Load transfer across cracks and joints in concrete slabs on grade

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Load transfer across cracks
and joints in concrete slabs
on grade
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• A Doctoral Thesis. Submitted in partial fulfillment of the requirements
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LOAD TRANSFER ACROSS CRACKS AND JOINTS IN
CONCRETE SLABS ON GRADE
By
Stuart John Arnold
A Doctoral Thesis Submitted
in fulfilment the for the
partial of requirements
award of
Doctor Philosophy University
Loughborough
of
of
20th February 2004
@Stuart John Arnold (2004)
ABSTRACT
This has investigated behaviour joints
the
research of and cracks under single and
load. This increased
multiple cycles of provides an understanding of concrete slab on
design
grade performance, enabling more effective and monitoring procedures.
Examination joints
the has
of geometry of cracks and within concrete slabs on grade
demonstrated that the formation is Measurements
commonly assumed parallel erroneous.
levelling have
using embedded strain gauges, coring and surface profile uncovered that a
high joints larger base,
percentage of will contain crack widths at the surface than at the
by differential The itself is linear; however,
caused shrinkage. opening relatively the top
50mm is higher due increased drying
of the slab prone to a gradient of movement to the
towards the
effect surface.
A deflection Falling Weight Deflectometer Prima dynamic
series of tests using a and
load be Four in total
plate enabled slab response under to evaluated. sites were examined
and correlations found between: load transfer, load step, edge cantilever and crack
geometry. This produced valuable information regarding the influence of load transfer
face free
and crack width on the overall slab behaviour. Foundation voiding and crack slip
was also shown to influence deflection
magnitude.
A test facility developed for deterioration in
small-scale was the assessment of various
'V' high loading. The data demonstrated
shaped and parallel crack widths under cycle
joint/crack failure four distinct deterioration, is
that contains phases of each of which
by different 'V' load
controlled a mechanism. shaped cracks produced a much greater
transfer than that of a parallel crack with the incorporation of A142 mesh and steel fibres
differential displacement. Load
reducing magnitude and aggregate size were also shown
have The found
to significant effects. value of reinforcement was to assist with
keeping displacement levels
serviceability requirements, within acceptable and preventing
degradation
the onset of serious
A finite developed load
element model was to enable the transfer from
mechanism results
laboratory be in full
the test to the Simulations field-
used assessment of slab response. of
lower bounds in
testing deflections
produced a series of respect to and the associated
Theoretical behaviour
response calculations. of a typical slab was assessed with subbase
joint
incorporation
support, stiffness, slab thickness and the of a subbase, found to be
highly influential in deflections.
reducing slab
The three data laboratory
main sections of work comprising site collection, testing and
Finite Element have been
modelling used together to provide a much greater
the influence joints. This has included deterioration
understanding of of cracks and the
of
how
cracks over time and an examination of this and other site-based factors affect
behaviour.
overall slab
Keywords: Concrete Joint behaviour, Load Deflection
transfer, testing,
slabs on grade,
Steelfibres, Concrete degradation, Finite Element
modelling.
ii
ACKNOWLEDGMENTS
Many have
people provided me with assistance, guidance and support over the last three
it have been
years, without whom would not possible to complete this thesis.
Firstly, I like to thank Professor Simon Austin, Dr. Paul Fleming Dr. Peter
would
and
Robins, have
who complemented each other perfectly to generate the model supervisory
team. Their knowledge, have
advice and carefully worded constructive criticism enhanced
both development.
my academic and personal
I like in department Civil
would also to thank many other staff members the of and
Building Engineering, laboratory Mark
most notably the expertise of the technicians
Harrod, Dave Spendlove David Houghton. Together they have that the
and shown with
inclusion be both highly
of experience and wisdom, practical research can rewarding and
free.
remarkably pain
My thanks go to the ACIIFC and all of the steering group members whose input has
enabled a project to be developed hopefully information to the
which will offer valuable
wider construction community.
There are many friends and family deserve for their input; however, two in
who praise
particular stand out, Adrian Holland and Karan Jalota. Both have been there academically
and emotionally through the good and the bad, and amazingly are still here today, proving
friends.
that they are very special
Heartfelt thanks to Maureen David Arnold faith in has been
go my parents and whose me
They have
a source of continual strength. supported and encouraged me
for I love dearly.
that them
endlessly and
To complete this PhD was not a solitary undertaking, there was always one other who
has
through
went every emotion and probably read and re-read every word as many times
I have. To
as show my total appreciation towards my partner Chrissie Pepper, I dedicate
her.
this thesis to
iii
CONTENTS OF THESIS
ABSTRACT
i
.........................................................................................................................
ACKNOWLEDGEMENTS
iii
...............................................................................................
CONTENTS OF TBESIS
iv
..................................................................................................
LIST OF TABLES
ix
.............................................................................................................
LIST OF FIGURES
x
.............................................................................................................
NOTATION
xviii
...................................................................................................................
1. INTRODUCTION I
.......................................................................................................
1.1 Background 1
........................................................................................................
1.2 Aims Objectives 2
and
..........................................................................................
1.3 Outline Research Methodology 2
of
....................................................................
1.4 Thesis Structure 4
.................................................................................................
2. CONCRETE SLABS/PAVEMENTS ON GRADE 8
.................................................. ..
2.1 Preface 8
..
...............................................................................................................
2.2 Concrete Slabs/Pavements Grade 9
on
...............................................................
2.2.1 Internal Floor Slabs 9
..
....................................................................................
2.2.2 External Hardstandings 12
..............................................................................
2.2.3 Concrete Pavements 14
...................................................................................
2.2.3.1 Jointed 15
........................................................................................................
2.2.3.2 Continuously Reinforced 15
............................................................................
2.2.4 Structure Comparison 15
................................................................................
2.3 Typical Actions for Concrete Slabs Grade 16
on
...............................................
2.3.1 Moisture 17
.....................................................................................................
2.3.1.1 Drying Shrinkage 17
.......................................................................................
2.3.1.2 Plastic Shrinkage 18
.......................................................................................
2.3.2 Thermal
18
......................................................................................................
2.3.3 Static Load 19
.................................................................. ...............................
2.3.4 Cyclic Dynamic Load 20
................................................................................
2.4 Serviceability Problems
21
...................................................................................
2.4.1 Cracking
21
................................................................... ..................................
2.4.2 Curling
23
............................................................. ..........................................
2.4.3 Pumping 26
........................................................
.............................................
2.4.4 Faulting/Dynamic Load Step 26
.......................
...................................... ........
2.4.5 Punch-Out 27
..................................................................................................
iv
2.4.6 Spalling
28
......................................................................................................
2.5 Concrete Slab Design
29
.......................................................................................
2.5.1 Concrete
properties 29
....................................................................................
2.5.2 Slab Reinforcement
29
....................................................................................
2.5.2.1 General
29
..................................................................................................
2.5.2.2 Fabric
30
....................................................................................................
2.5.2.3 Fibres
32
.....................................................................................................
2.5.2.4 Structural Reinforcing
33
steel
...................................................................
2.5.3 Structural Design 33
.......................................................................................
2.5.3.1 Elastic 34
method
.......................................................................................
2.5.3.2 Plastic Method 35
.......................................................................................
2.5.4 Detail Design 37
.............................................................................................
2.5.4.1 Crack Control 37
........................................................................................
2.5.4.2 Joint Types 39
.............................................................................................
2.5.4.3 Joint Layout 41
...........................................................................................
2.6 Slab/Pavement Foundation 43
.............................................................................
2.6.1 Subbase 43
......................................................................................................
2.6.2 Subgrade 4
..
....................................................................................................
2.6.3 Slip Membrane 45
...........................................................................................
2.7 Structural Modelling 46
.......................................................................................
2.7.1 Modelling Concrete 46
of
materials
................................................................
2.7.2 Modelling Foundation 47
of
materials
............................................................
2.7.3 Analysis Slabs Grade 49
of on
........................................................................
2.7.4 Modelling Limitations 51
...............................................................................
2.8 Conclusions 52
.......................................................................................................
3. LOAD TRANSFER ACROSS CRACKS/JOINTS 59
..................................................
3.1 Introduction 59
......................................................................................................
3.2 Influence Design 59
on
..........................................................................................
3.3 Crack Geometry
60
...............................................................................................
3.4 Load Transfer Mechanisms 62
............................................................................
3.4.1 Aggregate Interlock 62
...................................................................................
3.4.2 Dowel Bars
65
.................................................................................................
3.4.3 Steel Fabric
66
................................................................................................
3.4.4 Steel Fibres
67
.................................................................................................
3.4.5 Proprietary Systems
68
...................................................................................
3.5 Degradation Load Transfer 69
of
........................................................................
3.6 Slab Condition Testing 71
....................................................................................
V
3.6.1 Equipment 71
..................................................................................................
3.6.2 Investigation Techniques 72
...........................................................................
3.7 Joint Effectiveness Analysis 75
............................................................................
3.8 Summary 80
...........................................................................................................
4. SLAB CONDITION 90
.................................................................................................
4.1 Introduction 90
......................................................................................................
4.2 Crack Measurement 91
........................................................................................
4.2.1 Surface Measurements 92
...............................................................................
4.2.2 Embedded Strain Gauges 93
...........................................................................
93
4.2.3 Coring
........................................................................................................
94
4.3 CurlingfWarping
..............................................................................................
94
4.3.1 Introduction
................................................................................................
95
4.3.2 Precise Levelling
........................................................................................
95
4.3.3 Builder's Level
...........................................................................................
96
4.3.4 Profilometer
...............................................................................................
96
4.4 Deflection Measurement
..................................................................................
98
4.5 Slab Analysis
.....................................................................................................
99
4.5.1 Load Transfer
..
...........................................................................................
99
4.5.2 Load Step
..
.................................................................................................
4.5.3 Edge Cantilever 100
........................................................................................
100
4.5.4 Deflection Basins
.....................................................................................
4.5.5 Void Intercepts 101
.........................................................................................
101
4.6 Site Information
.............................................................................................
101
4.6.1 Daventry
...................................................................................................
102
4.6.2 Lutterworth
..............................................................................................
103
4.6.3 Ballymena
................................................................................................
104
4.6.4 Skelmersdale
............................................................................................
113
5. JOINT DETERIORATION
.....................................................................................
5.1 Introduction 113
....................................................................................................
5.2 Test Variables 114
.................................................................................................
5.2.1 Surface Crack Widths 114
..............................................................................
5.2.2 Steel Fibre Types 114
.....................................................................................
5.2.3 Steel Fibre Quantities 115
...............................................................................
5.2.4 Non Reinforced 115
........................................................................................
5.2.5 Mortar 115
......................................................................................................
5.2.6 Parallel Cracks 115
.........................................................................................
5.2.7 Fabric 115
.......................................................................................................
vi
5.2.8 Loads 115
........................................................................................................
5.2.9 Summary Test Variables 116
of
......................................................................
5.3 Load Test Development 116
.................................................................................
5.3.1 Simulation Method 116
...................................................................................
5.3.2 Specimen Geometry 118
.................................................................................
5.3.3 Crack Geometry 118
.......................................................................................
5.3.4 Subgrade Support 119
.....................................................................................
5.3.5 Load Magnitude 119
.......................................................................................
5.3.6 Loading 120
repetition
....................................................................................
121
5.3.7 Load
rate
..................................................................................................
121
5.4 Specimen Production
.....................................................................................
121
5.4.1 Introduction
..............................................................................................
122
5.4.2 Mix Design
...............................................................................................
123
5.4.3 Reinforcement
..........................................................................................
124
5.4.4 Casting
.....................................................................................................
125
5.5 Beam Preparation
..........................................................................................
125
5.5.1 Crack Timing
...........................................................................................
125
5.5.2 Crack Technique
......................................................................................
127
5.5.3 Crack Width Control
................................................................................
127
5.6 Test
procedure
................................................................................................
5.6.1 Overview 127
..................................................................................................
128
5.6.2 Beam Orientation
.....................................................................................
128
5.6.3 Rig Configuration
....................................................................................
129
5.6.4 LVDT Positioning
....................................................................................
5.6.5 Safety Precautions 130
....................................................................................
130
5.7 Data Logging
..................................................................................................
6. RESULTS, ANALYSIS & DISCUSSION 146
............................................................ .
6.1 General Introduction 146
.....................................................................................
6.2 Crack Geometry 146
............................................................................................ .
6.2.1 Core Samples 146
.......................................................................................... .
6.2.2 Strain Gauge Monitoring 151
........................................................................ .
Crack Measurements
6.2.3 Levelling Profiles 154
and
.......................................... .
6.2.4 Summary 156
................................................................................................. .
6.3 Slab Condition 157
............................................................................................... .
6.3.1 Introduction 157
............................................................................................. .
6.3.2 Load Transfer Evaluation 158
........................................................................ .
162
6.3.3 Load Step Evaluation
.............................................................................. .
vii