Reactivity Of Ash Research Articles

Mechanochemical activation for transforming bottom ash to reactive supplementary cementitious material

Due to the intrinsic low reactivity of bottom ash (BA), it is not typically used as a direct substitute for ordinary Portland cement (OPC). In this study, a BA-OPC composite was developed by applying small amount of diethanol isopropanolamine (DEIPA) as a chemical admixture. The activation of BA with DEIPA resulted in substantial improvement in the hydration properties of BA-OPC composite. Not only did the OPC hydrations accelerate in the early stage, but the induced pozzolanic reaction was also efficiently activated in the later stage, leading to the more formation of C-S-H. With the use of 0.1% DEIPA, the compressive strength increased by 26.5%, 50.0%, and 23.5% at curing dates of 3, 7, and 28 days, respectively, as compared to the sample without DEIPA. It has been demonstrated that very small amount of DEIPA could be sufficient to increase the chemical compatibility of the BA as supplementary cementitious materials.

Reactivity of MSWI-fly ash in Mg-K-phosphate cement

In this study, the behaviour and reactivity of Municipal Solid Waste Incineration Fly Ash (MSWI-FA), introduced in the formulation of magnesium potassium phosphate cement (MKPC), was investigated by considering the waste either as fully inert or reactive. MSWI-FA induced structural and compositional modifications in MKPC as a consequence of dissolution/precipitation processes which involved many MSWI-FA elements (e.g., Ca, Mg, Al, Si, Zn) and led to the formation of mostly amorphous phosphate secondary products. The reaction path has been described in terms of the early fast dissolution of MSWI-FA, with precipitation of very low solubility phases, and subsequent late precipitation due to pH changes and water subtraction during MKPC gelification. The increase in amorphous content peaked to 50 wt.% and it has been related to the improved behaviour with respect to the leaching of heavy metals (reduced by 70-99%), pointing to this cement as an excellent matrix for their chemical stabilization. The obtained MKPC microstructure exhibited better mechanical performance, with an improvement of up to 60% in compressive strength. All in all, the results indicated that the incorporation in MKPC is a viable recycling opportunity for MSWI-FA, although, for an effective cement formulation, its reactivity must be taken into account.

Leaching kinetics and reactivity evaluation of fly ash based on the synergistic effect of alkali and sulfate

This work evaluates the reactivity of various minerals of fly ash based on the backscattered electron images analysis (BSE-IA) method and discusses the influencing factors and kinetics of Si and Al selective leaching of fly ash in alkali solution and alkali-sulfate composite solution, respectively. The relationships among the physicochemical properties, dissolution behavior, and reactivity of fly ash have been revealed. There are three typical phases in fly ash, namely the Si–Al phase, Ca–Si–Al phase, and Fe phase. The Ca–Si–Al phase is more soluble and preferentially participates in the reaction process than the other two phases. The dissolution process is greatly affected by temperature. Alkali and sulfate have a compound synergistic effect and SO42− further promotes the dissolution of Si and Al mainly by changing the gel property wrapped on the surface of fly ash particles. The leaching kinetics results indicate that the internal diffusion controls the reaction process. The research method and system in this work can be applied to other solid waste, providing reference significance for quickly exploring its reaction activity. Moreover, the synergistic effect of alkali and sulfate can be used to establish an alkali-sulfate composite cementitious system, guiding the application of fly ash as a supplementary cementitious material.

Study of the Pozzolanic Reactivity of Sugar Cane Straw Ashes (SCSA) Burned under Controlled Conditions

The aims of this work were to evaluate the reactivity of sugarcane straw ashes (SCSA) burned under controlled conditions and to analyze their reactivity in blended cement and hydrated lime pastes by thermogravimetric analysis (TG) and calorimetry. Four different ashes were produced, and burned at 600 °C, 700 °C, 800 °C and 900 °C (SCSA600, SCSA700, SCSA800 and SCSA900, respectively). These ashes were characterized by X-ray fluorescence spectroscopy, X-ray diffractometry, particle size distribution by laser diffraction and specific area surfaces to assess their potential interest in the partial replacement of inorganic binders (Portland cement (OPC) and hydrated lime). The hydrated lime pastes were subjected to scanning electron microscopy (SEM) and TG. The blended cement pastes were analyzed by TG and calorimetry, compressive strength testing and mercury intrusion porosimetry. High lime fixation percentages were observed in the hydrated lime and OPC pastes and were higher than 75% and 50% for the ashes burned at 600 °C and 700 °C, respectively. Calorimetry showed a delay in the heat release of SCSA600 and SCSA700 compared to the control paste. These pastes also had higher compressive strength and a smaller total pore volume. The results indicate the positive response of preparing sugar cane ashes under controlled conditions (mainly for straw calcined within the 600–700 °C range) for their use as pozzolanic addition by partially replacing inorganic binders.

Reactivity and leaching potential of municipal solid waste incineration (MSWI) bottom ash as supplementary cementitious material and precursor for alkali-activated materials

This work evaluated the reactivity and leaching potential of municipal solid waste incineration (MSWI) bottom ash as supplementary cementitious material (SCM) and precursor for alkali-activated materials (AAM). The chemical composition of the amorphous phase in MSWI bottom ash was found to be in the same range as that of Class F coal fly ash. The reactivity of MSWI bottom ash as SCM and AAM precursor was tested to be much lower than that of blast furnace slag, but similar to that of Class F coal fly ash. The method of thermodynamic modeling was found useful in providing references for the mix design of MSWI bottom ash-based AAM. Grinding MSWI bottom ash into powder for the application of SCM and AAM precursor increased its leaching potential. Based on the findings of this study, recommendations were provided on how to use MSWI bottom ash to prepare blended cement pastes and AAM.

Utilization of low reactive bottom ash in cement formulation through Na2CO3 triggered pozzolanic reaction

In this study, the use of sodium carbonate anhydrous (Na2CO3) to enhance the reactivity of bottom ash (BA) in the ordinary Portland cement (OPC) system was investigated. The presence of Na2CO3 exerted an interactive effect on the hydration mechanism of the BA-OPC composite, leading to a significant enhancement in the pozzolanic reactions between BA and calcium hydroxide, following the improved silicate reactions. Consequently, remarkable improvements were observed in the mechanical properties of the BA-OPC composite with an extremely small amount of the activator. Specifically, the sample containing 0.025 % Na2CO3 exhibited the highest increase in compressive strength compared to the sample without Na2CO3, showing an improvement of 35.4 % at 7 days and 70.6 % at 28 days. Based on the proposed method, the reactivity of BA and silicate phases can be enhanced which contributes to the sustainable development of BA-OPC composite.

Enhancing physiochemical properties and reactivity of landfilled fly ash through thermo-mechanical beneficiation

This study investigates the impact of thermo-mechanical beneficiation techniques on the physiochemical characteristics and reactivity of landfilled fly ashes (LFAs) obtained from power plants in Wyoming and Colorado, USA. Thermo-mechanical beneficiation significantly improved the physiochemical properties of LFAs, leading to a decrease in loss in ignition (LOI) and an increase in fineness. The results revealed improvements in the strength activity index of all LFAs after beneficiation, surpassing the minimum requirement of 75% at 28 days. Beneficiation also enhanced heat release and calcium hydroxide consumption, indicating improved pozzolanic reactivity. The findings demonstrated that as beneficiation temperatures increased, there was a significant reduction in LOI, with levels falling below 3% at temperatures above 450 °C. The relationship between LOI and heat release indicated that reducing LOI could enhance the reactivity of fly ash. However, there was an inflection point at certain LOI thresholds, suggesting that further reductions in LOI may not significantly impact hydration kinetics. The results also showed that the specific surface area of LFA was correlated with heat release and calcium hydroxide consumption, emphasizing the importance of increased fineness for enhanced reactivity. The study also found associations between calcium hydroxide consumption, heat release, and early- and later-age strength activity indices. Higher calcium hydroxide consumption corresponded to increased heat release and reactivity, which in turn contributed to greater strength development over time, particularly at later.stages.

Novel porous ambient temperature cured fly ash geopolymer for lead adsorption from wastewaters

ABSTRACT This paper discusses the ability of the fly ash (FA) and abmbient cured Alkali activated Fly ash geopolymer (FAAG) for sequestering Pb (II) ions from aqueous solution. Various physiochemical properties such as the influence of pH and contact time were investigated for achieving the conditions for maximum removal via batch mode using powdered samples. The adsorbents were characterized by employing powder X-Ray diffraction, Attenuated Total Reflection Fourier Transform Infra-Red spectroscopy, and Scanning Electron Microscopy/EDAX before and after the treatment. The adsorption capacity of Pb2+ ions by raw FA and FAAG were examined by the Inductively coupled plasma mass spectrometry (ICP-MS). The results represented that the maximum adsorption capacity of Pb2+ ions by FAAG is 75 mg/g with attained equilibrium time of 120 min whereas raw fly ash at 150 min at 21.5 mg/g capacity. The pozzolanic reactivity of fly ash in water glass hardening resulted mainly N-A-S-H gel and traces of lead silicate due to the immobilization of lead in the network. This was conformed from the binding energy lines at 139.7 eV in XPS survey lines and lead silicate at 25 and 34° 2θ as identified in XRD phase assemblages. ICP-MS test results of leachate of lead immobilized geopolymer sample are devoid of lead ions and thus sorption sites of fly ash geopolymer lead to potential safety disposal of lead. Thus, recycling of fly ash into geopolymer by less energy intensive process and subsequent use in heavy metal disposal could achieve the concept of disposal waste and recycling, which could contribute to achieve the sustainable goals.

Assessing regional variability in chemical composition and pozzolanic reactivity of corn stover ash in the United States

This study examines the regional variability in the chemical composition and pozzolanic reactivity of corn stover ash (CSA) produced from corn stover samples collected from different locations in the U.S. Corn stover samples were collected from local farms in Nebraska and Iowa, while information about Kansas CSA was obtained from existing literature. The findings reveal significant variability in the chemical composition of untreated CSA across different regions. However, through the use of pretreatment techniques such as acid soaking, the compositional variations can be considerably reduced. The results of the modified R3 test demonstrate that CSA exhibits pozzolanic behavior that falls between that of fly ash and silica fume. The reactivity of CSA was found to be independent of geospatial factors but heavily influenced by the specific pretreatment methods employed in the study. Furthermore, the study indicates that the reactivity of CSA is less variable compared to fly ash and silica fume.

Deep insight into reactive chemical structures of Class F fly ash

Reactive amorphous aluminum silicates dominate the reactivity of fly ash in alkali cement; however, the quantitative characterization of valid chemical compositions and structures information is highly challenging due to the heterogeneity and complexity of these phases. To acquire this information, in this work, Class F fly ash was treated with 1% hydrofluoric acid, followed by step-by-step analysis using a scanning electron microscope with an energy dispersive spectrometer (SEM-EDS), solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR), and Fourier transform infrared (FT-IR) spectroscopy. Based on the acidolysis method, along with SEM-EDS statistical analysis, four amorphous aluminum silicate phases with relatively higher reactivity were successfully separated and quantitatively showcased, along with their respective average atomic percentage compositions (i.e., Si, Al, Ca, Fe, Na, K, and Mg%). In addition, the use of MAS-NMR and FT-IR analyses allowed for further quantitative insight into the reactive chemical structures and their associations with reactivity. The proposed characterization techniques have unique advantages for acquiring detailed reactive amorphous chemistries, which are difficult to obtain using conventional analysis procedures in alkali systems.

Carbon nanotube production from algal biochar using microwave irradiation technology

In this study, we evaluated the transformation of algal-based biochar into carbon nanotubes by irradiation in a microwave oven at low energies (100–300 W). Three species of algae (Macrocystis pyrifera, Sarcothalia crispata, and Scenedesmus almeriensis) were selected and pyrolyzed to obtain biochar for carbon nanotubes (CNTs) growth in the presence of ferrocene as the catalyst. The CNTs obtained were characterized by dynamic light scattering, UVVIS spectroscopy, Raman spectroscopy, transmission electron microscopy, X-ray diffraction, and electrical conductivity. The results indicate that algal biochar can be used for CNT growth. The heterogeneous structure of algal biochar can initiate the graphitization process for the formation of CNTs. The characteristics of synthesized CNTs vary with the biochar source used as a precursor. Thus, both the degree of graphitization of the wall and the content of nanotubes were higher using biochar with higher carbon content (from microalga Scenedesmus almeriensis); otherwise, the hydrodynamic diameter and electrical conductivity were higher using biochar with upper mineral ash content (from microalga Macrocystis pyrifera). Furthermore, it was found that a low catalyst concentration was required to promote growth due to the reactivity of the mineral ash of the biochar, and it was demonstrated that microwave heating conditions, such as microwave power and temperature, lead to variations in the optical properties of CNTs, such as the band gap energy, CNTs content, and measurement of the size such as the hydrodynamic diameter.

Role carbon nanomaterials in reinforcement of concrete and cement; A new perspective in civil engineering

Nanotechnology has resulted in many advantages in different majors of science and created new approaches to them. nanotechnology has more effect on civil engineering such as utilizing nanomaterials as cement reinforcement. The improvement in quality of materials used in civil engineering such as self-cleaning, self-structural health monitoring, self-sensing, self-vibration damping, self- rehabilitation, cement reinforcement, and self-healing created a new revolutionary civil engineering. Concrete is one of the important parts of civil engineering and especially in the discussion of building and bridge retrofitting. Nanotechnology plays an important role in the concrete process such as alkali silicate reactions (ASR), hydration reactions, and fly ash reactivity. Much of the research showed that nanomaterials improved compressive and flexural strength in concrete and created the best situation for building resistant structures such as bridges, towers, and tall buildings. Due to the mechanical behavior and tensile strength of carbon nanotubes (CNTs), these compounds play a special role in improving concrete properties. Prevention of cracking is one of the positive effects of using carbon nanotubes in improving concrete properties, which has increased significant growth in the application of it in the industry. The present review paper focused on the role of nanomaterials in improving and reinforcement of concrete and the advantages of them in civil engineering.

Effect of fluorite addition on the reactivity of a calcined treated spent pot lining in cementitious materials

Treating SPL by the low caustic leaching and liming process generates an inert nonhazardous residue called LCLL Ash and a fluorite byproduct Calcined LCLL Ash that is ground into a fine powder demonstrates pozzolanic behavior in cement. The effect of the calcination temperature and fluorite byproduct addition on the reactivity of LCLL Ash was studied by the compressive strength activity index, Frattini test and Rilem R3 tests followed by XRD analysis. At 800°C, the formation of nepheline causes alkali uptake, the LCLL Ash showed a slightly lower reactivity with 10% fluorite addition. At 1000°C, calcined LCLL Ash/CF showed a better amorphization of phases and increasing reactivity due to reactions between fluorite and sodium oxide. Unlike LCLL Ash, no delay in hydration or hydro reactivity was observed with calcined LCLL Ash/CF.

Characterization of Alkali Activated Materials Prepared from Continuous Attrition and Ball Milled Fly Ashes

Mechanical activation is known to greatly influence the reactivity of fly ashes. In this paper, we report a comparative study of the properties of alkali-activated geopolymer materials prepared using both ball-milled and attrition-milled fly ashes. Ball milling was carried out for 30 min and 60 min while attrition milling was carried out continuously in a high-speed attritor. The surface area of the raw fly ash decreased from 4017 cm2/g to 3999 cm2/g and 3912 cm2/g after ball milling for 30 min and 60 min, respectively. By contrast, the surface area of the continuously attrition-milled fly ash increased to 5545 cm2/g. Fly ash processed by continuous attrition milling showed a 50% particle size reduction to 25–38 μm, whereas fly ash ball-milled for 30 and 60 min was reduced in size by 33.4 and 42.9%. The milled fly ash samples were activated with 8 M NaOH solution and cured at 40 °C for 68 h. After curing, the samples were maintained at room temperature, and their 7-, 14-, and 28-day compressive strengths were measured. The compressive strength of the attrition-milled 28-day geopolymer paste was 24.6 MPa; that of the geopolymers ball-milled for 30 and 60 min was 23.37 MPa and 17.58 MPa, respectively; and that of the unmilled control geopolymer fly-ash-based paste was 17 MPa. The improvement in the mechanical properties is attributed to the increased gel formation resulting from the increased surface area (decreased particle size) in the fly ash glass starting material.

Characterization and reactivity of size-fractionated unconventional fly ashes

Characterization and reactivity of size-fractionated unconventional fly ashes

Evaluation of pozzolanic reactivity of maize straw ash as a binder supplement in concrete

Cementitious materials, irrespective of their sources, play a vital role in cement hydration reaction in concrete. Hence, it is critical to understand how each supplement affects the early and later age properties of concrete. Maize Straw Ash (MSA), being a material with minimal consideration as a pozzolan for partial replacement of cement, was evaluated based on different researcher’s reports. A range of outcomes involving the use of maize straw ash as replacement materials in concrete were examined based on their impact on concrete in the early and later stages, and the findings were presented in addition to assisting in their future use. The impact of pozzolanic material on both mechanical and durability property were analysed, and how certain treatment methods influence the property of concrete in the early and later period. The data revealed that maize straw ash has comparable behaviour when given the same treatment technique before use, ability to increase strength over a long duration compared with other Agricultural waste (agro) materials, and likewise act as a void filler when concrete hardens to improve durability, with the usage of these materials for optimal strength not exceeding 20% replacement, shrinkage control not exceeding 30%, and 10–15% for good workability. At (500–800 °C calcination heat), the pozzolanic reaction produces good results.

Reactivity of Unconventional Fly Ashes, SCMs, and Fillers: Effects of Sulfates, Carbonates, and Temperature

Abstract Reactivity information for a range of unconventional fly ashes is unavailable in literature. The objective of this study is to quantify the reactivity of numerous unconventional fly ashes using the R3 test (ASTM C1897-20, Standard Test Methods for Measuring the Reactivity of Supplementary Cementitious Materials by Isothermal Calorimetry and Bound Water Measurements) and the modified R3 test and to determine how sulfates, carbonates, and temperature affect the measured reactivity. A small set of other supplementary cementitious materials and fillers was used to benchmark the fly ash results. Heat release, calcium hydroxide consumption, and bound water were measured for the different materials. For siliceous materials with relatively low calcium oxide (CaO) + aluminum oxide (Al2O3) contents, temperature had a dominant effect on the heat release. On the other hand, for materials with higher CaO + Al2O3 contents, the effects of sulfates and carbonates dominated the effect of temperature. The slow but sustained reactivity of Class F fly ashes highlighted the importance of kinetic corrections or extrapolations to the reactivity measured in the R3 test. However, when testing at 50°C, the heat release curves of all tested materials plateaued at the end of 10 days, indicating that kinetic corrections were not required. Correlations between reactivity and early- and later-age paste properties are discussed.

How Brine Composition Affects Fly Ash Reactions: The Influence of (Cat-, An-)ion Type

Abstract Hypersaline brines can be solidified and stabilized via the hydraulic and pozzolanic reactions between fly ash(es) and calcium-based additives. Although recent work has examined fly ash reactivity in single-salt (“simple”) hypersaline brines (ionic strength, Im > 1 mol/L), the effects of mixed-salt solutions on fly ash reactivity remain unclear. Herein, the reactivity of a Class C (calcium oxide [CaO]-rich) or Class F (CaO-poor) fly ash mixture with calcium hydroxide is reacted in solutions bearing sodium chloride (NaCl), calcium chloride (CaCl2), magnesium chloride (MgCl2), sodium sulfate (Na2SO4), or combinations thereof for 1.5 ≤ Im ≤ 2.25 mol/L, from 1 week until 24 weeks. Expectedly, sulfate anions promote the formation of sulfate phases (i.e., ettringite, monosulfoaluminate, U-phase), while chloride anions induce the formation of Cl-AFm compounds (i.e., Kuzel’s and Friedel’s salt). Although the Class C fly ash’s reactivity is similar across different anions (for a fixed cation and Im), Class F fly ash shows a small change in reactivity depending on the anion present. NaCl suppresses (Class C and Class F) fly ash reactivity by up to 30 % as compared to neat CaCl2 and MgCl2-based brines. Thermodynamic modeling reveals that NaCl induces a considerable increase in pH—up to 13.7, where many hydrated phases of interest cease to be the major phase expected—as compared to CaCl2 and MgCl2 brines (pH < 13). In mixed-salt brines, anion immobilization is competitive: sulfate achieves a greater level of incorporation into the hydrates, as compared to chloride. These results offer new understanding of how the brine composition affects solidification and stabilization and thereby yield new insight into improved approaches for wastewater disposal.

Micro aggregate and pozzolanic reactivity of fly ash: effect on fracture properties

ABSTRACT The performance of fly ash blended concrete is influenced by the pozzolanic and/or micro-aggregate effect of fly ash particles based on the replacement levels. Dominance of either of this effect greatly influences the mechanical and fracture properties of fly ash blended concrete. In view of this, in the present study, 0%, 20%, 30%, 35%, 40%, 50%, 60% and 70% of fly ash is replaced for cement to investigate the dominance of pozzolanic or micro aggregate effect. The results obtained from the study indicate the reduced strength with increased replacement of fly ash. Similarly, the peak load at fracture decreases with the increased replacement of fly ash. Further, it is concluded that with the increased curing age the compressive strength increases and the fracture strength decreases. Furthermore, the decreased content of calcium hydroxide (CH) with increased fly ash content as obtained from thermo gravimetric analysis (TGA) confirms the presence of excessive fly ash that can contribute as filler material demonstrating the micro-aggregate effect.

Enhancing the Pozzolanic Reactivity of Spent Bleaching Earth Ash (SBEA) in Binary Blended Cement Mortar through Calcination

The effects of calcination on spent bleaching earth ash (SBEA) were investigated in terms of its contribution to pozzolanic reactivity as well as the strength of blended cement mortar when used as partial cement substitution. SBEA waste, which is plentiful in the global stock, showed some potential as pozzolanic material to reduce reliance on the traditional clinker cement. However, actual research on its use as cement replacement and how it may benefit from calcination was still very limited. This paper can conclude that SBEA contains sufficient silica and alumina oxides as well as satisfactory levels of pozzolanic reactivity to be classified Class N natural pozzolan. By calcining SBEA up to a temperature of 700 °C, its pozzolanic reactivity was improved due to the amorphisation of its contents, leading to an increase in the allowable level of replacements from 30 to 40 % as well as the peak strength achieved. These findings allowed calcined SBEA to be used in greater volume in cement mortar compared to an untreated SBEA. It is also worth noting that an excessively high calcination temperature around 900 °C was found to be detrimental to both the pozzolanic reactivity and strength development of cement mortars.