Yiannis Pontikes

Yiannis Pontikes
KU Leuven | ku leuven · Department of Materials Engineering

Professor

About

244
Publications
79,595
Reads
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6,327
Citations
Citations since 2016
158 Research Items
5476 Citations
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201620172018201920202021202202004006008001,000
201620172018201920202021202202004006008001,000
Additional affiliations
October 2006 - March 2007
Imperial College London
Position
  • Visiting Researcher
January 2005 - June 2005
New York State College of Ceramics at Alfred University, Alfred, New York, USA
Position
  • Visiting Researcher
February 2004 - May 2004
Centro Ceramico Bologna
Position
  • Visiting Researcher

Publications

Publications (244)
Conference Paper
Full-text available
The scope of this work is to investigate the reactions and phase transformations that occur during the low-temperature reduction of bauxite residue (BR) by hydrogen in the presence of NaOH, and how that affects the recovery downstream of the different elements. Different processing conditions were studied, such as temperature, time, and NaOH dosage...
Conference Paper
Full-text available
Bauxite residue (BR) has in principle a great potential to be used in the construction (concrete) industry considering its large availability. However, an implementation is hindered in Europe, mainly due to its classification as a waste, its alkaline nature, low reactivity and small particle size. Vitrification has been identified as a potential so...
Article
Full-text available
This paper explores the possibility to convert a metallurgical residue from a sponge iron production (MR) with approximately 20 wt% amorphous carbon into a hydraulic binder. The challenge lies in developing an industrially-realistic, simple and robust process that exploits the characteristics of the residue, instead of trying to introduce the resid...
Article
Full-text available
The high-temperature transformations and crystallization of K-based inorganic polymers made from FeO-SiO2 and FeO-SiO2-Al2O3 iron-rich model slags were investigated, with particular focus on the effect of the Al/K and Si/K molar ratios. Upon firing to 1100 °C, the main crystalline phases were hematite and (iron) leucite. Addition of corundum decrea...
Conference Paper
Full-text available
In recent years great attention has been placed by the building sector on alkali-activated technology based on metakaolin, fly ash and ground granulated blast furnace slag (GGBFS), but also on emerging precursors such as by-products from non-ferrous metallurgy. The present work focuses on the development of alkali-activated binders from two slags,...
Article
This study investigates the transformation of bauxite residue into a reactive precursor after heat treatment at 1200–1300 °C and the synthesis of high performance inorganic polymer mortars thereof. Minor amounts of C, CaO and SiO2 were added to bauxite residue, and the melt was water-quenched resulting in amorphous phase (25 up to 62 wt%), the rest...
Conference Paper
Full-text available
To enable the usage of non-ferrous metallurgy slags in alkali-activated materials (AAMs), the influence of the chemical composition of slags on durability must be better understood. In this work, two slags were synthesized with different MgO/(MgO + CaO) weight ratios to investigate the effect on the sulfate resistance (Na2SO4) of AAMs. Experimental...
Article
Full-text available
Carbonation of alkali activated materials is one of the main deteriorations affecting their durability. However, current understanding of the structural alteration of these materials exposed to an environment inducing carbonation at the nano/micro scale remains limited. This study examined the evolution of phase assemblages of alkali activated slag...
Conference Paper
Full-text available
In this study, limestone (LS), kaolin (K) and bauxite residue (BR) were considered as potential raw meal ingredients for the preparation of ferrite-belite (cement) clinkers. A forecast of the mineralogical composition for the different clinker composition, based on the major oxides, i.e., CaO (C), SiO2 (S), Al2O3 (A) and Fe2O3 (F) was obtained usin...
Article
The growing demand for sustainability in the recent decades has driven the exploration for new supplementary cementitious materials (SCM) such as the non-ferrous metallurgy (NFM) slags. In this study, the hydration of an iron-rich NFM slag incorporated in CAC-PC-calcium sulfate ternary binders was investigated. The dimensional stability of mortars...
Article
This study provides insights on the formation of crystalline phases from Fe-rich slag-based porous inorganic polymers (porous IPs), cured under hydrothermal conditions. The porous IPs were synthesised using synthetic slags with different chemistries (from FeO-SiO2-CaO to FeO-SiO2-Al2O3-CaO systems) as solid precursors, and a sodium silicate-based a...
Article
Full-text available
Alkali-activated materials (AAMs) provide an opportunity to up-cycle several residues into added-value materials. Although generally praised for their performance under thermal loads, the thermal behavior of AAMs is dictated by a multitude of factors and the performance of CaO-FeOx-rich systems may differ from geopolymers. Therefore, this work asce...
Conference Paper
Full-text available
Bauxite residue (BR) is an industrial by-product generated during the production of alumina from bauxite ores in the Bayer process. BR is environmentally hostile due to it is high alkalinity and fine particle size distribution. In this work, BR is blended with NaOH and subsequently reduced with hydrogen, in order to develop an intermediate material...
Conference Paper
Full-text available
In this study, thermodynamic modelling was carried out to predict the crystalline phase and provides a first stepping-stone to incorporate high amounts of BR in low-CO2 cement manufacturing. As raw materials, 35-66 wt% bauxite residue (BR) in combination with 33-64 wt% of limestone (LS) and 1-10 wt% of kaolin (K) were chosen as raw materials for hy...
Article
The initial reactivity in cementitious systems (i.e. alkali-activated and blended cement systems) of three slags produced using bauxite residue (BR) as the main raw material were assessed; these slags ranged from semi-vitrified to fully amorphous. Additions of C, SiO2 and CaO to BR decreased the liquidus, therefore, firing at 1200 °C was performed...
Article
The hydration of blended cements with up to 70 wt% iron-rich slag was investigated. Isothermal calorimetry revealed a retarding effect of the slag on Portland cement hydration during the first day, while from 2 days onwards the reaction extent of C3S, C3A and C4AF increased. The slag reacted to 20-30% after 150 days resulting in AFm phases, as well...
Article
Full-text available
To tackle the challenge of bauxite residue (BR), generated during the alumina production, as well as to recover some of its metal content, three combinatory H2-based processes were utilized. Firstly, Greek BR was mixed with NaOH to produce water soluble Na-aluminates and was roasted under pure H2 gas in order to reduce the Fe+3 content. Then the fi...
Preprint
Full-text available
Carbonation of alkali activated materials is one of the main deteriorations affecting their durability. However, current understanding in structural alteration of these materials exposed to an environment inducing carbonation at nano/micro scale remains limited. This study examined the evolution of phase assemblages of alkali activated slag mortars...
Article
Full-text available
The environmental impact of ordinary Portland cement (OPC) can be decreased by using alternative precursors, such as non-ferrous metallurgy slags (NFMS), which can be alkali-activated to form an inorganic polymer binder (IP). However, an IP demands the use of a high molarity alkali-solution, which is expensive, has a relative high environmental foo...
Article
In the search for CO2 mitigating cement technologies, alkali-activated Fe-rich slags present a possible alternative. The influence of the chemical composition of the synthetic Fe-silicate slag on the reaction mechanisms is assessed by varying the CaO/FeO molar ratio. The alkali-activated Fe-rich slags consist of trioctahedral layers that are shown...
Article
In the present work, calciumsulfoaluminate-ferrite clinker was produced using 35 wt% of bauxite residue in combination with alumina, clay, limestone and gypsum. At a temperature of 1300 °C, the hydraulic phases ye'elimite, ferrite and C2S were formed. Computed thermochemical predictions were a significantly better match for the real mineralogy than...
Article
Industrial applications using recycled fibres or resins are still rare due to inferior performance to cost ratio. In most cases, glass fibre reinforced polymer (GFRP) materials with thermoset matrices are considered unsuitable for reprocessing and reuse as a valuable reinforcement of composites. In this work, mechanical frictional grinding is utili...
Article
Iron-silicate slags, originating from metallurgical industry, are upon alkali-activation precursors for synthesis of inorganic polymer binders, which can be used in construction. The slag's rheology is important for certain construction applications, which is for alkali-activated Fe-rich slag suspensions (AAS) still largely unmapped. To identify th...
Article
Full-text available
With an outlook directed towards circular economy, the valorization of municipal waste streams and industrial residues has recently conveyed a variety of novel industrial by-products to various applications such as supplementary cementitious materials (SCM) in cement blends or as precursors to inorganic polymers. Despite the synergistic benefits on...
Conference Paper
Full-text available
After a heat treatment between 400-800°C, efficient dehydration of hydrated cement phases in concrete waste occurs and new reactive phases are formed by thermal activation. Therefore, there is great potential in converting the separated fine (< 0.2 mm) concrete waste fraction, rich in hydrated cement, into a high-value low-carbon recycled binder th...
Article
Full-text available
Inorganic polymer (IP) binder is formed upon alkali-activation of Fe-rich (41 wt%) metallurgical slag leading to materials with mechanical properties comparable to ordinary Portland cement binders. Crack formation is reported in IPs, which can be related to volumetric stability, which is to date not thoroughly understood in IPs. This study determin...
Article
Ordinary Portland cement (OPC) is a strong and durable material with a well-established composition defined by national and regional standards. The required chemistry limits the amount of iron-rich materials that can be used as a feedstock. The work described in this paper investigates how substitution of iron for aluminium affects OPC clinker prod...
Article
The development of new materials such as inorganic polymers (IPs) requires a deep understanding of the effect of the microstructural and the micromechanical properties on the strength. In this study, digital image processing technique were used to characterize SEM images of different IP microstructures. Via nanoindentation, the micromechanical prop...
Article
Global warming and depletion of resources have fueled research towards innovative building materials of low environmental impact and high performance engineering properties. Porous glass-ceramics were synthesized using municipal solid waste incinerator (MSWI) bottom ash (BA) as a starting material. BA was initially milled and then vitrified, as a p...
Article
Encouraging the transition to a circular economy, the valorization of municipal solid waste incinerator (MSWI) bottom ash (BA) has received considerable attention in many processes. In the present work, flash microwave vitrification was effectively realized in a single mode cavity operating at 2.45 GHz within 1.5 min. The closed-loop process was ev...
Article
Non-ferrous metallurgy slags, when highly amorphous, have been shown to behave as supplementary cementitious materials, albeit typically with low reactivity. Due to this feature, high-volume replacement of ordinary Portland cement (OPC) with non-ferrous metallurgy slag is not encouraged. A classical method of increasing slag reactivity is by increa...
Article
Full-text available
With an increasing number of low-grade primary ores starting to be cost-effectively mined, we are at the verge of mining a myriad of low-grade primary and secondary mineral materials. At the same time, mining practices and mineral waste recycling are both evolving towards sustainable near-zero-waste processing of low-grade resources within a circul...
Article
Full-text available
With an increasing number of low-grade primary ores starting to be cog-effectively mined, we are at the verge of mining a myriad of low-grade primary and secondary mineral materials. At the same time, mining practices and mineral waste recycling are both evolving towards sustainable near-zero-waste processing of low-grade resources within a circula...
Chapter
Full-text available
3D printing can lead to a technological breakthrough in the construction sector. However, the sustainability aspect of 3D printing mortar can be disputable, as 3D printable mortar contains a high amount of ordinary Portland cement (OPC). The sustainability can be increased by replacing OPC with an Fe-rich slag, which originates from the metallurgic...
Article
This study investigates the effect of NaOH content on alkali/sulfate-activated binders from 90 wt% ground granulated blast furnace slag (GGBFS) and 10 wt% phosphogypsum (PG). Alkali activators were prepared with a NaOH molarity ranging from 0 M to 4 M. The hydration was monitored using in-situ X-ray diffraction (XRD) and isothermal calorimetry. The...
Article
In search for alternative cementitious materials for radioactive waste encapsulation, geopolymers and inorganic polymers (IPs) have received wide attention. Moreover, Fe-rich IPs offer an interesting alternative to high density concretes for use in radiation shielding applications. Materials can however be altered when subjected to ionizing radiati...
Article
Full-text available
To future-proof alkali-activation technology, there is a need to look beyond well-established precursors such as fly ash and blast furnace slag, due to resource competition, geographical distribution and technical limitations. Clay minerals are abundant and diverse aluminosilicate resources available around the world. However, due to the mineralogi...
Article
Full-text available
Antimony is a common metalloid occurring in the form of Sb-sulfides and sulfosalts, in various base and noble metal deposits. It is also present in corresponding metallurgical products (concentrates) and, although antimony has been considered a penalty element in the past, recently it has gained interest due to its classification as a critical raw...
Article
Non-ferrous metallurgy slags are currently do not reach their full valorization potential. On a global scale, these slags are landfilled or used in low-value applications. Upcycling these slags to produce a sustainable cementitious binder, e.g. inorganic polymers, does not only substitute the vast CO2 emitting Portland cement, but also gives econom...
Article
In this investigation, ettringite-based mortars were synthesized from ladle slag (LS) and phosphogypsum (PG), promoting the concept of a circular economy. However, the reuse of naturally occurring radioactive materials (NORM), such as PG, requires radiological investigation. Also, the immobilization degree for contaminants contained in PG should be...
Article
The use of the alumina production waste bauxite residue (BR) in alkali-activated materials (AAM), such as geopolymers, inorganic polymers and hybrid binders, is attracting considerable interest. This work provides an in-depth review of the growing body of literature in the field of alkali-activated binders from BR and spent Bayer liquor, i.e. anoth...
Chapter
Alkali Activated Materials (AAMs) are interesting alternative binder materials to Ordinary Portland Cement (OPC) for application in nuclear safety structures and radioactive waste management. AAMs are highly chemical and temperature resistant and can reach a high shielding capacity for gamma irradiation. AAMs also have a low calcium content which e...
Article
Fe-rich inorganic polymers are rising in importance because of their low CO 2 emissions during production and their potential in upcycling metallurgical residues. Here, the oxidation of Fe during formation of the binder from 0.4CaO-1.2FeO x-SiO 2 slag is investigated in more detail using 57 Fe Mössbauer spectroscopy. It was shown that the oxidation...
Article
Bauxite residue, the waste product from the Bayer process, typically consists of approximately 40 wt% Fe2O3, which makes it a potential resource for Fe. This study presents an integrated process in which Fe is extracted in a first stage, followed by valorisation of the remaining residue towards alkali-activated binders. About 75 wt% of residue was...
Article
Full-text available
Volumetric stability is an important aspect of the performance of building materials, and the shrinkage of CaO-FeOx-Al 2 O 3-SiO 2-rich inorganic polymers (IPs) has not been thoroughly investigated yet. Hence, this paper describes the outcome of a study conducted to investigate ways to minimize their shrinkage using different curing regimes. Two di...
Article
Full-text available
Volumetric stability is an important aspect of the performance of building materials, and the shrinkage of CaO-FeOx-Al2O3-SiO2-rich inorganic polymers (IPs) has not been thoroughly investigated yet. Hence, this paper describes the outcome of a study conducted to investigate ways to minimize their shrinkage using different curing regimes. Two differ...
Article
Full-text available
Metakaolin is one of the most popular solid aluminosilicate precursors for the synthesis of geopolymers. Despite its high reactivity and availability, there is a noticeable move towards the use of other natural clays as alternative precursors, due to their plentiful supply and widespread availability. Natural clays usually consist of a combination...
Article
Non-ferrous metallurgy slags are gaining significant interest as a resource in the production of alternative low-energy cementitious materials. Their atomistic structures, however, are still not fully understood due to their glassy nature. In the work presented herein, a comprehensive description of the nano-structure of a CaO-FeOSiO2 slag was obta...
Conference Paper
Alkali-activated materials (AAMs) are emerging in the construction sector by providing an opportunity to upcycle several wastes in the production of highly performant and added-value materials for technical applications. One of the most attractive properties of AAMs is their performance under considerable thermal loads. Being generally praised for...
Conference Paper
The use of non-traditional binders has increased over the last decades and alkali-activated materials (AAM) are considered viable candidates for several industrial applications. However, AAM high susceptibility to shrinkage can hinder their wider use and several admixtures/additives have been tested attempting to reduce such phenomena. This work is...
Article
Full-text available
Aiming to reduce the carbon dioxide emissions associated with cement production, alternative binders such as inorganic polymers receive substantial attention and slags from the non‐ferrous metallurgy are notable precursors. However, studies correlating their chemistry and crystallinity with the newly formed binder remain limited. In the work herein...
Article
This paper describes the outcomes of a study conducted to investigate the influence of solid-to-liquid (S/L), K2O/SiO2 molar ratio and type of activation solution on reaction kinetic, structural development and final mechanical properties of Fe–Si–Ca rich inorganic polymers (IP). IPs were synthesized with alkali hydroxide and alkali hydroxide/silic...
Article
In this study the influence of porosity on radon emanation was examined when incorporating high volume bauxite residue, ranging from 30 to 90 wt%, in alkali-activated mortars. Samples were produced using the semi-dry pressing and the high-slump-casting techniques. The porosity and specific surface area were assessed by means of N2 adsorption/desorp...
Article
Full-text available
Belonging to the family of alternative cementitious materials, inorganic polymers are rising in importance because of the drive to decrease CO2 emissions of concrete production. A synthetic Fe-rich slag resembling industrial copper or lead slags, was mixed with a sodium silicate activating solution. 57Fe Mössbauer spectra analyses indicate that the...
Article
The effect of phosphogypsum (PG) in alkali-activated ground granulated blast furnace slag (GGBFS) on the reactivity, strength development and final matrix properties was investigated, as a function of alkali activator. The results were compared with alkali-activated reference samples from GGBFS. PG completely dissolves and takes part in solid react...
Article
Full-text available
Aiming to utilize phosphogypsum (PG) as a construction material, this study investigated the potential use of PG as a calcium sulfate source for the production of an ettringite-based binder (LSG). Six compositions with different percentages and PG's of different origin were hydrated with ladle slag (LS) to form LSG. The hydration, mineralogy and co...
Article
Full-text available
Microwave heating is a potential green technology demonstrating many advantages over conventional heating methods. Prior to designing an industrial microwave process, however, a fundamental knowledge of the dielectric properties of the material to be thermally treated is imperative, as these properties determine the response of the material to an a...