Search results for: Jannie S. J. Deventer

Items from 1 to 16 out of 16 results

article

Solid Reactant-Based Geopolymers from Rice Hull Ash and Sodium Aluminate

Ailar Hajimohammadi, Jannie S. J. Deventer

Waste and Biomass Valorization > 2017 > 8 > 6 > 2131-2140

High carbon rice hull ash and solid sodium aluminate were used as silica, alkali and alumina sources to synthesise one-part “just add water” geopolymer binders. Three binders with different Si/Al ratios and different water contents were studied. Due to the high carbon content of the samples, using a high amount of water is required to satisfy the workability of the binders. Similar to traditional...

article

Characterisation of One-Part Geopolymer Binders Made from Fly Ash

Ailar Hajimohammadi, Jannie S. J. Deventer

Waste and Biomass Valorization > 2017 > 8 > 1 > 225-233

The kinetics of one-part “just add water” geopolymerisation reaction is studied in the system of fly ash as an aluminosilicate precursor and solid sodium silicate as alkali activator. The rates of the release of Si and Al nutrients from source materials can significantly affect their availability for reaction and their extent of participation in geopolymer gel structure. The crystalline phases that...

chapter

Fundamental Developments in Understanding the Interactions Between Metal Cyanides and Functional Polymers

Grant C. Lukey, Jannie S. J. Deventer

Fundamentals and Applications of Anion Separations > 179-206

For the greater part of the 20^th century. the hydrometallurgical pathway used for the treatment of gold ores consisted of leaching the ore in cyanide solution followed by a complex solid-liquid separation stage, which separated the solid residues from the leach liquor. The leach liquor was then treated by zinc cementation to recover the gold. However. this process resulted in a poor gold recovery...

article

Time-resolved yield stress measurement of evolving materials using a creeping sphere

Alireza Kashani, John L. Provis, Ben B. G. Deventer, Greg G. Qiao, more

Rheologica Acta > 2015 > 54 > 5 > 365-376

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 precise measurement of the evolution of the yield...

article

Accelerated carbonation testing of alkali-activated slag/metakaolin blended concretes: effect of exposure conditions

Susan A. Bernal, John L. Provis, Ruby Mejía de Gutiérrez, Jannie S. J. Deventer

Materials and Structures > 2015 > 48 > 3 > 653-669

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 particularly significant in controlling carbonation...

article

Effect of molecular architecture of polycarboxylate ethers on plasticizing performance in alkali-activated slag paste

Alireza Kashani, John L. Provis, Jiangtao Xu, Adam R. Kilcullen, more

Journal of Materials Science > 2014 > 49 > 7 > 2761-2772

A range of anionic and cationic polycarboxylate ether (PCE) plasticizers with different molecular architectures (molecular weights, side chain lengths, and ratios of side chain density to backbone charge) are synthesized and tested to determine their effects on the rheological properties of fresh alkali-activated slag (AAS) pastes. A higher density of long side chains in the lower molecular weight...

article

Drying-induced changes in the structure of alkali-activated pastes

Idawati Ismail, Susan A. Bernal, John L. Provis, Sinin Hamdan, more

Journal of Materials Science > 2013 > 48 > 9 > 3566-3577

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 Portland cement, and therefore there is little understanding...

article

Microstructural changes in alkali activated fly ash/slag geopolymers with sulfate exposure

Idawati Ismail, Susan A. Bernal, John L. Provis, Sinin Hamdan, more

Materials and Structures > 2013 > 46 > 3 > 361-373

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-activated fly ash/slag geopolymer binders subjected...

article

Thermal Activation of Albite for the Synthesis of One‐Part Mix Geopolymers

Dingwu Feng, John L. Provis, Jannie S. J. Deventer, G. Scherer

Journal of the American Ceramic Society > 95 > 2 > 565 - 572

Precursors for the preparation of one‐part geopolymers are synthesized by thermal activation of albite with sodium hydroxide and sodium carbonate, then cooling and crushing the resulting product. Albite is stable under thermal treatment up to 1000°C, but is able to be converted to depolymerized, disordered, and X‐ray amorphous geopolymer precursors in the presence of sodium hydroxide or sodium carbonate...

article

Acid resistance of inorganic polymer binders. 1. Corrosion rate

Redmond R. Lloyd, John L. Provis, Jannie S. J. Deventer

Materials and Structures > 2012 > 45 > 1-2 > 1-14

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 corrosion, which contradicts some previous claims of extremely...

article

Chemical Research and Climate Change as Drivers in the Commercial Adoption of Alkali Activated Materials

Jannie S. J. Deventer, John L. Provis, Peter Duxson, David G. Brice

Waste and Biomass Valorization > 2010 > 1 > 1 > 145-155

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 changes in construction materials chemistry and synthesis...

article

Microscopy and microanalysis of inorganic polymer cements. 2: the gel binder

Redmond R. Lloyd, John L. Provis, Jannie S. J. Deventer

Journal of Materials Science > 2009 > 44 > 2 > 620-631

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, although it appears that calcium supplied by slag particles...

article

Microscopy and microanalysis of inorganic polymer cements. 1: remnant fly ash particles

Redmond R. Lloyd, John L. Provis, Jannie S. J. Deventer

Journal of Materials Science > 2009 > 44 > 2 > 608-619

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 insoluble mullite crystals becoming exposed by the retreat...

article

Direct measurement of the kinetics of geopolymerisation by in-situ energy dispersive X-ray diffractometry

John L. Provis, Jannie S. J. Deventer

Journal of Materials Science > 2007 > 42 > 9 > 2974-2981

In-situ energy dispersive X-ray diffractometry (EDXRD) using synchrotron radiation has been used to directly observe the kinetics of formation of a geopolymeric gel from a metakaolin precursor. The use of a purpose-built hydrothermal cell with polychromatic radiation from a wiggler source enables collection of a full diffraction pattern approximately every 150 s. This provides sufficient time resolution...

article

Physical evolution of Na-geopolymer derived from metakaolin up to 1000 °C

Peter Duxson, Grant C. Lukey, Jannie S. J. Deventer

Journal of Materials Science > 2007 > 42 > 9 > 3044-3054

The thermal shrinkage and weight loss of a systematic series of geopolymers with nominal composition of NaAlO₂(SiO₂)_z · 5.5H₂O (1.15 ≤ z ≤ 2.15) made by activation of metakaolin with sodium silicate solutions are presented. The thermal behaviour of Na-geopolymers are varied, but may be categorised into four regions of behaviour exhibited by all specimens. This investigation explores the effect of...

article

Editorial

Grant C. Lukey, Angel Palomo, John L. Provis, Jannie S. J. Deventer

Journal of Materials Science > 2007 > 42 > 9 > 2915-2916

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