A. van Riessen

Influence of calcium compounds on the mechanical properties of fly ash geopolymer pastes

The influence of calcium compounds (CaO and Ca(OH)(2)) on the mechanical properties of fly ash based geopolymers has been studied. Calcium compounds were substituted in fly ash at 1, 2 and 3 wt%, respectively. Curing of the geopolymers was performed at ambient temperature (20 degrees C) and 70 degrees C. Addition of calcium compounds as a fly ash substitute improved mechanical properties for the ambient temperature cured samples while decreasing properties for the 70 degrees C cured samples. Seven days compressive strength of the ambient temperature cured samples increased from 11.8 (2.9) to 22.8 (3.8)MPa and 29.2 (1.1)MPa for 3% CaO and 3% Ca(OH)(2) additions, respectively.

Effect of fly ash preliminary calcination on the properties of geopolymer

The influence of preliminary calcination of fly ashes on the geopolymerisation process has been studied. Preliminary calcination at 500 and 800 degrees C causes decarbonation of the fly ash while it also leads to a decrease of the amorphous content of the fly ashes from 60 to 57%. Geopolymer prepared using raw fly ash exhibited a compressive strength 55.7(9.2)MPa, while for 500 and 800 degrees C calcined samples it reduced to 54(5.8) and 44.4(5.4)MPa, respectively. The decrease in compressive strength of the geopolymers is discussed in terms of partial surface crystallisation of the fly ash particles. Reactivity of the fly ash also has been correlated with the shrinkage rate and presence of efflorescence on the surface of geopolymers.

The Influence of Short Fibres and Foaming Agents on the Physical and Thermal Behaviour of Geopolymer Composites

Foaming methods to reduce the density of geopolymers were investigated as low density geopolymers are increasingly being reported in the literature to be effective in improving the insulating properties. However, there is no consistency in foaming methods and as such this study was performed to compare different foaming agents in order to better understand their effect on the properties of geopolymers. In particular, a surfactant and hydrogen peroxide were used individually and in combination to ensure a homogeneous pore distribution in the slurry. Physical and microstructural properties of the hardened low density geopolymers are presented and discussed. The behaviour under fire conditions of fibre reinforced and foamed geopolymer samples will also be presented in order to appreciate the suitability of geopolymer composite in high temperature applications.

Structural determination of high Tc superconductor (Bi,Pb)2Sr2Ca2Cu3Ox (2223) phase with powder diffraction data

The (Bi,Pb)2Sr2Ca2Cu3Ox (2223) phase is regarded as the one of the most technologically significant high Tc phases in the Bi–Sr–Ca–Cu–O system. However, its structure has not been fully described so far. The definitive structure model of 2223 has been determined in this study by direct methods and Q-peak analysis of difference Fourier maps using synchrotron radiation data. Successive least squares refinement of the model with the preferred A 2aa space group was carried out by Rietveld procedures with neutron diffraction data. Anomalies were not observed for interatomic distances (bonded and non-bonded atoms), bond angles and isotropic temperature parameters. Two categories of copper atoms were clearly identified: (i) square coordinated to four oxygen atoms and (ii) pyramids with a fifth oxygen atom. The valence states of two Cu atoms have been estimated using bond valence calculations, as employed by Brown for YBCO. There is no direct bridging between the Cu squares and pyramids. The Bi3+ cations are coordinated by three oxygen atoms and form a single chain [BiO2]nn− along the a axis, which is the first report of this feature for the 2223 structure.

Introducing Bayer Liquor-Derived Geopolymers

Geopolymer- or alkali-activated material has been studied for many years. In fact there are now a number of examples of commercial products and large installations of alkali-activated materials (AAMs). Initially the benefits of low CO 2 compared with ordinary Portland cement (OPC) was one of the main points of distinction and fueled more research in this area. As the field of geopolymers matured it became obvious that more rigorous assessments of costs, CO 2 emissions, and embodied energy were required prior to increased commercialization. These assessments revealed that some of the initial assumptions about costs and CO 2 cannot be extended to all mix formulations and for all locations. There are a number of instances where AAMs are more expensive than their OPC counterparts and the CO 2 savings may be minimal. At first these results may appear to be disappointing but in fact they encouraged people to seek alternative precursors that offered lower overall CO 2 and embodied energy while retaining the benefits of AAMs.