ali mohammadi mohaghegh -...

ALI MOHAM

MADI M

OHAGHEGH Structural Properties of H

igh-Performance M

acro Basalt Fibre Concrete; Flexure, Shear, Punching Shear and Fire Spalling

ISBN 978-91-7729-659-1TRITA-BKN. BULLETIN 152, 2018 ISSN 1103-4270ISRN KTH/BKN/B-152-SE

KTH

2018

Structural Properties of High-Performance Macro Basalt Fibre Concrete; Flexure, Shear, Punching Shear and Fire SpallingALI MOHAMMADI MOHAGHEGH

DOCTORAL THESIS IN CIVIL AND ARCHITECTURAL ENGINEERINGSTOCKHOLM, SWEDEN 2018

KTH ROYAL INSTITUTE OF TECHNOLOGYSCHOOL OF ARCHITECTURE AND THE BUILT ENVIRONMENT www.kth.se

Structural Properties of

High-Performance Macro Basalt

Fibre Concrete; Flexure, Shear,

Punching Shear and Fire Spalling

ALI MOHAMMADI MOHAGHEGH

Doctoral Thesis

Stockholm, Sweden 2018

ii

Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskola i Stockholm

framlägges till offentlig granskning för avläggande av teknologie doktorsexamen i

byggvetenskap fredagen den 9 februari 2018 kl 9:30 i sal B1, Brinellvägen 23, Kungliga

Tekniska Högskolan, Stockholm.

© Ali Mohammadi Mohaghegh, January 2018

Tryck: Universitetsservice US-AB

TRITA-BKN. Bulletin 152, 2018

ISSN 1103-4270

ISRN KTH/BKN/B-152-SE

This dissertation is lovingly dedicated to my family

To Lena for being encouraging and supportive; and to our newborn

son, Artin-Carl for being a wonderful source of happiness and energy.

To my parents and my sister for their supports over the years.

i

Preface

This doctoral thesis is the result of an experimental research project, which was carried

out during a period of 4 years (May 2013 - May 2017). The project was performed at

the Department of Marine Operations and Civil Engineering, Norwegian University of

Science and Technology (NTNU), campus Ålesund and at the Department of Civil and

Architectural Engineering, the Division of Concrete Structures, at KTH Royal Institute

of Technology, Stockholm. The PhD project was financed by NTNU.

I hereby express my sincere gratitude to my main supervisor, Professor Johan

Silfwerbrand, KTH in Stockholm, who has encouraged me and given me thoughtful

comments and invaluable guidance throughout my PhD studies. Approaching the final

step was not possible without his continued support.

I also give my sincere gratitude to Vemund Årskog, Associate Professor at NTNU, for

invaluable supervision and comments. I also give my sincere gratitude to Dr Anniken

Karlsen at NTNU for being a professional co-supervisor, mentor and friend during the

process. Furthermore, I wish to thank Professor Håkan Sundquist, KTH, for reviewing

my thesis.

I would also like to acknowledge the support of colleagues at the NTNU laboratory,

Hans Christian Giske, Anders Sætersmoen, Andre Tranvåg and Siw-Helene Rydjord.

Especially Hans Christian Giske spent working hours to help me in the laboratory. The

support of Geirmund Oltedal, the former dean of the AIR Department at Aalesund

University College, should also be acknowledged.

I am also grateful to the companies ReforceTech, Ulstein Betong Marine, Norcem,

Elkem, Mapei and Moldskred for supplying the necessary materials for testing and their

interest in the project. I would also like to thank Dr Robert Jansson McNamee for letting

me use laboratory equipments at the SP Swedish Technical Research Institute.

Last but not least, I would like to thank my close friends and my amazing family for the

love, support, and constant encouragement I have received over the years.

Ålesund, Norway, January 2018

Ali M. Mohaghegh

iii

Abstract

Deterioration of concrete structures due to the corrosion of steel reinforcement is a universal

problem but especially in areas with a harsh climate. Consequently, Norwegian coastal

infrastructures, including bridges, harbours and floating structures, are also exposed to

degradation.

Moreover, there is an international movement focusing on using more environmentally friendly

and sustainable solutions in the construction sector. The use of fibre reinforced polymer (FRP)

materials with a high strength to density ratio and good corrosion resistance as a replacement

for carbon steel gives us a better alternative for design and construction of marine and coastal

structures.

Furthermore, according to the literature [1], corrosion of infrastructures has negative economic

consequences. In Norway, a land with an inclement climate and subject to a downturn in its

economy due to falling oil prices, using more durable construction techniques reduces the

maintenance cost of infrastructure.

Moreover, the use of fibre concrete for structural applications have been subject to extensive

studies. National and international standards and guidelines such as Swedish Standard (SS

812310:2014), fib Model Code (MC) 2010, RILEM TC162-TDF and ACI 544.6R-15 have

already been developed for the design of steel fibre concrete structures. The available standards

are based on more than five decades of experimental and analytical studies on steel fibre

concrete. If expanded to other fibre materials than steel, the design methods must be

experimentally verified for these materials.

Based on the literature study [2, 3], basalt fibre reinforcement polymers (BFRPs) show a good

corrosion resistance in seawater. Therefore, it can be considered as a possible replacement for

steel rebars. However, structural properties of macro basalt fibre concrete are scars in the

literature.

This PhD project is motivated by the need for characterizing macro basalt fibre concrete

properties, whereby the structural properties of basalt fibre concrete including flexure, shear,

punching shear and fire spalling are subject to testing. The choice of experimental methods and

small-scale specimens was related to a limited budget and limited size of laboratory equipments

and areas. The findings are presented in four appended papers and the extended summary

composes this thesis.

The test results indicate that post-cracking flexural tensile strength of macro basalt fibre

concrete is comparable with that of steel fibres concrete. As initially predicted, the flexural

tensile strength and toughness of concrete were improved by increasing the fibre content.

Moreover, the shear capacity of hybrid concrete beams reinforced with macro fibres and BFRP

iv

reinforcement bars also showed a substantial structural performance improvement by

increasing the fibre content. An important finding is that there is a good correlation between

the fib Model Code 2010 and Swedish Standard predictions and the experimental results.

To characterize the punching shear capacity, a simple test method was used. It was observed

that the rotation of the punching frustum of the cone was more or less prevented. The agreement

between the test results and a simple Swedish calculation model for fibre concrete slabs on

ground was better than the agreement with the fib Model Code 2010 which is based on the

critical shear crack theory, a method that was introduced by Muttoni and Schwartz. The model

in fib MC 2010 origins from rotation and a rotational crack which activates the fibres whereas

the purely empirically based Swedish model for slabs on ground also can be used for cases

where the rotation is more or less prevented.

The fire spalling resistance of basalt fibre concrete was assessed through a series of pilot

experiments. The fire test results show that macro basalt fibres do not improve the fire spalling

resistance of high-performance concrete. However, the use of basalt fibres does not increase

the spalling propensity of tested materials.

v

Sammanfattning

Nedbrytning av betongkonstruktioner på grund av armeringskorrosion är ett universellt

problem men i synnerhet i områden med ett aggressivt klimat. Följaktligen är

infrastrukturkonstruktioner längs norska atlantkusten såsom broar, hamnanläggningar och

flytande konstruktioner också utsatta för nedbrytning.

Vidare är det en internationell trend att använda mer miljövänliga och hållbara lösningar för

byggsektorn. Användning av fiberkompositer med ett högt förhållande mellan hållfasthet och

densitet samt god beständighet mot korrosion som ersättning till kolstål ger oss ett bättre

alternativ för projektering och produktion av konstruktioner i marina och kustnära miljöer.

Korrosion av infrastrukturkonstruktioner får också negativa ekonomiska konsekvenser. Norge

har ett aggressivt klimat och har dessutom sett sin ekonomi försämras till följd av sjunkande

oljepriser. Vid en övergång till beständigare byggtekniker kan man minska

underhållskostnaderna för infrastrukturen.

Tilläggas kan att användningen av fiberbetong i byggkonstruktioner har varit föremål för

omfattande studier. Nationella och internationella standarder som den svenska standarden SS

812 310:2014, fib Model Code (MC) 2010, RILEM TC162-TDF och ACI 544.6R-15 har redan

tagits fram för dimensionering av stålfiberbetongkonstruktioner. De tillgängliga standarderna

är baserade på mer än fem decenniers experimentella och teoretiska studier av stålfiberbetong.

För att överföra dessa standarder till andra fibermaterial än stål måste

dimensioneringsmetoderna verifieras experimentellt med dessa material.

Baserat på litteraturstudier kan man konstatera att basaltfiberarmerade polymerer (BFRP)

uppvisar en god korrosionsbeständighet i havsvatten. Därför finns det skäl att anta att materialet

skulle kunna vara en möjlig ersättare för stålarmering. Uppgifter om konstruktiva aspekter på

basaltfiberbetong är emellertid få i litteraturen.

Detta doktorandprojekt motiveras av behovet av en mekanisk karakterisering av

basaltfiberbetong. Egenskaper i böjning, skjuvning, stansning och brandspjälkning har

studerats genom provning. Valet av experimentella metoder och småskaliga provkroppar

bestämdes av en begränsad budget och begränsad storlek på laboratorieutrustning och ytor.

Resultaten presenteras i fyra artiklar som tillsammans med en utförlig sammanfattning utgör

denna avhandling.

Resultaten indikerar att basaltfiberbetongens böjdraghållfasthet efter uppsprickning är i paritet

med stålfiberbetongs. Som förväntat ökade såväl böjdraghållfastheten som segheten med ett

ökat fiberinnehåll. Vidare uppvisade betongbalkar med en kombination av armeringsstänger av

BFRP och basaltfibrer också ett väsentligt förbättrat verkningssätt vid ökande fiberinnehåll. Det

vi

är viktigt att notera att resultaten visar på en god överensstämmelse mellan fib Model Code

2010, den svenska fiberbetongstandarden och dessa försöksresultat.

För att undersöka genomstansningskapaciteten användes en enkel provningsmetod. Det visar

sig att stanskonens rotation här är mer eller mindre förhindrad. Överensstämmelsen mellan

försöksresultaten och en enkel svensk beräkningsmodell för fiberbetongplattor på mark visade

sig vara bättre än överensstämmelsen med mönsternormen fib Model Code 2010 som bygger

på teorin för en kritisk skjuvspricka, en metod som introducerats av Muttoni och Schwartz.

Modellen i fib MC 2010 utgår från rotation och en rotationspricka vilken aktiverar fibrerna

medan den rent empiriskt baserade svenska modellen för platta på mark också kan användas

för fall då rotationen är mer eller mindre förhindrad.

Motståndet mot brandspjälkning undersöktes i ett pilotförsök. Resultaten från brandförsöken

visar att basaltfibrer inte höjer motståndet mot brandspjälkning i höghållfast betong. Men å

andra sidan ledde användningen av basaltfibrer inte heller till någon ökad brandspjälkning i de

provade materialen.

vii

Sammendrag

Nedbryting av betongkonstruksjoner på grunn av armeringskorrosjon er et universelt problem

og spesielt i områder med et aggressivt klima. Dette fører til at infrastruktur-konstruksjoner

langs norskekysten, som bruer, havneanlegg og flytende konstruksjoner også er utsatt for

nedbryting.

Videre er det en internasjonal trend å anvende mer miljøvennlige og bestandige løsninger i

byggsektoren. Bruk av fiberkompositter med høy fasthet og lav densitet og med god

bestandighet mot korrosjon som erstatning for ordinært stål, gir oss et bedre alternativ for

prosjektering og produksjon av konstruksjoner i marine og kystnære miljøer.

Korrosjon av infrastruktur-konstruksjoner har også negative økonomiske konsekvenser. Norge

har et aggressivt kystklima og har dessuten fått en svakere økonomi på grunn av synkende

oljepriser. Bruk av mer bestandige konstruksjoner og konstruksjonsløsninger kan redusere

vedlikeholdskostnader for denne infrastrukturen.

Bruk av fiberbetong i byggkonstruksjoner har vært tema for omfattende studier. Nasjonale og

internasjonale standarder som den svenske standarden SS 812310:2014, fib Model Code (MC)

2010, RILEM TC162-TDF og ACI 544.6R-15 har regler for dimensjonering av

stålfiberbetongkonstruksjoner. De tilgjengelige standardene er basert på mer enn fem

decenniers eksperimentelle og teoretiske studier av stålfiberbetong. For å kunne bruke disse

standardene for andre fibermaterialer enn stål må dimensjoneringsmetodene verifiseres

eksperimentelt for disse materialene.

Basert på litteraturstudier kan man konstatere at basaltfiberarmerte polymerer (BFRP) har god

korrosjonsbestandighet i sjøvann. Det er derfor grunn til å anta at materialet kan være en mulig

erstatning for stålarmering. Det er imidlertid lite informasjon om konstruktive egenskaper for

basaltfiberbetong i litteraturen.

Dette doktorandprosjektet er motivert av behovet for en karakterisering av mekaniske

egenskaper for basaltfiberbetong. Egenskaper knyttet til bøye- og skjærpåkjenning,

gjennomlokking og avskalling ved brann er studert i et eksperimentelt program. Valg av

eksperimentelle metoder og småskala prøvestykker ble bestemt ut fra et begrenset budsjett og

begrenset størrelse på laboratorieutrustning och areal. Resultatene er presentert i fire artikler

som sammen med en utførlig sammenfatning utgjør denne avhandling.

Resultatene indikerer at basaltfiberbetongens reststrekkfasthet etter opprissing er

sammenlignbar med prøveresultater for stålfiberbetong. Som forventet økte både rest-

viii

strekkfasthet og duktilitet med økende fiberinnhold. Videre viste betongbjelker med en

kombinasjon av armeringsstenger av BFRP og basaltfiber også en vesentlig forbedret

lastrespons med økende fiberinnhold. Det er viktig å notere at resultatene viser god

overensstemmelse med fib Model Code 2010 og den svenske fiberbetongstandarden.

En enkel prøvemetode ble brukt for å undersöke gjennomlokkingskapasiteten. Det viser seg at

bruddkonens rotasjon her er mer eller mindre forhindret. Det var bedre samsvar mellom

forsøks-resultatene og en enkel svensk beregningsmodell for fiberbetongplater på mark enn

mellom forsøksresultatene og fib Model Code 2010 som bygger på teorien for et kritisk

skjærriss, en metode som ble introdusert av Muttoni og Schwartz. Modellen i fib Model Code

2010 er basert på rotasjon og et rotasjonsriss som aktiverer fibrene, mens den rent empiriske

svenske modellen for plate på mark også kan anvendes når rotasjonen er mer eller mindre

forhindret.

Motstand mot avskalling ved brann ble undersøkt i et pilotforsøk. Resultatene fra brannforsøket

viser at basaltfiber ikke gir økt motstand mot avskalling for høyfast betong. Men på den andre

siden viste prøveresultatene heller ikke økt avskalling for betong med basaltfiber.

ix

List of Publications

Four appended papers constitute the basis of this thesis work. They are referred to with their

Roman numbers in the text as follows:

Paper I: Mohammadi Mohaghegh, A., Silfwerbrand, J., Årskog, V. "Flexural Behaviour of

Medium-Strength and High-Performance Macro Basalt Fibre Concrete Aimed for

Marine Applications.", Nordic Concrete Research Journal, Publication No. 57,

Issue No. 2/2017, pp. 103-123.

Paper II: Mohammadi Mohaghegh, A., Silfwerbrand, J., Årskog, V. "Shear Behaviour of

High-Performance Basalt Fibre Concrete – Part I: Laboratory Shear Tests on

Beams with Macro Fibres and Bars.", Submitted to fib Structural Concrete

Journal (September 2017).

Paper III: Mohammadi Mohaghegh, A., Silfwerbrand, J., Årskog, V. " Shear Behaviour of

High-Performance Basalt Fibre Concrete – Part II: Laboratory Punching Shear

Tests on Small Slabs with Macro Fibres without Bars." Submitted to fib Structural

Concrete Journal (October 2017).

Paper IV: Mohammadi Mohaghegh, A., Silfwerbrand, J., Årskog, V., Jansson, R. "Fire

Spalling of High-Performance Basalt Fibre Concrete.", Nordic Concrete Research

Journal, Publication No. 57, Issue No. 2/2017, pp. 89-102.

The PhD candidate Ali Mohammadi Mohaghegh has performed the planning of the research

and has implemented the experimental work. He has also analysed the results, and have done

the main part of paper writing. The co-authors have contributed inputs to the planning of the

work and have participated in the improvement process of the papers with their comments and

recommendations on paper writing revisions.

xi

Other Publications by the Author

Other publications by the author related to the topics of this thesis are as follows.

▪ Mohammadi Mohaghegh, A., Silfwerbrand, J., Årskog, V. "Properties of

Fresh Macro Basalt Fibre (MiniBar) Self-Compacting Concrete (SCC) and

Conventional Slump Concrete (CSC) Aimed for Marine Applications", Nordic

Concrete Research Journal, Publication No. 52, Issue No. 1/2015, pp. 43-61.

▪ Mohammadi Mohaghegh, A., Silfwerbrand, J., Årskog, V. "An Initial

Investigation of the Possibility to Use Basalt Fibres for More Durable

Concrete Structures in Norwegian Fish Farming" Proceedings, XXII Nordic

Concrete Research Symposium, 13-15 August 2014, Reykjavik, Iceland, pp.

219-222.

xiii

List of Notations

Uppercase Roman Letters

A Specimen’s surface area (m2)

As Cross-sectional area of longitudinal rebars (mm2)

𝐷0 Ductility index of flexural fibre concrete members

𝐷1 Ductility index of flexural fibre concrete members

𝐷BZ𝑏 Energy absorption capacity of plain concrete

Dmin Minimum particle size (µm)

Dmax Maximum particle size (µm)

Dnssm Chloride diffusion coefficient (m2/s)

FIc Load at first crack (N)

Fj Load at CMOD

In Toughness index

𝐼ductility Ductility of fibre concrete members

LOP Limit of proportionality

L Length (thickness) of samples in electrical resistivity and (chloride diffusivity) tests

P(D) Modified Andreasen & Andersen (A&A) particle packing model

PJ Passing-ability value

R Measured resistance (Ω)

SF Slump-flow (mm)

SFJ Slump-flow of the J-ring test (mm)

T Average of the temperature at the start and end of the test (°C)

U Voltage (V)

U1 Area under the load-CMOD diagram for the intervals 0 - 0.6 mm (10-3 J)

U2 Area under the load-CMOD diagram for the intervals 0.6 - 3 mm (10-3 J)

Vf Fibre volume fraction (%)

𝑉fd Contribution of steel fibres in shear capacity of the beams (kN)

𝑉cd Contribution of concrete in shear capacity of the beams (kN)

Xd Average of the measured chloride penetration depth (mm)

xiv

Lowercase Roman Letters

a Shear span (mm)

bw Width of the cross-section in the tensile area (mm)

d1 Largest perpendicular diameter of the distributed concrete flow (mm)

d2 Largest perpendicular diameter of the distributed concrete flow (mm)

d Effective depth of the beam cross-section (mm)

fctk Characteristic tensile strength of plain concrete (MPa)

fcm Average compressive strength of concrete (MPa)

fck Characteristic compressive strength of concrete (MPa)

fFtuk Characteristic ultimate tensile strength of fibre concrete (MPa)

fIf First crack flexural strength (MPa)

fLK Characteristic value of concrete tensile strength corresponding to LOP

fRj Residual flexural tensile strength of fibre concrete (MPa)

fRjm Average values of residual flexural tensile strength of fibre concrete (MPa)

fR,j (fj K) Characteristic value of the residual flexural tensile strength of fibre concrete (MPa)

ftd Design tensile strength of concrete (MPa)

𝑓tk Characteristic value of tensile strength in FRP fibre concrete (MPa)

hsp Height of the fracture cross section (mm)

𝑘 Size effect factor

kA Material depended parameter (MPa)

kV Material depended parameter (MPa)

l Length (mm)

t Duration of the chloride diffusivity experiment (hour)

𝑣cd Shear capacity of concrete beams without stirrups (MPa)

𝑣D,ss Punching shear capacity of ground-supported concrete slabs (MPa)

𝑣RD,cf Shear capacity of concrete beams without stirrups (MPa) (fib MC 2010)

xv

Uppercase Greek Letters

∆ℎx Height difference between top of the J-ring and top of the concrete at the borders y-

dir.

∆ℎy Height difference between top of the J-ring and top of the concrete at the borders y-

dir.

∆ℎx0 Height difference between top of the J-ring and top of the concrete in the middle of

the ring.

Lowercase Greek Letters

γc Partial safety factor for concrete

γf Partial safety factor for fibre concrete

δL Mid-span deflection corresponding to the limit of proportionality (mm)

δIc Mid-span deflection corresponding to the first crack load (mm)

𝛿n δIc times n value (n = 3, 5.5, 10)

ρ Concrete bulk electrical resistivity (Ω.m)

ρ1 Longitudinal reinforcement ratio

σcp Average compressive stress (MPa)

𝜏fd Design value for the contribution of fibres (MPa)

xvii

Contents

Preface ........................................................................................................................................ i

Abstract .................................................................................................................................... iii

Sammanfattning ....................................................................................................................... v

Sammendrag ........................................................................................................................... vii

List of Publications .................................................................................................................. ix

Other Publications by the Author .......................................................................................... xi

List of Notations .................................................................................................................... xiii

1 Introduction ...................................................................................................................... 1

1.1 Background ............................................................................................................. 1

1.2 Aims ........................................................................................................................ 2

1.3 Scope ....................................................................................................................... 3

1.4 Limitations ............................................................................................................... 4

1.5 Research Contribution ............................................................................................. 6

1.6 Outline of the Thesis ............................................................................................... 7

2 Basalt Fibre Concrete ...................................................................................................... 9

2.1 Concrete Matrix ..................................................................................................... 10

2.2 Concrete Composition ........................................................................................... 13

2.3 Fresh Concrete Properties ..................................................................................... 14

2.4 Self-Compacting Macro Basalt Fibre Concrete .................................................... 14

2.5 Concrete Compressive Strength ............................................................................ 17

2.6 Durability of Macro Basalt Fibre Concrete ........................................................... 17

2.7 Basalt Fibre Reinforcement ................................................................................... 19

3 Flexural Strength ........................................................................................................... 21

3.1 General .................................................................................................................. 21

3.2 Residual Flexural Tensile Strength ....................................................................... 21

3.3 The Ductility of Fibre Concrete Members ............................................................ 23

4 Shear Strength................................................................................................................ 25

4.1 Shear Capacity of Fibre Concrete Beams According to RILEM TC 162-TDF

(2003) ............................................................................................................................... 25

4.2 Shear Capacity of Fibre Concrete Beams According to fib Model Code 2010 .... 26

xviii

4.3 Shear Capacity of Fibre Concrete Beams According to DNV-OS-C502 ............. 27

4.4 Experimental Assessment of Shear Capacity ........................................................ 27

4.5 Shear Capacity of Macro Basalt Fibre Concrete Beams ....................................... 28

4.6 Punching Shear Capacity of Fibre Concrete Slabs According to fib Model

Code 2010 ........................................................................................................................ 30

4.7 Punching Shear Capacity of the Ground Supported Slabs According to

Swedish Standard (SS 812310)........................................................................................ 31

4.8 Experimental Assessment of Punching Shear Capacity ........................................ 31

4.9 Punching Shear Capacity of Macro Basalt Fibre Concrete Slabs ......................... 32

5 Fire Spalling .................................................................................................................. 35

5.1 Fire Spalling of Fibre Concrete ............................................................................. 35

5.2 Fire Spalling Experiment ....................................................................................... 36

5.3 Results and Statistical Analysis ............................................................................. 37

6 Conclusions and Further Research .............................................................................. 39

6.1 General Conclusions .............................................................................................. 39

6.2 Further Research .................................................................................................... 40

Bibliography ........................................................................................................................... 43

1.1. BACKGROUND

1

1 Introduction

1.1 Background

Due to the harsh environment of the Northern Sea, the coastal infrastructures in Norway are

exposed to chloride-induced corrosion [4]. Based on the investigation performed by Årskog et

al. [5] on harbour structures and concrete barges, see Figure 1.1, there is a time-dependent

ingress of chloride ions that lead to corrosion of the steel reinforcement. Therefore, to improve

the durability and consequently the sustainability of concrete structures, alternative materials

should be used instead of conventional carbon steel [6].

Figure 1.1: A fish farming feeding and storage concrete barge (Courtesy of Ulstein Betong Marine

Company).

Fibre Reinforced Polymers (FRPs) are found to be very attractive for industries, such as the

aerospace industry, whereby the high strength to density ratio is necessary [7]. Furthermore,

FRPs have also dominated the petrochemical and marine industry where the high corrosion

resistance is essential [8]. Today, the use of FRPs within the construction sector is developing

[9-11]. The use of FRPs as a replacement for the steel rebars in marine concrete structures may

be very beneficial [12]. They may improve the durability and the lifetime of concrete structures

[8]. Correspondingly, the need for maintenance, rehabilitation or rebuilding new structures are

reduced. Consequently, this may save the amount of construction materials and can be seen as

an eco-friendly solution.

Chapter 1. Introduction

2

According to the Paris climate agreement, various countries agreed to reduce their greenhouse

gas emission [13]. Therefore, different industries are motivated to use more eco-friendly

approaches with a low carbon dioxide footprint. The industries involved with FRP materials

are also working on developing more environmentally friendly materials whereby the basalt

fibre is one of the alternatives [14, 15].

Moreover, after more than five decades of research and development, the use of fibre concrete

for structural applications is increasing every year. Replacing the traditional steel reinforcement

by structural fibres may be beneficial for the construction sector, especially in the Scandinavian

countries where the labour and transportation costs are very high. So far, most of the previous

studies and the available standards and guidelines are aimed for steel fibre concrete. Therefore,

there is a need for more research when it comes to the use of new types of fibre materials.

Especially when the macro fibres are already in use by the construction sector in several

countries.

This PhD project is based on the need for to characterize the structural properties of macro

basalt fibre concrete to be used for marine and other structural applications.

In this chapter, the author will discuss the motivations, aims, scope, limitations, and scientific

contribution of the project. Moreover, the structure of the thesis and the articles are also

discussed.

1.2 Aims

Research and development of new materials is a continuous process. When it comes to the

construction sector, new materials need to be verified by civil engineering research community

before they can be recognized as reliable construction materials. The main goal of this study

was to partially answer the question whether the recently developed macro basalt fibres can be

used for the structural applications, in particular for the marine construction. The first question

that comes to the mind concerning the use of new fibre materials is if it has a similar structural

performance to that of steel fibres. The steel fibre concrete has been the subject of many

research projects during the past 50 years. It has been found to be a competitive material to be

used as a replacement for the conventional steel rebar. Today, the use of steel fibres for the

structural applications has an increasing trend in the construction sector. The second important

question concerning the use of new materials, which usually has been highlighted by the

engineering community, is if there are reliable design methods that can be utilized when using

those materials. In this study, the structural properties of macro basalt fibre concrete members,

including flexural strength, shear capacity, punching shear strength and fire spalling on specific

applications, were characterized using small-scale experiments.

Post-cracking properties of macro basalt fibre concrete, to some extent, demonstrated similarity

to that of steel fibre concrete. Therefore, the experimental results were compared to the

predictions of methods that are initially developed for steel fibre concrete design. These

methods are presented in the existing standards and guidelines (e.g. fib Model Code 2010,

RILEM TC 162-TDF, Swedish Standard 812310:2014).

1.3. SCOPE

3

1.3 Scope

To reach the aim of the study, and by considering the limited budget, a series of experiments

were designed and performed on small-scale specimens. The use of high-performance concrete

has a growing trend. Accordingly, this has been considered in the concrete mix design. Two

series of test samples were produced with an average compressive strength of 67.6 MPa and

96.5 MPa, respectively.

The post-cracking strength or residual tensile strength of fibre concrete is the main parameter

to address its mechanical properties in the serviceability limit state (SLS) and ultimate limit

state (ULS) [16]. Therefore, as the first step, the residual tensile strength of the high-

performance and medium strength macro basalt fibre concrete has been characterized according

to the standard, EN 14651 [17], the results are presented in Paper I.

Extensive experimental and analytical studies have been performed in the past few decades

pertaining to the shear behaviour of steel fibre concrete beams reinforced with steel

reinforcement bars for flexure but without stirrups. Many of these studies aimed at investigating

the possibilities to replace the stirrups with steel fibres, but to the author’s knowledge, there is

no published literature pertaining to the shear behaviour of high-performance concrete beams

reinforced with macro basalt fibres and BFRP bars. In Paper II, the contribution of macro basalt

fibres to the shear strength of high-performance concrete beams reinforced with BFRP rebars

was studied. Moreover, the experimental results were compared with predicted values for shear

strength of the beams based on the fib MC 2010 [18] and SS 812310:2014 [19].

The punching shear phenomenon of reinforced concrete slabs has been the subject of many

studies. In fib MC 2010, a new physical approach has been used for prediction of punching

shear strength in concrete slabs [20]. This approach is based on the critical shear crack theory

(CSCT), which has also been adapted for the fibre concrete slabs [20]. Based on the literature

survey, there is no standard experimental method to characterize the contribution of fibres in

punching shear capacity of fibre concrete slabs. Paper III, provides the information regarding

the range of validity of the results of a recently introduced test method [21]. This approach has

been assessed based on the concept of the critical shear crack theory. Moreover, the

experimental results have been compared with the model introduced by SS 812310:2014 [19]

to assess the punching shear capacity of ground supported fibre concrete slabs.

The severe spalling, caused by a fire in some European tunnels, revealed the importance of fire

spalling in civil engineering concrete infrastructures [22]. The experimental studies, reported

in the literature, suggest that using polypropylene fibres prevents or reduces the fire spalling in

concrete structures. Motivated by this, the effect of basalt fibres on fire spalling of high-

performance concrete has been evaluated empirically. The results of the study have been

presented in Paper IV. Figure 1.2 shows a schematic picture of the research programme.


4

Figure 1.2: Schematic of the research programme.

1.4 Limitations

The author endorses the following limitations of this thesis:

▪ Paper I: Flexural Behaviour of Medium-Strength and High-Performance Macro Basalt

Fibre Concrete Aimed for Marine Applications.

In this experimental work, the authors have limited their study to high-performance and

medium strength fibre concrete. The post-cracking properties were assessed using small

beam specimens according to the EN 14651 standard. No air-entraining agent was

employed in the concrete recipes, which radically can affect the bonding strength

between fibres and the concrete matrix.

▪ Paper II: Shear Behaviour of High-Performance Basalt Fibre Concrete – Part I:

Laboratory Shear Tests on Beams with Macro Fibres and Bars

In this paper, only the beams with the shear span-effective depth ratio (a/d) of 2.0 were

considered. The experimental results were only compared with the predictions of

existing standards for fibre concrete, and investigation of all the other empirical existing

models was excluded from this study.

▪ Paper III: Shear Behaviour of High-Performance Basalt Fibre Concrete – Part II:

Laboratory Punching Shear Tests on Small Slabs with Macro Fibres without Bars

In this study, the authors limited their investigation to the use of a rather simple

experimental method for characterization of punching shear capacity of macro basalt

fibre concrete. Moreover, the validity and the limitations of this approach was assessed.

1.4. LIMITATIONS

5

▪ Paper IV: Fire Spalling of High-Performance Basalt Fibre Concrete.

In this paper, three specimens of a dense and high-performance concrete were explored.

The study was performed on a macro level. The investigation of the spalling mechanism

and the effect of fire on concrete microstructure were outside of the scope.

The following topics shall be considered as the general limitations of this research programme:

(1) no durability study was performed on the macro basalt fibre itself; (2) no life cycle

assessment was performed; (3) only experimental approach was used; (4) no large-scale

experiment was carried out; (4) the minimum characteristic compressive strength of the

specimens was about 60 MPa; (5) the design approaches investigated were limited to fib Model

Code 2010 [18, 23], RILEM TC162-TDF [24], SS 812310 [19] and DNV-OS-592 [25]; Figure

1.3 shows a schematic of the limitations of the project.

Figure 1.3: Schematic of the limitations of the project.


6

1.5 Research Contribution

The experimental investigation on macro basalt fibre concrete presented in this thesis has

resulted in the scientific contribution summarized below.

▪ Since the beginning of the 20th century, the material science and technology have been

developed, and a number of innovative construction materials were introduced. Use of

discrete fibre-mortar composites is not a new concept and has been used for centuries,

however, since the 1950s it was used as a basis for modern composite materials [26].

Steel fibre concrete has been the subject of many studies. The studies show that steel

fibres can enhance structural properties and durability of concrete members and based

on that, several standards have been developed for the design of fibre concrete members

[18, 19, 23]. Furthermore, practical experiences show that the use of discrete steel fibres

as a replacement for the steel rebars is economically beneficial [26]. Basalt fibre

originally was developed for military purposes, however, since the 1990s it was

available for civil applications [15]. Recently, basalt fibre reinforced polymers are

considered as an alternative for steel reinforcement [27, 28].

▪ Based on the existing knowledge, the post-cracking properties is the main parameter to

be used for the design of fibre concrete structures. A literature survey shows that the

residual tensile strength of macro basalt fibre concrete has not been the subject of many

studies. The material properties provided in this study can be used as an input for the

researchers while investigating the behaviour of macro basalt fibre concrete structures

using FEM software. Additionally, the results can be used by the engineering

community for design purposes.

▪ Several design guidelines have been developed for concrete members reinforced with

FRP rebars [29, 30]. However, based on the author’s knowledge, none of these

guidelines covers a hybrid system of FRP rebars and fibres. As the use of FRP materials

is growing, there is a need for further studies pertaining to a hybrid reinforcement

system, comprising FRP rebars and fibres. In this project, the shear capacity of concrete

beams reinforced with BFRP bars and fibres has been investigated. This can be a

pioneering reinforcement system to be used for future concrete structures in harsh

environments, also for the applications where lightweight reinforcing materials are

needed. Moreover, the results were compared with the values predicted using the

existing models for shear capacity of steel fibre concrete beams without stirrups.

▪ The punching shear capacity of steel fibre concrete slabs has been the subject of several

studies. In the literature, different experimental set-ups have been used to characterize

the punching shear capacity of fibre concrete slabs. Motivated by this insight a rather

simple method has been used to characterize the punching shear capacity of macro

basalt fibre concrete. Via this study, the validity and the limitations of the testing method

have been evaluated. The results, therefore, can be used as a basis for the choice of

punching shear-testing set-up in other research projects.

▪ The fire spalling resistance of concrete is necessary especially in structures such as

tunnels where the risk of fire exposure is high. The positive effect of polypropylene

fibres on reducing fire spalling is well-known [31, 32]. The fire spalling of high-

performance basalt fibre concrete has not been the subject of previous studies. Driven

by this background, the pilot experimental investigation presented in this thesis can be

1.6. OUTLINE OF THE THESIS

7

used as an indication of fire spalling properties of high-performance basalt fibre

concrete.

1.6 Outline of the Thesis

This thesis is based on the experimental research programme presented in the format of four

appended papers. The main objective of the thesis is to present the content of the papers in the

context of the research agenda. The thesis consists of six chapters. The research methods which

were used for characterization of the structural properties (flexural strength, shear capacity,

etc.), are presented separately in their corresponding sections. The material properties of fibres,

concrete composition and the general information about the concrete mixing procedure,

specimen preparation, fresh concrete properties and the durability test results of macro basalt

fibre concrete are presented in Chapter 2.

In Chapter 3, a summary of the available standard methods for characterization of fibre concrete

flexural strength is presented. Additionally, a summary of post-cracking properties of macro

basalt fibre concrete is presented.

In Chapter 4, a summary of standard models for prediction of shear capacity of fibre concrete

beams without stirrups and punching shear capacity of fibre concrete slabs is given. Moreover,

the experimental results presented in Papers II and III are discussed more thoroughly.

Chapter 5 presents the general, existing knowledge about the fire spalling of fibre concrete. A

brief discussion pertaining the results presented in Paper IV is also given.

Finally, the outcome and the general conclusions of the research project, as well as the possible

topics for the further investigations, are presented in Chapter 6.


8

1.6. OUTLINE OF THE THESIS

9

2 Basalt Fibre Concrete

Durability is an essential parameter for the design and construction of marine concrete

structures. Furthermore, the carbon dioxide gas emissions, global warming and the

environmental pollution are the new threats of our time. Thereby, the reduction of greenhouse

gas emission and using eco-friendly and sustainable materials are the focus of many engineering

studies. Moreover, the use of environmentally friendly solutions has been emphasized by the

Paris climate agreement [13]. It is well-known that the large amount of the global carbon

dioxide gas is produced by the cement industry [33]. Sustainable planning and construction

methods may reduce the need for rebuilding the infrastructures, and therefore reducing the

consumption of the cement. According to Hooton and Bickley [6], increasing the durability of

concrete structures is the best way to improve their sustainability. The corrosion of steel

reinforcement can significantly reduce the durability of concrete structures [34]. The metallic

corrosion has been shown to cause a considerable economic consequences [1]. According to

U.S Federal Highway Administration [1], research project between 1999 and 2001, the

corrosion cost of civil engineering structures has been estimated at $22.6 billion. Based on the

extensive network of the coastal infrastructure, the corrosion cost per capita can be even higher

in Norway.

Fibre reinforced polymers (FRPs) are composed of reinforcing fibres and polymeric matrix,

whereby the resin encapsulating the fibres enabling the fibres acting as a unified material [9,

35]. Furthermore, the resin performs as a protective layer against the environmental damages

[9]. The FRPs, alongside their advantages such as high strength and low density, are known for

their corrosion resistance properties [9]. Basalt fibre reinforced polymer (BFRP) bars and macro

basalt fibres made of BFRPs were introduced to the Norwegian market several years ago. The

BFRPs have been introduced as a replacement for carbon steel to increase the durability of

concrete structures [36, 37].

This thesis aims to study the structural properties of macro basalt fibre concrete (MBFC), made

of BFRPs. Thereby, this chapter presents the mix design and composition of high-performance

basalt fibre concrete which was used in the appended Papers.

This chapter also includes a summary of previous study on fresh properties of macro basalt

fibre concrete. Finally, the results from the bulk resistivity test and the chloride ingress

experiment are presented. These experiments were performed to characterize the effect of basalt

fibres on the long-term performance of concrete.

Chapter 2. Basalt Fibre Concrete

10

2.1 Concrete Matrix

To fulfil the requirements for the durability of concrete aimed for marine environments, the

recommendations of offshore concrete structures, DNV-OS-CS502 [25] and NS-EN 206-1

standard [38] were followed for the concrete mix design.

Considering the harsh environment where the marine concrete structures (concrete barges)

should stand, the exposure class of XS2 or XS3 shall be used for the structural design [38].

Fresh concrete comprises three physical states of solid, liquid and gas (air). Ernst Mørtsell [39,

40] introduced a new model whereby the combination of solid and liquid compounds were

considered as a dual phase material. In the new Matrix-Particle (MP) model, the matrix consists

of liquids and the solid components with the particle size smaller than 125 μm. Usually, binder

materials and so-called fillers have a particle size of smaller than 125 μm [39]. Contrary, the

particle phase comprises aggregates with the size of more than 125 μm [39]. Furthermore, in

fibre concrete, the fibres also should be considered as a part of particle phase. According to this

definition, high-performance concrete with a low water-binder ratio is a matrix dominated

mixture [39, 40]. According to the DNV-OS-CS502 standard, the water-binder ratio for the

marine concrete structures is limited to 0.4 for the members in the splash zone and 0.45 for the

other parts [25]. Therefore, this criterion was used to quantify the binder materials including

cement and silica.

In a matrix-dominated concrete, selecting a dense particle distribution reduces the contact and

friction between particles by a layer of the matrix surrounding the aggregates [39, 41].

Therefore, it increases the concrete workability [39, 41]. Furthermore, a densely compacted

matrix-particle phase is a crucial parameter to assure the durability and the high-performance

of concrete [42, 43]. Particle packing models have been successfully used to optimize the

concrete mixes by many researchers [42, 44-46]. Equation (2.1) shows the modified Andreasen

& Andersen (A&A) particle packing model [42].

𝑃(𝐷) =𝐷𝑞−𝐷min

𝑞

𝐷max𝑞

−𝐷min𝑞

(2.1)

where, Dmin and Dmax are the minimum and maximum particle sizes (µm) in the concrete matrix

and q is a constant [42].

Yu et al. [42, 44] employed A&A particle packing model to design ultra-high-performance

concrete (UHPFC). In their study, the Least Squares Method (LSM) was utilized for optimizing

the materials proportioning, through fitting the mix particle size distribution to a target curve

defined by the modified A&A packing curve [42, 44]. Furthermore, all the solid components

including the binders were incorporated into the optimization process [42, 44].

In this research, absolute volume method [47] was used for proportioning of concrete

components.

The binder content was determined by considering the criteria specified by DNV-OS-CS502

standard [25]. Furthermore, a semi-empirical method was utilized to optimize the particle

distribution of the aggregate mix. Similar to [42, 44], the aggregate mix was fitted to the

optimum modified A&A particle-packing curve via a simple trial and error approach. It ought

2.1. CONCRETE MATRIX

11

to be mentioned that this method is not as precise as the methods presented by Yu et al. [42,

44]. Table 2.1 shows the particle size distribution of the used aggregates. The maximum

aggregate size in the concrete mix was 16 mm. Based on the recommendation of Brouwers and

Radix, a q value of 0.25 was used in the A&A particle-packing model [48]. To see the effect of

using different Dmin values, modified A&A particle-packing curves with three various

alternatives for minimum particle sizes were investigated [49]. The minimum particle sizes of

0.5 μm, 63 μm and 125 μm were selected based on the finest cement particles; smallest sieve

size used in PSD experiment and the maximum size of the matrix particles in the MP model,

respectively, see Figure 2.3 [49]. In this study, based on the precision of the sieve test, Dmin was

assumed to be 63 µm [49].

In the literature [41, 48], different methods for incorporating the effect of fibres while using a

particle-packing model have been presented. However, based on the author’s knowledge there

is no empirically verified method for using the macro basalt fibres [49]. Therefore, in this study,

the effect of fibres has not been considered in the particle-packing model [49].

Figure 2.2 shows an example (reference concrete in Paper IV) whereby the modified A&A

particle-packing model has been used to design an optimum recipe. The figure shows the

particle size distribution of the used aggregates, the optimum curve, and the particle size

distribution of the mixed aggregates.

Table 2.1: Particle size distribution data of the used aggregates. From Paper I.

Sieve size (mm) Cumulative (%) finer than

0-4 mm 0-8 mm 0-16 mm

16 100 100 91.1

11.2 100 100 39.0

8 100 98.5 8.0

4 96.3 81.4 3.65

2 74.4 66.7 3.1

1 59.0 50.9 2.9

0.5 46.2 33.2 2.6

0.25 33.1 18.1 2.2

0.125 20.0 8.3 1.7

0.063 9.9 2.6 1.1


12

Figure 2.1: Particle size distribution (PSD) based on the modified Andreasen & Andersen model for the

maximum aggregate size of 16 mm. From [49].

Figure 2.2: PSDs of the ingredients, optimum curve (modified A&A curve for the minimum particle

size of 63 µm) and the grading line of mixed aggregates for the reference concrete mix in Paper IV.

0

10

20

30

40

50

60

70

80

90

100

0.1 1 10 100 1000 10000 100000

Per

cent

finer

(V

ol.

%)

Particle Size (µm)

Minimum Particle Size = 125 µm

Minimum Particle Size = 63 µm

Minimum Particle Size = 0,5 µm

0

10

20

30

40

50

60

70

80

90

100

50 500 5000 50000

Per

cent

finer

(V

ol.

%)

Particle size (µm)

Mixed aggregates

Optimum curve, Dmin= 63 µm

Gravel 8-16 mm

Sand 4-8 mm

Filler 0-4 mm

2.2. CONCRETE COMPOSITION

13

2.2 Concrete Composition

This section provides information pertaining the properties of concrete components including

the aggregates, binder medium and the additives.

This study aimed for high-performance concrete whereby concrete recipes contain substantial

amounts of cement. However, to reduce the carbon dioxide footprint, a fly ash (FA) cement,

CEM II/B-M 42.5R, has been used. The cement contains 19.2 percent fly ash and 1.7 percent

free lime. Physical properties and chemical composition of the cement are given in Table 2.2.

Furthermore, micro silica has been used as a part of the binding medium. Crushed granite with

a maximum aggregate size of 16 mm was used as coarse aggregate, see Table 2.1. A

polycarboxylate ether based superplasticizer Mapei Dynamon SX-23 was used to enhance the

flowability of the fresh concrete. According to the study performed by Kabay [50], void content

can influence the mechanical properties of fibre concrete. Therefore, to reduce the effect of

entrapped air, in Papers I-IV, air-entraining agent has not been used in the composition of

concrete mixes. Furthermore, Det Norske Veritas [25] limits the fibre content of marine

concrete structures to 2 percent, and the Italian guide for the design and construction of fibre

reinforced concrete structures, CNR [51] recommended a minimum fibre content of 0.3 volume

percent for the structural applications. Based on these criteria, the fibre volume content of

concrete mixes was selected to be in the range of 0.5 - 2 percent.

Table 2.3 shows an example of the used concrete recipes. The experimental procedure from

mixing the concrete, casting the samples and testing has been performed under a controlled

laboratory condition. Table 2.4 shows the mixing procedure that was used for the appended

Papers II-IV.

Table 2.2: Physical properties and chemical composition of the cement [52].

Chemical composition (%)

Compressive strength (MPa) CaO 51.01

1 day 22.0 SiO2 25.98

2 days 32.7 Al2O3 8.25

7 days 42.6 Fe2O3 3.94

28 days 53.8 K2O 1.15

Na2O 0.54

Physical properties MgO 2.18

Specific gravity (kg/m3) 3000 Na2O Eq. 1.30

Specific surface (cm2/g) 4500 TiO2 0.423

Volume expansion (mm/m) 1 P2O5 0.250

Setting time (start) min 154 Mn2O3 0.061

SO3 3.40

Cl- 0.061

Ʃ = 97.2


14

Table 2.3: Concrete composition used in Paper IV.

Specimen

Code

Cement

(kg/m3)

Silica

(kg/m3)

Filler

(kg/m3)

Sand

(kg/m3)

Gravel

(kg/m3)

Water

(litres)

Super

plasticizer

(kg/m3)

Fibre

(kg/m3)

[%]

W/B1

MIX-0-R 495.6 63.2 161.1 1066.6 419.3 190 7.9 [0] 0.34

MIX-0.5-C 495.6 63.2 159.7 1057.7 415.8 190 7.9 10.5 [0.5] 0.34

MIX-0.5-M 495.6 63.2 159.7 1057.7 415.8 190 7.9 10.5 [0.5] 0.34 1 B is the abbreviation for the binder content of the mix including FA-cement and silica.

Table 2.4: Concrete mixing process that was used in Papers II-IV. Modified from [42, 53].

Description of mixing sequence Duration (min)

1. Mixing the aggregates and silica 1

2. Adding the cement 2

2. Adding the water 2

3. Adding the superplasticizer 1

4. Relaxing of the mix 3

5. Mixing the paste with all ingredients 5

6. Adding the fibres with the rate of 5 gr/s and mix 2.5-5

Ʃ = 17.5-19

2.3 Fresh Concrete Properties

Fresh state properties of macro basalt fibre concrete were subject to a previous study [49]. In

this study, flowability and passing ability of fresh concrete were measured using the procedures

of European Standards, NS-EN 12350-8:2010 [54] and NS-EN 12350-12:2010 [55],

respectively. The results show that, for the maximum aggregate size of 16 mm and 43 mm

macro basalt fibres, it is possible to produce self-compacting concrete if the fibre volume

content does not exceed 1 percent. Furthermore, the slump and slump flow of concrete mixes

that were used in shear studies were also measured and presented in Paper II, Table 3. In this

study 4 - 5 percent of air content was aimed for the concrete mixes. The European Standard

method of NS-EN 12350-7:2009 [56] was used to measure the air content. However, due to the

technical reasons, the test was not successful.

2.4 Self-Compacting Macro Basalt Fibre Concrete

Table 2.5 shows the concrete recipes that were used to study the effect of adding macro basalt

fibres on fresh state properties of reference concrete. The reference concrete has been developed

based on the method presented in section 2.1 and aimed for minimum slump-flow of 750 mm.

It ought to be mentioned that only the final recipes are presented here and not the trail ones.

The performance of fresh state concrete has been evaluated using the slum-flow and J-ring

experiments.

2.4. SELF-COMPACTING MACRO BASALT FIBRE CONCRETE

15

Table 2.5: Concrete composition used for self-compacting macro basalt fibre concrete. From [49].

Specimen

Code

Cement

(kg/m3)

Silica

(kg/m3)

Filler

(kg/m3)

Sand

(kg/m3)

Gravel

(kg/m3)

Water

(litres)

Super

plasticizer

(kg/m3)

Fibre

(kg/m3)

[%]

W/B1

BF-SCC-A1 421.7 17.9 173.7 1078.8 462.1 183 10.8 [0] 0.42

BF-SCC-A2 421.7 17.9 173 1074.6 460.3 183 10.8 4.8 [0.23] 0.42

BF-SCC-A3 421.7 17.9 172.4 1070.4 458.4 183 10.8 9.5 [0.45] 0.42

BF-SCC-B1 421.7 17.9 173.4 1077 461.3 183 11.9 [0] 0.42

BF-SCC-B2 421.7 17.9 171.4 1064.4 455.9 183 11.9 14.3 [0.68] 0.42

BF-SCC-B3 421.7 17.9 170.7 1060.2 454.1 183 11.9 19 [0.9] 0.42

BF-SCC-B4 421.7 17.9 170.3 1057.6 453.0 183 11.9 21.9 [1.05] 0.42 1 B is the abbreviation for the binder content of the mix including FA-cement and silica.

2 All the recipes containing 8.8 litres of a viscosity modifier and 1.9 litres of (1:5) diluted MapeAir 25, air

entraining agent. The type of the used superplasticizer was Mapei Dynamon SX.

The SF value is the slump-flow, and t500 is the time that concrete flow needs to reach the border

of the circle with a diameter of 500 mm. These values were measured according to NS-EN

12350-8:2010 [54]. SFJ and tJ500 are the same parameters but measured during the J-ring test

according to NS-EN 12350-12:2010 [55]. The slump-flow values were calculated according to

Equation (2.2) [54].

𝑆𝐹 =(𝑑1

+𝑑2 )

2 (2.2)

where, d1 (mm) and d2 (mm) are largest perpendicular diameters of the distributed concrete

flow [54].

Furthermore, the passing-ability of SCCs were assessed by the J-ring test according to NS-

EN12350-12:2010 [55]. The spacing between the bars of the J-ring was set to (41±1) mm. The

passing-ability values were calculated according to Equation (2.3) [55].

𝑃𝐽 =( ∆ℎx1+∆ℎx2+∆ℎy1+∆ℎy2)

4− ∆ℎx0 (2.3)

where, ∆ℎx , ∆ℎy and ∆ℎx0 are the height difference between the top of J-ring and top of

concrete at the borders and in the middle of J-ring, respectively [55]. The 1 and 2 indices are

showing the measured values at two sides of the ring.

The outcomes of the experiments are summarized in Table 2.6.

Table 2.6: Fresh concrete test results of reference SCCs and BF-SCCs. From [49].

Specimen Code SF (mm)

t500 (s) SFJ (mm) PJ (mm) tJ500 (mm) Fibre (kg/m3)

[%]

BF-SCC-A1 780 1.5 770 7 2.1 [0]

BF-SCC-A2 755 1.6 680 27 2.6 4.8 [0.23]

BF-SCC-A3 710 2.7 595 39 4.7 9.5 [0.45]

BF-SCC-B1 775 2.0 730 6 1.9 [0]

BF-SCC-B2 735 2.2 575 49 4.9 14.3 [0.68]

BF-SCC-B3 710 2.8 545 69 8.7 19 [0.9]

BF-SCC-B4 690 2.4 560 78 6.6 21.9 [1.05]


16

Figure 2.3 shows a comparison between the flowability of macro basalt fibre concrete

containing 1.05 percent of fibres and the reference concrete.

Figure 2.3: On the left-hand side, reference concrete without the fibre (BF-SCC B1) is shown. The right-

hand side shows the SCC with a fibre content of 1.05% (BF-SCC B4). From [49]. Photo: Ali M.

Mohaghegh.

Since two different reference concrete recipes have been used, to compare the results, the flow-

ability ratio is defined as the ratio between the slump-flow of fibre concrete and reference

concrete. Figure 2.4 shows the slump-flow ratio of tested concrete recipes. As it was

predictable, the flowability decreases by increasing the fibre content. However, the flowability

change was small when adding the fibres. According to Yu et al. [42], the flowability of fibre

concrete is mainly influenced by the higher specific surface area and the increased internal

friction of concrete composition due to the addition of fibres.

Figure 2.4: Flowability ratio versus fibre volume content of BF-SCC A and B series. From [49].

10.97

0.91

10.95

0.920.89

0

0.5

1

1.5

0 0.2 0.4 0.6 0.8 1 1.2

Flo

wab

ilit

y R

atio

Vf (%)

BF-SSC A series

BF-SCC B series

2.5. CONCRETE COMPRESSIVE STRENGTH

17

2.5 Concrete Compressive Strength

The compressive strength of the hardened concrete was measured using the European standard,

NS-EN 12390-3 [57]. Cube specimens with a dimension of 100 × 100 × 100 mm3 and Ø 100 ×

200 mm cylinder specimens were cast and used for the measurement. The composition of the

used concrete mixes in the appended Papers are slightly different. Therefore, the results of the

compressive strength experiments for each concrete recipe is presented in the corresponding

Papers. It ought to be mentioned that two distinct types of micro silica have been used in the

Papers. In Paper I, densified silica and in Papers II-IV undensified silica were used. The results

show that by using undensified silica, there is a need for less binder content to reach the same

level of compressive strength.

2.6 Durability of Macro Basalt Fibre Concrete

This section presents the results of a pilot study regarding the effect of fibres on the durability

of concrete similar to the concrete used in the appended Papers. Table 2.7 shows the

composition of concrete mixes used for durability studies.

Table 2.7: Concrete composition that were used in the durability study.

Specimen

Code

Cement

(kg/m3)

Silica

(kg/m3)

Filler

(kg/m3)

Sand

(kg/m3)

Gravel

(kg/m3)

Water

(litres)

Super

plasticizer

(kg/m3)

Fibre

(kg/m3)

[%]

W/B1

MIX-1 381.3 38.1 179.1 1100.0 472.3 183 5.6 [0] 0.44

MIX-2 381.3 38.1 173.6 1066.4 457.8 183 5.6 38 [1.81] 0.44 1 B is the abbreviation for the binder content of the mix including FA-cement and silica. 2 MIXES 1 and 2 contain 2 litres of a viscosity modifier and 1.72 litres of (1:5) diluted MapeAir 25, air entraining

agent. The type of the used superplasticizer was Mapei Dynamon SX.

The chloride diffusion coefficient and bulk resistivity of concrete specimens with and without

fibres have been measured and compared. Furthermore, to investigate the long-term properties

of concrete, the bulk electrical resistivity of the water stored specimens were measured after a

period of more than two years. The water where specimens were stored had an ambient

temperature of 18 - 20 °C. The bulk resistivity ρ and chloride diffusion coefficient Dnssm (m2/s)

were measured using the equations (2.4) [58, 59] and (2.5) [60], respectively. The chloride

diffusion coefficient was measured according to the procedure of NT BUILD 492 [60].

𝜌 = 𝑅A

𝐿 (2.4)

where, R is the measured electrical resistance (Ω), A (m2) is the specimen’s surface area, and L

(m) is the length of samples [58, 59].

𝐷nssm =0.0239(273+𝑇)𝐿

(𝑈−2)𝑡(𝑋d − 0.0238

√(273+𝑇)𝐿 𝑋d

𝑈−2) (2.5)

where T (°C) is the average of the temperature at the start and end of the test, U (V) is the

voltage, L (mm) is the sample thickness, t (hour) is the duration of the experiment, Xd (mm) is

the average of the measured chloride penetration depth [60].


18

Three specimens for each concrete mix were prepared from standard Ø100 × 200 mm

cylindrical specimens. Figure 2.5 shows the split specimens after performing the tests.

According to NT BUILD 492 [60], 0.1 M silver nitride was used on the surface of the split

specimens to detect the chloride penetration depth. The lighter colour shows the depth of

chloride penetration. The construction period of concrete barges may take more than two

months depending on the size. Furthermore, concrete mixes containing fly ash need more time

for the strength development [61]. Therefore, in this study, chloride diffusion coefficient was

measured after a period of 90 days.

The bulk electrical resistivity test results show that; the rate of increasing the bulk resistivity of

hardened concrete specimens without viscosity modifier (VMA) is higher than the one with

VMA. The average bulk resistivity of the specimens similar to that of MIX-1 without VMA at

the age of 28 days, 60 days, and 90 days were 64.7 Ω.m, 170.6 Ω.m and 263.3 Ω.m, respectively.

This shows a higher rate of development in comparison with the values presented in Table 2.8

for MIX-1. Therefore, in Papers I-IV, VMA has been excluded from the concrete recipe.

Instead, to enhance the stability of fresh concrete and the compressive strength of hardened

concrete, the filler-gravel ratio and silica content have been increased. Table 2.9 present the

chloride diffusion coefficient (Dnssm) of concrete with and without fibres. The results show that

the difference between Dnssm of the macro fibre concrete and the reference concrete is small.

Therefore, adding macro basalt fibres did not have a significant effect on the chloride diffusivity

coefficient of the tested concrete samples. However, for a general conclusion regarding the

influence of using macro basalt fibres on the durability of concrete, there is a need for a more

comprehensive study.

(a) (b) (c)

Figure 2.5: (a) Geometry of concrete specimen with a thickness of 50 mm and a diameter of 100 mm

(b) concrete specimen without fibres (c) fibre concrete specimen. Photo: Ali M. Mohaghegh.

Table 2.10 shows the bulk resistivity (ρ) and compressive strength of concrete specimens that

were used in Paper IV. The ρ values presented in Table 2.10 are higher than the values presented

in Table 2.8.

2.7. BASALT FIBRE REINFORCEMENT

19

Table 2.8: Compressive strength and durability parameters of concrete specimens similar to that of used

in the appended Papers.

Specimen

Code

fcm (MPa)

(28 days)

fcm (MPa)

(90 days)

fcm (MPa)

(27 months)

Bulk

resistivity

(28 days)

Bulk

resistivity

(90 days)

Bulk

resistivity

(27 months)

Average Dnssm

(90 days)

MIX-1 49.4 [2.3] 67.5 [4.0] 77.2 [1.2] 88.0 245.7 595.3 4.77×10-12

MIX-2 53.5 [0.8] 69.0 [0.7] 78.4 [2.3] 87.2 263.9 720.5 4.44×10-12

Table 2.9: Measured values of chloride diffusion coefficients for the reference and macro fibre concrete.

Groups Sample 1 Sample 2 Sample 3 Average

Reference Concrete (MIX-1) 3.60×10-12 4.91×10-12 5.81×10-12 4.77×10-12

Macro Fibre Concrete (MIX-2) 4.56×10-12 4.93×10-12 3.83×10-12 4.44×10-12

Table 2.10: The compressive strength and the electrical resistivity of concrete mixes used in Paper IV.

Specimen

Code

Bulk wet density

(kg/m3)

Bulk resistivity

(Ω.m)

fcm1 (MPa) fcm

2 (MPa)

MIX-0-R 2416 434.3 94.9 [1.7]3 114.5 [2.2]

MIX-0.5-C 2411 446 88.5 [4.3] 117.5 [1.7]

MIX-0.5-M 2428 380 93.2 [1.4] 121.0 [1.1] 1 The average compressive strength of concrete at the age of 28 days. 2 The average compressive strength of concrete at the age of 65 days. 3 The values in [] show the standard deviation.

2.7 Basalt Fibre Reinforcement

Basalt stones have been used as a construction material for centuries, whereby some of the

historic buildings made of basalt are still standing [62]. This may be seen as an evidence for

functional resistance against environmental deterioration. The 20th century was a revolutionary

time for material science and technology whereby new construction materials have been

developed. The use of fibres for building has a route in the ancient time. However, new

generation of fibres have been used for about 120 years [26]. The concept of producing fibres

from basalt stones was introduced by French Paul Dhe in 1923 [15]. The properties of basalt

fibres such as high tensile strength and thermal resistant suit well with the material

characteristics which are essential for the military and aerospace technology [63, 64].

Therefore, Russian scientists launched extensive studies on the development of basalt fibres in

the mid-1950s and further to the first production line of continuous basalt fibres in 1985 [14,

65].

Continuous basalt fibres having the diameter of 10-20 μm are produced from melted basalt

stones through an extrusion process, similar to the manufacturing process of glass fibres [14].

However, the basalt fibres production process is more economical and environmentally friendly

comparison with glass fibres [14, 64]. The reason is that the only input of basalt fibre production

line is the natural basalt stones and also it uses less energy [14, 64]. The basalt fibres behave

elastically until the failure point without any plastic zone [14]. Similar behaviour was also

observed in BFRP materials, see Paper II. In the literature, there are contradictory opinions

regarding the durability of basalt fibre, whereby some are cited in Paper I. According to


20

Williams Portal [66], [67], the durability of basalt fibres is depending on the raw materials,

production process, sizing, etc. However, the durability study of basalt fibres or BFRPs is not

in the scope of this thesis work.

Figure 2.6 shows the geometry of the fibres that has been used in this study. The chopped fibres

were 13 mm long. The basalt macro fibres (MiniBars) had a diameter of 0.65 mm and a density

of 2100 kg/m3 [68]. The tensile strength and the elastic modulus of the fibres were 1000 MPa

and 44 GPa, respectively [68]. The number of fibres per kg based on the samples that were

counted in the laboratory was 27400 and 21600 for 43 and 55 mm fibres, respectively.

Figure 2.6: Geometry of fibres: chopped basalt fibres (left) macro basalt fibres (right). Photo: Ali M.

Mohaghegh.

Figure 2.7, shows the basalt bars that were used in Paper II. Both basalt bars and MiniBars are

made of BFRPs. The BFRP materials used in this study are composed of continuous basalt

fibres as the reinforcing component and a thermoset vinyl ester resin as the unifying matrix

[68]. The existing industrial experiences show that vinyl ester composites are resistant to

corrosive materials [69].

According to Banibayat and Patnaik [70], the variability of tensile test results of BFRPs

produced by new automated wet-layout process is similar to the other types of FRPs. They also

stated that ACI 440-3R [71] and ACI 440-1R [30] can be used for testing and determination of

BFRPs’ mechanical properties [70]. The results of the tensile test on the BFRP rebars are

presented in Paper II.

Figure 2.7: The 1200 mm basalt fibre reinforced polymer bars used in Paper II. The nominal diameter

of the bars was 8.9 mm. Photo: Ali M. Mohaghegh.

3.1. GENERAL

21

3 Flexural Strength

3.1 General

The vulnerability of concrete to a tensile failure is well known. The steel rebars are usually

carrying the tensile stresses in reinforced concrete. However, several decades of scientific work

and industrial experience suggest that steel fibres can be used as an alternative for the steel

rebars to enhance the tensile capacity of concrete members [72-74]. Fibres in concrete matrix

start to act as a tensile element when the concrete starts to crack [75]. Therefore, the post-

cracking properties of concrete are the main parameter to predict the structural capacity of

concrete members. Several standards [17, 76, 77] have been developed for characterization of

post-cracking properties of fibre concrete. This chapter presents a brief summary of standard

experimental methods for evaluating the residual tensile strength of fibre concrete.

Subsequently, the results of the residual tensile strength tests are presented for macro basalt

fibre concrete of various fibre dosage. Moreover, the ductility of fibre concrete is discussed.

3.2 Residual Flexural Tensile Strength

Characterization of fibre concrete has been the subject of many studies [78]. These studies led

to establishing the standard experimental methods. Among others, the following standards

aimed at evaluating the residual flexural tensile strength of fibre concrete members are

extensively cited in the literature:

▪ EN 14651, “Test method for metallic fibre concrete measuring the flexural tensile

strength” [17].

▪ C1609/C1609M – 12, “Standard test method for flexural performance of fibre-

reinforced concrete” [76].

▪ C1399/C1399M – 10, “Standard method for obtaining average residual-strength of

fibre-reinforced concrete” [77].

The outcomes of the three-point bending test according to EN 14651 [17] standard is used as

the input for computing the structural capacity of fibre concrete members in fib Model Code

2010 [18, 23] and other European standards, e.g. the Swedish standard SS 812310 [19].

Therefore, in this research programme, EN 14651 [17] was selected for evaluating the post-

cracking properties of macro basalt fibre concrete of different fibre dosages.

Chapter 3. Flexural Strength

22

In the above standards, the load-deflection and load-CMOD (crack mouth opening

displacement) curves were used to address the flexural properties of fibre concrete beams. In

the study presented in Paper I, both mid-span deflection and CMOD of the notched beams were

measured. The residual flexural tensile strengths (fR,j) of fibre concrete were computed using

the Equation (3.1) [17].

𝑓Rj =3

2

𝐹j𝑙

𝑏ℎsp2 (3.1)

where, b, l and hsp are width, length and height of the fracture cross section in millimetre,

respectively. Moreover, Fj (j = 1, 2, 3, 4) is the load at CMOD = 0.5, 1.5, 2.5 and 3.5 mm,

respectively [17].

The fRj values address the post-cracking properties of fibre concrete corresponding to

subsequent stages of loading from serviceability limited state to ultimate limit state [23]. The

classification method presented in fib Model Code 2010 [23] and the Swedish standard SS

812310 [19] aims for categorizing the fibre concrete based on their brittleness [79]. The 𝑓R3K

𝑓R1K ratio, is considered as the main criterion for this classification [79]. According to fib Model

Code 2010 [23], for structural applications, the relationship presented in Equations (3.2) and

(3.3) shall be satisfied. 𝑓R1K

𝑓LK> 0.4 (3.2)

𝑓R3K

𝑓R1K> 0.5 (3.3)

where fLK is the characteristic value of tensile strength corresponding to the limit of

proportionality [23].

In this study, a limited number of specimens of each fibre dosage were tested. Therefore only

the average values are presented and not the characteristic values. Table 3.1 shows the

computed values of 𝑓R1m

𝑓Lm and

𝑓R3m

𝑓R1m of the tested fibre concrete recipes.

Table 3.1: The summary of the three-point bending test results presented in Paper I.

Code MSC

-I

MSC

-II

MSC

-III-1

MSC

-III-2

HPC

-I-1

HPC

-I-2

HPC

-II-1

HPC

-II-2

HPC

-III

Vf (%) 0.94 0.94 1.97 1.97 0.71 0.71 0.94 0.94 1.88

fcm (MPa) 61.3 75.7 65.7 67.8 96.8 106.8 91.9 96.4 90.7

fR1m/ fLm 0.7 1.1 1.6 1.8 0.7 0.6 1.0 0.8 1.5

fR3m/ fR1m 0.7 0.4 0.6 1.0 0.4 0.4 0.5 0.7 0.8

According to the values presented in Table 3.1, the concrete mixes containing less than one

volume percent of macro basalt fibres showed values close to the limits given in Equations (3.2)

and (3.3). The mixes containing higher fibre volumes are promising candidates for structural

applications. It is worth mentioned that, depending on the type of steel fibres, post-cracking

properties of macro basalt fibre concrete may be comparable with steel fibre [75].

3.3. THE DUCTILITY OF FIBRE CONCRETE MEMBERS

23

3.3 The Ductility of Fibre Concrete Members

Various methods are used for evaluating the ductility and the toughness of concrete members

in literature [33, 80-82]. Ductility of fibre concrete members is a function of their energy

absorption capacity [81]. Akcay and Tasdemir [81] defined the ductility as the ratio of the fibre

concrete fracture energy to the plain concrete fracture energy. Olivito and Zuccarello [80]

introduced the Equations (3.4) and (3.5) for computing the ductility indexes of flexural fibre

concrete members.

𝐷0 =𝑓eq (0−0.6)

𝑓If (3.4)

𝐷1 =𝑓eq (0.6−3)

𝑓eq (0−0.6) (3.5)

In the above equations, the first crack flexural strength fIf is calculated using Equation (3.6)

[80]. Equations (3.7) and (3.8) are the equivalent flexural tensile strength corresponding to the

CMOD intervals of 0 - 0.6 mm and 0.6 - 3 mm, respectively [80].

𝑓Ic =𝐹Ic ·𝑙

𝑏ℎsp2 (MPa) (3.6)

where FIc is the first flexural crack load (N).

𝑓eq (0−0.6) =1

𝑏ℎsp2 ·

𝑈1

0.6 (3.7)

𝑓eq (0.6−3) =1

𝑏ℎsp2 ·

𝑈2

2.4 (3.8)

where U1 and U2 (10-3 J) are the area under the load-CMOD diagram for the intervals of 0 - 0.6

mm and 0.6 - 3 mm, respectively [80].

Similar to the above formulas, in Paper I, Equation (3.9) defined as the ductility of the fibre

concrete members. Equation (3.9) is adapted from Akcay and Tasdemir [81], and Olivito and

Zuccarello [80].

𝐼ductility =𝐷BZ

𝑏 +𝐷BZ,3𝑓

𝐷BZ𝑏 (3.9)

where,

𝐷BZ𝑏 is the energy absorption capacity of plain concrete [16, 83];

(𝐷BZ𝑏 + 𝐷BZ,3

𝑓) is the energy absorption capacity of fibre concrete corresponding to the mid-

span deflection of (𝛿 = 𝛿L + 2.65 mm) [16, 83]. δL is the value of the mid-span deflection

corresponding to the limit of proportionality [16, 83].

It ought to be mentioned that the toughness indices defined by ASTM C 1018 – 97 “Standard

test method for flexural toughness and first-crack strength of fibre-reinforced concrete” [84] is

Chapter 3. Flexural Strength

24

basically identical parameter as ductility. The toughness index In is defined by Equation (3.10)

[84, 85].

𝐼n = ∫ 𝐹(𝛿) · 𝑑𝛿

𝛿n0

∫ 𝐹(𝛿) · 𝑑𝛿𝛿Ic

0

(3.10)

𝛿𝑛 = 𝑛 · 𝛿Ic (3.11)

where δIc is the mid-span deflection corresponding to the first crack load in a three-point

bending test. Equation (3.11) presents δIc times n value (n = 3, 5.5, 10) [84].

The results presented in Paper I shows that the ductility value of the tested beams increases by

increasing the fibre dosage. See Figures 9, Paper I.

4.1. SHEAR CAPACITY OF FIBRE CONCRETE BEAMS ACCORDING TO RILEM TC 162-TDF

(2003)

25

4 Shear Strength

Several standards have been developed for designing steel fibre concrete members. fib Model

code 2010 [18] introduced a semi-empirical model for designing concrete beams where the

shear reinforcement bars are replaced by steel fibres [86]. Moreover, Model Code 2010 [18]

also introduced a model for prediction of punching shear capacity of elevated fibre concrete

slabs with rebars. This model is based on the critical shear crack theory (CSCT) introduced by

Muttoni and Schwartz [87]. Swedish standard (SS 812310) [19] among others introduced a

model for prediction of punching shear capacity of ground supported fibre concrete slabs. This

model is developed based on the study performed by Silfwerbrand [88]. This chapter presents

a brief summary of these design methods of fibre concrete beams and slabs. Moreover, the

results of an experimental assessment performed on macro basalt fibre concrete beams and slabs

are presented.

4.1 Shear Capacity of Fibre Concrete Beams According to

RILEM TC 162-TDF (2003)

RILEM TC 162-TDF (2003) [24] presented a method for computing the shear capacity of fibre

concrete beams, whereby, the contribution of concrete, fibres and the stirrups have been

considered separately. Equations (4.1) [24] and (4.2) [24] show the contribution of concrete and

steel fibres, respectively.

𝑉cd = {0.12 𝑘 · [100 · ⍴l · 𝑓ck ]1

3⁄ + 0.15 · 𝜎cp } · 𝑏𝑤 · 𝑑 (4.1)

where:

𝑘 = 1 + √200

𝑑 ≤ 2.0 is the size effect factor;

ρ1 is the longitudinal reinforcement ratio;

d is the effective depth of the cross section [mm];

bw is the width of the cross-section in the tensile area [mm];

σcp is the average compressive stress, if any, acting on the concrete cross-section;

𝑉fd = 0.7𝑘 𝜏fd · 𝑏𝑤 · 𝑑 (4.2)

where:

𝜏fd = 0.12𝑓R4k is the design value for the contribution of fibres in (MPa).

It ought to be mentioned that Equation (4.2) is presented in the specific form where, the beam

is without flange.

Chapter 4. Shear Strength

26


fib Model Code 2010

Model Code 2010 introduced a model for prediction of the shear capacity in steel fibre concrete

beams with longitudinal steel bars. This model is developed based on the Eurocode 2 [86]. The

toughness improvement due to the use of fibres is considered by increasing the contribution of

the concrete matrix in the shear capacity [86]. In another word, 𝑓ck is replaced by

(1 + 7.5 ·𝑓Ftuk

𝑓ctk ) · 𝑓ck in Eurocode 2 equation for the shear capacity of members without

stirrups. Equation (4.3) [18] is the proposed formula by fib MC 2010 and Swedish standard

(SS812310). However, there is a minor difference pertaining the assumption for the fFtuk value.

It ought to be mentioned that Equation (4.3) is developed for the beams with the 𝑎

𝑑 > 2.5.

𝑣RD,cf = {(0.18

𝛾C ) · 𝑘 · [100 · ⍴l (1 + 7.5 ·

𝑓Ftuk

𝑓ctk ) · 𝑓ck ]

13⁄

+ 0.15 · 𝜎cp } · 𝑏𝑤 · 𝑑 (4.3)

where:

k, ρ1, d, bw and σcp are identical to the parameters that are presented for Equation (4.1)

γc is the partial safety factor for concrete;

fFtuk is considered equal to 0.06 fR1 + 0.3 fR3 in fib MC 2010;

fFtuk is considered equal to fft, R3 (0.37 fR3) in SS 812310;

fctk is the characteristic tensile strength value of the concrete matrix [MPa];

Mondo [89] performed an extensive study to select the best formula for predicting the shear

capacity of fibre concrete beams. In her study, a database comprised of around one hundred

papers containing the result of shear tests on fibre concrete beams has been processed. Modern

standards usually consider the residual tensile strength as the main parameter for evaluating the

mechanical properties of fibre concrete members. Therefore, she used a back-analysis to extract

the post-cracking parameters corresponding the existing experimental data. Moreover, she

compared the experimental results with the calculated values based on the models suggested by

Narayanan and Darwish [90], RILEM TC 162-TDF (2003) [24] and CNR [51]. She found that

calculated values of shear capacity using the CNR [51] and RILEM [24] model show the best

agreement with the experimental results.

However, Mondo [89] stated that, CNR [51] formula is the best choice for a structural design

formula. This is due to a wider range of validity in comparison with RILEM, whereby, the

concrete compressive strength is limited to 50/60 MPa [89]. Similar models have been

suggested for prediction of shear capacity by both fib MC 2010 and the Swedish Standard

(SS812310) [19]. Therefore, in this study, the experimental results were only compared with

these two models.

In DNV-OS-C502 standard [25], the FRP fibres and rebars have been recognized as structural

materials. Therefore, the DNV method for computing the shear capacity of FRP fibre concrete

beams is briefly discussed in section 4.2.

4.3. SHEAR CAPACITY OF FIBRE CONCRETE BEAMS ACCORDING TO DNV-OS-C502

27


DNV-OS-C502

Equation (4.4) is suggested by DNV-OS-C502 [25] for computing the shear capacity of

concrete beams without stirrups. Furthermore, for fibre concrete beams, the contribution of

fibres in shear capacity of the beams is considered through the design value for the tensile

strength of concrete (ftd). Equation (4.5) presents the DNV formula for estimation of

characteristic value of tensile strength in FRP fibre concrete. Moreover, according to DNV-OS-

C502 [25] the increase in shear capacity due to the use of fibres is only allowed when the

calculated values of shear capacity are experimentally verified.

𝑣cd = 0.3 (𝑓td +𝑘A 𝐴s

𝛾𝑐𝑏w 𝑑) 𝑏𝑤 · 𝑑 · 𝑘V ≤ 0.6 𝑓td · 𝑏w · 𝑑 · 𝑘V (4.4)

where, bw (mm), d (mm) and As (mm2) are the width, effective depth and the cross-sectional

area of longitudinal rebars, respectively. Moreover, kA (MPa) and kV (MPa) are material

depended parameters. For BFRP rebars these parameters are presented in “DNV guidelines for

BFRP reinforcement bars in concrete structures” [91].

𝑓tk = (0.48 + 0.05 𝑉f) · (𝑓ck )0.5 (4.5)

where, Vf is the dosage of FRP fibres in volume percentage.

4.4 Experimental Assessment of Shear Capacity

There is no standard method for the assessment of shear capacity in fibre concrete beams.

However, an experimental set-up has been recommended by DNV-OS-C502 [25] to verify the

shear capacity of fibre concrete beams with steel rebars. In the recommended set-up, the test

beam shall be minimum 1350 mm in length, 200 mm in height (h) and 100 mm in width (b).

Furthermore, the shear span shall be minimum 500 mm.

In this study, small beams have been used to investigate the shear capacity of macro fibre

concrete beams, see Figure 4.1. The shear span ratio (a/d) of the beams was 2.0. The area of the

BFRP longitudinal rebars was 249 mm2. The load-mid span data were measured using a 200

kN load cell and two LVDTs. The measured data were recorded using a 50 Hz acquisition

system. Furthermore, the crack pattern of the beams was recorded from the initial crack up to

the critical crack using a 16 megapixels camera. The sequential pictures were merged to

establish a picture for the whole test duration.


28

Figure 4.1: The experimental set-up of the four-point loading shear test whereby two LVDTs mounted

on two sides of the beam were used to measure the mid-span deflection. The numbers are in mm. From

Paper II.

4.5 Shear Capacity of Macro Basalt Fibre Concrete Beams

Monitoring of the beams during the experiment showed that the initial cracks were flexural

cracks and they appeared in the middle of the beams. Afterward, the distribution of the cracks

developed further to the shear span region. As the beams were designed to fail in shear mode,

the fracture occurred when the critical shear crack grow until the beams were divided into two

main pieces. However, no signs of failure have been observed on the longitudinal rebars. Figure

4.2 shows a sample of crack patterns on the test beams.

Vf = 0.5%

Vf = 2.0%

Figure 4.2: Example of a crack pattern of fibre concrete beams with two different fibre contents under

the shear test. The load values written on the beams are the loads corresponding to each crack. From

Paper II.

4.5. SHEAR CAPACITY OF MACRO BASALT FIBRE CONCRETE BEAMS

29

Figure 4.3 shows the distribution of the fibres in the critical shear section of the beams with

various fibre contents. The fibres are pained with a red colour that can be distinguished from

the concrete matrix. As it can be seen, the fibres are uniformly distributed in the beam’s cross-

section. Furthermore, Figure 4.3 shows that the shear cracks are passing through the aggregates.

This is due to the high strength of concrete used in the test samples [92].

Contrary to the steel fibre concrete where the failure usually is due to fibre pull-out, in this

study the beams failed because of fibre rupture. The failure mode depends on the type of fibres

and the bonding strength of concrete matrix [93]. The pull-out failure may appear when the

concrete matrix fail first [93]. In high performance concrete, the failure mechanism may change

to a fibre rupture [93]. The shape and the distribution of the cracks were directly related to the

beam’s fibre volume content. The number of cracks has been increased by increasing the fibre

content. Furthermore, the results of the experiments show that; by increasing the fibre dosage,

the shear capacity of concrete beams have increased. To verify the possibility of using the

models that are initially developed for steel fibre concrete beams, predicted values of fib Model

Code 2010 and Swedish standard (SS 812310) were compared with the experimental results,

see Table 6, Paper II. The comparison shows promising results whereby the experimental

results demonstrated good correlation with the predicted values, see Figure 4.4. Furthermore,

using the fibre dosage of more than 1 volume percent shows a promising contribution in the

shear capacity of the beams. For the volume content of 2 percent, the shear capacity of the fibre

concrete beams has increased by 73 percent.

Figure 4.3: The distribution of fibres in the surface of critical shear cracks of the beams with different

fibre dosages. Photo: Ali M. Mohaghegh.

The data presented in Table 5, Paper II shows a linear relationship between the fibre volume

fraction and the number of fibres crossing the critical shear cracks. This alongside with Figure

4.3 indirectly shows the fibres were uniformly distributed in the beams even in higher fibre

volume content.


30

Figure 4.4: Computed values of shear capacity using the fib Model Code 2010 versus the experimental

results. After Paper II.

4.6 Punching Shear Capacity of Fibre Concrete Slabs

According to fib Model Code 2010

The method for computing the punching shear capacity of concrete slabs in fib Model Code

2010 is derived from the critical shear crack theory (CSCT), which is developed by Muttoni

and Schwartz [94]. According to Muttoni and Schwartz [87], the punching shear capacity of

concrete slabs is inversely corresponding to the width of critical shear crack. Figure 4.5 shows

a schematic picture of parameters determining the punching shear capacity of concrete slabs.

Muttoni and Fernández Ruiz [94] introduced a method for computing the punching shear

capacity of fibre concrete slabs based on the CSCT. Moreover, Model Code 2010 [18]

suggested a simple approach whereby the contribution of fibres in punching shear capacity is

considered as a function of ultimate crack opening and consequently the rotation of the slab.

Further details regarding the punching shear capacity of fibre concrete slabs can be found in

Section 7.7.3.5.3 of Model Code 2010 (Volume 2) [18].

4.7. PUNCHING SHEAR CAPACITY OF THE GROUND SUPPORTED SLABS ACCORDING TO SWEDISH

STANDARD (SS 812310)

31

Figure 4.5: Schematic picture of parameters influencing the punching shear capacity of concrete slabs

according to the critical shear crack theory according to Muttoni and Fernández Ruiz [94].

4.7 Punching Shear Capacity of the Ground Supported

Slabs According to Swedish Standard (SS 812310)

Equation (4.6) is the model for prediction of punching shear capacity of ground-supported slabs

developed by Swedish standard (SS 812310). The model is based on Silfwerbrand [88, 95]

obtained from the static equilibrium of internal and external forces acting on the punching shear

fracture cone.

𝑣D,ss = (1

𝛾f ) · (

𝑘

2) · 𝐶 · 𝑓R,3 (4.6)

where:

γf is the partial safety factor for fibre concrete, in this study γf = 1.

𝑘 = 1 + √200

𝑑≤ 2.0 is the size effect factor and C = 0.45.

fR,3 is the characteristic value of the residual flexural tensile strength of fibre concrete

corresponding to crack mouth opening displacement (CMOD) of 2.5 mm.

4.8 Experimental Assessment of Punching Shear Capacity

When it comes to the experimental study of physical and mechanical problems, using small-

scale experiments could be economically beneficial. However, the test set-up shall be

representative and simulate the real physics of the problem. Large-scale punching shear

experiments of the concrete slabs are normally expensive and need extensive laboratory

equipments. Thereby, few simplified experimental methods have been presented in the

literature [21, 96] for assessment of punching shear capacity of concrete slabs. Considering this

insight, a simple method introduced by Hassan, Mahmud [21] was selected for the assessment

of punching shear capacity of ground supported macro basalt fibre concrete slabs. Moreover,


32

the validity and limitation of this test method have been examined. For each fibre volume

content, two slabs series were tested. The A series slabs had a predefined fracture angle of 44°,

and the B series slabs had a predefined fracture angle of 29°. Figure 4.6 shows the cross-section

of the A and B series slabs, the induced fracture angle, load cell and LVDT arrangement. The

data measured using a 200 kN load cell and a 50-mm LVDT were recorded using a 50 Hz

acquisition system.

Figure 4.6: The cross-section of A and B series macro fibre concrete slabs and the layout of the load cell

and the LVDT sensor that were used in Paper III for assessment of punching shear capacity. The test

set-up is slightly modified from Hassan, Mahmud [21].

4.9 Punching Shear Capacity of Macro Basalt Fibre

Concrete Slabs

By studying the fracture surfaces, it is apparently visible that the critical shear cracks followed

the path between the notch tip and the closest loading point. The A series slabs showed greater

failure load in comparison with B series slabs. The greater recorded load bearing capacity is

due to the arching effect whereby the sizeable portion of the load transferred directly to the

circular support. Therefore, it cannot be represented as the shear capacity of the corresponding

concrete mix. Figure 4.7 shows the experimental results versus computed values using Equation

(4.6) [19]. As it can be seen, for the concrete slabs with the fibre dosage of more than 1 percent

there is a decent correlation between the calculated values and the experimental results.

Furthermore, the ductility of concrete specimens has been slightly improved by increasing the

fibre content. It ought to be mentioned that, the formula that was developed for the ductility of

fibre concrete slabs and presented in Paper III is only valid for the fibre dosage of 0.5 - 2 percent.

The study performed by De Hanai and Holanda [97] showed that there is a similarity between

the shear capacity of the beams and slabs of the resembling dimensions. However, as it is

presented in Paper III, the punching shear capacity of the tested slabs did not show the same

obvious effect of the fibres. If we see this with the perspective of the critical shear crack theory,

the restrained rotation of the slabs specimens could be the reason for the insignificant

contribution of the fibres. Therefore, as it is also discussed in Paper III, the results of this test

set up are only conditionally valid.

4.9. PUNCHING SHEAR CAPACITY OF MACRO BASALT FIBRE CONCRETE SLABS

33

The idea of using circular notches to induce a predefined failure surface, whereby the punching

shear capacity of the slabs can be studied is interesting for a specific fracture angle. However,

based the critical shear crack theory, to assess the contribution of the fibres, the experimental

set-up needs to be modified. The test on slabs shall have rotational freedom around the polar

axis perpendicular to the loading direction.

Figure 4.7: Computed values of punching shear capacity using the Swedish standard versus the

experimental results. From Paper III.


34

5.1. FIRE SPALLING OF FIBRE CONCRETE

35

5 Fire Spalling

The fire resistance of concrete is superior to that of most other construction materials [95].

However, fire incidents in some of the European tunnels show that moist high-performance

concrete is prone to fire spalling [22, 31, 95]. The fire spalling may risk the structural stability

and cause sizeable economic damages [22, 31, 95]. Fire spalling of high-performance concrete

(HPC) has been subject to many studies [32, 98]. Moreover, different theories concerning the

fire spalling mechanism may be found in the literatures [32]. The use of polypropylene fibres

has been recognized as a low-cost solution to protect the concrete from fire spalling [31]. Macro

basalt fibre concrete show to have a good structural performance. However, the fire spalling

resistance of macro basalt fibre concrete is not well known. This chapter presents the results of

the recent study (Paper IV) on fire spalling of MBFC.

5.1 Fire Spalling of Fibre Concrete

Contrary to polypropylene fibres, the steel fibres have only minor beneficial effect on fire

spalling resistance of concrete [99, 100]. The behaviour of polypropylene fibre concrete was

subject to many studies [22, 101, 102]. Figure 5.1 shows a schematic picture of how

polypropylene fibres can influence the fire spalling properties of concrete.

Figure 5.1: A schematic picture of the mechanism of polypropylene fibres in fire spalling. Based on

Robert Jansson’s Doctoral Thesis [32].

Chapter 5. Fire Spalling

36

Furthermore, information on fire spalling properties of other types of fibres including basalt

fibres is scarce in the literature. In sections 5.2 and 5.3, the results of pilot fire spalling

experiments on chopped basalt fibre concrete and macro basalt fibre concrete are presented.

5.2 Fire Spalling Experiment

Fire spalling of fibre concrete was evaluated using a comparative experimental approach. A

small-scale test set-up designed by SP Technical Research Institute of Sweden was selected for

this study [103]. Three specimens consisting of a reference concrete, a chopped basalt fibre

concrete and a macro basalt fibre concrete with the dimension of 500 × 600 × 200 mm3 were

cast and tested. A steel reinforcement ring was used to maintain the integrity of the specimens

during the experiments, see Figure 5.2 and Figure 2 in Paper IV for the details of the rebars.

The specimens were cured in a pool of water at a temperature of approximately 18°C for 28

days and 37 days outside the water. Figure 5.3 shows the SP fire spalling testing furnace. The

furnace temperature rise was measured using one millimetre shielded type K thermocouple.

The temperature rise was regulated by the control of gas flow according to the standard time-

temperature as defined in Eurocode 1 [104]. In all three specimens, spalling started after 6 - 7

minutes from the beginning of the test that is corresponding to the furnace temperature of

approximately 600°C. The experiments were continued for 40 minutes. Fire spalling of the

samples did not stop and progressively continued during the period of testing. Afterward, the

spalling depth values were measured and recorded to assess the effect of using fibres on the

spalling properties of concrete.

Figure 5.2: Reinforcement ring used in the slab specimens. Photo: Ali M. Mohaghegh.

5.3. RESULTS AND STATISTICAL ANALYSIS

37

Figure 5.3: Fire spalling test setup. From Paper IV. Photo: Ali M. Mohaghegh.

Figure 5.4 shows the concrete pieces separated during the fire spalling. The size of concrete

pieces for the specimen containing macro basalt fibre was about 5 - 70 mm long with a thickness

of 5 - 10 mm. It ought to be mentioned that the size of the pieces in the samples without fibres

or with chopped fibres was slightly smaller than the one with macro fibres. Moreover, as it can

be seen in Figure 5.4, basalt fibre filaments are still visible after the fire test while the resin has

disappeared due to decomposition and evaporation or due the burning.

Figure 5.4: Concrete pieces remaining in the furnace after fire spalling test of macro fibre concrete

specimens. Photo: Ali M. Mohaghegh.

5.3 Results and Statistical Analysis

Table 5.1 presents the spalling depth (cm) values of the tested concrete slabs. Moreover, Figure

5.5 shows the coordinates of the measurement points of fire spalling depth. ANOVA statistical

analysis method [105] was used to investigate the influence of fibres on fire spalling properties

Chapter 5. Fire Spalling

38

of the concrete specimens. The test was performed at the level of significance α = 0.05. Table

5.1 and 5.2 show the results of the ANOVA test. The null hypothesis assumed to be true if there

is no difference between the mean values of fire spalling in three specimens. Contrary, the

alternative hypothesis is correct when the mean values of three specimens are different. As it

can be seen in Table 5.3, the F statistic is smaller than F critical. Moreover, P-value is more

than 0.05. Therefore, the null hypothesis cannot be rejected. The results of the ANOVA test

shows that the difference between fire spalling of reference and fibre concrete is neglectable.

Figure 5.5: The coordinates of the measurement points specified in the sampling area.

Table 5.1: Fire spalling values (cm) of concrete specimens.

Concrete Specimen’s p1 p2 p3 p4 p5 p6 p7 p8 p9 p10

Reference Concrete 5.2 5.2 6.1 6.1 6.5 6.8 7.4 8.8 9.2 9.4

Chopped Fibre Concrete 5.9 6.7 7.0 7.2 7.7 7.9 8.0 8.0 8.2 9.4

Macro Fibre Concrete 3.4 4.6 5.0 5.6 6.5 6.9 7.0 7.4 8.7 8.8 1 The point p10 was measured where the spalling depth was maximum.

Table 5.2: Average and variance of the measured fire spalling values of concrete specimens.

Groups Count Sum Average Variance

Reference Concrete 10 70.7 7.07 2.48

Chopped Fibre Concrete 10 76 7.60 0.92

Macro Fibre Concrete 10 63.9 6.39 3.06

Table 5.3: The result of Analysis of variance for fire spalling of concrete specimens.

Source of

variation

Degree of

freedom

Sum of

squares

Mean

squares

F P-value F critical

Between Groups 2 7.358 3.679 1.709 0.199 3.354

Within Groups 27 58.09 2.151

Total 29 65.448

Based on the visual inspection of the tested specimens and the results of the hypothesis testing,

no beneficial effect of using basalt fibres was observed. On the other hand, the results also show

that using the macro basalt fibres and chopped basalt fibres did not have any detrimental effect

on the resistance against fire spalling in comparison with the reference sample.

6.1. GENERAL CONCLUSIONS

39

ob

6 Conclusions and Further Research

6.1 General Conclusions

The purpose of this research project was to identify the structural properties of basalt fibre

concrete. The primary focus was to characterize the unknown properties of basalt fibre concrete

members. Thereby, small-scale experiments were utilized to identify the flexural strength, shear

capacity, punching shear capacity and fire spalling propensity of macro basalt fibre concrete

(MBFC). The following conclusions may be drawn based on the investigation described in the

appended Papers.

▪ Compressive strength, density and electrical resistivity of hardened concrete seem to be

independent of the fibre content. Furthermore, based on the literature, the high values

of electrical resistivity of the designed concrete recipes can be taken as an implication

for the high durability in the marine environment.

▪ The post-cracking strength and the ductility of flexural members found to be a function

of fibre volume fraction. In fibre concrete members with the same fibre volume content,

the members with a smaller aspect ratio have shown to have a smaller scatter in the

results. That seems to be due to a high number of fibres. Contrary, greater post-cracking

peak values were observed for the members with a higher aspect ratio. However, since

only a few samples of two different fibres have been tested, it is not possible to draw a

conclusion regarding the effect of the fibre aspect ratio. Usually by increasing the fibres

aspect ratio the performance of fibre concrete improves.

▪ The shear capacity of basalt fibre concrete beams is a function of fibre content. The

shear capacity increases by increasing the fibre dosage. The results show that there is a

good correlation between the predicted values of the fib Model Code, the Swedish

Standard SS 812310 and the experimental outputs. The empirical models of the

standards are developed for steel fibre concrete beams reinforced with conventional

steel bars. The results show that the models presented in the standards are also valid for

the macro basalt fibre concrete beams reinforced with BFRP bars.

▪ The punching shear capacity of small-scale basalt fibre concrete slabs with a fracture

angle of 29º show slight improvement by increasing the fibre content. Furthermore, the

experimental results were comparable with predicted values using the Swedish Standard

(SS 812310:2014).

Chapter 6. Conclusions and Further Research

40

▪ The results of the fire spalling test show that using basalt fibres cannot prevent high-

performance concrete (HPC) from spalling. However, macro basalt fibres or chopped

basalt fibres do not increase the spalling propensity of the tested materials.

The contribution of this research project was the identification of the properties of macro basalt

fibre concrete to be used for structural design purposes. The above-stated conclusions show that

the design methods that were initially developed for the steel fibre concrete members are also

valid for the macro basalt fibre concrete members.

6.2 Further Research

In most research projects, the time, the budget and the experimental equipment abandon the

scope of the work. This project was not an exception. Thereby, there is still a need for more

comprehensive studies before basalt fibre concrete can be used as a structural material. The

author suggests the following items for further investigation.

▪ The results presented in this thesis are based on the small-scale experiments. Based on

the literature, the size effect is an important parameter affecting the behaviour of

structural members. Therefore, to identify the size effect in basalt fibre concrete

members, large-scale experiments are also needed.

▪ Only beams with the shear span-effective depth ratio of 2.0 was used to characterize the

shear capacity of basalt fibre concrete. Therefore, further investigation is needed to

quantify the shear strength of slender beams.

▪ The punching shear experiment was performed on the slabs with a restrained rotation.

That leads to a limited validity of the results. Therefore, there is a need for experimental

study whereby the slabs have freedom in rotation.

▪ The long-term properties of basalt fibre concrete such as its creep and fatigue behaviour

have not been the subject of intensive studies. The author suggests further studies in this

field to identify the long-term behaviour of macro basalt fibre concrete.

▪ Replacing conventional reinforcement with fibres is economical. Thereby, the use of

steel fibres in prestressed slabs has been developed. It would be useful to study the

mechanical properties of prestressed macro fibre concrete slabs and beams including

their shear and punching shear strength.

▪ There are different opinions regarding the durability of basalt fibres. However, the

information regarding the durability properties of BFRPs are scarce in the literature.

Therefore, the author suggests further studies to identify the durability properties of

macro basalt fibre concrete in alkali environment and seawater.

▪ In the Scandinavian countries, the freeze-thaw durability of concrete members is

essential. The freeze-thaw characteristics of macro basalt fibre concrete have not been

reported yet. Therefore, the author suggests for further studies on this subject.

6.2. FURTHER RESEARCH

41

▪ The effect of using an air-entraining agent on the interfacial properties of macro basalt

fibres and the concrete matrix is not well known. This may have a negative influence

on the bonding and consequently on the post-cracking strength of macro fibre concrete.

The use air-entraining agent in cold climate such as Scandinavian countries is essential.

Therefore, the author suggests for further investigation regarding the effect of the air-

entraining agent on the properties of macro basalt fibre concrete.

▪ The effect of polypropylene (PP) fibres on preventing the high-performance concrete

from fire spalling is well known. Furthermore, the macro basalt fibre concrete has

shown to have good structural properties. Therefore, it may be possible to enhance the

fire spalling resistance of macro basalt fibre concrete by adding the PP fibres to the

concrete mix. Considering this background, the author suggests for further investigation

on fire spalling properties of the combined fibre concrete. If the result of fire spalling

was confident, it is also necessary to measure the mechanical properties of the samples

after the fire.

Chapter 6. Conclusions and Further Research

42

43

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