PERPUSTAKAAN UMP

IIIihIIIIIIIihIIIIIihIIIIIIIIIIi/illhiiiiiiii 0000072556

WORKABILITY AND COMPRESSIVE STREN Gin OF KENAF FIBER

REINFORCED CONCRETE WITH DIFFERENCE WATER-CEMENT RATIO

MOHD IKRAM BIN MD YUSOFF

A thesis submitted in partial fulfillment of the

requirements for the awards of degree of

Bachelor of Civil Engineering with Environmental

Faculty of Civil Engineering & Earth Resources

Universiti Malaysia Pahang

JUNE 2012 PERPUSTAKA\AN

UNVERSTJ MALAYSiA P1 HANG

C63 No. Panggilan

Tarikh

29 MAR 2013I

ABSTRACT

The development of civil engineering products made from natural resources

are increasing worldwide, due to resources renewable issue and environmental

friendly concept. Among many different types of natural resources, kenaf plants have

been extensively exploited over the past few years. Therefore, this report presents an

overview of the developments made in kenaf fiber reinforced concrete (KFRC), in

terms of water-cement ratio and their physical properties. In this study, constant

volumes of kenaf fiber are used and difference water-cement ratio (w/c) in concrete

to be main focus. This study concentrated on the workability and compressive

strength of KFRC compared to conventional concrete. Three tests were conducted

for workability of fresh KFRC namely slump test, vebe test and compacting factor

test. Meanwhile, cubes sample were subjected to compressive strength test. All of the

specimens were cured in water for 7, 14 and 28 days. The result indicated that the

fresh KFRC exhibit a significant increase in workability with increasing of w/c ratio

in concrete mixture. However the strength of the KFRC is decreasing with increasing

w/c ratio. Besides that, the strength of KFRC is lower than normal concrete. This is

shows that addition of kenaf fiber in concrete did not increase the compression

strength of concrete.

LTA

ABSTRAK

Pembangunan produk kejuruteraan awam dari sumber asli semakin

meningkat di selurub dunia benikutan isu penggunaan semula sumber dan konsep

mesra alam sekitar. Antara pelbagai jenis sumber ash, pokok kenaf telah

dieksplojtasi dengan meluas sejak beberapa tahun kebelakangan mi. Oleh itu, laporan

mi membentangkan gambaran perkembangan yang dibuat menggunukan konkrit

bertetulang berserat kenaf (KFRC), dari segi nisbah air-simen dan juga sifat

fizikalnya. Dalam kajian mi, isipadu mahar serat kenaf digunakan dan perbezaan

nisbah air-simen (w/c) di dalam konkrit untuk menjadi tumpuan utama.. Kajian mi

tertumpu kepada kebolehketjaan dan kekuatan mampatan KFRC untuk dibandingkan

bersarna konkrit biasa. Tiga ujian telah dijalankan untuk kebolehkei:jaan KFRC basah iaitu ujian kemerosotan, ujian vebe dan ujian faktor pemadatan. Sementara itu,

sampel kiub digunakan didalam ujian kekuatan mampatan. Semua spesimen diawet

di dalam air selama 7, 14 dan 28 han. Hasilnya menunjukican bahawa KFRC segar mempamerkan peningkatan yang selari dalam keboleh]cerjaan konkrit dengan penjn*atan njsb w/c di dalam campuran konkrjt. Walau bagaimanapun, kekuatan

KFRC menurun apabila nisbah w/c konkrit meningkat. Selain itu, kekuatan KFRC

adalah Iebih rendah berbanding konicrit biasa. mi menunjuk]can bahawa tambahan

serat kenaf di dalam konktjt tidak men ingkatkan kekuatan mampatan konkrit.

.vi

INTRODUCTION

1.1 Background

1.2 Problem Statement

1.3 Objective

1.4 Scope of Work

1.5 Significant of Study

CHAPTER 1 1

1

3

4

5

5

TABLE OF CONTENTS

CHAPTER

TITLE

PAGE

TITLE 1

DECLARATION 11

DEDICATION

ACKNOWLEDGEMENT iv ABSTRACT V

ABSTRAK vi TABLE OF CONTENT vii LIST OF TABLES xi LIST OF FIGURES xlii

LIST OF ABBREVATIONS xvi

vii

CHAPTER 2 LITERATURE REVIEW 7

2.1 Background 7

2.2 Fiber Reinforce Concrete 8

2.3 Natural Fiber Reinforce Concrete 9

VI"

2.3.1 Properties of Natural Fiber Reinforce 10

Concrete

2.3.1.1 Properties in Fresh State 11

2.3.1.2 Properties in Hardened State 13

2.3.2 Properties of Kenaf Fiber Reinforce 16

Concrete

2.3.2.1 Mechanical Properties 16

2.3.2.2 Water Absorption Properties 17 2.4 Hibiscus Cannabinus L. (kenaf) 17

2.4.1 Kenaf Fiber. 19

2.4.2 Water Absorption of Kenaf Fiber. 20 2.5 Influence of Water-Cement Ratio to Concrete 21

2.5.1 Effect of Water-Cement Ratio to 21

Workability of Concrete

2.5.2 Effect of Water-Cement Ratio to 22

Concrete Strength

2.6 Factor Affecting Properties of Natural Fiber 24

Reinforced Concrete

CHAPTER 3 METHODOLOGY 25

3.1 Introduction 25 3.2 Experimental Program 26 3.3 Material Selection 27

3.3.1 Cement 27

3.3.2 Coarse Aggregate 28

3.3.3 Sand 29

3.3.4 Water 30

3.3.5 Hibiscus Cannabinus L. (kenaf) 30 3.4 Preparation of Concrete Specimens 31

3.4.1 Batching 32 3.4.2 Mixing Process 32 3.4.3 Casting 34

3.4.4 Curing Process 34

3.5 Workability Testing Method 35 3.5.1 Slump Test 35 3.5.2 Vebe Test 37 3.5.3 Compacting Factor Test 37

3.6 Compressive Strength Test 38 3.6.1 Compressive Strength Test Procedure 39

CHAPTER 4 RESULT AND DISCUSSION 40 4.1 Introduction 40 4.2 Physical Properties Test 41

4.2.1 Slump Test 41 4.2.1.1 Result and Analysis 41

4.2.2 Vebe Test 43 4.2.2.1 Result and Analysis 43

4.2.3 Compacting Factor Test 45 4.2.3.1 Result and Analysis 45

4.2.4 Discussion of Workability Test 47 4.3 Compressive Strength Test 49

4.3.1 Compressive Strength of Control Sample 50 4.3.2 Compressive Strength of KFRC with

0.50 Water-Cement Ratio 51 4.3.3 Compressive Strength of KFRC with

0.60 Water-Cement Ratio 53 4.3.4 Compressive Strength of KFRC with

0.70 Water-Cement Ratio 54 4.3.5 Comparison of Compressive Strength

between Control Samples with 56

Difference Water—Cement Ratio of

KFRC

4.3.6 Discussion of Compressive Strength Test 58

ix

CHAPTER 5 CONCLUSIONS AND RECOMM1NDAUONS 59 5.1 Conclusion

59

5.2 Recommendation 60

REFERENCES 61

APPENDICES 66

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Effects for Fiber Length and Concentration on Strength 14 Parameters

2.2 Modulus of Rupture of Sisal Fiber Reinforced Concrete 15

2.3 Ultimate Strength, Modulus of Elasticity and Poisson's 15 Ratio of Sugarcane Bagasse Fiber Reinforced Cement

Composites

2.4 Impact Strengths of Various NFRC 16

2.5 Factors Affecting Properties of Natural Fiber 24 Reinforced Concretes

3.1 Quantity of Cube Specimen Prepared 31

4.1 Slump Test Result 42

4.2 Vebe Test Result 44

4.3 Compacting Factor Test Result 45

4.4 Level of Workability 49

4.5 Workability Description Result 49

4.6 Compressive Strength of ControlO.50, 50

xi

XII

4.7 Compressive Strength of KFRC0.501 51

4.8 Compressive Strength of KFRCo.601 53

4.9 Compressive Strength of KFRCO.701 54

4.10 Comparison of Compressive Strength between 56 Contro10.50,, KFRCO.50WIC, KFRCO.60, and KFRC0.701

LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 Effect of Fiber Length on Tensile Strength 14

2.2 Effect of Fiber Content on Tensile Strength and 14

Modulus of Rupture

2.3 Effect of Casting Pressure on Modulus of Rupture 15

2.4 Kenaf Plants 18

2.5 Schematic Picture of Cell Wall of the Natural Plans 20

3.1 Flowchart of experimental work 26

3.2 Portland Cement 28

3.3 Coarse Aggregate 29

3.4 Sand 29

3.5 Kenaf Fiber 31

3.6 Mixing Process 33

3.7 Casting 34

3.8 Curing Tank 35

3.9 Slump Test Apparatus 36

xli'

3.10 Vebe Test Apparatus 37

3.11 Compacting Factor Test Apparatus 38

3.12 Compressive Strength Machine 39

4.1 Result of Slump Test with Different Water-Cement 42

Ratio

4.2 Slump Test 43

4.3 Result of Vebe Test with Different Water-Cement Ratio 44

4.4 Result of Compacting Factor Test with Different Water- 46

Cement Ratio

4.5 Compacting Factor Test 46

4.6 Result Compressive Strength of Control0.50 i 50

4.7 Cube Specimens Test for ControI0.50, in 7, 14 and 28 51

Days

4.8 Result Compressive Strength of KFRCO.50 w/c 52

4.9 Cube Specimens Test for KFRCO.50w/c in 7, 14 and 28 52

Days

4.10 Result Compressive Strength of KFRC0.60 1 53

4.11 Cube Specimens Test for KFRCO.60,v/c in 7, 14 and 28 54

Days

4.12 Result Compressive Strength of KFRCO.70,/c 55

4.13 Cube Specimens Test for KFRCO.60,,/c in 7, 14 and 28 55

Days

xiv

xv

4.14 Comparison of Compressive Strength between 57

Contro1O.50 i , KFRCO.50j, KFRCO.60, and

KFRCO.7O1

LIST OF ABBREVIATION

FRC - Fiber Reinforced Concrete

NFRC - Natural Fiber Reinforced Concrete

KFRC - Kenaf Fiber Reinforced Concrete

w/c - Water-Cement Ration

BS - British Standard

Control0.50, - Conventional Concrete with 0.50 water-cement ratio

KFRC0.50 1 - Kenaf Fiber Reinforced Concrete with 0.50 water-cement ratio

KFRCO.60WIC - Kenaf Fiber Reinforced Concrete with 0.60 water-cement ratio

KFRC0.70 1 - Kenaf Fiber Reinforced Concrete with 0.70 water-cement ratio MPa - Mega Pascal

Mm - millimeter

s - second

xvi

CHAPTER 1

INTRODUCTION

1.1 Background

Fiber is one of material that usually use in concrete to control cracking due to

shrinkage. The concrete containing fibrous material is called as fiber-reinforced

concrete (FRC). Fibers in concrete include steel, glass, synthetic and natural fiber.

FRC has known many developments and numerous studies have been carried out on

this material during the last three decades in order to overcome the tension weakness

common to all types of concretes. Although historically many fibers have been used

to reinforce various building materials, until recently little scientific effort has been

devoted to the use of natural fibers for reinforcement. The advantages of natural

FRC, including increased toughness, enhanced cracking behavior, enhanced

durability and improved fatigue and impact resistance have been well documented Previously. Among the many different types of natural fiber, Hibiscus Cannabinus L.

(kenaf) plants have been extensively exploited over the past few years.

Kenaf is a common wild plant of tropical and subtropical Africa and Asia. It

has been a source of textile fiber for such products as rope, twine, bagging and rugs.

Kenaf is a member of the mallow (Malvaceae) family, with okra and cotton as

relatives. The stem's outer bark contains the long soft bast fibers which are useful for cordage and textiles. Bast fibers make up 20% to 25% of the stem on a dry weight

2

basis. Kenaf fiber is extracted from bast fiber of kenaf plants. Kenaf fiber is unique

and potentially reliable. Properties of kenaf fiber composite are comparable to

conventional fiber composites. Kenaf fiber composite can be produced using

conventional fiber composite manufacturing. Kenaf fiber composite have a bright

future due to its renewability and eco-friendly. Besides that, kenaf fiber is one of

natural fiber that able to receive high tensional strength in the long term. Thus, this

characteristic enables to receive high tensional strength making it applicable and

ideal for fibrous material use in concrete. Inspection indicates that the tensile

properties of kenaf fibers are comparable to those of other natural fibers, such as jute,

flax and bamboo, which have been previously used to produce natural fiber reinforced concrete.

However, the fibers are basically comprised of a rigid, crystalline cellulose

microfibril reinforced amorphous lignin, and/or hemicelluloses matrix. Most plant

fibers, except for cotton, are composed of cellulose, hemicelluloses, lignin, waxes,

and several water-soluble compounds; where cellulose, hemicelluloses, and lignin

are the major constituents. An important attribute of plant fibers is their ability to

absorb moisture from the atmosphere in comparatively large quantities, because

cellulose is hygroscopic. Most polymeric fibers swell due to moisture absorption.

This absorption leads to alterations in weights and dimensions, as well as in strengths

and stiffness. Thus, besides able to receive high tensional strength, kenaf fiber has

very good performance in water absorption which tends to decrease of the workability in concrete.

An addition of kenaf fibers to concrete leads to reduced workability due to the increased surface area and water absorption of the fibers. It is important, however, that the mix be workable. A mix that is too stiff or too dry could lead to an

inadequately compacted final product which is likely to contain voids and/or

honeycombs. Beside that mix that is too wet will lead to unnecessary strength

reduction. Therefore, the right quantity of water-cement ratio (w/c) is crucial to Pro

duce the concrete with the optimum workability and strength.

3

In fact, w/c has hidden meaning which is directly linked to the spacing

between cement particles in the cement paste. The smaller the spacing, the faster the

cement hydrates fill in the gaps between cement particles, the stronger the links

created by these hydrates, and most importantly, the stronger the concrete.

Additionally, the smaller this spacing, the smaller the sizes of the pores created by

self-desiccation and the larger the stresses generating autogenous shrinkage.

Furthermore, w/c is inversely related to concrete strength and workability, where the

lower w/c, the grater the strength but the lower workability (Dale and Pierre, 2008).

In fact, too much water in fresh concrete will result in segregation of the sand and

aggregate components from the cement paste. Also, water that is not consumed by

the hydration reaction may leave the concrete as it hardens, resulting in microscopic

pores that will reduce the final strength of the concrete.

In this present study, the consistency of concrete reinforce with kenaf fiber

will be reviewed. However, most of the research only focuses on volume or

percentage of fiber in concrete mixture without concern about correct w/c for

optimum workability and strength of concrete. Hence, the optimum and ideal w/c

will be investigated to find the optimum strength and workability of kenaf FRC.

Also, effect of using difference w/c to concrete strength will be observed.

1.2 Problem Statement

Many researches has been conducted to identify the potential of Hibiscus Cannabjnus L. (kenaO in sector involving paper and particle board and related sectors

after it was introduced by National Tobacco Board (NTB) to make kenaf as a

Substitute in the production of fiber crops to recover the affect of national tobacco Income after the planting of tobacco slightly affect because of the quota system

Imposed by some word's government due to the adverse impact of tobacco on human

health. Thus, a joint effort by government has undertaken to review the kenaf plant in detailed

4

Kenaf fiber is known as natural fiber that cheap and has the high tensional

strength that works as same as jute, flax and bamboo. Besides that, it is easy to

produce and readily available in the raw. However, besides able to receive high

tensional strength, kenaf fiber has very good performance in water absorption which

makes decrease of the workability in concrete. The influence of the glucose retardant

from kenaf fibers also known as moisture absorption from concrete leads to reduced

workability due to the increased surface area and decrease of water-cement ratio.

Therefore future study must be conducted to investigate the ideal water-cement ratio

(w/c) in concrete with kenaf fiber as additive. In addition, increasing w/c without

controlling of amount or ration may result in bleeding and decrease the concrete

strength. The w/c should be considered to ensure the suitable mix proportion and

concrete strength.

1.3 Objective of Study

The objectives of this study are;

i) To determine the workability of fresh KFRC in different water-

cement ratio (w/c).

ii) To determine the compressive strength of concrete reinforced with

Hibiscus Cannabinus L. (kenaf).

5

1.4 Scope of Work

In this study, the workability of fresh concrete with kenaf fiber will be

investigated and the strength of hardened concrete will be controlled. The

workability of fresh concrete Containing constant percentage of kenaf fiber will be

focused on the effectiveness of using difference w/c to concrete mix design. There

are four (4) types of mix design prepare which are control sample (no kenaf fiber),

0.50 (KFRCO.50 0.60 (KFRCO.60 t) and 0.70 (KFRCO.70 i) of water-cement ratio (wic) with constant mix proportion of cement to fine aggregate to coarse

aggregate (1:2:3). The control concrete sample (ControlO.50 i) is made for grade 30

with constant w/c of 0.50. An additional of kenaf fiber to concrete mix design will be

fixed to 2% from total volume of concrete mix and the lengths of kenaf fiber will be

approximately of range of 25 mm to 38 mm.

The workability of the fresh concrete mixes will be tested through several

testing namely slump test, vebe test, and compacting factor test. All the testing will

be followed the standard such as BS 1881-102:1983 for slump test, BS 1881-

104:1983 for vebe test and BS 1881-103:1983 for compacting factor test. In addition,

for the compression concrete cube tests are accordance to BS 1881: Part 116:1983

and 36 cube sample will be prepared with dimension of 100 mm x 100 mm x 100

mm. The hardened concrete will be cured at water condition for 7, 14 and 28 day of curing age before test.

1.5 Significant of Study

This study will provide knowledge or records that can be useful in the devel

opment and innovation of new technology in the future field of Civil

Engineering The reason is all necessary information that students of Civil

rol

Engineering can be used in their future research. Therefore, this also encourage others

to study other alternative materials that can be used in construction.

Government may utilize different sources of reinforcement in their

infrastructures and structures mainly in their concrete buildings, highways and

bridges. Then, this move may generate livelihood and source of income since this

research needs human capital to extract the natural fibers.

CHAPTER 2

LITERATURE REVIEW

2.1 Background

Concrete is a composite material commonly used in construction work.

Concrete is a combination of four main element such as cement, coarse aggregate,

fine aggregate and water. This materials is added at a specified mixing ratio to

produce concrete in accordance with scale and strength that required by the industry.

Concrete is the one of the most important building materials and widely used in a

construction project. Concrete is used more than any other man-made material in the world. In year 2000, about 7.5 billion cubic meters of concrete are made each year,

more than one cubic meter for every person on Earth (Bjorn Lomborg, 2001). It was estimated that the present consumption of concrete in the world is the order of 11

billion metric tons every years. Concrete is compulsory materials used in construction

which must be workable, meet desire qualities of the hardened concrete for example, res

istance of freezing and thawing and deicing chemicals, low permeability, wear re

sistance and strength and economy (Metha and Monteiro, 2006). Although it is Pop

ular, it has limited properties such as low tensile strength, ductility and energy

absorption shrinkage and cracking associate with hardening and curing.

8

To overcome the problem that occurred in the concrete, various additives are

introduced including fiber reinforce concrete (FRC). FRC is concrete containing

fibrous material which increases its structural integrity. It contains short discrete

fibers that are uniformly distributed and randomly oriented. Fibers include steel, glass, synthetic and natural fiber.

2.2 Fiber Reinforce Concrete

Concrete has been well known as a low cost building material with high

strength and versatility. Though high in compressive strength, concrete is quite brittle

with a tensile strength of only 10% of its compressive strength (Midness et al., 2003).

An alternative method to improve concrete's brittleness is to mix short fibers into

concrete or known as fiber reinforced concrete, (FRC). Short natural fibers, such as

horse hair, hay and straw have been used for centuries to reinforce brittle materials.

Commercial fibers were first developed during the early 1900's using wire and metal

clips. FRC are structural materials developed through extensive research and

development during the last two decades. The earliest research into FRC date back to

the 1960's (Romualdi et al., n.d) and since then extensive research and development

has been carried out (Shah, 1986). Nowadays, fibers can be made or extracted from

various types of materials such as steel, plastic, carbon, natural and glass and used in

variety of applications such as industrial floor, tunneling, precast wall and shotcrete.

Over 30 years have passed since the initiation of the modern era of research

and development on FRC. In the early 1960s Romualdi, Batson and Mandel published

the papers (Romualdi et al., n.d) that brought FRC to the attention of academic and

industry research scientists around the world. The writer can report that at that time

there was a strong sense of discovery and an air of excitement regarding the promise

that FRC held for the future development of composite materials based on Portland

cement concrete According to terminology adopted by the American Concrete Institute (Ad) Committee 544(2010), Fiber Reinforced Concrete, there are four

categories of FRC based on fiber material type. These are SFRC, for steel FRC;

GFRC, for glass FRC; SNFRC, for synthetic FRC including carbon fibers; and NFRC, for natural FRC.

Fibers are usually used in concrete to control cracking due to both plastic

shrinkage and drying shrinkage. They also reduce the permeability of concrete and

thus reduce bleeding of water. Some types of fibers produce greater impact, abrasion

and shatter resistance in concrete. Generally fibers do not increase the flexural

strength of concrete, and so cannot replace moment resisting or structural steel

reinforcement. Indeed, some fibers actually reduce the strength of concrete. The

amount of fibers added to a concrete mix is expressed as a percentage of the total

volume of the composite (concrete and fibers), termed volume fraction (V1). VI

typically ranges from 0.1% to 3%. Aspect ratio (l/d) is calculated by dividing fiber length, (1) by its diameter,(d). Fibers with a non-circular cross section use an

equivalent diameter for the calculation of aspect ratio. If the modulus of elasticity of

the fiber is higher than the matrix (concrete or mortar binder), they help to carry the

load by increasing the tensile strength of the material. Increase in the aspect ratio of

the fiber in concrete usually subjected of changes the flexural strength and toughness

of the concrete. However, fibers which are too long tend to "ball" in the mix and create workability problems.

2.3 Natural Fiber Reinforce Concrete

The use of natural fiber reinforce concrete (NFRC) has been studied quite

heavily Over the past 40 years. Natural fibers are prospective reinforcing materials and

their use so long has been more traditional than technical. They have long served many useful purposes but the application of the material technology for the utilization

of natural fibers as the reinforcement in concrete took place in comparatively recent years. Economics and other related factors in many developing countries where

natural fibers of various origins are abundantly available, demand construction

10

engineers and builders to apply appropriate technology to utilize these natural fibers

as effectively and economically as possible to produce good quality fiber reinforced

concrete materials for housing and other needs.

Applications of NFRC for large-scale structural purposes have traditionally

been limited to special applications which are practically and economically justified.

One of the most promising fields for their application is that of composite

construction in which the NFRC forms a permanent strong and tough covering over a

weaker core. NFRC further provides architectural and ornamental features (Wells,

1982). Sisal fiber reinforced concrete tiles, corrugated roofing sheets, pipes, gas tanks,

water tanks and silos are also being used extensively in some African countries

(Swift, 1978).

2.3.1 Properties of Natural Fiber Reinforce Concrete

The properties of natural fiber reinforce concrete (NFRC) are dependent on a

number of factors including the type and the length of fibers used and the volume

fraction. Early research indicated that the minimum fiber volume fraction required to

provide significant improvement in the mechanical properties of cement composites

was approximately 3% (Rancines and Pama, n.d). NFRC constitute a new and distinct

group of building materials which exhibit almost the same behavior in performance as

that of conventional fiber reinforced concrete (FRC) produced from steel and other

inorganic or synthetic fibers. Like conventional FRC, the reinforcement in NFRC

Consists of small diameter discontinuous, discrete natural fibers of various origins

randomly dispersed throughout the concrete matrix.

The fibers act as crack-arresters which restrict the growth of flaws in the concrete matrix from enlarging under stress into visible cracks which ultimately cause

failure. By restricting the growth of cracks, the usable tensile strength of the concrete matrix is increased to a useful and predictable level. The dispersion of fibers in the

brittle matrix offers convenient and practical means of achieving improvements in

11

many of the engineering properties of the materials such as fracture, tensile and

flexural strengths, toughness, fatigue and impact resistance. Studies by Mansur and

Aziz in year 1982 revealed that jute FRC indicate that the compressive strength is not

significantly affected by the addition of fibers, while tensile and flexural strength and

toughness are all substantially increased.

Besides that, another studies conducted by A. Elsaid et al, (2011) shows that

decreasing compressive strength occured with increasing fiber content. Reduction of

strength is likely due to several factors such as additional water added to the concrete

mixture while adding the fibers in order to maintain the workability of the NFRC at

an acceptable level. Besides, reduction of compression strength is due not only

because of increasing of the w/c ratio necessary for workability, but also due to the

presence of high volume fraction of natural fibers in the concrete.

2.3.1.1 Properties in Fresh State

The incorporation of natural fibers into a mix decreases the workability and

increases the void content due to entrainment of additional air (Lewis and Mirihagalia,

1979). The decrease in workability is basically due to the surface area and especially

the size and shape of the fibers in relation to the other constituent particles in

concretes. Unworkable mixes generally lead to non-uniform fiber distribution

resulting in variation between specimens from the same mix. The increase in void

content is also due to the inadequate compaction of the unworkable mixes. The

amount of fibers that can be added to a mix is limited by the phenomenon of 'balling'

(Mansur and Aziz, 1982). If the fibers are long, which it have a high aspect ratio -

greater than 100, the fiber have a strong tendency to intermesh and form fiber balls

which cannot be easily separated. The balling of fibers results in an unworkable and segregated mix which ultimately produces a highly porous and honeycombed Concrete. The balling of fibers when large volume fractions are used can be reduced

by reducing the coarse aggregate content (Mansur and Aziz, 1982).