Bonding mechanism and performance of rectorite/ball clay bonded unfired high alumina bricks

In this study, the bonding mechanism and normal/high temperature performance of rectorite clay or ball clay bonded unfired high alumina bricks were investigated by using different techniques (XRD, TG-DSC, SEM, particle size distribution and rheology). The results showed that clay particles are separated into layer structural units in water due to the hydration swelling and electrostatic repulsive force, and rectorite layer structural units have larger aspect ratio than ball clay. Rectorite layer structural units form band-type structure with “face to face” after drying results in better bonding performance than ball clay (card-house structure with “edge to face”). The cold crushing strength of 9% rectorite/ball clay bonded unfired high alumina bricks after firing at the dehydroxylation temperature for 3 h reach 71 MPa and 50 MPa, respectively, and which can satisfy the strength requirement for the transportation and use of most high alumina bricks. The secondary mullitization and lower liquid phase content of ball clay bonded unfired high alumina brick under high temperature cause it has higher refractoriness under load and lower linear shrinkage than rectorite clay bonded brick. The T_0.6 refractoriness under load of 9% rectorite/ball clay bonded unfired high alumina brick are 1262.6 °C and 1580.3 °C, respectively. Thus, the 9% ball clay bonded unfired high alumina bricks have wider service temperature range than 9% rectorite bonded bricks.     

The use of solid residues derived from different industrial activities to obtain calcium silicates for use as insulating construction materials

Calcium silicates have obtained through solid state reaction of the different residues generated in various industrial activities. As a source of calcium oxide: marble, mussel shells, and the reagent commercial calcium hydroxide were used. The source of silica was biomass ash and fired ceramic residue formed by crushing pieces of broken and defective ceramic products from a brick factory (chamotte). From the raw materials, biomass ash and marble, biomass ash and commercial calcium hydroxide, and chamotte and crushed mussel shell dust, mixed in a molar ratio CaO:SiO₂ 1:1 and sintered at 1100 °C (24 h), calcium silicates such as wollastonite, gehlenite and larnite were obtained. Both the raw materials and the synthesized material were characterized by XRD, XRF and TGA-DTA. In order to use the calcium silicates obtained as low temperature thermal insulating ceramic materials, the materials obtained were compressed under uniaxial loading at 81.7 MPa to obtain bricks measuring 60 mm × 30 mm × 10 mm. The properties of the bricks were studied. The ceramic materials present conductivity values between 0.10 W/m² K and 0.18 W/m² K and compressive strength of 29.8-59.3 MPa, respectively. The bricks met the UNE guidelines for use as low-temperature structural insulation ceramics.     

Pozzolanic activity of Jordanian oil shale ash

The ash of the retort residue of the oil shale from central Jordan has been further tested to evaluate its pozzolanic activity. According to the preliminary experiments the ash had cementive properties. Thermogravimetric analyses were performed on ash, cement, ash blended cement and ash-lime pastes. In the blended pastes, addition of ash seemed to decrease the amount of lime generated. In the ash-lime paste the lime consumption by ash with time followed a similar trend to the reactions of trass and silica fume with lime. The ash-lime reaction was mainly a diffusion controlled process obeying the Ginstling-Brounshtein equation. The pozzolanic activity of the ash, as indicated by its lime activity and rate constant, was not as high as the other pozzolans compared, mainly due to its lower fineness. Tests on compressive strengths of cement and lime mortars blended with ash confirmed the findings, indicating that up to 20% of cement could be replaced by ash used as an admixture. Ash-lime mortars could gain moderate strengths under accelerated curing, suitable for some building units.     

利用金陵热电厂脱硫灰制备双免砖的研究

以金陵热电厂所排脱硫灰为主要原料,进行了免烧免蒸砖的研究。采用正交试验方法,设计了脱硫灰、水泥、集料、石膏、石灰的不同配比。试验结果表明,在配比为水泥8％、集料25％、石灰10％、石膏5％、粉煤灰52％时,生产的免烧砖强度最高。同时还研究了不同原材料对免烧砖强度的影响。     

利用活化粉煤灰制备高掺量粉煤灰烧结砖

研究了分别经机械和化学活化后的粉煤灰对高掺量粉煤灰烧结砖性能和显微结构的影响。结果表明:用磨细粉煤灰代替原灰配料,可以改善烧结砖的力学性能,尤其是砖的抗压强度能显著提高。当用掺量质量分数为60%的磨细灰制砖时,烧结砖的抗压强度提高至原灰烧结砖的2倍,并且有更为致密的微结构。在粉煤灰砖中加入质量分数为2%的外加剂D进行化学活化后,可明显改善干坯强度,并提高烧结砖的抗压强度。     

Non-ideal solid solution aqueous solution modeling of synthetic calcium silicate hydrate

New data relevant to calcium silicate hydrate (C-S-H) gels prepared at room temperature have been obtained over a time period of up to 112 weeks. X-ray diffraction (XRD) indicates equilibrium was attained after 64 weeks. Coupled with fourier transform infrared (FT-IR) spectroscopy, a phase change in C-S-H gel at Ca/Si ≈ 1.0 was identified and the occurrence of portlandite as a distinct phase for Ca/Si > 1.64. The incongruent dissolution of C-S-H gel was modeled as a non-ideal solid solution aqueous solution (SSAS) between the end-member components CaH₂SiO₄ (CSH) and Ca(OH)₂ (CH) using equations defining the solidus and solutus curves on a Lippmann phase diagram. Despite being semi-empirical, the model provides a reasonable and consistent fit to the solubility data and can therefore be used to describe the incongruent dissolution of C-S-H gels with compositions Ca/Si ≥ 1.0.     

NaOH-activated ground fly ash geopolymer cured at ambient temperature

NaOH-activated ground fly ash geopolymers, cured at room temperature, were studied in this paper. Ground fly ash (GFA), with a median particle size of 10.5 μm, was used as source material. NaOH concentrations of 4.5-16.5 M (M) were used as an alkali activator. Compressive strength tests and microstructure observations using SEM, EDX, XRD and FTIR were performed. Results indicated that GFA gave higher strength geopolymer paste compared to original fly ash. Ground fly ash could be used as a source material for making geopolymers cured at room temperature. An increase in NaOH concentration from 4.5 to 14.0 M increased the strength of GFA geopolymer pastes. Microstructure studies indicated that NaOH concentrations of 12.0-14.0 M created new crystalline products of sodium aluminosilicate. The compressive strengths at 28 days of 20.0-23.0 MPa were obtained with the NaOH concentrations of 9.5-14.0 M. Increasing the NaOH concentration beyond this point resulted in a decrease in the strength of the paste due to early precipitation of aluminosilicate products.     

Fire resistance of fired clay bricks-fly ash composite cement pastes

This work aims to study the effect of substitution of fly ash for homra on the hydration properties of composite cement pastes. The composite cements are composed of constant proportion of OPC (80%) with variable amounts of fly ash and homra. The addition of fly ash accelerates the initial and final sitting time, whereas the free lime and combined water contents decrease with fly ash content. The fly ash acts as nucleation sites which may accelerate the rate of formation of hydration products which fill some of the pores of the cement pastes. The fire resistance of composite cement pastes was evaluated after firing at 250, 450, 600, 800 °C with rate of firing 5 °C/min with soaking time for 2 h. The physico-mechanical properties such as bulk density and compressive strength were determined at each firing temperature. Moreover, the phase composition, free lime and microstructure for some selected samples were investigated. It can be concluded that the pozzolanic cement with 20 wt% fly ash can be used as fire resisting cement.     

Synthesis and characteristics of fly ash and bottom ash based geopolymers–A comparative study

The research was carried out to develop geopolymers mortars and concrete from fly ash and bottom ash and compare the characteristics deriving from either of these products. The mortars were produced by mixing the ashes with sodium silicate and sodium hydroxide as activator solution. After curing and drying, the bulk density, apparent density and porosity, of geopolymer samples were evaluated. The microstructure, phase composition and thermal behavior of geopolymer samples were characterized by scanning electron microscopy, XRD and TGA-DTA analysis respectively. FTIR analysis revealed higher degree of reaction in bottom ash based geopolymer. Mechanical characterization shows, geopolymer processed from fly ash having a compressive strength 61.4 MPa and Young's modulus of 2.9 GPa, whereas bottom ash geopolymer shows a compressive strength up to 55.2 MPa and Young's modulus of 2.8 GPa. The mechanical characterization depicts that bottom ash geopolymers are almost equally viable as fly ash geopolymer. Thermal conductivity analysis reveals that fly ash geopolymer shows lower thermal conductivity of 0.58 W/mK compared to bottom ash geopolymer 0.85 W/mK.     

Mineralogy and geochemistry of Greek and Chinese coal fly ash

In this paper the mineralogy and geochemistry of Greek and Chinese coal fly ash are examined. Annual production of fly ash in China is around 160 Mt while in Greece lignite fly ash accounts around 10 Mt. Even though the mineralogical and chemical composition of the fly ashes coming from these two countries differs, there are common questions on the utilization of this material. The variation of the Greek fly ash’ chemical composition, from Ca-poor to Ca-rich fly ash, has resulted to applications such as dam construction, use in cement and possibly in concrete and road construction. The Chinese fly ash, which is rich in mullite, is broadly applied for brick making.     

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     

Preparation and properties of anorthite-based ceramics by using metallurgical solid waste and fly ash

A large amount of metallurgical solid waste accumulation poses a serious threat to the environment. Study on synergistic reinforcement of synthetic process of metallurgical solid waste-based ceramics with fly ash is of great significance in reducing environmental pollution and resource utilization. A metallurgical solid waste-based ceramic used as building ceramic was developed with the erosion part of used MgO–C bricks and fly ash as main raw materials, and the amount of solid waste added to the prepared ceramics was at least 60 wt% and up to 90 wt%. The effects of fly ash content and sintering temperature on the crystalline phase transitions, morphologies, and the main physical and mechanical properties of ceramics were investigated by X-ray diffraction, scanning electron microscopy, and mechanical testing. The results show that the obtained ceramics presented maximum bending strength and minimum water absorption, 80.14 MPa and 5.04%, respectively, when the raw material proportions were the erosion part of used refractories accounted for 60 wt%, fly ash 20 wt%, pyrophyllite 10 wt%, and quartz sands 10 wt%, and the process parameters were the sintering temperature 1150°C, sintering time 120 min, and molding pressure 15 MPa.     

Increases in the strength of Si-additive mixture granules by presintering

In order to preserve a spherical granule shape in a porous sintered body, presintering technology was developed to enhance the strength of Si-mixture granules containing Y₂O₃-Al₂O₃-CaO as sintering additives prior to shaping. The fracture strength of the granules measured by a compression test was ≤0.2 MPa and ≤20 MPa for as-spray dried granule and presintered granules, respectively. Furthermore, the flowability of the presintered granules was retained by the presintering process done to 1300 °C.     

粉煤灰加气混凝土砌体力学性能与节能效应分析

利用室内试验方法制备了粉煤灰加气混凝土砌块和砌体,分别测试了混凝土砌块的抗拉抗压强度和砌体的抗拉和抗剪强度,分析了砌体抗压和抗剪强度随砂浆厚度的变化规律。在此基础上,建立了粉煤灰加气混凝土砌体节能效应的FLAC 3D数值计算模型。研究表明:(1)粉煤灰加气混凝土砌块的抗拉压强度平均值分别为4.53 MPa和0.75MPa;(2)粉煤灰加气混凝土砌体的整体抗压和抗剪强度随砂浆厚度的增大而分别减小和增大;(3)粉煤灰加气混凝土砌体的平均传热系数小于普通灰砂砖砌体,且随砂浆厚度的增大而减小。     

Orthogonal design process optimization and single factor analysis for bimodal acoustic agglomeration

Acoustic agglomeration is proved as a promising pretreatment to control the emission of fine particles. As to removal of coal-fired fly ash particles (first mode), this paper investigates the combination of acoustic agglomeration with the addition of lime seed particles (second mode). The bimodal acoustic agglomeration can improve agglomeration efficiency significantly. Orthogonal designs are carried out for the first time to optimize the agglomeration conditions. The factors range as follows: acoustic frequency, f = 1000-1800 Hz; sound pressure level, SPL = 135-150 dB; residence time, t = 3-7 s, lime seed particle mass fraction, m_lime% = 30%-90%. The results of difference analysis and analysis of variance reveal that frequency is the dominant factor and the optimal conditions are: f = 1400 Hz, SPL = 150 dB, t = 4 s, m_lime% = 30%. In addition, the detailed influences of single factor on agglomeration efficiency are investigated.     

Mode of occurrence of arsenic in feed coal and its derivative fly ash, Black Warrior Basin, Alabama

An arsenic-rich (As = 55 ppm) bituminous feed coal from the Black Warrior Basin, Alabama and its derivative fly ash (As = 230 ppm) were selected for detailed investigation of arsenic residence and chemical forms. Analytical techniques included microbeam analysis, selective extraction, and As K-edge X-ray absorption fine-structure (XAFS) spectroscopy. Most As in the coal is contained in a generation of As-bearing pyrite (FeS₂) that formed in response to epigenetic introduction of hydrothermal fluids. XAFS results indicate that approximately 50% of the As in the coal sample occurs as the oxidized As(V) species, possibly the result of incipient oxidation of coal and pyrite prior to our analysis. Combustion of pyrite and host coal produced fly ash in which 95% of As is present as As(V). Selective extraction of the fly ash with a carbonate buffer solution (pH = 10) removed 49% of the As. A different extraction with an HCl-NH₂OH mixture, which targets amorphous and poorly crystalline iron oxides, dissolved 79% of the As. XAFS spectroscopy of this highly acidic (pH = 3.0) fly ash indicated that As is associated with some combination of iron oxide, oxyhydroxide, or sulfate. In contrast, a highly alkaline (pH = 12.7) fly ash from Turkey shows most As associated with a phase similar to calcium orthoarsenate (Ca₃(AsO₄)₂). The combined XAFS results indicate that fly ash acidity, which is determined by coal composition and combustion conditions, may serve to predict arsenic speciation in fly ash.     

Fabrication of low to high duty fireclay refractory bricks from lignite fly ash

The development of refractory bricks made of new materials has recently drawn a lot of interest to address sustainability issues. So, in this study, the recycling of lignite fly ash produced by coal-fired thermal power plants has been investigated to make fireclay refractory bricks. The lignite fly ash and ball clay are the primary raw materials characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), X-ray fluorescence (XRF), and differential thermal analysis (DTA). The samples were prepared using a uniaxial hydraulic press, and firing was done in the range of 1000–1200 °C for 2 h. The fired samples were characterized in terms of chemical composition, mineralogical phase, and microstructural using different characterization tools such as XRF, XRD, and SEM. The physical, mechanical, and thermal properties such as linear firing shrinkage, apparent porosity (AP), bulk density (BD), cold crushing strength (CCS), cold modulus of rupture (CMOR), and thermal conductivity of the fired sample were investigated. The linear firing shrinkage, AP, BD, and CCS values were achieved estimated to be 5.32%, 2.10 g m/cc, 15%, and 52 MPa, respectively. The SEM analysis shows dense, rod-like mullite structure and interlocking microstructure of the fired samples. The results were well matched with ASTM standards and commercially available products. So, this promising result indicates lignite fly ash can be used as a potential raw material to produce fireclay refractory bricks.     

Recycled concrete and fly ash make calcium silicate bricks

It has been shown that calcium hydroxide from hydrated cement reacts with fly ash and siliceous particles in the crusher fines of recycled concrete to give calcium silicate products similar to sand-lime bricks when autoclaved. Such products achieved compressive strengths up to 12.5 MPa.     

Utilization of by-products from western coal combustion in the manufacture of mineral wool and other ceramic materials

The ash by-products from combustion or gasification of western U.S. coals have chemical and mineralogical characteristics that lend themselves to utilization in ceramic materials. Laboratory and pilot-scale fabrication of four such materials has been studied. Cyclone slag from four lignite-fired power plants and a dry scrubber ash have been fabricated into mineral wool insulation in a pilot-scale cupola. Extruded and fired mixtures of fly ash, clay and ground glass have produced ceramics with extraordinary high flexural strength. Ceramic glazed wall tile that utilize fly ash in place of clay have been prepared and shown to meet most specifications for fired clay tile. Both fired and unfired dry-pressed brick containing 100% western fly ash have met ASTM specifications for fired clay brick.     

Influences of Jameson flotation operation variables on the kinetics and recovery of unburned carbon

The purpose of this study was to investigate the influences of Jameson flotation operation variables on the recovery and kinetics of unburned carbon (UC). The waste sample of petroleum coke, filter powder or fly ash, used in the experiments was collected from lime calcination plant tailings. The effect of Jameson flotation parameters on the recovery and kinetics efficiencies of UC was systematically studied. The feasibility of separating unburned carbon and refuse was determined from the combustible recovery (CR) and ash reduction (AR) (%) curves. Within the range studied, the optimum diesel oil dosage was 3500 g/tonne, pine oil dosage was 2500 g/tonne, pulp density was 15%, wash water rate was 0.17 cm/s and downcomer immersion depth was 50 cm. The results indicate that the Jameson flotation technique is effective in removing the UC from waste filter powder. Furthermore, the classical first-order kinetic flotation model (R = R_∞ [1 − exp (− k ? t)]) was applied to data from the tests. The model was evaluated by statistical technique, after non-linear regression on the model parameters. It is found that the classical first order flotation kinetic model, most extensively used among flotation models, fits the tests data very well.