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UNIVERSITY OF OULU P .O. Box 8000 F I -90014 UNIVERSITY OF OULU FINLAND
A C T A U N I V E R S I T A T I S O U L U E N S I S
University Lecturer Tuomo Glumoff
University Lecturer Santeri Palviainen
Senior research fellow Jari Juuti
Professor Olli Vuolteenaho
University Lecturer Veli-Matti Ulvinen
Planning Director Pertti Tikkanen
Professor Jari Juga
University Lecturer Anu Soikkeli
Professor Olli Vuolteenaho
Publications Editor Kirsti Nurkkala
ISBN 978-952-62-2451-0 (Paperback)ISBN 978-952-62-2452-7 (PDF)ISSN 0355-3213 (Print)ISSN 1796-2226 (Online)
U N I V E R S I TAT I S O U L U E N S I SACTAC
TECHNICA
U N I V E R S I TAT I S O U L U E N S I SACTAC
TECHNICA
OULU 2019
C 727
Elijah D. Adesanya
A CEMENTITIOUS BINDER FROM HIGH-ALUMINASLAG GENERATED IN THE STEELMAKING PROCESS
UNIVERSITY OF OULU GRADUATE SCHOOL;UNIVERSITY OF OULU,FACULTY OF TECHNOLOGY
C 727
AC
TAE
lijah D. A
desanya
C727etukansi.fm Page 1 Friday, November 8, 2019 2:27 PM
ACTA UNIVERS ITAT I S OULUENS I SC Te c h n i c a 7 2 7
ELIJAH D. ADESANYA
A CEMENTITIOUS BINDER FROM HIGH-ALUMINA SLAG GENERATED IN THE STEELMAKING PROCESS
Academic dissertation to be presented with the assent ofthe Doctoral Training Committee of Technology andNatural Sciences of the University of Oulu for publicdefence in the OP auditorium (L10), Linnanmaa, on 13December 2019, at 12 noon
UNIVERSITY OF OULU, OULU 2019
Copyright © 2019Acta Univ. Oul. C 727, 2019
Supervised byProfessor Mirja IllikainenDoctor Päivö KinnunenDoctor Katja Ohenoja
Reviewed byProfessor Juan Manuel Manso VillalaínAssociate Professor Guang Ye
ISBN 978-952-62-2451-0 (Paperback)ISBN 978-952-62-2452-7 (PDF)
ISSN 0355-3213 (Printed)ISSN 1796-2226 (Online)
Cover DesignRaimo Ahonen
JUVENES PRINTTAMPERE 2019
OpponentAssociate Professor Maria Chiara Bignozzi
Adesanya, Elijah D., A cementitious binder from high-alumina slag generated inthe steelmaking process. University of Oulu Graduate School; University of Oulu, Faculty of TechnologyActa Univ. Oul. C 727, 2019University of Oulu, P.O. Box 8000, FI-90014 University of Oulu, Finland
Abstract
About 4 Mt of ladle slag is generated in steelmaking processes in Europe per year, a largeproportion of which (80%) is placed in landfills or stored. This pattern is expected to continuewithout further research for their valorisation due to increasing demand for quality steel productsworldwide. Ladle slag (LS) produced in Finland possesses large amounts of calcium andaluminium and mineralogical phases which can exhibit cementitious capabilities and can beutilized in applications where expensive commercial cements are currently being used. The aim ofthis thesis is to investigate the properties of ladle slag in different activation pathways, includingalkali activation and use as a hydraulic binder with gypsum.
The results showed that ladle slag can be used alone as a precursor in alkali activation or as thesole binder or a co-binder with gypsum in hydraulic binding. Depending on the activationpathway, compressive strength between 35-92 MPa can be achieved after 28 days. The reactionproperties of alkali activated ladle slag are characterized, and it is confirmed through X-raydiffraction (XRD) that the reaction product after alkali activation is mainly an x-ray amorphous(calcium aluminate silicate hydrate-like) phase. Characterization techniques (SEM, XRD, TGAand NMR) used to analyze the LS paste binder with just water showed the hydration products ofladle slag to be dicalcium aluminate octahydrate (C2AH8), tricalcium aluminate hexahydrate(C3AH6), gibbsite (AH3) and stratlingite (C2ASH8) was also identified after a prolonged period ofhydration. Furthermore, it was found that to minimize the conversion, the ideal water-to-binderratio is 0.35. The conversion mechanism is reduced at this ratio and the strength is slightlyaffected. Another pathway that can be used to annul the conversion of calcium aluminate hydratesformed in LS paste is through the addition of gypsum to the LS paste system to produce anettringite-rich binder (C6AS3H32). When ettringite is formed in place of calcium aluminatehydrates the strength increases, frost resistance is improved, and drying shrinkage is enhanced.
Lastly, a potential application of ladle slag as a refractory material was also investigated.
Keywords: alkali activation, calcium aluminate, high-alumina slag, ladle slag, refractory
Adesanya, Elijah D., Sementtimäinen sideaine terästeollisuuden alumiinirikkaastakuonasta. Oulun yliopiston tutkijakoulu; Oulun yliopisto, Teknillinen tiedekuntaActa Univ. Oul. C 727, 2019Oulun yliopisto, PL 8000, 90014 Oulun yliopisto
Tiivistelmä
Euroopassa syntyy vuosittain noin 4 Mt terästeollisuden sivutuotetta, JV-kuonaa, josta 80% läji-tetään tai kaatopaikoitetaan. Maailmanlaajuisesti syntyvän kuonan määrä tulee todennäköisestikasvamaan laadukkaiden terästuotteiden ennustetun kysynnän kanssa. Tämän vuoksi kuonalletulisi löytää hyötökäyttökohde, jota vältyttäisiin läjitykseltä. JV-kuona sisältääkin suuria määriäkalsiumia ja alumiinia sekä mineralogisia faaseja, joilla on sementtimäisiä ominaisuuksia. Näinkuonaa voitaisiin käyttää sovelluksissa, joissa tällä hetkellä käytetään kalliita kaupallisia sement-tejä. Tämän väitöskirjan tarkoituksena oli tutkia JV-kuonan ominaisuuksia sementtimäisenäsideaineena alkali-aktivoinnissa sekä hydraulisena sideaineena yksinään että kipsin kanssasekoitettuna.
Väitöskirjan tulokset osoittivat, että JV-kuonaa voidaan käyttää prekursorina alkali-aktivoin-nissa tai hydraulisena sideaineena pelkästään veden kanssa tai yhdessä kipsin ja veden kanssa.Saavutetut puristuslujuuset vaihtelivat 35 ja 92 MPa:n välillä, jotka vastaavat normaalin ja eri-tyislujan betonin lujuuksia. JV-kuonan reaktiotuotteet alkali-aktivonnin jälkeen analysoitiinXRD- ja FTIR-analyyseillä. Tuloksista nähtiin, että alkali-aktivoinnin jälkeen reaktiotuote onsementin kaltainen kalsium-aluminatti-silikaati-hydraati (C-A-S-H) –tyyppinen faasi. XRD,SEM, TGA ja NMR –analyysit osoittivat JV-kuonan hydrataatiotuotteiden olevan erilaisia kalsi-um-aluminaattihydraatteja (C2AH8, C3AH6, AH3 ja C2ASH8). Tämän vuoksi työssä tutkittiin erivesi-kuona –suhteita, ja havaittiin, että kun käytetään alhaista kuona-vesi –suhdetta (0,35), reak-tiotuoteiden muutos vähenee ja lujuus paranee. Toinen tapa, jolla voidaan estää reaktiotuottei-den muuttuminen, on kipsin lisäys: lisäämällä kipsiä tuotetaan runsaasti ettringiittiä (C6AS3H32).Kun ettringiittiä muodostuu kalsium-aluminaattihydraattien sijaan, lujuus kasvaa, pakkaskestä-vyys paranee ja kuivumiskutistuma paranee.
Väitöskirjan viimeisessä osiossa tutkittiin JV-kuonan mahdollista käyttöä tulenkestävänämateriaalina ja huomattiin, että sen tulenkestävyysominaisuudet vaihtelevat käytetyn aktivointi-tyypin mukaan.
Asiasanat: alkali-aktivointi, alumiinirikas kuona, JV-kuona, kalsiumaluminaatti,tulenkestävä
Because he lives, I can face tomorrow… Dedicated to the loving memory of my Dad, and to my
Wife and Bezalel
8
9
Acknowledgements
The research work reported in this thesis was carried out in the Fibre and Particle
Engineering Research Unit at the University of Oulu in the course of 2015-2019.
The research formed part of the MINSI project, with funding and support from
various companies (SSAB, Stora Enso, Oulun Energia, Pohjolan Voima and
Ekokem) and of the FLOW project, funded by Business Finland in the ERA-MIN
2 Innovation Programme, which is part of the EU Horizon 2020 programme. The
author would like to thank the Auramo Foundation and the Oulu University
Scholarship Foundation for their financial support.
My sincere gratitude goes to my principal supervisor, Professor Mirja
Illikainen, for giving me the opportunity to undertake my master’s and PhD
research under her guidance, with great support from Päiviö Kinnunen, PhD,
and Katja Ohenoja, DSc (Tech), both of whom guided, co-supervised and
contributed to all the research undertaken in this thesis. These brilliant people
introduced me to this field of study and nurtured me in it from an intern in 2014 to
a scholar in 2019. Also greatly appreciate the support and collaboration received
from Juho Yliniemi, DSc (Tech), during these years, and I would similarly
like to express my appreciation to Prof. Yiannis Pontikes for the opportunity
to visit his research unit at Katholieke Universiteit Leuven and to both him and
Dr. Lubica Kriskova for their supervision and support during that visit in 2017.
I would also like to express gratitude to all my past and present colleagues in
the Fibre and Particle Engineering Research Unit who have helped to create a
conducive working environment during my research. Special thanks go to Jarno
Karvonen, Jani Österlund, Elisa Wirkkala, Maria Tomperi and Johannes Kaarre for
their help in the laboratory, and to Simo Isokääntä of SSAB for providing the slag
used in this work. Malcolm Hicks is thanked for revising and proofreading the
language of this thesis. Professor Juan Manuel Manso and Associate Professor
Guang Ye are sincerely acknowledged for their thorough reviewing and
constructive feedback of this manuscript. Would also like to appreciate the
guidance from my follow-up group, chaired by Prof. Timo Fabritius and supported
by Dr. Petteri Piltonen and Pekka Tanskanen.
Finally, I wish to express my deepest gratitude to my parents, Baba Ijebu and
Iya Ijebu who went extra miles to ensure that my siblings and I would get the best
education and living conditions. I would also like to appreciate the efforts of my
siblings, most especially my mentor Gbenga Adesanya, Deborah Oguntosin,
Kayode Adesanya, Comfort Adesanya, and my Pastor Adeolu Osho, for always
10
believing in me and for their support through and through. Infinite appreciation and
thanks are due to my beloved wife Adefunke Adesanya and our son Bezalel
Adesanya, for their encouragement, support, love and patience during my studies
and during the writing of this thesis.
Oulu, May 2019 Elijah Damilola Adesanya
11
Abbreviations
AALS Alkali-activated ladle slag
AH3 Gibbsite
ASTM American society for testing and materials
BFS Blast furnace slag
BOF Basic oxygen furnace
C(N)ASH Calcium aluminate silicate hydrate with sodium composition
C2AH8 Dicalcium aluminate hydrate
C3AH6 Tricalcium aluminate hydrate
CAC Calcium aluminate cement
CAH10 Calcium aluminate decahydrate
CASH Calcium aluminate silicate hydrate
CSH Calcium silicate hydrate
d10 Particle size for cumulative 10% finer (µm)
d50 Median particle size (µm)
d90 Particle size for cumulative 90% finer (µm)
EAF Electric arc furnace
LOI Loss-on-ignition
LS Ladle slag
NASH Sodium aluminate silicate hydrate
OPC Ordinary Portland cement
W/B Water-to-binder ratio
XRD X-Ray diffraction
XRF X-Ray fluorescence
Greek symbols
β-C2S Larnite
γ-C2S Calcio-olivine
Standard cement chemistry notations were used; hence C denotes CaO, A is Al2O3,
S is SO4 and H is H2O.
12
13
Original publications
This thesis is based on the following publications, which are referred to throughout
the text by their Roman numerals:
I Adesanya, E., Ohenoja, K., Kinnunen, P., & Illikainen, M. (2017). Alkali activation of ladle slag from steel-making process. Journal of Sustainable Metallurgy 3(2), 300-310
II Adesanya, E., Ohenoja, K., Kinnunen, P., & Illikainen, M. (2017). Properties and durability of alkali-activated ladle slag. Journal of Materials and Structures, 50:255.
III Adesanya, E., Sreenivasan, H., Kantola, A.M, Telkki, V.-V., Ohenoja, K., Kinnunen, P., & Illikainen, M. (2018). Ladle slag cement – Characterization of hydration and conversion. Construction and Building Materials, 193, 128-134.
IV Nguyen, H., Adesanya, E., Ohenoja, K., Kriskova, L., Pontikes, Y., Kinnunen, P., & Illikainen, M. (2019). Byproduct-based ettringite binder – A synergy between ladle slag and gypsum. Construction and Building Materials, 197, 143-151.
V Adesanya, E., Karhu, M., Ismailov, A., Ohenoja, K., Kinnunen, P., & Illikainen, M. Thermal behaviour of ladle slag mortars containing ferrochrome slag aggregates. Advances in Cement Research, In press.
The author’s contributions to the above Papers I-V were as follows:
The author designed the study with guidance from the supervisors and co-authors,
performed the experiment, analysed the data and wrote the paper, on which the co-
authors provided valuable comments, corrections and proofreading (Papers I & II).
The author designed the study with guidance from the co-authors, performed the
experiment, analysed the data and wrote the paper, on which the co-authors
provided valuable comments, corrections and proofreading. HS, AK and VT helped
with the nuclear magnetic resonance experiment (Paper III).
The author made a partial contribution to the experimental design together with the
co-authors and did most of the experimental work, co-analysis of the results and
writing of the paper as a co-author (Paper IV).
The author designed the study with guidance from the supervisors and the co-
authors, performed the experiment, analysed the data and wrote the paper, on which
the co-authors provided valuable comments, corrections and proofreading. AI
(Tampere University) conducted the dilatometry experiments and MK (Technical
Research Centre of Finland, VTT) helped with the preliminary high temperature
experiments (Paper V).
14
15
Contents
Abstract
Tiivistelmä
Acknowledgements 9
Abbreviations 11
Original publications 13
Contents 15
1 Introduction 17
1.1 Background ............................................................................................. 17
1.2 Approach and aims of the thesis ............................................................. 18
1.3 Outline of the thesis ................................................................................ 19
2 State of the art 21
2.1 Steelmaking slags .................................................................................... 21
2.1.1 Production of different types of steel slag .................................... 21
2.1.2 Physico-chemical properties of ladle slag .................................... 22
2.2 Slag-based and high-alumina cementitious binders ................................ 24
2.2.1 Alkali-activated slags ................................................................... 25
2.2.2 Hydration of crystalline slag ........................................................ 27
2.2.3 Hydration of calcium aluminate cement ....................................... 28
2.3 Current and potential applications for ladle slag ..................................... 30
2.4 Remarks on literature review .................................................................. 32
3 Materials and Methods 33
3.1 Materials ................................................................................................. 33
3.1.1 Binders ......................................................................................... 33
3.1.2 Alkali activators ........................................................................... 34
3.1.3 Aggregates .................................................................................... 35
3.2 Methods ................................................................................................... 35
3.2.1 Characterisation of materials ........................................................ 35
3.2.2 Preparation of binder samples ...................................................... 36
3.2.3 Microstructural analytical methods .............................................. 38
3.2.4 Physical analyses performed on hardened materials .................... 39
4 Results and Discussion 43
4.1 Properties of ladle slag ............................................................................ 43
4.1.1 Reactivity/hydraulic potential of ladle slag .................................. 43
4.1.2 Mineralogy ................................................................................... 43
4.2 Effect of alkali activation on the reaction kinetics of LS ........................ 44
16
4.3 Identification of reaction products in AALS ........................................... 46
4.4 Effect of aggregates on strength and durability of AALS ....................... 48
4.4.1 Compressive strength ................................................................... 48
4.4.2 Durability properties of AALS mortars ........................................ 49
4.5 Hydraulic activity of LS .......................................................................... 51
4.5.1 The effect of water-to-binder ratio on compressive
strength of LS (HLS) .................................................................... 51
4.5.2 Characterization of the conversion of HLS hydration
products ........................................................................................ 53
4.6 Modification of ladle slag hydration products ........................................ 56
4.6.1 Hydration kinetics of modified ladle slag (in the presence
of gypsum - LSG) ......................................................................... 56
4.6.2 Characterization of LSG hydration products ................................ 58
4.6.3 Microstructure of LSG binder hydration products ....................... 62
4.7 Strength and durability of HLS and LSG mortars. .................................. 63
4.7.1 Effect of modification of ladle slag hydration products on
strength ......................................................................................... 63
4.7.2 Effect of ettringite formation on mortars length change ............... 63
4.7.3 Freeze-thaw of mortars ................................................................. 64
4.8 Fire resistance of ladle slag mortars ........................................................ 65
4.8.1 Residual mechanical strength ....................................................... 66
4.8.2 Dilatometry of the thermal shrinkage and expansion of
mortars .......................................................................................... 67
4.8.3 Quality of mortars after exposure to elevated temperatures ......... 68
5 Summary and concluding remarks 71
List of references 73
Appendices 85
Original publications 89
17
1 Introduction
1.1 Background
The amount of slag produced by the steelmaking industry has increased constantly
over the last decade due to the worldwide demand for quality steels for construction
and allied purposes. During the production of 1 ton of steel, 4 tons of waste and by-
products are generated, including slags, dusts and sludges [1]. One of these slags is
high-alumina ladle slag (LS), also known as ladle furnace slag and falling or
reducing slag. LS is generated from the secondary steelmaking operations in which
molten steel from the electric arc furnace (EAF) is further refined to obtain high
grade steel. To achieve this desired quality in the steel, fluxes such as lime and
dolomites are added as reducing agents to prevent oxides from forming on the
surface of the molten steel and to absorb impurities which are later seen as residuals
in the slag [2].
At the same time, cement production is currently responsible for 7-9% of
global anthropogenic carbon emissions, coupled with the fact that there is an
increasing demand for cement worldwide [3], [4]. Various methods have been
extensively studied and proposed with the aim of finding environmental-friendly
and sustainable alternative binders to replace ordinary Portland cement (OPC).
Partial substitution and blending of OPC with supplementary cementitious
materials such as fly ash from coal burning and biomass incineration, slags from
iron and steelmaking processes, rice husk ash and other pozzolanic materials, have
been experimented with, for example [5]–[9], while another pathway for reducing
greenhouse gas emissions accruing from OPC production and utilizing industrial
waste and by-products that has been studied is the alkali activation method [10]–
[14]. In this case industrial side-streams including fly ash and slags are mixed with
alkaline activators such as sodium hydroxide (NaOH) and/or sodium silicate to
form a hardened matrix with properties comparable or superior to OPC [12], [15].
Four million tonnes of LS annually is estimated to be generated in Europe alone,
and about 80% of this total amount of regionally generated slag is either stored or
used a landfill material [16], [17]. The environmental footprint and economic cost
of landfilling makes this method unsustainable, and it has been designated under
the European Union (EU) Framework Directive on Waste and By-products as the
least acceptable method [18].
18
Unlike other iron and steel slags such as blast furnace slag (BFS), basic oxygen
furnace (BOF) slag and EAF slag, LS is generated as a fine powder due to self-
pulverization during the cooling process and cannot be used as a coarse aggregate
(>100µm) in concrete [19]. The utilization of both BOF and EAF steel slags as
cementitious materials and aggregates has been studied widely, but the possibility
of using LS as a sole cementitious binder has received less attention and few
publications exist on the topic. Various methods have been proposed for alternative
uses of LS, such as fillers in self-compacting concrete, use in masonry mortars, also
landfill covering on filtering beds and the stabilizing soft clayey soils [17], [20]–
[22], but in view of the chemical, mineralogical and morphological properties of
this slag, the potential as a high-value binder appears promising and it is this that
forms the topic of the present thesis.
1.2 Approach and aims of the thesis
This thesis sets out to explore the possibilities for utilizing LS as a cementitious
material. The specific objectives of the work were summed up in advance as
follows:
1. To investigate the reactivity of LS as the sole precursor in an alkali-activated
mortar by optimizing the recipe/mix design of the slag and alkaline activators
to achieve high compressive strength (Paper I).
2. To examine the durability properties of the alkali-activated ladle slag (AALS)
designed here by means of freeze-thaw and drying shrinkage tests (Paper II).
3. To determine the hydraulicity of LS and evaluate the effect of water content on
the conversion mechanism of the hydration products and the similarities of
hydration with this slag to that with calcium aluminate cement (CAC) (Paper
III).
4. To find an alternative method for the modification of the hydration products of
LS through the addition of gypsum and to assess the durability of the plain and
modified binders (Paper IV).
5. To evaluate the refractory properties of LS mortars prepared through alkali
activation and just water hydration (Paper V).
19
1.3 Outline of the thesis
This thesis is organized into five chapters. Chapter 1 gives a brief introduction to
the work and states the approach adopted and the aims of the research. Chapter 2
describes the production of slags during steelmaking processes and the properties
of LS. Chapter 3 presents the materials used in the research and the experimental
and characterization methods. Chapter 4 presents the results and a discussion of the
findings, while a summary of the research and the conclusions to be drawn from it
is presented in Chapter 5.
20
21
2 State of the art
2.1 Steelmaking slags
Steel slags, i.e. industrial by-products or waste from steelmaking processes, include
EAF and BOF slags (also known as converter slag and Linz-Donawitz slag,
respectively), named after the furnaces in which they are formed. In some steel
plants other secondary metallurgical slags are also generated while refining the
molten steel to produce high-quality steel. These secondary slags include LS,
desulfurization slag, vacuum oxygen decarburization and argon oxygen
decarburization slag. A flowchart of the processes involved in the generation of
slags is shown in Figure 1.
Fig. 1. Schematic and flow chart of steel and slags production (Reprinted with
permission © SSAB Oy).
2.1.1 Production of different types of steel slag
In the basic-oxygen furnace, scrap steel (10-20%) is recycled in the furnace and
molten iron (80-90%) from a blast furnace is then injected into the furnace on top
of the scrap. Oxygen is fed into the furnace while maintaining the temperature at
1600 ºC-1650 ºC to oxidize the impurities in the mix and to promote the combustion
of the carbon in the steel [2]. Furthermore, to remove undesirable chemicals from
the molten mix, a fluxing agent such as dolomite (MgCa(CO3)2) or lime (CaO) is
22
added. The impurities compound with the burnt fluxing agent to form BOF slags,
which remain floating on top of the molten steel.
The molten steel is separated from the slag and further refined in a secondary
steelmaking process (i.e. a ladle furnace) or sent for subsequent casting, while the
slag is sent to a pit for cooling. In an electric arc furnace the steel scrap is recycled
by melting at a high temperature to produce crude steel, after which fluxing agents
are introduced into the furnace by a similar mechanism to that used in a basic-oxide
furnace. The molten steel is then removed to a ladle furnace for further refining or
sent for subsequent casting, while the EAF slag is also separated and transported to
a pit.
Depending on the type or quality of steel required, both BOF and EAF molten
steels are further refined in a ladle furnace or else sent for casting. In a ladle furnace
the molten steel is deoxidized, de-sulphured and appropriately alloyed with fluxing
agents such as calcium aluminates or calcium fluoride, calcium oxides or
magnesium oxides and calcium silicates to lower the sulphur content and other
impurities in the molten steel [23], [24]. Deoxidation forms silica and alumina
oxides which are absorbed with the ladle furnace slag generated during the refining
process [2]. Due to these modification processes and the addition of various fluxing
agents to the ladle furnace, the compositions and properties of the generated LS are
quite different from those of both BOF and EAF slags [23], having a high alumina
content.
2.1.2 Physico-chemical properties of ladle slag
The properties of LS vary from one production line to another and are dependent
on conditions during and after steel production such as; raw material/scrap used,
types of fluxing agent or alloys added, furnace conditions and the cooling procedure
in the slag pit yard. The chemistry and mineralogy of LS, as collected from various
sources literature, are shown in Table 1.
The chemical composition of LS is typically CaO (30-70%), Al2O3 (15-40%),
SiO2 (5-25%) and MgO (5-8%) [25]–[28]. The high CaO in the slag forms different
compounds with Al2O3 and SiO2, and in some cases fails to react or remains as free
CaO. Other minor components include SO3, TiO2, Fe2O3 and MnO. Typically, LS
is predominantly crystalline, with major mineral phases identified in almost all LS
reviewed being mayenite (C12A7) and polymorphs of dicalcium silicate (C2S).
Other minor phases present can include tricalcium aluminate (C3A), dicalcium
23
ferrite (C2F), Portlandite (Ca(OH)2) and periclase (MgO). C2S is abundantly
present in LS, where it exists in four distinct polymorphs: α, α՛, γ and β-C2S.
During natural air-cooling of molten LS the slag crystal undergoes self-
pulverization due to phase transformation from α-C2S to β-C2S at 630 ºC, and at a
lower temperature (400-500 ºC), this β-C2S transforms to γ-C2S. This
transformation increases the volume of the slags between 10-12% due to disruption
of their crystal structure. Due to this self-pulverization the slags exist as a fine
powder and are therefore unsuitable for use as coarse aggregates [2], [19]. By
comparison, blast furnace molten slags, after being poured into the slag pit, are
initially cooled in air before water is sprayed on the partially air-cooled solidified
slag, thereby preventing the conversion of β-C2S to γ-C2S. Thus, the mineral
content is prevented from crystallizing but form glassy minerals which are
hydraulic compared with the crystalline minerals in steel slags [29], [30]. Water
cooling is rarely use, if at all, in the cooling of molten steel slags, because of its
higher viscosity. Hence water can be confined in the slag easily and cause an
explosion [31], [32]. This mechanism differentiates steel slags from BFS in general
and affects their hydration properties.
Additionally, some LS contains free lime (f-CaO) and/or free periclase (f-
MgO). The f-CaO and f-MgO can vary with different batches of steel produced and
type of fluxing agent used. The f-CaO and f-MgO content of steel slags increases
according to whether CaO or MgCa(CO3)2 is used [33]. f-CaO in the presence of
water quickly hydrates to form calcium hydroxide (or portlandite). This product
has a lower density than CaO and thus, changes the microstructure of the concrete
through volume expansion which is deleterious to the concrete [2]. On the other
hand, f-MgO hydrates slowly with water to form magnesium hydroxide, initiating
significant volume changes over a period of months or years. This volumetric factor
is problematic and limits the use of steel slags in construction structures. In the
standard recommendation for the use of fly ash in concrete (EN 450) a maximum
limit of 1.5% of free lime is stipulated. The free lime content of the LS used here
(Papers I-V), was below 1.5%, so that no soundness problem could be envisaged.
24
Table 1. Chemical compositions (wt.%) and mineralogy of ladle slag reported in the
literature.
References Source CaO
(%)
SiO2
(%)
Al2O3
(%)
MgO
(%)
Fetotal
(%)
f-CaO
(%)
Mineralogy
[34]
Canada 57-66 6-13 16-24 3-5 0.7-4 7-11 CH, MgO, C2S/C3S, CaO,
C12A7, C3MS2, C2AS and C2F
[24] Spain 50-58 12-20 4-19 7-12 1.6-3.3 3.5-19 C3MS2, C3A, β-C2S, γ-C2S,
CA4, MgO, C2F, Spinel, CH,
C12A7etc.
Papers I-V Finland 46-51 8-10 27-29 6-8 1-5 0-0.4 C12A7, γ-C2S, C3A and MgO
[21]
Spain 58.0 17.0 12.0 10.0 - 18-22 Spinel, C3MS2, MgO, β-C2S,
γ-C2S, CaSO4, CH, Alite and
Bregidite.
[35]
Sweden 40.0 5.0 32.5 5.9 4.8 - C12A7,C3A, FeO,
C20A13M3S3, β-C2S, CM�̅�2,
C2F and C2MS2
[36]–[38]
Italy 55-42 9-18 11- 23 4-9 2-7 - C12A7, MgO, γ-C2S,
gehlenite, CaCO3, β-C2S,
quartz
[39]
Greece 56 23-26 1.3-2.0 4.3-7 1.5-1.7 0.6-0.9 γ-C2S, CH, C2F and CaCO3
[40]
Italy 54.5 16.4 11.1 4.0 8.7 - γ-C2S, MgO, CaCO3, C12A7,
CaS, β-C2S and Mg CO3
[41]
Romania 49.6 14.7 25.5 7.8 1.1 - β-C2S, Anorthite, CaS and
α-Al2O3
[42] Taiwan 48.6 23.7 4.2 8.1 1.21 - -
2.2 Slag-based and high-alumina cementitious binders
Methods for utilizing slags as binders in cementitious systems have been studied
and have gained wide acceptance in civil engineering applications and scientific
research over the past decades. This section will provide a general overview of the
alkali activation of slags, the hydration of crystalline slags and CAC hydration. It
should be mentioned that quite a number of high-quality reviews, books and papers
on the state of the art with regard to alkali-activated slags and slag hydration have
been published, providing a further understanding of this research (e.g. [13], [43]–
[45]), and the hydration and mechanism action of CAC will be introduced in this
current review, too, as high-alumina LS has proved to have similar properties.
25
2.2.1 Alkali-activated slags
The principle of the alkaline activation of slags was identified in the 1940s, but
systematic research into the synthesis of the binder was not undertaken until the
early 1960s [46]. Until the early 2000s, most of the studies on the alkali activation
of slags had been focused on blast furnace slags, and it is only in the past two
decades that attention has turned significantly towards the use of slags from other
metallurgical processes for alkali activation. The number of publications with the
keywords “alkali-activated” and “slags” published in Scopus (Figure 2) shows that
research in this field has grown immensely in recent years.
Fig. 2. Numbers of publications per year with the keywords “alkali-activated” and “slags”
in the last three decades (total: 1024). The data were collected and analysed from the
Scopus database
The basic principle behind this type of cement involves mixing finely ground slag
with a suitable alkali activator, which subsequently hardens to form a concrete-like
structure. Alkali hydroxides or alkali silicates, or both together, are popular
activators that have been used successfully in recent studies. The strength of the
resulting matrix is dependent on the type and dosage of the activator, the fineness
of the slag, the water-to-slag ratio and in some cases the curing temperature [47].
26
The reaction mechanism and products for alkali-activated slags are not
comprehensively understood, but they are dependent on the mineralogy and
fineness of the slag, the pH and type of the alkaline activator, the additives added
and in some cases the curing conditions. Nevertheless, authors of studies dealing
with the alkali activation of slag have described the process as beginning with the
dissolution of Me-O (Me=Ca,Mg) and Si-O-Si bonds to form C-S-H-type reaction
products having a low Ca/Si ratio [48], [49]. Depending on the Al content and
reactivity of the initial slag material, various levels of participation of Al in the
reaction to form a C-A-S-H-type reaction product have been reported previously
[50], [51]. In Figure 3, a schematic representation of the process of alkaline
activation of a high-calcium precursor is given and the reaction products described,
modified from two literature sources [52], [53].
Fig. 3. Mechanism for the dissolving of calcio-aluminosilicate glass (Modified from [52]
and [53]).
The activation pattern in an alkali-activated system has generally been categorised
into one of three types:
Alkaline activation of high-calcium systems: (Na, K)2O-CaO-Al2O3-SiO2-H2O,
Model 1. This model explains the synthesis in high-calcium and silicon-rich
materials, as in the alkali-activation of slags. The main reaction product in this
system is a calcium aluminate silicate hydrate (C-A-S-H) gel. This gel differs from
the C-S-H gel in hydrated OPC, as it has a low Ca/Si ratio and a distinct structure
[54]. The C-A-S-H gel chains in alkaline cements are longer, with up to 13
tetrahedral units as compared with 3 to 5 for the C-S-H gel chains in OPC systems,
in addition to which the gel structure in the former includes aluminium, which
replaces silicon in the cross-linking positions [55]. The main reaction product can
also be written as C-(N)-A-S-H with significant quantities of sodium acting as
charge balancing units or absorbed onto the gel [36]–[38].
27
Activation of low-calcium systems under alkaline conditions: (Na, K)2O-Al2O3-
SiO2-H2O, Model 2. This model describes the synthesis of materials with major
occurrences of aluminium and silicon in their composition, such as metakaolin, fly
ash and other aluminosilicate materials with a low CaO content. The main reaction
product in this model is described as a three-dimensional inorganic alkaline
polymer of sodium aluminosilicate hydrate (N-A-S-H) gel [58]. This model of
synthesis is known as geopolymerization, and the reaction gel is termed a
geopolymer or inorganic polymer [57].
Hybrid or blended alkaline cement systems: Model 3. This third model is a
combination of the previous two. The materials in the synthesis are blends of
aluminosilicates and calcium aluminosilicates (i.e. OPC + BFS + fly ash or LS +
metakaolin), and the reaction products are a complex mix of cementitious gels
which may include a C-A-S-H gel which has sodium in its gel composition and a
high calcium N-A-S-H gel that can be denoted as (N,C)-A-S-H [59].
These reaction products are accompanied by other secondary reaction products,
depending on the type of activating solution used, i.e. monosulphoaluminate
(AFm)-type phases in NaOH-activated binders [60], [61] and AFm phase
strätlingite in alkaline silicate-activated binders [56], [62]. Other factors include the
MgO content of the starting material. Hydrotalcite has been reported in high-MgO
slags [48], [56], [63] and crystalline zeolites in low-MgO precursors (less than 5%)
[53], [64] and some carbonated phases. It is proposed here that the alkali activation
of LS follows Model 1, with some new reaction products that will be discussed
later.
2.2.2 Hydration of crystalline slag
The reactivity of steel slags varies significantly from one slag to another. This is
due to the differences in mineralogy and chemical composition between the raw
materials, furnace processes and cooling methods used. When cooled rapidly with
water, dicalcium silicate (β-C2S) in the slag is stabilized and not transformed to γ-C2S, which is predominant in steel slags. With the exception of LS, some EAF and
BOF when rapidly cooled tend to crystallize further [65], [66]. Hence, most steel
slags are termed crystalline slags because of predominant crystalline mineral
phases and lower glassy content.
Steel slags are generally termed cementitious, though with low activity due to
their mineralogical phases (i.e. γ-C2S), which have lower hydraulic activity than
those in OPC [67], and they therefore require activation in a high-pH environment
28
in order for some of the mineral phases to hydrate. Another factor limiting the use
of steel slags alone in concrete is the potential volumetric instability associated with
the f-CaO and/or f-MgO reaction in the slag [2], [23].
Nevertheless, when ground to fine particle sizes, these slags have shown to be
reactive and have also been used as a co-binder with OPC, fly ash or some other
hydraulic binder [68]–[70]. Other methods that have been used to increase the
reactivity and hydration of steel slags include thermal treatment followed by rapid
cooling [66], [71], [72]. In one previous study pulverized LS was reheated at 900 °C
and rapidly cooled with high-pressure air. It was reported that after this pre-
treatment the slag had a glass content of 92% compared with 6.5% in slowly-cooled
slag. Also, the f-CaO content was negligible after this treatment [71].
In another similar study [66] the authors used water jet cooling after re-melting
EAF and LS and reported an increase in the glass content of the slags. The LS used
in the present work was deficient in f-CaO, however, and pre-treatment methods
are beyond the scope of this study.
2.2.3 Hydration of calcium aluminate cement
LS containing high alumina and calcium bares certain similarities to CAC, mainly
since the elemental composition of CAC consists of calcium, alumina and iron,
with minor proportions of silicon and titanium [73]. Also, these cements are four
or five times more expensive than OPC and thus not an economic replacement for
it. They are nevertheless used in some special applications, either as the main binder
or as a co-binder with other materials (e.g. OPC, gypsum) in a hybrid mix [73].
Other CAC applications include:
– fast-setting concrete
– refractory applications
– resistance to chemical (acid) attacks resistance to impacts and abrasion.
The basic difference between OPC and CAC lies in the main mineralogical phase
that contributes to setting and hardening. The main mineral phases in OPC are
dicalcium and tricalcium silicates (C2S and C3S), which in contact with water forms
calcium silicate hydroxide (C-S-H) and calcium hydroxide (CH). Although, unlike
OPC, there is a wide fluctuation in the chemical composition and mineralogy of
CAC, its major mineralogical phases are calcium aluminate phases such as
monocalcium aluminate (CA), dodecacalcium hepta-aluminate (C12A7), also
known as mayenite, and tricalcium aluminate (C3A). When these phases are
29
hydrated, calcium aluminate hydrates are produced [74]. These calcium aluminate
hydrate formations are chemically quite different from OPC, as their hydrates
include CAH10, C2AH8, C3AH6 and poorly-crystallized AH3. Both CAH10 and
C2AH8 are metastable, in that they form temporarily and convert to a stable product
(C3AH6 and AH3, respectively) over a period of time, as shown in the following
equations [75], [76]:
For monocalcium aluminate: 𝐶𝐴 10𝐻 → 𝐶𝐴𝐻 , (1) 2𝐶𝐴 16𝐻 → 𝐶 𝐴𝐻 𝐴𝐻 . (2)
These products subsequently convert to the following stable phases:
2𝐶𝐴𝐻 → 𝐶 𝐴𝐻 𝐴𝐻 9𝐻 , (3) 3𝐶 𝐴𝐻 → 2𝐶 𝐴𝐻 𝐴𝐻 9𝐻 . (4)
Similar reaction equations can be written for C12A7 and C3A. In C12A7-rich CAC,
C2AH8 is favoured as the metastable hydrated phase and not CAH10 [19], [73], and
the equation can thus be written as:
For mayenite:
𝐶 𝐴 51𝐻 → 6𝐶 𝐴𝐻 𝐴𝐻 , (5)
which then converts to:
3𝐶 𝐴𝐻 → 2𝐶 𝐴𝐻 𝐴𝐻 9𝐻. (6)
For tricalcium aluminate:
2𝐶 𝐴 27𝐻 → 𝐶 𝐴𝐻 𝐶 𝐴𝐻 , (7) 𝐶 𝐴𝐻 𝐶 𝐴𝐻 → 𝐶 𝐴𝐻 . (8)
In the case of equations 7 and 8, C4AH19 loses part of its interlayer water at a relative
humidity less than 88%, to form C4AH13, which is detectable in dried samples as
used for X-ray diffraction (XRD) [76]. The initial product can therefore vary
depending on the curing conditions. According to Scrivener [73], there is a change
in the microstructural morphology as a consequence of a reduction in the total solid
volume and an increment in the porosity when conversion occurs in a calcium
aluminate-rich system. Water is also released, which is then available to hydrate the
unreacted phases. This phase evolution consequently reduces the strength of the
binder.
An understanding of these different hydrates and the mechanisms behind their
conversion is necessary in order to have form a basic background for the reactions
30
of high-alumina cementitious binders. LS is depicted in the ternary system that it
forms with the other cementitious binders in Figure 4.
Fig. 4. Compositions of cements/binders within the CaO-SiO2-Al2O3 system
2.3 Current and potential applications for ladle slag
Alternative cements have been designed from slags through hydration and alkali
activation, thus offering a viable and sustainable method to partially replacing OPC
and reducing the environmental footprint. These binders are also specifically
designed for special applications where the properties of OPC are not deemed
sufficient, e.g. in refractory concrete, rapid hardening, wastewater purification,
immobilization of heavy metals and contact with radioactive waste.
The mining and extraction of non-renewable natural materials for OPC
production is not a sustainable practise, and a partial alternative would be to use
industrial side-streams such as LS to substitute for OPC usage in structural niche
applications. The cements used in the construction industry are regulated and
required to fulfil certain continental or national specifications, which means that
31
the potential for using a sustainable alternative cement is then dependent on
satisfying the specifications and requirements (i.e. strength) for the structural
applications in which the OPC and other commercial cements would have been
used. The ASTM standard requirements and specifications for cements used in
structural applications are shown in Table 2. Although not limited to the
specifications in Table 2, there are other applications of these alternative binders
developed from industrial by-products. Due to its short reaction and setting times,
LS can be used in structural repairs, where immediate strength is required, in
underwater construction, in cold weather, on foundry floors, in underground
tunnelling and in mine backfilling. Additionally, its reactivity means that it can also
be used as a reactive component in blends with other materials. In some earlier
studies, LS was used as a co-binder with other materials e.g. metakaolin, fly ash
and bottom ash in alkali-activated materials [37], [38], [40], but the present work
(reported in Papers I, II and V), was concerned entirely with the alkali activation
and durability properties of LS as a sole binder.
Table 2. ASTM standard requirements for cement materials used in structural
applications [77].
Title of specification ASTM
designation
Type/grade Minimum compressive
strength (MPa)
Maximum water
absorption (%)
Structural clay load
bearing wall tiles
C34-03 LBX 9.6 16
LB 6.8 25
Building brick C62-10 SW 20.7 17
MW 17.2 22
NW 10.3 No limit
Solid masonry unit C126-99 VC 20.7 NA
HC 13.8 NA
Facing brick C216-07A SW 20.7 17
NW 17.2 22
In view of its high calcium content and low proportion of heavy metals, a certain
amount of LS produced during steelmaking is used in agriculture as a liming and
fertilizing agent to reduce soil acidity [78]–[80]. The calcium and magnesium in
slag are readily soluble when used instead of the naturally occurring materials used
for these purposes, i.e. dolomite and limestone [81]. Apart from increasing the pH
in acidic soils, LS can be used in combination with phosphorous and silicon to
increase the nutrients in soil [80] and similarly for soil stabilization, with results
32
reported after stabilization showing improvements in the bearing capacity of the
soil and properties comparable to those achieved with lime stabilization [82]. The
use of LS in construction work has also been suggested when designing materials
for paving roads, as it is suitable for use in a soil-cement mix or as a filler in asphalt
mixes [83], [84]. Another application of an LS binder is in masonry mortars,
together with OPC, sand and admixtures [21], [85]. When 30% LS was used as a
cementitious substitute for OPC, or as 25% aggregate substitute for sand, a 90-day
strength of 19.5 MPa and a longer setting time were achieved [85].
The present results have led to the development of LS-based high-performance
fibre-reinforced composites [86]–[89], while other potential uses of LS could be in
refractory applications. The calcium aluminate cements which are largely used in
these applications are four to five times more expensive than OPC, whereas LS
possesses similar chemical and mineralogical properties to some grades of CAC
and can potentially be an economical and sustainable alternative to it. The potential
for this is studied and discussed in Papers III and V.
2.4 Remarks on literature review
From the reviewed literatures, the variances in the chemical and mineralogical
properties of ladle slags produced and utilised, differs according to the country and
steelmaking plants processes. Thus, the LS reactivity and utilization pathways are
different, and care has to be taken in reproducibility of results. For example, LS
produced from steelmaking in Canada and Spain have high content (7-22%) of f-
CaO while the LS produced in Finland and Greece have lower (< 1%) content. Also,
the chemical composition and main reactive minerals varies similarly. Nevertheless,
the reviewed publications have successfully showed methods of utilizing this slag.
Here in this thesis, a high-value application of the LS produced in Finland is studied,
its similarities with CAC, conversion mechanism and various application pathways
suggested.
33
3 Materials and Methods
3.1 Materials
The materials used as binders in this work were LS, gypsum and calcium aluminate
cement. Standard sand and ferrochrome slag were used as aggregates, while sodium
hydroxide, potassium hydroxide, diatomaceous earth and sodium silicate were used
as alkaline activators. Deionised water was added during alkali activation when
necessary and was mainly used for the hydration of slag. The properties of the
various materials are described in the following subsections.
3.1.1 Binders
Four batches of slowly-cooled LS were provided by SSAB Europe Oy (Raahe,
Finland) for use in these experiments (Paper I-V). They were collected at different
times from the cooling pit, where they have been exposed to different natural
weather conditions. To enhance their reactivity, the as-received slags were milled
for two hrs using a 10 L roller ball mill (Germatec, Germany) with a grinding
medium filling ratio of 60% to achieve average particle sizes (d50) between 8-12
µm. The LS used in the work reported in Paper V comprised equal amounts of
milled and raw slag, in order to ensure optimal particle packing in the mortars.
The CAC (CALIGHT 40) used in this research (Paper V) was supplied by
CALTRA (Netherlands). The initial setting time as indicated by the producer is 70
min and a compressive strength of approximately 66 MPa is achieved after 24 h.
The chemical composition, free lime content and particle sizes of each milled LS
used and of the CAC (provides stated by the producer) are described in Table 3.
34
Table 3. Chemical composition (in wt.%), free lime content and particle sizes of LS and
CAC.
Oxides LS Paper 1 LS Paper II LS Paper III & IV LS Paper V CAC (Paper V)
CaO 48.40 46.30 50.96 45.77 37-39
SiO2 11.20 8.60 8.27 9.50 5-6.50
Al2O3 28.50 28.30 27.87 29.83 38-40.50
Fe2O3 3.10 5.00 1.13 0.83 15-18
Na2O 0.10 0.00 0.06 0.03 -
K2O 0.10 0.10 0.06 0.05 -
MgO 6.20 7.40 6.31 6.19 -
P2O5 0.00 0.00 0.02 0.00 -
TiO2 1.30 1.00 0.40 4.53 -
SO3 1.10 0.50 0.80 0.39 -
Cl < 0.01 0.00 0.05 0.04 -
f-CaO 0.0 0.0 0.4 0.0 -
<10% (µm) 1.3 1.3 0.9 1.2 0.84
<50% (µm) 9.1 8.0 7.9 12.3 6.2
<90% (µm) 33.4 34.6 46.5 64.9 29.8
The gypsum (CaO-41%, SO3-53.8%) used as a calcium sulphate source was
procured from VWR Finland (product code 22451.360) (Paper IV). Its median
particle size (d50) was 11.5 µm.
3.1.2 Alkali activators
Potassium hydroxide (KOH) pellets, sodium silicate (Na-Sil), diatomaceous earth
(DE) and deionised water were used as alkaline activators in Papers I and II, and
sodium hydroxide (NaOH) pellets, Na-Sil solution and deionised water were used
in Paper V. To retard the reaction of the matrix, 0.8-1.0% (wt.% of water) citric acid
(Tokyo Chemical Industry Co., Ltd., Japan) was added to the solution/water as a
retardant (Papers III, IV and V).
The KOH, NaOH pellets and Na-Sil were supplied by Merck KGaA chemicals, as
was the Na-Sil solution with SiO2/Na2O=3.5 and 65.5% water.
Since the dissolving of alkaline hydroxide in water is an exothermic process,
all the alkaline solutions were prepared by stirring in a plastic container a day
before experiment to ensure equilibration and cooling of the solution.
35
3.1.3 Aggregates
CEN standard sand supplied by Normensand GmbH and conforming to EN 196-1
[90] requirements was used for the aggregates (Papers II, IV and V). Ferrochrome
slag (Fs) supplied by Outokumpu Chrome Oy (Tornio, Finland) was used as
aggregate in Paper V. The as-received Fs was dried in an oven at 100 °C for 24 h
and then sieved through a 2 mm mesh to remove slag with a > 2 mm particle size,
so that the particle size distribution after sieving would range between 0 and 2 mm.
Fs was used as an alternative aggregate to sand due to its particle structure and it is
produced as an industrial residue during stainless steel production. Thereby
enhancing the sustainability of the mortars. The chemical composition of the as-
received slag is shown in Table 4.
Table 4. Chemical composition of as-received ferrochrome slag
Oxides CaO SiO2 Al2O3 Fe2O3 Na2O K2O MgO Cr2O3 SO3 TiO2
1.8 28.9 25.1 7.5 0.14 0.22 22.8 14.9 0.2 0.5
3.2 Methods
3.2.1 Characterisation of materials
Particle size distribution
The particle size distributions of all the materials were determined using a Beckman
Coulter LS 13320 device. The average volumetric sizes of three repetitions are
reported (d10, d50 and d90).
Chemical composition
The chemical compositions of all the materials used in this research (except CAC)
were determined from X-ray fluorescence (XRF) analyses of 1.5-g samples of the
material melted at 1150 ºC with 7.5 g of X-ray Flux Type 66:34 (66% Li2B4O7 and
34% LiBO2). The elemental concentrations in the material were then determined
by means of an inductively coupled, plasma-optical emission spectrometer (ICP-
OES Thermo Electron IRIS Intrepid II XDL Duo, Thermo Scientific). The
36
materials were pre-treated by microwave-assisted wet digestion with a 3:1 mixture
of HNO3 and HCL for 0.5 g of sample.
X-ray diffraction measurement
The mineralogical compositions of the samples were determined by X-ray
diffraction (XRD) using a Rigaku SmartLab (Siemens D500 AG, Germany) 9 kW
X-ray diffraction device equipped with Cu-kα radiation (Kα1 = 1.78892 Å;
Kα2 = 1.79278 Å; Kα1/Kα2 = 0.5) at a scan rate of 3 º/min. Phase identification
was carried out using PANalytical X’pert HighScore Plus software and the samples
were quantified by Rietveld quantitative phase analysis was performed using 10%
titanium oxide as an internal standard.
Scanning electron microscopy
Scanning electron microscopy (SEM) was performed to analyse the
microstructures of the samples in both powdered and fractured form. Two
microscopes were used: a Zeiss Sigma microscope with a voltage of 5-15 kV
(Papers III and V) and a Zeiss Ultra Plus instrument fitted with energy dispersive
x-ray spectroscopy and having an accelerating voltage of 15 kV.
3.2.2 Preparation of binder samples
Alkali-activated samples
The alkali activation of LS in Papers I and II was carried out according to the
methods described in EN 196-1 [90, p. 196]. Milled LS and the already prepared
alkali activator were mixed to a homogenous paste in a Kenwood mixer. A sand-
to-binder ratio of 2:3 (represented as SS3) was used in the mortar sample and the
equivalent sand content was then added to the paste and mixed further. The sample
was then jolted to remove entrapped bubbles and to ensure matrix uniformity, after
which the sample was cast in rectangular moulds (20 x 20 x 80 mm3, for the strength
test), sealed in a plastic bag and cured at 60 ºC for 24h before being removed from
the moulds and cured further under moist conditions at room temperature until the
testing time. The samples for the shrinkage and freeze-thaw measurements were
cast in 40 x 40 x 160 mm3 moulds, cured at 60 ºC for 24 h and removed from the
37
moulds after a further 24 h and placed in a humidity chamber (50% RH) at 23 ºC.
The molar ratios of the mix of binder and activators were: SiO2/(Na2O+K2O) = 4.5
mol, CaO/SiO2 = 1.4 mol and H2O/(Na2O+K2O) = 21.3 mol. The water-to-cement
ratio was kept constant at 0.40.
Hydration of ladle slag/gypsum
The LS paste samples were prepared by mixing milled LS with varying amounts of
deionised water (water-to-cement ratios: 0.35 and 0.50). The deionised water
contained 1 wt.% of citric acid added to retard the fast setting of the slag during
hydration. The mixture was then stirred using high-shear mixer for four minutes
to achieve a uniform composition, and the samples were then cast in rectangular
stainless-steel prisms (20 x 20 x 80 mm3), sealed and stored at room temperature
before removal from the moulds after 24 h. Thereafter, the samples were kept under
moist conditions at 95% ± 3 RH and 22 ± 3 °C until the testing time (Paper III).
To modify the hydration product, 30% of the LS was replaced with gypsum using
a water-to-cement ratio of 0.45. Samples were then prepared for both neat LS mortars
and LS-gypsum mortars. Both LS and gypsum were initially mixed for a minute and
the subsequent mixing was carried out according to the methods described in EN-196-
1 [90, p. 196]. The sand-to-cement ratio was kept constant at 3:1. The samples for the
strength test were then cast in rectangular stainless-steel prisms (40 x 40 x 160 mm3),
sealed and stored at room temperature before removal from the moulds after 24 h.
For the shrinkage measurements, the matrix was cast in 40 x 40 x 160 mm3 moulds,
cured at room temperature and removed from the moulds after 24 h and placed in
a humidity chamber (50% RH) at 23 ºC. For comparison, neat LS hydration with w/b
of 0.45 was also performed (Paper IV).
Refractory mortar from ladle and ferrochrome slags
The mortars were prepared by mixing the CAC or slag with demineralized water in
a Kenwood mixer according to the EN 196-1 standard. For the alkali-activated slag,
sodium silicate and analytical-grade sodium hydroxide pellets were used as alkali
activators. The compositions of the mixes are shown in Table 5. The solution was
prepared 24 h before mixing, and 1% citric acid was added to the water to retard
the fast setting of the slag. The molar ratios of the mix of binder and activators were:
SiO2/(Na2O+K2O) = 2.0 mol, CaO/SiO2 = 2.2 mol and H2O/(Na2O+K2O) = 10.1
mol. The SiO2/(Na2O+K2O) here was reduced to avoid elevated temperature (110-
38
300 °C) degradation of silica containing reaction products. To achieve a good
packing in the slag mortar, the LS used in the mix contained equal amounts of
milled slag and as-received slag, optimized using a modification of Andreassen’s
packing model with a distribution coefficient (q) of 0.20, a maximum particle size
of 2 mm, and a slag density of 3.01 g/cm3. The water-to-cement (w/c) ratio for all
the mortars was kept at 0.35. All the samples tested here were cured at room
temperature in sealed bags (Paper V).
Table 5. Mix composition of mortars used in refractory investigation (Reprinted by
permission from Paper V © ICE publishing).
Sample name LS (g) Na-Sil (g) NaOH (g) w/c CAC (g) sand (g) FS (g)
AALS-Ss 500 246 9 0.35 - 500±5 -
HLS-Ss 500 - - 0.35 - 500±5 -
CAC-Ss - - - 0.35 500 500±5 -
AALS-Fs 500 246 9 0.35 - - 500±5
HLS-Fs 500 - - 0.35 - - 500±5
CAC-Fs - - - 0.35 500 - 500±5
3.2.3 Microstructural analytical methods
Isothermal calorimetry
Calorimetry was performed at room temperature (20 °C) to analyse the heat flow
in the samples (Paper IV) early in the hydration times. A TAM Air isothermal
calorimeter was used, and the samples were mixed in situ using an admix ampoule.
Thermogravimetry analysis
To verify the reaction and hydration products of the matrix, thermogravimetric
analyses were performed on the paste samples using the Precisa Gravimetrics
“prepASH automatic drying and ashing system”. The samples were heated from
room temperature to 1000 ºC in an inert nitrogen atmosphere.
Nuclear magnetic resonance - 27Al NMR
Nuclear magnetic resonance (NMR - 27Al NMR spectra) was used to verify the
conversion mechanism (Paper III) by means of a Bruker Avance III 300
39
spectrometer operating at 78.24 MHz for 27Al. For the MAS experiments the
samples were packed into 7 mm zirconia rotors, a rotation frequency of 7 kHz was
applied, and 2048 scans were collected at a repetition rate of two seconds. The
chemical shifts were referenced to Al(NO3)3 set to zero ppm.
Fourier transform analysis
The samples were characterized using the diffuse reflectance infrared Fourier
transform (DRIFT) method (Paper I). Spectra in the 400–4000 cm−1 range were
collected by means of a Bruker Vertex 80v spectrometer, taking 40 scans at a
resolution of 1 cm−1 for each sample.
Scanning electron microscopy
SEM observation was done for the paste samples on Zeiss Sigma using a secondary
electron detector with a voltage of 5–15 kV. The broken paste samples were coated
with platinum before analysis.
Free calcium quantification
The free calcium oxide content of the LS used here was determined according to
the recommendations laid down in the EN 451-1 standard.
3.2.4 Physical analyses performed on hardened materials
Strength tests
The compressive strength tests were performed using a Zwick testing machine with
a maximum load of 100 kN and a loading force of 2.4 kN/s for Papers II, III, IV
and V and an Instron 8500 testing machine with a maximum load of 200 kN and a
loading force of 2.4 kN/s for Paper I.
Freeze-thaw durability test
The freeze-thaw (F-T) resistance of the mortars was assessed by immersing half of
the samples in water and the other half in air. The chamber temperature was then
40
varied from -20 ºC to +15 ºC, with each cycle consisting of lowering the
temperature from 15 ºC to -20 ºC for 2 h and then maintaining it for another 2 h
and vice versa. The freeze-thaw experiment was started when the samples were
aged 35 days in Paper II and 28 days in Paper IV.
Ultrasonic pulse velocity (UPV) equipment (Matest, Italy) was used to analyse
the damage in terms of structural uniformity after the freeze-thaw routine (Papers
II and IV) and after exposure of the specimens to elevated temperatures (Paper V).
The velocity (Vp) and relative dynamic modulus of elasticity (Rd) were then
calculated using equations (9) and (10), respectively.
𝑉 , (9)
where d is the distance between the two transducers and t is the time taken for
the pulse to reach the receiver.
𝑅 𝑉 𝑉 , (10)
where Vpn is the velocity after n cycles and Vp0 is the velocity at cycle 0 [91].
Drying shrinkage
For the shrinkage measurements, the mortars with dimension 40 x 40 x 160 mm3,
stored in a humidity-controlled room (50% RH) at 23 ºC were used. The drying
shrinkage properties of the mortars were measured using Matest length comparator
equipment. The length change (L) over time was calculated using equation (11):
L 100 (11)
where Li is the initial reading after 24 h of preparing the sample, Lx is the length
of the sample at each curing age and G is the nominal effective length.
Refractory testing
The mortars were subjected to elevated temperature treatment (Paper V) by first
drying the samples at 105 ºC for 18 h to remove the capillary water and reduce the
spalling tendency. The mortars were then exposed to thermal loads of 200, 400,
600, 800, and 1000 °C at a heating rate of 6 °C/min. A dwelling time of 1h at each
temperature was used and after the last of these the samples were removed from
the furnace and allowed to cool naturally. The heating regime is shown in Figure 5.
The residual compressive strength and mortar quality using UPV were tested after
thermal exposure.
41
Fig. 5. The heating regime applied to the mortars (Reprinted by permission from Paper
V © ICE publishing).
Dilatometry
Dilatometry (Paper V) was carried out using a NETZSCH DIL 402 Expedis dilatometer, with samples approximately 8×8×10 mm3 in size. The samples were heated to 1000 ºC at 6 ºC/min and there was a one-hour dwelling time at the peak temperature, after which the furnace was set to a cooling rate of 10 °C/min for the final stage. The heating chamber was open-ended, with a constant flow of nitrogen (40 ml/min) as the purge gas to prevent unwanted gaseous/evaporated matter from entering the measurement chamber, which was separate from the heating chamber and sample holder. The in-situ volume expansion and/or shrinkage during heating was then analysed.
42
43
4 Results and Discussion
4.1 Properties of ladle slag
4.1.1 Reactivity/hydraulic potential of ladle slag
Slags are categorized into three groups according to their basicity coefficient (Mb):
acidic (Mb < 1), basic (Mb >1) and neutral (Mb = 1). Using the equation [Mb =
(CaO + MgO)/(SiO2+Al2O3)] it is clear from their chemical compositions that the
basicity coefficient of all the LS samples used in this study (see Table 3) ranges
between 1.3-1.6, and thus the slag can be classified as basic and potentially
hydraulic [57], [92].
4.1.2 Mineralogy
Quantitative X-ray diffraction (QXRD) was used to determine the amorphous and
crystalline content of the various LS samples, as shown in Table 6. Due to the slow
cooling of LS, the amorphous content of the slag is low and below the
recommended glass phase content of 30-90% reported to be essential for slag
reactivity during alkali activation [92]–[94]. Although the vitreous content of some
slags may play a role in their reactivity, it has been shown in new studies of highly
crystalline slags that there is no general correlation between the glassy phase slags
in their reactivity or hydraulicity [48], [65], [95], [96]. This claim will be
additionally verified in the later part of this section. It suffices here to state, however,
that LS consists mineralogically of mayenite (C12A7), calcio-olivine (γ-C2S),
periclase (MgO), and tricalcium aluminate (C3A), as shown in Figure 6.
44
Fig. 6. XRD pattern for LS showing the mineralogy phases: a=mayenite/C12A7, b=calcio-
olivine/γ-C2S, c=periclase/MgO, and d=tricalcium aluminate/C3A.
Table 6. Quantitative mineralogy of ladle slag.
Phase C12A7 γ – C2S C3A MgO Amorphous
Wt.% 26-35 18-22 11-19 7-13 15-22
Since the free lime content of the slag determined using the method described in
EN 450-1 [97, pp. 450–1] varied between 0.0 and 0.4% (see Table 3) of the overall
CaO content of the LS, it may be concluded that the potential volume instability
associated with steel slags is not applicable to the LS used here.
4.2 Effect of alkali activation on the reaction kinetics of LS
Alkali activation of LS results in rapid, intense heat generation, as shown in Figure
7. An exothermic peak is recorded immediately after mixing of the alkaline
activator with the slag and can be attributed to the wetting and initial dissolving of
the slag particles. This peak is similar to the well-known pre-induction period that
occurs in cement hydration, although the physicochemical reactions involved are
markedly different. The breadth of this peak may suggest initial formation of
45
reaction products immediately after adding the activator to the slag. The addition
of citric acid had no significant effect on the reactions, as the induction period was
very short, and further reactions of the binder continued after 3.5 hours. The rapid,
intense heat released in this period is mainly due to the fast-setting properties of the
mayenite phase in the slag.
Furthermore, the acceleration peak was followed by a more intense peak with
a maximum heat release of approximately 16 J/h·g after 5 hours of the reaction,
this peak being attributed to a second formation and precipitation of reaction
products such as C-A-S-H [98] and calcium aluminate hydrates in the activated
slag [99]. The cumulative heat released after 50 hours of reaction was about 125
J/g, which is lower than that observed after 50 hours in hydrated OPC, around 225
to 280 kJ/kg, and similar to the cumulative heat released in alkali-activated blast
furnace slag [100]–[102]. This calorimetry is representative of the alkali-activated
LS with no added silica source (i.e. diatomaceous silica) used in this study (Paper
V).
Fig. 7. Heat evolution in the first 50 hours of the alkali activation of LS. The first 10
hours of the reaction are shown in the inset.
46
4.3 Identification of reaction products in AALS
The dissolving of the vitreous and crystalline phases of LS resulted in formation of
x-ray amorphous reaction product in the AALS (Figure 8) determined after 28 days
of reaction. The broad hump featured between 24° 2θ and 30° 2θ after alkali
activation is consistent with the formation of amorphous phase of aluminosilicates,
typically a C-A-S-H and N-A-S-H or hybrid C-(N)-A-S-H gel, as previously
reported in the literature [103], [104]. A similar amorphous hump can be observed
with an increase in the silica content of the matrix, but it is broader and more intense
and may indicate an increase in the formation of the amorphous phase. No other
new crystalline phases were detected in the AALS diffractograms. The FTIR
spectra in Figure 9 supplement the observations of the formation of a new
amorphous gel gained from the XRD findings.
47
Fig. 8. X-ray diffractograms of raw LS, AALS (Ca/Si=1.6) and AALS (Ca/Si=1.2). a=
mayenite (C12A7) b= dicalcium silicate (ɣ-C2S) and c= periclase (MgO) (Modified from
Paper I).
The IR spectra in Figure 9 represent the bands before and after alkali activation of
the LS. The spectra of the alkali activated LS exhibit a stronger band at 1650 cm-1,
which is assigned to the stretching vibration (-OH) consistent with the presence of
a reaction product [104], [105]. This band is not intense in raw LS. Meanwhile, the
broad band at 1030 cm-1 may be attributed to asymmetric stretching vibration in the
T-O-Si (T=Al or Si) bonds [106]–[108] and shifts to a higher wavenumber after
alkali activation and with increasing silica content, which is consistent with the
formation of polymerized units in an amorphous structure [107], [109]–[111] and
may indicate reduced substitution of Si for Al in the C-A-S-H gel with increasing
silica content [105], [107].
48
Fig. 9. FTIR spectra for raw LS and AALS paste (data from Paper I).
4.4 Effect of aggregates on strength and durability of AALS
4.4.1 Compressive strength
The aggregate content of the AALS mortars had a significant effect on their strength
and durability, as studied in Paper II. As shown in Figure 10, the mortar sample
(SS3) had a greater strength at all ages than the paste samples (SS0). Due to the
low water content, high viscosity and low workability of the mix, the standard sand-
to-binder ratio of 3:1 was unattainable. Hence for SS3, the sand-to-binder ratio used
was 2.3. As observed at 28 days, both samples suffered strength loss due to changes
in the reaction product. This mechanism, known as “metastable hydrate
conversion”, will be discussed further in the next section (see subsection 4.5). In
addition, both samples continued to gain strength after 28 days of conversion, the
effect increasing until the final testing time at 90 days.
49
Fig. 10. Compressive strength of AALS paste and mortar at different curing days
(Reprinted by permission from Paper II © 2017 RILEM).
4.4.2 Durability properties of AALS mortars
The AALS mortar also showed good durability properties when subjected to
normal and extreme environments. The frost resistance test results after 60 cycles
of extreme freezing and thawing are shown in Table 6. The mortar sample exhibited
good resistance to these conditions with a minimal effect on its physical appearance,
whereas the paste sample showed serious failure after 35 cycles due to high water
retention in the microstructure of the paste compared with the mortar sample. Thus,
the superior properties during frost resistance test of SS3 over SS0 is attributed to
the sand aggregate in the mortar having low water absorption and retention
compared with the paste sample. The residual data on the samples are shown in
Figure 11.
50
Table 7. Residual data of the samples after 60 F-T cycles (Reprinted by permission from
Paper II © 2017 RILEM).
Sample name
Surface
appearance
Compressive strength (MPa)
Weight loss (%) Reference After 60 cycles Reduction (%)
SS0-paste Damaged 56 ± 1.1 Failed 100 -
SS3-mortar Good 50 ± 0.6 49 ± 1.3 0.96 1.71
Fig. 11. Appearance of the mortars after F-T (Reprinted by permission from Paper II ©
2017 RILEM).
The drying shrinkage of the AALS samples was also determined, and the length
changes are reported in Figure 12. Both samples experienced a marked length
change in the early days after activation and stabilized after 28 days of analysis, but
the AALS mortar (SS3) shrank 7 times more than did the OPC sample (with s/b:3),
while the paste sample shrank significantly more than did the mortar sample. These
findings are consistent with a previous report on the effect of aggregates on the
shrinkage of alkali-activated materials [112]. Previous studies have similarly
shown that alkali-activated slags shrinks between 3 and 6 times more than OPC
[113]–[115]. The reduction in the sand content of the AALS mortars in the present
study most likely caused the drying shrinkage recorded here to exceed this range
reported for alkali activated mortars (s/b:3) in the literatures.
51
Fig. 12. Drying shrinkage of AALS samples by comparison with OPC (data from Paper
II).
4.5 Hydraulic activity of LS
The results presented in Papers III and IV offer a low-cost alternative to the use of
LS without alkaline activators. Compared with other steel slags and blast furnace
slag, the LS used in these experiments contained large amounts of the calcium
aluminate phases C12A7 and C3A (37-54%), suggesting that a high mayenite content
in the mineral system may be of specific relevance for the hydraulicity potential of
LS. Mayenite is a fast-setting mineral phase, especially when in contact with water
[116].
4.5.1 The effect of water-to-binder ratio on compressive strength of
LS (HLS)
As expected, the HLS paste sample with a w/b of 0.35 (HLS/0.35) had a higher
compressive strength than that with a w/b of 0.50 (HLS/0.5) throughout strength
test, the maximum strength achieved for HLS/0.35 being about 43 MPa, after 7
days. Overall, however, a reduction in strength was observed during curing, as seen
52
in Figure 13, this being similar to the reduction in strength observed earlier in the
AALS samples (Figure 10). This effect may be attributed to conversion of the
hydration products in the slag, comparable with that in high-alumina cements
(equations 5 and 7). The increase in strength noted in both samples after 28 days
may be attributed partly to the formation of strätlingite (C2ASH8) later during the
curing period, as detected in the mineralogy of HLS by means of XRD (Appendix
A). The formation of this phase is dependent on the reactive silica in the slag, the
alkalinity of the binding system and the water-to binder ratio. Hydration and
hardening of γ–C2S during longer periods of curing has been reported earlier in the
literature [117], [118].
Fig. 13. Compressive strengths of the paste samples at 3, 7, 28 and 90 days of hydration
(Reprinted by permission from Paper III © 2018 Elsevier Ltd.).
The conversion that occurs in this system is accompanied by a change in the crystal
structure of the hexagonal metastable hydrate C2AH8 to that of a cubic stable one,
C3AH6. These aluminate hydrates possess different specific densities, C2AH8
53
having a density of 1750 kg/m3 and C3AH6 2520 kg/m3 [116]. Consequently, this
transformation results in a significant change in the volume of solids in the hydrated
slag, yielding a more porous structure and a decrease in strength. In addition, the
water released during the conversion (equation 6) is readily available to react with
any unreacted anhydrous slag when the w/b ratio is initially low, to form more
C2AH8, which then leads to an increase in strength, as seen for HLS/0.35 in Figure
13.
4.5.2 Characterization of the conversion of HLS hydration products
The conversion that occurs in hydrated LS is accompanied by a change in the
crystal structure of the initially formed hexagonal metastable calcium-aluminate
hydration product C2AH8 to a cubic stable hydration product C3AH6. These
aluminate hydrates differ in density, C2AH8 having a density of 1750 kg/m3 and
C3AH6 2520 kg/m3 [116]. Consequently, this transformation results in significant
change in the volume of solids in the hydrated slag, resulting in a more porous
structure, increased free water and a decrease in strength.
The preferred analytical method for determining and verifying the conversion
of these hydration products is thermogravimetric (DTG) analysis, the results of
which when applied to the HLS samples are shown in Figure 14. The comparative
range of hydration products arising in high-alumina cement hydration has been
detailed in the literature, and this information was used here for reference purposes
[119], [120]. The metastable hydration product (C2AH8) has a decomposition peak
in the temperature range 100-200 °C, while the stable hydration products AH3 and
C3AH6 have decomposition peaks at 200-250 °C and 300-380 °C, respectively. The
DTG curves in both thermograms were de-convoluted using Origin software’s
Gaussian peak fitting algorithm (Originlab Corporation, US).
The rate of conversion can be analysed in terms of the increase in the intensities
of the decomposing peaks for C3AH6 and the decrease in the decomposing peaks
for C2AH8. The DTG curves for HLS/0.50 in Figure 14a show that the broad peaks
at 3 days consisted of overlapping hydrates associated with all three hydration
products. The decomposing peaks for the C3AH6 continue to increase up to 90 days,
while a decrease occurs in the decomposing peaks for C2AH8. This is consistent
with the known conversion of the metastable hydration product to a stable hydrate.
54
Fig. 14. DTG curves for the hydrated ladle slag (HLS) using (a) w/b 0.50 and (b) w/b 0.35.
(a=C2AH8, b=AH3 and c=C3AH6) (Reprinted by permission from Paper III © 2018 Elsevier
Ltd.).
The effect of a lower water content in reducing conversion is seen in Figure 14b,
where decomposing peaks for C2AH8 increased with the duration of curing up to a
maximum at 90 days with an intensity higher than the corresponding peaks for
C3AH6. The reduction in converted phases in this system and the increment in the
C2AH8 phase may partly be attributed to the continued hydration of anhydrous LS
with water released during conversion [73]. This also contributed to the gain in
strength in the HLS/0.35 case, as discussed earlier. By contrast, in the HLS/0.50
system, where a greater amount of water is readily available for large-scale
hydration of the slag, the conversion is rapid and comprehensive.
In addition, the conversion of HLS hydrates was further analysed by means of
NMR spectra. The 27Al NMR spectra for the samples (Figure 15a and b) show a
coordination of three aluminium species (AlIV, AlV and AlVI) detectable between
the chemical shifts 52 and 80 ppm, 30 and 40 ppm, and 10 and 20 ppm, respectively
[121], [122]. The broad peak for the raw sample, with its highest intensity at 70
ppm may be assigned to the mayenite phase in the slag, while the less intense peak
55
at 10 ppm indicates slight hydration of the slag during storage at the steelmaking
plant.
Furthermore, the peak in the AlIV region of the HLS/0.35 spectrum shown in
Figure 15a reduced after hydration as a result of consumption of the mayenite phase.
At the same time, the peak in the AlVI region increased due to the formation of
hydration products. The 27Al NMR spectrum for this sample had peaks near 10 ppm,
which may be assigned to the formation of the hexagonal hydrate C2AH8 [123]. The
shift in the spectrum between day 3 (10.8 ppm) and day 90 (10.5 ppm) could
indicate continuous formation of C2AH8.
In the spectrum for the HLS/0.5 sample (Figure 15b), massive conversion of
the metastable product to a stable product may be verified from the change in signal
peaks. The spectrum contains peaks near 12 ppm associated with formation of the
cubic hydrate C3AH6 [123], [124], in addition to which the spectrum signal peaks
shifted from 11.5 ppm at 3 days towards a maximum of 12.2 ppm at 90 days, which
may suggest continuous conversion of C2AH8 to C3AH6. The spectra for both
hydrated slag samples still show minor signals in the 70 ppm range due to unreacted
slag.
Fig. 15. 27Al MAS NMR spectra of the anhydrous and hydrated slag; HLS/0.35 (a) and
HLS/0.50 (b) slags at 3, 28 and 90 days (Reprinted by permission from Paper III © 2018
Elsevier Ltd.).
The effect of water content (w/b ratio) on the impact of conversion can be described
further. When the water-to-binder ratio is set low (i.e. w/b: < 0.40), there is
insufficient water and space for all the slag to dissolve or react to form these
metastable hydrates [73]. The water released from the conversion of the hydrated
56
slag reacts with the unreacted slag and form new hydrates. Thus, the rate of
conversion is lower compared to a paste with high volume of water.
4.6 Modification of ladle slag hydration products
Another alternative for lowering the conversion of hydration products apart from
reducing the water-to-binder ratio of the LS is by modifying its hydration products.
Both C12A7 and C3A will react with gypsum to form ettringite (Aft – C6A�̅�3H32)
and later monosulphoaluminate (AFm - C4A�̅�H12) in two-stage processes as shown
in the equations below.
C12A7 with water alone: 𝐶 𝐴 51𝐻 → 6𝐶 𝐴𝐻 𝐴𝐻 (12)
In the presence of gypsum (1st stage):
𝐶 𝐴 12𝐶�̅�𝐻 113𝐻 → 4𝐶 𝐴�̅� 𝐻 3𝐴𝐻 (13)
(2nd stage): 2𝐶 𝐴 4𝐶 𝐴�̅� 𝐻 34𝐻 → 12𝐶 𝐴�̅�𝐻 6𝐴𝐻 . (14)
C3A with water alone:
2𝐶 𝐴 27𝐻 → 𝐶 𝐴𝐻 𝐶 𝐴𝐻 (15)
In the presence of gypsum (1st stage):
𝐶 𝐴 3𝐶�̅�𝐻 26𝐻 → 𝐶 𝐴�̅� 𝐻 (16)
(2nd stage): 2𝐶 𝐴 𝐶 𝐴�̅� 𝐻 4𝐻 → 3𝐶 𝐴�̅�𝐻 (17)
The formation of AFm and the rate at which it is produced are dependent on the
initial amount of gypsum used in the hydration. A previous study on the hydration
of C3A with varying amounts of gypsum [125] has reported different durations for
AFm formation following depletion of the gypsum in the initial mix.
4.6.1 Hydration kinetics of modified ladle slag (in the presence of
gypsum - LSG)
The calorimetric results for the heat that evolved during the first 50 hours of
hydration of a mix containing LS, gypsum and water (LSG) are shown in Figure
57
16, along with HLS heat evolution for comparison purposes. Three significant
peaks and a shoulder can be seen in the calorimetric curve for LSG, and these are
similar to hydration periods of OPC as described in a previous publication [126].
The first peak, denoting the initial dissolution period starting from the very first
minute of hydration, may be attributed to the combined effect of heat release from
wetting of the precursors and initial hydration of the calcium aluminate phases in
the LS and gypsum [126].
This is followed by a dormant period, or induction period, lasting up to 8 h that
is caused by the cumulative effect of retardation by citrate ions and gypsum. In
OPC, gypsum is added to the clinker to serve as a set retarder, slowing down the
hydration of calcium aluminate. It has also been proposed that the adsorption of
calcium and sulphate ions to active dissolving sites on the calcium aluminate phases
serves to retard the reaction rate [125], [127], [128].
Fig. 16. Heat evolution of LSG and HLS as a function of hydration time (Reprinted by
permission from Paper IV © 2018 Elsevier Ltd.).
The second sharp peak in LSG curve, denoting an acceleration period, can be
observed after 8 h, with its heat flow peaking after 10 h of hydration. This peak
suggests the end of mix retardation and may be attributed to heat evolving from the
precipitation of hydrates (AFt and AH3) that leads to the setting and hardening of
the binder. The sharpness of this peak may also suggest the consumption of calcium
58
aluminate phases in the slag. The second peak may be attributed to the second
formation of ettringite [129], [130], hypothetically on account of a longer delay
caused by the retarding effect of the citrate ions on C3A hydration. In addition, the
decrease of the reaction of the curve after the second peak may be because of the
formation of hydration products were covered on the surface of unreacted products.
The reaction changes in the third broad peak to the diffusion control of this covered
slag and may suggest moderate consumption of the calcium aluminate phases in
the covered unhydrated slag particles.
The broad shoulder (hump) on the third peak is due to the formation of
monosulphoaluminate (AFm). This arises when the sulphate ions in the binder
matrix decrease on account of gypsum depletion and the remaining C12A7 and C3A
starts to react with ettringite and water to form monosulphoaluminate (equation (14)
and (15) [125]. Nonetheless, this does not mean total exhaustion of the ettringite in
the matrix, a fact that is consistent with the XRD analyses and is confirmed by them.
In addition, the cumulative heat flow shows a higher amount of total heat generated
(325 J/g) during 50 h of hydration, more than in the case of LS hydration (275 J/g),
representing the cumulative contribution of the heat released by Aft, AFm and AH3.
As seen in equation (12) and (13), the quantity of AH3 produced in the hydration
of LS and gypsum is three times greater than in the hydration of LS alone.
Two distinct peaks are seen in the curve for the heat released by HLS hydration,
an initial peak attributable to the dissolving and wetting of the slag particles, which
is followed by a short dormant period of less than 2 hours, and then a second peak,
the acceleration peak, caused by the formation of hydration products in the matrix.
4.6.2 Characterization of LSG hydration products
The DTG results in Figure 17 show modification of the LS calcium aluminate
phases to ettringite after the addition of gypsum. The decomposition peaks for LSG
and the reference HLS paste after 7 and 28 days are presented in Figure 17a and b,
respectively. Ettringite, gibbsite (AH3) and possibly an AFm phase are the major
phases identifiable in the LSG thermograms. The well-defined decomposing peak
in the range 50-350 °C corresponds to ettringite decomposition [131], [132], while
the shoulder visible between 250 and 320 °C may correspond to the decomposition
of AH3 [119] and can also overlap with AFm, which has its decomposition peak
between 200 and 250 °C [133]. The quantification of ettringite by
thermogravimetric analysis is a complex process because of the possibility that the
59
ettringite peaks may overlap with those of other hydrated product phases, e.g.
C2ASH8 [119].
The DTG curves for HLS are similar to those described in the previous
subsection 4.5.2. The conversion of C2AH8 (100-200 °C) to C3AH6 (300-380 °C)
was likewise observed, along with a decrease in the metastable peak and an
increment in the stable decomposition peak.
Fig. 17. Differential thermogravimetric (DTG) analyses of HLS and LSG paste samples
at (a) 7 days and (b) 28 days (Reprinted by permission from Paper IV © 2018 Elsevier
Ltd.).
The mineralogical phases of the LSG sample were identified and quantified by
XRD/Rietveld analysis, yielding the results shown in Figures 18 and 19. As seen
in Figure 18, AFt was the dominant phase in the LSG diffractograms at both 7 and
28 days, amounting to 34.4 wt.% and 27.3 wt.% at the two time points, respectively.
The reduction in the quantity of AFt at 28 days is attributable to the formation of
an AFm phase after depletion of the gypsum. The AFm phase increased in quantity
from 0.5 wt.% at 7 days to 5.3 wt.% at 28 days, and the amorphous content of the
binding system also increased slightly (by 1%) during this period. Ettringite and an
amorphous hydration product are the main strength-imparting phases in this system.
It is clear from equation 13 and 16 that AH3 is one of the predictable hydration
products of the reaction between mayenite and gypsum, so that although it is
scarcely crystalline and is difficult to detect and identify in XRD, it may contribute
to the amorphous content of the LSG sample.
60
Fig. 18. X-ray diffractograms of LSG paste at 7 and 28 days (Reprinted by permission
from Paper IV © 2018 Elsevier Ltd.).
Fig. 19. Quantified phases of LSG at 7 and 28 days (Reprinted by permission from Paper
IV © 2018 Elsevier Ltd.).
61
The diffractograms for HLS in Figure 20 can additionally be used to verify
conversion of the hydrate phases during curing. It was not possible to quantify the
HLS paste sample by Rietveld analysis due to the number of coordination
anomalies, but a C2AH8 peak was identified at 7 days which had been diminished
significantly by 28 days, while C3AH6 was identified at both points in time but with
an increased peak intensity at 28 days. This may suggest or confirm that conversion
of the hydrate phases had taken place in the paste. This would be consistent with
previous observations regarding CAC hydration [121]. Strätlingite was observed in
the diffractograms at 28 days, and it can be postulated that this phase may be the
result of a reaction between C2AH8/C3AH6 and dissolved silica from the weakly
hydraulic calcio-olivine (γ-C2S). In any case, traces of strätlingite have been
reported earlier in CAC after prolonged hydration [134], [135].
Fig. 20. XRD of HLS phases at 7 and 28 days after hydration (Reprinted by permission
from Paper IV © 2018 Elsevier Ltd.).
62
4.6.3 Microstructure of LSG binder hydration products
The SEM analysis in Figure 21 confirms the phases detected in the LSG and HLS
samples by means of DTG and XRD. Needle-like crystals consistent with those of
ettringite in a cementitious binder could be seen in the LSG microstructure from 7
days onwards, as shown in Figure 21a. This agrees with equation 13 and 16
regarding the formation of ettringite after hydration, although no hexagonal plates
consistent with AFm phases were identified in the area analysed [127]. In contrast,
the microstructure of the HLS sample showed a different evolution at both points
in the analysis (Figure 21b). At 7 days the microstructure of HLS showed plate-like
crystals, as is consistent with the hexagonal structure of C2AH8 [136], while a
significant change in the morphology of the hydrates in the HLS sample could be
seen at 28 days, when the microstructure showed cubic crystals identifiable to the
C3AH6 crystal structure [137]. These microstructural alterations further verify the
conversion of the hydration product in the LS samples.
Fig. 21. SEM images showing the microstructural evolution of (a) LSG and (b) HLS at 7
(left) and 28 (right) days (Reprinted by permission from Paper IV © 2018 Elsevier Ltd.).
63
4.7 Strength and durability of HLS and LSG mortars.
4.7.1 Effect of modification of ladle slag hydration products on
strength
The alteration in the LS hydration products brought about by the addition of
gypsum (LSG) enhances their strength and eliminate the conversion anomaly in the
case of HLS mortars. The results of testing the strength of the LSG and comparing
it with HLS, shown in Figure 22, imply that LSG achieved a relatively good
compressive strength of 30 MPa at 7 days and 35 MPa at 28 days. In contrast, HLS,
as previously discussed, suffered a loss of 25% of its day-7 strength after 28 days.
Similar observations were made with regard to flexural strength in both samples.
This confirms modification of the hydration products in both systems. The strength-
enhancing hydration products in LSG are thought to be Aft, the AFm phases and
AH3, as confirmed earlier in the XRD and TGA analyses, as confirmed earlier from
XRD and TGA analyses.
Fig. 22. Strength test of mortars at 7 and 28 days (a) compressive strength and (b)
flexural strength (Reprinted by permission from Paper IV © 2018 Elsevier Ltd.).
4.7.2 Effect of ettringite formation on mortars length change
The LSG mortars exhibited lower shrinkage than the HLS one throughout the 90
days of the analysis, as shown in Figure 23, and the shrinkage values for LSG were
64
considerably lower than those for HLS on all the days analysed. The HLS material
shrank approximately 6 times more than the LSG, experiencing pronounced
shrinkage during the early days of curing (up to 28 days) and having almost
stabilized by 90 days. The overall shrinkage, however, was comparable to the
values recorded elsewhere for BFS mortars [138]. The lower shrinkage of LSG is
attributed to the expansive contribution of ettringite formed in the modified system
at early ages of hydration [139]. These results are in agreement with other studies
on the low shrinkage values recorded in ettringite-based binder systems [140],
[141].
However, it is noteworthy to mention that to avoid delayed ettringite formation
leading to expansion of the mortars, the starting material elemental composition
was optimised (here we used bogue’s formula) so as to have sufficient calcium
aluminate to react or deplete all the gypsum in the early days of hydration.
Fig. 23. Drying shrinkage values for LSG and HLS during 90 days of curing (Reprinted
by permission from Paper IV © 2018 Elsevier Ltd.).
4.7.3 Freeze-thaw of mortars
The residual strengths of the samples after exposure to severe weathering are shown
in Figure 24. LSG experienced a strength gain of up to 30% of that in the reference
65
mortar after 120 cycles of exposure to freezing-thaw cycling. This strength gain
under destructive conditions may be due to the further formation of ettringite in a
moist environment, which favours the continuous formation of ettringite [142].
After 120 cycles of freeze-thaw the strength decreased slightly, retaining 30 MPa
after 300 cycles, which implies a strength reduction of 15% relative to the reference
mortar. On the other hand, HLS suffered a 20% strength loss after 60 cycle,
although it showed a slight strength gain after 120 cycles. Overall, the mortar failed
(disintegrated) after 180 cycles and was not analysed further. As seen in the mass
loss curves, LSG experienced a gain in mass during the freeze-thaw cycles and
exhibited a loss of mass of less than 2% by the end of the experiment.
Fig. 24. (a) Residual strength after freeze-thaw and (b) mass loss/gain for both mortar
samples (Reprinted by permission from Paper IV © 2018 Elsevier Ltd.).
The strength exhibited by the LSG and its frost resistance values conform to the
standards for structural design [143, p. 132] and many ASTM designations.
4.8 Fire resistance of ladle slag mortars
LSG mortar sample was not analysed during the investigation into the thermal
resistance of ladle slag mortars under elevated temperature (110 -1000 °C), due to
the early decomposition of ettringite under elevated temperatures below 300°C.
From results presented earlier, it is clear that water-to-binder ratio for HLS sample
(w/b: 0.35) is ideal for all the mortar samples and was maintained in the mortars
for fire resistance. To reduce costs and the use of metallurgical by-products in the
mortar, ferrochrome slag (Fs) was used as an aggregate. The results were then
66
compared with a commercial CAC mortar and sand (Ss) as aggregates. To reduce
the spalling tendency under high temperatures, all the samples were dried at 110 °C
before exposure to elevated temperatures starting from 200 °C. The visual
appearance of the mortars after exposure to elevated temperatures is shown in
Appendix B.
4.8.1 Residual mechanical strength
LS and Fs showed significant potential as refractory materials in a hydraulic binder
and similarities to CAC and sand, respectively. The residual strengths of mortars
made with Ss and Fs after thermal exposure are shown in Figure 25. The superior
initial strength of AALS_Fs mortars at 23 °C is assisted by the reaction of the binder
with the Fs aggregates. The ferrochrome aggregates in fact acted as bilateral
materials, i.e. both as a binder and as aggregates in the AALS mortars. Similar
observations have been reported in alkali-activated materials containing
ferrochrome aggregates [144]. Usually in mortars or concretes, aggregates used are
chemically inactive. However, some aggregates can react under high alkaline
environment, this behaviour is termed alkali-aggregates reaction, and these may
either be deleterious or beneficial to the mortar properties. The latter was the case
concerning AALS_Fs in this study (See Appendix C, Fig.C1e).
Furthermore, after drying at 110 °C, both AALS mortars suffered between 57
and 71% losses of strength due to dehydration of the strength-giving phases in the
mortar, i.e. C-S-H like reaction product. The changes in strength from 200 °C
upwards were gradual, and clearly below those seen in CAC and HLS mortars,
while an increase in strength at 1000 °C was observed for AALS_Ss and could be
attributed to densification of the sample through sintering of the binder, and perhaps
also to a phase transformation in the sand, as this was not observed in the AALS_Fs
mortar. Similar increments in strength have been reported in alkali-activated
materials exposed to high-temperatures [145]–[147]. Overall, the loss of strength
in these AALS mortars may be attributed to the thermal shrinkage of the binder and
expansion of the aggregates. The drying of free water and hydroxyls at 110 °C may
also have contributed to the deterioration in strength of the mortars [148].
The HLS mortars experienced an increment in strength after drying at 110 °C,
and this continued up to 200 °C for the HLS_Ss mortars, while the CAC mortars
had a slight reduction in strength at this point. After 200 °C both the HLS and CAC
mortars experienced similar a downward trend in strength loss until 1000 °C, and
by the end of the exposure to 1000 °C the HLS_Fs, CAC_Ss and AALS_Ss
67
materials had all recorded residual strength of approximately 18 MPa, representing
52%, 70% and 76% losses of strength respectively compared with the unexposed
reference strength. It is important to note that the residual strengths of these mortars
(e.g. HLS) are all above the minimum required in a structural clay load-bearing
wall in applications designated by ASTM C34-03- [149].
Fig. 25. Residual strength of mortars with (a) sand and (b) ferrochrome aggregates after
exposure to elevated temperature (Reprinted by permission from Paper V © ICE
Publishing).
4.8.2 Dilatometry of the thermal shrinkage and expansion of mortars
The results of dilatometric studies of the mortars given in Figure 26 show that their
shrinkage/expansion is dependent on the type of aggregate used. In mortars with
sand aggregates (Figure 26a), no substantial expansion/shrinkage occurred until
100 °C, except for the AALS_Ss sample, which shrank after 80 °C due to loss of
free water in the mortar. Furthermore, AALS_Ss continued to shrink further in the
temperature range 100–230 °C, which corresponds to dehydration of the reaction
product in the binder. Similar dimensional behaviour has been reported for alkali-
activated materials [150]–[152]. Between 230 °C and 570 °C a gradual expansion
of the AALS_Ss mortar could be observed. This was due to expansion of the quartz
towards its phase transformation at 573 °C, since the net expansion of quartz
dominated over the shrinkage of the binder. Furthermore, the sample then shrank
until 750 °C due to densification of the binder at this temperature [153]. This agrees
with the strength gain recorded here, and no further shrinkage or expansion was
recorded beyond 750 °C.
68
HLS_Ss and CAC_Ss exhibited similar dimensional behaviour throughout the
experiment, expanding slightly immediately after reaching 100 °C and continuing
up to 250 °C, after which both samples shrank (at 250-300 °C) on account of the
loss of pore water and collapse of the pores in the matrix. This expansion continued
until 570 °C before stabilizing, with minimal shrinkage or expansion recorded
afterwards. The expansion seen in the HLS_Ss mortars was due to expansion of the
aggregates at high temperatures (on account of quartz transformation), which may
have caused cracking of the matrix.
Fig. 26. Dilatometric curves showing expansion and shrinkage of the mortars with (a)
sand and (b) ferrochrome aggregates at elevated temperatures (Reprinted by
permission from Paper V © ICE Publishing).
The mortars containing Fs slag as aggregates exhibited a different dilatometry
pattern (Figure 26b). The AALS_Fs experienced major shrinkage and little
expansion throughout the experiment. This difference between this pattern and that
observed with AALS_Ss is related to the reaction of the Fs aggregate to a highly
alkaline environment, as discussed earlier, while HLS_Fs and CAC_Fs, showed
similar patterns, with slight shrinkage and expansion until 1000 °C. Overall,
HLS_Fs shrank to just slightly below the initial value, whereas CAC_Fs, expanded
to slightly above the initial value.
4.8.3 Quality of mortars after exposure to elevated temperatures
A non-destructive technique was used to check the quality of the mortars after
thermal exposure. By measuring the time taken for the pulse from the transmitter
69
probe to reach the receiver probe, the ultrasonic pulse velocity (UPV) can be
calculated used to predict the microstructure and mechanical behaviour of the
sample. The higher the velocity, the fewer the internal pores and defects in the
sample. As can be seen in Figure 27, mortars containing Fs aggregate achieved
better UPV values than sand-based mortars, partly on account of the irregular
shapes of the Fs particles, which may have contributed to packing and to superior
mechanical bonding between the aggregate and the binder [144]. Bonding between
the aggregate and the binder may also have partly contributed to the result gained
with the AALS mortar. Fs bonded better with the paste than sand aggregate
attributed to aggregate reaction with the paste (See appendix C, Fig.C1e).
Fig. 27. Ultrasonic pulse velocity for mortars with (a) sand and (b) ferrochrome slag
aggregates (Reprinted by permission from Paper V © ICE Publishing).
70
71
5 Summary and concluding remarks
The aim of this work was to study the utilization of LS, a by-product of the
steelmaking process, in high-value applications by determining the potential
hydraulic activity of this slag on the basis of its chemical composition and
mineralogy. Papers I, II and V of this thesis investigated the alkali activation of this
slag and studied its durability after hardening. Since the activated sample set rapidly
by virtue of its major mineral phase, mayenite, citric acid was added as a retarder
between 0.8 and 1 wt.% (of the water content) to prolong its setting.
After alkali activation LS showed considerable mechanical strength, so that it
could be used as a sole precursor in alkali-activated materials. The reaction product
formed in AALS was analysed by XRD and FTIR and shown to be possibly a C-
A-S-H-like gel and, in view of the stoichiometry of the mix with sodium in its
structure, to be acting as a charge balance or to be absorbed onto the gel. Unlike
the situation in fly ash or other aluminosilicates alkali activation, elevated
temperatures are not required for the hardening or curing of AALS as it had no
significant influence on the strength of the matrix.
When the durability of AALS mortars under conditions of severe weathering
was studied, the mortar sample exhibited good frost resistance after 60 freeze-thaw
cycles, losing less than 1% of its strength and less than 2% of its weight. On the
other hand, the shrinkage of the AALS mortar on drying was almost twice that
reported for alkali-activated BFS and 7 times more than for OPC.
In spite of the lower strength, the hydraulic properties of LS (yielding HLS)
offers a cheaper alternative method for utilizing LS. The main hydration products
emerging from this hydraulic system were found to convert from metastable C2AH8
to stable C3AH6 during curing, thereby undergoing a loss of strength. By lowering
the water content of the system to a maximum of w/b: 0.35, the rate of conversion
could be lowered, irrespective of the w/b ratio, while all the samples tested recorded
a continuous gain in strength from 28 days onwards.
To modify and stop the conversion of hydration products in this HLS system,
the HLS was blended with gypsum to form an ettringite system. Upon adding the
gypsum, the calcium aluminate phases (mayenite and tricalcium aluminate) reacted
to form ettringite and gibbsite, and later monosulphoaluminate was also detected
as a modified hydration product. No strength loss was recorded in this modified
ettringite binder, and when the efficiency of the modified system was analysed
under severe conditions, the sample exhibited superior durability properties and
strength to those of the HLS mortars. The gypsum used in this case can also be
72
potentially replaced by gypsum produced as a by-product in the phosphoric acid
industry. Gypsum-modified LS binder is a potential low-cost cementitious material.
The last paper in this thesis studied the refractory applications of the mortars
designed here (except for LSG) using a w/b of 0.35. The results obtained by
exposing the mortars to high temperatures (110-1000 °C) showed that HLS
containing ferrochrome aggregate had a better resistance and structural appearance
than commercial refractory cement or AALS mortars. The HLS mortar sample
retained a strength of approximately 18 MPa after exposure to 1000 °C. In a high
alkaline environment (AALS), the introduction of ferrochrome slag as an aggregate
increased the strength of the mortar before its exposure to elevated temperatures.
The increment in strength compared with AALS with sand may be partly attributed
to the alkali-aggregate reaction occurring in the system, and for this reason
ferrochrome slag may not be suitable as an aggregate in high temperature
applications of alkali-activated materials.
The results of this study on the use of LS as a cementitious binder show that
LS could be used to achieve high-strength mortars. Additionally, as a cementitious
material with almost zero environmental footprints, it could be used as a cheaper
alternative to commercial calcium aluminate cement and Portland cement in
refractory and structural applications in civil engineering. The fast setting of this
slag and its rapid gain in strength can be advantageous when using it for structural
repairs. In addition, to avoid strength loss, the optimal water-to-binder ratio of 0.35
should be used, save if the composition of the mix is modified with an addition of
gypsum. And it is imperative that proper strength value is considered before use in
structural design. However, it is also necessary to point out that the free lime
content of the slags used in this thesis was below 1% which pose no deleterious
effect on the mortars. Also, free MgO (<5% recommended) content should be put
into consideration before the use of the slag in structural applications due to long
term volumetric expansion caused by carbonation and hydration of the free MgO.
Here in this thesis, the content of the ladle slag varies between 0 to 7%. The use
should be limited if it’s above the recommended value of below 5%. The presence
can however be specially utilized under suitable conditions for their gainful use in
structural applications.
To conclude, the present results contribute to the scientific understanding of
high-alumina slag hydration, including its relation to CAC cements, modification
of the reaction and potential fields for its utilization in connection with inorganic
binders.
73
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85
Appendices
Appendix A
Fig. A1. XRD of HLS samples with different w/b ratio (a) 0.35 and (b) 0.50. The letters
indicate A-mayenite (C12A7), B-calcio-olivine (γ-C2S), C-periclase (MgO), D-tricalcium
aluminate (C3A), S -strätlingite (C2ASH8), x-dicalcium aluminate hydrate (C2AH8) and y-
katoite (C3AH6) (Reprinted by permission from Paper III © 2019 Elsevier).
86
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ix B
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. B
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87
Appendix C
Fig. C1. BSE-SEM image of the mortars before exposure; (a) HLS_Fs, (c) HLS_Ss, (e)
AALS_Fs and (g) AALS_Ss and after exposure to 1000 °C; (b) HLS_Fs, (d) HLS_Ss, (f)
AALS_Fs and (h) AALS_Ss. Fs: Ferrochrome aggregate; B: Binder and LS: Unreacted
ladle slag/aggregate. Red rings show the area of sintering/densification in the mortar
and rectangular box shows the interfacial zone (ITZ) between the alkali binder and the
ferrochrome aggregate (Reprinted by permission from Paper V © ICE Publishing).
88
89
Original publications
I Adesanya, E., Ohenoja, K., Kinnunen, P., & Illikainen, M. (2017). Alkali activation of ladle slag from steel-making process. Journal of Sustainable Metallurgy 3(2), 300-310
II Adesanya, E., Ohenoja, K., Kinnunen, P., & Illikainen, M. (2017). Properties and durability of alkali-activated ladle slag. Journal of Materials and Structures, 50:255.
III Adesanya, E., Sreenivasan, H., Kantola, A.M, Telkki, V.-V., Ohenoja, K., Kinnunen, P., & Illikainen, M. (2018). Ladle slag cement – Characterization of hydration and conversion. Construction and Building Materials, 193, 128-134.
IV Nguyen, H., Adesanya, E., Ohenoja, K., Kriskova, L., Pontikes, Y., Kinnunen, P., & Illikainen, M. (2019). Byproduct-based ettringite binder – A synergy between ladle slag and gypsum. Construction and Building Materials, 197, 143-151.
V Adesanya, E., Karhu, M., Ismailov, A., Ohenoja, K., Kinnunen, P., & Illikainen, M. Thermal behaviour of ladle slag mortars containing ferrochrome slag aggregates. Advances in Cement Research, In press.
Reprinted with permission from Springer Nature (I, II), Elsevier Ltd. (III, IV)
and ICE Publishing (V).
The original publications are not included in the electronic version of this thesis.
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Elijah D. Adesanya
A CEMENTITIOUS BINDER FROM HIGH-ALUMINASLAG GENERATED IN THE STEELMAKING PROCESS
UNIVERSITY OF OULU GRADUATE SCHOOL;UNIVERSITY OF OULU,FACULTY OF TECHNOLOGY
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