The properties of fly ash based geopolymer mortars made with dune sand

This paper reports the properties of fly ash based geopolymer mortars made with dune sand. The geopolymer mortars of different cation type, namely sodium based (Na), potassium based (K) and a mixed Na/K, were prepared with dune sand (DS) and river sand (RS). The corresponding geopolymer pastes were also prepared. A series of tests including compressive strength, modulus of elasticity, splitting tensile strength, microanalysis (using scanning electron microscopy), porosity (using mercury intrusion porosimetry), sorptivity and air void (using section analysis method) were carried out. The results showed a strong correlation between strength and porosity of geopolymeric materials. The addition of DS had influences on the chemical compositions and physical properties of geopolymer mortars. These influences were dependent on the type of cation. Based on the results of mechanical properties, DS can be utilised as the fine aggregate for the production of geopolymer based construction material.

Using geopolymer to minimise metals leaching from brown coal fly ash

Fly ash is generated from combustion of brown coal in power stations. The majority of fly ash is removed by electrostatic precipitators (ESP) and finally disposed into the landfill as prescribed wastes. A method was studied to add clay materials to the brown coal fly ash in order to form the so-called geopolymer network, which is effective at stopping the metal contents from leaching, and have minimum impact to the environment. The experiments were conducted parallel on leached fly ash and dry precipitator fly ash. The ratios of fly ash and added clay materials were varied to determine the effects of different compositions on leaching rates. Both X-ray diffraction analysis and scanning electron microscopy images showed that as the percentage of fly ash was increased, the formation of geopolymer is reduced. Eighteen metals and heavy metals were targeted during the leaching tests and the leachate samples were analysed using ICP-AES and ICP-MS. It was found that the reduction of metal leaching was achieved by adding up to 60% of fly ash to form the geopolymer like structure. Significant reductions were observed for calcium, strontium and barium. Leached fly ash achieved better stabilisation than dry precipitator fly ash for major elements. It's hard to quantify its effects on trace metals leaching due to their ultra low concentration in the fly ash. The samples spiked with trace metals of lead, zinc, mercury and barium showed remarkable reduction in leaching.

Evidence for the direct interaction between methylene blue and guanine bases using DNA-modified carbon paste electrodes

It is explored that methylene blue interacts with the guanine bases specifically, rather than the bases of ss-DNA in general. This interaction can be used as a method of quantifying the amount of oligonucleotide that is immobilized onto an electrode surface.

Development of an intelligent system for the solder paste printing process

A neurogenetic-based hybrid framework is developed where the main components within the framework are artificial neural networks (ANNs) and genetic algorithms (GAs). The investigation covers a mode of combination or hybridisation between the two components that is called task hybridisation. The combination between ANNs and GAs using task hybridisation leads to the development of a hybrid multilayer feedforward network, trained using supervised learning. This paper discusses the GA method used to optimize the process parameters, using the ANN developed as the process mode, in a solder paste printing process, which is part of the process in the surface mount technology (SMT) method. The results obtained showed that the GA-based optimization method works well under various optimization criteria

Reinforcing effects of graphene oxide on portland cement paste

Abstract: In this experimental study, the reinforcing effects of graphene oxide (GO) on portland cement paste are investigated. It is discovered that the introduction of 0.03% by weight GO sheets into the cement paste can increase the compressive strength and tensile strength of the cement composite by more than 40% due to the reduction of the pore structure of the cement paste. Moreover, the inclusion of the GO sheets enhances the degree of hydration of the cement paste. However, the workability of the GO-cement composite becomes somewhat reduced. The overall results indicate that GO could be a promising nanofillers for reinforcing the engineering properties of portland cement paste.

Change in microstructure and compressive strength of alkali-activated slag paste at temperature exposure of 50°C

This paper presents a study on the evolution of strength and alteration microstructure of alkali-activated slag (AAS) pastes exposed to 50°C. Ground granulated blast furnace slag (GGBFS) was used as thestarting material to prepare slags pastes which were then activated with a range of activators. The preliminary results from the study of these pastes are presented. It was found that all the pastes show a significantlystrength loss after exposure to 50°C for 24 hours. This is independent on the activators used. The paste samples were further examined by X-ray diffraction (XRD), differential thermal analysis (DTA), scanning electronmicroscopy (SEM) and sorptivity tests. A hypothesis for strength loss is proposed based on the observations in change of microstructure. This hypothesis will be further validated by the study of the AAS pastesprepared by using phosphorus slags.

The properties of fly ash based geopolymer mortars made with dune sand

Geopolymer cement utilises industrial by-products and is associated with low CO2 emissions. The use of dune sand as fine aggregate could reduce the environmental impact of mining activities. The present study is to examine the feasibility of using dune sand in geopolymer-based construction materials. The geopolymer mortars made with dune sand (DSM) were prepared by using alkali activators of different cations(Na, K and Na/K). In order to compare, the corresponding geopolymer mortars made with normal sand (NSM) were also prepared. It was found that dune sand has little influence on the strength of geopolymer mortars, especially for K based mortars. However, the alkali cation has significant influence on the compressive strength of geopolymer mortars. This influence was found to be correlated to porosity. Low compressive strength is associated with high porosity. For all investigated alkali cations, the tensile strengths of DSM compare favourably to those predicted by the relevant Standards for construction materials. Based on the experimental results, Australian dune sand can be used as fine aggregate for the production of geopolymer based construction materials.

Strain rate effects for strength of geopolymer concrete

The effects of strain rate on compressive and tensile strength of fly ash based geopolymer concrete were investigated experimentally. Four mixes of geopolymer concrete using different alkaline solutions and under vary curing conditions were prepared. One mix of ordinary Portland cement (OPC) concrete was prepared for comparison. Both Quasi-Static tests using standard MTS and dynamic tests using Split-Hopkinson pressures bar (SHPB) were conducted, which were giving varying strain rate loadings from 10‾⁷ to 103 per second. The strain rate effect is presented as the ratio of dynamic compressive strength to static compressive strength (DIF). Results show that DIFs of geopolymer concrete are generally higher than those of OPC concrete at strain range of 187/s to 346/s (compression tests) and 7/s to 13/s (splitting tensile tests), respectively. This tendency is independent on loading regimes (compression or tension). This suggests that geopolymer concrete can be used as an alternative construction material to OPC concrete for the structures which has a high risk of being subjected to impact loadings.

Damping capacity of fly ash-based geopolymer

As environmentally-friendly materials, geopolymers have the potential to replace ordinary Portland cement (OPC) for the construction of railway sleepers and multi-flue chimneys, where the vibration control capabilities of the material must be considered. The critical damping value (ξ) is the main parameter in relation to vibration reduction. In this study, the traditional logarithmic decrement technique was used to measure the ξ of geopolymers. Geopolymers were prepared by activating fly ash using alkali solutions with different SiO2/Na2O ratios. The results show that the ξ of the geopolymers is similar to that of the OPC counterpart. Finite element analysis (FEM) based on the Rayleigh damping model was conducted to replicate the test results, and scanning electron microscopy and mercury-intrusion porosimetry were used to study the microstructure of the geopolymers. A discussion of the possible damping mechanisms based on the microstructural investigation and the FEM analysis is presented.

An investigation of major factor of influence of strength gain or loss of geopolymer when exposed to 800° C

When fly ash based geopolymer mortars were exposed to an elevated temperature of 800oC, it was found that the strength after the exposure sometimes decreased, but at other times increased compared to the original strength. The aim of this investigation is to find the reason for this contrasting behaviour. Fol-lowing exposure to high temperature, residual strengths of specimens prepared with two different fly ashes, with initial strengths ranging from 5MPa to 60MPa, were investigated. The parameter that was found to have a major influence on the contrasting behaviour was the ductility of the mortars. The results indicate that the higher the ductility the lower the strength loss. This correlation is attributed to the fact that mortars with high ductility could provide higher capacity to accommodate thermal incompatibility than mortars with low ductil-ity. Beyond the particular threshold of ductility, some mortars even increased strength after the exposure, pos-sibly due to sintering.

Reduction of metal leaching in brown coal fly ash using geopolymers

Current regulations classify fly ash as a prescribed waste and prohibit its disposal in regular landfill. Treatment of the fly ash can reduce the leach rate of metals, and allow it to be disposed in less prescribed landfill. A geopolymer matrix was investigated as a potential stabilisation method for brown coal fly ash. Precipitator fly ash was obtained from electrostatic precipitators and leached fly ash was collected from ash disposal ponds, and leaching tests were conducted on both types of geopolymer stabilised fly ashes. The ratio of fly ash to geopolymer was varied to determine the effects of different compositions on leaching rates.

Using inorganic polymer to reduce leach rates of metals from brown coal fly ash

The burning of brown coal for electricity generation produces thousands of tonnes of fly ash each year. Treatment of the fly ash can reduce leach rates of metals and allow it to be disposed in less prescribed landfill. A geopolymer matrix was investigated as a potential stabilisation method for fly ash obtained from electrostatic precipitators and ash disposal ponds. The ratio of fly ash and geopolymer was varied to determine the effects of different compositions on leaching rates. The major element leachate concentrations obtained from pond ash were lower than that of precipitator fly ash. Conversely, precipitator ash-geopolymers were better for trace heavy metal stabilisation. Effective reduction of elemental concentrations in the leachate has been achieved, particularly for calcium, arsenic, selenium, strontium and barium. Scanning electron microscopy revealed the distribution of metals originated from fly ash and from added geopolymer material. It also showed that some elements are leached from ash particles to the geopolymer phase and others remained as undissolved particles. Qualitative analysis showed that fly ash particles interacted with the geopolymers phase through surface reactions.

The tangled web internet plagiarism and international students` academic writing

This study explores the notion of plagiarism and the Internet from 11 English as Second Language (ESL) teachers and 186 first-year ESL students at South-Coast University in Melbourne, Australia. Data collection was by a questionnaire and semi-structured interviews, and coded using SPSS and N*Vivo software to ascertain trends in response. The most significant difference in response related to the concept of the Internet as copyrightable space. ESL teachers in this study regarded cyberspace as a limitless environment for ‘cut and paste’ plagiarism in students’ academic writing, whereas ESL students considered the Internet a ‘free zone’ and not governed by legal proprietary rights. These conflicting views, it is suggested, relate to differing notions of authorship and attribution: the Romantic notion protected by legal theory and sanctions versus literary theory and techno-literacy notions of authorship. This research highlights the need to reformulate plagiarism policies in light of global and technological perspectives of authorship and attribution of text.