Reinforcement effect on mechanical properties of 3D printing concrete

By
Doctor of Philosophy
Department of Civil, Environmental and Mining Engineering
School of Engineering
November 2021
This thesis is dedicated to my family, supervisors and friends for their unreserved loves, supports
and encouragements.
THESIS DECLARATION
I, Miao Liu, certify that:
This thesis has been substantially accomplished during enrolment in this degree.
This thesis does not contain material which has been submitted for the award of
any other degree or diploma in my name, in any university or other tertiary institution.
In the future, no part of this thesis will be used in a submission in my name, for
any other degree or diploma in any university or other tertiary institution without the
prior approval of The University of Western Australia and where applicable, any partner
institution responsible for the joint-award of this degree.
This thesis does not contain any material previously published or written by
another person, except where due reference has been made in the text and, where
relevant, in the Authorship Declaration that follows.
This thesis does not violate or infringe any copyright, trademark, patent, or other
rights whatsoever of any person.
This thesis contains published work and or work prepared for publication, some
of which has been co-authored.
Signature:
ABSTRACT
iii
ABSTRACT
3D concrete printing technology has made waves in construction industries due
to its construction flexibility, high precision and efficiency, cost effectiveness in terms
of labor and formwork, and superior worker safety. 3D concrete printing is expected to
revolutionize the conventional construction techniques towards intelligence, automation
and individualized customization. On the other hand, it is argued unfavorably that the
printed concrete yields low tensile strength and poor toughness in view of that course
aggregate cannot be integrated into the printable materials. Weak trace between layer
and filament interfaces due to voids intrinsic to the printing procedure is another
negating factor. The situation is worsen by the fact that effective reinforcing measure
for 3D printed concrete is lacking. To this gap, this research project develops and
investigates the behaviors of the printed concrete reinforced with steel wire mesh and
the printed jackets-reinforced concrete, which realize the improvement of strength and
toughness of the 3D printed concrete. The main research works and results are outlined
as follows:
(1) The basic material properties of 3D printed composite specimens reinforced
by steel wire mesh (SWM) are evaluated by a series of tests. Compared with
that of the non-reinforced 3D printed counterpart, the tested tensile
properties of the printed concrete reinforced with SWM in terms of pre- and
post-cracking load and ultimate load are improved substantially. The strain-
hardening behavior and multiple micro-cracks are observed in the uniaxial
tensile test of SWM reinforced 3D printed concrete specimen. Direct shear
ABSTRACT
iv
test results indicate that the peak shear load depends on the grid size of
SWM instead of the position of SWM in the specimens. On the other hand,
the post-peak load is remarkably affected by the position of SWM. Pull-out
test results show that no bond-slip occurs indicating robust interface bond
between SWM and concrete.
(2) The effect of different layers SWM and wire-diameters on the flexural
properties of reinforced printed concrete are explored. The results indicate
that SWM reinforcement improves the bending failure modes of printed
concrete from brittle (non-reinforced) to ductile (reinforced). For the under-
reinforced case, a single crack, once initiates, propagates immediately to the
compression zone. The load is then borne by the SWM until it ruptures. For
the balanced-reinforced case, the flexural cracking and maximum loads are
enhanced by the increase of SWM reinforcement ratio. The deflection
hardening and multiple cracking behavior are observed. However, on a
negative note, the deflection and ductility of specimens decrease as the
number of reinforcement layers increases. It could be explained by that
horizontal SWM reinforcement cannot provide sufficient shear resistance.
Although the loading capacity is improved, shear failure still occur
prematurely to negate the ductility.
(3) To improve the shear performance of the printed concrete, a novel
reinforcing approach of U-type SWM is developed and instrumented via a
inclined printing nozzle. The shear behaviors of the U-type SWM reinforced
printed specimens are tested. The results indicate that introduction of the U-
type SWM into the printed concrete increase the maximum load capacity and
ductility of the printed specimens. Compared to the control specimens
ABSTRACT
v
without reinforcement, extension of the major inclined crack from the
support towards the load region is restrained by the addition of U-type SWM.
Increasing the vertical reinforcement ratio results in improvement of the
flexural-shear capacity of the specimen at the expense of reduced ductility
due to compressive crushing from the excessive reinforcement of SWM.
Strut-and-tie model (STM) is modified to predict the load capacities of the
U-type SWM strengthened 3D printed specimens.
(4) An in-process printed reinforcement of fibre-jacket-reinforced formwork is
developed. Specimens are fabricated to investigate the strengthening effect
on both flexural and tensile capacities. Results from both tests show that an
appropriate printing path can significantly improve the tensile and flexural
strengths of 3D-printed mortar due to the fibre alignment. Meanwhile, both
strengths of the fibre-jacket-reinforced specimens with six reinforcement
layers almost reach similar strengths of a fully printed fibre-reinforced
specimen, but the amount of fibre is reduced by half. In addition, an
analytical model is developed to predict the enhanced bending capacities of
the proposed fibre-jacket-reinforced specimens.
ACKNOWLEDGEMENTS
vi
ACKNOWLEDGEMENTS
I would like to express my deep and sincere gratitude to those who have guided,
supported, assisted, and encouraged me during my PhD study. Without their guidance,
support, help and encouragement, I would not have been able to finish this dissertation
and with such good results.
First of all, I would like to express my sincere appreciation and thank towards
my supervisor, Prof. Guowei Ma, for his invaluable academic guidance and support. His
critical suggestions, warm encouragement and great dedication to research inspire me to
complete this research work.
I would also like to thank my co-supervisor, Dr Farhad Aslani, for his insightful
suggestions regarding this research. In addition, I wish to express my great appreciation
to Prof. Fang Wang, Dr. Yimiao Huang, Dr. Li Wang and Dr. Zhijian Li for their
helpful suggestions and comments during the execution of my experimental program
and writing of this thesis. My thanks also go to my colleagues and friends: Dr Yang
Wang, Dr Tuo Li, Dr Yun Chen, Dr Junfei Zhang, Dr Huidong Wang, Junbo Sun,
Youyu Wang, Wei Dong, Gang Bai, Bolin Wang, Wenwei Yang, Yaoyao Wu, Qian
Wan, Jun Zhang and Lisa Wei for their help and encouragement. I am also grateful to
UWA administrative and academic staffs for the supports in life and study.
Finally, my biggest thanks go to my family for their unconditional love and
support over all the years.
AUTHORSHIP DECLARATION
AUTHORSHIP DECLARATION
This thesis contains work that has been published and/or prepared for publication, which has been co-authored. The bibliographical details of the work and where it appears in the thesis are outlined below.
Paper 1
Details of the work: Miao Liu, Qiyun Zhang, Zhendong Tan, Li Wang, Zhijian Li, Guowei Ma. Investigation of steel wire mesh reinforcement method for 3D concrete printing[J]. Archives of Civil and Mechanical Engineering, 2021, 21(1): 1-18.
Location in thesis: Chapters 4
Student contribution to work: The estimated percentage contribution of the candidate is 80%
Co-author signatures and dates:
Paper 2
Details of the work: Miao Liu, Yimiao Huang, Fang Wang, Junbo Sun, Guowei Ma. Tensile and flexural properties of 3D-printed jackets-reinforced mortar[J]. Construction and Building Materials, 2021, 296: 123639.
Location in thesis: Chapters 6
Student contribution to work: The estimated percentage contribution of the candidate is 80%
Co-author signatures and dates:
Paper 3
Details of the work: Miao Liu, Li Wang, Guowei Ma. An experimental study on flexural behavior of steel wire mesh reinforced 3D printing concrete. Submitted to Journal of Building Engineering
Location in thesis: Chapter 4
Student contribution to work: The estimated percentage contribution of the candidate is 80%
Co-author signatures and dates:
Paper 4
Details of the work: Miao Liu, Li Wang, Zhijian Li, Guowei Ma. Influence of U-type steel wire mesh on the flexural behavior of printed concrete: A novel reinforcement approach for 3D printing concretes. Submitted to Materials Letters
Location in thesis: Chapter 5
Student contribution to work: The estimated percentage contribution of the candidate is 80%
Co-author signatures and dates:
CHAPTER 2 LITERATURE REVIEW..................................................................... 30
2.1 Introduction ........................................................................................................... 30
2.2.1 Classification of 3D printing technologies used in construction sector ..........31
2.2.2 Printable materials .......................................................................................... 33
2.3.1 Short fibres ......................................................................................................34
2.3.3 Penetration reinforcement ...............................................................................38
2.3.5 Steel bar with or without pre-stress ................................................................ 42
2.4 Analytical calculation methods ............................................................................. 46
2.4.1 For cast concrete ............................................................................................. 46
2.4.2 For printed concrete ........................................................................................ 53
2.5 Summary ................................................................................................................55
PRINTED CONCRETE............................................................................................... 56
3.2.1 Materials ......................................................................................................... 59
3.2.3 Test setup ........................................................................................................ 64
3.3.1 Uniaxial tensile tests ....................................................................................... 67
3.3.2 Splitting tensile tests ....................................................................................... 74
TABLE OF CONTENTS
3.4.1 Load-displacement curves .............................................................................. 75
3.4.3 Shear strength calculation for reinforced specimens ...................................... 81
3.5 Results and discussions for pull-out and compression tests ..................................83
3.5.1 Pull out test ..................................................................................................... 83
3.5.2 Uniaxial compression tests ............................................................................. 84
3.6 Conclusions ........................................................................................................... 88
PRINTED CONCRETE............................................................................................... 90
4.2.2 3D concrete printer ......................................................................................... 94
4.2.3 3D concrete printing and SWM reinforcement ...............................................95
4.2.4 Test set-up and procedure ............................................................................... 98
4.3 Results and discussions ....................................................................................... 100
4.3.1 Under-reinforced case ...................................................................................100
4.3.2 Balanced-reinforced case ..............................................................................115
4.4 Conclusions ......................................................................................................... 135
TABLE OF CONTENTS
PRINTED CONCRETE............................................................................................. 138
5.2.1 USWM fabrication technology .....................................................................142
5.3 Materials and methods .........................................................................................145
5.3.3 Test setup and instrumentation ..................................................................... 149
5.4 Results and discussions ....................................................................................... 151
5.4.1 Load-displacement behaviors of specimens ................................................. 151
5.4.2 Failure modes and concrete cracking behaviors ........................................... 154
5.4.3 Effect of U-type SWM reinforcement .......................................................... 159
5.4.4 Effect of mesh size of SWM reinforcement ................................................. 160
5.5 Analytical predictions of ultimate load ............................................................... 161
5.6 Conclusions ......................................................................................................... 166
JACKET-REINFORCED CONCRETE...................................................................168
6.2.1 Material preparation ......................................................................................171
6.2.2 3D printing system........................................................................................173
6.2.4 Test setups .................................................................................................... 179
6.3.1 Test results .................................................................................................... 182
6.4.2 Maximum capacities .....................................................................................196
6.5 Conclusions ......................................................................................................... 197
7.1 Conclusions ......................................................................................................... 199
7.2 Future works ........................................................................................................202
Figure 2- 1 Classification of general 3D printing processes. ................................. 31
Figure 2- 2 Structures printed by: (a) D-shape [50]; (b) Contour crafting [51]; (c)
Concrete printing [52]. .................................................................................... 33
Figure 2- 3 Examples of the use of short fibres in 3D printing: (a) multiple cracks
of printed specimens with 1.40% fibres [72], (b) observation of fibre
alignment of printed fibre reinforced concrete [114]. .....................................35
Figure 2- 4 Automatic reinforcing device: (a) active reinforcement entrainment
device for cable reinforcement [76]; (b) schematic for entertaining process of
micro-cable in geopolymer filaments [79]; (c) schematic for nozzle with the
steel cable extruder [78]; (d) a device depositing mineral-impregnated carbon
yarns into extruded filaments [83]; (e) a device called Flow-Based Pultrusion
[211]. ............................................................................................................... 37
Figure 2- 5 Reinforcement approaches using penetration: (a) layout of U-nails in
the 3D printed concrete [85]; (b) reinforcement placed in clay print for
experimentation [86]; (c) schematic for steel nails’ penetration [87]; (d)
schematic for screw reinforcement penetration [88]; (e) printed wall with steel
bars penetrating through [90]; (f) penetration of short reinforcement bars by
an automated, robot-guided device during Shotcrete-3D-Printing process [92].40
Figure 2- 6 Reinforcement approaches: (a) placement of 2.5D textile between
layers in printed concrete [93]; (b) incorporating alkali-resistant-glass textile
between the printed concrete layers [94]; (c) shotcreteing on a carbon grids
LIST OF TABLES
xv
[95]; (d) laying carbon grid on a 3D-printed wall after concrete hardening [96];
(e) overlapping mesh reinforcement while printing [97]; (f) two-dimensional
mineral-impregnated carbon fibre composite reinforcement [84]. ................. 42
Figure 2- 7 Reinforcement strategies using steel bars: (a) placement of horizontal
reinforcements on printed layer [98]; (b) pressing straight bars into print layer
[99]; (c) 3D-printed reinforcement bars [100]; (d) placement of reinforcement
in between a split nozzle [101]; (e) welding short bars as vertical
reinforcement while printing [102]; (f) placement of horizontal and vertical
reinforcement in shotcrete 3D printing [103]; (g) members assembled printed
segments with external reinforcement system [104]; (h) 3D printed concrete
bridge with post-tensioned prestressing tendons [105]; (i) post-tensioned
girder combining 3D concrete printing and topology optimization [106]; (j) a
printed formwork with steel reinforcement cage [107]. ..................................46
Figure 2- 8 Strain and stress distributions at different deformation stages. ........... 47
Figure 2- 9 Strut-and-tie model of reinforced concrete beam. ............................... 50
Figure 2- 10 Two-parameter kinematic theory for concrete beam: (a) deformation
patterns and degrees of freedom; (b) shear forces along the critical diagonal
crack. ............................................................................................................... 52
Figure 2- 11 Solution of the two-parameter kinematic theory (data from [209]). . 53
Figure 3- 1 Geometries of the SWM: (a)(b)(c) specimens for tensile tests; (c)(d)(e)
specimen for shear tests. ................................................................................. 60
Figure 3- 2 3D printer for: (a) normal printing; (b) inclined printing. ................... 61
Figure 3- 3 Specimens: (a) for uniaxial tensile tests; (b) for splitting tensile tests;
(c) and (d) for shear tests; (e) for pull-out tests. ..............................................61
Figure 3- 4 Schematic: (a) uniaxial tensile test setup; (b) splitting tensile test setup.64
LIST OF TABLES
Figure 3- 5 Schematic for the direct shear test setup. .............................................65
Figure 3- 6 Schematic: (a) pull-out test setup; (b) uniaxial compression test setup.66
Figure 3- 7 Comparison of force-displacement curves. ......................................... 67
Figure 3- 8 Failure modes of specimens strengthened with three types of SWM: (a)
0.6 mm wire diameter; (b) 0.8 mm wire diameter; (c) 1.0 mm wire diameter.68
Figure 3- 9 Strain fields of specimens with major penetrating crack: (a)
strengthened with 0.6 mm wire diameter SWM; (b) strengthened with 0.8 mm
wire diameter SWM; (c) strengthened with 1.0 mm wire diameter SWM. .... 69
Figure 3- 10 Failure modes from tensile tests: (a) single major penetrating crack &
SWM tensile failure, (b) multiple minor cracks & SWM tensile failure. ....... 70
Figure 3- 11 Stress-strain curves from tensile tests: (a) strains evaluated by DIC
technique; (b) comparison between calculated and measured stress-strain data;
(c) comparison between calculated and measured stress-strain data; (d)
calculated stress-strain data of WD0.8; (e) calculated stress-strain data of
WD1.0. ............................................................................................................ 72
Figure 3- 12 Splitting tensile test results: (a) axial load-displacement curves of the
cubic specimens; (b) splitting tensile strength of specimens. ......................... 74
Figure 3- 13 Typical curve of shear loading-displacement subject to direct
shearing. .......................................................................................................... 76
Figure 3- 14 Load-displacement curves from shear tests: (a) plain specimens; (b)
specimens S1 reinforced with WS12; (c) specimens S1 reinforced with WS8;
(d) specimens S1 reinforced with WS6; (e) specimens S2 reinforced with
WS12; (f) specimens S2 reinforced with WS8; (g) specimens S2 reinforced
with WS6. ........................................................................................................77
xvii
Figure 3- 15 Schematic for bridging mechanism of SWM for shear resistance: (a)
series S1 before cracking; (b) series S1 after cracking; (c) series S2 before
cracking; (d) series S2 after cracking. .............................................................80
Figure 3- 16 Toughness up to specified displacement for specimens in direct shear
test. .................................................................................................................. 81
Figure 3- 17 Energy absorption of SWM during shear test. ...................................81
Figure 3- 18 Comparison between test values and calculated values. ................... 82
Figure 3- 19 Load-displacement curves of pull out test. ........................................ 83
Figure 3- 20 Failure modes of specimens under pull-out test: (a) 70 mm bond
depth; (b) 35 mm bond depth; (c) 18 mm bond depth. ................................... 84
Figure 3- 21 Compressive load versus displacement of both print and cast
specimens. ....................................................................................................... 86
Figure 3- 22 Vertical and transversal strain vs pressure of samples under uniaxial
compression: (a) cast sample CC0-1; (b) cast sample CC0-2; (c) print sample
PC0-1; (d) print sample PC0-2. .......................................................................87
Figure 3- 23 Compressive failure patterns: (a) cast specimen; (b) print specimen.87
Figure 4- 1 Particle size distribution of the components. .......................................93
Figure 4- 2 Illustration of 3D printer for cementitious concrete printing. ..............94
Figure 4- 3 Steel wire mesh as reinforcement for 3D printed concrete. .................96
Figure 4- 4 SWM placement during printing process. ........................................... 96
Figure 4- 5 Printed beam specimen (a) before and (b) after cutting. ..................... 96
Figure 4- 6 Schematic of reinforced specimens beam: front and cross-sectional
view. ................................................................................................................ 97
xviii
Figure 4- 7 Schematic: (a) printed specimens reinforced with SWM with 0.6 mm
wire diameter; (b) printed specimens reinforced with SWM with 0.8 mm and
1.0 mm wire diameters. .................................................................................100
Figure 4- 8 Load-deflection curves: (a) unreinforced and (b) reinforced cast and
printed specimens; (c) cracking point on load-deflection curves of reinforced
specimens. ..................................................................................................... 104
Figure 4- 9 Tested results: (a) flexural strength; (b) maximum deflection at middle
span; (c) flexural strain; (d) fracture energy of beam specimens with different
reinforcing rates subject to flexural bending. ................................................105
Figure 4- 10 Flexural failure patterns of printed beams with: (a) two; (b) four and
(c) six layers of SWMs. .................................................................................106
Figure 4- 11 Conductance of PZTs: (a) two-layer (b) four-layer and (c) six-layer
SWM reinforcement at different loading stages of three-point bending; (d)
RMSD values. ............................................................................................... 109
Figure 4- 12 Ideal stress-strain curves of concrete and SWM. .............................111
Figure 4- 13 Cross-section strain, stress and force distribution of (a) linear elastic
stage and (b) failure stage. ............................................................................ 112
Figure 4- 14 Flexural load-deflection curves of specimens: (a) with 2 layers SWM;
(b) with 4 layers SWM; (c) with 6 layers SWM. .......................................... 117
Figure 4- 15 Comparison of first-crack, peak and ultimate flexural (a) loads and (b)
deflections. .................................................................................................... 120
Figure 4- 16 Failure modes of SWM reinforced beams: (a) bending failure; (b)
bending-shear failure; (c) bending-shear failure; (d) bending-shear failure; (e)
shear failure; (f) shear failure. .......................................................................121
LIST OF TABLES
xix
Figure 4- 17 Crack propagations for three typical failure patterns: (a) bending
failure (pp0.8-2L); (b) bending-shear failure (pp1.0-2L); (c) shear failure
(pp1.0-6L). .................................................................................................... 122
Figure 4- 18 Toughness index based on ASTM C 1018. ..................................... 124
Figure 4- 19 Influence of SWM ratio on (a) toughness and (b) toughness index.125
Figure 4- 20 Specification of displacements for calculation of ductility index. .. 128
Figure 4- 21 Ductility index of specimens. .......................................................... 128
Figure 4- 22 A predicted model: (a) modified strut-and-tie model; (b)
determination of tensile and compressive stress at nodal zone. ....................134
Figure 5- 1 USWM fabrication using 6-axis robot arm. ...................................... 143
Figure 5- 2 End effectors: (a) wire straightening, feeding and shaping device; (b)
wire cutting and welding device. .................................................................. 144
Figure 5- 3 SWMs with different mesh grid sizes. ...............................................146
Figure 5- 4 (a) Collision between nozzle and vertical SWM; (b) ideal nozzle
inclination; (c) ideal print path without collisions; (d) USWM reinforced
specimens in printing process. ...................................................................... 149
Figure 5- 5 Schema for (a) four-point bending and (b) speckle area. .................. 150
Figure 5- 6 Load-displacement curves: (a) effect of U-type SWM; (b) effect of
mesh grid size of U-type SWM; (c) effect of shear span ratio. .....................153
Figure 5- 7 Typical load versus displacement curve with stage indication for
specimen subject to four-point bending. ....................................................... 154
Figure 5- 8 Effects of different U-type SWM reinforcing types and shear span
ratios on ultimate load of the tested specimens. ............................................154
Figure 5- 9 Failure modes of specimens. ..............................................................157
Figure 5- 10 Crack patterns (a) at service load; (b) at ultimate load. ...................158
LIST OF TABLES
xx
Figure 5- 11 Comparison of test results for specimens with and without U-type
SWM. ............................................................................................................ 160
Figure 5- 12 Effects of mesh grid size on load capacity and displacement of
specimens. ..................................................................................................... 161
Figure 5- 13 Determination of tensile and compressive stresses at nodal zone by
currently proposed strut-and-tie model. ........................................................ 166
Figure 6- 1 Mixing procedure of printable cementitious material. ...................... 173
Figure 6- 2 (a) 3D concrete printer (b) extrusion device. .....................................174
Figure 6- 3 (a) Models for printed frame; (b) diagram from section view for
printed frame with path1. .............................................................................. 177
Figure 6- 4 Printing paths for different layers. ..................................................... 177
Figure 6-…