High Fly Research Articles

Study on the Properties of High Fly Ash Content Alkali-Activated Fly Ash Slag Pastes and Fiber-Reinforced Mortar Under Normal Temperature Curing.

In order to efficiently utilize industrial solid waste while minimizing the preparation cost of engineering materials and the technical difficulty of construction, this paper prepared a high fly ash content alkali-activated fly ash slag composite system at normal temperatures and conducted an in-depth investigation on it. A systematic study was conducted on the workability, mechanical properties, and microstructures of the alkali-activated fly ash slag pastes, including setting times, strength, phase, and molecular structures. We then designed and prepared fiber-reinforced alkali-activated fly ash slag mortar and studied the effects of the alkali activator modulus, glass fiber (GF), and polypropylene fiber (PPF) on the workability, mechanical properties, and frost resistance of the mortar. The following main conclusions were drawn: By adjusting the modulus of alkali activator for alkali-activated fly ash slag pastes, characteristics that meet engineering requirements could be obtained. The compressive strength of the pastes decreased with increasing proportions of fly ash, and it first increased and then decreased with increases in the activator modulus. The flexural strength decreased to varying degrees as the modulus of the activator increased. Through SEM, fly ash particles with different reaction degrees could be observed, indicating that the reaction was still ongoing. The addition of GF and PPF reduced the fluidity of mortar and significantly improved its strength and frost resistance. Fiber had the most significant effect on improving the strength of the mortar, as an activator modulus of 1.0. 0.45% PPF increased the flexural and compressive strength of the mortar by 14.33% and 29.1%, respectively, while 0.90% GF increased the flexural and compressive strength of the mortar by 3.12% and 19.21%, respectively. The frost resistance of the mortar with an activator modulus of 1.0 was significantly better than that of the mortar with an activator modulus of 1.4. 0.45% PPF and reduced the quality loss rate of the mortar by 49.30%, effectively delaying the deterioration of its freeze-thaw performance.

Triethanolamine assisted ball milling activation of high alumina fly ash: grinding kinetics, activation mechanism

Triethanolamine assisted ball milling activation of high alumina fly ash: grinding kinetics, activation mechanism

A study on the diversity of phlebotomine sand flies (Diptera, Psychodidae) in karstic limestone areas in Vientiane Province, Laos, with a description of two new species of Sergentomyia França and & Parrot

BackgroundSoutheast Asia is well known as a hotspot of biodiversity. However, very little is known about cave-dwelling hematophagous insects that are medically important. Taxonomic knowledge and ecology of phlebotomine sand flies are very poorly studied in Laos, as well as in other countries in the region. Herein, we report species diversity data and some notes on the ecology of the detected species from these karstic limestone areas of Laos.MethodsPhlebotomine sand flies were collected using Centers for Disease Control and Prevention (CDC) light traps from limestone cave locations in three districts of Vientiane Province, Laos. Both morphological and molecular techniques were used for sand fly identification. Species diversity and abundance were analyzed according to sites, locations, collection seasons, and trapping positions.ResultsA total of 6564 sand flies, of which 5038 were females and 1526 were males, were morphologically identified into 20 species belonging to five genera (Chinius, Idiophlebotomus, Phlebotomus, Sergentomyia, and Grassomyia). The most abundant species were Chinius eunicegalatiae, Phlebotomus stantoni, Sergentomyia hivernus, Se. siamensis, and Idiophlebotomus longiforceps. Cytochrome b analysis results supported the morphological identification and revealed that Se. siamensis was separated from other members of the Se. barraudi group. Two new species, Se. dvoraki n. sp. and Se. marolii n. sp., were described. Sand fly density was generally high except in a cave in Vangvieng, with species richness ranging from 14 to 18 across different caves. Outside caves had higher species richness (R = 20) and diversity (H = 2.50) than cave entrances (R = 18, H = 2.41) and interiors (R = 16, H = 2.13). Seasonal variations showed high sand fly density in Feung and Hinheup during both dry and rainy seasons, while Vangvieng had a notable decrease in density during the dry season (D = 6.29).ConclusionsThis study revealed that the diversity of phlebotomine sand fly fauna in Laos, particularly in karstic limestone areas, is greater than previously known. However, the taxonomic status of many species in Laos, as well as Southeast Asia, still needs more in-depth study using both morphological characters and molecular methods. Many species could be found from inside, at the entrance, and outside of caves, indicating a wide range of host-seeking behavior or possible natural breeding in the karstic cave areas.Graphical abstract

Insight into immobilization mechanisms of metal/metalloid ions and herbicide molecules on waste-derived Na-X zeolite covered with macromolecules

Immobilization of toxic compounds on the solids limits their bioavailability in natural ecosystems. The use of waste-derived adsorbents for this purpose has additional benefit – the possibility of managing undesirable and dangerous by-products. Thus, the main aim of the study was to explore immobilization mechanism of metals (Cd, Cu), metalloids (As, Se), and herbicides (diuron, glyphosate) on zeolite Na-X free of ash residue, coming from waste solution after high carbon fly ash (HiC FA) conversion, under specific conditions – in multicomponent solutions as well as after solid modification with polymers. Immobilization strength was assessed based on adsorption/desorption studies, whereas the solid surface was investigated by XPS, FTIR, SEM-EDS, etc. The results obtained for Na-X was compared with those measured for its precursor, HiC FA. It was found that Na-X was a good adsorbent of Cu(II) and Cd(II) cations – it bound 195.8 mg/g (58.7 %) of Cd(II) and 126.9 mg/g (38.1 %) of Cu(II) mainly in the form of hydroxides. The Na-X modification with polymers made its adsorption capacity towards metalloid anions and herbicides higher. Anionic polyacrylamide increased the Se(IV) adsorption from 0.2 to 67.5 mg/g. Cationic polyacrylamide contributed to higher immobilization of glyphosate and diuron by 43.9 % and 46.4 %, respectively.

Improved high quality sand fly assemblies enabled by ultra low input long read sequencing

Phlebotomine sand flies are the vectors of leishmaniasis, a neglected tropical disease. High-quality reference genomes are an important tool for understanding the biology and eco-evolutionary dynamics underpinning disease epidemiology. Previous leishmaniasis vector reference sequences were limited by sequencing technologies available at the time and inadequate for high-resolution genomic inquiry. Here, we present updated reference assemblies of two sand flies, Phlebotomus papatasi and Lutzomyia longipalpis. These chromosome-level assemblies were generated using an ultra-low input library protocol, PacBio HiFi long reads, and Hi-C technology. The new P. papatasi reference has a final assembly span of 351.6 Mb and contig and scaffold N50s of 926 kb and 111.8 Mb, respectively. The new Lu. longipalpis reference has a final assembly span of 147.8 Mb and contig and scaffold N50s of 1.09 Mb and 40.6 Mb, respectively. Benchmarking Universal Single-Copy Orthologue (BUSCO) assessments indicated 94.5% and 95.6% complete single copy insecta orthologs for P. papatasi and Lu. longipalpis. These improved assemblies will serve as an invaluable resource for future genomic work on phlebotomine sandflies.

Development of insulating backfill materials produced from the ternary mixtures of red mud, fly ash and preformed foam

Many public utility lines to transport power, water, natural gas, water, sewer, and communication are placed beneath trafficable areas. However, insufficient or inadequate backfill induces sudden subsidence, damage, or pothole on the road. This study aims to develop lightweight controlled low-strength materials (CLSM) with low thermal conductivity using the ternary mixtures of red mud to replace aggregate sand, high carbon fly ash, and preformed foam. Changes in flow consistency, air void characteristics, bulk unit weight, unconfined compressive strength (UCS), and thermal conductivity (k) of the tested materials with varying red mud contents were investigated as a function of the foam volume ratio (FVR). The results demonstrate that the UCS and k of tested materials decreased with increasing FVR due the decrease in unit weight, and a greater UCS but smaller k was observed at a given FVR with increasing red mud content because the inclusion of red mud in the lightweight CLSM mix design helps improve the stability of air bubbles and achieve uniform distribution of air voids. In addition, the red mud can act as a NaOH supplier, leading to the developed material had additional strength gain from the alkali activation. Thus, the developed insulating backfill material showed 43 % decrease in k while maintaining UCS similar to non-foam CLSM without red mud.

The Influence of Silica Fly Ash and Wood Bottom Ash on Cement Hydration and Durability of Concrete.

This research addresses a notable gap in understanding the synergistic effects of high carbon wood bottom ash (BA) and silica fly ash (FA) on cement hydration and concrete durability by using them as a supplementary material to reduce the amount of cement in concrete and CO2 emissions during cement production. This study analyses the synergistic effect of FA and BA on cement hydration through X-ray diffraction (XRD), thermal analysis (TG, DTG), scanning electron microscopy (SEM), density, ultrasonic pulse velocity (UPV), compressive strength, and temperature monitoring tests. In addition, it evaluates concrete properties, including compressive strength, UPV, density, water absorption kinetics, porosity parameters, predicted resistance to freezing and thawing cycles, and results of freeze-thawing resistance. The concrete raw materials were supplemented with varying percentages of BA and FA, replacing both cement and fine aggregate at levels of 0%, 2.5%, 5%, 10% and 15%. The results indicate that a 15% substitution of BA and FA delays cement hydration by approximately 5 h and results in only a 6% reduction in compressive strength, with the hardened cement paste showing a strength similar to a 15% replacement with FA. Concrete mixtures with 2.5% BA and 2.5% FA maintained the same maximum hydration temperature and duration as the reference mix. Furthermore, the combined use of both ashes provided adequate resistance to freeze-thaw cycles, with only a 4.7% reduction in compressive strength after 150 cycles. Other properties, such as density, UPV and water absorption, exhibited minimal changes with partial cement replacement by both ashes. This study highlights the potential benefits of using BA and FA together, offering a sustainable alternative that maintains concrete performance while using waste materials.

Crack-healing and rheological properties of high content fly ash/slag/silica fume green and sustainable cement-based materials incorporating crystalline admixture and calcium alginate biomass hydrogel

Cracking is an important factor affecting the durability of concrete. Rheological properties are important performance indicators of the workability of fresh concrete. Ion chelator (CA) is one kind of crystalline admixture, which can enhance crack-healing of concrete by promoting the formation of calcium carbonate in wet environment. Calcium alginate hydrogel (CaAlg) can maintain the humidity of cementitious matrix and promote the crystallization of inorganic minerals. Therefore, in this study, CaAlg bead was prepared to further improve the crack-healing of cementitious materials containing CA. Self-healing performance was evaluated by visual crack closure and water permeability test. Rheological property was measured by rotor rheometer. Healing mechanism of cementitious materials with CA and CaAlg was analyzed. Results showed that with the increase of CaAlg dosage, yield stress and plastic viscosity of paste decreased gradually. Meanwhile, fly ash and slag reduced viscosity of pastes, while silica fume increased the viscosity of pastes. CA could evidently improve the permeability and mechanical properties of mortar, especially for slag mortar. Self-healing performance test and characterization showed that CaAlg could further enhance crack-healing process of mortar with CA, especially for pure cement and slag mortar. Microscopic testing indicates that CaAlg could induce the formation of vaterite and calcite on its surface to further improve crack-healing efficiency.

Dynamic analysis of a skeet-inspired vehicle to achieve a spiral scanning detection motion

A short cylindrical vehicle (the ratio of length to diameter is less than 2) equipped with an outer/inner detector is developed, which is inspired by the Tennis racket theorem and Olympic skeet shooting sports to achieve a regular scanning spiral on the ground. The sensitivity of the asymmetric mass distribution of the skeet-inspired vehicle (SIV) to the spatial position of the inertial principal axis is evaluated. Subsequently, a dynamics model with six degrees of freedom for the SIV at a large initial angle of attack (≈60–90°) is established. The numerical results of solving the dynamic differential equations indicate that the special initial conditions—namely, high initial flying velocity and rotational speed—are prerequisites for achieving the regular scanning spiral. Additionally, the analysis demonstrates that asymmetric mass distribution, rather than asymmetric aerodynamics, serves as the key factor in achieving the regular scanning spiral in the present skeet-inspired vehicle. Our new strategy, using the principal axes as the initial rotation axis, offers better scanning performance (such as a larger detection area, faster scan frequency, and more stable scanning motion) compared to the other platforms (e.g., rotating decelerators with wings or parachutes) that rely on asymmetrical aerodynamics. The analyses can provide guidance for the structural design of various types of spiral scanning vehicles.

Evolution of physicochemical and leaching characteristics of municipal solid waste incineration fly ash in China under ultra-low emission standard

The physical and chemical characteristics of fly ash has changed significantly under ultra-low emission system and the current leaching system is no longer suitable for high alkalinity fly ash. This work investigated the pH values and evolution of physical and chemical characteristics of fly ash from 24 typical municipal solid waste incineration plants in China. The pH value of the leaching solution obtained by HJ/T 300–2007 presented two different acid and alkali characteristics, where high and low alkalinity fly ash accounted for 54.17% and 45.83%, respectively. The alkali content in fly ash increased significantly after ultra-low emission standard, increasing by 18.24% compared with before the implementation of GB 18485-2014. The leaching behavior of high alkalinity fly ash showed the illusion that they could enter the landfill only by the addition of a small amount of chelating agent or even without stabilization treatment, and its long-term landfill risk is significant. The phase change of high alkalinity fly ash and pH value change of the leaching solution after carbonation were the key factors for the leaching concentration change of heavy metals. Therefore, it is recommended to improve the existing leaching system or conduct accelerated carbonization experiments to scientifically evaluate the long-term leaching characteristics of high alkalinity fly ash, and to reduce the risk of heavy metal release from high alkalinity FA after entering the landfill site.

Approaching the circular economy: Biological, physicochemical, and electrochemical methods to valorize agro-industrial residues, wastewater, and industrial wastes

The circular economy policy enables the use of waste as an input to generate value repeatedly or at least to have the opportunity to be used a second time to extract valuable substances such as metals, dyes, hydrogen, phosphorus, nitrogen, nutrients, and fertilizers. For this reason, the present paper discusses approaches to valorizing wastewater, communal production, and agricultural wastes. In particular, techniques are considered to valorize biomass, lignin-containing residues, wastewater with a high organic content, sewage sludge, oily sludge, mine tailings, fly ashes, and iron production wastes. The procedures evaluated include biological processes, microbial fuel cells, electrokinetics, electro-demulsification, electrodialysis, and the Fenton process; their rational application promotes the reuse of different chemical and biological compounds to eventually supply some economic sectors with raw materials in a sustainable manner, solve the problem of pollution in the environment, and generate power at the same time. Of particular and emerging interest is the valorization of iron wastes, which serves to obtain low-cost catalysts for wastewater treatment processes. Additionally, the correct characterization of the chemical composition of wastes and determination of their final use allows better results and less time to valorize any wastes considered.

Tailoring high ductility cementitious composite incorporating recycled fine aggregate based on shrinkage and mechanical properties

High ductility cementitious composite (HDCC) is recognized as an ideal structural bonding and repair material due to multiple steady-state cracking and strain-hardening properties. However， higher shrinkage strains and low economic and environmental friendliness limit its wide application. To promote the application of HDCC, recycled high ductility cementitious composite (R-HDCC) was prepared by using recycled fine aggregate (RFA) to replace natural fine aggregate (NFA), and the effects of RFA substitution rate and fly ash content on the mechanical and shrinkage properties of R-HDCC were thoroughly investigated. The results showed that the compressive strength of R-HDCC gradually decreased with the increase of RFA substitution, but its tensile strain was enhanced. R-HDCC, with 100 % RFA substitution, still maintained a tensile strength of 2.66 MPa and a tensile strain capacity of 2.46 %. The high fly ash content improved the matrix ductility, resulting in a 54.19 % increase in tensile strain over natural HDCC. In addition, the incorporation of RFA and fly ash reduced the autogenous shrinkage of R-HDCC due to the internal curing effect, but the total drying shrinkage of the matrix increased with increasing RFA substitution rate. R100-70 showed optimal environmental benefits and engineering application value through environmental impact assessment and economic analysis. Finally, this paper is expected to guide the design of ecological, economical, and high-performance R-HDCC.

Strength reinforcement of coal fly ash based non-sintered lightweight aggregates by autoclave curing and H2O2-modified basalt fiber addition

Coal fly ash, an industrial solid waste, occupies land and pollutes the environment in long-term stockpiling. Utilization of coal fly ash to produce non-sintered lightweight aggregates is a simple and cheap process with low energy consumption. However, it is still a challenge to produce coal fly ash based non-sintered lightweight aggregates with high mechanical and physical properties. In this work, high strength coal fly ash based non-sintered lightweight aggregates with low initial Ca/Si ratio were produced by autoclave curing and 1 h H2O2-modified basalt fiber addition. The cylinder compressive strength, 1 h water absorption, the bulk density and apparent density of the produced aggregates are 15.52 MPa, 4.85 %, 1089.83 kg/m3 and 1762.43 kg/m3 respectively. By analyzing the phase composition, microstructure and pore structure of the produced aggregates by XRD, SEM, FT-IR and MIP, it suggested that honeycomb-like C-A-S-H gel was formed and filled the pores in the aggregate matrix. Shown in the 3D profiles, a highly rough surface was formed on the basalt fiber after 1 h H2O2-modification. The rough surface provided as anchoring points for the interaction between the aggregate matrix and the fiber. Autoclave curing and basalt fiber modification synergistically improved the mechanical and physical properties of coal fly ash based non-sintered lightweight aggregates through “chemical filling-physical occupancy”.

Leadership feedback reduction: Are high flyers flying in the dark?

Leadership feedback reduction: Are high flyers flying in the dark?

The Influence of Recycled Coarse Aggregate Content on the Properties of High-Fly-Ash Self-Compacting Concrete

In Vietnam, solid waste from construction activities significantly impacts environmental pollution. Recycled concrete aggregate (RCA), derived from waste concrete, can serve as a coarse aggregate in concrete production. However, compared to natural aggregates, RCA exhibits distinct characteristics, including lower strength, higher water absorption, and an increased angular and rough surface. These properties may influence concrete’s workability, compressive strength, and durability. This research investigates the influence of RCA on the properties of High-Fly-Ash Self-Compacting Concrete (SCC). The study explores various replacement levels of natural coarse aggregate with RCA (0%, 50%, 75%, and 100%), alongside a 50% volume fraction of fly ash. Key concrete properties evaluated include workability, compressive strength, flexural strength, and chloride ion permeability. The findings reveal that using 100% RCA in combination with a high fly ash content (50%) produces SCC that meets workability requirements according to EFNARC standards. However, there are trade-offs: the compressive strength decreases by 4.61%, the flexural strength decreases by 3.1%, and chloride ion permeability increases by 57.57% compared to the control sample (using natural aggregates). Notably, the chloride ion permeability of SCC using 100% RCA falls into the category of low permeability. Doi: 10.28991/CEJ-SP2024-010-04 Full Text: PDF

Development of hydration temperatures on cement pastes

This article deals with the possible combination of high temperature fly ash with fluidised bed fly ash. The main objective of the experiment is to verify the effect of the combination of these two energy by-products on simpler systems – cement pastes. In the experimental part, the evolution of hydration temperatures and the time course of volume changes were monitored. The results obtained indicate that the addition of fluid fly ash to the mixture intensifies the hydration reaction, despite the increase in the value of the water to cement ratio of the mixture. At the same time, there is a slight increase in volume changes, which can be considered as a very valuable contribution to technical practice, taking into account possible ecological or economic aspects.

Utilization of high fly ash dosage to reduce cement consumption in concrete formulations

The concrete production is responsible for high proportion of total carbon dioxide emission due to enormous consumption of Portland cement. This traditional binder system is due to high autogenous emission during calcination the main carrier of such negative environmental impact. The effective way to reduce the use of Portland cement is to replace that this binding material exhibiting lower energy demandingness. This paper deals with the utilization of fly ash as Portland cement replacement, which is frequently applied in concrete industry. The paper deals the highest replacement level in accordance with valid regulations. The experimental program was focused on the properties of fresh concrete mixture and basic physical and mechanical properties of hardened concrete. The attained results confirmed good potential of this approach, however the increase of plasticizer dosage was necessary to maintain a similar consistency of fresh mixture. That is why the fresh mixture exhibited lower level of air content.

Utilization of waste high calcium oxide fly ash as hybrid activator for vulcanization of natural rubber/carbon black composites: Reducing zinc oxide requirement

A high calcium oxide fly ash (FA), a by-product waste of electric power generation has been used as hybrid activator in natural rubber (NR) composites filled with carbon black (CB). The aim of using FA is to reduce the environmental contamination by zinc oxide (ZnO) needed as activator for sulfur-vulcanization/crosslinking in final NR products. The FA was varied by adding in the composites with and without ZnO, and it was observed that chemical crosslinking could be generated although no ZnO was used anymore. The synergistic FA/ZnO-blend with FA 9 phr and ZnO 3 phr presented the best fit for the NR/CB composites, where it showed a proper crosslink density, reinforcement efficiency, cure characteristics, and mechanical properties in terms of modulus, tensile strength, elongation at break and tear resistance. This relates to the inorganic composition of the FA, in particular calcium oxide (CaO), which induces the thermal conductivity throughout the NR matrix and activates crosslinking between the NR molecules. The results showed effective use of FA in the composites, which can be applied to the CB-based formulations used in commercial NR applications like tires, barriers, and elastic stopper.

Bond Model for High Calcium Fly Ash Geopolymer Concrete

Concrete industries and researchers have devoted great efforts to promoting sustainability in the construction sector. This includes finding innovative alternatives to OPC concrete to ensure environmental sustainability and prevent the depletion of natural resources. The present research explained the steps to develop a bond stress-slip model for high calcium fly ash (HCFA) geopolymer concrete based on the experimental results in the literature. This model is based on the concrete compressive strength (fc), concrete cover (Cc), and bar diameter (db), which are considered the most influential parameters on the bond response between the reinforcement and surrounding concrete. The regressed model shows a quite accurate prediction of the bond behaviour of HCFA, particularly those with high strength. The slight difference was attributed to the difficulty in identifying the exact values of Slips (δr1 and δr2).

Sodium sulfate and magnesium sulfate resistances of mortar with multi-binder systems of calcined kaolinite clay, fly ash, and limestone powder

This study aimed to assess the durability of mortars subjected to sulfate solutions (specifically Na2SO4 and MgSO4). The effectiveness of cement replacement materials (CRMs) such as calcined kaolinite clay (C), high CaO fly ash (F), and limestone powder (L) in multi-binder systems was studied. The pastes’ microstructure, phase assemblage, and elemental profiles were examined. The results showed that mortars containing calcined kaolinite clay and high CaO fly ash (C30F15) had the lowest expansion when exposed to Na2SO4 and MgSO4. This was caused by the decreased portlandite and expansive products, improved mortar’s compressive strength, and refined pore structure (smallest pore size and lowest pore volume). However, the use of the CRMs, especially when calcined kaolinite clay was combined with fly ash or limestone powder, raised the weight loss and surface deterioration of mortars in a MgSO4 solution because of the lowered pH in the pore solution and formation of MSH.