Behaviour of reinforced concrete beams with 50 percentage fly ash

International Journal of Civil Engineering and Technology (IJCIET), ISSN 0976 – 6308 (Print),

ISSN 0976 – 6316(Online) Volume 4, Issue 2, March - April (2013), © IAEME

36

BEHAVIOUR OF REINFORCED CONCRETE BEAMS WITH 50

PERCENTAGE FLY ASH

P.S.Joanna1, Jessy Rooby

2, Angeline Prabhavathy

3, R.Preetha

4, C.Sivathanu Pillai

5

1Civil Engineering Department, Hindustan University,Padur- 603103, India.

2Professor, Civil Engineering Department, Hindustan University,Padur- 603103, India.

3Professor, Civil Engineering Department, Hindustan University, Padur-603103, India.

4Scientific Officer,Civil Engineering Division,Indira Ghandhi Centre for Atomic

Research,Kalpakkam- 603 102, India. 5Associate Director,Civil Engineering Division,Indira Ghandhi Centre for Atomic

Research, Kalpakkam- 603 102, India.

ABSTRACT

Fly ash has emerged as novel engineering materials which lead to global sustainable

development and lowest possible environmental impact with considerable promise as binders

in the manufacture of concrete. In this paper, the results of laboratory investigation conducted

on the structural behavior of reinforced concrete beam with high volume of low calcium

(class F) fly ash are presented. Experimental investigation included testing of nine reinforced

concrete beams with and without fly ash. Portland cement was replaced with 50% fly ash and

Conplast SP430 was used as superplastisizer for the casting of beams. Data presented include

the load-deflection characteristics, cracking behavior, ductility indices, moment- curvature

and end rotations of the reinforced concrete beams with and without fly ash when tested at 28

days, 56 days and 75 days. The investigation revealed that there is a significant improvement

in flexural strength of reinforced fly ash concrete beams beyond 28 days.

Key Words: Ordinary Portland Cement, Reinforced Fly Ash concrete beams, ductility,

moment- curvature.

INTERNATIONAL JOURNAL OF CIVIL ENGINEERING AND

TECHNOLOGY (IJCIET)

ISSN 0976 – 6308 (Print)

ISSN 0976 – 6316(Online)

Volume 4, Issue 2, March - April (2013), pp. 36-48

© IAEME: www.iaeme.com/ijciet.asp

Journal Impact Factor (2013): 5.3277 (Calculated by GISI)

www.jifactor.com

IJCIET

© IAEME



37

1. INTRODUCTION

The Ordinary Portland Cement (OPC) is one of the main ingredients used for the

production of concrete and has no alternative in the construction industry. Unfortunately,

production of cement involves emission of large amounts of carbon-dioxide gas in to the

atmosphere, a major contributor for green house effect and the global warming. Hence it is

inevitable either to search for another material or partly replace it by some other material. Fly

ash is one such pozzolanic material which can be used in concrete as partial replacement of

cement.

Jiang and Malhotra (2000) found that the incorporation of 50% fly ash in concrete

gives good compressive strength at 91 days. Gopalakrishnan et al. (2001) showed that the fly

ash concretes have superior durability properties. Rafat Siddique (2004) studied the

compressive strength and flexural strength of High Volume Class-F Fly Ash concrete and

found that there is a significant improvement of strength properties beyond 28 days. They

also found that the strength of concrete with 40%, 45% and 50% fly ash content, even at 28

days is sufficient enough for use in reinforced cement concrete construction. Khatib (2008)

found that the concrete with 60% fly ash replacement for cement can produce self

compacting concrete with adequate strength. Dakshina Murthy and Sudheer Reddy (2010)

found that fly ash replacement up to 30% in concrete gives good improvement in flexural

strength at 28 days. Sunilaa et al. (2011) found that the addition of 40% fly ash gives better

resistance against shear at 28 days.

Extensive research has been done on the compressive strength and flexural strength of

High Volume Fly Ash Concrete (HVFAC). Hence in this investigation, behavior of

Reinforced Concrete (RC) beams with HVFAC was carried out. 50% of cement was replaced

with fly ash and Conplast (SP430) was used as superplastisizer for the casting of beams. A

total of nine reinforced concrete beams with and without fly ash were cast and tested. Out of

the nine specimens, four controlled specimens were cast without fly ash and the other five

specimens were cast with 50% fly ash. Data presented include the deflection characteristics,

cracking behavior, ductility indices, moment-curvature and end rotations of the specimens.

2. EXPERIMENTAL INVESTIGATIONS

2.1 Materials and mix proportions In the current investigation 50% of cement was replaced with Fly Ash in the casting

of RC beams. The materials used in the mix were Ordinary Portland Cement (OPC), river

sand, low calcium Fly Ash (Class F), aggregate and potable water. Conplast (SP430)

superplastisizer was incorporated in the mix to increase the workability. Beams were made

with M30 grade concrete. Water-cement ratio of 0.45 and 0.75% Conplast superplastisizer

were used for reinforced OPC concrete beams. Water/cement & Fly ash ratio of 0.45 and

1.5% Conplast superplastisizer were used for 50% fly ash concrete beams. Fe 500 grade steel

was used for longitudinal reinforcement and for stirrups.

2.2 Test beam details Nine numbers of reinforced concrete beams with and without fly ash were cast and

tested in the loading frame. The span of the beam was 2500 mm and of size 150mm x

250mm. The specimens were designed as per IS: 456-2000. Out of the nine specimens tested,



38

four specimens were cast without fly ash and four specimens were cast with 50% fly ash.

Two specimens were cast in each series. Four specimens were tested at 28th

day, four

specimens were tested at 56th

day and one specimen was tested at 75th

day from the date of

casting. Reinforcement details for the beam and the details of the specimens tested are given

in Table 1. A five lettered designation is given to the specimens. First 2 letters represents the

beam with Conplast superplastisizer, 3rd

one % of fly ash added, 4th

one identity of specimen

in a particular series as two specimens were tested in each series and the last one indicates the

day on which the specimen is being tested.

Table 1: Test beam details

SL.No. Beam

Number

Testing

of

Beams

(days)

Reinforcement in beams

Longitudinal Stirrups

Nos. and

size at top

Nos. and

size at

bottom

Diameter

(mm)

Spacing

(mm)

1 CB0% 1-28

28

2#10

2#12 + 1#16

8

120 2 CB0% 2-28

3 CB50% 1-28

4 CB50% 2-28

5 CB0% 1-56

56

2#10

2#12 + 1#16

8

120 6 CB0% 2-56

7 CB50% 1-56

8 CB50% 2-56

9 CB50% 1-75 75 2#10 2#12 + 1#16 8 120

3. TEST SET-UP

The testing was carried out in a loading frame of 400 kN capacity. TML strain gauge

was fixed at the mid span of the tension bar and then protected using coating tape to avoid

accidental damage during pouring of concrete. Strain gauges were also attached to the

concrete surface in the central region of the beam to measure the strain at different depths.

The top surface of the beam was instrumented with strain gauge to measure the concrete

compressive strains in the pure bending region. Linear Voltage Displacement Transducers

(LVDTs) were used for measuring deflections at several locations, one at mid span, two

directly below the loading points and two near the end supports as shown in the Figure 1.

Strain gauges and LVDTs were connected to a data logger from which the readings were

captured by a computer at every load intervals until failure of the beam occurred. The beams

were subjected to two-point loads under a load control mode. The development of cracks

were observed and the crack widths were measured using a hand-held microscope with an

optical magnification of X50 and a sensitivity of 0.02 mm. Figure 2 shows the test set-up.



39

25 mm

25 mm

25 mm10 mm

10 mm

10 mm

50 mm

10 mm

Strain Gauge

Hydraulic Jack

Load Cell

LVDT

Steel Support

DC DR1 DR2DL1DL2

FCS1

FCS2

FCS3

FCS4

TCS (Extreme fibre concrete strain)

CSS ( Center Steel Strain)

Figure 1: Position of LVDTs and Strain gauges

Figure 2: Test set-up



40

4. TEST RESULTS

4.1. General observations Vertical flexural cracks were observed in the constant-moment region and final failure

occurred due to crushing of the compression concrete with significant amount of ultimate

deflection. When the maximum load was reached, the concrete cover on the compression

zone started to fall for the beams with and without fly ash. Figure 3. shows the failure pattern

of the test specimens. Crack formations were marked on the beam at every load interval at the

tension steel level. Initial cracking was formed at 17% and 20% of ultimate load for beams

with and without fly ash respectively at 28 days and it is 16% and 20.4% at 56 days. Initial

crack for fly ash concrete beam at 75 days is 18.6% of ultimate load. It was noticed that the

first crack always appears close to the mid span of the beam. The cracks formed on the

surface of the beams were mostly vertical, suggesting flexural failure of the beams. The crack

widths at service loads for fly ash concrete beams ranged between 0.18mm to 0.2mm and this

is within the maximum allowable value as stipulated by IS: 456-2000 for durability

requirements.

(a) CB0% 1-28 (b) CB50% 1-28

Figure 3: Failure Pattern of the beams with 50% fly ash and without fly ash

4.2. Load-Deflection curve

The experimental load-deflection curves of the RC beams with 50% fly ash and

without fly ash when tested at 28th

day, 56th

day and 75th

day are shown in Figure 4 Figure 5

and Figure 6 respectively. The average ultimate loads for both the reinforced OPC concrete

beams and 50% fly ash concrete beams are 182 kN & 152 kN respectively at 28th

day and it is

186 kN & 168 kN respectively at 56th

day. The ultimate load for fly ash concrete beam at 75th

day is found to be 197 kN. Though the ultimate loads for the fly ash concrete beam is 16%

and 9.6% less than the OPC beams at 28th

day and 56th

day respectively, its ultimate load

increases at 75th

day. The average span-deflection ratios under the design service loads for the

reinforced concrete fly ash beams are 290 at 28th

day 258 at 56th

day and 251 at 75th

day,

which are within allowable limit as per IS: 456-2000.



41

(a) CB0% 1-28 (b) CB0% 2-28

(c) CB50% 1-28 (d) CB50% 2-28

Figure 4: Load- Deflection curves for the beams tested at 28 days

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30 35 40Lo

ad

(kN

)

Deflection (mm)

DC

DR1

DR2

DL1

DL2

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25

Loa

d (

kN

)

Deflection (mm)

DR1

DR2

DL1

DL2

DC

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30

Loa

d(k

N)

Deflection (mm)

DC

DR1

DL1

DR2

DL2

0

20

40

60

80

100

120

140

160

0 5 10 15 20 25 30

Loa

d (

kN

)

Deflection (mm)

DC

DR1

DL1

DR2

DL2



42

(a) CB0% 1-56 (b) CB0% 2-56

(c) CB50% 1-56 (d) CB50% 2-56

Figure 5: Load- Deflection curves for the beams tested at 56 days

(e) CB50% 1-75

Figure 6: Load- Deflection curves for the beam tested at 75 days

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30

Loa

d (

kN

)

Deflection (mm)

DC

DR1

DR2

DL1

DL2

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30 35 40

Loa

d (

kN

)

Deflection (mm)

DC

DR1

DR2

DL1

DL2

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25 30

Loa

d (

kN

)

Deflection (mm)

DC

DR1

DL1

DR2

DL2

0

20

40

60

80

100

120

140

160

180

0 5 10 15 20 25 30

Loa

d (

kN

)

Deflection (mm)

DC

DR1

DR2

DL1

DL2

0

20

40

60

80

100

120

140

160

180

200

0 5 10 15 20 25 30 35 40

Loa

d (

kN

)

Deflection (mm)

DC

DR1

DL1

DR2

DL2



43

4.3. Displacement Ductility

Displacement ductility is the ratio of ultimate to first yield deflection. In general high

ductility ratios indicate that a structural member is capable of undergoing large deflections

prior to failure. The average displacement ductility for fly ash concrete beams and OPC

concrete beams are 4.8 & 5.8 respectively when tested at 56th

day. The displacement ductility

for fly ash concrete beams increases at 75 days. Table 2 shows the ductility of beams. Thus

the fly ash concrete beams shows adequate displacement ductility and can be considered for

structural members subjected to large displacement such as sudden forces caused by

earthquake.

Table 2: Displacement ductility of beams

Beam

Specification

Deflection at yield (mm) Max. deflection

(mm)

Displacement ductility

CB0% 1-28 4.8 20.0 4.17

CB0% 2-28 5.4 27.5 5.09

CB50% 1-28 5.0 19.3 3.86

CB50% 2-28 5.0 22.2 4.44

CB0% 1-56 4.6 24.6 5.34

CB0% 2-56 3.5 22.0 6.28

CB50% 1-56 5.0 21.6 4.32

CB50% 2-56 4.0 20.5 5.13

CB50% 2-75 4.3 27.0 6.30

4.4. End rotation The moment-end rotation curves of fly ash concrete beams and OPC concrete beams

are presented in Figure 7 when tested at 28,56 and 75 days respectively. It was observed that

the average end rotations of the fly ash concrete beams and OPC concrete beams at ultimate

loads are 1.70 & 1.8

0 respectively when tested at 56 days and it is 2

0 at 75 days. Thus the end

rotations of the beams with fly ash are comparable with OPC concrete beams.

Figure 7: Moment-Rotation curves for beams tested at 28, 56 and 75 days

0

10

20

30

40

50

60

70

80

0 1 2 3

Mo

men

t (k

N.m

)

End rotation (o)

CB0% 1-56

CB0% 2-56

CB50% 1-56

CB50% 2-56

CB50% 1-75

0

10

20

30

40

50

60

70

80

0 0.5 1 1.5 2 2.5 3

Mo

men

t (k

N.m

)

End rotation (0)

CB0% 1-28

CB0% 2-28

CB50% 1-28

CB50% 2-28



44

4.5. Concrete and steel strain

The concrete and steel strains were measured at every load increments. The strain

distribution for the concrete and steel at 28th

day 56th

day and 75th

day are presented in Figure

8 and Figure 9 respectively. The measured concrete strains at the top surface and steel strains

at ultimate load varied from 2167x10-6

to 3073 x10-6

and 12342x10-6

to 15320 x10-6

respectively for OPC beams and it is from 2919 x10-6

to 3816 x10-6

and 9385 x10-6

to 25986

x10-6

respectively for fly ash concrete beams when tested at 28th

days. These results also

show that fly ash concrete is able to achieve its full strain capacity under flexural loading.

Figure 10.and Figure 11.shows the comparison of concrete strain at top surface and steel

strains for all beams at 28 and 56 and 75 days.

(a) CB0% 1-28 (b) CB0% 2-28

(c) CB50% 1-28 (d) CB50% 2-28

Figure 8: Load- Strain curves for beams tested at 28 days

0

20

40

60

80

100

120

140

160

180

200

-30000 -20000 -10000 0 10000

Loa

d (

KN

Strain (x10-6)

FCS1

FCS2

FCS4

FCS3

TCS

CSS

0

20

40

60

80

100

120

140

160

180

200

-20000 -15000 -10000 -5000 0 5000

Loa

d (

kN

)

Strain (x10-6)

FCS1

TCS

FCS2

FCS4

FCS3

CSS

0

20

40

60

80

100

120

140

160

-30000 -20000 -10000 0 10000

Load

(k

N)

Strain (x10-6 )

TCS

FCS1

FCS2

FCS3

FCS4

CSS

0

20

40

60

80

100

120

140

160

-15000 -10000 -5000 0 5000

Loa

d(k

N)

Strain (x10-6)

TCS

FCS1

FCS2

FCS3

FCS4

CSS



45

(a) CB0% 1-56 (b) CB0% 2-56

(c) CB50% 1-56 (d) CB50% 2-56

(d) CB50% 1-75

Figure 9: Load- Strain curves for beams tested at 56 days and 75 days

0

20

40

60

80

100

120

140

160

180

200

-25000 -20000 -15000 -10000 -5000 0 5000

Loa

d(k

N)

Strain (x10-6)

TCS

FCS1

FCS2

FCS3

FCS4

CSS

0

20

40

60

80

100

120

140

160

180

200

-20000 -15000 -10000 -5000 0 5000

Loa

d (

kN

)

Strain (x10-6)

FCS1

FCS2

FCS3

TCS

FCS4

CSS

0

50

100

150

200

-10000 -5000 0 5000

Loa

d (

kN

)

Strain (x10-6)

TCS

FCS1

FCS2

FCS3

FCS4

CSS

0

20

40

60

80

100

120

140

160

180

-20000 -15000 -10000 -5000 0 5000

Loa

d (

kN

)

Strain (X10-6)

FCS1

FCS2

FCS3

FCS4

TCS

CSS

0

20

40

60

80

100

120

140

160

180

200

-20000 -15000 -10000 -5000 0 5000

Loa

d(k

N)

Strain(x10-6)

FCS1

FCS2

FCS3

TCS

CSS



46

a) Steel and Concrete Strain at 28 days a) Steel and Concrete Strain at 28 & 56 days

Figure 10: Comparison of Steel and Concrete Strain at 28, 56 and 75 days

4.6. Moment-curvature:

Moment-Curvature diagrams were generated for all the beams based on the concrete

strain and steel strain. The moment-curvature of the beams at 28, 56 and 75 days is shown in

figure 11. Thus the curvature of the beams with fly ash is comparable with OPC concrete

beams. Table 3 shows the overall performance of the OPC Concrete beams and Reinforced

Fly Ash Concrete beams.

Figure 11: Moment- Curvature for beams tested at 28, 56 and 75 days

0

20

40

60

80

100

120

140

160

180

200

-30000-25000-20000-15000-10000 -5000 0 5000 10000

Loa

d (

kN

)

Strain (x10-6)CB0% 1-TCS CB0% 1-CSS CB0% 2-TCS

CB0% 2-CSS CB50% 1-TCS CB50% 1-CSS

0

20

40

60

80

100

120

140

160

180

200

-25000 -20000 -15000 -10000 -5000 0 5000

Loa

d (

kN

)

Strain (x10-6)

CB0% 1-TCS-56 CB0% 1-CSS-56 CB0% 2-TCS-56 CB0% 2-CSS-56

CB50% 1-TCS-56 CB50% 1-CSS-56 CB50% 2-TCS-56 CB50% 2-CSS-56

CB50% 1-TCS-75 CB50% 1-CSS-75

0

10

20

30

40

50

60

70

0 20 40 60 80 100 120 140

Mo

men

t (k

N-m

)

Curvature (x10-6)

CB0% -28

CBO% 2-28

CB50% 1-28

CB50% 2-28

0

10

20

30

40

50

60

70

80

0 50 100 150

Mom

ent

(k

N-m

)

Curvature (x10-6)

CB0% 1-56

CB0% 2-56

CB50% 1-56

CB50% 2-56

CB50% 1-75



47

Table 3: Performance details of reinforced fly ash concrete beams and OPC concrete beams

5. CONCLUSIONS

The following observations and conclusions can be made on the basis of the

experiments conducted on the nine RC beam specimens. From the experimental

investigation, it is generally observed that the flexural behavior of RC beams with 50% fly

ash is comparable to that of OPC concrete beams.

1. The ultimate moment capacity of fly ash concrete beam is 16% less than the

ordinary concrete beam when tested at 28th

day. But its moment capacity increases

with age. It increases by 23% at 75th

day than at 28th

day.

2. The deflections under the design service loads for fly ash concrete beams were

within the allowable limit provided by IS: 456-2000.

3. Reinforced fly ash concrete beams with 50% fly ash showed displacement

ductility in the range of 4 to 6 which is adequate for structural members subjected

to large displacement such as sudden forces caused by earthquake.

4. The crack widths at service loads for fly ash concrete beams ranged between

0.18mm to 0.2mm and this is within the maximum allowable value as stipulated

by IS: 456-2000 for durability requirements.

5. Results of this investigation suggest that concrete with 50% fly ash replacement

for cement could be used for RC beams.

ACKNOWLEDGEMENT

This project is funded by Department of Atomic Energy, under Board of Research in

Nuclear Science(BRNS) research grant No. 2011/36/05-BRNS/308.The experiments were

carried out in the research laboratories of Hindustan University, Tamil Nadu, India.

Beam

designation

Max.

Load

(kN)

Deflection

at max.

Load

(mm)

Max.

Moment

(kN.m)

Strain in

concrete

at max.

load

Displace

ment

ductility

Strain

in steel

Load

at first

crack

(kN)

Deflection

at service

loads

(mm)

CB0% 1-28 177.5 20.0 65.1 0.0012 4.17 0.0103 32.92 7.1

CB0% 2-28 186.8 27.5 68.5 0.0023 5.09 0.0253 36.20 8.0

CB50% 1-28 151.1 19.3 55.4 0.0029 3.86 0.0042 29.30 7.2

CB50% 2-28 153.5 22.2 56.3 0.0036 4.44 0.0041 22.80 8.0

CB0% 1-56 182.2 28.6 66.8 0.0005 5.34 0.0111 36.80 7.8

CB0% 2-56 189.7 22.0 69.6 0.0016 6.28 0.0131 38.85 9.9

CB50% 1-56 166.6 21.6 61.1 0.0035 4.32 0.0049 29.00 8.9

CB50% 2-56 169.3 20.5 62.1 0.0021 5.13 0.0113 23.60 9.7

CB50% 1-75 197.2 27.0 72.3 0.0018 6.30 0.0031 32.60 8.8



48

REFERENCES

[1]. Jiang .L.H and Malhotra .V.M (2000), “Reduction in water demand of non-air-

entrained concrete incorporating large volumes of fly ash”, Cement and Concrete Research,

Vol.30, pp. 1785- 1789.

[2]. Rafat Siddique (2004), “Performance characteristics of high volume Class-F fly ash

concrete”, Cement and Concrete Research, 34, pp. 487-493.

[3]. Khatib .J.M (2008), “Performance of Self-Compacting Concrete Containing Fly Ash”,

Construction and Building Materials, 22, pp. 1963-1971.

[4]. Dakshina Murthy and Sudheer Reddy (2010), “Moment-Curvature Characteristics of

ordinary grade Fly Ash Concrete beams”, International Journal of Civil and structural

Engineering, Vol.1, No 3.

[5]. Sunilaa George., et. al. (2011), “Experimental study on shear behavior of activated fly

ash concrete beams, Journal of structural engineering, Vol.37, No.6.

[6]. P.A. Ganeshwaran, Suji and S. Deepashri, “Evaluation of Mechanical Properties of

Self Compacting Concrete with Manufactured Sand and Fly Ash” International Journal of

Civil Engineering & Technology (IJCIET), Volume 3, Issue 2, 2012, pp. 60 - 69, ISSN Print:

0976 – 6308, ISSN Online: 0976 – 6316, Published by IAEME.

[7]. Aravindkumar.B.Harwalkar and Dr.S.S.Awanti, “Fatigue Behavior of High Volume

Fly Ash Concrete Under Constant Amplitude and Compound Loading” International Journal

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Documents

Behaviour of reinforced concrete beams with 50 percentage fly ash