UNIVERSITY
_{OF }
SALFORD
DEPARTMENT OF CIVIL ENGINEERING
POLYPROPYLENE
FIBRE
REINFORCFJFNIT
OF
HARDEND
ffYENT
PASTE
BY
DINESH
GANDHI
A THESIS SUBMITTED FOR THE DEGREE OF
DOCrOR OF PHILOSOPHY
Ci)
LECLARATION
No part of this work has been previously submitted in support of an
application for any degree or qualification from this or any other
university or institution of learning.
4. &ý4.
D. GANDHI
(ii)
ACKNOWLEDBUffS
The work presented in this thesis has been carried _{out under } the
supervision of Dr. R. Baggott who guided both the progress of the
experimental work and the preparation of this thesis. It has been
a pleasure to work with him.
Invaluable _{assistance } has been given by Messrs. _{N. Beaver and }
P. Burton _{with } the experimental _{work. } The author is particularly
indebted to Mr. Beaver, _{who not only } helped _{with } _{the testing } _{of }
specimens _{and showed a genuine } interest in the work, but made
himself _{readily } _{available } _{at all } _{times. }
Special thanks _{are extended } _{to the Science } _{Research } _{Council } _{and }
Plasticisers Limited for _{the } _{award } _{of } _{a CASE Research } _{Studentship, }
during _{the tenure } _{of which } _{this } _{work has been undertaken. }
Finally, _{the author } is indebted _{to his } _{parents } for _{their } _{constant }
(iii)
ABSTMCT
This thesis _{considers } the tensile deformation _{characteristics } _{of }
polypropylene fibre reinforced hardened cement paste having hetero
geneous fibre geometries and a range of volume concentrations.
Polypropylene fibres _{were prepared } _{under } _{various } _{manufacturing }
conditions using a laboratory extruder, to ascertain the effect of
these _{conditions } _{on fibre } _{characteristics. }
The relevant properties of cement paste likely to influence the
polypropylene fibres and the eventual composite were investigated.
An investigation _{of } _{continuous } _{aligned } fibre _{composites } in tension, containing various volume concentrations of fibres, showed that
multiple cracking occurred despite the _{elastic } modulus of the fibre being _{considerably } lower _{than } _{that } _{of } _{the } hardened _{cement } _{paste. }
Factors _{which } _{enabled } fibre/matrix _{contact } _{to be maintained } during the _{multiple } _{cracking } _{process, } despite the _{unfavourable } Poisson's
ratio of polypropylene, were considered.
Discontinuous _{aligned } fibre _{composites } _{were } tested in tension, to
ascertain the effect of volume concentration and length of fibres on
the shear stress transfer between fibre and matrix and on multiple
cracking.
Composites _{containing } _{parallel } fibres, _{with } fibre directions _{at }
varying angles to the direction of applied tensile stress, allowed
an assessment to be made of the role of inclination. Crack
Uv)
of composites were investigated.
Finally, _{random fibre } _{reinforced } _{composites } _{were evaluated } _{to provide }
a comparison with the Continuous, Discontinuous and Inclined fibre
reinforced systems.
In addition to determining _{the mechanical } deformation _{of the various }
composites, the acoustic emission associated with internal deformation
mechanisms was studied. This was undertaken with equipment capable
(v)
CNENTS
PAGE NO.
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TABLES
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LIST
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FIGURES
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LIST
OF
PLATES
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(Xix)
alAPTER
ONE
_{ INTRODUCTION }
1.1 _{GENERAL }
1.2 _{OBJECTIVES } 1.3 _{STRUCTURE }
1.4 _{DEFINITION } _{OF A COMPOSITE }
CHAPTER
_{TWO }
_{ LITERATURE }
_{REVIEW }
so so is so is so so so
7
2.1
_{FIBRE COMPOSITES }
_{7 }
2.1.1
_{Historical }
_{Developments }
_{7 }
2.1.2
_{Fibre Composite Theories }
_{Cementitious }
_{Systems }
8
2.1.2.1
_{The mechanics of crack arrest }
_{in cementitious }
matrices
_{ Romualdi and Batson's }
theory
8
2.1.2.2
_{Single }
_{and multiple }
_{fracture }
_{ Aveston, }
Cooper and Kelly's
theory
11
2.1.3
_{Properties }
_{of Fibre Composites }
_{13 }
2.1.3.1
Tensile
_{strength }
13
2.1.3.2
_{Flexural }
_{strength }
_{17 }
2.1.3.3
_{Impact strength }
(vi)
PAGE NO.
2.1.3.4 _{Bond strength } 22
2.1.4 _{Polypropylene } _{Fibre } _{Reinforced } Cementitious 24
Matrices _{ State } _{of } the Art 24
2.1.4.1 _{Introduction } _{24 }
2.1.4.2 _{Tensile } _{strength } _{25 }
2.1.4.3 _{Flexural } _{strength }
.... .... .... 25
2.1.4.4 _{Impact } _{strength } _{26 }
2.1.4.5 _{Bond } _{strength } _{27 }
2.1.4.6 _{Conclusions } 27
WER THFEE POLYPROPYLENE
FIBRE
N@ MTRIX
so so me
283.1 _{PREAMBLE } 28
3.2 _{MATERIAL } 29
3.2.1 _{Polypropylene } _{29 }
3.2.2 _{Fibres } _{30 }
3.3 _{FABRICATION } _{STUDY } _{32 }
3.3.1 _{Laboratory } _{Extruder } _{32 }
3.4 _{TEST PROCEDURE } 34
3.4.1 _{Tensile } _{Modulus } _{of } _{Elasticity } _{34 }
3.4.2 _{Determination } _{of } _{Elastic } _{Modulus } _{at } Low Strain
Using _{a Contraves } Extensometer 35
3.5 _{ANALYSIS } _{AND DISCUSSION } OF RESULTS 36
3.5.1 _{Laboratory } Extruder 36
3.5.2 _{Elastic } Modulus _{at } Low Strain 39
3.6 _{MATERIAL } 39
3.7 _{FABRICATION } 40
3.7.1 _{Mix } _{Procedure } 40
3.7.2 _{Casting } _{and Curing } 40
(vii)
PAGE NO.
3.8 _{TEST PROCEDURE } 42
3.8.1 _{Tensile } _{Strength } 42
3.8.2 _{Strain } _{Measurement } 43
3.9 _{ANALYSIS AND DISCUSSION OF RESULTS } 44
3.10 CONCLUSIONS 44
CIVM MUR
_{ WINUOUS }
ALIME) FOE W10RCED
ffAff PPSTE
464.1 _{PREAMBLE } _{46 }
4.2 _{MATERIALS } 46
4.2.1 _{Cement } 46
4.2.2 _{Fibres } 47
4.3 _{FABRICATION } 47
4.3.1 _{Continuous } _{Aligned } _{Fibre } _{System }
.... .... .. 47
4.3.2 _{Mix Procedure } 48
4.3.3 _{Casting } 48
4.3.4 _{Curing } 48
4.3.4.1 _{Method 1 } 48
4.3.4.2 _{Method 2 } 49
4.3.5 _{Specimen Particulars } 49
4.4 _{TEST PROCEDURE } 49
4.4.1 _{Tensile } _{Strength } 49
4.4.2 _{Strain } _{Measurement } 50
4.4.3 _{Crack Spacing } Measurement 50
4.4.4 _{Scanning } _{Electron } Microscopy 50
4.5 _{ANALYSIS AND DISCUSSION OF RESULTS } 51
4.5.1 _{Cracking } Stress Levels 51
(Viii)
PAGE NO.
4.5.3 _{Cracking } Phenomena 57
4.5.4 _{Elastic } Modulus 66
4.6 CONCLUSIONS 67
CHAMER
FIVE
_{ DISCONTINWUS }
ALIGNED
FIBRE.
UNFORCED
CEW
PAST
705.1 _{PREAMBLE } 70
5.2 _{MATERIALS } 70
5.2.1 Cement 70
5.2.2 _{Fibres } 71
5.3 _{FABRICATION } 71
5.3.1 Mix Procedure 71
5.3.2 Casting _{and Curing } 71
5.4 _{TEST PROCEDURE } 72
5.4.1 _{Tensile } _{Strength } 72
5.4.2 _{Strain } Measurement 72
5.4.3 Crack Spacing Measurement 72
5.5 _{ANALYSIS AND DISCUSSION OF RESULTS } 72
5.5.1 Cracking _{Phenomena .... } _{.. } 72
5.5.2 _{Interfacial } Shear Stress 74
5.5.3 _{Elastic } Modulus 78
5.6 _{CONCLUSIONS } 78
GIAPTER
_{SIX  INCLINED }
AND
RM FIBRE
REINFORCED
CEMENT'
PASTE 80
6.1 _{PREAMBLE } 80
6.2 _{MATERIALS } 80
6.2.1 Cement _{o } _{o. } 80
UX)
PAGE NO.
6.3 _{FABRICATION } 81
6.3.1 _{Inclined } _{Fibre } _{System } 81
6.3.2 _{Random Fibre } _{System } 83
6.3.3 _{Mix Procedure } 83
6.3.4 _{Curing } 83
6.4 _{TEST PROCEDURE } 84
6.4.1 _{Tensile } _{Strength } 84
6.5 _{ANALYSIS } _{AND DISCUSSION } _{OF RESULTS } 84
6.5.1 _{Cracking } _{Phenomena  Inclined } _{Fibre } _{System } 84
6.5.2 _{Cracking } _{Phenomena  Random Fibre System .... }
.. 88
6.6 _{APPRAISAL .... }
.... .... .... .... o. .... 88
6.7 _{CONCLUSIONS }
.... _{.... } _{.... } _{.... } _{.... } _{o. } _{.. } 89
CHAPTER
SM
ACOUSTIC
_{EMISSION }
_{STUDIES }
917.1 _{PREAMBLE } _{91 }
7.2 _{PRINCIPLES OF ACOUSTIC EMISSION } _{91 }
7.2.1 _{Generation } _{of Acoustic } _{Emission } _{91 }
7.2.2 _{Detection } _{of Acoustic } _{Em ission } _{92 }
7.2.3 _{Signal } _{Processing } _{and Analysis } 93
7.3 _{HISTORICAL BACKGROUND .... }
.. o. 95
7.4 _{ACOUSTIC EMISSION IN FIBRE REINFORCED COMPOSITES } 97
7.5 _{TEST PROCEDURE .. }
o. .... .... o. .... 99
7.5.1 _{Tensile } Strength 99
7.5.2 _{Acoustic } Emission Instrumentation _{and Settingup }
(x)
PAGE NO.
7.5.3 _{Data Recording } _{and Processing } _{101 }
7.5.3.1 _{Position } _{control } _{101 }
7.5.3.2 _{Load control } _{103 }
7.6 _{ANALYSIS } _{AND DISCUSSION } _{OF RESULTS } _{105 }
7.6.1 _{Kaiser } _{Effect } _{105 }
7.6.2 _{Position } _{Control } _{108 }
7.6.3 _{Continuous } _{Aligned } _{Fibre } _{Reinforced } _{Cement Paste } _{108 }
7.6.4 _{Discontinuous } _{Aligned } _{Fibre } _{Reinforced } _{Cement Paste } ill
7.6.5 _{Inclined } _{and Random Fibre } _{Reinforced } _{Cement Paste }
.. 112
7.7 _{CONCLUSIONS } 113
CHAPTER
EIGHT
_{ CONCLUSIONS }
_{AND }
_{RECUMDATIONS }
_{FOR }
_{FURTHER }
INVESTIGATIONS
1168.1 _{CONCLUSIONS } _{116 }
8.2 _{RECOMMENDATIONS FOR FURTHER INVESTIGATIONS } _{119 }
[EFEIENCES
.. IIIIIIIIIIIIIa1611aIII108a
120APPENDIX
A STANDAP0
DEFINITIONS
OF
TEPPS
RELýATING
TO
ACOýSTIC
EMISSION
.IIIIIIIIIIIIIIIIII11
128APPENDIX
B BIBLIOGRAPHY
Ia8111811aIIIIa16118
130APPENDIX
C AVERAGE
FIRST
_{SLOPE }
VALUES
FOR
DIFFERENT
MODES
OF
ACOUSTIC
EMISSION
TESTS
CARRIED
OUT
UNDER
CONSTANT
LOAD
CONTROL
.. IIIIaI1011911aIIa6
136APPENDIX
D AVERAGE
SECOND
SLOPE
VALUES
FOR
DIFFERENT
MODES
_{OF }
ACOUSTIC
EMISSION
TESTS
CARRIED
_{OUT }
UNlR
CONSTANT
LOAD
CONTROL
.. so mmsi so osma, a@svo
137APPENDIX
E INTERSECTION
VALUES
OF
AVERAGE
FIRST
AND
SECOND
SLOPES
UNDER
DIFFERENT
MODES
OF
ACOUSTIC
EMISSION
TESTS
CARRI
ED
OUT
UNDER
_{CONSTANT }
_{LOAD }
_{CONTROL }
(xi)
NOTAT
I ON
A _{Crosssection } _{area } _{of } _{composite }
c
C _{Fibre/matrix } _{cohesion }
d _{Fibre } diameter
dc _{Critical } _{diameter }
Ec _{Elastic } _{modulus } _{of } _{the } _{composite }
Ef Elastic _{modulus } _{of } the fibre
Em Elastic _{modulus } _{of } _{the } _{matrix }
F Force
K Constant
P, _{Fibre } _{length }
P.
c Critical fibre length
N _{Number } _{of } _{fibres }
Q _{Relative } _{displacement } _{of } _{fibre } _{and matrix }
r Fibre _{radius }
S Spacing between _{the } _{centroids } _{of } _{the } _{fibres }
Vf _{Volume } fraction _{of } _{the } _{fibre }
Iým _{Volume } fraction _{of } _{the } _{matrix }
xv Transfer length for stress for long fibres xd Transfer length for stress for short fibres
e Composite strain
c
C _{ft } Longitudinal strain in the fibre bridging the _{crack }
e Fibre ultimate strain
fu
e Matrix ultimate _{strain }
mu
11 Coefficient _{of } friction
V Poisson's _{ratio } _{of } the _{composite }
c
Vf Poisson's ratio of the fibre
V Poisson's _{ratio } _{of } the _{matrix }
(xii)
c Stress in the composite
Stress in the matrix
m
an Normal _{compressive } force at fibre/matrix interface
aý Fibre stress at onset of cracking
a
fu Fibre ultimate stress
a Matrix _{ultimate } _{stress }
mu
T Fibre/matrix shear stress
Initial frictional _{stress }
(Xiii)
LIST.
CFTPBLES
1.1 Relative _{costs } _{of various } fibres _{and matrices } (after
reference
2.1 _{Properties } _{of individual } _{fibres } _{and binder } _{materials }
(after _{reference } (21))
3.1 _{Oxide } _{composition } _{of ordinary } _{Portland } _{cement }
4.1 _{Continuous } _{aligned } fibre _{reinforced } _{cement paste. specimens }
cured by method I
4.2 Continuous _{aligned } _{fibre } _{reinforced } _{cement paste } _{specimens }
cured by method 2
4.3 _{Dynamic } _{interfacial } _{shear } _{stress } _{(T }
dynamic ) calculated by using _{multiple } fibre _{pullout } data for _{a batch } of specimens
cured by method 2
4.4 _{Criteria } _{for } _{predicting } _{multiple } _{cracking }
5.1 _{Discontinuous } _{aligned } _{fibre } _{reinforced } _{cement paste } _{specimens }
5.2 _{Dynamic } _{interfacial } _{shear } _{stress } (T
dynamic ) calculated by
using multiple fibre pullout data for discontinuous aligned
fibre _{reinforced } _{cement past } _{specimens }
5.3 _{Dynamic } interfacial _{shear } _{stress } (T
dynamic ) calculated using
respective fibre length with progressive fibre _{pullout } load
for discontinuous _{aligned } fibre _{composite }
(Xiv)
6.2 _{Random fibre } _{reinforced } _{cement paste } _{specimens } _{properties }
7.1 _{Typical } _{example } _{of } _{maximum } _{number } _{of } _{events } in _{amplitude } _{mode } for _{continuous } _{aligned } fibre _{reinforced } _{cement } _{paste } _{containing }
5.5% Vf
7.2 _{Typical } _{example } _{of maximum number of events } _{in sum amplitude }
mode for continuous aligned fibre reinforced cement paste
containing 5.5% Vf
7.3 _{Typical } _{example } _{of } _{maximum } _{number } _{of } _{events } in _{counts } _{mode } for _{continuous } _{aligned } fibre _{reinforced } _{cement } _{paste }
containing 5.5% Vf
7.4 _{Typical } _{example } _{of maximum number of events } _{in sum counts } _{mode }
for _{continuous } _{aligned } fibre _{reinforced } _{cement paste } _{containing }
5.5% Vf
7.5 _{Typical } _{example } _{of } _{maximum } _{number } _{of } _{events } in _{pulse } _{width }
mode for continuous aligned fibre reinforced cement paste
containing 5.5% Vf
7.6 _{Typical } _{example } _{of maximum number of events } in sum pulse width
mode for continuous aligned fibre reinforced cement paste
(XV)
LIST
OF
FIGUIES
3.1 _{Chord modulus v extrusion } _{temperature }
3.2 _{Tangent } _{modulus } _{v extrusion } temperate
3.3 _{Chord modulus v hauloff } _{speed ratios } _{and roller } _{temperature }
3.4 _{Tangent } _{modulus } _{v hauloff } _{speed ratios } _{and roller } _{temperature }
3.5 _{Chord modulus v rate } _{of cross } _{head movement of Instron } _{test }
machine
3.6 _{Tangent } _{modulus } _{v rate } _{of cross } _{head movement of Instron }
test _{machine }
3.7 _{Elastic } _{modulus } _{of polypropylene } fibre _{at low strain }
4.1 _{Schematic } diagram _{of aligned } fibre layup jig
4.2 _{Typical } _{tensile } _{load/crosshead } _{displacement } _{curve } for
cement paste reinforced with 1.4 volume % concentration
of 340 pm diameter _{polypropylene } fibre
4.3 _{Typical } _{tensile } _{load/crosshead } _{displacement } _{curve } for
cement paste reinforced with 2.4 volume % concentration
of 340 pm diameter polypropylene fibre
4.4 _{Typical } _{tensile } _{load/crosshead. } displacement _{curve } for
cement paste reinforced with 4.2 volume % concentration
of 340 pm diameter polypropylene fibre
4.5 _{Typical } _{tensile } load/crosshead displacement _{curve } for
cement paste reinforced with 5.5 volume % concentration
of 340 pm diameter polypropylene fibre
4.6 _{Typical } _{tensile } load/crosshead displacement _{curve } for
cement paste reinforced with 8.7 volume % concentration
of 340 pm diameter polypropylene fibre
4.7 _{Crack spacing } _{v (IVf)/Vf } for _{specimens } _{cured by method 1 }
(Xvi)
4.9 _{Schematic } illustrations _{of } (a) Kelly _{and Zweben model, }
(b) Pinchin _{model, } (c) proposed _{model. } The Poisson
contractions have been greatly exaggerated for clarity
4.10 _{Relationship } between fibre _{and matrix } deformations
5.1 _{Typical } tensile load/crosshead displacement _{curve } for
discontinuous _{aligned } fibre _{composite } _{consisting } _{of 10 mm }
chopped fibre and 1.4% volume concentration
5.2 _{Typical } _{tensile } load/crosshead displacement _{curve } for
discontinuous _{aligned } fibre _{composite } _{consisting } _{of 26 mm }
chopped fibre and 1.4% volume concentration
5.3 _{Typical } tensile load/crosshead displacement _{curve } for
discontinuous _{aligned } fibre _{composite } _{consisting } _{of 60 mm }
chopped fibre and 1.4% volume concentration
5.4 _{Typical } _{tensile } load/crosshead displacement _{curve } for
discontinuous _{aligned } _{fibre } _{composite } _{consisting } _{of 10 mm. }
chopped fibre _{and 4.2% volume } _{concentration }
5.5 _{Typical } _{tensile } _{load/crosshead } _{displacement } _{curve } for
discontinuous _{aligned } _{fibre } _{composite } _{consisting } _{of 26 mm }
chopped fibre and 4.2% volume concentration
5.6 _{Typical } _{tensile } load/crosshead displacement _{curve } for
discontinuous _{aligned } fibre _{composite } _{consisting } _{of 60 mm }
chopped fibre and 4.2% volume concentration
5.7 _{Typical } tensile load/crosshead displacement curve for
discontinuous _{aligned } fibre _{composite } consisting of Go mm
chopped fibre and 8.7% volume concentration
6.1 _{Schematic } diagram _{of inclined } fibre layup jig
6.2 _{Typical } tensile load/crosshead displacement _{curve } for
cement paste reinforced with 3.5 volume % concentration
of 340 pm diameter polypropylene fibre inclined at 750
6.3 _{Typical } tensile load/crosshead. displacement _{curve } for
cement paste reinforced with 3.65 volume % concentration
(Xvii)
6.4 _{Typical } tensile load/crosshead displacement _{curve } for
cement paste reinforced with 3.61 volume % concentration
of 340 pm diameter polypropylene fibre inclined at 450
6.5 _{Typical } _{tensile } _{load/crosshead } displacement _{curve } for
cement paste reinforced with 3.65 volume % concentration
of 340 pm diameter polypropylene fibre inclined at 300
6.6 _{Typical } _{tensile } load/crosshead displacement _{curve } for
cement paste reinforced with 3.5 volume % concentration
of 340 pm diameter polypropylene fibre inclined at 15 0
6.7 _{Typical } _{tensile } _{load/crosshead } displacement _{curve } for
cement paste reinforced with 3.86 volume % concentration
of 340 pm diameter polypropylene fibre in a mesh form
960900
6.8 _{Typical } _{tensile } _{load/crosshead. } _{displacement } _{curve } for
random fibre _{composite } _{consisting } _{of 60 mm chopped } fibre
and 4.2 volume % concentration
6.9 _{Typical } _{tensile } _{load/crosshead } _{displacement } _{curve } _{for }
random fibre _{composite } consisting of 26 mm chopped fibre
and 4.2 volume % concentration
7.1 _{Representation } _{of an acoustic } _{emission } _{event } _{and different }
parameters
7.2 _{Block } _{diagram } _{of acoustic } _{emission } detection _{equipment }
7.3 _{Ringdown } _{counting } _{method }
7.4 _{Typical } _{stress } _{v maximum number of events } in amplitude _{mode }
curve, for continuous aligned fibre system containing 5.5%
volume concentration
7.5 _{Typical } _{stress } _{v maximum number of events } in sum amplitude
mode curve, for continuous aligned fibre system containing
5.5% volume concentration
7.6 _{Typical } _{stress } _{v maximum number of events } _{in counts } _{mode }
(Xviii)
7.7 _{Typical } _{stress } _{v maximum } _{number } _{of } _{events } in _{sum counts } _{mode } curve, for continuous aligned fibre system containing 5.5% Vf
7.8 _{Typical } _{stress } _{v maximum number of events } in pulse width _{mode }
curve, for continuous aligned fibre system containing 5.5% Vf
7.9 _{Typical } _{stress } _{v maximum number of events } _{in sum pulse width }
mode curve, for continuous aligned fibre system containing
5.5% Vf
7.10 _{Typical } load _{v energy } _{curve } for _{continuous } _{aligned } fibre
system containing 5.5% Vf
7.11 _{Typical } load _{v cumulative } _{counts } _{curve'for } _{continuous } _{aligned }
fibre _{system } _{containing } 5.5% Vf
7.12 _{Neat cement paste } _{specimen } _{loaded, } _{unloaded } _{and reloaded }
to ascertain _{grip } _{noise. } _{Load v energy } plotted
7.13 _{Neat cement paste } _{specimen } _{loaded, } _{unloaded } _{and reloaded }
to ascertain _{grip } _{noise. } _{Load v cumulative } counts plotted
7.14 _{Checking } _{for } _{Kaiser } _{effect } _{in continuous } _{aligned } fibre
system containing 1.4% Vf
7.15 _{Checking } _{for } _{Kaiser } _{effect } _{in continuous } _{aligned } fibre
system containing 1.4% V
7.16 _{Typical } _{tensile } _{load v energy curve for continuous } _{aligned }
fibre _{reinforced } _{cement paste } _{containing } 5.5% volume
concentration of fibre
7.17 _{Typical } _{tensile } load v cumulative _{curve } for _{continuous }
aligned fibre reinforced cement paste containing 5.5%
volume concentration of fibre
7.18
_{Relationship }
_{between average second slope for maximum }
number of events in amplitude mode and volume concentration
(Xix)
LIST
OF
PLATES
3.1 _{Continuous } _{monofilament } _{fibre } _{wound on mandrel } (top) _{and }
chopped polypropylene fibre (bottom)
3.2 _{Laboratory } _{extruder }
3.3 _{Contraves } _{extensometer } _{used to determine } _{elastic } _{modulus } _{of }
340 pm diameter fibre _{at low strain }
3.4 _{Wedge type } _{grips }
3.5 _{Specimen with } hessian _{attached } _{to the grip } _{area }
3.6 _{Tensile } test _{setup }
3.7 _{Specimen } _{clamped } _{in the extensometer }
3.8 _{Twin pen YYT recorder }
4.1 _{General } _{view of the aligned } _{fibre } _{layup } _{jig } (top) _{and }
end details (bottom)
4.2 _{Typical } _{crack } _{spacing } _{obtained } _{with } _{increasing } _{volume } _{% }
of fibre _{after } _{carrying } _{out tensile } test. A 1.4% Vfl
B=2.4% Vf; C=4.2% Vf; D=5.5% _{Vf and E } 8.7% Vf
4.3 _{Asperities } _{on the } _{surface } _{of a 340 pm diameter } _{polypropylene }
fibre
4.4 _{Shavings } _{produced } _{from 340 pm diameter } _{polypropylene } fibre
6.1 _{Shows specimen } fabrication jigs (15 0,75 0,309 _{and 660 fibre }
inclination)
6.2 _{Shows specimen } fabrication jigs _{(450 and 900900 fibre }
inclination)
6.3 _{Typical } _{crack } _{patterns } _{obtained } for _{the different } fibre
inclinations, A= 75 0, B= 660, C= 45 0, D= 360, E= 150
and F= 90090o mesh. Inclination angle measured with
respect to tensile axis
7.1 _{Dunegan/Endevco } _{3000 series } _{acoustic } _{emission } _{instrumentation }
(xx)
7.3 _{Acoustic } _{emission } _{preamplifiers }
7.4 _{Transducers } _{secured } _{on to the test } _{specimen } _{with } _{insulating }
tape and preamplifiers are located near the transducers
7.5 _{Shows entire } _{test } _{setup, } _{which } _{includes } _{Losenhausen }
testing _{machine, } Dunegan/Endevco 3000 series _{acoustic }
emission equipment with various XY recorders
7.6 _{HewlettPackard } _{XY recorder } _{plotting } _{load v acoustic } _{energy }
7.7 _{Typical } _{example } _{of events } _{in amplitude } _{mode of continuous }
aligned fibre reinforced cement paste containing 5.5% Vf
7.8 _{Typical } _{example } _{of events } _{in sum amplitude } _{mode of continuous }
aligned fibre reinforced _{cement paste } containing 5.5% Vf
(summation _{of Plate } _{7.7 data } _{from right } _{to left) }
7.9 _{Typical } _{example } _{of events } _{in counts mode of continous } _{aligned }
fibre _{reinforced } _{cement paste } _{containing } _{5.5% Vf }
7.10 _{Typical } _{example of events } _{in sum counts mode of continuous }
aligned fibre _{reinforced } _{cement paste } _{containing } 5.5% Vf
(summation _{of Plate } _{7.9 data } _{from right } _{to left) }
7.11 _{Typical } _{example } _{of } _{events } _{in } _{pulse } _{width } _{mode of } _{continuous }
aligned fibre reinforced cement paste containing 5.5% Vf
7.12 _{Typical } _{example } _{of events } _{in sum pulse width } _{mode of }
continuous aligned fibre reinforced cement paste containing
1
GMER ONE
INTRODUCTIM
1.1 _{GENERAL }
Today's _{construction } industry _{requires } the development _{of new types } _{of }
materials having combinations _{of various } valuable properties, such as
durability _{and stiffness. } _{Construction } _{materials } for _{most applications }
must of necessity have a long service life of at least 50 years. This
long life _{tends } _{to obscure } _{the fact } _{that } individual _{materials } _{or products }
have also a life cycle of successful use which can range from periods of
many centuries in the case of bricks, to periods _{of only } _{a few years } in
the case of materials _{such as paints, } _{mastics } _{and sealants, } _{with } rapidly
developing _{technologies. }
There _{are } _{many reasons } _{for } _{the } _{death } _{of } _{a material } _{or product, } _{for } instance
a cheaper or a technidally _{superior } _{alternative } becomes _{available, } _{or } _{a } long _{term } disadvantage _{is } _{recognised. } _{Exhaustion } _{of } _{raw material } _{is }
another reason.
One material which is currently _{under } threat isasbestos _{cement, } _{which }
results _{when cement paste } _{and asbestos } fibres _{are combined. } _{A consider }
able part of the world's asbestos _{production } is used in the manufacture
of fibrereinforced _{materials, } _{e. g. flat } _{sheet } _{and corrugated } _{roofing }
materials, side _{panels, } asbestos _{cement pipes, } fireproof _{and insulation }
materials _{of various } types. In 1950, the world _{asbestos } _{consumption } _{was }
about one million tons, in 1958, two million tons _{and in 1970 four } _{million }
tons, _{and it } is predicted('" _{that } _{the world's } _{deposit } _{of asbestos } _{may }
2
well be exhausted before the turn of the century. Furthermore, it has
been realised in recent years that there is a considerable health risk
for _{persons } _{working } _{with } _{asbestos } _{and the public } health _{authorities } in
several countries have already banned the use of asbestos altogether for
the manufacture of certain of the abovementioned products. Yet another
parameter in the asbestos equation is the fact that the success of
(2)
asbestos cement stems back to 1900 Since then a very wide range of
applications has been established, this has stimulated the development
of competitive materials because of the large turnover of the material
involved. _{These materials } _{range } _{from steel } _{sheeting, } _{plastic } _{sheeting }
to cementitious board'reinforced _{with } _{alternative } _{fibres } _{to asbestos. }
The attraction _{of the } latter _{alternative } _{is that } _{it } _{retains } _{the desirable }
characteristics _{of the cement paste. } Cement paste is about six times
stiffer _{and one hundred } times _{cheaper } _{than many resins } _{and is durable }
under most environmental _{conditions } _{encountered } in building _{applications. }
However, it _{has the overriding } disadvantage _{of a very } _{low failure } _{strain. }
It _{was to overcome } _{this } _{main disadvantage } _{that } _{asbestos } _{fibres } _{were }
incorporated _{in the first } _{instance. } _{It } _{follows } _{that } _{if } _{an alternative }
fibre _{such as cellulose, } _{glass, } _{polypropylene } _{etc. } _{can be incorporated }
in the cement paste to achieve similar property improvements, then an
alternative to asbestos _{cement will } _{result. }
However, _{only } _{two types } _{of nonasbestos } _{fibre } _{reinforced } _{cement products }
are at present in commercial _{production, } _{namely cellulose } _{and glass }
fibre _{reinforced } _{cement. } _{The concept } _{of using } _{polypropylene } _{fibres } _{to }
reinforce _{cement paste } is considered _{valid } but Poses some interesting
problems. From the viewpoint _{of mechanical } _{properties, } _{the fibres } _{have }
3
polypropylene is particularly of interest for cement reinforcement on
account of its relatively low cost# see Table 1.1
(3)
, good chemical
resistance, low specific gravity and moisture resistance. It has the
disadvantages _{of low elastic } _{modulus } _{and poor bonding } _{surface. } Poly
propylene was discovered in 1954 and used in large scale production since
1962; therefore _{in terms of a time scale } it _{is a fairly } _{new material. }
Its _{potential } _{as a reinforcing } fibre for _{cement paste } has not been fully
evaluated. Furthermore, the basic principles associated with mechanical
properties established for composites with high modular ratio (Fibre
Modulus/Matrix Modulusj, have not been shown to be necessarily _{applicable }
to the low modular ratio system. _{It } is against this background that
polypropylene reinforced _{cement paste } _{composite } _{was chosen for } study.
1.2 _{OBJECTIVES }
The overall objectives of this study were to identify and explain some of
the major physical _{principles } _{which } determine _{the mechanical } _{properties }
of polypropylene reinforced cement paste composite, with a view to
providing a foundation for understanding composite behaviour.
Specific _{objectives } _{were related } _{to basic } _{questions } _{concerning } _{polypropylenE }
fibre, and its _{role } _{in cement paste. } _{The most important } _{of these } _{questions }
are summarised in this _{chapter } to give _{an overall } _{perspective } _{of the }
investigation, _{e. g. }
(A) _{Does the variation } _{of fibre } _{manufacturing } _{conditions } _{improve }
TABLE 1.1 _{ } _{RELATIVE } _{COSTS OF VARIOUS FIBRES } _{AND MATRICES } (AFTER REFERENCE
Material _{Cost Per Unit } _{of Volume }
Fibres: E/M 3
Polypropylene
Fibrillated Tape
Filament
900990
9901620
Asbestos _{9451212 }
Glass
E
AlkaliResistant
24702990
44205200
Steel 31203900
Carbon Fibre 95000152000
Matrix:
Cement Paste 57
4
(B) _{Does multiple } _{cracking } _{occur } _{in continuous } _{aligned } _{polypropylene }
reinforced cement paste composite, and if so, do the same
relationships apply as those derived for high modulus fibre
ccmposites?
(C) _{What type } _{of shear } _{stress } _{transfer } _{mechanism } _{occurs } between fibre
and matrix in
Continuous _{aligned } fibre _{composite }
Discontinuous _{aligned } fibre _{composites }
(iii) _{Inclined } _{fibre } _{composite } _{and }
(iv) _{Random fibre } _{composite } _{systems? }
(D) _{Can. acoustic } _{emission } _{analysis } _{be employed to identify } internal
mechanisms during _{composite } deformation?
1.3 STRUCTURE
A literature _{survey } _{was carried } _{out on fibre } _{reinforced } _{cementitious }
composites _{generally } _{and polypropylene } _{reinforced } _{cementitious } ccmposites
in particular, to determine _{the current } _{stateoftheart } _{and to identify }
research _{objectives. }
Since the final _{composite } _{material } _{was to contain } _{polypropylene } fibres
in hardened _{cement paste, } it _{was thought } _{appropriate } to investigate the
modulus of elasticity and tensile strength of each phase separately.
In view of the disadvantageously low modulus of elasticityof poly
propylene fibre, an assessment was made of the effects of manufacturing
conditions on polypropylene fibre modulus, by means of a laboratory
extruder. This part of the investigation is detailed in chapter 3.
The logic _{of the subsequent } investigation, _{was to examine } the behaviour
5
tensile loading. Starting _{with } the simplest _{system } frcm _{a theoretical }
point of view, i. e. continuous fibre aligned parallel to the direction
of applied tensile stress. Considered in chapter 4.
The next stage was to ascertain the effect of fibre length in the aligned
arrangement. This was achieved by incorporating discontinuous aligned
fibres _{of various } lengths. _{Studies } _{of these } investigations _{are reported }
in chapter 5.
In order to approach further towards _{a 'practical' } _{composite, } the effect
of inclination of fibre was studied by incorporating fibres at angles
ranging from 15 0 to 75 0 to the tensile axis. In addition, two
dimensional _{random fibre } _{composites } _{incorporating } _{fibre } length _{of 26 }
and 60 mm were also investigated. This latter type of fibre composite
approaches _{most closely } _{to existing } _{commercial } fibre _{reinforced } materials,
see chapter 6.
Throughout the investigation, _{acoustic } _{emission } data _{was recorded } during
the deformation _{of most specimens } tested. An overall assessment of
which is made in chapter 7.
1.4 _{DEFINITION } _{OF A COMPOSITE }
Since this thesis is primarily _{concerned } _{with } fibre _{composite } _{material, }
it _{was thought } _{appropriate } to define _{such a material } _{at this } _{stage. }
A general definition of a composite material is:
Two or more materials in which the combined material formed has
Improved _{structural } _{properties } _{not exhibited } by any of the materials
(4) separately
6
for _{a modern composite } _{material } (5) is:
(A) _{The composite } _{must be manmade }
(B) _{The composite } _{must be a combination } _{of at least } _{two chemically }
distinct _{materials, } _{with } _{a distinct } interface _{separating } _{the }
components
(C) _{The separate } _{materials } _{forming } _{the composite } _{must be combined }
three dimensionally
(D) _{The composite } _{material } _{should } _{be created } _{to obtain } _{properties }
which _{would not be achieved } by any of the components _{acting } _{alone. }
Hence, the definition _{of a fibre } _{reinforced } _{composite } _{would incorporate }
the above terms together _{with } _{the additional } limitation that _{at least }
one of the chemically distinct _{materials } _{should } be of fibrous shape.
A generally _{accepted } definition _{of a fibrous } _{shape is not available, }
accordingly _{an arbitrary } _{definition } _{is suggested } _{as one having } _{an }
aspect ratio, i. e. (Fibre _{Length/Maximurd } CrossSectional Dimension) >3,
where in this instance _{a maximum crosssectional } dimension _{of fibre }
7
GWER TWO
LITEMTU[F
UIEW
2.1 _{FIBRE COMPOSITES }
2.1.1 _{Historical } _{Developments }
The concept of fibre reinforcedmaterials is far from being an idea of
the twentieth _{century. } Straw (6) has been employed to reinforce sundried
mud bricks and horse hair or sisai to reinforce gypsum plaster for many
centuries. Asbestos _{was probably } the first inorganic fibre used in
composite materials. It has been established that fine anthophyllite
asbestos fibres _{were used in Finland } _{as early } _{as 2500 B. C. to strengthen }
the sides of lightly fired _{pottery. }
Although _{the significant } _{advancement } _{of nonasbestos } fibre _{reinforced }
cement and concrete has only taken place over the last two decades, many
patents on the use of miscellaneous reinforcing elements in cement matrices
(6)
exist, one of the earliest being that _{of Berard } in the year 1674
(21 During the late 19th _{century }
, the inclusion of asbestos fibres in
cement matrices enabled a whole new range of products to be manufactured
for _{the } _{construction } industry, _{this } _{basic } _{material } _{i. e. asbestos } _{cement, }
was probably the greatest isolated development to effect the entire field of composites.
The concept of concrete strengthened by the inclusion _{of short } _{pieces } _{of }
(7)
steel was demonstrated _{as early } _{as 1910 by Porter }
Much of the pioneering _{work on the use of glass } fibre _{reinforcement } in
cementitious _{matrices } _{was carried } _{out by Biryukovich } _{et al } (8)
8
conducted investigations into Eglass fibre reinforcement _{and reported }
(9)
significant improvements in the mechanical _{properties. } Krenchel
also worked with ELglass fibres incorporated'in Portland _{cement and he }
investigated both _{theoretically } _{and practically } _{the strengths } _{of such }
composites. Thus by 1960, the practical benefits that _{could } be derived
by incorporating fibres _{in cementitious } _{matrices } _{were well } _{established, }
but _{there } _{were not available } _{detailed } _{explanation } _{of their } _{mechanisms. }
Since then _{a considerable } _{amount of experimental } _{work has taken } _{place }
into _{the investigation } _{of nonasbestos } _{fibre } _{reinforcement } _{(see later }
sections for details). In parallel _{withthis, } theoretical _{models have }
been developed. _{However, } _{progress } _{towards } _{understanding } _{the mechanics }
of fibre reinforcement did not take place _{until } the investigations _{of }
Romualdi _{and Batson } (10), (11) _{in 1963, who proposed } _{a crack } _{arrest }
mechanism to account for the improvement in the mechanical _{properties } _{of }
concrete incorporating _{steel } fibres.
The next major development _{was in 1971, when a theory } _{was published } by
Aveston, _{Cooper and Kelly } (121
, in which a new approých was adopted to
explain the behaviour of fibre _{reinforced } _{cements and mortar, } based on
the formation _{of fine } _{multiple } _{cracks. } _{Both the Romualdi } _{and }
Batson's (10, (. 11) _{and Aveston, } _{Cooper } _{and Kelly' } 412) _{work, } _{will } _{be discussed }
further _{in the next section. }
2.1.2 _{Fibre } _{Composite. Theories } _{ Cementitious } _{Systems }
2.1.2.1 _{The mechanics } _{of crack } _{arrest } _{in cementitious } _{matrices }

Romualdi _{and Batson's } _{theory }
(10).
'(11)
In 19G3 Romualdi and Batson published
_{two papers }
_{, }
_{in which }
9
strength of steel fibre reinforced mortar. A detailed treatment
of this theory is given in references 10 and 11.
Their _{analysis } _{was based on the application } _{of linear } _{elastic } fracture
mechanics to concrete. They showed that the crack extension stress
is inversely _{proportional } _{to the flaw } _{or crack } diameter _{and argued }
that the inherent _{cracks } _{and flaws, } _{in the mass of the concrete, } _{could }
be prevented from enlarging and propagating by the use of closely
spaced fibre reinforcement. Assuming that the maximiim flaw in a
fibre _{reinforced } _{concrete } _{mass would have a diameter } _{equal } to the
fibre _{spacing, } they _{also } _{concluded } that _{the smaller } _{the spacing, } the
smaller the flaw size and hence the higher the concrete tensile
strength. Thus, for a constant volume fraction of fibres, a higher
cracking stress could be expected for a decreasing fibre diameter
because _{of decreasing } fibre _{spacing, } _{since } _{the spacing } is directly
proportional to the fibre diameter. The average fibre spacing was
shown as (13)
S= 13.8d (2.1)
Vf
where S is the spacing between the centroids of the fibres,
d is the f ibre diameter _{and }
Vf is _{the volume fraction } _{of the fibres. }
It _{was further } _{shown that } _{the tensile } _{strength } _{and the first } _{crack }
flexural _{strength } _{should } be inversely _{proportional } _{to the square root }
of the fibre spacing. This theoretical _{concept } _{was for } _{steel } _{wire }
reinforced mortar in indirect tension _{and the results } _{appeared } to
substantiate the theory.
However, _{Broms and Shah } (14) _{noted } _{that } _{Romualdi } _{et al, } _{had not }
'10
and on recalculating the ultimate resisting moments, concluded that
the effects of fibres on the ultimate strength were slight. The
work of Shah and Rangan (15) _{, suggested } that fibre spacing alone had
little _{effect } _{on the tensile } _{strength } _{of the composite, } _{but that }
decreasing the fibre _{spacing } did increase _{the toughness } _{of fibre }
reinforced concrete. Apart from the main objections to the Romualdi
and Batson's(lo)'(11) theory made by Shah et. al (15) _{, other } workers
voiced their reservations regarding the experimental verifications
to theory _{and ability } _{of bending } tests _{and indirect } tensile tests
used by Romualdi et al (10)'(11) to provide true estimates of the
tensile _{strength. } Hannant (16) _{reviewed } the different tests _{used }
to determine the tensile _{strength } _{of concrete, } _{which } included direct
tension, flexure _{at third } _{point } _{and centre } _{point } loading _{and the }
indirect _{tensile } _{tests. } _{ýConclud. Lng that } _{for } _{third } _{point } loading,
the tensile _{strength } _{calculated } _{as the modulus } _{of rupture, } _{using }
the elastic beam theory _{and assuming } full _{elasticity } _{up to failure }
is not correct and gives an overestimation of the true tensile
stress at the extreme fibres of the beam. It was also shown by
Wright (17) _{, that } _{the modulus of rupture } is dependent _{on the beam }
size, the longer beams giving _{a lower } _{measured modulus } _{of rupture. }
He also showed that the modulus _{of rupture } _{calculated } from centre
point loading, gave values which _{were 25% higher } than those from
third _{point } loading, because _{the probability } _{of a weak element } being
subjected to a critical _{stress } is considerably _{greater } _{under } third
point loading than when a central load acts, _{since } _{the maximum stress }
in the latter _{case is } limited _{to a very small region } _{immediately }
underneath the load point.
These disagreements, however, _{were based on experimental } _{results } _{and }
11
behaviour _{of fibre } _{reinforced } _{cement based materials. }
2.1.2.2 _{Single } _{and multiple } fracture _{ Aveston, } _{Cooper and Kelly's } theory
In 1971 Aveston, Cooper _{and Kelly } (12) _{, } introduced _{a number of ideas }
which improved the understanding of the type of cracking found in
reinforced brittle matrices. Their theory includes the consider
ation of matrices of small failure strain, which contain fibres
having _{a much larger } failure _{strain. } only _{the pertinent } _{points }
of the theory are outlined here, a detailed account of which is given
in reference 12.
Considering _{continuous } _{aligned } fibres bonded to the matrix, the
initial _{modulus, } for _{all } _{practical } _{purposes, } is given by the rule of
mixtures
EmVm+E
fvf (2.2)
where Ec is the elastic modulus of the composite
E is the elastic _{modulus } _{of the matrix }
m
Ef is the _{elastic } _{modulus } _{of } the fibre
V is the _{volume } fraction _{of } the _{matrix } _{and } m
Vf is the _{volume } fraction _{of } the fibre.
If the fibre diameter is _{not } too _{small, } the _{more } brittle _{matrix } _{phase }
will fail at its normal failure strain and the subsequent behaviour
will depend on whether the less brittle fibre phase can withstand the
additional load thrown upon it (18) _{, } i. e. whether
afuv f>EcE mu (e fu >c _{mu }) (2.3)
C
12
where _{cr fu is the fibre } _{ultimate } _{stress }
a is the matrix _{ultimate } _{stress }
mu
c fu is the fibre ultimate strain and
C
mu is the matrix ultimate strain.
If the fibres _{cannot } _{support } this load, then they _{will } _{also } fracture
1ý1
and the composite will fail with a single crack. However, if the
fibres _{can support } _{the additional } load _{then the matrix } _{will } be broken
down into _{a series } _{of blocks } _{of lengths } _{between } _{xI and 2x,. } _{Aveston, }
CooPer and Kelly (12) _{, } haveshown _{that }
V a r
xv =m
_{vf 2T }mu
(2.5)where x' is the transfer length for stress for long fibres
r is the fibre _{radius } and
T is the fibre/matrix _{shear } _{stress. }
The additional load _{on the fibres } _{due to the cracking } _{of the matrix }
varies between a V /V _{at the crack } _{and zero, } _{at a distance } between
mu mf
x' and 2x' from the crack _{surface, } _{so that } the average _{additional }
strain in the fibres is given by
cEV ac
Ac _{= } mu mm mu (2.6)
f 2E
fvf2 EV
where a=Emvm
ff
on completion of the cracking, the blocks of matrix will all be less
than the length 2xI required _{to transfer } their breaking load a
mu vm
and so a further increase in the load on the composite results in the
fibres _{sliding } _{relative } _{to the matrix. }
Thus in a low strain to failure _{matrix, } _{the merit, } if _{any, } _{of fibre }
inclusion _{must lie } _{in the load carrying } _{ability } _{of the fibres } _{after }
matrix cracking has occurred. If fine _{multiple } cracking ensues,
13
show rising stress/strain curve characteristics. In addition the
cracks need to be invisible to the naked eye if the composite is to
be acceptable _{as a practical } _{material. }
2.1.3 _{Properties } _{of Fibre } _{Composites }
2.1.3.1
_{Tensile }
_{strength }
Cement pastes (19) are not used on their own as a material for
construction, as they crack easily due to dimensional instability
which may be caused by environmental conditions. Portland cements
expand slightly if allowed to set and harden in water. on drying
they _{undergo } _{a shrinkage } _{which } is only in part _{reversible } if the
cement paste is subsequently rewetted. The inclusion of aggregates
reduces this _{effect } _{and also makes the material } _{more economically }
viable, but the resulting _{products, } _{mortar } _{and concrete, } _{are still }
weak in tension and fail in a brittle fashion. Fibre reinforcement
is used to overcome these deficiencies. It has been shown that it
can also reduce shrinkage, for _{example Briggs } _{et al } (20) have reported
marked reductions in both the expansion and shrinkage of cements
brought _{about } _{by the incorporation } _{of 5.6% volume } _{of high modulus }
graphite fibres.
A very wide range of fibre types _{are available } for use as reinforcement
(21)
to cement based matrices _{A range of mechanical, } physical and
chemical properties are given in Table 2.1. These are compared
with typical values for Ordinary Portland cement, high alumina
cement and plaster.
Before _{considering } the tensile _{strength } _{of the composite, } it _{is worth }
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