Jannie S J Van Deventer

Jannie S J Van Deventer
University of Melbourne | MSD · Department of Chemical and Biomolecular Engineering

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324
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Publications

Publications (324)
Chapter
This chapter provides an overview of fly ash-based geopolymer materials. Key parameters that must be considered when using a fly ash as the raw material for geopolymer production are discussed, including fly ash chemical composition, amorphicity, and morphology. In addition, external parameters that lead to the final mechanical, structural, and dur...
Conference Paper
Full-text available
The structures of synthetic alkali-activated cements are identified through application of 23 Na and 27 Al triple quantum magic angle spinning (3QMAS) solid state nuclear magnetic resonance (NMR) spectroscopy to isotopically enriched gels of differing Si/Al ratios. The alkali aluminosilicate gels contain Q 4 (4Al) Si units in which the negative cha...
Article
The long-term behaviour of concrete beams constructed with geopolymer concrete (GPC) is investigated. Self-weight and sustained load of 1 kPa are applied on top of the beams at the age of 14 days to simulate construction conditions. Creep tests on cylinders conducted with sustained loading commenced at the ages of 14 days and 28 days. The results f...
Conference Paper
A mini-beam test has been designed to assess the flexural creep and shrinkage behaviors of paste and mortar samples. It is a four-point bending test carried out on a plate sample of 350 mm long. In total seven sets of samples, pastes and mortars made of ordinary Portland cement (OPC) and geopolymer were tested. Test results of OPC and geopolymer pa...
Article
Full-text available
The extent to which the composition of the reaction mix affects the formation of a biphasic C–(A)–S–H/N–A–S–H geopolymer framework, and how the interaction of these phases affects geopolymer microstructure, can only be studied by strict stoichiometric control. Stoichiometrically controlled geopolymers containing both C–(A)–S–H and N–A–S–H gels are...
Article
Physicochemical phenomena influenced by aging or reaction can result in rheological changes across several orders of magnitude, but the classical rheometry methods available for analysis of concentrated suspensions can face challenges in correctly measuring the yield stress of aging/reacting (evolving) materials and need some precautions to enable...
Article
Full-text available
The effect of modifying the water content of an alkali-activated slag binder was assessed, in terms of the kinetics of reaction and the structural development of the material. There is not a systematic correlation between the water content of the mix and the rate of reaction, indicating that there is an optimal value that favours dissolution of the...
Article
The process of the dissolution of metakaolin in an alkaline environment remains incompletely understood; there are many mechanistic details which still require elucidation. Here, we apply X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) to provide new information regarding the bonding environments in the alt...
Article
Full-text available
Cement and concrete are critical to the world economic system; the construction sector as a whole contributed US$3.3 trillion to the global economy in 2008 [1]. The fraction of this figure which is directly attributable to materials costs varies markedly from country to country – particularly between developing and developed countries. Worldwide pr...
Conference Paper
Coexistence of both C-(A)-S-H and N-A-S-H gel frameworks within alkali-activated binders results in complex thermodynamic and chemical interactions, the nature of which dictate material properties and performance. The extent to which the composition of the reaction mix affects the formation of a biphasic C-(A)-S-H/N-A-S-H geopolymer framework, and...
Conference Paper
In cementitious systems, the transition from a fluid (or semi-solid) state to a solid state resulting from the reaction of the binder has a large impact on workability and hence practical application. Measurement of rheological properties such as yield stress help in monitoring changes in the workability. The transition from a fluid to solid state...
Article
Alkali-activated slag concretes stored for 7 years under atmospheric conditions are assessed, and the structural characteristics of naturally carbonated regions are determined. Concretes formulated with a 400 kg/m3 and water/binder (w/b) ratio between 0.42 and 0.48 present similar natural carbonation depths, although these concretes report differen...
Article
Full-text available
This paper addresses the effects of relative humidity (RH) and carbon dioxide (CO2) concentration on the rate and effects of accelerated carbonation in alkali-activated slag/metakaolin (MK) concretes. Strength and water absorption are used alongside phenolphthalein measurements to monitor carbonation, and the effects of drying at different RHs are...
Article
Alkali-activated "geopolymer" concrete has been commercialized in Australia, and it is meeting with strong demand from the end-user community and approval from regulatory authorities. Interest in the application of this technology throughout the Asia-Pacific region is growing, as end- users, engineers, and architects increase their environmental aw...
Article
Drying of cement paste, mortar, or concrete specimens is usually required as a pre-conditioning step prior to the determination of permeability-related properties according to standard testing methods. The reaction process, and consequently the structure, of an alkali-activated slag or slag/fly ash blend geopolymer binder differs from that of Portl...
Article
The ability of albite, an aluminosilicate mineral typical of those present in many gold ores, to adsorb gold is examined at varied pH levels in chloride media. The adsorption of gold on albite is intimately associated with the leaching behaviour of albite in acidic solutions. The preferential leaching of Na and Al from albite leads to the formation...
Article
The microstructural evolution of alkali-activated binders based on blast furnace slag, fly ash and their blends during the first six months of sealed curing is assessed. The nature of the main binding gels in these blends shows distinct characteristics with respect to binder composition. It is evident that the incorporation of fly ash as an additio...
Article
The carbonation resistance of alkali-activated binders is often tested via accelerated test protocols designed for Portland cements, without questioning whether the tests replicate the mechanisms observed in service. Thus, validation of accelerated methods is required to enable realistic prediction of material performance. Changes in pore solution...
Article
The use of dilatometry as a screening tool for the analysis of fly ash reactivity in geopolymers is presented and validated by testing six fly ash sources across a range of mix designs. In particular, a prediction of geopolymer mechanical performance can be obtained from the temperature at which the high-temperature expansion peak attributed to the...
Article
Full-text available
This paper presents the outcomes of a series of beamline-based studies, the results of which are combined to provide a more detailed multiscale understanding of the structure and chemistry of geopolymer binders. The range of beamline-based characterization techniques which have been applied to the study of geopolymer binders is increasing rapidly;...
Article
Durability of alkali-activated binders is of vital importance in their commercial application, and depends strongly on microstructure and pore network characteristics. X-ray microtomography (mu CT) offers, for the first time, direct insight into microstructural and pore structure characteristics in three dimensions. Here, mu CT is performed on a se...
Article
IntroductionExperimental Methods Results and DiscussionSummaryAcknowledgments
Article
Sulfate attack is recognized as a significant threat to many concrete structures, and often takes place in soil or marine environments. However, the understanding of the behavior of alkali-activated and geopolymer materials in sulfate-rich environments is limited. Therefore, the aim of this study is to investigate the performance of alkali silicate...
Article
The resistance to acid-induced corrosion of inorganic polymer (including “fly ash geopolymer”) binders is examined, by exposing specimens to nitric and sulphuric acids at pH values between 1 and 3, and measuring the corroded depth as a function of exposure time. The inorganic polymer binders are shown to be affected by acid attack by surface corros...
Article
The carbonation resistance of alkali-activated binders is often tested via accelerated test protocols designed for Portland cements, without questioning whether the tests replicate the mechanisms observed in service. Thus, validation of accelerated methods is required to enable realistic prediction of material performance. Changes in pore solution...
Article
Full-text available
Geopolymer concrete is being proposed as a potential construction material in carbon capture and storage facilities, in particular the harsh chemical environments found in post-combustion capture solvent columns. Geopolymer concrete is synthesised by reacting industrial wastes (coal fly ash and/or metallurgical slags), with an alkali source to form...
Article
This paper examines a series of fly ash and ground granulated blast furnace slag binders formulated to examine the effects of composition and mix design on performance and durability when exposed to aggressive environments found in carbon capture facilities (monoethanolamine or concentrated potassium carbonate, as well as distilled water). Ordinary...
Article
The ability of framework and layer silicates to adsorb gold in a chloride medium is examined. Experiments are conducted on quartz, feldspar, kaolinite and pyrophyllite powders (0.1–2.5μm) under acidic and alkaline conditions (pH 2.5–8).The adsorption of gold (supplied as HAuCl4) in acidic media is strong for all silicates evaluated. The maximum ext...
Article
Amino acids L-valine, glycine, DL-α-alanine and L-histidine were applied in the ammoniacal thiosulphate leaching of a pyrite concentrate. Amino acids formed more stable complexes with cupric ions than does ammonia, resulting in lower thiosulphate consumption due to reduced interaction between thiosulphate and the copper complexes. Overall gold extr...
Article
The mechanistic details of the structural changes occurring during the initial stages of silica polymerization to form gels or zeolites remain largely unknown due mainly to the complexity of sol–gel synthesis processes. Previous simulation studies have applied simple lattice models to qualitatively replicate spontaneous silica nanoparticle formatio...
Article
We provide a discussion of some issues raised by a recent paper published in Journal of Materials Chemistry regarding the local structure of metakaolin. Furthermore, we show using synchrotron X-ray absorption near-edge spectroscopy (XANES) that tri-coordinated aluminium sites can exist in metakaolin, providing new evidence regarding the coordinatio...
Article
Geopolymer cement is fast becoming a technologically important alternative to ceramics and traditional cement. However, the amorphous nature of the phases which participate in the molecular processes occurring during evolution of geopolymer gel has made nanoscale research challenging. Here, for the first time, the local structural correlations of m...
Conference Paper
Full-text available
In the development of new low-CO2 binders for use in concretes, the ability to predict, control and prove durability is paramount in importance. Alkali activation of aluminosilicate materials, particularly fly ash and ground granulated blast furnace slag, leads to the formation of binders with excellent mechanical properties, and advances in techno...
Article
The effect of silica availability on geopolymer binder formation is investigated in the geothermal silica–sodium aluminate–water system, using sodium silicate solution as an additional, highly available silica source. Time-resolved and spatially-resolved FTIR data are combined to provide a mechanistic understanding of the role of silica availabilit...
Article
The effects of sodium orthophosphate and hexametaphosphate, were investigated in ammoniacal thiosulphate leaching of pure gold and a sulphide gold ore. Hexametaphosphate and orthophosphate readily complexed with copper(II) ions and prevented the substitution of thiosulphate into the copper(II) inner coordination sphere, thereby stabilising thiosulp...
Article
Common throughout sol-gel chemistry, including zeolite synthesis, aluminosilicate glass formation and geopolymerisation, is the process of inorganic oxide polymerisation and deprotonation. In this investigation, some of the fundamental reactions occurring during zeolite synthesis and geopolymerisation at high pH are investigated using density funct...
Article
Carboxymethyl cellulose (CMC) was introduced as a surfactant in the leaching of pure gold as well as a sulphide ore using ammoniacal thiosulphate medium. Competing with thiosulphate anions to complex with the cupric ion at the axial coordinate sites, CMC in small quantities reduced the consumption of thiosulphate in the ammoniacal thiosulphate leac...
Article
If formulated optimally, geopolymer cement made from fly ash, metallurgical slags and natural pozzolans could reduce by 80% the CO2 emissions associated with the manufacturing of cement. However, almost all standards and design codes governing the use of cementitious binders and concrete in construction are based on the use of Portland cement. The...
Article
Geopolymer mortar samples were prepared using Australian fly ash and ground granulated blast furnace slag (slag) as binders. Equal amount of these precursors were mixed together and activated by solid anhydrous sodium silicate (Na 2SiO 3).Water content was varied to produce a series of samples, with water to binder ratios ranging from 0.40 to 0.60....
Article
Kaolinite intercalated with potassium acetate is of great interest in the areas of environmental remediation and industrial application; however, its exact atomic structure and the changes which occur when heated have remained largely elusive. Here, neutron pair distribution function analysis is used to investigate the local structural characterist...
Article
Gold leaching with calcium, sodium and ammonium thiosulphate salts was investigated in both pure gold and ore leaching systems. The type of thiosulphate salts was found to influence significantly the solution and surface chemistry, and hence the leaching of pure gold and the pyrite concentrate in the ammoniacal thiosulphate solutions. Calcium thios...
Article
Extraction of pore solutions from hardened inorganic polymer cement (“geopolymer”) paste samples shows that the pore network of these materials is rich in alkali cations and has pH>13, with a relatively low dissolved Si concentration. However, there is little soluble Ca available in these materials to play a buffering role similar to Ca(OH)2 or hig...
Article
Full-text available
Geopolymer technology has emerged as an effective solution for the stabilization of industrial by-products and the immobilization of heavy metals. It has been established that the nature of the source materials used during synthesis has a significant effect on the final chemical and physical properties of the geopolymeric matrix. In particular, it...
Article
Neutron pair distribution function (PDF) analysis is utilized to advance the understanding of the local atomic structural characteristics of geopolymer binders derived from metakaolin, specifically the nature and amount of the water associated with these materials. Samples were heated in air to temperatures up to 1200°C, then analyzed ex situ by hi...
Article
ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Article
Metallic iron and ferric ions were subjected to wet grinding with a sulphide ore in a ceramic ball mill to simulate the fine grinding process using mild steel, in an attempt to investigate the effect of iron species on the ammoniacal thiosulphate leaching of gold. Metallic iron and ferric ions decreased gold leaching in both kinetics and overall ex...
Article
Understanding the atomic structure of complex metastable (including glassy) materials is of great importance in research and industry, however, such materials resist solution by most standard techniques. Here, a novel technique combining thermodynamics and local structure is presented to solve the structure of the metastable aluminosilicate materia...
Article
Full-text available
Portland cement production has been identified as a primary contributor to the world’s Greenhouse gas emissions, calculated at around 5–8% of all manmade emissions worldwide. The majority of these emissions are inherent to the chemistry of cement and the high-temperature processing required for its synthesis, and so can only be avoided by radical c...
Article
Understanding the atomic-level changes that occur as kaolinite is converted (thermally dehydroxylated) to metakaolin is critical to the optimization of this large-scale industrial process. Metakaolin is X-ray amorphous; therefore, conventional crystallographic techniques do not reveal the changes in local structure during its formation. Local struc...
Article
A diagnostic leaching showed that partial oxidation of the sulphide minerals in a gold ore was beneficial for thiosulphate leaching of gold. A pre-treatment process with oxidative ammoniacal solution enhanced the thiosulphate leaching of the sulphide ore, while the thiosulphate consumption was substantially reduced. The sulphide minerals partially...
Article
The addition of low levels of ethylenediaminetetraacetic acid (EDTA) in the ammoniacal thiosulphate gold leach system lowered the catalytic cupric/cuprous redox equilibrium potential, hence the mixed solution potential and reduced the consumption of thiosulphate. In the leaching of pure gold, gold dissolution was enhanced in the presence of EDTA at...
Article
This paper presents a brief review of the role of particle technology in the development of low-CO2 aluminosilicate ‘geopolymer’ binders and concretes as an alternative to traditional Portland cement-based materials. The role of particle shape in particular is highlighted, both in the context of its effect on paste rheology and on water demand. The...
Article
The production of geopolymer binders and concretes from industrial wastes-predominantly coal fly ash and metallurgical slags-offers the opportunity for highly significant carbon dioxide savings in the construction materials industry when compared to the use of traditional Portland cementbased materials. As the third largest emitter of carbon dioxid...
Chapter
One of the major unanswered questions in the field of geopolymer technology relates to the long-term performance of geopolymeric materials in cement replacement applications. There are many different mechanisms by which traditional concretes become corroded and eventually fail, and the successful introduction of a new alternative to ordinary Portla...
Article
By scanning electron microscopy and microanalysis of fly ash-based and mixed fly ash-slag inorganic polymer cement (i.e., “fly ash geopolymer”) binders, a more detailed understanding of the gel structure and its formation mechanism have been developed. The binder is predominantly an aluminosilicate gel charge balanced by alkali metal cations, altho...
Article
Inorganic polymer cements, or ‘geopolymers’, are now finding use as a replacement for Portland cement in concrete production, and have a complex pore structure which has proven difficult to measure accurately by gas or mercury porosimetry. These materials consist of an alkali aluminosilicate-based gel binder phase, within which are embedded unreact...
Chapter
The article contains sections titled: 1. Introduction 2. Process Engineering to Optimize Metals Extraction 2.1. Residence Time Distributions: Plug Flow and Mixed Flow 2.2. Dispersion in Flow-Through Systems 2.3. Networks of Reactor Components 2.4. Maximizing Extraction by Control of Equilibria 3. Modeling Complex Processes 3.1. Combining M...
Article
The nanoscale distribution of elements within fly ash and the aluminosilicate gel products of its alkaline activation ("fly ash geopolymers") are analyzed by means of synchrotron X-ray fluorescence using a hard X-ray Nanoprobe instrument. The distribution of calcium within a hydroxide-activated (fly ash/KOH solution) geopolymer gel is seen to be hi...
Article
Full-text available
Coal fly ashes and metallurgical slags are currently widely used as supplementary cementitious materials in production of Portland cement-based concretes. However, this application makes very poor use of the intrinsic reactivity of the glassy phases present in the waste materials, and can hardly therefore be considered 'valorisation' in the true se...
Chapter
This chapter presents a discussion of the factors influencing the commercial uptake of geopolymer (or, more broadly, alkaline activation) technology in the construction industry: why it has historically not been achieved on a large scale, the factors in the current global environment which are generating massively increased interest at present, and...
Chapter
This introductory chapter provides a brief overview of some important aspects of geopolymer technology, in particular its historical development and the terminology by which geopolymers are described. An introduction to geopolymer technology from a scientific viewpoint is also given. The scope of this review is confined to predominantly lowcalcium...
Book
A geopolymer is a solid aluminosilicate material usually formed by alkali hydroxide or alkali silicate activation of a solid precursor such as coal fly ash, calcined clay and/or metallurgical slag. Today the primary application of geopolymer technology is in the development of reduced-CO2 construction materials as an alternative to Portland-based c...
Article
Density functional modeling of the crystalline layered aluminosilicate mineral kaolinite is conducted, first to reconcile discrepancies in the literature regarding the exact geometry of the inner and inner surface hydroxyl groups, and second to investigate the performance of selected exchange-correlation functionals in providing accurate structural...
Article
The correlation between mechanical and dilatometric properties of aluminosilicate geopolymer binders is highlighted by analysis of a set of samples synthesised from a single ash source using different activating solution compositions and liquid/solid ratios. The geopolymers which display the best strength performance also show a small expansion in...
Chapter
Full-text available
Geopolymer concretes are currently being commercialised in Australia and elsewhere around the world, with a view towards enhancing the sustainability of the world’s construction industry. The fundamental geopolymer binder is an aluminosilicate gel which displays key structural features on every length scale from Ångstroms up to centimetres, meaning...
Article
Metakaolin has been used extensively as a cement additive and paint extender, and recently as a geopolymer precursor. This disordered layered aluminosilicate is formed via the dehydroxylation of kaolinite. However, an accurate representation of its atomic structure has bever before been presented. Here, a novel synergy between total scattering and...
Article
The effect of adding significant percentages of alkaline earth carbonate minerals (calcite and dolomite) to metakaolin-based geopolymers is investigated by compressive strength testing, X-ray diffractometry and electron microscopy, with the aim of better understanding the role played by calcium ions, carbonate ions and mineral surfaces in geopolyme...
Article
The cement industry is a major contributor of increasing greenhouse gas emissions. International Energy Agency reported that the cement industry is contributing around 5-8% of human-derived carbon dioxide and this figure is expected to be increased by 10% with the increasing demand of cement. Cement production involve combustion of limestone with s...
Article
In geopolymer technology, silicate solutions are frequently used as alkali activators to dissolve the solid aluminosilicate precursor and aid in binder formation. These corrosive and often viscous solutions are not user-friendly and would be difficult to use for bulk production. Developing geopolymers as a one-part mixture (“just add water”), simil...
Article
Alkali activation of fly ash by sodium silicate solutions, forming geopolymeric binders, provides a potential means of treating wastes containing heavy metals. Here, the effects on geopolymer structure of contamination of geopolymers by Cr(VI), Cd(II) and Pb(II) in the forms of various nitrate and chromate salts are investigated. The addition of so...
Article
Full-text available
Alternating current impedance spectroscopy (ACIS) is used to monitor in situ the kinetics of geopolymer formation by alkali silicate activation of metakaolin at 40 °C. The evolution of conductivity and resistivity as a function of time are found to correlate very well with existing models of geopolymerisation kinetics. The dissolution of metakaolin...
Article
The atomic pair distribution function (PDF) method was used to study the structure of cesium aluminosilicate geopolymer (Cs 2 O · Al 2 O 3 · 4SiO 2 · xH 2 O, with x ∼ 11). The geopolymer was prepared by reacting metakaolin with cesium silicate solution followed by curing at 50 °C for 24 h in a sealed container. Heating of Cs-geopolymer above 1000 °...
Article
The use of fly ash-based geopolymer binders to immobilize chromium is investigated in detail, with particular regard to the role of the sulfide ion as a reductant for Cr(VI) treatment. In the absence of sulfide, Cr added as Cr(VI) is highly leachable. However, addition of a small quantity of Na2S reduces the Cr to Cr(III), and enables leaching effi...
Article
Seven different calcium silicate materials were used to investigate the role of calcium in geopolymerisation. At low alkalinity, the compressive strength of matrices prepared with predominantly amorphous calcium silicates (blast furnace slag) or containing crystalline phases specifically manufactured for reactivity (cement) is much higher than when...
Article
Seeding of hydroxide-activated geopolymer syntheses with high surface area Al2O3 nanoparticles causes significant changes both in the kinetics of the reaction and in the structures of the products formed, as shown by in situ and ex situ ATR-FTIR spectroscopy. Nucleation at the seed surfaces leads to the formation of phase-separated gels from very e...
Article
The disintegration of agglomerates of solid charge used in a nickel flash furnace has been investigated to improve the understanding and modelling of furnace operation. A laboratory-scale experimental rig was constructed to non-intrusively measure the agglomerate size distribution of solid charge suspended in air, and to observe the powder injectio...
Article
The strength of agglomerates of nickel flash furnace concentrate and dust was determined from experimental observations of agglomerates forming under controlled conditions, combined with mathematical equations from the literature. It was found that the agglomerates had a tensile strength ranging from 0.01 Pa to 38.7 Pa, while inter-particle forces...
Article
Slag concretes, activated by carbonates or carbonate/hydroxide mixtures and cast between 1964 and 1982, are examined. These concretes have served for prolonged periods under conditions in which portland cements would have deteriorated rapidly, and yet have remained sound and actually increased in strength over their service life. By a combination o...
Article
Accurate and precise electron microscopic analysis of the remnant solid precursor (fly ash and blast furnace slag) particles embedded in an inorganic polymer cement (or “fly ash geopolymer”) provides critical information regarding the process of gel binder formation. Differential solubility of phases in the fly ash is seen to be important, with ins...
Article
The potential position of and drivers for inorganic polymers (“geopolymers”) as an element of the push for a sustainable concrete industry are discussed. These materials are alkali-activated aluminosilicates, with a much smaller CO2 footprint than traditional Portland cements, and display very good strength and chemical resistance properties as wel...
Article
The kinetics of geopolymer formation are monitored using a novel in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopic technique. Reaction rates are determined from the intensity variation of the bands related to the geopolymer gel network and the unreacted fly ash particles. Comparison with deuterated geopolymer...
Article
Structural changes in fly ash geopolymers activated with different sodium hydroxide and silicate concentrations are investigated using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy over a period of 200 days. A strong correlation is found between the concentration of silicate monomer in the activating solution and t...
Article
Geopolymers could be used as non-combustible adhesives for steel, so that it is important to understand the interaction of stainless steel and pure iron with geopolymeric gel. Different artificial gel forming solutions with varied concentrations of alkali and Si/Al ratio were used to investigate the effect of the Al–Si precursors on the interaction...
Article
The structural evolution of a systematic series of geopolymers derived from metakaolin is explored. The onset temperature of crystallization, phase composition and densification of the specimens in the current work are determined by quantitative XRD, FTIR and dilatometric analyses. Alkali cation is observed to have no significant effect on the onse...
Article
The chemical interactions between natural siliceous aggregates and a low-Ca alkali-activated cement (geopolymer) were studied. By leaching ideal aluminosilicate minerals such as kaolinite and albite in various alkaline solutions with or without soluble silicates, it was found that addition of 0.5 M SiO2 to a highly alkaline activating solution ([OH...