DEVELOPMENT OF POLYPROPYLENE FIBER AS CONCRETE REINFORCING FIBER

REINFORCING FIBER
M.Sc. (Wood Science), The University of British Columbia, 2009
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF
MASTER OF APPLIED SCIENCE
(CIVIL ENGINEERING)
(Vancouver)
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ABSTRACT
The objective of this research is to produce polypropylene fibers with improved interface
bonding with a concrete matrix. The Laboratory Mixing Extruder paired with the Randcastle
fiberline drawing device was used for producing fiber from polypropylene (PP) chips. A target
diameter of 0.5 mm fiber was obtained from a 2-stage process in the production line. The effort
to improve the fiber surface by applying aluminum oxide sol-gel coating was unsatisfactory
due to the failure of the coating materials to adhere to the fiber. Incorporating silica fume (SF)
powder in the fiber extrusion process enhanced fiber properties. Silica fume co-extruded PP
(SFPP) fiber has different characteristics in appearance, flexibility and surface roughness. Most
importantly, the co-extrusions produced significance improvements in surface characteristics.
Silica fume particles caused significant changes in the surface roughness of the fiber and
contributed to the improved bonding performance in a cement-based matrix. The inclusion of
the extruded fibers in a concrete matrix also improved the flexural toughness. Additional
testing was conducted to examine the performance of extruded fiber in preventing plastic
shrinkage cracking. Fiber reinforced mortar containing RPP and SFPP fibers were evaluated.
Based on total crack area reduction efficiency, and crack width reduction efficiency SFPP
fibers performed better than RPP fibers. These results indicate that the objective of developing
a concrete reinforcing fiber using laboratory equipment was successfully achieved. The
inclusion of silica fume particles in the extrusion process significantly changed the properties
of the fiber and therefore contributed to the performance of these extruded fibers in the concrete
matrix.
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PREFACE
This thesis is original, unpublished, independent work by the author, Ricky Novry Ratu,
under the supervision of Professor Nemkumar Banthia.
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2.3 Types of Fiber in Concrete Application ...................................................................... 8
2.4 Significance of Polypropylene Fibers ........................................................................12
2.4.1 Polypropylene Material .........................................................................................12
2.4.2 Polypropylene Fiber ..............................................................................................14
2.5 Application of Polypropylene Fiber in Concrete........................................................17
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2.7 Summary ..................................................................................................................27
Chapter Three29
3.3.3 Limitation and Controls .........................................................................................38
3.4.1 Aluminum Oxide Coatings ....................................................................................41
3.4.1.1 Sol gel preparation .........................................................................................41
3.4.1.2 Coating of fiber ..............................................................................................42
3.5.2 Comparison of Extruded Fibers .............................................................................56
3.6 Summary ..................................................................................................................63
Chapter Four64
EXTRUDED PP FIBERS64
4.2.3 Experimental Setup for Flexural Toughness and Testing Procedure .......................68
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4.3.1 Compressive Strength ............................................................................................71
4.3.2 Flexural Testing ....................................................................................................72
4.3.2.1 Fracture mode ................................................................................................72
4.3.2.2 Flexural response ...........................................................................................74
4.3.2.3 Flexural toughness .........................................................................................75
OVERLAY79
5.2.1.1 Substrate base.................................................................................................80
5.2.3 Testing Procedure and Crack Assessment ..............................................................87
5.3 Experimental Results and Discussions ......................................................................92
5.3.1 Crack Development ...............................................................................................92
6.1 General Conclusions .................................................................................................99
REFERENCES.................................................................................................................. 103
LIST OF TABLES
Table 2.1: Types of cracking in concrete structures (Source: Concrete, p 507, Mindess et.al.,
1996) ............................................................................................................................. 7
Table 3.2: Extrusion parameter ............................................................................................37
Table 4.1: Mixture Proportion .............................................................................................65
Table 4.3: Average flexural toughness parameter according to ASTM C1609 ......................77
Table 5.1: Mixture proportion ..............................................................................................81
Table 5.3: Crack analysis .....................................................................................................96
Figure 2.2: Plastic shrinkage crack on beam specimens ........................................................ 6
Figure 2.3: Different types of steel fibers .............................................................................. 8
Figure 2.4: Various types of carbon fibers (a, b, c) and glass fibers (d, e) .............................. 9
Figure 2.5: Various types of synthetic fibers (a-g) and some natural fibers (h-j) ...................11
Figure 2.6: Various types of polypropylene fiber product ....................................................15
Figure 3.1: The layout of Laboratory Mixing Extruder (LME) .............................................31
Figure 3.2: Randcastle fiberlines drawers (Slow drawer, left; Fast drawer, right; and the oven,
middle) .........................................................................................................................32
Figure 3.3: Actual image of fiber drawing showing the setting of the devices used ..............33
Figure 3.4: Sample of polypropylene chips used in this experiment .....................................34
Figure 3.5: Extruded fiber was pulled to the godet roll .........................................................36
Figure 3.6: Typical amorphous PP fiber produced using LME .............................................37
Figure 3.7: Polypropylene fiber with a final size of 0.5 mm diameter, 50 mm length ...........38
Figure 3.8: Layout of the extrusion system ..........................................................................39
Figure 3.9: Comparison of extruded PP fiber: Amorphous state (lower) and Semi Crystalline
(upper) .........................................................................................................................40
Figure 3.10: Aluminum isopropoxide powder (left) and PVA powder (right) .......................41
Figure 3.11: Refrigerated incubator shaker (left), and Aluminus oxide sol gel (right) ...........42
Figure 3.12: Comparison of uncoated and coated PP fiber ...................................................43
Figure 3.13: Surface image of uncoated (left) and coated (right) PP fiber at 20x magnification
.....................................................................................................................................44
Figure 3.14: Silica fume application on the surface of PP fiber ............................................46
Figure 3.15: Proportion of PP chips and silica fume powder prior mixing (left); Uncoated and
SF coated PP chips (right) ............................................................................................46
Figure 3.16: Surface of PP chips at 20x magnification: Uncoated (right) and SF coated (right)
.....................................................................................................................................47
Figure 3.17: Fiber extrusion process showing SF co-extruded PP fiber ................................48
Figure 3.18: Silica fume co-extruded PP fiber (Amorphous, left and semi-crystalline, right) 49
Figure 3.19: Microscope image of SF co-extruded PP fiber at 5x magnification ..................49
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Figure 3.20: Confocal microscope image of the surface SFPP fiber at 20x magnification
(Normal exposure, left and high contrast, right) ............................................................50
Figure 3.21: Dogbone-shaped molds for fiber pull out testing ..............................................51
Figure 3.22: Dogbone-shaped specimens prior to testing .....................................................51
Figure 3.23: The lay out of pull out testing apparatus ...........................................................52
Figure 3.24: Images of pull out specimens placed in its grip prior (upper) and during (lower)
testing ..........................................................................................................................53
Figure 3.25: Pull out load - end slip relationship performance of uncoated fiber ..................54
Figure 3.26: Pull out load - end slip relationship performance of Al2O3 coated fiber ............55
Figure 3.27: Typical failure pattern of coated fiber during pull out test ................................55
Figure 3.28: Pull out load - end slip relationship of SFPP fiber ............................................56
Figure 3.29: Extruded amorphous PP fiber, 1.5 mm diameter (center); Final product (0.5 mm
diameter) semi-crystalline PP fiber: SFPP (bottom left) and RPP (top right), ................57
Figure 3.30: Microscope image of extruded amorphous PP fibers ........................................58
Figure 3.31: Microscope image of semi-crystalline extruded PP fibers ................................59
Figure 3.32: Images of EDS spectrum of minerals on the surface of extruded PP fibers: RPP
(top) and SFPP (middle) ...............................................................................................60
Figure 3.33: Tensile strength of extruded PP fiber ...............................................................61
Figure 3.34: Lay out setting of strength evaluation of the fiber ............................................61
Figure 3.35: Pull out load - end slip relationship of extruded PP fibers ................................62
Figure 4.1: Extruded PP fibers 0.5 mm diameter, 50 mm length. RPP (left), SFPP (right) ....65
Figure 4.2: Sample calculation of mixture ingredients of FRC .............................................66
Figure 4.3: Pan mixer used (left) and cast specimens (right) ................................................67
Figure 4.4: Image of beam and cylinder specimens in curing rack........................................68
Figure 4.5: Testing set up showing Instron machine, data acquisition panel and computer ...68
Figure 4.6: Beam specimens with deflection fixture (yoke) ..................................................69
Figure 4.7: Test set up for determining cylinder compression strength .................................71
Figure 4.8: Images of specimens of each mix after testing. RPP (left) and SFPP (right) .......72
Figure 4.9: Typical fracture mode in concrete beam.............................................................73
Figure 4.10: Images of fiber bridging at the exposed cracks .................................................73
Figure 4.11: Load - Deflection curve Mix 1 with regular PP fiber ........................................74
Figure 4.12: Load - Deflection curve Mix 2 with SF co-extruded PP fiber ...........................75
Figure 4.13: Averaged flexural response of FRC containing extruded fibers ........................76
Figure 5.1: Dimension of substrate base (source: Gupta, Thesis 2008) .................................80
Figure 5.2: Sample calculation of mixture ingredients of concrete base for shrinkage tests ..82
Figure 5.3: Molds for substrate base ....................................................................................83
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Figure 5.4: Image of base specimens in curing room............................................................83
Figure 5.5: Extruded PP fibers, 0.5 mm diameter, 50 mm length. RPP (lef) and SFPP (right)
.....................................................................................................................................84
Figure 5.6: Sample calculation of overlay mortar .................................................................85
Figure 5.7: Molds for plastic shrinkage testing showing substrate base placement ...............86
Figure 5.8: Repair overlay specimens after finishing and before starting the test ..................87
Figure 5.9: Environmental chamber showing the placement of specimens ...........................88
Figure 5.10: Specimens after demolding ..............................................................................89
Figure 5.11: Image of cracked specimens after testing and tools used for measuring the crack
.....................................................................................................................................90
Figure 5.12: Crack progression on plain overlay specimen #1 ..............................................92
Figure 5.13: Crack progression on SFPP fiber reinforced overlay specimen #1 ....................93
Figure 5.14: Complete set of overlay specimens after testing ...............................................94
Figure 5.15: Crack mapping ................................................................................................95
Figure 5.16: Crack control efficiency of RPP, SFPP and PVAPP .........................................97
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ACKNOWLEDGEMENTS
1 I would like to thank all the people who helped and encouraged me during my graduate
studies at the Department of Civil Engineering, Faculty of Applied Science the University
of British Columbia. 2
3 I especially want to thank my supervisor, Professor Nemkumar Banthia, for his support,
valuable advice and encouragement throughout the course of my research. I also thank
him for giving me the opportunity to participate in various seminars, meetings and
conferences including the regular ACI - BC Chapter meetings, EFCECM 2014, and
CONMAT 2015. 4
5 I would like to thank Professor Frank Ko, the leader at the Advanced Fibrous Materials
lab, for allowing me to work using his lab facilities and for his generous comments about
my research outcome. Also, many thanks to his group members, especially Dr. Heejae
Yang and Dr. Yuqin Wan, for their help during fiber production in the AMPEL lab. 6
7 Technicians in the Machine Shop at the Department of Civil Engineering have my thanks
for supporting my academic research. Special thanks to Mr. Harald Schrempp for helping
with all the technical problems in the lab and for keeping the “LME” in good shape. Also,
thanks to Ms. Paula Parkinson in Environmental lab for helping me with the chemical
related work. 8
9 I also thank Dr. Sidney Mindess for his time, constructive comments and approval as a
second examiner of this thesis. 10
11 I am grateful to all members of the Materials research group for making the lab a pleasant
place to work. Special appreciation goes to Ms. Jane Wu for helping with SEM work and
arranging the equipment schedule availability for everyone. Also thanks to Dr. Obinna
Onuaguluchi for giving feedback and correction for some parts of my thesis manuscript.
Thanks to my former fellow graduate students Sudip Talukdar, Tasnuba Islam, Sahar
Ranjbar and Qiannan Wang for their help in my early years in the research group and for
their friendship. My thanks also to Dr. Cristina Zanotti, Negar Roghanian, Brigitte Goffin,
Mohammed Farooq and all the members of this wonderful group. 12
13 I also acknowledge the involvement financial contributions of Natural Sciences and
Engineering Research Council (NSERC) of Canada. 14
15 My deepest gratitude goes to my family; my wife, Mitsi Singal and the boys, Leri, Valdi
and Verrel for their support, love and prayer throughout my life. 16
17 Most overall, praise be to God forever and ever. He has made everything beautiful in its
time.
18 "There is surely a future hope for you, and your hope will not be cut off (Proverbs 23:18)"
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1.1 Introductory Remarks
In general, fiber has become an integral part of concrete application. Vast ranges of
materials have been tested such as steel, carbon, glass, plastic, polypropylene, nylon, and even
natural materials such as cotton. In general, the introduction of fibers into the concrete matrix
was found to significantly alter the brittle tension response of the concrete material.
Before cracking the addition of fibres has little effect. However, even small amounts of
fiber addition leads to significant increases in the post-cracked toughness and ductility of
concrete (Shah and Rangan, 1971). As well, significant improvements in crack control can be
achieved, with a reduction in crack width and crack spacing in the concrete (Banthia et al.,
1993; Banthia and Gupta, 2006). The smaller crack widths and increased abrasion resistance
promotes an improvement in the long-term serviceability of the structure by preventing the
ingress of chemicals and water that can have deleterious effects (Johnston, 2001).
Synthetic fiber, such as polypropylene fiber, is gaining popularity due to its low cost and
non-corrosive nature. This type of fiber is of particular interest due to its corrosion resistance
relative to steel, resistance to alkali attack, relatively low cost, and durability with a long
service life. Polypropylene fibers can also be made into a variety of cross-sectional shapes and
can be designed with different surface finishes, allowing for further improvement in bond
properties (Wang et al., 1987).
However, its hydrophobic nature is a major drawback and this still needs to be
overcome. Polypropylene fibers are not expected to bond chemically in concrete matrix, but
bonding has been shown to occur by mechanical interaction. The effort to explore and optimize
2
its potential both in academic research and industrial development has been tremendously
increased in the past decade.
In this thesis, the effort to improve polypropylene material as a concrete reinforcing fiber
is described. The possibility to improve the performance of interface bonding between fiber
and concrete matrices by surface modification is explored. This includes the application of sol
gel coating and silica fume (SF) particles inclusion in the fiber extrusion process.
1.2 Research Objective
The purpose of this research is to explore the optimum performance of polypropylene
fiber in concrete application by improving its bond properties with a matrix.
This process includes:
Developing an extrusion process of polypropylene fiber
Optimizing the settings of the equipment used for extruding the fiber
Applying a coating layer for surface modification of the fiber
Developing a novel procedure in fiber production by incorporating supplementary
materials as fillers in the extrusion process
Testing the performance of the fibers including bond, flexural performance and
plastic shrinkage crack resistance
1.3 Study Outline
This Chapter provides an introduction and the rationale for the study as well as the
general outline of the study. Chapter 2 reviews the relevant literature on fiber reinforced
concrete, including types of fiber, the application of fibers in concrete and efforts to maximize
the benefit gained from fiber inclusion. Chapter 2 also reviews the process of producing
polypropylene fiber.
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In Chapter 3, the development of polypropylene fiber is described. The process of
production using a laboratory scale extruder and drawing equipment is explained. The attempt
to modify the surface of the fiber using aluminum oxide sol gel and its bonding performance
with concrete mortar is discussed. Chapter 3 also discusses the addition of silica fume and
polyvinyl alcohol particles in extruding process of the fiber. The comparison between these
co-extruded fibers and regular extruded fiber including surface characteristics and performance
in concrete matrix is deliberated. Other properties such as tensile strength of the fiber are also
determined.
Chapter 4 and Chapter 5 describe experiments that were carried out to test the
performance of the fibers in flexural response (Chapter 4) and plastic shrinkage cracking
(Chapter 5). The experimental method and test results of both tests are discussed. Finally,
General conclusions and Recommendations for further research are summarized in Chapter 6.
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2.1 Introduction
The use of fibers to reinforce concrete materials is a well-known concept. It has been
practiced since ancient times, with straw mixed into mud bricks and horsehair in mortars. Straw
was used to reinforce sun-baked bricks and horsehair was used to reinforce masonry mortar
and plaster (ACI 544). The concept of fiber reinforcement of cement based materials using
asbestos started with the invention of the Hatschek process in 1898. Later, glass fibers were
proposed as reinforcement of cement paste and mortar (Biryukovich et al., 1965). In modern
times, the choice of fibers can vary from synthetic organic materials such as polypropylene or
carbon, synthetic inorganic such as steel or glass, natural organic such as cellulose or sisal to
natural inorganic asbestos.
Using fibers in concrete matrices addresses the issue of cracking in cement based
materials. Concrete is considered to be a relatively brittle material with a low tensile strength
compared to its compressive strength. When subjected to tensile stresses, unreinforced
concrete will crack and fail. The use of fibers modifies properties of concrete both in plastic
and hardened stages and results in a more durable concrete.
Figure 2.1: Image of fibers crack bridging
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Fiber-reinforced concrete (FRC) has become an important material in the construction
of buildings and other structures. Reinforcing fiber’s ability to support load after cracking
(Figure 2.1) and to reduce the brittleness of concrete has positive effects on the structural
performance of concrete.
This section describes the general role of fibers in improving concrete performance and
the involvement of polypropylene fibers, in particular. The properties of polypropylene
material and the production process of the fiber are also presented. Finally, studies
incorporating polypropylene fiber in concrete applications are reviewed.
2.2 Factors Affecting Concrete Cracking
Cracks can develop due to a number of reasons. The main causes are low tensile
strength of concrete, intrinsic volumetric instability and deleterious chemical reactions.
Concrete is a brittle material and is prone to cracking in the plastic as well as the hardened
stage.
Plastic shrinkage occurs due to the loss of moisture from the concrete surface in its
plastic state. This state is defined as the first 24 hours after cement hydration begins. When the
rate of water evaporation from the surface of the concrete exceeds its bleeding rate, the surface
begins to dry resulting in high capillary stress near the concrete surface (Cohen et al., 1990).
Since concrete is very weak to tension, especially in its plastic stage, a volume change can
cause the surface to crack.
Plastic shrinkage cracks (Figure 2.2) are short cracks that occur before final finishing
on days when wind, a low humidity, and a high temperature occur. Surface moisture evaporates
faster than it can be replaced by rising bleed water, causing the surface to shrink more than the
interior concrete. Because the interior concrete restrains shrinkage of the surface concrete,
stresses can develop that exceed the concrete's tensile strength resulting in surface cracks.
Plastic shrinkage cracks are of varying lengths and are spaced from a few centimeters up to 3
m apart and often penetrate to mid-depth of a slab (PCA, 2001).
6
Figure 2.2: Plastic shrinkage crack on beam specimens
Cracks that occur after hardening are usually the result of drying shrinkage, thermal
contraction, or subgrade settlement. After hardening, if there is loss of water concrete will
shrink due to the volume change, which if restrained by the subgrade and reinforcement will
crack. Because of the evaporation of moisture in concrete, the tensile stresses that are confined
to the surface tension of the water are transferred to the capillary walls. This tension in the
capillary walls causes the shrinkage of concrete (Brown et al., 2001).
A major factor influencing the drying shrinkage properties of concrete is the total water
content of the concrete. As the water content increases, the amount of shrinkage increases
proportionally. Large increases in the sand content and significant reductions in the size of the
coarse aggregate increase shrinkage because total water content is increased and smaller coarse
aggregates provide less internal restraint to shrinkage. This causes tensile stress to develop in
hardened concrete causing the concrete to crack.
Cracking can be also the result of one or a combination of factors such as subgrade
settlement, thermal contraction, restraint (external or internal) to shortening, and applied loads.
Settlement cracks may develop over embedded items, such as reinforcing steel, or adjacent to
forms or hardened concrete as the concrete settles or subsides. Settlement cracking results from
insufficient consolidation, high slump, or a lack of adequate cover over embedded items.
7
Thermal expansion and contraction can also cause cracking. Concrete has a coefficient
of thermal expansion of approximately 10 x 10-6 per °C. Concrete placed during hot midday
temperatures will contract as it cools during the night. A 22 °C drop in temperature between
day and night would cause about 0.7 mm of contraction in a 3 m length of concrete, sufficient
to cause cracking if the concrete is restrained (PCA, 2001).
Cracks can also be caused by freezing and thawing of saturated…