

coarse aggregate blending in a particular coarse aggregate content has significant

effect on unit weight, MOE and STS of SCC mixes.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Age (days)

Split

ting

Tens

ile S

treng

th (M

Pa)

M2528_60:4028_40:6032_40:60

28 56 112

CA

P 44

80

CA

P 70

10

CA

P 39

20

CA

P 44

80

CA

P 44

80

CA

P 70

10

CA

P 39

20

CA

P 44

80

CA

P 44

80

CA

P 70

10

CA

P 39

20

CA

P 44

80

Fig. 3.26 STS versus age

135

The ACI 363R (ACI, 1992)8 and CEB-FIP (1990)26 predicted equations for

STS of concrete are presented in the Table 3.38.

Table 3.38 Expressions for STS

Code of practice Expression for fct (MPa)Range of concrete

strength

ACI 363R (ACI 1992) 0.59 (f’c)0.5 21 MPa < f’c < 83 MPa

CEB-FIP (1990) 1.563

2

108'

cf f’c < 80 MPa

The measured STS of all mixes after 28, 56 and 112 days of curing have been

compared with the ACI 363R (ACI, 1992)8 and CEB-FIP (1990)26 predicted equations

and presented in the Table 3.39.

Table 3.39 Comparison of measured and predicted STS of all mixes

Splitting tensile strength, fct (MPa)Mix type Age (days)

Experiment ACI 363R CEB-FIP

M25 (CC) 3.68 3.29 2.73

28_60:40 3.02 3.35 2.82

28_40:60 2.71 3.31 2.76

32_40:60

28

2.92 3.33 2.78

M25 (CC) 3.96 3.53 3.09

28_60:40 3.68 3.68 3.31

28_40:60 3.30 3.64 3.25

32_40:60

56

3.61 3.65 3.27

M25 (CC) 4.24 3.67 3.32

28_60:40 4.39 4.09 3.94

28_40:60 3.95 4.08 3.93

32_40:60

112

4.29 4.09 3.93

136

It is seen from the Table 3.39, ACI 363R (ACI, 1992)8 equation gives a

reasonable estimate of splitting tensile strength especially for SCC mixes.

Whereas, CEB-FIP model (1990)26, under estimates the value of STS as compared to

those of experimental values for all mixes.

If we consider CEB-FIP26 predicted values as lower bound and ACI 363R

(ACI, 1992)8 predicted values as upper bound for SCC mixes, a suitable STS range

can obtained for a given concrete strength after 28 and 56 days of curing as shown in

Fig. 3.27.

2.6

2.8

3

3.2

3.4

3.6

3.8

4

4.2

4.4

4.6

30 35 40 45 50

Compressive Strength (MPa)

Split

ting

Tens

ile S

treng

th (M

Pa)

Experiment

ACI363R

CEB-FIP

Fig. 3.27 STS versus compressive strength of SCC mixes

137

As per the STS range (2.76 MPa – 3.35 MPa) of SCC mixes at 28 days for a

given strength, it can be concluded that all SCC mixes are within the acceptable

range. Similarly, as per the STS range (3.27 MPa – 3.68 MPa) of SCC mixes at 56

days for a given strength, it can be concluded that all SCC mixes are within the

acceptable range. Also at 112 days, though the SCC mixes 28_60:40 and 32_40:60

have attained higher STS values as compared to those of CC, ACI 363R (ACI, 1992)8

estimated the STS values of SCC mixes reasonably when compared to CEB-FIP26.

Hence, it can be concluded that though the coarse aggregate blending and coarse

aggregate content have an effect on STS of SCC mixes at all ages for the given

concrete strength, ACI 363R (ACI, 1992)8 predicted the STS values of SCC mixes

reasonably.

3.7 DRYING SHRINKAGE

This section is mainly focused on the determination of drying shrinkage of

SCC and CC at different drying periods. Drying shrinkage strains need to be

investigated as they can have adverse effects on the serviceability and durability of

concrete. Due to higher paste volume and lower coarse aggregate content, SCC leads

to higher drying shrinkage than that of CC (ACI 237R-07, 2007)6. Ozyildirim and

Lane (2003)153 recommended a large nominal maximum aggregate size, large amount

of coarse aggregate, and low water content to mitigate high drying shrinkage in SCC

applications. Studies already revealed that the incorporation of fly ash reduced the

drying shrinkage of SCC by densifying the paste matrix and also by serving the

unhydrated fly ash particles as fine aggregate to restrain the shrinkage deformation

(Poppe and De Schutter, 2005; Khatib, 2008; Gesoglu et al., 2009)162, 96, 57.

138


Our objective was to investigate the drying shrinkage strains of M 25 grade of

SCC and CC after 1, 7, 14, 28, 56 and 112 days of drying after 7 days of curing. From

the results obtained in the compressive strengths of SCC mixes as shown in Table

3.35, the SCC mixes 28_60:40, 28_40:60 and 32_40:60 have been selected as M 25

grade of SCC mixes to evaluate the effect of coarse aggregate blending and its content

on the drying shrinkage of SCC.

The test procedure for determining the drying shrinkage of all mixes is

described in the section 3.2.4. For each concrete mixture, three 150 mm x 300 mm

concrete cylinders were cast for drying shrinkage test. These cylinders were cured for

7 days. Drying shrinkage of all mixes was carried out using length comparator after

1, 7, 14, 28, 56 and 112 days of drying after 7 days of curing as shown in Fig. 3.28.

Fig. 3.28 Shrinkage measurement of 28_60:40 at 112 days using length comparator

139

Mix types with percentage relative proportions along with CAP and mix

proportions of constituent materials of M 25 grade SCC mixes and CC are shown in

Tables 3.33 and 3.34.


The average drying shrinkage strains of M 25 grade of SCC and CC after

1, 7, 14, 28, 56 and 112 days of drying after 7 days of curing are presented in the

Table 3.40. The drying shrinkage of all mixes as a function of drying period was

plotted and shown in Fig. 3.29.

Table 3.40 Average drying shrinkage values of M 25 grade of SCC and CC

Drying shrinkage (microstrain)Mix type

1-day 7-day 14-day 28-day 56-day 112-day

28_60:40 0 134 232 356 484 616

28_40:60 0 139 242 366 499 621

32_40:60 0 130 228 355 478 603

M 25 0 117 188 295 375 475

It was observed that CC has attained a lower drying shrinkage strain of

475 x 10-6 (475 microstrain) after 112 days of drying as compared to that of all SCC

mixes. This was mainly attributed to the lower paste volume, higher coarse aggregate

content and higher CAP value of CC as compared to those of SCC mixes.

For a given coarse aggregate content (28%), the mix 28_60:40 has exhibited

slightly lower 112-day drying shrinkage than that of the mix 28_40:60. It is mainly

due to the higher content of 20 mm (60%) in the mix 28_60:40 as compared to that of

the mix 28_40:60. So, it is practically seen that for a given mix proportion and coarse

aggregate content, higher the maximum size aggregate volume in a coarse aggregate

blending, higher is the CAP value and lower is the drying shrinkage of concrete.

140

It is concluded that the change in coarse aggregate blending in a given coarse

aggregate content certainly affects the drying shrinkage of concrete. For a given

coarse aggregate blending (40:60), the mix 32_40:60 has exhibited slightly lower

112-day drying shrinkage than that of the mix 28_40:60. It is mainly due to the

increase in coarse aggregate content from 28% to 32%. Hence, for a given mix

proportion and coarse aggregate blending, higher the coarse aggregate content, higher

is the CAP value and lower is the drying shrinkage of concrete.

Among the three SCC mixes, the two SCC mixes 28_60:40 and 32_40:60

have attained almost the same value of 112-day drying shrinkage strain as shown in

Table 3.40. Though these two SCC mixes had different coarse aggregate contents

(28% and 32%) with different coarse aggregate blending (60:40 and 40:60), they had

the same CAP value as shown in Table 3.33. From the results, it can be concluded

that for a given mix proportion, the mixes with the same CAP value can exhibit

almost similar values of drying shrinkage of concrete.

0

100

200

300

400

500

600

700

0 20 40 60 80 100 120

Drying period (Days)

Dryi

ng s

hrin

kage

(Mic

rost

rain

)

M2528_60:4028_40:6032_40:60

Fig. 3.29 Drying shrinkage of SCC and CC

141

3.8 MICROLEVEL PROPERTIES

This investigation is mainly focused on the effect of class F fly ash on the

microlevel properties of SCC at different curing periods. The microlevel properties

studied were the microcrack widths between aggregate and paste; and the chemical

elements and atomic Calcium-Silica (Ca/Si) ratio of the paste near the interfacial

transition zone (ITZ). It has been suggested that microcracks in the ITZ play an

important part in determining not only the mechanical properties but also the

permeability and durability of concrete (Mehta and Monteiro, 2006)125.

Modification of the microstructure in the ITZ has been one of great concern since

durability, permeability and strength of concrete are significantly influenced. The

addition of mineral admixtures is successful approach in improving the microstructure

of concrete (Jing and Stroeven, 2004)90. The pozzolanic reaction of fly ash reduces

the amount of Ca(OH)2 produced and lowers the Ca/Si ratio of the C-S-H in the

cement/fly-ash mix (Wesche, 1991)207. The pozzolanic reaction gives a fly ash

concrete its fine pore structure, low permeability, long-term strength gain properties

and enhanced durability properties (Sear, 2001)175. The Scanning electron microscopy

(SEM) has been a powerful tool in the examination of cement and concrete

microstructure (Nemati, 1997; Stutzman, 2000)133, 190. The energy dispersive x-ray

analysis (EDAX) can be used for spectrum analysis to determine the chemical

elements and their peaks along with their relative concentrations (Stutzman, 2000)190.


In the last few decades, a lot of research has been done regarding the

improvement of the concrete performance. Self-compacting concrete with high

cementitious content, a lower volume and maximum size of coarse aggregate are

142

expected to affect the ITZ in a positive manner, promoting a less porous

microstructure and improvement in the mechanical properties. To better understand

and correlate the micro and macrolevel (mechanical) properties, this investigation is

mainly focused on the effect of class F fly ash on the micro and macrolevel properties

of SCC after 28, 56 and 112 days of curing. SEM analysis was carried out to examine

the widths of microcracks between aggregate and paste and EDAX analysis was

carried out to determine the chemical elements and atomic Ca/Si ratio of the paste

matrix near the ITZ at different ages. These properties were also examined on M 25

grade of CC at different days. For this investigation, M 25 grade of SCC mix

28_60:40 and M 25 grade of CC have been considered.

The sample preparation and test procedure for determining the microlevel

properties of concrete is described in the section 3.2.5. To carry out SEM and EDAX,

the samples of approximate size 10 mm x 10 mm x 5 mm were collected from the

tested cylindrical specimens after the compressive strength tests as per IS 516

(1959)77 on SCC and CC at different ages. Mix types with percentage relative

proportions and mix proportions of constituent materials of M 25 grade SCC and CC

are shown in Tables 3.33 and 3.34.


3.8.2.1 Microlevel Properties

This section describes the microlevel properties i.e., the microcracking width

and Ca/Si ratio of SCC and CC at different ages.

3.8.2.1.1 Microcracking Width

SEM analysis was carried out on SCC and CC samples to observe the

microcracking width between coarse aggregate and paste at different ages.

143

As the microcracking width is not uniform in concrete microstructure

(Mindess et al., 2003)126, the microcracking width has been measured at three

different places for each sample at each age and the average microcracking width has

been calculated and represented in Table 3.41.

Table 3.41 Microcrack widths of CC and SCC (28_60:40)

Microcrack width (μm)Curing period

(days) CC SCC

28 4.80 3.73

56 0.93 1.47

112 0.67 0.53

The microstructure of SCC especially the widths of microcracking after 28, 56

and 112 days of curing have been shown in Figs. 3.30, 3.31 and 3.32 respectively.

Fig. 3.30 SEM image of SCC microcrack width at 28 days

144



145

It is seen from the Fig. 3.30, the microcracking width of SCC at 28 days was

3.73 μm. After 56 days of curing, the microcracking width was decreased from

3.73 μm to 1.47 μm as shown in Fig. 3.31. After 112 days of curing, the

microcracking width was further reduced to 0.53 μm as shown in Fig. 3.32.

It is clearly seen from the results that significant reduction in the

microcracking width of SCC was observed with the increasing curing period.

This significant reduction in the microcracking width is mainly due to the pozzolanic

action of class F fly ash which improves the microstructure of ITZ at later ages.

The microcracking widths of CC after 28, 56 and 112 days of curing have

been shown in Figs. 3.33, 3.34 and 3.35 respectively.

Fig. 3.33 SEM image of CC microcrack width at 28 days

146



147

The microcracking width of CC at 28 days was 4.80 μm as shown in Fig. 3.33.

After 56 days of curing, the microcracking width was decreased from 4.80 μm to

0.93 μm as shown in Fig. 3.34. From the Fig. 3.35, it is to be noted that there was no

significant reduction in the microcracking width (0.93 μm) after 112 days of curing as

compared to the microcracking width (0.67 μm) at 56 days. It is clearly seen from the

results that there was no significant improvement observed in the microcracking

width of CC at later ages as compared to that of fly ash blended SCC. Hence,

improvement in the mechanical properties of CC was not significant as compared to

that of SCC at later ages.

As there was significant reduction in the microcracking width of SCC with the

increasing curing period, improvement in the mechanical properties i.e., compressive

strength, modulus of elasticity (MOE) and splitting tensile strength (STS) was

observed in SCC as shown in the Table 3.28. Though MOE and STS of SCC were

lower than that of CC after 28 and 56 days of curing, SCC has attained higher MOE

and STS than that of CC after 112 days of curing as shown in Figs. 3.44 and 3.45.

This is particularly due to significant improvement in the compressive strength of

SCC at later ages. Hence, it is concluded that pozzolanic action of fly ash reduces the

microcracking width of SCC with age that results in the improvement of bond

between coarse aggregate and paste (Kuroda et al., 2000; Wong and Buenfeld, 2006;

Xiong et al., 2002)110, 208, 212 and improvement in the SCC mechanical properties.

3.8.2.1.2 Atomic Ca/Si Ratio

EDAX analysis was carried out on the paste near the interface at different ages

in order to determine the chemical elements with the peaks and their relative

intensities.

148

Figs. 3.36-3.38 represent the spectrum analysis of chemical elements and their

relative intensities of SCC after 28, 56 and 112 days of curing.

Fig. 3.36 EDAX analysis of SCC at 28 days


149


Figs. 3.39-3.41 represent the spectrum analysis of chemical elements and their

relative intensities of CC after 28, 56 and 112 days of curing.

Fig. 3.39 EDAX analysis of CC at 28 days

150



151

Table 3.42 and Fig. 3.42 represent the atomic Ca/Si ratio of SCC and CC after

28, 56 and 112 days of curing.

Table 3.42 Atomic Ca/Si ratio of CC and SCC

Atomic Ca/Si ratioCuring period

(days) CC SCC

28 0.599 0.478

56 0.647 0.422

112 0.651 0.381

Fig. 3.42 Ca/Si ratio versus age

Table 3.42 shows that Ca/Si ratio of SCC was 0.478, 0.422 and 0.381 after 28,

56 and 112 days of curing respectively. Results show that Ca/Si ratio in fly ash

blended SCC has been decreased with age as shown in Fig. 3.42.

152

It can be seen from the Figs. 3.43-3.45, as Ca/Si ratio decreases with age,

significant improvement observed in the SCC mechanical properties. It is mainly

attributed to pozzolanic action of low calcium class F fly ash which reduces the

amount of Ca(OH)2 produced during hydration or transforming the calcium hydroxide

into C-S-H by the pozzolanic reaction (Kuroda et al., 2000; Wong and Buenfeld,

2006; Xiong et al., 2002)110, 208, 212. Hence, it results in fine pore structure and

reduction of the microcracking width in SCC. From the results obtained by SEM and

EDAX analysis on SCC as shown in Figs. 3.30-3.32 and 3.36-3.38, it is concluded

that the decrease in Ca/Si ratio can be correlated to the reduction of the microcracking

width which indicates the densification of microstructure of SCC.

Fig. 3.43 Compressive strength versus age

153

Fig. 3.44 Modulus of elasticity versus age

Fig. 3.45 Splitting tensile strength versus age

154

This improvement in the microlevel properties caused the improvement of

macrolevel (mechanical) properties of SCC with age as shown in Table 3.28. So, it is

to be said that pozzolanic action of class F fly ash densifies the concrete

microstructure by improving microlevel properties i.e., reducing the atomic Ca/Si

ratio and the microcracking width. And hence, long-term mechanical (macrolevel)

properties of SCC can be obtained.

Whereas, the atomic Ca/Si ratio of CC was observed as 0.599, 0.647 and 0.651

after 28, 56 and 112 days of curing as shown in Table 3.42. Fig. 3.42 shows that Ca/Si

ratio in CC has been increased with age (Hewlett, 2003)69. It is attributed to the

hydration of cement in CC which increases the calcium hydroxide during hydration.

Hence, from the Figs. 3.43-3.45, it is clearly seen that significant improvement was

not observed in the mechanical properties of CC at later ages as compared to that of

SCC. This clearly indicates that the gain of strength in CC will not be significant at

later ages as compared to that of fly ash blended SCC as shown in Table 3.28 and

Fig. 3.43.

When comparing the properties of SCC and CC, significant improvement has

been observed in microlevel properties SCC as compared to CC and hence, SCC has

attained enhanced macrolevel (mechanical) properties than that of CC at later ages.

Whereas, in the case of CC, though the microcracking width gradually reduces with

age as shown in Table 3.41, the Ca/Si ratio has been increased due to hydration of

cement as shown in Fig. 3.42. So, the decrease in microcracking width and increase in

Ca/Si ratio in CC can be said to be less improvement in the microlevel properties and

caused less improvement in the mechanical properties of CC at later ages as shown in

Figs. 3.43-3.45.

155

So, it can be revealed that both microlevel and macrolevel properties are

reasonably correlated such that better the microlevel properties of concrete, better are

the macrolevel properties. So, it is evidently concluded that the use of class F fly ash

densifies the microstructure of SCC by improving the microlevel properties i.e.,

reducing Ca/Si ratio and the microcracking width and thus improves the bond

between aggregate and paste and enhances the macrolevel mechanical properties.

Studies already revealed that mechanical properties of fly ash concrete

continued to increase with age (Liu, 2010; Siddique, 2003; Siddique, 2011)118, 182, 183.

This study investigated and concluded that the reason being the continuous

improvement in the microlevel properties.

3.0 development of m 25 grade of self compacting...

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