Fly Ash Mixtures Research Articles

Structure and microstructure of sintered ceramic obtained by crystallization of fly ash mixtures and glass cullet

Glass waste such as fly ash, granulated slags or glass cullet found their application, among others, as fluxes in the sintered ceramics production. The high content of alkali oxide present in wastes causes the formation of a liquid phase during sintering, intensifying this process. However, the role of these materials in the sintering process is not limited to this function. Glassy waste grains have high free energy associated with the lack of long-range ordering, which can additionally affect the intensification of sintering processes in the initial stages, because the degree of diffusion on the grain surfaces and in the glassy material volume is higher than in the crystalline material. Moreover, during heating, the glass undergoes processes of ordering its structure: transition and subsequent possible crystallization (devitrification). This second process is particularly important because the phase devitrification can change the direction of the reaction sintering of the entire ceramic mixture in which the vitreous additive has been introduced. These phases may be nuclei of homo or heterogeneous crystallization or may be substrates for the synthesis of other phases. Therefore, it is quite important to predict the direction of crystallization of vitreous waste, which is difficult due to the influence of many variables parameters. This research focused on identifying and characterizing sinters of fly ash and glass cullet mixture. To characterize the starting materials, X-ray diffraction (XRD), X-ray fluorescence (XRF) techniques were used. The sinters were obtained through thermal treatment at 850 °C as well as 1050 °C. The structural changes occurring during the devitrification of glass waste mixtures were studied by means of 27Al MAS NMR and FTIR spectroscopy. The microstructure of sintered samples etched in hydrofluoric acid was studied by SEM technique. During the crystallization of glass mixtures, the proportions of octahedral versus tetrahedral coordination of Al substantially change.

Effect of Chloride Ions on Concrete with Geopolymer Coatings in Coastal Area

This paper presents the effects of chloride ions on OPC (Ordinary Portland Cement) concrete coated with fly ash-based geopolymer mortar. The coating was applied to protect concrete in coastal areas. The mortar was a mixture of fly ash and alkali activator with a mass ratio of 65:35. The alkali activator was a mixture of Na2SiO3 and NaOH 12M with a mass ratio of 2.5:1. The coating thickness varied at 2.5 cm, 4 cm, and 6 cm. All specimens were exposed to a marine area with seawater curing for 90 days. The mechanical properties of the specimen were determined by compressive strength. Chloride penetration was assessed for durability. A series of tests were carried out after 0, 30, 60, and 90 days of immersion. Compressive strength after a 90-day immersion increased by 34.16%, 39.81% and 31.38% for thickness 2.5 cm, 4 cm, and 6 cm respectively. Compressive strength with a thickness of 4 cm reached 52 MPa, which was the highest strength. The binding capacity of the chloride in geopolymer coatings was more than 80% and could reduce the free chloride content in concrete. Geopolymer mortar coating on OPC concrete showed good results in compressive strength and resistance to chloride attack from sea water. The recommended coating thickness for optimum results suitable for application is 4 cm.

Synthesis and Characterization of Microfiltration Ceramic Membrane Based on Fly Ash and Clay Mixture Using Sintering Method

Ceramic membranes made from low-cost materials have increasingly been developed. Fly ash is a waste from cement industries, while clay is a natural resource that can be easily found to be used as economical mixed materials in the production of ceramic membrane. The manufacture of microfiltration ceramic membrane from fly ash - clay mixture has been carried out using the sintering method for 4 hours at low sintering temperatures variations at 750 °C (M1), 800 °C (M2), 850 °C (M3) and 900 °C (M4), respectively. The results showed that the ceramic membrane that was sintered at a temperature of 900 °C (M4) had the optimum characteristics with a porosity of 40.82%, a density of 1.0026 gr/cm3. From scanning elctron microscopy (SEM) analysis showed that the M4 membrane was classified as a microfiltration membrane with an average pore size of 0.64 μm. The energy diepersive x-ray (EDX) analysis showed that the composition of the M4 membrane was dominated by elements O, Si, and Al. Moreover, the x-ray diffraction (XRD) analysis showed that the fraction patterns of the membranes (M1, M2, M3, M4) were dominated by the quartz phase (SiO2) and illite phase ((KH3O)Al2Si3AlO10(OH)2).

Closure to “Optimum Mixing Ratio and Shear Strength of Granulated Rubber–Fly Ash Mixtures” by Bhargav Kumar Karnam Prabhakara, Prashant Vyankatesh Guda, and Umashankar Balunaini

Closure to “Optimum Mixing Ratio and Shear Strength of Granulated Rubber–Fly Ash Mixtures” by Bhargav Kumar Karnam Prabhakara, Prashant Vyankatesh Guda, and Umashankar Balunaini

Discussion of “Optimum Mixing Ratio and Shear Strength of Granulated Rubber–Fly Ash Mixtures” by Bhargav Kumar Karnam Prabhakara, Prashant Vyankatesh Guda, and Umashankar Balunaini

Discussion of “Optimum Mixing Ratio and Shear Strength of Granulated Rubber–Fly Ash Mixtures” by Bhargav Kumar Karnam Prabhakara, Prashant Vyankatesh Guda, and Umashankar Balunaini

Workability, mechanical, and durability properties of self‐compacting concrete using the treated wastewater

AbstractUrban development, industrialization, and increasing population increase water consumption. Limited water resources, especially in an arid climate, are a challenging issue; therefore, water reuse is vital. A huge amount of treated wastewater is discharged to the rivers and groundwater daily. The construction industry, especially for producing concrete uses a huge amount of tap water. Hence, we studied the feasibility of using the treated domestic wastewater to produce self‐compacting concrete (SCC) with different concrete mix designs, using silica fume, fly ash, slag, zeolite, and a mixture of silica fume and fly ash according to ASTM and BS standards. The experimental work included workability, mechanical, and durability properties of different concrete mix designs using the treated wastewater. The results of workability (filling ability) including Slump flow, T50, and V funnel were 600–800 mm, 2–5 s, and 6–12 s, respectively, and satisfied the European guidelines for SCC. Also, the results of passing ability, including J‐ring and L box experiments, complied with the European guidelines. The compressive strength of different types of the concrete mixes using treated wastewater was found to be one to 8% below using the tap water in 7, 28, 56, and 90 days after the concrete samples were made. Scanning electron microscope images confirmed the results. Using the treated wastewater decreased the electrical resistivity of concrete in the SCC in different concrete mix designs. However, the results of chloride ion permeability remained in the very low range (37–254 Ω/m) of the AASHTO (95) standard.

Possibilities of Using Fly Ash with Other Industrial Waste to Obtain Geosorbents and Composite Materials

The authors have studied the conditions of using waste obtained after thermal and chemical processing of minerals (coal, apatite, etc.) and unused natural polymer lignin formed as a result of wood hydrolysis. It has been established that these wastes, individually and in various combinations, can be used as an effective geosorbent for lanthanum ions from wastewater, in the form of composite electrochemical coatings and in the manufacture of ceramic products. The degree of trapping of lanthanum ions from concentrated wastewater with a mixture of fly ash and hydrolytic lignin reaches 96%. Internal stresses and microhardness of composite electrochemical coatings (CEC) nickel – fly ash decrease with increasing thickness and content of fly ash in the nickel layer due to the presence of 4.23% iron fraction with increasing its strength. The use of fluorogips and fly ash in the manufacture of mixtures for the production of ceramic products, including red brick, gives positive results in reducing shrinkage during high-temperature processing of the composite.

Possibilities of Using Fly Ash with Other Industrial Waste to Obtain Geosorbents and Composite Materials

The authors have studied the conditions of using waste obtained after thermal and chemical processing of minerals (coal, apatite, etc.) and unused natural polymer lignin formed as a result of wood hydrolysis. It has been established that these wastes, individually and in various combinations, can be used as an effective geosorbent for lanthanum ions from wastewater, in the form of composite electrochemical coatings and in the manufacture of ceramic products. The degree of trapping of lanthanum ions from concentrated wastewater with a mixture of fly ash and hydrolytic lignin reaches 96%. Internal stresses and microhardness of composite electrochemical coatings (CEC) nickel – fly ash decrease with increasing thickness and content of fly ash in the nickel layer due to the presence of 4.23% iron fraction with increasing its strength. The use of fluorogips and fly ash in the manufacture of mixtures for the production of ceramic products, including red brick, gives positive results in reducing shrinkage during high-temperature processing of the composite.

The influence of clay addition in fly ash concrete mixture for nuclear shielding

The disposal of ashes from power plants has caused health issues and reduce the air quality of the surrounding areas. The ashes have a potential to be used in construction of concrete mixture as partial replacement for cement. This research studies the potential fly ash and clay mixture (FAC) as a nuclear shielding material in concrete mixture. The raw materials and the testing were all done in Agensi Nuklear Malaysia. All concrete mixtures had a constant water/cement ratio of 0.266. The hardened concrete mixtures were tested for compressive strength. Scanning electron microscopy (SEM), energy dispersive X-ray (EDX) and small angle neutron microscopy (SANS) are used to characterize the properties of the mixtures. The results suggested that mixture of FAC concrete with 10% of clay addition showing good potential for nuclear shielding compared to other ratios.

Mechanical properties and meso-structure response of cemented gangue-fly ash backfill with cracks under seepage- stress coupling

Seepage and cracks are two important factors affecting the stability of the cemented gangue-fly ash backfill (CGFB, a mixture of coal gangue, fly ash, cement and water). In this study, the CGFB samples with a 45° single crack were prepared and the mechanical properties of CGFB with cracks under different seepage water pressures were studied. Based on the theory of damage mechanics, the damage variable which can evaluate the seepage effect and crack effect was introduced, and the damage evolution law of CGFB with cracks under the seepage-stress coupling was discussed. The research hat: The mechanical properties of CGFB with cracks under seepage-stress coupling are mainly determined by the seepage water pressure, prefabricated crack and their coupling effects. Seepage and crack aggravate the attenuation of the peak strength and elastic modulus of CGFB, but with the increase of seepage water pressure, the deterioration effect of the crack weakens. Seepage and crack have significant effects on the damage of CGFB. Finally, based on the discrete element software, damage mechanism of CGFB with cracks under seepage-stress coupling was analyzed from a microscopic perspective. The research results can lay a foundation for the long-term stability analysis and instability prediction of CGFB with geological defects such as joints and cracks in water-rich mines.

Characterization of High-Temperature Hierarchical Porous Mullite Washcoat Synthesized Using Aluminum Dross and Coal Fly Ash

Mixture of aluminum dross (AD) and coal fly ash (CFA) was used to produce high-temperature porous mullite for washcoat application. CFA is the combustion by-product of pulverized coal in a coal-fired power plant, while AD is a waste product produced in secondary aluminum refining. In this study, 80 wt% of AD and 20 wt% of CFA was used to prepare a mullite precursor (MP) via acid leaching and dry-milling. The precursor was coated on a substrate and subsequently fired at 1500 °C. The results showed that the precursor transformed to a hierarchical porous microstructure assembled by large interlocked acicular mullite crystals. The pore structures consisted of large interconnected open pores and small pores. The specific surface area of the mullite washcoat was 4.85 m2g−1 after heating at 1500 °C for 4 h. The specific surface area was compatible with the specific surface area of other high-temperature washcoats.

Transformation of industrial solid wastes into carbon-infused infrastructure materials

In this study, we developed a recycling technique for converting solid waste together with carbon dioxide into a new type of carbon-infused waste-derived concrete. Using fly ash as an example, the concrete was instantaneously consolidated from a semi-dry fly ash mixture via compaction molding and was then cemented and hardened via hydration and accelerated carbonation. We examined the roles of Na2CO3 activation and accelerated carbonation on the reaction chemistry, phase assemblage, mechanical properties, and microstructure of the new waste-derived concrete. The addition of Na2CO3 accelerated the hydration of fly ash mixtures, but an excessive dosage (2% addition) appeared to curtail the hydration. The accelerated carbon curing (up to 4 h) improved the mechanical strength and microstructural integrity of the fly ash concrete, which performed more efficiently upon the addition of Na2CO3 to the mixtures. The Na2CO3-activated mixtures produced diverse hydration products because of the increased alkalinity and the dissociated CO32− ions. The accelerated carbonation transformed the initial hydration products and thus promoted continuous hydration as well as natural carbonation. The microscopic crystalline phases developed through carbonation were merged well with the hydrated matrix phases. The cured matrix demonstrated pronounced calcium features and a wide range of phase compositions because of the synergy of Na2CO3 activation and carbonation. Being deposited on and intermixed with the original hydrated matrix phases, the in-situ formed carbonate-based products acted as cementing agents to form a new cementitious and cohesive microstructure in the waste-derived concrete, without consuming conventional cements. Through a series of laboratory experiments, this method was technically evaluated, indicating that it has the potential to be used for converting large quantities of solid waste from the waste site, along with carbon dioxide, into new types of cement-free carbon-infused waste-derived concrete for cleaner urban and infrastructural development.

Model Test for the Seismic Response of an Entrance on a Shallow-Buried Double-Staggered Mountain Tunnel

The theoretical analysis of the seismic response of tunnels is still insufficient. The shaking table test is an effective way to study the earthquake resistance of tunnels; because of the complex nonlinear constitutive model of rock soil and the complicated seismic dynamic equation. In the LEBUGUOLAJI tunnel, the similarity ratio is 1:30. A thermal molten mixture of river sand, oil, and fly ash is used as the similar material of the surrounding rock, and gypsum is used as the similar material of the tunnel lining. A strain gauge is symmetrically pasted inside and outside the tunnel model lining to monitor the strain stress, and a structural accelerometer is installed on the tunnel model and shaking table to invert the surrounding rock of the model. The earthquake damage characteristics and engineering shock absorption measures of a shallow-buried double-staggered tunnel are determined using the large shaking table model test. Results show that the surrounding rock of the tunnel model exerts obvious enlargement effect on the input seismic wave, and its frequency spectrum changes. The seismic wave in frequency bands below 15 Hz is strengthened, whereas those in other frequency bands are attenuated. The seismic response of the tunnel is reduced by the confinement effect of rock and soil. On the basis of the similarity ratio of the model test, 45 m can be used as the fortification length of the tunnel entrance. The weak link of the tunnel portal section is the wall angle and the 45° of arch shoulder on the tunnel slope. The seismic damage in the gap section of the tunnel is more serious than that in other parts of the tunnel in the entrance. Thus, the rock and soil volume can be increased at the staggered area to enhance the rock and soil constraints of the site in design. A strong dynamic interaction occurs in the shallow-buried double-hole staggered mountain tunnel under seismic wave action. The seismic response of the tunnel with a large damping structure can be effectively reduced to minimize the damage of the lining strain.

Effect of citric acid on calcium sulfoaluminate cements synthesised from industrial wastes at low temperature

A study of the effects of citric acid on the mechanical properties of calcium sulfoaluminate (C4A3S̄) cements in hydraulic pastes and mortars was performed. Clinker made up of C4A3S̄ was obtained from the calcination of a mixture of fly ash, aluminium dross and fluorogypsum at 1100°C. The C4A3S̄ cement was prepared by mixing the clinker with certain percentages of commercial hemihydrate. Hydraulic pastes and mortars were prepared with 0·05% citric acid relative to the total weight of the cement in order to slow down the reactions and also to act as a structural modifier. The initial and final setting times of the pastes were up to 189 and 336 min, respectively. The compressive strength was evaluated in specimens cured at room temperature, reaching, in some mortar formulations, more than 80 MPa at 360 d with high initial development. Hydration reactions were significantly affected by both the citric acid and the increase in temperature, as confirmed by isothermal conduction calorimetry. The main hydration product was ettringite, which promoted the formation of dense and compact microstructures.

Effectiveness of Expanded Polystyrene (EPS) Beads Size on Fly Ash Properties

The present study focused on laboratory investigation of fly ash mixed with expanded polystyrene (EPS) beads. Different sizes of EPS beads were mixed with fly ash to study the effect on maximum dry unit weight, cohesion, angle of internal friction, California bearing ratio (CBR) value, coefficient of consolidation, and permeability. The different EPS beads sizes used in the present study are 1 mm, 2 mm, 3 mm, 4 mm, and 6 mm with 28 kg/m3, 19 kg/m3, 16 kg/m3, 11 kg/m3 and 6 kg/m3 densities, respectively. The effects of EPS beads sizes on geotechnical properties of fly ash mixture were investigated. The constant EPS beads content of 0.6% was considered for comparing the effect of different sizes of EPS beads in the fly ash. The smaller EPS beads–fly ash mix was observed to be suitable for improving the shear strength and bigger EPS beads were good enough to reduce the unit weight of fly ash–beads mix. The CBR value and permeability of fly ash–EPS beads mixtures were increased with a decrease in the size of EPS beads. The coefficient of consolidation increased up to 4-mm size of beads and then decreased for 6-mm size of beads. The fly ash reinforced with 0.6% EPS beads of different sizes, specifically 1-mm and 2-mm size, can be useful for constructions on weak soils. Each size of EPS beads has benefits as per the requirements in engineering applications and field conditions.

Co-composting and vermicomposting of coal fly-ash with press mud: Changes in nutrients, micro-nutrients and enzyme activities

Abstract The present study was designed to determine the effect of vermicomposting on physico-chemical properties, nutrient status and heavy metal concentration of buffalo dung, fly ash and press mud. Different ratios of buffalo dung, fly ash and press mud mixtures were used with/without Eisenia fetida in this study. Vermicomposting of different feedstock mixtures for 90 days leads to significant reduction in pH, TOC, CN ratio and augmentation of plant nutrients such as sodium, potassium, phosphorous and calcium. Enzymatic activities (Dehydrogenase, urease, and phosphatase) were found elevated in the vermicompost feedstocks on day-30 followed by reduction up to 90 days. Moreover, the vermicomposting approach significantly reduced the heavy metals (Cu, Zn, Pb, Cr, Co, Cd, and As) in the feedstocks. It was found that an appropriate amount of buffalo dung, press mud, and fly ash favors the reproduction and growth of earthworms. The study results further supported the germination index on tomato plant seeds (Solanum lycopersicum). The results suggested that vermicomposting of press mud and fly ash with Eisenia fetida increased the nutrition content in a short amount of time.

Effect of accelerated curing regimes on high volume Fly ash mixtures in precast manufacturing plants

Fly ash is becoming a common replacement for cement in concrete. Not only does it reduce CO2 emissions, but it is cost effective and often times improves various fresh and hardened properties of concrete. Currently, Fly ash isn't replaced in percentages greater than 25–35% in structural applications because of the delayed concrete setting time. This study presents an experimental investigation to evaluate the performance of mortar mixtures incorporating up to 70% cement replacement with Fly ash under the effect of accelerated curing. Different accelerated curing regimes were investigated in terms of the preset time, curing temperature, and curing time. Fresh and hardened properties of HVFA mortar mixtures were obtained for three replacement level and their results were compared at different ages. The accelerated curing regimes successfully developed high early-age strength mixtures that can be used in the precast industry. Some curing regimes revealed the ability to reduce energy as well as curing time.

Effect of Bentonite Addition on the Properties of Fly Ash as a Material for Landfill Sealing Layers

Landfill sealing layers protect groundwater and soil against contamination from waste leachate. Fly ash, which is a coal combustion by-product, might be used as a substitute material for natural soils to build sealing layers. To improve its properties, different additives can be used. In this study, bentonite in the amounts of 5%, 10% and 15% of the dry mass of fly ash was used as an addition. Compacted fly ash and fly ash-bentonite mixtures were tested in order to verify how bentonite and the amount of addition affect the properties of the materials. Therefore, hydraulic conductivity, as the most important parameter, which determines the suitability of a material for construction landfill sealing layers, were tested. Results indicate that bentonite changes the properties of fly ash and allows the achievement of smaller hydraulic conductivity values. To provide a comparison to the natural soil, sandy silty clay that meets the criteria for natural soils for sealing layers was tested and the differences are presented. Fly ash with 15% of bentonite addition reached a value of hydraulic conductivity for the material suitable to build compacted landfill sealing layers.

Sequestration of simulated carbon dioxide (CO2) using churning cementations waste and fly-ash in a thermo-stable batch reactor (TSBR).

The degrees of mineral carbonation in (a) construction and demolition waste (C&DW) and (b) a mixture of cement and fly ash were studied through a dynamic experimental method to determine the variation in the rate and extent of CO2 sequestration achievable under simulated outdoor conditions. A number of experiments were performed in a self-designed rotating batch reactor by churning the two samples together with CO2, which was passed through the mixtures by using water vapor as the medium of transfer. At an injection flow rate of 1L/min for CO2, the theoretical extent of carbonation was observed to be 39.1% for the mixture of cement and fly ash and 25% for C&DW. It was further observed that upon increasing the CO2 flow rate to 10L/min, the carbonation in the mixture of cement and fly ash increased by 37.2% after 15h of rotation at 60 rounds per hour (rph) for a temperature of 40°C. Weighing, scanning electron microscopy (SEM), and energy dispersive spectrometry (EDS) were performed for the samples before and after the batch reaction to study the quantitative, qualitative and morphological aspects of the process.

Shearing resistance of tailing sand waste pollutants mixed with different contents of fly ash.

The co-placement of mine tailings and fly ash (CMF) can reduce acid mine drainage (AMD) production and decrease metal mobilization. This aids in waste management construction. However, few people have studied a large number of tailing sand-fly ash mixtures under the condition of neutral saturated solution in tailing ponds, wherein the pozzolanic reaction is highly gradual. In this study, a series of tests were conducted to determine the monotonic and cyclic shear characteristics of a mixture of fly ash and tailings. In particular, the effects of the fly ash content on the monotonic shear peak, shear strength parameters, dynamic modulus, and damping ratio of the mixture were analyzed. The results reveal that in a monotonic shear test, the peak shear strength of the saturated CMF mixture decreases as the fly ash content increases. The shear strength parameters (cohesion c and internal friction angle φ) were observed to increase and decrease linearly, respectively, as the fly ash content increased. Furthermore, the maximum dynamic shear modulus was observed to decrease by 41.4% as the fly ash content increased from 0 to 50%, during the cyclic cutting process. Moreover, the experimental results fit well with the fitting formula for the variation in shear modulus in the cyclic shear process of the saturated CMF mixture with varying fly ash content. Meanwhile, the initial damping ratio of the cyclic shear was observed to increase from 10.3 to 13.6% as the fly ash content increased. Therefore, when the CMF method is used to treat AMD waste, it is necessary to consider the extent to which the design stability of the tailing pond may be reduced. These experimental results can be used as a reference for similar CMF projects.