studies on elevated temperature of fiber reinforced phosphogypsum concrete

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 7, Issue 2, March-April 2016, pp. 234–246, Article ID: IJCIET_07_02_021

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ISSN Print: 0976-6308 and ISSN Online: 0976-6316

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STUDIES ON ELEVATED TEMPERATURE

OF FIBER REINFORCED

PHOSPHOGYPSUM CONCRETE

Umadevi R Research Scholar, Department of Civil Engineering,

BMS College of Engineering, INDIA

Kavitha S

Research Scholar, Department of Civil Engineering,

Dr MGR Educational Research Institute & University, INDIA

Shashi kiran C R

Research Scholar, Department of Civil Engineering,

BMS College of Engineering, INDIA

Sugandha N

Asst Professor, Department of Civil Engineering,

ACS College of Engineering, INDIA

ABSTRACT

Deterioration of concrete structures due to steel corrosion is a matter of

considerable concern since the repairing of these structures proved to be a

costly process. Repair and rehabilitation of the civil structures needs an

enduring repair material. The ideal durable material should have low

shrinkage, good thermal expansion, and substantial modulus of elasticity, high

tensile strength, improved fatigue and impact resistance. Fire represents one

of the most severe exposure conditions and hence provisions for appropriate

fire resistance for structural members are major safety requirements for any

building design.

The present paper deals with the experimental investigation on elevated

temperature of concrete and compressive, tensile strength of partially cement

replaced phosphogypsum concrete and 0.75% of fiber reinforced and 0%,

10%, 20% & 30% replacement with water-binder ration of 0.50 are studied. It

is shown that a part of Ordinary Portland cement can be replaced with

phosphogypsum to develop a good and hardened concrete economically.

Key words: Phosphogypsum (PG), Flexural Strength, Fiber Reinforced

concrete (FRC)

Studies on Elevated Temperature of Fiber Reinforced Phosphogypsum Concrete


Cite this Article: Umadevi R, Kavitha S, Shashi kiran C R and Sugandha N,

Studies on Elevated Temperature of Fiber Reinforced Phosphogypsum

Concrete, International Journal of Civil Engineering and Technology, 7(2),

2016, pp. 226–233.

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1. INTRODUCTION

Fiber Reinforced concrete (FRC) may be defined as a composite materials made with

Portland cement, aggregate and incorporating discrete discontinuous fibres. Plain

concrete possesses a very low tensile strength, limited ductility and Plain concrete

possesses a very low tensile strength, limited ductility and little resistance to cracking.

Internal micro cracks are inherently present in the concrete and its poor tensile

strength is due to the propagation of such micro cracks, eventually leading to brittle

fracture of the concrete. It has been recognized that the addition of small, closely

spaced and uniformly dispersed fibers to the concrete would act as crack arrester and

would substantially improve its Compressive and flexural strength properties. This

type of concrete is known as “fiber reinforced concrete”.

Civil structures made of steel reinforced concrete normally suffer from corrosion

normally suffer corrosion of the steel by the salt, which results in the failure of those

structures. Constant maintenance and repairing is needed to enhance the life cycle of

those civil structures. There are many ways to minimize the failure of the concrete

structures made of steel reinforce concrete. The custom approach is to adhesively

bond fibers polymer composites onto the structure. This also helps to increase the

toughness and tensile strength and improve the racking and deformation

characteristics of the resultant composite. But this method adds another layer, which

is prone to degradation. These fibers polymer composites have been shown to suffer

from degradation when exposed to marine environment due to surface blistering. As

a results, the adhesive bond strength is reduced, which results in the de-lamination of

the composite. Another approach is to replace the bars in the steel with fibers to

produce a fiber reinforced concrete and this is termed as FRC. Basically this method

of reinforcing the concrete substantially alters the properties of the non-reinforced

cement-based matrix which is brittle in nature. Possessed little tensile strength

compared to the inherent compressive strength.

The principal reason for incorporating fiber into a cement matrix is to increase the

toughness and tensile strength, and improve the cracking deformation characteristics

of the resultant composite. In order for fibers reinforced concrete (FRC) to be a

viable construction material, it must be able to compete economically with existing

reinforcing systems.

2. MATERIALS AND METHODOLOGY

Experimental investigation was planned to provide sufficient information about the

resistance of fiber reinforced Phosphogypsum based cement concrete.

MATERIALS USED

The different materials used in this investigation are:

53 grade ordinary Portland cement

Coarse Aggregate

Fine Aggregate

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Umadevi R, Kavitha S, Shashi kiran C R and Sugandha N


Phospogypsum

Steel Fiber

Cement

The cement used in all mixtures was commercially available 53 grade Ordinary

Portland Cement (OPC).

Coarse aggregates

The coarse aggregate having 20mm normal size well-graded aggregate according to

IS-383 is used in this study. The coarse aggregate procured from quarry was sieved

through 20mm, 16mm, 12.5mm, 10mm and 4.75mm sieves. The material retained on

12.5mm, 10mm and 4.75mm sieves was filled in bags and stacked separately and used

in the production of Self Compacting Concrete.

Fine aggregates

The fine aggregate that falls in zone-I was obtained from a nearby river course. The

sand obtained was sieved through all the sieves (i.e.4.75mm, 2.36mm, 1.18mm, 600,

300, 150). Sand retained on each sieve was filled in different bags and stacked

separately for use. To obtain zone-I sand correctly, sand retained on each sieve is

mixed in appropriate proportion.

Phosphogypsum

Generally, a ton of phosphoric acid production generates about 4.5 to 5 tonnes of

phospho-gypsum. Major phosphogypsum producing fertilizer units are Coromandal

Fertilizer Ltd, Visakhapatnam in Andhra Pradesh; Gujarat State Fertilizers and

Chemicals Ltd, Vadodara in Gujarat; FACT Udyogmandal, Ernakulam in Kerala,

RCF, Chembur, Mumbai in Maharashtra; Paradeep Phosphates Ltd in Orissa, SPIC

Tuticorin and Coromandal Fertilizers Ltd, Thiruvalur in Tamil Nadu.

Phosphogypsum is a by-product in the wet process for manufacture of phosphoric

acid (ammonium phosphate fertilizer) by the action of sulphuric acid on the rock

phosphate. It is produced by various processes such as dehydrate, hemihydrate or

anhydrite processes. In India the majority of phosphogypsum is produced by the

dehydrate process due to its simplicity in operation and lower maintenance as

compared to other processes. The other sources of phosphogypsum are by-products of

hydrofluoric acid and boric acid industries.

Figure 1 Phosphogypsum Material

http://en.wikipedia.org/wiki/Quartzite



Current worldwide production of phosphoric acid yields over 100 million tons of

phosphogypsum per year. While most of the rest of the world looked at

phosphogypsum as a valuable raw material and developed process to utilize it in

chemical manufacture and building products, India blessed with abundant low-cost

natural gypsum piled the phosphogypsum up rather than bear the additional expense

of utilizing it as a raw material. It should be noted that during most of this time period

the primary reason phosphogypsum was not used for construction products in India

was because it contained small quantities of silica, fluorine and phosphate (P205) as

impurities and fuel was required to dry it before it could be processed for some

applications as a substitute for natural gypsum, which is a material of higher purity.

However, these impurities impair the strength development of calcined products. It

has only been in recent years that the question of radioactivity has been raised and this

question now influences every decision relative to potential use in building products

in this country.

Some attempts have been made to utilize phosphogypsum as base and fill

materials (in the form of cement-stabilized phosphogypsum mix) in the construction

of highways, runways, etc. In other attempts, phosphogypsum was recycled for

manufacture of fibrous gypsum boards, blocks, gypsum plaster, composite mortars

using Portland cement, masonry cement, and super-sulphate cement.

Steel Fibers

Fibers reinforced concrete may be defined as composite materials made with Portland

cement, aggregate and incorporating discrete discontinuous fibers.

When the fiber reinforcement is in the form of short discrete fibers, they act

effectively as rigid inclusions in the concrete matrix. Physically, they have thus the

same order of magnitude as aggregate inclusions, steel fibers reinforcement cannot be

therefore regarded as a direct replacement of longitudinal reinforcement in reinforced

and prestressed structural members. However, because of the inherent material

properties of fibers concrete, the presence of fibers in the body of the concrete or the

provision of a tensile skin of fibers concrete can be expected to improve the resistance

of conventionally reinforced structural members to cracking, deflection and other

serviceability conditions.

Figure 2 Shape of Steel fibers



The fibers reinforcmement may be used in the form of three – dimensionally

randomly distributed fibers throughout the structual member when the added

advantages of the fibers to shear resistance and crack control can be further utilised.

One the other hand, the fiber reinforced concrete may also be used as a tensile skin to

cover the steel reinforcment when a more efficeint two – dimensional orientation of

the fibers could be obtained.

Technical Data and specification of steel fibre:

Type of steel fiber reinforced : Crimped steel fiber

Size : 0.50mm dia & 30mm length

Strength of strain resistance : More than 1100 N/mm2

Repeated flexure : 3 times

Density : 7.83mm3

Average in cross section : 1.716 mm2

Figure 3 Crimped Steel Fiber Reinforced material

Water

The potable water, which is free from concentration of acids and organic substances

was used for mixing the concrete.

METHODOLOGY

An experimental study is conducted on fiber reinforced cement concrete by

replacing 10%, 20%, 30% of cement by Phosphogypsum and total volume of concrete

by 0.75% of fiber reinforcement for different elevated temperatures. Absolute volume

method is carried out with various percentages of Phosphogypsum replacing cement

has been made use in the present investigation. The test consisted of carrying out

compressive strength test on cubes, split tensile strength test on cylinders and to study

the strength variation of concrete with addition of fiber reinforcement and

phosphogypsum partially.

http://en.wikipedia.org/wiki/Nonlinearity










Design Mix Proportion Used in Phosphogypsum & Steel Fiber Reinforced

Concrete for M20 Grade

Water Cement Fine aggregate Coarse aggregate

191.6 litre 383 kg 600 kg 1144 kg

0.50 : 1 : 1.567 : 2.987

Experimental investigations were carried out to study the physical properties of all

the materials used and the results are tabulated

Table1 Physical properties of cement

Sl. No Property Experimental Values Suggested value as per IS:

12269-1987 code

1. Specific gravity 3.15 3.14

2. Normal Consistency 33.75% -

3. Initial Setting Time 75min Min 30 minutes

4. Final Setting Time 245min Max 10 Hours

Table 2 Physical properties of aggregate

Sl. No Property coarse aggregate fine aggregate

1. Specific gravity 2.67 2.61

2. Bulk density 1239 Kg/m3 1574 Kg/m

3

3. Water Absorption 0.5%

4. Fineness modulus 7.36 3.14

5 Grading Zone-I

Table 3 Abstract of workability values of fresh of Steel fiber reinforced & phosphogypsum

concrete mixes

Sl. No % of Phosphogypsum

% of

Steel

fiber

Slump

value

Compaction

factor value

Vee - Bee

degree

(seconds)

1 0% 0.75 24.6 0.85 4.8

2 10% 0.75 26.0 0.84 7.3

3 20% 0.75 27.4 0.82 9.0

4 30% 0.75 29.1 0.74 12.5

3. ANALYSIS AND DISCUSSIONS

Experiments were carried out to study the Strength of Steel fiber reinforced

phosphogypsum concrete. Cubes and cylinders were casted by replacing cement with

phosphogypsum for 10%, 20%, 30% and cured for 28days. The cubes and cylinders

were exposed to elevated temperature for different durations. The results obtained

were tabulated



Table 4 Compressive Strength of Steel fiber & Phosphogypsum Mixes at Elevated

Temperatures

Sl.N

o.

Designation

of Mix

Temperatur

e in 0 C

Duration of

Exposure in

hrs

Compressive

strength (Mpa)

% Variation over

reference mix

% Varitation of

corresponding mix at

room temperature

Increase Decrease Increase Decrease

1 0% of PG RoomTemp

31.52

100 4 32.11

1.87

6 32.98

4.63

8 30.02

4.76

200 4 29.47

6.50

6 27.88

11.55

8 25.55

18.94

300 4 24.53

22.18

6 22.64

28.17

8 19.82

37.12

2 10% of PG Room Temp

34.21 8.53

100 4 34.60 7.74

1.13

6 35.09 6.40

2.57

8 33.87 12.82

1.00

200 4 33.62 14.07

1.74

6 32.47 16.47

5.08

8 31.69 24.04

7.36

300 4 30.54 24.48

10.74

6 29.28 29.34

14.41

8 28.34 42.97

17.17


21.78

30.90

100 4 22.47

30.01 3.18

6 23.31

29.32 7.02

8 21.74

27.59

0.20

200 4 21.67

26.47

0.51

6 20.91

25.00

3.99

8 20.57

19.49

5.56

300 4 20.01

18.43

8.13

6 19.67

13.13

9.70

8 18.58

6.26

14.70


16.61

47.30

100 4 16.87

47.45 1.59

6 17.14

48.04 3.18

8 16.41

45.33

1.19

200 4 15.95

45.88

3.97

6 15.41

44.72

7.22

8 15.10

40.89

9.07

300 4 14.67

40.18

11.66

6 14.11

37.66

15.03

8 13.61

31.35

18.08



Table 5 Split tensile Strengths of Steel Fiber & Phosphogypsum Mixes at Elevated

Temperatures

Sl.No Designation

of Mix

Temperat

ure in 0 C

Duration

of

Exposure

in hrs

Split tensile

Streng th

(Mpa)

% Variation over

reference mix

% Varitation of

corresponding mix

at room

temperature

Increase Decrease Increase Decrease

1. 0% of PG Room

Temp 3.83

100 4 4.13 7.83

6 4.54 18.54

8 3.07 19.84

200 4 2.94 23.24

6 2.85 25.59

8 2.56 33.16

300 4 2.32 39.43

6 2.10 45.17

8 1.63 57.44

2 10% of PG Room

Temp 5.21 36.07

100 4 5.69 37.78 9.20

6 5.95 31.15 14.25

8 3.82 24.48 26.67

200 4 3.75 27.54 28.05

6 3.71 30.31 28.74

8 3.64 42.26 30.11

300 4 3.35 44.59 35.63

6 3.27 55.74 37.24

8 3.08 88.89 40.92

3 20% of PG Room

Temp 3.08 19.61

100 4 3.31 19.94 7.39

6 3.56 21.63 15.56

8 2.76 10.25 10.51

200 4 2.70 8.32 12.45

6 2.66 6.68 13.62

8 2.37 7.34 22.96

300 4 2.22 4.47 28.02

6 2.01 4.16 34.63

8 1.57 3.72 49.03

4 30% of PG Room

Temp 2.37 38.07

100 4 2.55 38.21 7.58

6 2.66 41.42 12.12

8 2.34 23.91 1.52

200 4 2.29 22.17 3.54

6 2.18 23.50 8.08

8 2.04 20.45 14.14

300 4 1.94 16.35 18.18

6 1.83 12.72 22.73

8 1.46 10.33 38.38



Figure 4 Variation of compressive strength for change in % replacement of cement by

phosphogypsum at room temp

Figure 5 Variation of split tensile strength for change in % replacement of cement by

phosphogypsum at room temp

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

0% 10% 20% 30%

PG+FR (Room Temp.)

% REPLACEMENT OF CEMENT BY PHOSPHOGYPSUM

Co

mp

ress

ive

STR

ENG

TH (

Mp

a)

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0% 10% 20% 30%

PG+FR (Room Temp.)


SPLI

T TE

NSI

LE S

TREN

GTH

(M

pa)




phosphogypsum at 1000C



0

5

10

15

20

25

30

35

40

0% 10% 20% 30%

4 Hrs

6 Hrs

8 Hrs

CO

MP

RES

SIV

E ST

REN

GTH

(Mp

a)

PG+FR(1000C)


0

5

10

15

20

25

30

35

40

0% 10% 20% 30%

4 Hrs

6 Hrs

8 Hrs

CO

MP

RES

SIV

E ST

REN

GTH

(Mp

a)

PG+FR(2000C)






Figure 9 Variation of Split tensile strength for change in % replacement of cement by


0

5

10

15

20

25

30

35

0% 10% 20% 30%

4 Hrs

6 Hrs

8 Hrs

CO

MP

RES

SIV

E ST

REN

GTH

(Mp

a)

PG+FR(3000C)


0

1

2

3

4

5

6

7

0% 10% 20% 30%

4 Hrs

6 Hrs

8 Hrs

SPLI

T T

ENSI

LE S

TREN

GTH

(Mp

a)

PG+FR(1000C)








From Fig 4 to Fig 10 it is observed that both compressive strength and split tensile

strength increased at 10 % replacement of cement by phosphogypsum even at

different elevated temperatures and duration of exposure.

It is also observed that there is decrease in compressive strength and split tensile

strength for replacing cement by phospogypsum greater than 10%, however up to

20% replacement of cement by phosphogypsum has same strength as that of

conventional concrete.

0

0.5

1

1.5

2

2.5

3

3.5

4

0% 10% 20% 30%

4 Hrs

6 Hrs

8 Hrs

SPLI

T T

ENSI

LE S

TREN

GTH

(Mp

a)

PG+FR(2000C)


0

0.5

1

1.5

2

2.5

3

3.5

4

0% 10% 20% 30%

4 Hrs

6 Hrs

8 Hrs

SPLI

T T

ENSI

LE S

TREN

GTH

(Mp

a)

PG+FR(3000C)




4. CONCLUSIONS

Based on experimental investigation conducted and the analysis of test results, the

following has been concluded.

From the study it is observed that up to 10% phosphogypsum & steel fiber

reinforcement is the optimum dosage which can be mixed as partial replacement to

cement for giving maximum possible increase of compressive strength and split

tensile strength.

It was also observed that for 10% phosphogypsum both the compressive strength and

split tensile strength was is high at 1000 C for exposure duration of 4 and 6 hrs.

The normal transporting, placing and finishing methods used for plain concrete can

also used for SFRPGC.

REFERENCES

[1] M. Singh, Physio – chemical studies on phosphogypsum for use in building

materials, Ph. D.thesis, University of Roorkee, Roorkee, India, 1980.

[2] N. Ghafoori, Phosphogypsum based concrete: Engineering characteristics and

road applications,Ph. D. thesis, University of Miami, Corel Gables, Florida,

(December 1986).

[3] W. F. Chang, and M. I. Mantell., Engineering properties and construction

applications of phosphogypsum, University of Miami press, Florida, 1990.

[4] R. K. H. Ho, R. W. Williams, L. L. Cogdill and W. F. Chang., Columbia county

experimental road,Volume II, Proceedings of the second International symposium

on phosphogypsum, University of Miami, Florida Institute of Phosphate

Research, Bartow, Florida, (January 1988) 397 – 416.

[5] M. M. Smadi, R. H. Haddad and A. M. Akour., Potential use of phosphogypsum

in concrete,Cement and Concrete Research, Volume 29, Number 7, (1999) 1419

– 1425.

[6] IS: 12679 - 1989. “By-product gypsum for the use in plaster, blocks and boards

specification.”Bureau of Indian Standards, New Delhi.

http://en.wikipedia.org/wiki/Compressive_strength




