concrete armour units for breakwaters

231 Pages·2007·32.04 MB·English

MSc Thesis - Final report - November 2007

CONCRETE ARMOUR UNITS FOR BREAKWATERS

A study on the structural integrity

Master Thesis

By Nina FOZEIN KWANKE

Nina FOZEIN KWANKE - i -
MSc Thesis - Final report - November 2007

Nina FOZEIN KWANKE - ii -
MSc Thesis - Final report - November 2007

CONCRETE ARMOUR UNITS FOR BREAKWATERS

A study on the structural integrity

Master Thesis

Delft University of Technology (TU Delft) Delta Marine Consultants B.V. (DMC)
Faculty of Civil Engineering and Geosciences (CiTG) part of Royal BAM Group (took over
Section: Structural engineering the HBG- Hollandsche Beton Groep)
Specialization: Concrete structures

Student information: Graduation committee:

Names : N.J.C. FOZEIN KWANKE Ir. W.J. Bouwmeester (DMC)
Student number : 1052136 Dr. ir. A.L.A. Fraaij (TU Delft)
Course code : CT5060 Dr. ir. E.A.B. Koenders (TU Delft)
Date : November 2007 Prof. dr. ir. J.C. Walraven (TU Delft)

Nina FOZEIN KWANKE - iii -
MSc Thesis - Final report - November 2007

Pictures on the front page:
- “Newly placed concrete blocks at IJmuiden 1” made by RWS (Bouwdienst Utrecht/ Dienstkring
IJmuiden)
- “Damaged concrete armour units at IJmuiden”(from left to right): 1 + 2 made by Nina FOZEIN
KWANKE, 3 + 4 made by Coastal Team / Bas Reedijk (DMC)
- “Brazilian kid playing with sand” made by Nina FOZEIN KWANKE.
Picture on page iii:
- “Newly placed concrete blocks at IJmuiden 2” made by RWS (Bouwdienst Utrecht/ Dienstkring
IJmuiden)
Lay-out: Nina FOZEIN KWANKE

Nina FOZEIN KWANKE - iv -
MSc Thesis - Final report - November 2007

PREFACE

This report is the result of conducted research for the final graduation project in order to complete
the Master study of Civil Engineering at the University of Technology of Delft (the Netherlands). Based on
the gained knowledge and skills acquired during the study, investigation was done on a problem often
worldwide encountered by civil engineers in practice: cracking and breakage of concrete armour units on
breakwaters.

Nina FOZEIN KWANKE - v -
MSc Thesis - Final report - November 2007

Nina FOZEIN KWANKE - vi -
MSc Thesis - Final report - November 2007

ACKNOWLEDGMENTS

First of all, I would like to thank all the members of my Graduation Committee (ir. W.J.
Bouwmeester, dr. ir. E.A.B. Koenders, dr. ir. A.L.A. Fraaij and Prof. dr. ir. J.C. Walraven) for the precious
support, guidance and time they took for me in order to let me achieve this part of my study under the best
circumstances. Thanks! I think I really learned a lot. Thanks also for always having showed interest
throughout the study and the time taken for further elucidation on subjects during specific courses.

I would also like to express my gratitude to Wim Heerens of the BAM Laboratory in Schiedam for
his precious help during the realization of the different experiments (although it was at really unusual hours
for a student!), ir. Bas Reedijk (DMC) for giving me the interest on the subject and the explications, ir. Frank
Nijland (DMC) for his valuable help in understanding the computer program FeC S, ing. Peter Prins and ing.
3
Rob van Berkel (DMC) always willing to help and to give me the supplementary information in order to get a
better insight in the practical circumstances in which civil engineering projects occur.

My recognition goes also to all the following companies/ institutions and their representatives for the
precious cooperation, interesting discussions, site visits and/or their willingness to provide me the necessary
material for realizing the experiments, documents, information, practical insight, explanations and/or
pictures for my research:

(cid:1) De Branding v/h J. Stolk (Joost Kuijs, L.J. (Rien) Stolk)
(cid:1) ENCI (Bart Brieffies and his team, Fred Gladdinnes, Mehmet Kilic)
(cid:1) Dienstkring IJmuiden (Frans de Haan, Hans Koppes)
(cid:1) CORUS (Teun Bakker, Hans Kobesen)
(cid:1) Liapor Lias B.V. (Harry Vos)
(cid:1) MEBIN (Jaap van Eldik)
(cid:1) MINELCO (Peter Duifhuis, Leon Hendriks)
(cid:1) ORCEM (Erik Langelaan, Ton Kapitein)
(cid:1) Rijkswaterstaat (RWS) Utrecht (Louis Donicie, Hans Janssen, Marinus de Vries,
Dick de Wilde)
(cid:1) TU Delft (Pierre C.J.Hoogenboom, Henk-Jan Verhagen)
(cid:1) Vliegasunie (Jan van de Berg)

Last but not least...To Oma, one of the most special persons in the world...To my other
grandma...To my grandpas who did not have the chance to see me graduating but probably are proud from
where they are... To my mum, always there... No matters what circumstances and always taking care... To
my dad who still believes his twins can grab the moon, although I try to persuade him of the contrary!!!!! To
my twin brother Tom, always my best friend ever... The one I probably laugh the most with...To Ndonfack
Bienvenu (waaay! lui-même!!! Le 1 des 1! ☺), who gave me his love for mathematics and the first I started
to bother with my questions!!!! To all my family and friends in Cameroon, the Netherlands, France or
elsewhere in the world...To Monica, Jocelyn, Victoria and Sontia, thanks for all the encouragements! To my
former high school teachers: Mrs. Ango Ela, Mrs. Dagba and Mrs. Yimga who accomplish an amazing work
despite not always easy working circumstances.... Thanks a lot for your support throughout the years!
Seeing former pupils graduate is probably one of the most beautiful awards! To Jo Kaf, Pascal, Ariane,
Piccard, Alain, Charles... For the deployed energy and for the interests they always have in what I am
doing...To all the ones I had a great time with during my student time at parties, dinners or at the
library!!!!....To all my roommates! And to all the special and interesting people I had the chance to meet
during travels or nearby, people who impress(ed) me because of their vision of life, their work or their
passions and who are an example for me or changed my perception of things....Zot’ (pa ka) sav’???!!!!
Peut-être, peut-être pas! Au futur… Tchin tchin! ☺☺☺

Nina J.C. FOZEIN KWANKE

Delft, November 2007

Nina FOZEIN KWANKE - vii -
MSc Thesis - Final report - November 2007

Nina FOZEIN KWANKE - viii -
MSc Thesis - Final report - November 2007

EXECUTIVE SUMMARY

Already since the ancient Egyptian, Phoenician, Greek and Roman cultures, breakwaters are
constructed worldwide in order to protect harbours, vessels in port, habitats or beaches against too high
waves. Of the different breakwaters that exist, one of the most basic types is the rubble mound breakwater
which in essence is a heap of stones consisting of a core of fine material covered by an armour layer of big
concrete elements. Mostly unreinforced, these concrete elements exist in different sizes and geometries
varying from massive concrete cubes to more complicated shapes like Dolos, Tetrapodes®, Accropodes® or
Xblocs®.
In the past, concrete armour units were mainly designed on their resistance against wave action:
the hydraulic stability. However, severe cracking and/or breakage of units which were part of the
breakwaters of Sines (Portugal), Arzew (Algeria) or Tripoli (Libya) revealed the importance of taking also the
structural integrity of the elements into account in order to avoid cracking and breakage.

The reaction of cement with water is exothermic and an unequal heating up and cooling down of the
massive units can lead to too high tensile stresses which lead to cracking in case the actual tensile strength
of the concrete is exceeded. Therefore, in this thesis, the main focus is on the production and hardening
process of the units. What internal mechanisms during the hardening stage might lead to cracking and/or
breakage of these colossal concrete armour units?

For six different concrete mixes, the thermal and strength properties were experimentally
determined and analyzed. The found results were used as input for a numerical hardening model which was
set up in FeC S®, an application built within the framework of the Finite Element program Ansys. The model
3
permits to give an estimation of the expected temperature rise, the eigenstress development as well as an
indication of the possible cracking trajectories. Using the probabilistic approach of Van Breugel, an
assessment on the risk of failure could be done at material level. A further analysis using the Mohr-Coulomb
criterion gave also the possibility to evaluate possible breakage patterns at element level. For a reference
mix, a parametrical study was done regarding the influence of specific hardening circumstances like type of
formwork, moment of removal or the type of mix used. In a last step, the implemented hardening model has
been used to analyze a specific case-study in the Netherlands where concrete armour units are severely
damaged.

The conducted research put in evidence the importance of maintaining the eigenstresses at low
values in order to reduce considerably the risk on cracking. The different parametrical studies showed that
different factors play a prominent role in getting a higher or lower risk of cracking, namely: the choice of a
specific type of formwork, the demoulding stage, the sizes of the elements and the casting and
environmental temperatures.
Moreover, the implementation of the model to other concrete mixes, revealed the importance of the
mix choice on the temperature and stress development. In case for instance fillers or binders are used to
replace partly the needed amount of cement, it is important to make a thorough study on their quality and
reactivity.

It can be concluded the elaborated hardening model gives a good indication of expected
temperature rise, stresses and cracking patterns and that the adopted calculation methods give a good
indication of weak and critical points in the elements and possible cracking and breakage patterns and
mechanisms. The results show high probabilities on crack occurrence and crack patterns that agree very
well with the block damages observed at the practical case in the Netherlands. Further investigations
regarding the influence of the shape, an analysis on micro scale of weak points in the structure and the
effect of the quality of binders are recommended to get a broader scope and to extend the hardening model
which was set-up. Moreover, it is of crucial importance designers integrate all together the aspects from
concrete technology and hydraulic/ coastal engineering point of views to come up with a final design for
concrete armour units of breakwaters.

Nina FOZEIN KWANKE - ix -
MSc Thesis - Final report - November 2007

TABLE OF CONTENTS
PREFACE..............................................................................................................................................................................................V
ACKNOWLEDGMENTS......................................................................................................................................................................VII
EXECUTIVE SUMMARY.......................................................................................................................................................................IX
LIST OF FIGURES.............................................................................................................................................................................XIV
LIST OF TABLES...............................................................................................................................................................................XV
LIST OF SYMBOLS AND ABBREVIATIONS...................................................................................................................................XVI
1 . GENERAL INTRODUCTION...........................................................................................................................................................1
1.1 INTRODUCTION.............................................................................................................................................................................1
1.2 PROBLEM DESCRIPTION................................................................................................................................................................1
1.3 PROBLEM ANALYSIS......................................................................................................................................................................1
1.3.1 Positioning the subject...................................................................................................................................................1
1.3.2 Further delimitation of the problem................................................................................................................................2
1.3.3 Objectives of the thesis..................................................................................................................................................3
1.4 RESEARCH METHODOLOGY...........................................................................................................................................................3
1.4.1 General..........................................................................................................................................................................3
1.4.2 Set-up of the report........................................................................................................................................................3
1.5 REFERENCES...............................................................................................................................................................................4
2 . BREAKWATERS IN GENERAL......................................................................................................................................................5
2.1 FUNCTION OF BREAKWATERS........................................................................................................................................................5
2.2 TYPES OF BREAKWATERS.............................................................................................................................................................5
2.2.1 Mound breakwaters........................................................................................................................................................5
2.2.2 Vertical or monolithic breakwaters.................................................................................................................................6
2.2.3 Composite breakwaters.................................................................................................................................................6
2.2.4 Special unconventional types.........................................................................................................................................7
2.3 RUBBLE MOUND BREAKWATERS....................................................................................................................................................7
2.3.1 General..........................................................................................................................................................................7
2.3.2 Description of a conventional rubble mound breakwater...............................................................................................7
2.3.3 Rock or concrete blocks on rubble mound breakwaters?..............................................................................................8
2.4 FAILURE MECHANISMS OF BREAKWATERS......................................................................................................................................9
2.4.1 Definition of failure.........................................................................................................................................................9
2.4.2 Failure mechanisms.......................................................................................................................................................9
2.4.3 Different types of concrete armour units......................................................................................................................10
2.4.4 Methods for the design of concrete armour layers.......................................................................................................11
2.5 DISCUSSION...............................................................................................................................................................................12
2.6 REFERENCES.............................................................................................................................................................................13
3 . NUMERICAL SIMULATION OF HARDENING CONCRETE.......................................................................................................14
3.1 CONCRETE: ORIGINS, HARDENING, MAIN STEPS FOR NUMERICAL SIMULATION...............................................................................14
3.1.1 Concrete as a construction material: Composition and fabrication..............................................................................14
3.1.2 Hardening concrete: the need of a numerical simulation tool......................................................................................14
3.1.3 General overview of the method of approach of a numerical simulation.....................................................................14
3.2 TEMPERATURE CALCULATIONS IN HARDENING CONCRETE............................................................................................................16
3.2.1 The differential equation of Fourier..............................................................................................................................16
3.2.2 The adiabatic and semi-adiabatic hydration curves.....................................................................................................19
3.2.3 The thermal properties of concrete..............................................................................................................................21
3.2.4 Effects of thermal boundary conditions on temperature development.........................................................................23
3.2.5 In summary..................................................................................................................................................................23
3.3 STRUCTURAL CALCULATIONS IN HARDENING CONCRETE...............................................................................................................24
3.3.1 Origins of the stresses in concrete...............................................................................................................................24
3.3.2 Calculation of strains and stresses occurring in concrete............................................................................................24
3.3.3 From stresses to probability of failure..........................................................................................................................25
3.3.4 In summary..................................................................................................................................................................26
3.4 DISCUSSION...............................................................................................................................................................................26
3.5 REFERENCES.............................................................................................................................................................................26
4 . THE COMPUTER PROGRAM FECS AS A NUMERICAL TOOL................................................................................................27
3

Nina FOZEIN KWANKE - x -