Addition Of Fly Ash Research Articles

Exploratory Analysis on the Physical and Microstructural Properties of Aluminum/Fly-Ash Composite

Metal Matrix Composite (MMC) is an innovative material that has the ability to address demands in a number of industries, including mining, automotive, and aerospace. Stir casting is a well-known technique for making MMC. With weight fractions of 10%, 20%, 30%, and 40%, this study aims to analyze the impact of fly ash addition on the physical properties of aluminum (matrix) - FA (reinforcing phase) composites.The test for water absorbent was carried for each samples at 25°C immersed in water at different time interval of 24hrs, 48hrs, 72hrs, and 96hrs. The density test was carried out on the AL/FA composite samples. The water absorption test results showed that at 20wt% of fly ash composite, the optimum water absorption (0.4%) result was obtained at 24hrs, and also at 48hrs for 10wt%. The density of the composites increased with increasing amount of fly ash, and attained optimum of 4.08g/cm3 at 30wt%. The surface morphology of the samples was observed using digital metallurgical microscope. The scope of this study is to determine the physical and morphological properties of Al/FA reinforced composites.

Impact of fly-ash (silica) on amorphous phase formation ain NaNO3-Sr(NO3)2 composite solid electrolytes

In the current research, various weight percentages of flyash were incorporated into a mixed system of 85.32% NaNO3 and 14.68% Sr(NO3)2. The system was analyzed using the studies of conductivity, dielectric and electric modulus. An increase in DC conductivity was observed with the addition of flyash, peaking at 10% by weight. Beyond this concentration, the conductivity began to decrease. This increase in conductivity is attributed to the formation of an amorphous phase within the mixed sytem. XRD, FTIR, SEM, and DSC analyses of the flyash dispersed systems indicated the formation of an amorphous phase. The amorphous phase may be due to the surface interaction between fly-ash(silica)and phase of mixed system. The AC conductivity, which depends on frequency, adheres to universal power law. Power law parameter were determined.

Studying the Constitutive Model of Damage for a Stainless Steel Argon–Oxygen Decarburization Slag Mixture

The purpose of this study was to fully explore the mechanical properties of five different doses of an Argon–Oxygen Decarburization slag mixture in an unconfined compressive strength test. The peak stress, elastic modulus, and stress–strain curve of the mixture were studied for 90 days. Based on the experimental data and according to the theory of damage mechanics, the concept of damage threshold (t) was introduced to construct a damage constitutive model. Referring to the damage threshold of concrete, that of the mixture was determined to be 0.7 times higher than the peak strain, and the correlation coefficient between the established model and the test curve was above 0.85. These results indicate that the addition of AOD slag and fly ash can cause hydration reactions, increase the quantity of hydration products, and enhance the peak stress and elastic modulus of the mixture. The maximum increases were 94.9% and 43.1%, respectively. Parameters a and b reflect the peak stress and brittleness of the mixture, respectively. The incorporation of Argon–Oxygen Decarburization slag can make the mixture less brittle and improve its properties. The incorporation of Argon–Oxygen Decarburization slag can protect the mixture from damage. The maximum decrease is 40.2%.

Frost resistance and improvement techniques of recycled concrete: a comprehensive review

In the pursuit of sustainable construction practices, the utilization of recycled concrete has emerged as a pivotal strategy, distinguished by its commitment to resource conservation and environmental stewardship. Nevertheless, the inherent micro-porosity and micro-cracking within the old mortar of recycled concrete may lead to weak bonding performance at the interfacial transition zone, culminating in diminished strength, reduced density, and elevated water absorption rates compared to conventional concrete, which critically impairs its performance in cold climates subjected to freeze-thaw cycles. Consequently, this paper provides a structured examination of the frost resistance properties of recycled concrete subjected to freeze-thaw cycling. Initially, the study delineates the mechanisms of frost-induced damage in recycled concrete by synthesizing the degradation pathways observed in both conventional and recycled concrete during freeze-thaw exposure. Subsequently, a detailed analysis is conducted to identify the pivotal factors affecting frost resistance, encompassing the proportion and moisture affinity of recycled aggregates, the addition of silica fume and fly ash, the water-to-cement ratio, and the degree of water saturation. In the final segment, the study compiles and reviews the strategies for bolstering the frost resistance of recycled concrete, including the incorporation of air-entraining admixtures, fiber reinforcement, and aggregate modification approaches. The objective of this research is to offer a thorough comprehension of recycled concrete, with a concentration on the mechanisms of frost damage, the critical determinants of frost resistance, and interventions to augment its resilience against freezing conditions. On this basis, the present paper, in conjunction with the characteristics and current research status of recycled concrete, proposes recommendations for the application of recycled concrete in cold regions. This review is anticipated to facilitate researchers in gaining a comprehensive understanding of the freeze-thaw characteristics of recycled concrete and the measures to enhance its frost resistance. Furthermore, it aims to assist engineering and technical personnel in selecting appropriate treatment methods to improve the frost resistance of recycled concrete in cold regions, thereby promoting the practical engineering application of recycled concrete in such areas.

Experimental and numerical study on the chloride ions penetration in recycled aggregate concrete

Recycled aggregate concrete (RAC) offers a practical solution for improving resource efficiency and reducing environmental impact. Durability degradation in concrete structures is primarily caused by the corrosion of internal reinforcement due to chloride ion penetration. Thus, the resistance of RAC to chloride ion penetration is a crucial durability indicator. This study investigates the effects of recycled coarse aggregate (RCA) and mineral powder on RAC's chloride penetration resistance using rapid chloride ions migration (RCM) tests. Results show that increasing the RCA replacement ratio reduces its resistance to chloride ions penetration. The addition of slag improves resistance to chloride ions of RAC by up to 30 %, while fly ash addition shows an initial increase followed by a decline in resistance to chloride ions penetration of RAC. To address the variability in the spatial distribution and thickness of old mortar within RCA, a two-dimensional random aggregate model incorporating ellipsoids and internal polygons was developed. Five distinct phases were considered in the model: natural aggregate, new motar, old mortar, old interface transition zone (ITZ) between natural aggregate and old mortar, new ITZ between old mortar and new mortar. The model simulated the random placement of aggregates by randomizing geometric shapes, considering factors such as the RCA replacement ratio and particle size. COMSOL software was used to simulate chloride ions penetration in RAC with 30 % RCA, and the simulation model's accuracy was verified through ion chromatography. This study takes into account the random distribution of old mortar on the surfaces of RCA to provide a deeper investigation into chloride transport within RAC.

Study on the chloride ion binding rate of sulfoaluminate cement mortars containing different mineral admixtures

In this study, the chloride ion (Cl−) binding rate of sulfoaluminate cement (SAC) mortars containing different mineral admixtures was investigated. This is essential to improve the durability of concrete structures in high Cl− environments, especially where they are susceptible to Cl− attack such as coastlines and marine structures. The effects of Cl− concentration, curing age, and the type and amount of mineral admixture on the Cl− binding rate of SAC mortars were analyzed. It was found that the content of water-soluble Cl− in SAC mortars decreased with the increase of curing age, while the Cl− binding ratio increased accordingly, indicating that its resistance to internal Cl− permeation increased. The addition of fly ash (FA) and ground granulated blast furnace slag (GGBS) can significantly improve the Cl− binding rate of SAC mortars, and the Cl− binding rate increases to 46.6% with 20% of FA and 38.7% with 40% of GGBS. The effects of mineral admixtures on the microstructure and phase composition of SAC mortars were further investigated by X-ray diffraction (XRD) analysis. The results showed that the addition of FA and GGBS promoted the formation of C-S-H (calcium silicate hydrate) gels and improved the resistance of SAC mortars to Cl− penetration. On the other hand, the excessive addition of silica fume (SF) decreased the Cl− binding rate, whereas a moderate amount of limestone powder (LP) improved the Cl− binding rate. The study of the Cl− binding rate of SAC mortars can help to evaluate their resistance to Cl− erosion in real projects, thus guiding the optimization of concrete formulations and the improvement of durability.

Evaluation, tribological examination, and multi‐objective optimization of aluminum‐fly ash‐egg shell composites for sustainability

AbstractThis study addresses the technological challenge of enhancing the mechanical and tribological properties of Al 6082 alloy by incorporating fly ash (FA) and eggshell (ES) as reinforcing materials. The objective is to fabricate hybrid metal matrix composites using sand casting, with varying weight percentages of eggshell and fly ash: 4 wt% eggshell with 6 wt% fly ash, 5 wt% eggshell with 5 wt% fly ash, and 6 wt% eggshell with 4 wt% fly ash. The experimental methodology involved designing experiments with response surface methodology (RSM), considering applied load, sliding velocity, and sliding distance as variables. The outcomes showed that the composite with 6 wt% eggshell and 4 wt% fly ash exhibited superior hardness, tensile strength, and impact resistance compared to pure Al 6082 and other composite variations. Additionally, this composite reduced the coefficient of friction (COF) from 0.489 for the base Al 6082 to 0.265. ANOVA based on RSM identified sliding distance as the most influential factor affecting COF. Optimal conditions for minimizing COF were determined to be a 40 N load, 0.215 m/s sliding velocity, and 800 m sliding distance through confirmatory trials. Scanning electron microscopy (SEM) analysis of the worn surfaces provided further insights into the wear mechanisms. The research reveals that integrating the addition of eggshell and fly ash significantly enhances the mechanical properties and reduces the friction of Al 6082, with sliding distance being a critical factor in tribological performance. This investigation is distinctive due to its innovative use of dual reinforcement with fly ash and eggshell, which are abundant, cost‐effective, and rarely employed together in this context. The research thoroughly investigates various reinforcement ratios, providing vital insights into how they affect the composite's properties, particularly in terms of improving tribological properties. Using RSM and ANOVA makes the findings more precise and reliable. The investigation highlights sliding distance as the key factor affecting the tribological behavior of the composites.

Evaluating the impact of industrial wastes on the compressive strength of concrete using closed-form machine learning algorithms

Industrial wastes have found great use in the built environment due to the role they play in the sustainable infrastructure development especially in green concrete production. In this research investigation, the impact of wastes from the industry on the compressive strength of concrete incorporating fly ash (FA) and silica fume (SF) as additional components alongside traditional concrete mixes has been studied through the application of machine learning (ML). A green concrete database comprising 330 concrete mix data points has been collected and modelled to estimate the unconfined compressive strength behaviour. Considering the concerning environmental ramifications associated with concrete production and its utilization in construction activities, there is a pressing need to perform predictive model exercise. Furthermore, given the prevalent reliance of concrete production professionals on laboratory experiments, it is imperative to propose smart equations aimed at diminishing this dependency. These equations should be applicable for use in the design, construction, and performance assessment of concrete infrastructure, thereby reflecting the multi-objective nature of this research endeavour. It has been proposed by previous research works that the addition of FA and SF in concrete has a reduction impact on the environmental influence indicators due to reduced cement use. The artificial neural network (ANN) and the M5P models were applied in this exercise to predict the compressive strength of FA- and SF-mixed concrete also considering the impact of water reducing agent in the concrete. A sensitivity analysis was also conducted to determine the impact of the concrete components on the strength of the concrete. At the end, closed-form equations were proposed by the ANN and M5P with performance indices which outperformed previous models conducted on the same database size. The result of the sensitivity analysis showed that FA is most impactful of all the studied components thereby emphasizing the importance of adding industrial wastes in concrete production for improved mechanical properties and reduced carbon footprint in the concrete construction activities. Also, the M5P and ANN models with R2 of 0.99 showed a potential for use as decisive models to predict the compressive strength of FA- and SF-mixed concrete.

Detailed Analytical EPMA Study of the OPC Pastes Prepared with the Addition of Raw and Milled Fly Ashes

Concrete and cement pastes belong to the most used building materials in human history and represent a solidified mixture of ordinary Portland cement (OPC), water, course and fine-grained aggregates. Fly ash is used as a pozzolanic additive to improve concrete properties. The fly ash property can also be modified by various treatments such as milling or size reduction with sieving. It was suggested that a beneficial pozzolanic reaction with fly ash gives high mechanical properties. Such pozzolanic reaction results in calcium silicate hydrate (C-S-H) phase formation. In this research comparative analytical EPMA study of the paste samples prepared with the addition of the milled and non-milled fly ashes has been performed to elucidate the pozzolanic reaction of the OPC with the milled and non-milled fly ashes. A higher pozzolanic reaction with CSH phase formation was observed in milled fly ash added paste.

Influence of fly ash and granulated blast furnace slag on autogenous shrinkage and drying shrinkage of cement-based materials mixed with alkali accelerator and alkali-free accelerator

Shotcrete shrinkage and cracking are getting more threatening due to its high content of cementitious materials, small aggregate particle size and a large amount of accelerator, which poses a great threat to the construction safety of engineering structures. This paper studies the volume stability of cement mortar with different contents of fly ash (FA) and granulated blast furnace slag (GBFS) (10%/20%/30%) under the condition that the dosage of alkali liquid accelerator is 4% and that of the alkali-free liquid accelerator is 7%. This work is designed to provide a guidance for the basic research and practical application. By comparing the autogenous shrinkage, drying shrinkage, mass loss caused by drying condition, and internal humidity change of drying condition of cement mortar within 180 days of age. Combined with MIP analysis, XRD hydration product analysis, and SEM hydration product morphology analysis, the results show that both fly ash and granulated blast furnace slag can reduce the autogenous shrinkage and drying shrinkage of cement mortar mixed with accelerator to a certain extent, and the shrinkage reduction effect of FA is more prominent. The reduction effect of GBFS is more obvious at high dosages. Adding FA and high content of GBFS can increase the mass loss of cement mortar under drying shrinkage conditions. The high content of mineral admixtures will exacerbate the rate of decrease in the internal humidity of the cement mortar. The reasons for the reduction of autogenous shrinkage and drying shrinkage of cement mortar mixed with accelerators due to the addition of FA and GBFS are: the early activity of the two mineral admixtures is low, and the hydration process is slow. And the reduction of pore size with the range of 5-50nm leads to the reduction of capillary tensile stress and the weakening of the driving force for shrinkage deformation. Among them, the shrinkage reduction effect of fly ash is more pronounced. Therefore, mineral admixture can be used to replace a certain amount of cement in actual shotcrete construction, so as to increase the volume stability of shotcrete.

Exploring cement content's impact on self-healing in super absorbent polymer-modified concrete

This study shows the impact of varying cement content while maintaining a constant water-to-cement (w/c) ratio on the performance of self-healing concrete. It also explores the effect of F-type fly ash on the self-healing mechanism of concrete. Self-healing concrete, incorporating super absorbent polymers, offers a viable remedy to diminish the detrimental effects of cracks, enhancing the durability and lifespan of concrete structures. While the w/c ratio is a crucial factor influencing concrete properties, the impact of varying cement content under a constant w/c ratio in self-healing concrete remains understudied. Therefore, this experiment involved preparing 18 different concrete mixtures using three distinct cement contents under three specific w/c ratios. Fly ash was mixed in half of the specimens. Super absorbent polymers are incorporated into all mixtures to facilitate autonomous healing by absorbing and retaining water, which is released upon crack formation. Specimens were pre-cacked using a stress-controlled UTM machine. To evaluate the self-healing mechanism, low water pressure permeability test, water absorption test, and image analysis were conducted at 7, 14, 28, and 56 days. The findings of this study show that a w/c ratio of 0.35 yielded the best performance which indicates a lower w/c shows a higher self-healing performance. Additionally, the specimen containing a higher cement content exhibited enhanced healing capacity compared to other specimens. However, the specimens with fly ash failed to show a satisfactory result on self-healing capacity because the addition of silicon-based fly ash (F type) created an adverse effect on the self-healing mechanism.

The Effect of Fly Ash Additive on the Thermal Conductivity of Polystyrene Concrete

The use of fly ash in compositions as a substitute for a part of cement is economically favorable and ecologically feasible in connection with large accumulations of waste at the enterprises of the energy sector. In addition, the technology of cement production provides high-temperature treatment of mineral substances in kilns with significant emissions of carbon dioxide. One of the most effective directions of the utilization of fly ash is their use in concrete composites. The use of this material will provide the required temperature and humidity conditions in residential premises, solve the problem of “cold bridges” in structures, minimize heat losses of the structure, and increase the energy efficiency of buildings in general. At the same time, polystyrene concrete, due to its structural structure and the presence of thermally conductive concrete, has limited opportunities for thermal and physical–mechanical properties. To improve the operational properties of polystyrene concrete, it is proposed to use composite binders, including fly ash from the thermal power station of Astana. The main aim of this study is to develop compositions of polystyrene concrete with reduced thermal conductivity and improved physical and mechanical properties. The objectives of this study include the determination of characteristics of fly ash from Astana, formulation of polystyrene concrete mixtures with different proportions of fly ash, and evaluation of their thermal conductivity properties. These tasks are in line with the objectives of the ISO 50001 standard to improve energy efficiency and reduce environmental impact. The results showed that the addition of fly ash from Astana to polystyrene concrete leads to a marked reduction in thermal conductivity, contributing to improved energy efficiency of the building envelope. Optimal results were achieved by using 15% of Astana fly ash as an additive in polystyrene concrete, which led to a significant reduction in thermal conductivity of 51.47%. This reduction is in line with improving the energy efficiency of building materials, especially in cold climates.

The influence of addition of fly ash from biomass combustion on selected properties of red building ceramics

The paper characterizes waste in the form of fly ash generated in a power plant during the combustion of biomass in a fluidized bed in terms of its possible use in the ceramic building materials industry. This is important from the point of view of environmental protection. In order to assess the possibility of using ash in the production of red ceramics (e.g. bricks), two different clay raw materials (Clay I and Clay II) were selected to prepare the raw material sets. First of all, the investigated fly ash was subjected to thermogravimetric TG-DTG analysis and its basic chemical composition was determined. Then the specific density was determined for all the raw materials, XRD analysis was also performed and finally characteristic temperatures were determined by means of a high-temperature microscope. The basic raw material sets included clayey raw material and fly ash in various contents: 5 wt%, 10 wt% and 15 wt%. Samples were pressed from the ready sets and fired at the temperature of 1000℃. Afterwards, the obtained samples were subjected to XRD and microstructural tests, then selected physical properties were determined, i.e. water absorption, porosity, apparent density, and compressive strength. Based on the research and analysis of the results, it was found that the introduction of fly ash from biomass combustion into the raw material set in the range of 5–15 wt% has a positive effect on the insulating properties of red ceramics. In addition, the density of the red ceramics decreases with the increase in the addition of fly ash, while its porosity and water absorption increase. Furthermore, the addition of fly ash decreases the compressive strength and visually brightens the microstructure of the products.

Improvement of Fluidity and Long-term Strength of Cemented Paste Backfill with Low Calcium Fly-ash

ABSTRACT Waste rocks and tailings are widely applied materials in underground metal mines to backfill mined-out areas. To test the effect of low calcium fly ash on slurry fluidity and long-term strength of cemented paste backfill, orthogonal experiments of backfill proportions with variable levels of waste, tailing, fly ash, water and their combinations were carried out. Results show that slurry slump is most sensitive to mass concentration, and slurry fluidity is optimal when fly ash-cement ration is 1:1. The longterm strength of cemented paste backfill after curing for 56 days is significantly affected by cement-(tailing + waste) ratio, and slightly evolves regardless of fly ash-cement ratio. Fly ash promotes the generation of active silicon oxide and aluminum oxide, which fills the pores within the backfill. The optimal proportion of cemented paste backfill is 77% mass concentration, 8:2 tailing–waste ratio, 1:30 cement-(tailing + waste) ratio and 1:1 fly ash–cement ratio. The correlative slurry slump and long-term backfill strength meet the requirement of pumping and backfill mining. Additionally, an industrial scale loop pumping test of backfill slurry shows the pipeline transportation resistance is 4 kPa/m, pipeline diameter is optimal at 150 mm, and flow rate is optimal at 90–100 m3/h. The experiment confirms that proper addition of low calcium fly ash is conducive to improve the slurry fluidity and long-term strength of cemented paste backfill.

Waste electric porcelain-based refractory bricks with significantly enhanced mechanical properties: preparation, characterization and mechanism

Using waste electric porcelain to produce refractory bricks is a viable technology. However, these bricks currently have lower mechanical strength compared to those made from mineral raw materials. This study optimized the proportions and sintering process to develop high-strength refractory bricks from waste electric porcelain. The impact of physical phase, crystallinity, sintering temperature, and fly ash content on the bricks properties was examined. The research found that low crystallinity in waste electric porcelain leads to disorganized growth of mullite nano whiskers at high temperatures, reducing mechanical strength due to insufficient support structures and stress concentration zones. The addition of fly ash promotes the formation of uniformly dispersed mullite columns through non-uniform nucleation, significantly improving mechanical properties by creating a collective tetrahedral structure. Bricks with 20 wt% fly ash sintered at 1440 °C achieved a flexural strength of 77.3 MPa, a compressive strength of 156 MPa, and an apparent porosity of 10.89%. High-temperature simulations indicate that these bricks exhibit good compressive strength and deformation resistance, with no adhesion observed. These high strength refractory bricks have promising potential for use in various high-temperature applications, including kiln linings, high-temperature flue, high-temperature support components and other industrial processes where durability and thermal stability are critical.

Intensive coagulation of secondary effluent to mitigate reverse osmosis membrane fouling at low temperatures: Strategies of pre-oxidation and coagulant aids addition

Conventional coagulation-sedimentation, typically used as a pretreatment for ultrafiltration-reverse osmosis, is ineffective in solving the problem of reverse osmosis membrane fouling at low temperatures. In this study, the coagulation enhancement effect of pre-oxidation and the addition of coagulant aids on conventional coagulation with polyaluminum chloride as a coagulant was investigated. The results showed that the addition of fly ash, powdered activated carbon, or diatomite as coagulant aids improved the reduction of turbidity, dissolved organic carbon (DOC), and ultraviolet absorbance at 254 nm (UV254), and also reduced the residual content of dissolved aluminum ions. Among them, diatomite was superior. Pre-oxidation before conventional coagulation increased the reduction of turbidity and UV254 by about 50 % and doubled the removal of proteins, polysaccharides, and DOC compared to conventional coagulation. Ozone was superior to sodium hypochlorite. The combination of ozone pre-oxidation and diatomite addition with conventional coagulation further increased the pollutant removal rate, with the removal rates of turbidity, UV254, polysaccharides, proteins, and DOC reaching 82.20 %, 52.35 %, 26.34 %, 24.89 %, and 26.38 %, respectively. In addition, the residual content of dissolved aluminum ions decreased to 0.84 mg/L. The reverse osmosis filtration simulation test showed that pretreating the feed water with the enhanced coagulation by the combination of ozone pre-oxidation and diatomite addition resulted in a slower decrease in membrane flux, reduced foulant content on the membrane surface, and the smallest increase in contact angle. The results of this research may offer a viable pretreatment method to reduce fouling in reverse osmosis membranes operating at low temperatures.

STIR CASTING OF ALUMINUM METAL MATRIX COMPOSITE FOR AUTOMOBILE APPLICATION — A REVIEW

The development of lightweight and high-strength materials is critical for many industries, including aerospace, automotive, and electronics. Metal matrix composites (MMCs) have shown great promise in meeting these requirements. The structural and physical properties of Al6061 alloy reinforced with hybrid MMCs, including TiB2, SiC, and fly ash (FA), were investigated in this research review. The MMCs investigated were made using the stir-casting process. Their microstructure, structural characteristics, and mechanical features were examined. The inclusion of TiB2 and SiC enhanced the composite’s hardness, tensile strength, and wear resistance, while the addition of FA lowered its density and improved its thermal and corrosion resistance. However, the volume percentage, particle dimension, and arrangement of the reinforcing components all had an effect on the physical characteristics of the composite. Therefore, the optimum combination of the reinforcing materials must be carefully selected to achieve the desired properties. The result of this review provides valuable insights into the development of high-performance MMCs for various industrial applications.

Technology of Manufacturing Hollow Soil-Cement Blocks

The author analyzed technological solutions for the production of blocks from soil cement. It is proposed to make soil cement blocks from portland cement brand 400 in the amount of 20 % of the mass of soil and water. Experimental addition of fly ash to the solution in different amounts depending on the cement content. It is proposed to add ash removed from the Darnytsya thermal power plant, which was sifted through a 4 mm sieve, because the ash contains a significant amount of impurities. The content of inclusions from 1 to 4 mm was up to 40 %. It is proposed to make blocks from soil cement with the addition of fly ash with the aim of improving the thermotechnical properties. It is proposed to make soil-cement blocks with two voids. To ensure high-quality compaction of products in forms, the moisture content of the content for most soils should be within 14–23 %. The maximum force that the sample can withstand was taken as a destructive load. It was decided that the use of fly ash as part of the mixture in the production of soil cement gives a positive effect. With an increase in the period of exposure of samples in water to 90 days, the average compressive strength of soil cement samples without additives and with the addition of the appropriate percentage of fly ash increases.

Analysis of porous alkali activated materials using bauxite residue as principal precursor

Bauxite residue is a red-hued and mineral-rich material that is released from the production of alumina during the Bayer process. There are large areas of land across the world dedicated to the storage of this underutilized material. The growing nature of the alumina-producing industry implies that the production of bauxite residue will increase, which necessitates solutions for valorizing bauxite residue. One area of research involves using bauxite residue as a precursor in preparation of porous alkali activated materials and the novelty of the study is to make porous alkali-activated material with bauxite residue. Porous AAMs have applications as industrial adsorbents and as insulating materials. This study focused on the pore analysis of AAMs prepared with a high proportion of bauxite residue and fly ash addition, using varying percentages of hydrogen peroxide and added water to form the pore structure, with hydrogen peroxide and water acting as a “green reagent”. The sample containing the highest percentage of added water displayed the highest open porosity, with the sample consisting of large millipores and the widest distribution of pore sizes out of all the samples. The samples containing only hydrogen peroxide displayed a uniform distribution of smaller pores as measured by nitrogen adsorption. The study describes a process to create highly porous AAMs in low temperatures using a limited number of constituents. Furthermore, it optimizes the variation of hydrogen peroxide and added water to tailor the pore character depending on the desired application of the material, with only as much as 3 % hydrogen peroxide needed for porosity. The porous alkali-activated bauxite residue has the potential to be used as insulating material in the building.

Mechanical properties and corrosion mechanism of steel fiber reinforced concrete (SFRC) subjected to stray current

The application of steel fiber reinforced concrete (SFRC) in electric railways shows an obvious advantage due to its excellent mechanical properties. However, stray current induced corrosion is a potential threat to SFRC. In this study, the mechanical properties evolution of SFRC suffered from the action of stray current was investigated, including the compressive strength, flexural and splitting-tensile properties. Meanwhile, the effects of water to cement ratio (W/C), fly ash and slag on the corrosion resistance of SFRC were considered. Moreover, the corrosion mechanism of SFRC subjected to stray current was analyzed. It was found that the mechanical properties of SFRC degraded gradually under the action of stray current, since two electrolytic-cell reactions took place in the corrosion process. However, the addition of fly ash and slag can greatly improve its resistance to the attack of stray current, this makes it possible to the application of SFRC in electric railways.