Australian Fly Ash Research Articles

The use of machine learning in boron-based geopolymers: Function approximation of compressive strength by ANN and GP

This paper employs artificial intelligence methods in order to create a function for compressive strength of the boroaluminosilicate geopolymers based on mixture proportion variables. Boroaluminosilicate geopolymers (BASGs), a group of boron-based alkali-activated materials, not only minimise the carbon footprint in the construction industry but also decrease the consumption of energy and natural resources. Australian fly ash and iron making slag are activated in sodium and boron-based alkaline medium in order to produce the geopolymer binders. The current study employs artificial neural network in order to classify the collected data into train, test, and validation followed by genetic programming for developing a function to approximate the compressive strength of BASGs. The independent variables comprise the percentage of fly ash and slag as well as ratios of boron, silicon, and sodium ions in the alkaline solution. The performance of each method is assessed by the acquired regression and the error parameters. The obtained results show that the percent of silicon and boron ions, with positive direct correlation and the largest power in the function respectively, have the most significant effects on the compressive strength of BASG. The assessment factors, including R-squared 0.95 and root-mean-square error 0.07 in the testing data, indicate that the model explains all the variability of the response data around its mean. It implies a high level of accuracy and reliability for the model.

Factors Affecting the Bond Strength Between the Fly Ash-based Geopolymer Concrete and Steel Reinforcement

In this study, the effect of fly ash characteristics, the content of the fly ash and mix proportion of the Fly Ash-Based Geopolymer Concrete (FBGC) on the bond strength between the FBGC and steel reinforcement were examined. Australian fly ashes from five different sources (Eraring, Mt-Piper, Bayswater, Gladstone and Collie) were used in producing FBGC. A total of 45 FBGC mixes with different fly ash content (300, 400 and 500 kg/m3) and different proportions of alkaline activator were prepared. The use of different fly ashes and in different amounts showed significant differences in the bond strength between the FBGC and steel reinforcement. It was found that the fly ash characteristics including particle size distribution and the content of SiO2 Al2O3 and CaO influenced the bond strength of the FBGC significantly. The results showed that the FBGC that was mixed with Gladstone (GL) fly ash exhibited the highest average bond strength between the FBGC and steel reinforcement (25 MPa). While the FBGC that was mixed with Bayswater (BW) fly ash showed the lowest average bond strength between the FBGC and steel reinforcement (10 MPa). The results also indicated that the increase in the fly ash content in the FBGC significantly increased the bond strength between the FBGC and steel reinforcement. The bond strength of the FBGC responded differently to changes in the Na2SiO3/NaOH ratio in the alkaline activator corresponding to the use of different fly ash.

From Hydration to Strength Properties of Fly Ash Based Mortar

Fly ash (FA) is important alternative or supplement to cement to reduce the environmental impact of concrete industry. However, early age strength development of FA is a concern due to the slower reaction rate of FA compared to cement. This paper examines the early age hydration properties of cement paste containing typical Australian FA and establishes correlations between the degree of hydration and the early-age strength development properties of mortar mixes. All mixes have the same mixture proportion of water to binder (w:b) ratio. FA sourced from different power plants are used for the tests. Cement replacement levels of 0%, 10%, 30% and 40% by mass are considered. The degree of hydration was established from the heat production of the mixes by using isothermal calorimetry. The hydration properties were characterized by hydration curve parameters obtained from curve fitting. The results show that both hydration rate and strength of the binder materials (FA and cement) were reduced with higher replacement levels of FA contributing to a reduced hydration rate at early ages. Linear relationship could be obtained between degree of hydration and strength at early ages for all the fly ash binders.

Influence and role of feedstock Si and Al content in Geopolymer synthesis

This study evaluates the role and relationship between SiO2 and Al2O3 contents of aluminosilicate material on the properties of Si-rich geopolymer systems using Australian fly ashes and existing published data. The selected fly ashes, with varying amounts of amorphous and total SiO2 and Al2O3 were assessed for their overall reactivity. XRD analyses yielded traces of sodalite in addition to conventional amorphous geopolymer phase for the fly ash mixtures with amorphous SiO2/Al2O3 = 3.31. The other two fly ashes with higher amorphous SiO2/Al2O3 ratio tended to produce sodium aluminosilicate zeolitic phases comprising mainly of Na-P1 zeolite and faujasite. These latter phases originate from Na2O–Al2O3–SiO2–H2O gel assemblages but the pathway appears to be governed by the available reactive SiO2 and Al2O3 in the reaction environment. However, indices based on the amorphous content or more precisely amorphous SiO2/Al2O3 ratio provided a relatively good correlation with the compressive strength of the final product.

Characterization of various fly ashes for preparation of geopolymers with advanced applications

Fly ashes from different power stations in Australia (Collie, Eraring, Tarong) and Mongolia (4th thermal power station, Ulaanbaatar city) have been characterized by various techniques. It was determined that the Australian fly ashes are class F while the Mongolian fly ashes are class C. Due to their chemical and mineralogical differences, the fly ashes behaved differently when alkali activated to make geopolymers. The influence of various parameters on the preparation of geopolymers have been investigated and the results are used to establish a procedure for the routine manufacture of alkaline activated products. The applicability of using fly ash for building structural elements, corrosion resistant and thermally resistant materials will be presented.

Boron contents and solubility in Australian fly ashes and its uptake by canola (Brassica napus L.) from the ash-amended soils

Phytotoxicity due to excessive boron (B) uptake by plants impedes routine agronomic utilisation of coal fly ash. We assessed 11 fly ashes (pH 3.14–10.77) having total B content (Bt) of 12–136 mg/kg, of which 20–30% was hot water soluble (Bs) in the acidic ashes (pH <5) and 5–10% in the alkaline ashes, for their potential to supply B to plants and their risk associated with phytotoxicity. We found the Bs/Bt to be negatively correlated (R2 = 0.63**, N = 11) with ash pH. We conducted two pot trials in which canola was grown in soils amended with fly ash. In the first trial, an alkaline fly ash (Bt 66 mg/kg) was incorporated at 5 rates of up to 625 Mg/ha into the top 50 mm of 2 acidic soils in 0.30-m-long intact cores, and sown with canola. Boron concentration in leaves at flowering reached the phytotoxic threshold, and both plant growth and seed yield were reduced, only at 625 Mg/ha. In the second trial, 4 fly ashes (pH 3.29–10.77, Bt 12–127 mg/kg) were incorporated at 4 rates of up to 108 Mg/ha into the top 0.10 m of 2 acidic soils in 1.0-m-long intact cores and then sown with canola. Ashes with highest Bt, when applied at 108 Mg/ha, increased B concentration in the topsoil only. Of the 2 ashes with the highest Bt, only that which produced low soil pH and applied at 108 Mg/ha increased B concentration in the shoot, but was still below phytotoxic threshold. The results suggest that B derived from these ashes may not cause phytotoxicity and excessive soil B accumulation if the ashes are applied at modest rates (<36 Mg/ha) to the topsoil layers.

Determining the Reactivity of a Fly Ash for Production of Geopolymer

A Western Australian fly ash has been analyzed by various techniques in order to quantify the reactive component that can be utilized in geopolymerization. Once the reactive amorphous aluminosilicate material was determined an estimate was made on how much material was left to act as filler material. Two approaches were used, the first a combination of XRD and XRF and the second an alkaline dissolution of fly ash. XRD/XRF results show that approximately 52 wt% of the fly ash is amorphous aluminosilicate material while the dissolution experiment provided a lower value of 39 wt%. Quantitative evaluation of minerals by scanning electron microscopy results showed an increase of iron oxide concentration in the undissolved component with increase in dissolution time leading to the conclusion that the amorphous iron does not participate in the geopolymerization process.

Speciation of chromium in Australian fly ash

The concentrations of chromium (III) and (VI) in fly ash from nine Australian coal fired power stations were determined. Cr(VI) was completely leached by extraction with 0.01 M NaOH solution and the concentration was determined by inductively coupled plasma atomic emission spectrometry (ICP-AES). This was confirmed by determining Cr(III) and Cr(VI) in the extracts of fly ash that had been spiked with chromium salts. These analytical measurements were done using a combination of ion-exchange chromatography and ICP-AES. The elutant was 0.05 M HNO 3 containing 0.5%-CH 3OH. When the column was operated at a flow rate of 1.2 ml min −1 and samples were injected by use of a sample loop with a volume of 100 μl, Cr(III) and Cr(VI) in sample solution was exclusively separated within approximately 10 min. The detection limits (3 σ) were 5 ng for Cr(III) (0.050 mg l −1) and 9 ng for Cr(VI) (0.090 mg l −1), respectively. A relative standard deviation of 1.9% ( n = 6) was obtained for the determination by IC–ICP–AES of 0.25 mg l −1 Cr(III) and Cr(VI).

06/02110 Mobility of trace elements from selected Australian fly ashes and its potential impact on aquatic ecosystems: Jankowski, J. et al. Fuel, 2006, 85, (2), 243–256.

06/02110 Mobility of trace elements from selected Australian fly ashes and its potential impact on aquatic ecosystems: Jankowski, J. et al. Fuel, 2006, 85, (2), 243–256.

Mobility of trace elements from selected Australian fly ashes and its potential impact on aquatic ecosystems

Abstract Batch leaching tests have been performed on fly ashes collected from four Australian power stations fuelled by chemically different coals. Two acidic and two alkaline fly ashes were subjected to long-term (144 h) leaching tests, and the behaviour of As, B, Mo and Se was investigated to obtain data on their potential for mobilisation during fly ash–water interactions. All four elements are mobile under different conditions and over different leaching times. The concentrations of these elements released in leaching solutions with initial pH values of 4, 7 and 10 were used to assess the influence of pH conditions on element mobility from the acidic and alkaline fly ashes. The most mobile of the four elements leached were Mo from alkaline fly ashes and B from acidic fly ashes. Arsenic concentration increased with time in leachate solutions from acidic and alkaline fly ashes; however, in solutions in contact with alkaline fly ashes the As concentration, after reaching a maximum, later decreased with time. Selenium mobility shows a similar pattern to that of As, with similar leaching concentrations. Boron has the highest relative mobility of all four elements. A process possibly responsible for the decrease in concentration of B, As and Se in alkaline leaching solutions is the formation of ettringite. Equilibrium between the solid phase (ash) and the leaching solution was not reached in any of the leaching experiments. The pH of the leaching solution is the key factor affecting the mobility of these trace elements in these fly ashes.

Comparative assessment of Australian fly ash and conventional concrete bricks

A comparative study of the chemical composition, mineralogy, morphology and crushing strengths of fly ash bricks, conventional concrete bricks and fly ash samples has been undertaken. The main chemicals present in the products were silica and alumina while their main minerals were quartz, mullite, illite, vaterite, and calcite. Elemental analysis by XPS showed that the major elements in the samples were oxygen, silicon, carbon, calcium and aluminium; and scanning electron microscopy revealed that the fly ash samples consist of spherically-shaped particles with surface attachment containing needle-like particles. Compared with conventional concrete bricks, fly ash bricks generally have higher atomic silicon and crushing strengths but lower crystalline silica. The implication of the results on the suitability of fly ash bricks as replacements for conventional concrete bricks in the building industry is discussed from the point of view of human health and occupational safety. Copyright © 2004 Society of Chemical Industry

Western Australian fly ash on sandy soils for clover production

An experiment was conducted to determine the value of fly ash collected from flue gases of the Kwinana coal fired power station in Western Australia, as an amendment for sandy soils and as a replacement for phosphorus or potassium fertilizers. The results showed large increases in clover dry matter production (49% to 278%), attributed to improvements in nutrient and water retention from the fly ash. The fly ash provided a substantial amount of the phosphorus needed by the clover, although application of phosphorus fertilizer further increased dry matter production in the presence of fly ash. No evidence was obtained from plant growth or tissue analysis that the fly ash provided potassium to the pasture. The maximum yield was achieved when 501 ha‐1 of fly ash was applied to the soil. However, only 10 to 401 ha‐1 was required to achieve 75 to 90% of the maximum production. Although a statistically significant increase in cadmium and mercury concentration could be attributed to fly ash, the increase was small and within the range of natural variation of levels found at the sites.

Testing Fly Ash for Fineness to ASTM C 430: Sieve Calibration

ABSTRACTFollowing dissatisfaction with the existing calibration factor for standard fly ash used in Australia to AS 1129–1971, “Fly Ash for Use in Concrete,” a joint investigation was made by Amatek Limited and Construction Technology Laboratories Inc. Test results for five reference materials and two Australian fly ashes from tests to ASTM C 430 on both electroformed and woven wire sieves were examined and “corrected” by several means.The ASTM standard method of sieve correction is challenged, both in the use of Standard Reference Material (SRM) cement and the basis of sieve correction for coarse samples. Preferred bases of correction are suggested.

Plant uptake and phytotoxicity of boron in Australian fly ashes

French bean (Phaseolus vulgaris cv. Redland Pioneer) and Rhodes grass (Chloris gayana cv. Pioneer) were grown in glasshouse experiments to examine the potential for phytotoxicity of B in a range of Australian fly ashes. In each experiment, the ashes used were either untreated, leached or adjusted to pH 6.5 and subsequently leached. In the first eperiment, the yield and B status of plants grown on five fly ashes mixed (5 and 10% by weight) with an acid-washed sand were measured and, with the exception of one ash, yield differences among ash sources and among ash treatments were attributed to differences in the degree of B toxicity. In a subsequent experiment, a fly ash with properties representative of most Australian ashes was mixed (0, 15, 30, 70 and 100% by weight) with a sandy loam, and the yield and mineral composition of plants grown on these mixtures determined. Although the available water capacity of the soil was substantially increased by fly ash addition, incorporating large proportions of untreated fly ash resulted in poor plant growth primarily due to B toxicity. In both experiments, leaching the ash reduced the potential for B toxicity, whereas adjustment of the pH to 6.5 and subsequent leaching of the fly ash resulted in plants with normal levels of B. There were marked differences in both the tissue levels of B and the extent of B toxicity symptoms between the two species. Rhodes grass appeared to be able to tolerate higher B contents in the growing medium by taking up much less of the element than French bean. The results indicate that phytotoxicity of B would be a major problem in establishing vegetation on ash dams and in the agronomic utilization of unweathered fly ashes in Australia.

Properties of Australian fly ashes relevant to their agronomic utilization

Of the 13 fly ashes from Australian power stations, all were dominated by both amorphous and crystalline aluminosilicates and quartz, and these were associated with minor amounts of Fe oxides, lesser amounts of Ca, Mg, Na, K, Ti and P oxides, and variable levels of incompletely combusted C. The ashes consisted of particles predominantly in the silt plus fine sand fraction (67-98%), and electron microscopy revealed that ash matrices consisted of glassy spherical particles and less regularly shaped spongy particles. The available water capacity was high and varied from 27 to 105% with 11 of the 13 samples having values > 40%. Twelve of the 13 ashes were alkaline to strongly alkaline (pH range 8.0-12.8). Soluble salt levels were related to the coal source, and electrical conductivity of the saturation extracts (ECse) varied from 0.63 to 7.0 mS cm -1 for 11 of the samples; two ashes produced from brown coal had ECse values of 46.0 and 55.0 mS cm-1. The nutritional status of the ashes was assessed on samples leached with water to reduce the soluble salts to equilibrium levels. The ashes contained negligible amounts of N, but their P status was variable. The amounts of NH4OAc-extractable Ca and Mg were generally high in most samples and were considered more than adequate for most plant species; however, NH4OAc-extractable K values were generally low. Adequate levels of sulfate-S existed in 12 of the 13 samples, and levels of DTPAextractable Cu, Zn, Mn and Fe were high when compared with published critical values. Most of the unleached samples contained potentially toxic levels of B. The results are discussed with reference to the establishment of vegetation on ash dumps and to the use of fly ash in ameliorating the properties of soils.

High gradient magnetic separation of fly ash

Preliminary experiments have been performed on the high gradient magnetic separation (HGMS) of three fly ash samples. The enrichment of trace elements has been studied in order to determine whether retrieval of raw materials and the removal of harmful elements which might otherwise be leached from the disposed fly ash are feasible. Results are analyzed in terms of the capture efficiency, the magnetization and the elemental composition of the magnetically separated fractions. In all samples the retrieval of iron was quite high, and for the Australian fly ash enrichment by at least a factor of 2 was observed for several trace elements. Explanations are offered for the differences in processing characteristics among the various fly ash samples, and suggestions are given for additional testing to confirm these theories.