Ash Blends Research Articles

Some aspects of local fuel processing

Fuel peat plays an important part in meeting heat supply requirements of people and municipal–domestic facilities in the Republic of Belarus. Generalized long-term studies show that peat produced recently has an increased humidity and a decreased density. The energy efficiency of briquetting in case of steam tube drying is the most tightly connected with the product humidity. The actual energy consumption grows with the increasing final humidity. Efficiency of the resource- and energy-saving methods and activities aimed at reduction of energy consumption in production of solid domestic fuel is evaluated. The influence of the physical and mechanical properties of milled peat on the performance of peat briquetting plants is determined. The variants of the humidity / ash blending of primary products are proposed, with addition of import lignite during drying, towards improvement of quality of briquettes and reduction of raw-materials consumption. The calculation procedure of specific raw-material consumption per unit product is developed for the flue-gas and steam tube driers with a view to reducing specific energy consumption. The balance sheet of materials is calculated for the two types of the driers, and the factors which enable reduction in raw-materials consumption are identified. The mathematical relations are obtained to find the influence exerted by the physical and mechanical properties (humidity, ash content) of the raw material on the quality of briquettes (calorific efficiency) and on the peat briquetting plant performance (specific raw-material consumption). It is found that the ash content of peat grows as peat milling advances and thickness of the mill layer decreases. The influence of the raw material humidity on its consumption is determined as it is closely connected with the parameters of hot drying of peat.

Liquefaction resistance of polypropylene strips reinforced sand-fly ash blend under strain-controlled cyclic triaxial test

Liquefaction resistance of polypropylene strips reinforced sand-fly ash blend under strain-controlled cyclic triaxial test

The influence of curing temperature on the strength and phase assemblage of hybrid cements based on GGBFS/FA blends

Hybrid cements are composites made of Portland cement or Portland clinker and one or more supplementary cementitious materials like slag, fly ash or metakaolin, activated with an alkali salt. To date, their hydration mechanism and the phase formation at various temperatures is insufficiently understood, partly due to the large variability of the raw materials used. In the present study, three hybrid cements based on ground granulated blast furnace slag, fly ash, Portland clinker and sodium sulfate, and an alkali-activated slag/fly ash blend were cured at 10 and 21.5°C, and subsequently analyzed by XRD, 27Al MAS NMR, and TGA. The compressive strength of the hybrid cements was higher by up to 27% after 91-day curing at 10°C, compared to curing at 21.5°C. The experimental results as well as thermodynamic modeling indicate that the differences in compressive strength were related to a different phase assemblage, mainly differing amounts of strätlingite and C-N-A-S-H, and the associated differences of the volume of hydration products. While the strätlingite was amorphous to X-rays, it could be identified by 27Al MAS NMR spectroscopy, TGA and thermodynamic modeling. The microstructural properties of the hybrid cements and the alkali-activated slag/fly ash blend as well as the compatibility between thermodynamic modeling results and experimental data as a function of curing temperature and time are discussed.

Long-Term Mechanical Properties of Blended Fly Ash—Rice Husk Ash Alkali-Activated Concrete

Long-Term Mechanical Properties of Blended Fly Ash—Rice Husk Ash Alkali-Activated Concrete

Investigation on thermal conversion, kinetics and thermodynamics of coal gasification filter cake ash in oxygen fuel combustion

Coal gasification fine ash (CGFA) has the characteristics of high carbon content, fine-grained, and large annual output, causing environmental pollution and energy wastage. Oxygen fuel combustion is an effective way to solve the CGFA problem. In this paper, the effects of thermal conversion, kinetics and thermodynamics during the oxygen-fuel combustion of CGFA are analysed. The results show that the combustion of CGFA in an oxygen-fuel atmosphere significantly improves its burn-up performance and combustion stability, but the improvement in ignition performance is not significant. an increase in oxygen concentration of more than 30% in an O2/Ar atmosphere also improves the activation energy to some extent, but the improvement in combustion performance is not significant. The average activation energy of CGFA under 30% O2/70% Ar condition is 104.25 kJ/mol, and its combustion performance is comparable to that of bituminous coal blended gasification ash at 70%. A kinetic model was developed to describe the oxygen-fuel combustion process of FCA, which can be efficiently and cleanly burned under oxygen-fuel conditions and consumed on a largescale.

Effects of supplementary cementitious materials on the durability of glass aggregate mortars

The durability performance and sustainability of concrete and mortar can be enhanced by incorporating supplementary cementitious materials (SCMs), such as fly ash, slag (SG), silica fume (SF), and metakaolin (MK). In this study, binary and ternary blends of the aforementioned SCMs were investigated to determine an optimal combination that enhances the durability of glass aggregate mortars. Compressive strength, chloride permeability, and sorptivity experiments were conducted for all mixtures at specimen ages of 28 and 90 days. Fourteen day alkali silica reaction tests were also performed to determine the expansion properties. It was determined that ternary blends of fly ash and SF effectively mitigate expansions, with mixtures containing fly ash being most effective due to its high silica (SiO2) content. Ternary blends of SG and SF were also found to be successful in reducing permeability. In addition, it was determined that optimal durability performance can be achieved with 10% MK and SF replacements.

Properties of Slag-Fly Ash Blended Geopolymer Concrete Reinforced with Hybrid Glass Fibers

Geopolymer concrete is typically characterized by a brittle behavior and limited crack resistance. This study evaluates the performance of ambient-cured slag-fly ash blended geopolymer concrete reinforced with glass fibers. Two types of glass fibers were used exclusively or as a hybrid combination. The workability of glass fiber-reinforced geopolymer concrete was assessed using the slump, compaction factor, and vebe time. The compressive strength, splitting tensile strength, and modulus of elasticity were used to characterize the mechanical properties, while water absorption, sorptivity, abrasion resistance, and ultrasonic pulse velocity were employed in evaluating the durability. Experimental results showed that the slump and compaction factor decreased by up to 75% and 18%, respectively, with glass fiber addition but less significantly in mixes reinforced with hybrid fiber combinations. Meanwhile, the vebe time increased by up to 43%. Hybrid glass fibers led to superior mechanical and durability properties compared to plain mixes and those reinforced with a single type of glass fiber, even at higher volume fractions. The compressive strength, splitting tensile strength, and modulus of elasticity increased by up to 77%, 60%, and 85%, respectively. While the water absorption decreased by up to 42%, the sorptivity, abrasion resistance, and ultrasonic pulse velocity increased by up to 67%, 38%, and 280%, respectively. Analytical regression models were established to predict the mechanical and durability characteristics of glass fiber-reinforced slag-fly ash blended geopolymer concrete and were compared to those of design codes.

Reliability based predictive model for estimating shear strength values of locust bean waste ash compacted black cotton soil

A cheap and eco-friendly method of soil improvement is vital in achieving a reduction in the negative effect of climate change and cost of construction. Black cotton soil (BCS)–locust bean waste ash (LBWA) blend was evaluated via laboratory test, thereafter subjected the results to computer base program. Soil was treated with 0, 2, 4, 6, 8 and 10% LBWA by dry weight and compacted with different energies. A regression equation was developed from the laboratory measured values to serve as a limit state equation and integrated into a FORTRAN program, to generate safety index (SI) for shear strength values in the range of coefficient of variation (COV) of 10–100%. Results of statistical analysis show strong interaction between the shear strength values and the soil parameters (Locust bean waste ash, LBWA; Cohesion, CO; Friction angle, FA; Plasticity index, PI; Maximum dry density, MDD; Optimum moisture content, OMC; Percentage fine, PF; Cation exchange capacity, CEC; Specific gravity,Gs and Compactive effort, CE).Results show that for the laboratory model, safety indices are sensitive to changes in all the parameters considered. Results showed that among the entire variables, MDD, PI and OMC have major effect denoted by wide variations in their safety indices, seriously influenced by the COV. Safety indices for the effect of LBWA changed from −0.263 to −0.256, −0.134 to −0.13 and 0.00253 to −0.00246 for BSL,WAS and BSH, in that order. Aslo, values for untreated soil changed from −1.19 to −1.17, −1.08 to −1.06 and −0.973 to −0.954 for BSL, WAS and BSH, in that order. Similar pattern was recorded for other variables. Results obtained fell to meet up with the minimum regulatory value of 1.0 as stated by the Nordic Committee on Build Regulations at 10–100% COV as expected. The recorded safety indices for all the independent variables considered shows higher values when compared to that of the untreated soil. A more effective additive such as cement or lime blended with LBWA is commended to model shear strength values of the modified soil for dams or embankment applications.

Mechanical Performance of Blended Fly Ash-based Geopolymer Concrete with GGBS and Metakaolin

One of the most user-friendly alternatives to ordinary concrete is geopolymer concrete(GPC), which achieves the same result. GPC is a unique substance made by activating source materials with a high concentration of silica and alumina. As a result, geopolymer binders use less raw resources and emit less carbon dioxide. For these reasons, most academics are focusing on these sorts of resins to develop eco-friendly housing. This article reports on an experimental investigation that examined the Mechanical Performance of Blended Fly Ash based Geopolymer concrete at 7,28 and 360 days made with two different activator solution molarities and varying R (SiO2/Al2O3) ratios. Positive findings were seen at a larger percentage of GGBS (36%) with a concentration of a sodium hydroxide solution of 10 M and an R ratio of 2.75, compared with other proportions. The test findings indicate that increasing the concentration of sodium hydroxide (NaOH) solution and R enhances the compressive strength and decreases water absorption of geopolymer concrete.

MECHANICAL PERFORMANCE OF ALKALIACTIVATED CONCRETE INCORPORATING RECYCLED AGGREGATES AND STEEL FIBERS

This study evaluates the mechanical performance of alkali-activated concrete cured at ambient conditions and made with recycled aggregates (RA) and steel fibers. The precursor binder was either ground granulated blast furnace slag or a blend of slag and fly ash (3:1 and 1:1). The alkaline activator solution was a blend of sodium hydroxide and sodium silicate. Coarse aggregates were either natural aggregates (NA) or RA, while fine aggregates comprised desert dune sand. Steel fibers were incorporated, in 2%, by volume, in RA-based concrete mixes. Results showed that replacing NA by 100% RA in plain alkali-activated slag concrete led to decreases of 21, 23, and 51% in compressive, tensile splitting, and flexural strengths, respectively. Meanwhile, alkaliactivated slag-fly ash blended (3:1 and 1:1) mixes experienced respective losses of up to 65, 50, and 57%. The corresponding properties of alkali-activated counterparts made with 100% RA increased by up to 172, 273, and 167% upon the addition of 2% steel fibers, by volume. Yet, the impacts of RA and steel fiber incorporation on the mechanical properties were more pronounced in concrete mixes having higher fly ash replacement. Alkali-activated slag and slag-fly ash blended concrete mixes incorporating 2% steel fibers, by volume, and 100% RA exhibited equivalent compressive strength and superior tensile splitting and flexural strengths to those of NA-based counterparts.

Co-pyrolysis of cashew nut, coconut shells, and rice husk waste: kinetic and thermodynamic investigations

ABSTRACT Co-pyrolysis of low ash content of coconut shell (CNS) and cashew nuts shells (CCS), and high ash content rice husk (RH) blends was performed using thermal gravimetric analysis (TGA). RH was blended with both CCS and CNS at 0, 30, 60, and 100% RH by mass. Results showed that CCS and CNS have low ash contents of 2.7 and 1.5%, respectively, while RH has high ash content of 26.7% on dry basis. TGA under nitrogen gas study was carried out at three heating rates of 10, 15, and 20 K/min. It was observed that the increase of CCS/CNS increased decomposition rates of blends. For example, RH increased from 6 to 7.7%/min when CNS was added. Furthermore, addition of low ash content leads to high decrease of maximum decomposition rates compared to high-high or low-low ash blends. Synergistic analysis has found out that a positive effect is observed when CNS/CCS is added to RH. The decrease of maximum decomposition temperature of 60–63°C compared to other studies of 10°C for all low and 40° for all high ashes is of great advantage. Flynn-Wall-Ozawa (FWO), Kissinger-Akahra-Sunose (KAS), and DAEM kinetic model analysis for 0.1 ≤ α ≤ 0.75 were used between 315 and 840°C. FWO model gave activation energy of 85, 70, and 75 kJ/mol, for RH, CNS, and CCS, respectively. Addition of low ash content biomass reduced activation energy of RH, activation energy of RH was reduced from 85 to 72 kJ/mol when CNS was added. RH requires high energy than the rest, example, RH needed 66.29 kJ/mol of energy compared to 51% of CNS and 56 kJ/mol for CCS. The entropy results were negative which implies a different orientation of molecules from origin samples properties. The Gibbs-free energies were positive and thus non-spontaneous process. Empirical models generated using SB model indicated that kinetics depends on reaction order and acceleration mechanism rather than diffusion and nuclei growth. Kinetically, the blending of high and low ash content biomass leads to high decrease of operating temperature and activation energy compared to low-low or high-high ash content blends. It has been recommended to further study on quality and quantity of product from such blends and the possibility of pre-treatment methods such as microwaves to improve pyrolysis of such blend.

Mechanical Strength and Chloride Ions' Penetration of Alkali-Activated Concretes (AAC) with Blended Precursor.

The purpose of this study was to investigate the properties of hardened alkali-activated concrete, which is considered an eco-friendly alternative to Portland cement concrete. In this paper, the precursors for alkali-activated concrete preparations are blends of fly ash and ground-granulated blast-furnace slag in three slag proportions: 5%, 20%, and 35%, expressed as a percentage of fly ash mass. Thus, three concretes were designed and cast, denominated as AAC5, AAC20, and AAC35. Their physical and mechanical characteristics were investigated at 28 and 180 days, as well as their properties of chloride ion transport. The modified NT BUILD 492 migration test was applied to determine the chloride ions’ penetration of the alkali-activated concretes. Improvement of mechanical strength and resistance to chloride aggression was observed with ground-granulated blast-furnace slag content increase in the compositions of the tested concretes. Mercury intrusion porosimetry tests provided insight into the open pore structures of concretes. A significant decrease in the total pore volume of the concrete and a change in the nature of the pore diameter distribution due to the addition of ground granulated blast furnace slag were demonstrated.

Role of pore structure on resistance to physical crystallization damage of calcium sulfoaluminate belite (CSAB) cement blends

The resistance to physical sulfate damage was tested for a variety of cementitious mixtures including ordinary portland cement, calcium sulfoaluminate belite (CSAB) cement, a CSAB-fly ash blend and an air-entrained CSAB. Mortar bars were exposed to DI water or 5 % sodium sulfate solutions under cyclical wet-dry conditions. The expansions of the specimens were measured after each wetting cycle. A water sorptivity test, thermogravimetric analysis, x-ray diffraction analysis, mercury intrusion porosimetry method, and micro-computed tomography were applied to study differences in expansion and cracking in the mixtures. The results showed that the incorporation of fly ash into the CSAB matrix reduced cumulative pore volumes and slightly increased micropore sizes – both of which contributed to failure of the CSAB-fly ash systems. Use of the air-entraining agent in CSAB produced more, smaller, and more uniform pores, but did not influence the performance of CSAB. Both the CSAB and air entrained CSAB mixtures showed good resistance to physical sulfate damage. Samples with average pore diameters <15 nm prevented infiltration of sulfate ions and slowed the onset of salt crystalization damage.

Belitic calcium sulfoaluminate cement subjected to sulfate attack and sulfuric acid

Belitic calcium sulfoaluminate (BCSA) cement is a hydraulic rapid-setting cement with a different composition and properties compared to portland cement. There is currently limited information about its sulfate resistance and its resistance to sulfuric acid is not known. The ASTM C1012, Standard Test Method for Length Change of Hydraulic-Cement Mortars Exposed to a Sulfate Solution and a modified ASTM C1012 accelerated method were used to compare the sulfate resistance of BCSA cement, portland cement (PC), and PC-fly ash blends. BCSA cement, citric acid dosages in BCSA cement mixes, PC, and PC-fly ash blends were examined through mortar bar expansion. The most sulfate-resistant mixes contained BCSA cement or a blend of PC and class F fly ash. Citric acid dosage did not appear to affect resistance of BCSA cement to sulfate attack. Resistance of PC, PC-fly ash blends, and BCSA cement to a sulfuric acid solution was also compared. Compressive strength and volumetric changes were measured after prolonged immersion in sulfuric acid. Water to cementitious material (w/cm) ratios and curing time for BCSA were also analyzed to establish if these factors influenced resistance to sulfuric acid attack. The most acid resistant mix contained a blend of PC and class F fly ash. A higher w/cm (0.56) was found to be more resistant against sulfuric acid attack when using BCSA, while differing cure times did not clearly indicate sulfuric acid resistance.

Effect of carbonation curing on physicochemical properties of mineral admixture blended belite-rich cement

The present study investigates the effect of CO2 curing on carbonation degree, CO2 uptake, mechanical and physicochemical properties of mineral admixtures blended with belite-rich cement (BRC). Pulverized coal combustion (PCC) ash, circulating fluidized bed combustion (CFBC) ash, and blast furnace slag (SG) were utilized as mineral admixtures. The results revealed that the PCC ash blended with BRC attained the highest compressive strength under CO2 curing. CFBC ash was comparable to PCC ash in terms of the ability to improve the mechanical and physicochemical properties. TG analysis revealed that CFBC ash blended BRC was excellent for promoting carbonation and CO2 uptake. TG, MIP, XRD, and 29Si NMR results showed that the SG was the least reactive mineral admixture with BRC under CO2 curing and negatively affects the strength attainment outcome, carbonation degree, and CO2 uptake. 29Si NMR confirmed the potential of PCC ash and CFBC ash in enhancing the reactivity of BRC under CO2 curing than the SG. Therefore, it is concluded that the blending of PCC ash and CFBC ash is beneficial in promoting the CO2 sequestration characteristics and compressive strength of BRC.

Experimental study on the effects of reheat temperatures on the ammonium bisulfate and ash blend deposition

Ammonium bisulfate (ABS) and ash blend deposition blocks and corrodes air preheaters in coal-fired power plants, seriously affecting the safe operation of the boiler, especially when the selective catalytic reduction (SCR) system is widely used. In this work, a self-reheating probe was used to investigate the effects of reheat temperatures on ash deposition cleaning. The results showed that reheating could significantly reduce the ash deposition. When the reheat temperature exceeded 365 °C, the metal surface of the probe could be clearly seen. After ash deposition, the stable relative heat flux was about 0.881, and it increased significantly after reheating. For cases 4 (365 °C), 5 (385 °C) and 6 (430 °C), the relative heat flux after reheating was 0.986, 0.997 and 0.997, respectively. Microstructure results showed that the phenomenon of particle agglomeration was obviously reduced after reheating. X-ray diffraction (XRD) and thermal gravimetric analyzer (TGA) results indicated that the contents of ABS and Ammonium sulfate (AS) were significantly reduced in case 4, and they hardly existed in cases 5 and 6. This work provides a new method for cleaning ash deposition, which has a guiding role in the safe operation of the air preheater.

Influence of Clinker Replacement and Curing Temperature on Hydration Kinetics, Strength Development, and Phase Assemblage of Fly Ash–Blended Cements

Influence of Clinker Replacement and Curing Temperature on Hydration Kinetics, Strength Development, and Phase Assemblage of Fly Ash–Blended Cements

MECHANICAL PERFORMANCE OF ALKALIACTIVATED CONCRETE INCORPORATING RECYCLED AGGREGATES AND STEEL FIBERS

This study evaluates the mechanical performance of alkali-activated concrete cured at ambient conditions and made with recycled aggregates (RA) and steel fibers. The precursor binder was either ground granulated blast furnace slag or a blend of slag and fly ash (3:1 and 1:1). The alkaline activator solution was a blend of sodium hydroxide and sodium silicate. Coarse aggregates were either natural aggregates (NA) or RA, while fine aggregates comprised desert dune sand. Steel fibers were incorporated, in 2%, by volume, in RA-based concrete mixes. Results showed that replacing NA by 100% RA in plain alkali-activated slag concrete led to decreases of 21, 23, and 51% in compressive, tensile splitting, and flexural strengths, respectively. Meanwhile, alkaliactivated slag-fly ash blended (3:1 and 1:1) mixes experienced respective losses of up to 65, 50, and 57%. The corresponding properties of alkali-activated counterparts made with 100% RA increased by up to 172, 273, and 167% upon the addition of 2% steel fibers, by volume. Yet, the impacts of RA and steel fiber incorporation on the mechanical properties were more pronounced in concrete mixes having higher fly ash replacement. Alkali-activated slag and slag-fly ash blended concrete mixes incorporating 2% steel fibers, by volume, and 100% RA exhibited equivalent compressive strength and superior tensile splitting and flexural strengths to those of NA-based counterparts.

Assessment of blended coal source fly ashes and blended fly ashes

The availability of traditional siliceous Class F fly ash, produced when burning bituminous coals, is decreasing around the world as many countries begin to switch to renewable energy sources. Existing coal burning power plants are also starting to convert from bituminous to subbituminous coals, which produce calcareous Class C fly ash, or to a blend of the two to reduce emissions and cost. To prolong the availability of siliceous fly ash, suppliers have started distributing blended coal ashes and have also begun to blend siliceous fly ash with other coal combustion products (CCPs), such as calcareous fly ash or bottom ash, or natural pozzolans. A variety of these blended fly ashes were examined in this study and compared to a traditional siliceous fly ash. Although these fly ashes have similar oxide compositions and physical characteristics to a traditional siliceous fly ash, the crystalline and glassy phases present in the fly ash may differ. This can alter cement hydration and result in failure to mitigate expansion due to sulfate attack. In all other performance and durability tests conducted in this study, all fly ashes performed well in cement-based mixtures.

Utilization of waste glass in alkali activated slag/fly ash blends: reaction process, microstructure, and chloride diffusion behavior

This study aims to investigate the chloride diffusion behavior of alkali activated slag and fly ash blends with different contents of waste glass powder (GP) addition. The reaction heat flow of alkali activated slag/fly ash/waste glass is characterized. The reaction products are determined by X-ray diffraction and thermogravimetric analysis (TGA). N2 adsorption analysis (BET) is used to evaluate the microstructure of samples. The accelerated chloride penetration test (ACPT) is applied to study the chloride resistance of the AAMs. Subsequently, the leaching test of chloride penetrated samples are conducted and ion chromatography is utilized to measure the chloride content in the samples. According to the BET results, the total volume of mesopores decreases with increasing GP content. The results of ACPT show that the increasing GP in AAMs shows an enhancement of chloride resistance.