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Use of Macro Basalt Fibre Concrete for Marine
Applications
Ali Mohammadi Mohaghegh
Licentiate Thesis
KTH Royal Institute of Technology
Department of Civil and Architectural Engineering
Division of Concrete Structures
Stockholm, Sweden, 2016
TRITA-BKN. Bulletin 140, 2016 KTH School of ABE
ISSN 1103-4270 SE-100 44 Stockholm
ISRN KTH/BKN/B—140—SE SWEDEN
Akademisk avhandling som med tillstånd av Kungliga Tekniska högskolan
framlägges till offentlig granskning för avläggande av teknologie licentiatexamen
i Byggvetenskap, med inriktning mot Betongbyggnad fredagen den 10 june 2016
kl. 10.00 i sal B1, Kungliga Tekniska högskolan, Brinellvägen 23, Stockholm.
© Ali Mohammadi Mohaghegh, May 2016
PREFACE
I hereby express my sincere gratitude to my main supervisor, Professor Johan Silfwerbrand,
KTH in Stockholm, who has encouraged me, and given me thoughtful suggestions and
invaluable guidance throughout the research process. I also give my sincere gratitude to
Vemund Årskog, Associate Professor at NTNU in Ålesund, for valuable supervision and
comments. I would also like to thank Dr. Anniken Karlsen at NTNU in Ålesund for being a
supportive and professional supervisor. Furthermore, I wish to thank Adjunct Professor Malin
Löfsjögård, KTH, for reviewing the thesis. Pertaining to NTNU, I am grateful for you financing
my Ph.D. I am also grateful for the support of the Dean, Geirmund Oltedal. The contributions
from colleagues at the Faculty of Engineering and Natural Sciences, Hans Christian Giske,
Anders Sætersmoen, Andre Tranvåg and Siw-Helene Rydjord, in terms of developing necessary
experimental tools have been vital for accomplishing the experimental programme. I would
also thank the companies ReforceTech, Ulstein Betong Marine, Moldskred, Norcem, Mapei for
their valuable support and interest in the project. Finally, a warm gratitude goes to Lena and to
my family and friends for great support and encouragements during the writing process.
Norway, Ålesund, May 2016
Ali Mohammadi Mohaghegh
IV
V
ABSTRACT
Deterioration of concrete structures due to the corrosion of embedded steel is a well-known
universal problem. Norway with its numerous bridges, ports, offshore and floating structures
along its coastline, is also encountered with corrosion degradation. The harsh environment of
the Norwegian Sea regarding its low temperature, wind, and waves, makes the design and
construction of marine structures more demanding. In recent years, usage of sustainable
composite materials in the field of structural engineering has been rising. The usage of natural
fibre reinforced polymer materials in the form of reinforcement bars or macro fibres with a low
density, high strength, and excellent corrosion resistance, gives us better choices for the design
and construction of marine structures. Our knowledge about the fibre reinforced self-
compacting concrete has increased as a result of introducing it as a building material some
decades ago. However, more research is still needed when it comes to the application of new
types of fibres. This thesis is a result of this need, whereby the author has done two series of
experimental programmes regarding the subject. In the first series, the flow characteristics of
fresh state, conventional and self-compacting macro basalt fibre concrete were studied. In the
second series, mechanical properties of high performance and medium strength macro basalt
fibre concrete including the post-cracking behaviour, compressive strength and electrical
resistivity were in focus. The findings were presented in three appended papers and the
extended summary composing this thesis. Additionally, the thesis presents an overview of the
design procedure of floating concrete structures and the possibility of using macro basalt fibre
concrete via a case study. The author’s literature review shows that basalt fibres have an
adequate resistance against alkali environment of the concrete matrix and corrosive
environment of seawater.
Keywords: Concrete Barges, Reinforcement Corrosion, Floating Structures, Macro Basalt
Fibres, Self-Compacting Fiber Concrete
VI
VII
SAMMENDRAG
Nedbryting av armerte betongkonstruksjoner på grunn av armeringskorrosjon er et velkjent og
universelt problem. Norge med sine mange bruer, havner, offshorekonstruksjoner og flytende
konstruksjoner langs kystlinjen er også utsatt for korrosjonsproblem. Det aggressive miljøet i
Nordsjøen med lav temperatur, vind og bølger gjør konstruksjon og bygging av marine
konstruksjoner krevende. I senere år har bruk av bærekraftige komposittmaterialer for
konstruksjonsformål økt. Bruk av fiberarmerte polymermaterialer i form av armeringsstenger
eller makrofiber med lav egenvekt, høy styrke og god korrosjonsmotstand gir oss nye valg-
muligheter for konstruksjon og bygging av marine betongkonstruksjoner. Vår kunnskap om
fiberarmert, selvkomprimerende betong har økt siden den ble tatt i bruk som byggemateriale
for noen tiår siden. Men det er fortsatt behov for mer forskning når det gjelder anvendelse av
nye typer av basaltfiber. Denne oppgaven er et resultat av dette behovet, der forfatteren har
utført to forsøksserier innen dette emnet. I den første forsøksserien – om karakterisering av den
ferske betongens flytegenskaper – ble konvensjonell betong og selvkomprimerende betong med
makrobasaltfiber undersøkt. Den andre forsøksserien hadde fokus på mekaniske egenskaper så
som reststrekkfasthet etter opprissing, trykkfasthet og elektrisk motstandsevne for normal- og
høyfast basaltfiberbetong. Resultatene er presentert i tre vedlagte artikler som sammen med et
lengre sammendrag (”kappen”) utgjør avhandlingen. I tillegg til forsøksresultatene inneholder
avhandlingen en oversikt over dimensjoneringsmetoden for flytende betongkonstruksjoner og
mulighetene for å bruke fiber-betong gjennom et mulighetsstudie. Forfatterens litteraturstudie
viser at basaltfiber har tilstrekkelig motstandsevne både mot det alkaliske miljøet i betongen og
det korrosive miljøet i sjøvannet.
Nøkkelord: Betonglektere, Armeringskorrosjon, Flytende konstruksjoner, Makro basaltfibre,
Selvkomprimerende fiberbetong
VIII
IX
SAMMANFATTNING
Nedbrytning av armerade betongkonstruktioner på grund av korrosion av armeringen är ett
välkänt universellt problem. Norge med sina många broar, hamnar, offshoreanläggningar och
flytande konstruktioner längs kustlinjen är också utsatt för korrosionsproblem. Den aggressiva
miljön i Nordsjön med sin låga temperatur, vind och vågor gör byggandet av marina
konstruktioner krävande. De senaste åren har användningen av hållfasta kompostmaterial ökat
inom konstruktionstekniken. Användningen av polymermaterial armerade med naturliga fibrer
i armeringsstänger och som makrofibrer med täthet, hög hållfasthet och utmärkt
korrosionsskydd ger oss bättre valmöjligheter för dimensionering och byggande av marina
konstruktioner. Vår kunskap om den självkompakterande fiberbetongen har ökat som ett
resultat av att dessa material sedan någon tid tillbaka har blivit tillgängliga som
byggnadsmaterial. Men det finns ett fortsatt behov av forskning när det gäller användning av
nya typer av basaltfibrer. Denna uppsats är ett resultat av detta behov, varvid författaren
genomfört två försöksserier inom det aktuella området. I den första försöksserien – om
karakterisering av den färska betongens flödesegenskaper – studerades konventionellt gjuten
och självkompakterande betong innehållande makrobasaltfibrer. I den andra försöksserien låg
fokus på mekaniska egenskaper såsom verkningssätt efter uppsprickning, tryckhållfasthet och
elektrisk resistivitet hos normal- och höghållfast basaltfiberbetong. Resultaten har presenterats
i tre bilagda artiklar som tillsammans med en längre sammanfattning (”kappan”) utgör
avhandlingen. Utöver försöksresultaten innehåller avhandlingen en översikt över
dimensioneringsmetoden för flytande betongkonstruktioner och möjligheterna att använda
fiberbetong genom en fallstudie. Författarens litteraturstudie visar att basaltfibrer har tillräcklig
motståndskraft mot såväl den alkaliska miljön i betongen som den korrosiva miljön i
havsvattnet.
Nyckelord: Betongpråm, Armeringskorrosion, Flytande konstruktioner, Macro basaltfibrer,
Självkompakterande fiberbetong
X
XI
LIST OF PAPERS
Three appended papers are included in the thesis. They are referred to with their Roman
numbers in the text as follows:
I. An Initial Investigation of the Possibility to Use Basalt Fibres for More Durable
Concrete Structures in Norwegian Fish Farming
Mohammadi Mohaghegh, A., Silfwerbrand, J., Årskog, V., Proceedings XXII Nordic
Concrete Research Symposium, Reykjavik, Iceland, 2014, pp. 219-222.
II. Properties of Fresh Macro Basalt Fibre (MiniBar) Self-Compacting Concrete (SCC)
and Conventional Slump Concrete (CSC) Aimed for Marine Applications
Mohammadi Mohaghegh, A., Silfwerbrand, J., Årskog, V., Nordic Concrete Research,
Publication No. 52, Issue No. 1/2015, pp. 43-61.
III. Flexural Behaviour of Medium-Strength and High-Performance Macro Basalt Fibre
Concrete Aimed for Marine Applications
Mohammadi Mohaghegh, A., Silfwerbrand, J., Årskog, V., Submitted to RILEM Materials
and Structures Journal.
The papers were prepared in co-operation with the co-authors. The author of this thesis took on
the following paper responsibilities:
Paper I: The author performed the literature survey and the writing.
Paper II and Paper III: The author performed the literature survey and was responsible for the
planning and performing of the experiments as well as the writing.
XII
XIII
CONTENTS
PREFACE .................................................................................................................. III ABSTRACT ................................................................................................................ V SAMMENDRAG ....................................................................................................... VII SAMMANFATTNING ................................................................................................. IX LIST OF PAPERS ..................................................................................................... XI CONTENTS ............................................................................................................. XIII
CHAPTER 1 – Introduction .................................................................................................... 1 1.1 Background ...................................................................................................................... 1 1.2 Aims and Limitations ....................................................................................................... 2 1.3 Outline of the Thesis ........................................................................................................ 2
CHAPTER 2 – Basalt Fibre Reinforced Polymers (BFRPs) ................................................ 5 2.1 History of Using Basalt .................................................................................................... 5 2.2 Chemical Composition of Basalt Fibres ........................................................................... 5 2.3 Production Process of Continuous Basalt Fibres ............................................................. 6
2.4 Mechanical Properties of Basalt Fibres ............................................................................ 8 2.5 Basalt Fibre Reinforced Polymer Composites ................................................................. 9
2.6 Degradation in Seawater ................................................................................................ 10 2.7 Degradation in Alkaline Environment ........................................................................... 11
CHAPTER 3 – Fibre Concrete.............................................................................................. 13 3.1 Post-Cracking Behaviour of Fibre Concrete .................................................................. 13 3.2 A Brief Overview on the Design Methods of Fibre Concrete ........................................ 14
CHAPTER 4 – Floating Concrete Structures ...................................................................... 17 4.1 Floating Structures ......................................................................................................... 17
4.2 Loading and Design Principles of Floating Concrete Vessels ....................................... 19 4.3 Fatigue in Marine Concrete Structures ........................................................................... 22 4.4 A Case Study .................................................................................................................. 22
CHAPTER 5 – Summary of Methods .................................................................................. 25 5.1 Self Compacting Concrete Mix Design ......................................................................... 25 5.2 Experimental Methods for Fresh Concrete .................................................................... 25 5.3 Experimental Methods for Evaluation of Hardened Concrete ....................................... 26
CHAPTER 6 – Results and Discussions ............................................................................... 27 6.1 Results from the Evaluation of Fresh Fibre Concrete .................................................... 27
6.2 Results from the Assessment of Hardened Fibre Concrete ............................................ 28
CHAPTER 7 – Conclusions ................................................................................................... 29
CHAPTER 8 – Further Research ......................................................................................... 31
References ............................................................................................................................... 33
APPENDED PAPERS I-III
XIV
Use of Macro Basalt Fibre Concrete for Marine Applications
1
CHAPTER 1 – INTRODUCTION
1.1 BACKGROUND
Norway is famous for its long coastline (the coastline is 25148 km according to the Norwegian
Mapping Authority), with deep fjords and numerous islands. Because of the natural resources
of the country, including fish and oil, the lifestyle and economy of the Norwegian people is
connected to the Atlantic Ocean and the North Sea. The privilege of living at the seaside has
led to a developed network of infrastructures. There are more than 9000 harbours and many
bridges along the Norwegian coastline [1]. Also due to the national oil industry and the
aquaculture industry, with an income of 31.4 billion NOK annually and 21000 employees
(reported by the Norwegian Ministry of Trade, Industry, and Fisheries) many marine and
offshore structures have been installed in the Norwegian Sea.
August Gunderson, who developed the Tremie method for submarine casting of concrete,
started the construction of the new generation of coastal concrete structures in Norway [2].
Today most of the world’s offshore concrete structures are located in The Norwegian Sea [2].
Figure 1.1 shows the Troll platform, the largest offshore installation made of concrete ever
built.
Figure 1.1 – Troll platform, world’s largest offshore structure [3, 4].
However, due to the severe environment of the Norwegian Sea, the steel reinforcement in
marine concrete structures is subject to chloride-induced corrosion. The chloride-induced
corrosion could become a universal and costly problem. The investigation performed on
harbour and concrete barges by Årskog et al. [1] revealed that, the chloride ions reaches the
steel reinforcement while the probability of failure by de-passivation is more than 10%.
Use of Macro Basalt Fibre Concrete for Marine Applications
2
Therefore, to increase the durability and consequently the sustainability of concrete structures,
a suitable method should be applied for corrosion protection. Natural resources for producing
stainless steel grade for marine construction will be finished one day. Therefore, to prevent
future economic and environmental disasters, new materials and novel solutions should be used
to enhance the sustainability of structures [5]. New developments of fibre-reinforced polymers
(FRPs), introduce promising solutions for significant enhancement of sustainability of
structures especially in the harsh marine environment [5]. Environmental loads beside the self-
weight are the major payloads in marine structures. The use of FRP materials, with its low
density and high strength, could potentially save a lot of construction materials and natural
resources by reducing the corresponding stresses to the weight of structural elements [5].
Recently, basalt fibres as a natural, non-toxic material have been in the focus of many
researchers in the development of a new generation of eco-friendly FRPs [6, 7]. The need to
develop a new generation of environmental friendly cementitious composite materials
motivated this licentiate thesis. The thesis discusses the properties of lately developed macro
basalt fibre concrete for marine applications, especially pertaining to concrete barges.
1.2 AIMS AND LIMITATIONS
The thesis project was performed at the Norwegian University of Science and Technology
(NTNU) in Ålesund. Three aims were set for this project.
To study the possibility and advantages of using macro basalt fibre concrete in
marine structures. The literature survey was limited to the performance of reinforced
concrete in marine environments, the marine standard requirement for the design
and construction of fibre concrete and properties of basalt macro fibres (Paper I).
To develop an optimised method for producing self-compacting macro basalt fibre
concrete. Ulstein Betong Marine, Reforcetech Companies, Norcem and Mapei
supplied the necessary materials for this study. To have a better understanding of
the fresh state properties of fibre concrete, the concrete mixes were assessed
according to European standards (Paper II).
To investigate mechanical properties of macro basalt fibre for design purposes. The
post-cracking behaviour of medium and high strength concrete reinforced with a
limited range of fibre content has been evaluated based on the related standards
(Paper III).
1.3 OUTLINE OF THE THESIS
The thesis content is based on a literature survey and an experimental programme presented in
the three appended papers. As an introduction to the study, the history of using basalt as a
construction material, its production process, and corresponding properties of basalt fibres are
presented in Chapter 2. In Chapter 3, some of the design aspects of fibre concrete alongside
with an introduction to basalt fibre concrete are discussed. Chapter 4 contains a review of the
loading and design procedure of marine floating structures, with a particular focus on concrete
barges. In addition, the design considerations about the use of fibre concrete for marine
Use of Macro Basalt Fibre Concrete for Marine Applications
3
applications are discussed in the same chapter. Chapter 5 gives an overview of fibre self-
compacting concrete mixture design and the experimental methods used to evaluate the
properties of fresh and hardened concrete. The results are presented in Chapter 6 and
conclusions are drawn in Chapter 7. In the last chapter, Chapter 8, a list of proposals for further
research is presented.
Use of Macro Basalt Fibre Concrete for Marine Applications
4
Use of Macro Basalt Fibre Concrete for Marine Applications
5
CHAPTER 2 – BASALT FIBRE REINFORCED
POLYMERS (BFRPS)
2.1 HISTORY OF USING BASALT
Basalt in the form of stone blocks has been used as a building material since the time of the
Roman Empire [8]. Basalt with its shiny appearance is one of the most common types of rock
in the world [8]. The basalt grains are finer than in granite, and of the two, basalt has a higher
magnesium and iron content [8]. The density of basalt is between 2.8 and 2.9 gr/cm³ [8].
The idea of using basalt stones to produce fibres was presented by the American scientist,
French Paul Dhe in 1923 [9]. In the 1960’s basalt fibres became a research topic for the
development of military and aerospace grade materials by both American and Soviet scientists
[9]. While American scientists closed their project in the 70’s due to a new proposal of using
glass fibres, the Russians continued their research and development activities [9]. The first
industrial production line of continuous basalt fibres was installed in Ukraine in 1985 [6]. In
1991, the research results of the Kiev study were declassified and published for public usage
[9]. Due to the availability of basalt resources several countries like Japan, South Korea, China,
Austria and the USA, are working on continuous basalt fibre (CBF) technology [8].
Pertaining to the high strength, thermal and corrosion resistance, basalt fibres are used for a
variety of applications. Basalt fibres have been applied as heat and sound insulations, filtering,
fitting, reinforcing of the polymer composites, fibre concrete, human and environmental
protection against radioactive wastes and many other applications [10, 11].
2.2 CHEMICAL COMPOSITION OF BASALT FIBRES
Basalt is the name of a verity of volcanic rocks that can be easily found all over the world [9].
Basalt is chemically rich in silicon oxide; however, it also consists of Al2O3, Fe2O3, FeO, CaO
and MgO [7]. The content of silicon oxide specifies the properties of the raw materials [9]. For
silicon oxide up to a level of 42%, the material is alkaline, for the range of 43% to 46%, it is
mildly acidic and while over 46% the material is acidic [9]. Only the acidic basalt sources with
a low content of CaO and MgO and high content of SiO2 and Al2O3 are suitable for producing
basalt fibres [11]. Basalt fibres are composed of pyroxene, clinopyroxene, olivine and
plagioclase, however; the percentage of each element varies for different mineral resources [7].
Fig. 2.1 describes various phases of basalt associated with its silicate content. Table 2.1 shows
the chemical composition of CBF.
Use of Macro Basalt Fibre Concrete for Marine Applications
6
Figure 2.1 – Different phases of basalt mineral based on the silicate content [7].
Table 2.1 – Chemical composition of continuous basalt fibres (CBF).
Component Content [wt.%]
[10] [7] [7]
SiO2 52.8 43.3-47 42.43-55.69
Al2O3 17.5 11-13 14.21-17.97
Fe2O3 10.3
Use of Macro Basalt Fibre Concrete for Marine Applications
7
Additionally, holding the molten materials at a temperature of 1447 ºC for two hours will
remove the gases in the melt and this is an important phase to ensure the production of high-
quality fibres [13].
Figure 2.2 – Graph of the continuous basalt fibre production line [6].
Figure 2.3 shows the tensile strength of fibres as a function of the melt holding time at the
temperature of 1447 ºC. The treatment of the molten material by an electromagnetic field,
reduces the size of crystals and consequently increases the tensile strength of the fibres [13].
Figure 2.4 shows the microstructure of basalt fibres before and after electromagnetic treatment.
After the treatment, molten basalt passes through platinum-rhodium spinneret feeders by use of
hydrostatic pressure [9]. Finally, a winder is used to make a spool of continuous basalt fibres
[10]. The diameter of filaments produced by this method is in the range of 10-20 μm [7].
Figure 2.3 – Relationship between tensile strength of basalt fibres and melt holding time [13].
Figure 2.4 – The structure of basalt fibres (a) before and after (b) electromagnetic treatment [13].
Use of Macro Basalt Fibre Concrete for Marine Applications
8
Table 2.2 – The effect of melting temperature on the mechanical properties of continuous basalt fibres (CBF) [9].
Melting temperature (°C) Tensile strength (MPa) Modulus of elasticity (GPa)
1220 1300 78
1380 2230 90
The mechanical properties (tensile strength and modulus of elasticity) of continuous fibres are
dependent on chemical bonds of components [12]. The speed of attenuation spinning can
directly affect the chemical bonds between the oxygen and other metallic elements of uni-
dimensional, pseudo-amorphous fibre structure [12]. By increasing the attenuation speed (20-
80 m/s), due to reduction of the diameter of fibres, the number of Al atoms in the structure
increases [12]. The Al atoms have the strongest bonding strength with the oxygen atoms [12].
Consequently, reduction of the diameters leads to an increase in the strength and flexibility of
fibres [12].
At a low attenuation speed, the O-Al bonds are more prone to form three-dimensional crystals
than amorphous structures [12]. Hence, reduction of attenuation rate leads to a weak three-
dimensional structure [12].
2.4 MECHANICAL PROPERTIES OF BASALT FIBRES
Basalt fibres show a high level of strength, high modulus of elasticity and elastic behaviour [6].
The properties of continuous basalt fibres are comparable corresponding ones of E-glass fibres
[6]. The mechanical properties of CBF are associated with the quality of raw materials and its
production process [6]. Accordingly, the properties of basalt fibres are described differently in
various references. Figure 2.5, Figure 2.6, Table 2.3, and Table 2.4 present comparative data
between a variety of fibres. Figure 2.5 shows the stress-strain curve of continuous basalt fibres
in comparison with short basalt fibres and glass fibres. Basalt fibres demonstrate a rigid
behaviour without a plastic zone [6].
Figure 2.5 – Stress-strain diagram of basalt and glass fibres [6].
Use of Macro Basalt Fibre Concrete for Marine Applications
9
Figure 2.6 shows the result of a tensile test on a single filament of basalt. The sample had a
diameter of 10.6 µm, the length of 20 mm and a density of 2.593 g/cm3 [14]. The test was
performed by the use of a 5 N actuator. The loading rate was 1 mm/min.
Figure 2.6 – The test specimen and the result of tensile test [14].
Table 2.3 shows a comparison between the test result of a basalt filament and the tensile strength
of carbon and S-glass fibres.
Table 2.3 – Mechanical properties of basalt fibres in comparison with carbon and S-glass fibres [14].
Property Basalt Carbon Glass (S-glass)
Tensile strength (MPa) 992.4 3528.1 1798.3
Modules of elasticity (GPa) 76
Elongation failure (%) 2.56
Table 2.4 shows the physical properties of basalt fibres in comparison to other types of fibres.
Table 2.4 – Physical properties of basalt continuous fibres in comparison with variety of fibres [10].
Property Continuous basalt Fibre Glass Fibre (E-glass) Glass Fibre (S-glass) Carbon Fibre
Breaking strength (MPa) 3000-4840 3100-3800 4020-4650 3500-6000
Modules of elasticity (GPa) 79.3-93.1 72.5-75.5 83-86 230-600
Elongation failure (%) 3.1 4.7 5.3 1.5-2.0
Fibre diameter 6-21 6-21 6-21 5-15
Working temperature (°C) -260 ~ +700 -50 ~ +380 -50 ~ +380 -50 ~ +700
2.5 BASALT FIBRE REINFORCED POLYMER COMPOSITES
A composite material consists of two or more phases, and gives a better performance than its
compounds [15]. Usually, the composites are made of two compounds; the weaker continuous
phase is identified as the matrix and the stronger phase is known as the reinforcement [15]. In
recent years, thermoset polymer matrix as epoxy, polyester and vinyl are used for the production
of basalt fibre composites [6].
Czigany et al. [6] carried out a comparative study on mechanical properties of composites
composed of basalt fibre with a weight content of 30% and matrixes of vinyl ester and vinyl
ester/epoxy hybrid resins [6]. The experimental results show that both strength and toughness
could be enhanced by using a hybrid resin of vinyl ester/epoxy with the ratio of 1 to 1 [6].
The study performed by Colombo et al. [6] on epoxy and vinyl ester-based basalt fibre
composites produced by vacuum infusion process shows that BFRP produced with epoxy has
higher values of mechanical properties than vinyl ester composite. The stress-strain relationship
Use of Macro Basalt Fibre Concrete for Marine Applications
10
of different types of fibre-reinforced polymers, presented in Figure 2.7, shows that basalt fibre
composite has a higher tensile strength in comparison with E-glass fibre composite.
Figure 2.7 – The stress-strain relationship of several types of FRPs [5].
Basalt fibre reinforced polymer (BFRP products) is commercially available in different forms
for different applications. The main objective of this thesis work is to study the properties of
macro basalt fibre concrete.
2.6 DEGRADATION IN SEAWATER
The marine sector is one of the fields whereby BFRP products can be used as structural
elements. To study the long-term behaviour of BFRPs in marine environments, Bin Wei et al.
[16] launched an experimental programme for a period of 90 days. Artificial seawater was used
for the treatment of basalt and glass fibre reinforced epoxy resin laminates [16]. Mass gain,
tensile and flexural strength of the specimens were used for the evaluation of the long-term
performance of materials [16]. Additionally, an electron microscopy technique was used to
study the fracture mechanism of the materials. Figure 2.8 shows the relationship between the
immersion time in the seawater and tensile strength of the composites. The results revealed that
the reduction of the tensile strength has a direct relation to the exposure time of materials in the
seawater [16]. Hence, after 90 days BFRPs still had a higher tensile strength [16].
Use of Macro Basalt Fibre Concrete for Marine Applications
11
Figure 2.8 – The tensile strength of basalt and glass fibre reinforced polymers after treatment as a function of
immersion time [16].
Figure 2.9 shows a possible schematic picture of corrosion mechanism in BFRPs. During the
immersion, Cl-, Na+ ions and H2O, O2, CO2 molecules penetrate to the matrix through the
existing defects in the polymer structure [16]. Simultaneously alkaline ions leach from the
basalt fibre and may form a hydroxide layer in the interfaces [16]. These changes in the
microstructure of interface make it prone to crack propagation and fracture at a lower load [16].
The main difference between BFRP and GFRP degradation mechanism is due to the reaction
between Cl- and Fe+2 ions [16]. Due to the similar stability of basalt glass fibre polymers,
reduction of Fe+2 ions could lead to a higher durability of BFRPs in the sea water [16].
Figure 2.9 – A schematic of corrosion mechanism in BFRPs [16].
2.7 DEGRADATION IN ALKALINE ENVIRONMENT
Since 1981, many scientists have investigated the alkaline resistance of basalt fibres [17, 18].
A summary of the results of their research is presented in Paper III. Hence, this Section presents
the development of new methods for increasing the alkali resistance of basalt fibres by use of
zirconia.
The nature of failure mechanism characterises the post-cracking behaviour of fibre concrete.
Debonding and sliding of fibres as failure modes in fibre concrete occur in the interfacial zone
between cement matrix and fibres [19]. In basalt and glass fibre concrete, the interfacial region
Use of Macro Basalt Fibre Concrete for Marine Applications
12
not only control friction and bonding but also protect the fibres facing the corrosive
environment of cement matrix [19]. It is possible to improve the alkali resistance of basalt
fibres in cement matrix by modifying the chemical composition of fibres using zirconia
additives or deposition of zirconia as a protective layer [19, 20].
The investigation performed by Lipatov et al. [21, 22] shows that basalt fibre containing
zirconia had a comparable performance with AR-glass fibres. Moreover, the results revealed
that highest alkali resistance was obtained by adding 5.7 weight percentage of ZrO2 [22].
Rybin et al. [20] developed a sol-gel approach for deposition of a zirconia coating on the surface
of basalt fibres. The formation of Zr-O-Si chemical bonds lead to a strong cohesive between
the coating layer and the fibres [19, 20]. The SEM analysis shows that the alkali environment
of concrete matrix is less effective on the coated fibres in comparison with as received basalt
fibres [19, 20].
Use of Macro Basalt Fibre Concrete for Marine Applications
13
CHAPTER 3 – FIBRE CONCRETE
Fibre concrete has the potential to be a predominant structural material in the future thanks to
its good performance. Due to its attractive properties, many researchers for e.g. [23-29] have
investigated different aspects of fibre concrete. Quite a few investigations have been carried out
on the effect of various components of the concrete mix, as well as the change of fibre
characteristics on the rheology. Additionally, mechanical properties of fibre concrete, the effect
of fibre distribution on the mechanical properties of hardened concrete, and the structural design
methods among others have been subject to research. The study of the different aspects of fibre
concrete is not a focus of this thesis. Hence, only brief summary of the design methods of fibre
concrete based on the fib Model code 2010 [30] and RILEM is presented in this chapter.
3.1 POST-CRACKING BEHAVIOUR OF FIBRE CONCRETE
Concrete is a common construction material, and it is well known for its high compressive
strength and its low tensile toughness. Using the discontinuous fibres as a reinforcing
component in the concrete matrix leads to a great increase of toughness and tensile capacity of
concrete [31-33]. The fibres begin to be activated as soon as the concrete starts to crack.
The fibres improve the post-cracking response of fibre concrete by participating in the tensile
load bearing capacity by bridging the cracks and changing the cracking type from macro cracks
to micro cracks [33]. Depending on the fibre type and content, different fibre concrete show
different ductility levels and post-cracking behaviour, Figure 3.1 shows various categories of
fibre concrete based on the Naaman and Reinhardt classification [34]. The post-cracking
performance of fibre concrete is a function of fibre volume fraction. Based on the Italian guide
[35] for the design and construction of fibre concrete, the minimum volume fraction of fibres
shall not be less than 0.3%. In small fibre volume fractions, fibre concrete shows a strain-
softening post-cracking behaviour [35]. The strain hardening behaviour is obtainable when the
fibre content is more than a particular value [36]. This value is a function of several variables
including the fibre type, fibre aspect ratio, strength of concrete matrix, bonding strength of the
interface between fibres and concrete, etc. [36].
The study performed by Doo-Yeol et al. [26] about the post-cracking behaviour of normal and
high strength steel fibre concrete shows that there is a direct relation between the volume
percentage of the fibres and post-peak ductility and flexural strength of fibre concrete.
Use of Macro Basalt Fibre Concrete for Marine Applications
14
Chang et al. [36] carried out an investigation regarding the influence of fibre type on flexural
behaviour of fibre concrete. The results unveiled that to obtain a strain-hardening behaviour,
use of both high strength concrete and large fibre aspect ratio is necessary [36].
Figure 3.1 – Performance based classification of fibre concrete [34].
3.2 A BRIEF OVERVIEW ON THE DESIGN METHODS OF FIBRE CONCRETE
This Section provides a brief summary of some items of interest for basalt fibre concrete from
fib, CEN, and RILEM. According to fib model code 2010 [30], the conventional reinforcement
could be replaced partially or entirely by fibre concrete. For the design purposes, the residual
Use of Macro Basalt Fibre Concrete for Marine Applications
15
flexural tensile strength (fR) of fibre concrete could be determined using a three point bending
test [30, 35]. The fR values are evaluated using the load-crack mouth opening displacement
(CMOD) relationship [30, 35]. The definition of post-cracking parameters of fibre concrete
according to the RILEM TC-162TDF [37, 38] and NS-EN 14651:2005 [39] are presented in
Paper III, Section 4. The fibre concrete could be used as replacement for the conventional
reinforcement at ultimate limit state only when the following equations are satisfied [30]:
𝑓R1k
𝑓lk > 0.4 Eq. 3.1
𝑓R3k
𝑓R1k > 0.5 Eq. 3.2
where, fRik (i = 1, 2, 3, 4), is the characteristic residual flexural tensile stress at CMOD = 0.5,
1.5, 2.5 and 3.5 mm respectively. In addition, fLK is the characteristic residual stress
corresponding to the limit of proportionality (LOP).
Table 3.1 and Figure 3.2 present characteristic values of 43 mm macro basalt fibre concrete,
which is calculated based on the experiments performed by Reforcetech Company [40].
According to Eq. 3.1 and Eq. 3.2, the concretes with a fibre volume fraction of more than 2.5%
volume fraction have the potential to be used in the structural elements.
Table 3.1 – Characteristic values of post-cracking parameters for 43 mm macro basalt fibre concrete (Courtesy
of Reforcetech Company) [40].
FVF (%) fcck fLk fR1k fR2k fR3k fR4k fR3k/fR1k fR3k/ fLk class
0.3 25 3.79 0.67 0.73 0.51 0.35 0.76 0.14 b
2.5 25 5.26 7.48 7.65 6.69 5.83 0.89 1.27 b
4.0 25 5.51 9.33 9.63 9.19 8.72 0.98 1.67 c
0.3 50 4.43 1.11 1.05 0.90 0.72 0.81 0.2 b
2.5 50 5.23 8.10 8.33 7.49 6.95 0.92 1.43 c
4.0 50 4.76 8.88 10.30 9.47 8.16 1.10 1.99 d
Figure 3.2 – Relationships between the residual tensile stress and CMOD of 43 mm macro basalt fibre concrete
with variety of concrete strength and fibre volume fraction (Courtesy of Reforcetech Company) [40].
0
2
4
6
8
10
12
0 0,5 1 1,5 2 2,5 3 3,5 4
Res
idu
al T
ensi
le S
tres
s (M
Pa)
CMOD (mm)
C25 - 0.3 Volume (%)
C25 - 2.5 Volume (%)
C25 - 4.0 Volume (%)
C50 - 0.3 Volume (%)
C50 - 2.5 Volume (%)
C50 - 4.0 Volume (%)
Use of Macro Basalt Fibre Concrete for Marine Applications
16
fib model code 2010 [30] suggests a simplified linear post-cracking model for the structural
design purposes. Based on the suggested model, serviceability tensile strength fFts and ultimate
tensile strength fFtu of fibre concrete can be calculated as follows:
fFts= 0.45 fR1 Eq. 3.3
fFtu = fFts – 𝑊u
𝐶𝑀𝑂𝐷3 (fFts - 0.5 fR3 + 0.2 fR1) = 0.45 fR1 –
𝑊u
2.5 (0.65 fR1 - 0.5 fR3) ≥ 0 Eq. 3.4
Table 3.2 – The characteristic values for residual tensile strength of 43 mm macro basalt fibre concrete according
to fib model code 2010. FVF (%) fcck fFtsk fFtuka fFtudb
0.3 25 0.3 0.19 0.13
2.5 25 3.37 2.46 1.64
4.0 25 4.2 3.32 2.21
0.3 50 0.5 0.34 0.22
2.5 50 3.65 2.74 1.82
4.0 50 4 3.38 2.25 a By considering wu = 1.5 mm, fFtuk is the characteristic value of residual tensile strength [35]. b 𝑓Ftud =
𝑓Ftuk
1.5 is the design value of residual tensile strength [30, 35].
Only fibre concrete with strain hardening behaviour is allowed to be used for the members
without conventional longitudinal and shear reinforcement [35]. The principle tensile stress, σ1,
shall be less than fFtud [35].
In marine structures, according to the DNV [41], for the serviceability limit state design for
steel reinforcement, the crack width should not exceed 0.4 mm for submerged elements and
0.30 mm for the tidal, splash and spray zone.
Use of Macro Basalt Fibre Concrete for Marine Applications
17
CHAPTER 4 – FLOATING CONCRETE STRUCTURES
Since the primary objective of this thesis was to study the use of basalt fibre concrete for marine
applications, Section 4.1 is reviewing the worldwide experiences and advantages of using
floating concrete structures. Moreover, Section 4.2 presents a brief summary of loading and
design principle of floating vessels. The aquaculture is an important industry on the west coast
of Norway. Employing the concrete barges as feeding and control facilities for fish farming is
popular in Norway. Accordingly, in Section 4.3, the possibility of using macro basalt fibres as
a replacement for the conventional steel reinforcement or as a part of hybrid system in
combination with BFRP rebars was studied for a small concrete barge.
4.1 FLOATING STRUCTURES
During the 20th century, the quality of human life has been changed that leads to unexpected
expansion in the world's population. Presently the human population is over seven billion
people [42]. Since the beginning of history, living on the coastline close to the ocean has been
attractive for humans. More than half of the world’s population are living within 200 kilometres
of coastline (reported by UN Atlas of the Oceans) [43]. Due to the increase of the urban
population, novel methods are needed for accommodating the growing population.
Development of the settlement areas by use of land reclamation is a conventional method in
Japan, The Netherlands, Singapore and some other countries [44]. However, drawbacks of this
approach, including the necessary time (2-5 years) for the soil consolidation prior the beginning
of construction process, its environmental effect by destroying the life in the seabed, etc. [44].
lead to the necessary developing and utilizing of new methods. The floating structures have
been used from the ancient times. In 480 BC, during the invasion of Greece, the Persian king
Xerxes built a floating bridge in Dardanelles Strait, Turkey [44]. A new concept of large floating
structures for the living applications is one of the possible solutions. In comparison with
reclamation, the floating structures are less disruptive to the environment and more flexible
regarding the mobility [44]. Additionally, there is a possibility of relocation to a new site [44].
In cities like London, the high land prices are an economic motivation to use floating houses
instead of inland residential buildings. Increase in the sea level because of global warming and
the probability of floods in some parts of Europe and the world make the use of floating
structures more interesting.
The idea of using reinforced concrete for construction of floating vessels is attributed to Joseph
Louis Lambot, who constructed a concrete boat, reinforced by iron bars in 1848 [45, 46]. N. K.
Fougner built the first self-propelled concrete ship that was launched in 1917 in Norway [45].
Use of Macro Basalt Fibre Concrete for Marine Applications
18
Because of shortage of steel during the World War I, concrete ships were built in U.S. [45]. The
first pre-stressed concrete barge was also built by U.S. Navy built in 1943 [45].
Since 1917, concrete floating structures were used worldwide for a variety of applications; for
residential purposes, electrical power plants, water and wastewater treatment plants, fish
farming feeding and storage facilities, floating dry docks, oil production plants, liquefaction
and LPG storage terminals, etc. [45, 47, 48]. Based on the DNV rules for classification of ships,
barges are defined as vessels without self-propulsion system [49]. Therefore, for transit or
transportation, an external propulsion system is pre-assumed [49]. Figure 4.1 shows a concrete
barge designed for the fish farming purposes. The development of using concrete for floating
structures is owing to its unique properties and advantages.
Figure 4.1 – Fish farming feeding and storage facilities (Courtesy of Ulstein Betong Marine Company).
The main advantages of using concrete instead of steel in floating vessels are categorized as
follows [45, 47]:
The concrete with a correct composition is almost a maintenance free material with a
high durability.
Concrete in general is a fire resistance material. Steel loses its structural capacity when
the temperature increases to a certain extent. While, concrete structures usually satisfy
the requirement of the standards regarding the fire resistance design. Therefore, concrete
structures are qualified for 60 percent reduction of insurance rate for the fire endurance
and prolonged indemnity of the structure.
Due to its sparks free and thermal properties, it has a great potential for storing the
highly flammable and hygienic liquids.
Lower construction cost in comparison with the similar steel vessel.
Lower maintenance cost and downtime of the structure; concrete barges can be designed
for a service life of up to 200 years, like floating N’Kossa oil processing plant.
Therefore, concrete is a trustable replacement of steel for offshore construction, see
Table 4.1.
Due to corrosion resistance and low thermal conductivity, the pollution from the
concrete vessels is minimum.
The concrete floating structures can carry heavy topside loading.
Use of Macro Basalt Fibre Concrete for Marine Applications
19
In comparison with a steel hull, a concrete hull has a better performance in the sea. Due
to their higher weight and depth, concrete hulls have better motion characteristics.
Because of the high fatigue resistance of reinforced concrete, there is a possibility of
extension in the design life from 30 years to 50 years or more without extra cost.
Table 4.1 – Economical comparison between concrete and steel hulls, after [45, 47].
Concrete floating
structure
Year of building Saving in the
construction cost
Annual saving in
maintenance cost
Downtime of
structure
19 pre-stressed
concrete hulls
1964-1966 16% saving in built
cost compared with
similar steel hull
1/3 of the
maintenance cost of
a similar steel hull
1/4 of the
downtime of a
similar steel hull
4.2 LOADING AND DESIGN PRINCIPLES OF FLOATING CONCRETE VESSELS
Floating structures operate based on the buoyancy principle [50]. The immersion occurs,
because of the upward thrust with an equal magnitude to the weight of the displaced liquid [50].
Wave-induced loads are the predominant environmental loads on the floating structures [50].
The sea-state is usually described by use of significant wave height and the peak wave period,
which are the continuous function of time [50]. These parameters are functions of different
variables such as wind velocity and wind direction [50]. It is proved that the extremely irregular
and random state of the sea surface could be defined using a combination of regular wave series
with different characteristics. Pierson et al. [50] demonstrated that the sea surface could be
represented using numerous regular sinusoidal waves with a variety of frequencies. Pierson et
al. also suggested Eq. 4.1 for the surface elevation of the sea [50].
ℎ(𝑥, 𝑡) = limN→∞
∑ 𝑎𝑙 sin(− 𝑘𝑙𝑥 − ɷ𝑙𝑡 + ɵ𝑙)∞
𝑙=1 Eq.4.1
In this equation, 𝑎 is the wave amplitude, k is the wave number, ɷ is the wave frequency, and
ɵ is the wave angle. It should be highlighted that only a small portion of the wave frequencies
affects the motion, and consequently, the exerted loads on the floating structures [50].
Figure 4.2 shows the six degrees of freedom of a floating structure. Suitable mooring may
restrain the degrees of freedom.
Figure 4.2 – Six degrees of freedom in a floating vessel [51].
Ships, floating and offshore structures in the ocean are subjected to various load patterns with
different magnitudes [52]. Accordingly, the structural designers need to know the principles of
the static and dynamic stability and the load characteristics concerning the floating structures
Use of Macro Basalt Fibre Concrete for Marine Applications
20
[52]. The best method to categorize the loads acting on the vessel’s hull structure is as follows
[52]:
Longitudinal loads
Transverse loads
Local loads
The vessel’s hull structure behaves like a beam [52]. The longitudinal loads are the loads
involving the moments, shear and torsional forces that are acting on the main hull structure
[52]. The dynamic longitudinal loads generated by waves should be calculated for both sagging
and hogging conditions [52]. Figure 4.3 shows a schematic picture of sagging and hogging of
a floating vessel [45].
Figure 4.3 – Schematic picture of sagging and hogging of a floating vessel [53].
The transverse loads can be categorized as follows [54]:
Hydrostatic and hydrodynamic pressures
Weight of the structural elements and cargo
Inertia forces produced by the motion of the floating structure
Impact loads
The local loads are the loads affecting the local structural elements. Figure 4.4 shows a
schematic picture of the transverse loads (external pressures in sagging and hogging conditions)
on the cross section of a vessel.
Figure 4.4 – Schematic picture of the eternal pressure on the cross section of a vessel [53].
Use of Macro Basalt Fibre Concrete for Marine Applications
21
In the design process of concrete floating structures, accidental loads, construction loads,
thermal loads, etc. should also be taken into account [45]. The environmental (wave-induced)
loads can be determined through a time-frequency domain, dynamic approach or a quasi-static
procedure [45]. Hence, it is adequate to use the quasi-static method for most of the purposes
[45]. DNV also follows a quasi-static approach. The moment and global shear forces should be
determined in both still water and transient conditions [52]. Figure 4.5 summarizes the
structural design procedure of concrete barges according to the DNV rules.
Figure 4.5 – Structural design procedure of concrete barges according to the DNV rules [41, 49, 55].
Figure 4.6 shows the distribution of the loads and resultant forces of a floating vessel in still
water condition. For the design purposes, the internal forces should be determined for both still
water and wave-induced forces along the hull girder [45].
Figure 4.6 – Schematic of the loads and the distribution of internal forces in a floating vessel [53].
Wave-induced bending
moments and shear forces
caused by waves
Bending moments and shear
forces in still water condition
DNV rules for ships: Pt.5 Ch.7 Sec.14, Pt.3 Ch.1 Sec.5 B202, and Pt.3 Ch.1 Sec.5 B203
Serviceability data, geometry,
arrangement and loading
manual
FEM analysis and concrete design
according to DNV-OS-C502
Use of Macro Basalt Fibre Concrete for Marine Applications
22
4.3 FATIGUE IN MARINE CONCRETE STRUCTURES
Due to the cyclic nature of loads in the marine environment, the floating and offshore structures
are more prone to fatigue damages in comparison with inland structures [56]. In the design
process of marine structures, both low and high cycle loads should be considered [57].
Nevertheless, the high amplitude low-frequency loads, which produce the cracks that can be
extended by lesser amplitude loads, are the major fatigue risk [57]. A simulated fatigue test
with a frequency of less than 3 Hz is used for evaluation of fatigue performance of concrete
elements in the air and seawater [57]. The results indicated that continuous hydration process
and accumulation of salt lead to the crack blocking [57]. Therefore, fatigue life of concrete
elements in seawater is higher in comparison with air [57].
4.4 A CASE STUDY
This Section presents a review of a feasibility study concerning the macro basalt fibre concrete
(BFC) to be used as a structural material in concrete barges. Figures 4.7 and 4.8 show the
geometry of the selected concrete barge as a case study. The density of basalt macro fibre
concrete (approximately 2400 kg/m3, see Paper III, Table 7), is lower than the density of steel
reinforced concrete (around 2550 kg/m3). Therefore, by use of basalt macro fibre concrete, due
to the reduction of total weight, based on the buoyancy and stability calculation, the height of
the barge could be reduced to 3.25 m instead of 3.62 m. The thickness of external walls, internal
walls and the slabs are respectively 0.22 m, 0.15 mm and 0.2 meters.
Figure 4.7 – Side views of the case study barge (Courtesy of Moldskred Company).
Figure 4.8 – Topside plan and cross-section of the case study barge (Courtesy of Moldskred Company).
Use of Macro Basalt Fibre Concrete for Marine Applications
23
The environmental loads and global moments were calculated according to the DNV
procedures. The results of finite element analysis expressed as principle tensile stresses are
summarised in Table 4.2 and Table 4.3.
Table 4.2 – Principle stresses in mid span of structural elements.
Structural elements Load combinationa σ1 (MPa)
Bottom slab ULS 2.4
Deck slab ULS 1.19
External walls ULS 2
Internal walls ALS 1.8 a ULS (Ultimate Limit State); ALS (Accidental Limit State).
Table 4.3 – Principle stresses in the connection zone between structural elements.
Structural elements Load combinationa σ1 (MPa)
Bottom slab ULS 3.8
Deck slab ULS 1.8
External walls ULS 1.8
Internal walls ALS 2 a ULS (Ultimate Limit State); ALS (Accidental Limit State).
The comparison of the FEM results presented in Table 4.2 and Table 4.3 with allowable design
stresses (Table 3.2) show that fibre concrete could be used as the main structural material in the
concrete barge. However, for the construction joints and partially for the bottom slab, additional
BFRP rebars are needed.
Use of Macro Basalt Fibre Concrete for Marine Applications
24
Use of Macro Basalt Fibre Concrete for Marine Applications
25
CHAPTER 5 – SUMMARY OF METHODS
5.1 SELF COMPACTING CONCRETE MIX DESIGN
Considering that, the aim of my study was to investigate the fresh state and mechanical
properties of macro basalt fibre concrete intended for marine applications; two experimental
programmes were designed. The first part of the study focused on developing an optimised self-
compacting concrete (SCC), i.e. a concrete that satisfies the requirements of offshore
applications.
The Japanese scientist, Ozawa in 1988 [58], introduced SCC. Since then, various aspects of
SCC have been investigated. Additionally, SCC was used in different projects worldwide. The
flow ability and passing ability of SCC are the two most important characteristics that
differentiate it from conventional slump concrete (CSC). According to the particle-matrix
model, both types of concrete consist of two phases, aggregate (particles > 125 μm) and matrix
(particles < 125 μm) [59, 60]. Based on this definition, SCC is a matrix-dominated material [59,
60].
Det Norske Veritas (DNV) OS-C502 standard [41] for the design and construction of offshore
concrete structures was used as the main criteria. Figure 1, Paper II summarises the principles
that were utilised for the concrete mixture design.
In the matrix-dominated cementitious materials, applying a particle-packing model reduces the
internal friction and consequently increases the workability of concrete [60]. Accordingly, in
this study, Andreasen and Andersen particle-packing model [24] was used for proportioning of
aggregate content. Additionally, the absolute volume method was used for proportioning of the
ingredients. The assumptions and the properties of concrete components are given in Paper II,
Section 2, Materials and methods.
5.2 EXPERIMENTAL METHODS FOR FRESH CONCRETE
There are different approaches to characterise the fresh properties of self-compacting concrete,
such as slump flow test, L-box test, J-ring test, sieve stability test, V-funnel test, Orimet test
and penetration test. In this study, the fresh state properties of macro basalt fibre self-
compacting concrete were assessed based on the experimental procedure of the European
standards. To evaluate the flow ability and filling ability of the fresh concrete, the slump-flow
test was performed according to NS-EN12350-8:2010 [61]. Passing ability of SCC was
determined by use of J-ring test according to NS-EN12350-12:2010 [62]. Figure 5.1, shows the
test set-up for the evaluation of fibre self-compacting concrete.
Use of Macro Basalt Fibre Concrete for Marine Applications
26
Figure 5.1 – In the left hand side, the slump-flow test of fibre concrete, and in the right hand side the J-ring test
are shown.
5.3 EXPERIMENTAL METHODS FOR EVALUATION OF HARDENED CONCRETE
The mechanical properties of hardened fibre concrete are characterised by its compressive
strength and post-cracking flexural tensile strength. To evaluate the compressive strength of
fibre concrete, the test was performed according to NS-EN 12390-3 [63].
The post-cracking properties of macro basalt fibre concrete were characterised based on the
European standard for measuring the flexural tensile strength of steel fibre concrete, NS-
EN14651 [39]. Figure 5.2 shows the test set-up that was used in this study for assessment of
fibre concrete properties. The details of the test set-up are presented in Paper III.
Figure 5.2 – Experimental set-up for characterisation of flexural tensile capacity.
Due to the importance of the resistance against chloride ingress, a bulk resistivity test was
employed to estimate the durability of the concrete specimens in the marine environment. The
experimental procedure is described in Paper III.
Use of Macro Basalt Fibre Concrete for Marine Applications
27
CHAPTER 6 – RESULTS AND DISCUSSIONS
6.1 RESULTS FROM THE EVALUATION OF FRESH FIBRE CONCRETE
The results of the flow ability and passing ability experiments of BF-SCC show a moderate
sensitivity to the maximum aggregate size and the super plasticizer volume percentage;
nevertheless of the concrete mix, the disparity is not noticeable. Based on the results presented
in Paper II, employing the Andreasen and Andersen particle-packing model leads to a flow able
self-compacting concrete mixture with a high stability. The flow ability of more than 750 mm
could be reached for the reference (without fibres) mixes by applying this method.
Considering, the differences between reference mixes; the dimensionless parameters were
introduced in Paper II to assess the flow ability and passing ability of the BF-SCC. The
experiments show that the flow ability decreases by increasing the fibre content. Additionally,
due to a critical point, by increasing the fibre volume fraction, the clustering effect and an
immense change in flow ability could be observed. Consequently, to cast self-compacting
concrete containing basalt macro fibres with the aspect ratio of 65 and the maximum aggregate
size of 16 mm the fibre volume fraction shall be limited to 1.15% and for the maximum
aggregate size of 12 mm; it shall be limited to 1%.
Based on the observations, due to a critical point, increasing the superplasticizer leads to the
segregation of concrete mix. Above this point, aggregates and fibres will be separated from the
concrete matrix, see Figure 6.1. Use of viscosity modifier agent and air-entering agent will
increase the stability of the concrete mixture nonetheless; it will decrease the concrete
compressive strength. Based on the author’s experience, use of the correct volume fraction of
the binder materials including cement, silica and fly ash. In addition, a suitable amount of filler
is the best way to overcome the stability problems.
Dynamic segregation and the other SCC flow properties are presented in Paper II. Based on the
slump flow test, the slump of the conventional concrete mix will drastically change by
increasing the fibre content further than 1.5%.
Use of Macro Basalt Fibre Concrete for Marine Applications
28
Figure 6.1 – In the left hand side, a stable concrete with a suitable amount of superplasticizer is shown. In the
right hand side, an unstable concrete mix with an excessive superplasticizer (the aggregates and fibres are
separated from the concrete matrix).
6.2 RESULTS FROM THE ASSESSMENT OF HARDENED FIBRE CONCRETE
The experimental results of hardened concrete are presented in Paper III. The research findings
indicate that the effect of fibre content on the density of fibre concrete is not noticeable. Based
on the bulk resistivity test, the designed concrete mixtures seem to have a high durability in
marine environments.
The results of flexural testing can also be found in Paper III. The research findings indicate that
the fibre content has a minor influence on flexural capacity corresponding to the limit of
proportionality. Although, by increasing the compressive strength the flexural strength was
slightly increased. As reported in Table 9, the post cracking properties of fibre concrete has a
direct relationship with the volume fraction of the fibres. Additionally, the comparison between
post-cracking properties of fibre concrete with the aspect ratio of 65 and 83 show that, due to
the higher anchorage length, the fibre concrete with the aspect ratio of 83 has a higher post
cracking peak and feq,2 value.
Use of Macro Basalt Fibre Concrete for Marine Applications
29
CHAPTER 7 – CONCLUSIONS
Use of fibre concrete as a construction material is increasing. Several investigations have been
performed to understand its mechanism and to characterise its mechanical properties. However,
the demand for using sustainable materials leads to the development of fibres with natural
origins. Basalt fibres as a non-toxic, eco-friendly material with rather simple and energy saving
production line are in the focus of many on-going types of research experiments.
The corrosion resistance properties of basalt fibres make them a suitable choice for use in the
inclement condition of the marine environment. Due to the attractive properties of basalt fibres,
in this research project the properties of newly developed macro basalt fibre concrete have been
investigated. The primary goal of this study has been to develop an optimised macro basalt fibre
self-compacting concrete and as the second aim, to investigate the fresh concrete and
mechanical properties of macro basalt fibre concrete. The author based on two series of related
experimental programmes draws following conclusions:
Based on the literature study, the basalt fibres and basalt fibre reinforced polymers
(BFRPs) have a high tensile strength, good resistance to alkaline and marine
environments. Hence, macro basalt fibres produced of BFRPs are suitable to be used for
fibre concrete aimed for offshore and marine applications.
In both series of experiments, the mix design followed the recommendations of DNV
rules to satisfy the requirements of concrete grades for marine applications. The
maximum aggregate size of 16 mm was used for the concrete composition. The test
results show that for the reference self-compacting concrete, which was designed based
on the modified Andreasen and Andersen particle-packing model; the flow ability could
exceed the target of 750 mm.
For the fibres with the aspect ratio of 65, and maximum aggregate size of 16 mm, self-
compacting concrete is obtainable for a maximum fibre volume fraction of up to 1.15
percent.
The flow ability and passing ability of the concrete mixture will be reduced by
increasing the fibre content. Since the J-ring test is intended for the assessment of
passing ability, the test set-up should be adjusted based on the minimum distance
between the reinforcement bars and additionally between the rebars and forms.
Use of Macro Basalt Fibre Concrete for Marine Applications
30
The fibre volume fraction has an insignificant effect on the density of macro basalt fibre
concrete.
Based on the results of bulk electrical resistivity test, the macro basalt fibre concrete has
excellent resistance to chloride ingress.
Increasing the fibre volume fraction leads to the expansion of the post-cracking flexural
tensile strength of fibre concrete.
The post-cracking properties of macro basalt fibre concrete were found to be a function
of 𝑉f √𝑓cm3
and the ductility a function of 𝑉f√𝑓cm where 𝑉f is volume fraction of fibres and
𝑓cmis the mean value of concrete compressive strength.
The results indicate that, by increasing the length and consequently anchorage length of the
fibres, the post cracking peak and feq,2 value of fibre concrete increase.
The drawn conclusions are only valid for the materials and concrete compositions, which were
used for this experimental study. However, the knowledge obtained in this study can be used to
estimate the fresh state behaviour and mechanical properties of macro basalt fibre concrete.
Use of Macro Basalt Fibre Concrete for Marine Applications
31
CHAPTER 8 – FURTHER RESEARCH
Basalt fibre reinforced polymers (BFRPs) are eco-friendly composite materials with high
tensile strength and excellent resistance to harsh environments. Due to their properties, BFRPs
may be used as a replacement for steel in marine concrete structures. In this study, some aspects
of basalt macro fibre concrete have been studied. Nevertheless, there is a demand for further
research to assess the properties of this type of fibre concrete for structural applications. The
author suggests the following topics for further investigations:
Use of high-performance fibre concrete is continually growing. However, there are a limited
number of publications pertaining the development of high-performance self-compacting
fibre concrete. The fibre shape, aspect ratio and fibre content are not integrated into the
available particle packing models. Additionally, the performance of equivalent particle size
corresponding to the fibres is not verified. Therefore, further research needs to be performed
in this field.
Marine structures are subjected to cyclic loads; consequently, the fatigue needs to be
considered in the design process. However, there are limited numbers of references
concerning the fatigue behaviour of basalt fibre concrete.
Based on the author’s knowledge shear capacity, shrinkage properties and creep of
macro basalt fibre concrete have not been investigated. Hence, there is a need for
experimental studies in this field.
Considering that, chopped basalt fibres and macro basalt fibres are designed to control
two different types of cracks; it would be interesting to study the behaviour of hybrid
systems of both types of fibres.
There is limited knowledge about the bonding mechanism between macro basalt fibres
and concrete matrix. Additionally, the aggregate size and chemical additives such as air
entrainment and bond increasing additives affect the mechanical properties of fibre
concrete. Therefore, the author suggests for further investigation in both micro and
macro scale; the results of such an investigation could also be used for modelling fibre
concrete structures in finite element analysis software.
Use of Macro Basalt Fibre Concrete for Marine Applications
32
Use of Macro Basalt Fibre Concrete for Marine Applications
33
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