university of nigeria chukwuemeka_1987... · university of nigeria research publications ... tg s...
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University of Nigeria Research Publications
OKIKA, Philip Chukwuemeka
Aut
hor
PG/MENGR /82/1563
Title
Natural Fibre – Reinforced Cement Composites
Facu
lty
Engineering
Dep
artm
ent
Civil Engineering
Dat
e
May, 1987
Sign
atur
e
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NATURAL FZw-%REINE'ORaD
CEMENT CGNr'CSTThL
PHILIP C-IUKWEMEKA KANAYO O K I K k
( PG/M, ENGX, O2/1563
Submitted to t h e De?astmcnt of Civil Engineering
I n Partial Ftdfilinent of t he Requirement f o r
the A w a r d of the Degree of
%st= of Engineering
of the
University of Nigeria, Nsukka
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D E D I C A T I O N
TO
I* WIFE C X I N k E
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A C K N O h ? L E P G E M E M T - ---- -------
The author is indebted t o Prof , R, P?, Madu, for
h i s valuable advice, c lose supervision and general
guidance,
fq~preciat ion i s expressed t o Mr, S, A, Dogbe of
the Department of Materials Technology, Federal Polytechnic
Idah, Benue State ; M r , 3, Ue Asogwa of the Concrete
Testing Labora tary ) Civi l Engineering Department,
University of Nigeria, Nsukka and t h e Turners Asbestos
Company, Emene - Enuq f o r t h e i r immense contribution
towards the accomplishment of the project ,
Okika, P. C,K,
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This project has h e n ap2roved by the
Department of Civil Engineering,
Universi ty of Nigeria, Nsukka,
Prof. 12, M, lkdu Supervisor Head of Dept,
External E2mninex
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QWPTEH 1: General b a
l a 1 Abstract f3 ,+
1.2 Notations and def in i t ions
10201 Notations o n
1.2.2 Definitions e O
CHAPTER 2: Li terature Review
2-1 Introduction a O
2.2 Factors a f fec t ing properties of natural f i b r e - reinforced cement composites . , o
2.3 Nechanical Properties of natural fibre-reinforcsd cement composites based on Iaboratory expert-tal work 0 0
2.3.1 Tensile s t rength a 0 0
2.3.2 Flexural s t rength o a
2.3.3 Coqressive s t rength rn C )
2.3,4 Fracture toughness O a
2.3.5 Impact s t rength O I
2e3.6 Other properties of natural f i b r e reinforced cement composites
2.4 Natural fibre-reinforced cement products . rn
2 *4.1 Coconut fibre-reinforced corrugated sheets and slabs e D
2.4.2 Si sa l fibre reinforced corrugatdd s labs .
2-5 Other observations on tests and result 44
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v i
m R 3: Fj bre $repaz?ation and tests o~
3.1 F i l re extx'aceion nrdl tests m e
3.2 Stjvcture and physical properkies of some natural f ibres .
3.2.1 Ph: *sf cal appearance
3,2.2 M&:ro-strc~cture 0 . CHAPTER 4: C x n p o s i t e a
4.1 Pr2paraUon of composite epocimns
Ma terials
Mi xes
q p e - of Spscfnens
PI ocedure for f abric~tlon
TG s tlng
Y e s t results and discussions
E qerimental results m d 0: ~servations
S xength properties
Ddormational properties
C Lseussion of results
5.2.1 E E f e c t s of fibre characteris tic8 ~ n d mtrix qualities .
5.2.2 C,ther influencing factors . CXAPTER 6: S u n a a r y and Comrlusicm
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w a r s affecting properties d ndkural fibtsdeinforced concrete
EFfects of incorporation of rsoconut fibre on properties of concrete
U l t i m a t e strength, nloduli of elas t ic i ty and poissoncs ratio of sugarcane bagasse f i b ~ e i n f o r c e d cement composites
Effects of length and concentration of jute fib^? on strength parameters
Propertie:: of cellulose (Pfnw Radiata) cement composites
Properties of f l a x fibre reinforced cement morrtars
Flexural s t rength data of fibre concrete
Mulus of rupture of sisal f ibre reinforced concrete
Mechanical. properties of cellulose-cerme~t
kmuLts of: impact strdgth tebts on p ~ h f n cone:rete, jute, bamboo and coir f5bre concrete
Snpact strengths of various natural f ibre reirforced concretes
1Eherml ccnductivity of coir f i b r e wrmgated slabs
Sound absorpUon coeEficient (values are in % absorbed) for coir f ibre building materials
Typical thermal conductivitfa of building materials
Comparison of physlcal properties of wLr fibre reinforced roofing sheets and asbest3s roofing sheets
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16. b a d bearing capacity i n Kgf(~) at the limit of prouortionali ty for s i sa l fbre corwgated s'leets
17 Loadbearing capacity at the limit of proportiona1:tty in kgf per metre width of sheeC, kgf/m (N/m) for sisal fibre corrugated sheets
18 Tensile test results for coconut 5ibres
19 Tensile test results for plantain fibres
20 Tensile test results for rafia fibxes
21 Properties of natural f ibre cement mortars
Figures
E f f e t t of fiEre content on tensile strength 8
Effect of fibre length on tensile strength 9
variakiwr of t a i l e d d bend dt tengthr with majr fraction of cellulose fibr&s 11
Young s Variakion of . 4 modulus in bending and in tension w l t h mads f r a t t i o n 14
Effect of flax f ibre content on flexural stre?gth a t various test conditions 15
Effects of refining flax fibres on nmodulus of rupture
Effects of fibre content on flexural strength at various fceeness values 18
Effect of f i b r e content on flexural strength following various preconditioning treatments 19
Relationship lzetweah casting pressure and modulus of rupture for coconut fibre reinf n r r d c m m ~ n t na.rte 20
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ix Page
Relaticnship between ncdulus of rupture of composites and volume f r ac t i cn f o r coconut fibres
Stress-strain behaviour f o r un- reinforced and chopped sisal. fibre reinforced concrete 2 3
Stress-strain khaviour f o r concrete reinforced w i t h continuous sisal fibres 2 3
Effect 3n the stress-strain behaviour for Continuous sisal fibre concrete whrn th: matrix quality is changed 24
Effect on the stress-strain behavbur f o r continuous sisal fibre concrete f o r changinq volume f rac t ion of fibres 25
Compressive strength re la t ion with age 27
Compressive strength f a t i o for varying f i b r e content 2 8
Effect of freeness on fractwe toughness a t various values of fibre content 30
Effect of fibre content on f rac ture Dcwghness following various pre-con- d i t ioning treatment 31
Effect of f lax fibre concentration on fracture toughness a t various test conditicns 32
Coripmis on of modulus of rupture with volume f ' raction fo r corrugated coir fibre slab 37
Comparison of modulus of rupture with fibre length at 3% volume fraction 3 7
Production a t the vi l lage level ,of Sisal fibre reinforced products when chopped fibres are used 42
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Production i n small scale industries of fibre reinforced products uslng fibre nets
Production of sisal flbre concrete sheets In mechanize1 industries
Coconut fibr.3 glued t o timber plates f o r tensile test
Mean stress-strain curve f o r coconut fibre
k a n stress-strain m e f o r plantain f i k e
%!an stress-strain curve f o r rafia f i b r e
Micro-photograph's of fibre cross-sections in natural dry state
Tensile t e s t set- for fibre-mortar briquette
Flexural t e s t set~up for f ibre-mortar prism
Compressibn test Set-up f o r fibre- mortar cube
Effect of doir Eibm on the tensile strength of mortar
E f f e c t of plantain fibre on the tensile strength of mortar
Effect of rafia fibre on the tmile strength of nortar
Effect of c o i r fibre on the flexural s t rength of n~artar
Wfect of plantain f i b r e on the flexural strength of mortar
Effect of raf'ia f ibre on the f lexural strength of mortar
Page
4 3
4 3
4 7
49
52
55
57-58
61
62
62
66
67
68
71
7 2
73
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xl
Effect of flbre content on eube e m pressive strength of mortar
Effect of fibre content en cube - pressive strength of mortar
Effect of f ibre content on cube compressive strength of mortar
Failure pa t t e rn of tensile specimaas
Failure pattern of flexural specimens
Fkilwe pattiern of compression specimens
Strese-strain behavlour of fibre m m r
References
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OIAPTER 1: _II-
G E N E R A L ----
1.1 ABSTi-WCT:
Chopped natural f i b re s from coconut husk, plantain
stern and r a f i a palm leaves were examined, testej and
incorporated i n cement mortar, The resu l t ing cgmposites
were then studied t o ascer ta in the effects of f i b r e
presence on the m o r t a r properties. The relevant properties
of these natural f i b re s and t h e bchaviour of t h z i r cement
mortar composites are presented i n this paper.
In this study, some mechanical properties: t ens i l e ,
f l exura l and comp:essive strengths of mortars reinforced
with these fibres were obtaind and compared with those
of equivalent pla:.n mortar with a view to devehping
natural f i b r e r e i n f o r e d ternent mortar building products
comparable t o asbestos cement products.
The experiments show t h a t workable homogenms mixes
are obtainable wLng w e l l proportioned mixes. Ihe findings
also confirm t h a t the f i b r e mass f rac t ion affects the
mechanical proper'lies of composites. I n tensiorl, f l exure
and compression, w e n though f iber& composites d i d not
give higher o r conclusively higher strengths t h m p la in
mortar, t h e i r deformational properties improved and
reasonable strengzhs w e r e obtainable through careful choice
of f i b r e length and content.
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1.2 NOTATION3 ii,ND DEFINITIONS - li2-1 Notations .-
Et =
=
Em =
Ef =
f - - +cu =
f p =
fmin =
ft =
fb =
fC =
P - - L - -
Young's modulus i n tension
Young 1 s modulus i n hencli:~g
Void f r x matrix modulus
Fibre mxlulus
St ress
Cube compressive strength
F i r s t crack stress
Stress rotairled after first cracking
U l t i m a t s tensile strength
W u l u s of rupture
Maxtmum post-crack stress
M%imum applied load ( in N)
Diskano-. between axes of t h e support r o l l e r s
( i n nun)
Width OF beam at the l i n e of fracture (mm)
Depth o f beam at the line of f rac tu re ( i n m)
Fibre l m g t h
Fibre mass f r ac t i on
Composite void fraction
Fibre vdume feaction
Raduis of fibre (for non-cylinderkal f ibres
fi'3re cross section area - % :fibre primeter -1
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RH
OD
WET
CSF
Densi t y of .fiSre
Density of carilpasite
Ideal der~s i ty OF zonposi ta
Averase f ibrc-matrlx interfacia 1 ho-4 s tren j.th
Fracture toughness oE composite
Mass of saturated composite i n air
Dry mass of composite
Mass of saturated composite under water
Largest grain s i z e
Defini t ions - --- Controlled atmosphere of 50 + 5% relative - humidity and tamprof 22 + ~ O C for 5 days, - Oven heating at 100 - 1 0 5 ~ ~ for 24 h r s - then
cooling i n a des iccator*
Sodking in water for 48 hrs w i t h excess water
remove3 with cloth prior to tes t ing.
Canadi m S t a n d d Freeness
_Lens* pf flbm- h m ) Aspect r a t i o = 2 x radius of fibre (mm)
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C W F E R 2 -- ---------- - -----me---
LI ?ZRATURE L V I C t J --- ---------- ---- --- - -- ---------- - 2.1 INTRODUCTIOI --,
Cement pastt , r r ~ r t a r and concrete a r c capable of high
s-rength i n cornpi-ession, weak i n tension, have low s t r a i n
a t failure and are 5enerally very b r i t t l e , Fibres a r e
required i n thest- cment composites t o ovaxorne some of
these shortcornincs, Already, several types of filxes
have been u s 4 ir> t 5 production of many cementitious
bui lding product:, Ihese include asbestos-cement, ferro-
cement, s teel - f i t r, :oncrete, glass-fibre concrete and
polypropylene E i k r ? concrete (19). The most widely used,
asbestos-cement, ?mxgh of sa t i s fac tory i l exuaa l s t rength
still has low i m p c: strength. b r eove r , the asbestos
f i b r e is a b i g h e ~ l th hazard and t h e pr ice i s hich. The
decline i n world c-,momy too is now compelling developing
countries: particl: w l y the t rop ica l ones, t o inves t iga te
all possible ways c f u t i l i z i n g some of t h e n - t u r d fibres
which most of then h m e i n abundance and which are r e l a t i v e l y
cheaper than asbestof .
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Some o f t h e s e na tu ra l f i b r e s under i n v e s t i g a t i o n
f o r over a decade n3w, inc lude those fram sisal (16, 17,
331, coconut husk ( 3 , 7, 8, 12, 13, 15, 31, 34) j u t e
(3, 27, 311, bamboo (9, 311, sugarcane bagasse (?4),
aktlara ( l o ) , f l a x (321, wood (351, c e l l u l o s e (231,
p lan ta in and musambs ( 18, 201,
This growing i n t e r e s t i n na tu ra l f ibre-reinforced
cement composites i s aimed a t f ind ing n full or p a r t i a l
substitute f o r asbestos. The r e s u l t s o f researcb work
done s o f a r show improved bending and t e n s i l e s t r eng ths ,
post-cracking res i s t ance , high energy absorbing
c h a r a c t e r i s t i c s and f a t i g u e s t r eng th (7, 8, 12, 13, 14, 16,
27). bwever , t h e ~ b v i o u s problems associa ted with
t h e use of n a t u r a l f i b r e s such a s g rea t s k i l l remirement
i n f i b r e procurement, d i f f i c u l t y i n mixing and placing
of composites, unpraven d u r a b i l i t y of f i b r e s i n concrete,
etc a r e y e t t o be o-~ercome.
From the work of researchers on natural f ib re -
reinforced cement composites, a lot of f a c t o r s are now
known t o a f f e c t t h e proper t ies of such composites.
Table 1 gives a l is t of some of t h e s e f ac to r s .
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However, t he mechanical properties are depenclent
principally on t h e following parameters: cas.t-3ng pressure,
fibre volume fract ion anb aspect ratio, water/cement
r a t i o , properties of t h e fibre and quality OF the cement
paste or mortar (13, 34).
Tab1 e I . Factom- affectina n r o ~ ~ r k i es of natural f i hre
reinforced concrete (26).
Factors Cons ti tuents
Fibre type
Fibre geometry
Fibre form
Fibre surface
Fbtrix properties
Mix design
Mixing method
Placing method
Casting method
Curing method
c ~ o n u t , s i s a l , sugarcane bagasse, wood, bamboo, jute, akwar?., elephant grass, waber-reef., plantain, msamba, cel lulose, etc.
length, diameter, cross-section, rings and hooked ends, etc:,
mono-filament, strands, crimped, single- knotted, etc.
smoothness, coatings, etc.
cement type, aggregate t y ~ e and grading, addi t ive types, etc,
water content, workability aids, &foaming agents, fibre content ,etc,
type of mixes, sequence of adding consti tuents, method of adding f i b re s , duration and speed of mixing etc.
conventional vibration, vacuum dewatering a a sprayed-up concrete rnemker, extrusion, guniting, etc.
conventional, special method, etc.
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I n t h i s review, the uark has been divi.ded i n t o two
broad categories: 1,) thost$ findings based on purely
laboratory experinental work on specimens of f jbre - reinforced cement paste, mortar and concrete arid 2.)
those based on t e s t s on fibre - reinforced cerncnt
products s imilar t o those of asbestos cement c u r r e n t l y h use'
2,,3 MECHANICAL PROPEXTIES OF NfiTUXAL F I B R E - HEINFOl3CED CEMENT COP'IPOSITES PASED ON LABOlaITOlIY EXPERIMENTAL WORK
2.3.1 Tensile Strenqth
2.3.1.1 Coconut f i b r e ~ornpos_it-e-s_
The r e su l t s of d i r e c t t ens f l e tests by Da.s Gupta
et a 1 (13) on specimens of coconut fibre-reinfmxed
cement paste show t h a t tensile s t rength is increased by
the incorporation of fibres with the t ens i l e s:rength
increasing with increase i n fi!xe volume fraction up t o
a maximum a t about 4% (Vf for 3Gmm f i b r e len jths and
then decreashy f o r fur ther volume f rac t ion increase as
shown i n Figure 1 (13)-
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6 7 8
f16Rf I'OL UME FRACTION, / p c r u n t )
--
strength based on Das Qupta, Figure 1 E f f e c t of f i b r e content on tensile
Paranrasivam and Lee (131,
With fibre volune f rac t ion fixed a t i ts optihm of 474,
t e n s i l e strength of the composite was seen to increase
w i t h increasing fibre length up to a maximum lt about
to 38mm and decrees& for any further fibre lerlgth
X
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This i s i l lustrated i n FFgurc 2 (13)
%
I NBPE LENGTH, mm i
I i Agure 2. E f f e c t of fibre length on tensile ' s trength (13)
Consequently, Das Oupta e t a1 (13) concluded tha t
coconut f ibres , when Incorporated i n cement psste, a t
their optimum vcdume fract ion and length, improved the
t e n s i l e strength of composites by 50% They a l so defined
t h e optimum fibre content as 4% volume f r a c t i m f r o m
strength point of view.
Sla t e (8) also investigated the effects of coconut
f i b r e refnforcenient on t h e t e n s i l e strength of cement
mortar using varying fibre mass fract ions f o r strong
(1:2.75) and weak (I:.?) mortar. It was found t h a t
t ens f l e strength of coconut f i b r e - re inforce? mortar
as measured by br iquet te test was increased i n the
range of 5% t o 2'3% while using 25mm long fibres.
@ - - rn-Ll- m t n \
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10.
Table 2 EFFECTS OF' INC~R'L;%A:ITPN OF C K O W T FIEZES
CN PROPERTIES CrF 0TCNCRETE ( 8 )
Each value is the average of four t e s t s , except that
E, PL, and toughness are for one test (only one reasured
s tra in) -
' S t r e s s from Mc/I, and strain is ave, of top and bottom.
"Area under stress-strain curve as for E,
No strain values beyond 85% max, load.
Andonian et a:L (23) showed that the ultimate tens i le
strength and corresponding Young's modulus of cellulose
fibre - reinforced cement - silica composites hcreased
gradually with fibre mass fraction up to about 0.06 and
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Table 3 U l t i m a t e Strengths, Koduli of Elas tic3 ty and
Poissonls Ratfo of Sugarcane Bagasse Fibre
Reinforced Cement Composites based on Kacines and
Pama (145
Fibre U l t i m a t e strength Pbdulus of Po isson ' s r a t i o volume e l a s t i c i t y fract ion (%I ~ / r n ~ ~ / m m ~ x 1 0 ~
Direct tension t e s t
-- - - - - - .- -
1 3.87 32-40 0.202
2 2*95 0e54 0 235
a 2043 6,40 0.240 -I____
Compression test - -- 1 21003 13e06 0 c. 246
2 12.26 9 e 9 9 0,260
3 6e26 6,78 0,201
2,3,1,4 Ju te filxe-reinforced cement paste
Mansur and Azlz (27) found tha t tens i le strength of
fibre-reinforced cement paste could be increased by good
choice of both f ib re length and f i b r e volume f raz t ion
w i t h optimum values at 2 5 m and 3% respectively. This
is i l lu s t r a t ed i n S'able 4 1271,
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Table 4 Effects of length and concentration of jute
fibre on strength parameters based on Mansur
and Aziz (27)
Fibre Fibre Comp-- 41ncr-. length volume resive ease in
fr ac- stren- tensile t ion gth
s tren- gth
tm) (Perc- m/m2) (iJerc- ent 1 ent 1
"ncro: *Incre Young's modulus ase i n ase i n (xlo3 ~/mrn2 f lenural flexural
strength toughn- ess
(Percent) (~e rcen t ) Comp- Tensile ress- ive
- - - - . - -. -. . - - -
+Relative to plain cement paste
2.3.2 Flexural S-trenqth
M x t of the literature under review considered the
flexural strength of fibre-reinforced cement composites
( 8 , 13? l 6 ? 17, 23, 31, 32, 35).
2.3,2.1 Cellulosi~: fib=+-reinforced cement co~os i t e s
The flexural strengths measured by Andonian e t a1
(23) fo r centre-poht loading on an Instron machine using
150 x 20 x 8mm test specimens ofgPinus Radiatal
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14 s
cellulose flbre reinforced cernznt - silica mortar were
seen to increase gradually stith fibre maes fraction up
to the same mass fraction limit of 6% as for tensile
strength* Byond this 69: limit, measured values of
flexural strength remained nearly constant (Figuke 31,
Also, measured values of Young's modulus in flexure
remained approximately equal up to fibre mass fraction
< showing a slight decrease for furthcr m f
increase to 10%. See Fig. 4 (231,
0 2 L 6 8 10 12 30 ---
Eb- PREDICTED *- . .. --2-. -0 I 1
2 0 - - 8WNO i5 P
10 P 9 :!.. :: . - . .
0 2 L 6 8 Y3 12 MASS FRACTION OF FBRES. mf (%I
Figure .I$ Variation of Young's modulus in bending and in tension wit.4 mass fraction of fibres. Bars indicate the standard deviation.
Upperbound: E,=30 GPa, E,=3 7 GPa; lowerbound: E,=30 GPa, Em=23 GPa.
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Coutts (32) in his own work, used various mass
f ract ions of beaten flax fibres i n cast ing specimens
(125 x 40m x varing thickness) of cement - silica (1:1) mortar cured under two pro-test conditions ar.d tested,
Flexural strength was found to be optimized at. fibra
loading of 8 - ( m f ) with values i n excess of 20
Mpa obtainable as shown i n Figure 5 (32).
Fig. 5 Effect of f l ax fibre content on flexural
strength a t various test conditions 132).
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Table 6 P r o p e r t i e s of flax f ibre reinforced CE -- h d u l u s of r u p t u r e ( P h ) Fractrtrc tmuqhness
Fibre Freeness p e r c e n t . ~ q e CSP - by inass BH 513. 2 17.421.8
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17,
h e strength V a l u e s SQ obtetLncd are comparable t o those
f r o m similar tests on :Pinus Radiate1 fibres-ccnrpare
Tables 5 and 6 (35, 3 2 i , Howver, unlike the case of
'Pinus Radiata' fibre-reinforced ceinent-silica mortar,
the degree of beating appeared not to affect t h e nmdulus
of rupture of the composite for 2 10% loading of flax
fibres used, This is illustr~ted in Fig, 6 C32).
Fig, 6. Effects of refining flax fibres on modulus of rupture (32).
In another work, mutts (35) s t d i e d the effect of
refining (beating) fibres from *Pinus Radiatal ?craft
wood pulp, the degree of beating being measwed by a
Canadian s tandard Freeness Tester ( CSF 1. Flexur 31 tests
carried out on 125 x 40 x 5-8mm specimens of the fibre-
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of refining (bsating) stuciicd, opti~nurn condition
occurrd a t f iSR freeness value of about 553m1 CSF
and the sample had about 10% fibre nd as show in
Figure 7 (35). The work also showed tha t fle:mral
strength values e r e further f nfluenced by t h e type
pre-test kretitment of the specimens, See
(35).
also Mg.
I
FL~.-~ Effect of f i b K cbnteiitt onnf lexural s treng th
at various freeness values (3510
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I _ - F~twe content l% by truss)
Fig, 8 Effect of ffbre content on flexural strength
following various preconditioning treatments
(35)
2-3-2.2 -nut fibre-reinforced cement composites
In flexural tests with coconut: fibre-reinforced
mortar, slate ((3) determined modulus of rupture, secant
modulus of elasti.city at 45% maximum load and propor-
tional l i m i t using SO x SO x 20Om beams cast f r o m 1:4
mortar of varying fibre contente The mcdu1.u~ of rdptme
results did not show any clear effect of the presence of
fibres as seen from Table 2.
Das Gupta et a1 (131 unlike Slate ( 8 ) arrived a t
d e f i n i t e conclusions on the effect of coconut f ibre
loading on t h e modul.us of rupture of the composite. By
means of flexural tests an specimens prepared under
optirmun casting pressure pre-determined from rn earlier
experiment (Fig . 9) and incorporating optimun fibre
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20,
lengths, they established that modulus of rup tu re of
the composite increased with increasing volurre fraction
2 reaching a maxirmun of a b u t 5-4 ~ / m n and decr:easing
FIBER LENGTH 38 mm (1.5 in) I' 1 ' 1 2
VOLUME FRACTION 3 %
I) '$
pressure and
modulus of rupture for coconut fibre
rehforced cement: paste, (13).
They concluded that by using coconut fibres at
optfmum content: and length, flexural strength of the
composite can be improved by 75%.
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FIBER LENGTH 38 mm (1.5 in)
I CASTING PRESSUAE 3.1 ~ / m m
(450 ps i )
1 I I 1
' 1 2 3 L . 5 6 n
VOLUME FRACTlON ('I.; - - - ig, lo-- T?d.ationSKp &tween modulus of -Epture of
composites and volume fraction for coconut
fibres (13).
Ramaswamy et a1 (31) tensile spl i t t ing strength
and modulus of rupture tests on coconut fibre-r.xinforced
concrete using 10C x 100 x 600mm prisms with op",mum
sand content gave lower 284ay strength values than
those of plain concrete specimens, Generally, the
flexural to compressive strength ratio was improved for
various test ages as shown i n Table 7 (31).
- .
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Table 7 Flexural strength data of fibre conQ.&e (31)
Ratio of modulw of rupture to cube compressive strength a t
Type of concrete 3 days 1week 4 weeks 1 2 weeks U
1 Plain coneetb (no fibre) Om14 0.19 O O X ) 0.22
2 Concrete with i$ jute fibre 0017 0.24 0.26 0,28
3 Concrete wlth 1% coir fibres 0017 0-22 0.22 0.26
4 Concrete with i% bamboo fibres 0014 0.20 0021 0,23
Cubes 100 mm, modulus of rupture 100 x 100 x 600 m prisms.
2.3.2.3 Si-sal fibre-refnforced cement composit~
Swift and Smith (16) studied the effect of sisal fibre
reinforcement on hbth cement mortar and concrete. Generally,
the results showed improvements in flexural strengt'ns. A
sumnary of these results is shown in Table 8 (16).
Table 8 Modulus of rupture of s isal fibre reinforced concrete based on Swift and S m i t h (16)
Mix praportion Water Fibre Fibre Curing Specimen Modulus ( cement ; sand ; cerr ent length volume period size of coarse aggre- ratio f rac- rupture
gate) tion hd (%I (days) (4 d m 2
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Persson and Skarendahl (17) also investigated sisal
fibre-reinforced cement mortar first, usltng choppcd
fibres (15-50 mm) and later with continuous f i k r e s (up to
'J1F00 mm). They found that continuous fibres produced a
more pronounced increase in flexural strength. Typical
strers-strain curves for the tvo cases are shown in Rgs sod 12 (17). -- -
- Linit'of proportionality for unreinforced concrete
Limit o f proportionalily for s ~ s a l fibre concrete
Sisal fibre concrete
Unteinforced concrete
1 I
a -
with continuous sisal fibres based on Ekrsson and
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With continuous fibres of fixed volume f rac t ion , the
stress-strain behavfarr for changing qualify of matrix
was established (Fig, 13) and with increasing volume
f r a c t i o n but constant matrix qualtty the cormsponding
stress-strain pat te rn was established too (Fig. 14). --
I Increasing n;atr.ix cjirality
Figure 13. Effect on t h e s t ress -s t ra in behaviour -for continuous s i sa l f i b r e concrete when t h e mat~ix quality is changed, based on Persson and Skarendahl ( 17)
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/ -- I increasirtg voltlme-I fractiori of fibres
Figure 14. Effect on the s t ress -s t ra in behaviour fo r continuous s i s a l f ibre concrete f o r changing volume f rac t ion of f i b r e s (17).
2,3,2,4 Ju t e fibre-reinforced cement composites
Flexural tests on j u t e fibre-reinforced cement
composites carr ied out by Mansur and Aziz (27) show
c l ea r ly t h a t t he f lexura l s t rength of the composite
increases with f i b r e volume f rac t ion up t o a maximum a t
an optfmum value of about 3% ( V f ) f o r fixed f i b r e
lengths and s imilar ly with f i b r e length a t an optimum
value of about 2 5 m f o r f ixed f i b r e volume fraction.
These are well i l l u s t r a t e d i n Table 4,
On the other hand, l'\amaswamy et a1 (31) carr ied
out similar t e s t s with ju te f i b r e reinforced cement
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composites with inconclusive r e su l t s except for imyrov$-
f l exu ra l t o compressive s t rength r a t i o shown i n Table 7,
2,3,3 Compressive Str-eat
While S l a t e ( 8 ) observed t h a t compressive s t rength
of cement mortar was not much affected by the presence of
coconut f i b re s i n the composites (Table 21, Das Oupta et a1
(13) concluded a f t e r t h e i r tests on coconut f i b r e - refnfbrced cement paste t h a t the ultimate compressive
s t rength of t h e reinforced composite was l e s s than t h a t
of t h e p l a in cement paste, They inferred t h a t a s t he
f i b r e volume f r ac t ion increased, t he compressive s t rength
decreased up t o a maximum reduction of about 10% a t 6%
volume fract ion,
Ramaswamy et a 1 (31) carr ied out compressive
s t rength t e s t s on 1% volume f rac t ion of co i r , j u t e and
bamboo fibre-reinforced concrete, Their r e su l t s showed
t h a t only c o i r f i b r e s performed as w e l l a s p la in
concrete whi le bamboo and jute fibre concretes showed
lower compressive strengths than equivalent pla in
concrete. See Figure 15 ( 31 1,
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(Cont~nuously curca In w a t e r ) M ~ X 1:3.58 : 2.87
W/C 0.65
Figure 15. Compressive s (31)
However, it was observed cnaL me ~ J L ~ I I I U I I r l u ~ e
volume fractions for compressive strength are 0,5%
for j u t e and bamboo fibres and 1% for coir filres
as shown in Figure 16 (31).
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[a ) JUTE 7 ( c ) BAMBOO
F i g u r e 16. Compressive s t r e rq th ratio for wrying fibre content (33.1
2.3.4 Fracture Touqhnes:
2.3.4,l Cellulosic fibre-reinfaxed cement composites
Fracture toughness t e s t s by Amlonian et a1 (23) was
w i t h notched beams (150 x 20 x 8mm) of cellulose fibre
reinforced mortar with crack depth to spedmcn width
ra t io of 0.50 subjected to three ~ o i n t bendir a,
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Specific work of f rac ture ( R ) was d e t d n e d from Guxey's
irreversible work area methd (21. A summary of the
experimental results i s shown on Table 9 (23).
Table 9 Mechanfcal propertics of cellulose-cement ( ! 3 )
Specific
Mass fraction Modulus (GPa)
of Cellulose
Strength ( M 'a) work 05 fracture R
01 standard deviation, sample s i z e = 6
+*I standard deviation, sample s h e = 15
+I standard deviation, sample size = 5
Compared to values for asbestos-cement a t equivalent fibre
mass fractions (22), R is a h u t 5% - 100% less, For example,
2 for mf = 1W, R + 1.6 .t OO6KJ/m for asbestos cement md L
2 0.97 + 0.17KJ/m for cellulose cement composite, -
Cautts (35) also tested refined wood fibre-reinf3rced
mortar specimens (125 x 40 x 54mm), fracture energy ~ e i n g
calculated from the area under the load - deflection m e
and fracture toughness from fracture enerw cross section area of s >ecimen
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It was found t h a t fngcmzzal, fox constant mf of fi >re,
toughness tended to decrease as the fihre was furtler
beaten and that there was a rapid improvem?nt i n
toughness as the fibre content was increased as sh >wn
in Figures 17 and 18 (3511
Figure 17. Effect of freeness an fracture toughnes s a t various values of fibre content (35:
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- F ~ b e cnnren! (3'. bvmassl ----- I
igure 18. Effect of fibre content on fracture toughness following varioua pre- conditioning treatments (35)
Sn another investiga43on, Coutts (32) studiec t h e
effect of refined flax fibre incorporation in mor'ar on
the fracture toughness of the composite, A f t e r tt s t s
on 125 x 40mm strips of varying thickness it w s jowd
that fracture toughness increased as the fibre cot tent
increased, further toughness increase being obser?ed
frm w e t samples as can be seen in Figure 19 (32).
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I
I L E * - I 3 I ? FIBRE 1 OH7Lhi 1 % t ly a o r r l l~ Figure 19. Effect of f-%b?Pco=emonir
fracture toughness at various test conditions based on Coutts (32)
In general, these R values were approximately half the
corresponding values for the 'Pinus Radiatal coqosite.
2.3-4.2 Sisal fibr_e-lc_elnforced cement comositcs_
Persaon and Skarendahl (17) carried out frar tui-e
toughness t e s t s on sisal fibre-reinforced mortars and
concluded that toughness is higher fo r s i sa l f ibre
concrete than for plain concrete. However, the i i report
d id not include any experimental results to back up
the above conclusionm
2.3.4-3 Coconut and Jute Fibre-reinforced cemer $ ~p_mpos ites
The effect of coconut fibre on the fracture
toughness of the composite was investigated by S l a t e (8).
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By measuring modulus of bughness f r o m the area w d e t
the stress-strain curve at 05% of msximurn load, if was
observed that moduLus of toughness of the reinforced
composite increased 95% and 60% for 0.00% and O . l t % fibres
respectively. See Table 2,
Rmswamy et a1 (311 reported that fracture
toughness was distincbly higher for jute, coir am
bamboo fibre-reinforced mortars. This is a purel!
qualitative observation as there were no experimertal
results to substantiate it, However, the work of Mansur
and Aziz (27) mnfirms this observation for jute fibre-
reinforced copsites only (Tabic 4).
2.3.5 *act Strenqth
Within the literature i n review, only th?:ce apers
considered t h e effect of f i b r e incorporation orl tle
impact strength of fibre - reidorced cement compcsites ( 3 , 27, 31).
Rarnamamy et al (31) compared the impact encrgy at
first crack of plain concreka specimens to those c f
jute, bamboo and coir fibre - reinforced concretes.
They observed that the values of impact energy me~sured
by the drop ball method far the three types of fl bres
were about 10 * 20% higher than those for unreinfcrced
specimens as seen in Table 10 (311,
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Table 10, Results of impact s t rength tests on plz i n concrete, jute, bamboo and c o i r fibr concrete 12 1 !
Average impact energy N o c (kg c m ) a t f irst crack blows ror rauure on v i rg in specimens --
Type of concrete slabs beams slabs beams
Plain 0% fibres 240 5 5 2 3 Jhte 1% fibres 290 68 5 5 Bamboo 1% fibres 275 61 3 3 C o i r 1% fibres 290 60 4 4 Coir % X fibres 2 70 61 4 3
Note: Slab specimens 300 x 300 x 25 rnm were simp11 supported at all four edges and beam.
Specimens 330 x 100 x 25 m were simply supported only a t tvm opposite shor t edges.
&ah value imlicated in t h e Cable represents t he mean of s i x specimens.
Weight of drop ball: Skg for slabs and 1 kg :'or beams,
Height of a l l 480 - 580 m
This improvement i n impact resistance of nab ral
fibre-reinforced concrete was also observed by Si:*askar
and Kumar ( 3) as a result of inpact tests on coco~ iut
and jute fibre-reinforced concrete the results of which
are shown in Table 11 (31,
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Table 11. I'mpact sk-sngths of r a ~ i o u s n a t u r ~ l fi:m reinforced concretes based 0.1 Siraskar and Kumar ( 3 )
-.. - -- Impact strength, N c m / m 2 .--. - ---
Concrete type Curing periods, d ~ y s -. -
lo Plain concrete 135 20 3 608 2. 3% coconut fibre reinforced 473 1,148 ! ,093 3, 3"/,ute fibre reinforced 270 473 !,025
Considerable irnprovenent i n impact strength as
observed by Phnsur and Aziz (27) from resu l t s of :ests
w i t h j u t e fibre-.reinforced ceinent paste with f i b r ?s a t
optimum length and volume fraction, The maximum
increase was i n the region of 400% of the value f x
plain concrete.
2.3.6 Other Pro~ert ies of Natural .- Fi-b~q-Reinforc Cement Composites
Density of fibre-reinforced composites were
found to decrease with increase In f ibre mass fra:tion
while water absorption increased w i t h increase i n mass
fraction (35) remaining d e p e d e n t on density of
composite ( 32).
Cment content and sand gradation were t he
control l ing fac tors for watertightness (17).
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Abrasion resis tar1~3, k k ~ m a l rtnd acouetie p~ . p-:L c: I =.c:
of f ibre-rei.nEorced cement composites were good,
par t icu lar ly with sisal, jute and sugarcane bagas:@
fibres (14, 16, 271,
Creep &is seen to be somewhat higher while
shrinkage was substantially lower than fo r plain
concrete (31),
2e4,1 Coconut Fibre-Keinfarced Cbrruqated --.I-u- Sheets - and Slabs -
The investigations made by Parumasivam et E L
(34) was aimed a t f inding a simple simple and
systematic method of casting corrugated coconut fibre-
reinforced slabs su14able for use i n l o w cost horsing
f o r developing countries. Tests were carr ied out on
corrugated slabs made from cement-sand (1: 0,s) mc lrtar
retnforced with coconut fibres of varying volume
f rac t ion and aspect ratio, The test r e su l t s sholr that
2 a f lexura l strength of up t o 22N/m i s obtalnab .e
using optimum values of V f = 3% and fibre length =
25 rnm, See Figs . 20 and 21 (34).
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- 25 rnm --- 38 mrn
Vo lume f r a c t i o n ( "I.) igo 20 Comparison oi rncx2ulm or rupcure u r n
volume fraction for corrugated coir fibre Slab (34)
fibre length at 3% volume fraction ( 3 1.1
The above f lermral strength value Is higher 'tha I the
dnimum bending strength of 15.7 PN/m2 iqx?cifi d
for asbestos - cement corrugated sheets ( 5 1.
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sound absorption coefficients of 3 - 8% for low
frequency and i:hermal conductivity of 0.64 W/$K
(Tables 1 2 and 13) which compare w i t h those for
asbestos cement boards (Table 14).
Table 12. Thermal conductivity of coir f i b r e ccrrugated slabs (34)
Specimen Thermal - conductivi' y
Volume ~ i b r e length Thickness (W/mOK) fract ion (mm) (mm)
Table 13, Sound absorption coefficient (values are in % absorbed) for coir fibre corrug ited slabs based on Paramasivam, Nathan ald Das Gupta (34)
S o u . absorption coefficie nt (961 for
Frequency
121 250 500 0 200C 4000 Specimen - Volume Thickness f r ace
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Table 14. Typical thermal conductivities of building materials (34)
-- -- Thermal
mterials ~~X'ql~tiiiit I W/m0K ) -* --- +- I..._ -I.- ..-YI-
AeSes tos cernvlt imarrs O o E 5 Asbestos insuJ-ating boards 0,10&.0,13 5 Fibreboard ( ceiiiei te 0,C 5 Plaster board 0,1; 3 Hard bard C,2C 1 T i l e s , clay G,8C 6 Wood C n l L 4
Singh (15), on h i s part, compared the rhysical
properties of coconut fibre-reinforced corn gated
roofing sheets and asbestos roofing sheets. The
comparison is sho-rn in Table 15 ( I S ) *
Table 15. Comparison of physical propertie: of coir f ibre reinforced roofing sht :ets and aebestos roofing sheets base l on Singh (15
Coc0l Characteristics and reil Properties roof:
Pitch of corrugation, mm 146 146 ~ e p t h of corrugation, m 40 48 Length of sheets, m 1.5-2.0 1.5-3.0 Width -of sheets, m 1 .O 1.05
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Weight, kg/m 2
Breaking load of 60 an, ~ / m Breaking load
12 eS-12mO 1 ) a 5 for a span
50 I
at a span of 100 an, ~ / m 19 i0 Thermal conductivity, k, cal/cm/m2 0.09 0, !4 Water permeability through finished surface i n 24 hours almost nil - Acid resistance as p l.Se : 59lLl970, N/m ?? 9.30 x toms3 9 ,26x1f3
2,4,2 Sisal Fibre-Reinforced Corruqated Slabs
In Uselotte Johanssm's (33) work on sisal Xbre-
reinforced corrugated sAeets, a draft standard f lr
t e s t methods for corrugated sheets of natural f i x e o tries was presented, Sheets ?f varying
concrete sultab!eyor develop~cement /sand - rat LO:-
A) 1:2, B) 1:3, C) 1:4, Dl 1:7 and a f ibre
volume fraction were produced and la ter tested i l
A) and B) passed the strength tests with large nwgins
uhlle those of mixes C) and D) were near the
~ l s o all the sheets passed the watertightness t e s t ,
Table 16. Laadbearing capadty i n kgf(~) at thc l i m i t of proportionality for s isal f ibre corrugated sheets based on Liselotte Johansson (33)
I
Group A B C D 205(2010) 215(2108) 140 (1373) 11 Q(1569 210 (ZOSS) 270 (2647) 115 ( ' - 290(2843) 200(1961) 165('
Mean value 232(2275) 228(2235) 140 ( '
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Table 17. Loadbearing c a m Q at the l imit of proportionality in kgf per me=@ width of sheet, k&m ( N / d for s i s 11 fibre! corrugated sheets &is& on Mlelot te Johansson (33)
G ~ U P A n c D
Wan 288(2824) 280( 2745 1 171 (1i ;76) 196(1922)
For sisal fibre-reinforced products. Persson and
Skanderahl (17) considered design criteria such as
loads, stresses, choice of safety factor: , crack wi*,
watertightness, impact resistance, fibre resistance
and so on. They considered also, the actual
prdductfon process f o r sisal-fibre c o n a t e sheets on
the basis of
(I) Material flow using
a) Chopped fibres
Mixing-Casting-Wing Storing water
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b) Continuous fibres
sisal -"-\ \ sand Mixing-Ca~ting-Arrir 3-Storing
water --&" (If) Level of Production
a) Production at the village level - Figure 22 (17)
b) Production by small-scale industry - Fig, 23 (17)
C ) Production i n mechanized i n d u s t r i e s - Fig. 24 (17)
CEMENT
SAND
. . . . . . .. .. .
WATER
@ SISAL F I B R E S
ifler rags1 STORING
Fig, 22, Production a t the vil lage level when chapped f ibres are used (17
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I CEMENT
i SISAL F I B R E NETS
MIXING CAST IN G
1 CO~JTINUOUS FEEDING i /'
. I , K
o: laminate I
A
CON? INbOUS MOULD- --- - . . .-
. . -
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2.5 OTHER OBSERVATIONS ON TESTS AND RES JLTS 3-.
In the literature under review, the m !thocis of
f ibre extraction and treatment are m a t i s !actory.
There is need t o establish economical and lare & ; f i a t
f ibre preparation processes.
The Absence of either international s :andads or
local standanis for the testing of f ibre r!inforced
cement composites has led t o a p r o l i f e r a t i m of casting
and testing parameters such as specimen 6i :el age of
t e s t , casting and curing conditions, type )f cement
(ordinary portland or rapid
aggregate - to name just a
used briquette tests for d i r e c z censue r e iung co
ASTM t es t method, C 190-72 - Tensile Strmgth of
Hydraulic Cement Mortars (4) while Andonia 1 et a1 (23)
used rectangular strips 150 x 20 x 8m t e b d i n an
Inskon machine apparently to no w i s u n g ttandards on
f i b r e concrete.
Flexural tests m e dn different beam sizes a d
loading arrangements and these t w o factors are known to
affect modulus of rupture values (25 1. In fact, ofly
Andonian et a1 (23 1, Cbutt~ ( 32) and Cout ;S (35
maintained some consistency in flexural st-ngth and
fracture toughness tests.
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Even in the papers on fibre reirWwccrJ cement
prducts , only one stdndard (El) for fibrc reinforced
concrete sheets was mentioned. Other star3ards used
relate to corrugated sheets of asbestos cfnent (1, 5 , 11,
28, 29). Zn fact, most of the t e s t s =re cone to asbestos
cement t e s t procedures. Much progress w i l l be made in
the quality control of f ibre reinforced crrnent products
if t h e draft standard proposed by Uselott e Johansson
(33) is adopted.
Presently, It is d i f f i c u l t to correlcte tho
results of the same tests by the various investigators.
None of the researchers tried t o invrstigate the
possibility of finding general optimum vzlues of volume
fraction and fib= length for strerigth fox each type
of vegetable fibre,
Finally, only two works (13, 23) t r i ~ 9 an analytical
verification of their results. The rest vzre silent on
that aspect.
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FIBRE PREPARATION AND TESTS
3.1 FIBRE EXTRACTION AND TESTS
coconut husk. First, the husks were s p l i 5 open and
after the in ter ior nut had been removed, :hey (husks)
were broken into three or more pieces . E I& husk piece
wan IR+PY snf+~nnrl hv b a t i n n and than *n,lcd in w a f ~ r
the natural c
to rid t h e m c
The fibres were swjeccea ro cesrs KO aecxnune cne
tensile strength and specific gfavity.
Fibres for the tensile t e s t had both ends glued
to timber plates as shown in Figure 25.
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