Conventional Fly Ash Research Articles

Feasibility of upcycling red mud for low-CO2 cement via calcination: A comparative study with FA and GGBFS based in China

This study examines the feasibility of developing low-CO2 cement using calcined red mud (RM) and explores positive scenarios that simultaneously attain technical, environmental, and economic benefits in reference to conventional fly ash (FA) and ground granulated blast furnace slag (GGBFS) cements. Based on the variables of RM's content and calcination temperature, we investigated the fresh properties (paste rheology and mortar flowability), strength development, microstructure, embodied CO2 emissions, and cost of the RM-blended cement. The results show that there was an optimal range of RM's calcination temperature (400–600 °C) that improved the cement paste viscosity while attaining a higher strength than that of FA cement. Considering the cradle-to-gate CO2 emissions and cost of cement production, the optimal cement composition is comprised of up to 30% RM calcined at 600 °C, where the cement cost is lowered by 19.3% compared to the FA reference having a comparable CO2 footprint. According to the geographical analysis, the calcined RM shows minimal advantages over GGBFS but could substitute FA as a cleaner, cheaper, and more reactive supplementary cementitious material in regions where electricity grid is dominated by clean energy. Therefore, RM offers a plausible solution to future low-CO2 cement in light of the increasing shortage of FA led by the declining use of coal-powered electricity.

Investigation of the mechanical and durability properties of concrete containing modified fly ash and modified zeolite powder: An effective transport model for sulfate ions in concrete

The application of conventional fly ash and zeolite powder in the field of concrete durability is limited. In this study, durability tests coupling dry-wet cycling and sulfate erosion were conducted on concrete with varying dosages of modified fly ash (MFA) and modified zeolite powder (MZP). The compressive strength, failure mode, water absorption rate, and ion concentration changes were systematically investigated. The reaction products and structure were analyzed through SEM, EDS, and XRD tests, correlating with macroscopic parameters. An effective transport model for sulfate ions in concrete was established, considering the material influence coefficient km and the effective diffusion coefficient De. The results indicate that a higher content of Ca phases in MFA leads to a reduction in concrete early strength, while later stages exhibit rapid strength growth due to pozzolanic reactions. MZP contains a significant amount of Al and Si phases, which promote both early and later-stage concrete strength. MFA and MZP enhance the resistance of concrete to sulfate erosion, with MZP exhibiting a significantly superior improvement effect compared to MFA. This is attributed to the following factors: on the one hand, the addition of MFA and MZP reduces the porosity and improves the pore structure of concrete, thus delaying the diffusion of sulfate ions into the concrete; on the other hand, the pozzolanic reactions of MFA and MZP consume available calcium hydroxide, leading to the formation of C–S–H and C-A-S-H gels, which densify the microstructure and reduce the probability of leaching erosion of hydration products, thereby limiting the formation of ettringite. The applicability and reliability of the sulfate-ion effective transport model were verified based on experimental data. The model can be employed to predict the distribution of sulfate ions in different types of concrete under various erosion durations, reducing workload and providing a theoretical basis for the durability design and service life prediction of concrete structures in sulfate environments.

Stress Strain Behaviour of Solid Block Masonry Prism under Axial Compression

Masonry is possibly the primary construction element currently in widespread use throughout the world. Load-bearing masonry building is prevalent in developing countries for home construction. When properly constructed, masonry is frequently a more cost-effective and energy-efficient alternative to reinforced concrete for wall building. In addition to performing the dual roles of supporting weight and enclosing space, structural masonry boasts a high level of fire resistance, thermal and acoustic insulation, and exposure protection. The remarkable durability and low maintenance costs are further evident benefits. Masonry has a significant role in building construction, particularly in structures, as it is regarded as the primary component of the building. The eco-friendly solid block is prepared by adding the following by-products like coal ash, granite powder, olivine sand etc., all these ingredients used for manufacturing the solid block are waste materials from various industries. Thus, extensive testing is necessary to assess their load carrying capacity and secant modulus accurately. Masonry prisms were developed with five-layer solid blocks and tested for their stress-strain characteristics and secant modulus and the test outcomes were compared with conventional fly ash cement blocks. Eco-friendly solid blocks offer a persuasive substitute for ecologically conscious approaches to building by preserving structural integrity and functionality while promoting sustainability.

Sulphate resistance of low-clinker engineered cementitious composites examined by MicroXRF imaging.

Engineered cementitious composites (ECC) are a class of high-performing fibre-reinforced cementitious materials recognised for their increased ductility and durability compared to conventional cement-based materials, owing to their autogenously controlled tight crack widths, even when subjected to high strains. To reduce ECC's environmental impact, this research examines the use of a low-clinker binder - limestone-calcined clay cement (LC3) - as an alternative to portland cement (PC), along with fly ash to further reduce the clinker proportion and the embodied CO2 of the formulations. In conventional concrete, LC3 hydrates to a denser microstructure resulting from the synergistic reaction between limestone and calcined clay. At the lower water contents typical of ECC and with the presence of fly ash, the influence of the binder composition on the microstructure is difficult to anticipate. To examine the influence of these compositional variables on microstructure, permeability and durability, the sulphate resistance of LC3-based ECC is explored. Specifically, the ECC-LC3 blends are designed with high clinker replacement rate of 75% by mass of binder and contain either conventional fly ash or reclaimed fly ash at 50% by mass of binder. Expansion of ECC-LC3 samples subjected to standard sodium sulphate test conditions was measured up to 12 months and the depth of penetration of sulphates into the ECC-LC3 of varying compositions was quantified using micro-X-Ray Fluorescence (microXRF) imaging and modelling. The expansion results show that the ECC-LC3 formulations performed better than the PC samples and can provide adequate resistance to external sulphate attack, even when reclaimed fly ashes are used in place of the conventional ash. In addition, the shallow penetration of sulphate into these cementitious composites demonstrates the low diffusion coefficients values that were determined using the quantitative data from MicroXRF imaging.

Novel cost-effective oxygen-enriched melting method for MSWI fly ash

ABSTRACT Herein, a novel oxygen-enriched melting process for fly ash, which uses the biogas produced from the leachate of municipal solid waste incineration (MSWI) plants, is proposed to reduce the high cost of conventional fly ash – melting technology. The fly ash composition was estimated via X-ray fluorescence analysis; the six constituent elements detected in fly ash in the decreasing order of their content were calcium, chlorine, silicon, sulfur, sodium, and potassium. Based on literature and actual production data, the average yield of the leachate was 15% of the total waste entering the MSWI plants and the COD of leachate was 30,000–75,000 mg/L. The amount of biogas that can be used per ton of fly ash was calculated to be 62.0–157.0 m3. The analysis of melting thermal equilibrium revealed the amount of biogas required per ton of fly ash as 57.8 m3. The aforementioned research findings indicate that the biogas produced by MSWI plants can successfully meet the demands of the oxygen-enriched melting of fly ash produced in these plants. By establishing an oxygen-enriched-melting pilot platform, the pilot tests of melting were conducted on fly ash; the results revealed the good melting effects of fly ash. The X-ray diffraction analysis of the slag demonstrated that the content of the vitreous body met the technical requirements for glassy substances. Furthermore, the leaching toxicity test results revealed that heavy metals were well solidified in the slag. This study presents a novel fly ash – melting scheme for MSWI fly ash, namely, biogas oxygen-enriched melting strategy, which has the advantages of technical feasibility and cost-effectiveness. The proposed technique exhibits considerable prospects for widespread application in MSWI plants in China and can play an important role in the safe disposal of fly ash. Implications: In this paper, a low-cost melting method of municipal solid waste incineration(MSWI) fly ash is proposed. This method uses the biogas generated by MSWI plant itself as fuel for melting. Through research, it has been found that the production of biogas can meet the demand for fly ash melting. Adopting biogas as a molten fuel can significantly reduce the cost of melting, thereby significantly reducing the cost of fly ash melting. This study established a pilot scale platform for the melting of biogas and conducted pilot scale experiments on fly ash and additives. The experimental results showed that the melting system operated well and achieved the vitrification of fly ash. The leaching test results of the molten slag showed that heavy metals were well solidified in the slag. The research results can be extended to the MSWI plant for application, which can significantly reduce the cost of fly ash melting disposal, and has broad application prospects.

Performance assessment on manufacturing of unfired bricks using industrial wastes

This paper presents eco-friendly unburnt bricks made up of fly ash, waste plastic powder, waste glass powder, lime, gypsum and crusher sand as alternatives to conventional burnt clay bricks for sustainable development. The research focuses on the maximum utilization of industrial waste in eco-friendly unburnt brick production. Materials are characterized according to their chemical and geotechnical properties. In this research, we use a milled waste glass powder of size less than 600μm and plastic powder obtained from plastic waste of size less than 600μm are added along with crushed sand, gypsum, lime and fly ash with various mix proportions concerning FaL-G mix concept. All the proportions were taken on a weight basis. Compressive strength, water absorption, and efflorescence are the key parameters chosen for comparing the innovative brick with conventional fly ash brick. There are five different mixes (Type A, B, C, D & E) are made in this research. The plastic and glass powders are replaced by crusher sand at the increased rate of 2% in every mix whereas 2%,4%,6%,8%, and 10%. It was found that the type B bricks have 17.63% strength was increased when compared to base mix. From the test results, type B bricks have enhanced mechanical performance when compared to all other mixes.

The Technology of Processing of Bed Combustion Fly Ash for Cement Composite Production

Insufficient offer of high-temperature fly ash meeting the requirements of standard EN 4501 is becoming an increasingly significant problem for concrete technology. This trend is generally caused by relentless effort to green electricity generation and reduce the carbon footprint, leading to the decommissioning of coal-fired power plants and the greening of existing. The most often ways are combustion processes of fluidized-bed and selective non-catalytic nitrogen oxide reduction (SNCR) processes. Thanks to these processes, the demand for this raw material has significantly exceeded its supply in recent years. It is, therefore, more than current to look for ways to use the large amount of ash produced from coal combustion, which is not high-temperature fly ash, but can be classified as a bed combustion fly ash or cinder. The paper aims to show the possible processing and subsequent use of these waste materials for the production of cement composites. The possibilities of grinding these coarse-grained fly ashes and the subsequent impact of their use on the cement composite in comparison with conventional fly ash according to the standard EN 450 from the same sources were verified. The impact of their use on the properties of composites in the fresh and hardened state was analysed, and these impacts were related to, for example, their chemistry, grain morphology, loss on ignition, or fineness.

Characterization and quantification of the pozzolanic reactivity of natural and non-conventional pozzolans

High quality pozzolans are needed to produce durable and low CO2 concrete. While extensive literature is available on pozzolanic reactivity and reaction products of conventional fly ash and slag cement, similar information is scarce for natural and non-conventional pozzolans (NNPs), impeding their use in concrete. This study presents a comprehensive evaluation of eleven NNPs, including calcined clays, volcanic ashes, ground bottom ashes, and fluidized bed combustion (FBC) fly ashes. The chemistry, mineralogy, physical properties, and pozzolanic reactivity of these materials were evaluated and benchmarked against conventional pozzolans. Except for one case of high SO3, all NNPs met ASTM C618 specifications as well as RILEM limits of pozzolanic reactivity. Based on ASTM C1897 (the R3 test), calcined clays were found to be significantly more reactive than fly ash and comparable with slag and silica fume. Volcanic ashes and FBC fly ashes showed similar pozzolanic reactivity to that of Class F fly ash, while ground bottom ashes were comparable with the top 50% of Class F fly ashes. The reaction products of these NNPs were identified using QXRD and thermodynamic modeling as C-A-S-H, mono- and hemi-carboaluminate, monosulfate, and ettringite. Calcined clays formed monosulfate and little to no ettringite while other NNPs formed ettringite but no monosulfate. This was attributed to the availability and dissolution kinetics of alumina versus calcite in the R3 experiment.

Development of Eco-Friendly Bricks for Sustainable Construction

Plastic and stubble are some of the industrial and agricultural wastes whose disposal has become a menace over the last decade. Their extreme production has impacted their disposal which in turn is deteriorating the environment. This study presents four different brick development methodologies utilizing plastic and stubble wastes in building bricks. First brick was developed using the application of stubble having a 1:5 cement to sand ratio. The second had the application of PET bottle with 1:3 cement to sand ratio. The third and fourth bricks were developed using waste plastic polybags. The study further evaluated the performance analysis, energy efficiency along with a comparative cost analysis. A comparative analysis was also carried out with the conventional fly ash bricks. Study observed that the energy efficiency of such bricks is significantly higher and their application potential as building bricks is immense. However, the strength of such bricks was observed to be lower. This further requires optimization of design mix and plastic waste. For stubble-based bricks further long term, durability analysis is required.

Development of Geopolymers Based on Fly Ashes from Different Combustion Processes.

The main aim of this research is to assess different fly ashes as raw materials for the manufacturing of geopolymers. Three different fly ashes have been investigated. First, a conventional fly ash from the Skawina coal power plant (Poland), obtained at a temperature of 900–1100 °C. Second, ultra-fine fly ash from a power plant in China; the side product received at 1300 °C. The third fly ash was waste was obtained after combustion in incineration plants. To predict the properties and suitability of materials in the geopolymerization process, methods based on X-ray analysis were used. The applied precursors were tested for elemental and chemical compounds. The investigations of geopolymer materials based on these three fly ashes are also presented. The materials produced on the basis of applied precursors were subjected to strength evaluation. The following research methods were applied for this study: density, X-ray fluorescence (XRF), X-ray diffraction analysis (XRD), Scanning Electron Microscopy (SEM), flexural and compressive strength. The obtained results show that materials based on fly ashes had a similar compressive strength (about 60 MPa), while significant differences were observed during the bending test from 0.1 to 5.3 MPa. Ultra-fine fly ash had a lower flexural strength compared to conventional fly ash. This study revealed the need for process optimization for materials based on a precursor from a waste incineration plant.

Strength and durability studies on sustainable eco-friendly green solid blocks

ABSTRACT Masonry blocks are the most common material in the construction industry due to their excellent properties in terms of strength and durability. The present article deals with the innovative Solid Block prepared using fly ash, coal ash, lime, olivine sand, granite powder, and crusher sand. Olivine sand is partially substituted for crusher sand and the properties of the Solid Blocks are studied. The properties of the Solid Block are inferred under various parameters and the results are compared with the Conventional Fly Ash Blocks (CFAB). Scanning electron microscopy(SEM) and Energy Dispersive Spectroscopy(EDS) were used to investigate the microstructural characteristics of olivine sand and Solid Block powder. The Green Solid Blocks (SB) are checked for properties like compressive strength, water absorption, weight density, Initial Rate of Absorption (IRA) and sorptivity properties. The chemical resistance behavior of the green Solid Block samples is evaluated. The properties of the green Solid Blocks are interpreted and the innovative green block are found to be greater compared with conventional fly ash Solid Blocks due to the inclusion of olivine sand, thus promoting a sustainable technology with industrial by products. The compressive strength of the solid block is enhanced up to a 15% utilization of olivine sand; beyond that, the compressive strength is gradually decreased.

Hydration Processes of Four-Component Binders Containing a Low Amount of Cement.

Results of research on hydration of four-component binders containing very high amounts of supplementary cementitious materials were presented. The samples were composed of blended pozzolana (a mix of conventional fly ash and spent aluminosilicate catalyst), cement (about 20 wt.% in the binder) and Ca(OH)2. Spent aluminosilicate catalyst was proposed as activating component which can improve properties of low-cement blends, while the role of Ca(OH)2 was to enhance pozzolanic reaction. Early and later hydration periods of such blends were investigated by calorimetry, TG/DTG, FTIR and X-ray diffraction. Initial setting time as well as compressive strength were also determined. It was concluded that enhancement of reactivity and improvement of properties of fly ash–cement binders are possible by replacing a part of fly ash with more active fine-grained pozzolana and introducing additional amounts of Ca(OH)2. The spent catalyst is mainly responsible for accelerating action during the first hours of hydration and for progress of early pozzolanic reaction. Fly ash develops its activity over time, thus synergic effect influences the later properties of composites. Samples containing blended pozzolana exhibit shorter initial setting times and higher compressive strength, as well as faster consumption of Ca(OH)2 compared to the reference. Investigated mixtures seem to be promising as “green” binders, alternatives to cement, after optimizing their compositions or additional activating procedure.

Physicochemical characterization of unconventional fly ashes

As the supply-demand disparity of virgin fly ash increases, there is an urgent need for utilization of unconventional fly ashes. This paper characterizes a set of 19 different fly ashes, including marginal, off-spec, landfilled, or beneficiated materials using extensive physicochemical powder characterization. The chemical composition, mineralogical composition, moisture content, loss on ignition, fineness, morphology, and specific gravity of the fly ashes were determined. Some fly ashes displayed unusual properties; however, many unconventional source fly ashes did not show properties substantially different from conventional fly ashes. Several interesting correlations in the measured properties were found for the fly ashes. The three measures of fineness or particle size correlated with each other. Loss on ignition values measured using a furnace and thermogravimetric analysis correlated but both temperature and atmosphere affected the measured values and the correlation. Electron microscopy provides important information regarding particle sizes, shapes, and potential contaminants for the unconventional fly ashes.

Effects of unconventional fly ashes on cementitious paste properties

The availability of fly ash for concrete has decreased due to the shutdowns of coal-fired power plants. Alternatives to conventional fly ash are needed to ensure sustainable and durable concrete. In this study, the impacts of numerous unconventional fly ashes – reclaimed, beneficiated off-spec, and marginal fly ashes on early and later-age properties of cementitious paste were assessed. Heat release characteristics, bulk resistivity, compressive strength, calcium hydroxide content and bound water content were studied. “Unconventional” fly ash performance was compared to conventional fly ashes, inert materials and a cement control. Substantial differences between Class C and Class F fly ashes were observed, even for unconventional fly ashes. The fly ash CaO content is positively correlated with several early-age paste properties, however, certain other properties did not show significant early-age differences based on fly ash type. Class F fly ashes showed significantly higher bulk resistivity at 91-days, while Class C fly ashes showed higher bound water contents. All tested unconventional fly ashes were reactive, contributed to strength development, and did not negatively affect cement hydration. Some fly ashes resulted in properties that varied significantly from those expected for conventional fly ashes, but there did not appear to be a simple correlation between a fly ash being either off-spec, marginal, reclaimed, or beneficiated and its performance being different from what is expected from similar class fly ashes. The results suggest that fly ash specifications need to be broadened to include unconventional fly ashes.

Tribo-Mechanical Behavior of Geopolymer Composites with Wasted Flax Fibers

The paper presents the research results on the mechanical and tribological properties of geopolymers reinforced with natural fibers. As a matrix, conventional fly ash and dry construction sand in proportion 1:1 were used. Materials were activated with Na activator. Wasted flax tow in an amount of 0.25-1% by weight was introduced as a reinforcement. The test results showed that with the increase in the fiber content, the bending strength increases, while the compressive properties are comparable to the matrix material. Based on the obtained research results, the optimal content of flax tow was determined at the level of 0.5% by weight. In addition, the abrasion resistance of geopolymer composites was determined using the so-called Boehme shield. This test consists of measuring the change in sample height. The sample is placed on a disc sprinkled with abrasive powder, then pressed and put into rotation. The abrasion results showed that the addition of fibers in the form of waste pulps does not reduce the abrasion resistance, which should be considered as a positive effect. Research also revealed that wasted flax fibers could be successfully used as a reinforcing material in geopolymeric materials as an alternative to the utilization of waste fibers, and additionally may also have a positive effect on the mechanical and tribological properties of geopolymers materials.

Enhancement of road pavement material using conventional and nano-crude oil fly ash

Enhancement of road pavement material using conventional and nano-crude oil fly ash

Production of colored bi-layered bricks from stone processing wastes: Structural and spectroscopic characterization

Stone processing wastes, being inherently colored, present an attractive option to develop the building façade products. In this study, four different types of stone processing wastes are characterized using X-ray diffraction, FTIR & Raman spectroscopies, and their suitability is evaluated to develop the colored bi-layered bricks. The stone processing wastes are blended with ground granulated blast-furnace slag to produce colored geopolymer mortars, and their compressive strengths are compared. Incorporation of stone waste decreased the compressive strength of geopolymer mortars. Particularly, Ca-rich stone wastes decreased the compressive strength less as compared to Si-rich stone waste. However, the stone waste blended geopolymer mortars still attained a value greater than 10 MPa, while achieving the desired color property. This corroborates the high potential of stone waste for producing colored masonry bricks equivalent to class designation 10 fly ash bricks as per IS 12894. The bi-layered bricks are conceptualized to make them economically viable, and their manufacturability is demonstrated at the laboratory scale via a four-step process in an existing industrial set-up (used for conventional fly ash bricks). The economic viability of these colored bi-layered bricks is compared against conventional single-layered fly ash bricks. It is found that colored bi-layered bricks have tremendous potential for cost-saving of up to 35% of the overall cost (accounting for the cost of a finished brick surface). This study presents a first-of-its-kind detailed study to produce colored bi-layered bricks using stone processing wastes. These new bricks combine the desired features of aesthetics and durability, and therefore, show a great promise as a cost-effective alternative to conventional fly ash bricks.

Coal gasification and composite ashes as partial replacements for Portland cement in concrete — strength and selected durability performance

AbstractThis study investigated the use of mixed weathered coal fine ash (MWA) and coal gasification ash (CGA), sourced from Sasol® Ltd, South Africa, as partial replacements (10%, 15% and 30% by mass) of Portland Cement (PC) in concrete. The objective was to assess the feasibility of using the ashes, which are generally of lower quality than FA, in concrete in order to avert their negative environmental impact i.e. disposal in heaps and landfills. Companion reference concretes were made using conventional fly ash (FA). Two water-to-binder (w/b) ratios (0.50 and 0.60) were used. The concretes were tested for compressive strength (7, 28 and 56 days) and durability (gas permeability and chloride resistance at 28 and 56 days). In general, the results strongly suggest that the ashes can be used in conventional structural concrete – both from strength and durability viewpoints. Aspects that require attention when they are used include decrease in both workability and rate of strength gain. The gas permeability of the CGA and MWA concretes were similar to those for FA at all replacement levels but a 15% replacement level gave higher chloride resistance.

Reactive ultra-fine fly ash as an additive for cement-based materials

This study examined the permeability of concrete in which a portion of the cement was replaced with reactive ultra-fine fly ash (RUFA) or silica fume. RUFA is an industrial by-product from thermal power plants, with spherical particles ranging in size from 0.1 μm to 10 μm, which is smaller than the particles in conventional fly ash. In experiments, the water-to-binder ratio was fixed at 0.45, and various proportions of the cement (5 % or 10 %) were replaced with RUFA, silica fume, or a combination of the two (5 % RUFA + 5 % silica fume, or 8 % RUFA + 2 % silica fume). The inclusion of RUFA was shown to enhance workability and promote the pozzolanic reaction resulting in the formation of C-S-H colloids. The filling of pore structures by colloids increased the compactness and compressive strength of the specimens, and reduced dry shrinkage. The inclusion of RUFA was also shown to reduce chloride ion penetration and the non-steady-state migration coefficient, which are indicative of improved mechanical properties and reduced permeability. Overall, RUFA proved superior to silica fume as a cement replacement in terms of workability, permeability, and mechanical properties.

Design of eco-efficient housing with sustainable alkali-activated bricks

Increasing construction demand in urban cities due to haphazard growth in population has led to overconsumption of construction materials, which adversely affects the environment and society. Responsible production and consumption of building materials is one of the necessary steps towards achieving the sustainability goal. In this study, sustainable alkali-activated bricks using industrial wastes (co-fired blended ash and stone dust) were developed and tested for physico-mechanical, thermal and durability related properties. The experimental investigation resulted in high strength, low thermal conductivity and durable bricks, thus proposed for its utilization in load bearing building structure. A study was carried out to compare the performance of existing case of residential building (framed structure with conventional fly ash masonry) and proposed sustainable solution of load bearing structure with developed alkali-activated bricks in terms of cost and energy consumption. Proposed strategy resulted in eco-efficient construction that reduced the cost, embodied energy and operational energy by about 7%, 22% and 13% respectively, as against conventional practice.