Search Results (84)

In this study, syntactic composite foams were developed by incorporating cenosphere (CS) particles recovered from recycled fly ash into a one-component polyurethane (PU) foam system. During production, CS was added to the spray-applied PU foam at specific ratios, and the foaming reaction was simultaneously initiated via manual mixing. This approach minimized particle settling caused by the filler–matrix density difference and promoted a more homogeneous structure. Two types of CS, with mean sizes of approximately 70 µm and 130 µm, were incorporated at five loadings ranging from 5 wt% to 15 wt%. The resulting composites were evaluated for their acoustic, mechanical, and thermal performance. Thermal analyses revealed that CS addition increased the glass-transition temperature (Tg) by ≈12 °C and delayed the 5% mass-loss temperature (T₅%) by ≈30–35 °C compared with the neat N2 foam, confirming the stabilizing role of cenospheres. The refoaming process with manual mixing promoted finer cell diameters and thicker walls, enhancing the sound absorption coefficient (α), particularly at medium and high frequencies. Moreover, increasing the filler content improved both the sound transmission loss (STL) and compressive strength, alongside density, although further gains in α and STL were limited beyond a 10 wt% filler content. Significant enhancements in compressive strength were achieved at filler ratios above 12.5 wt%. Unlike conventional two-component PU foams, this study demonstrates a sustainable one-component PU system reinforced with recycled cenospheres that simultaneously achieves acoustic, mechanical, and thermal multifunctionality. To the best of our knowledge, this is the first report on incorporating recycled cenospheres into a one-component PU foam system, overcoming dispersion challenges of conventional two-component formulations and presenting an environmentally responsible route for developing versatile insulation materials. Full article

Nowadays, there is wide advocacy for a transition to circular economic models. Fly Ash (FA) in particular is a major by-product of coal combustion and its annual waste has reached one million tonnes. Cenospheres (CSs) are considered as possibly the most valuable element within FA. Thus, in this research, polymeric foam replication was employed to fabricate ceramic foams based on a CS matrix, for potential biomedical applications. For the fabrication of foams, four types of natural marine sponges were used as templates along with a binder agent. The specimens were sintered at 1200 °C for 1 h. The results were encouraging as the specimens obtained retained the given shape and geometry. Further research will enhance the potential of such materials for future use in biomedical engineering. Full article

This study aims to investigate the effectiveness of two machine learning methods for the prediction of the mechanical and fracture properties of Cenosphere-reinforced lightweight thermoset polyurethane composites. To evaluate the effectiveness of the models, datasets from our experimental study of composites made of five different volume fractions (0% to 40%) of Cenospheres (hollow Aluminum Silicate particles) in increments of 10% are fabricated. Experiments are conducted to determine the effect of the volume fraction of Cenospheres on Young’s modulus (both in tension and compression), percentage elongation at break, tensile strength, specific tensile strength, and fracture toughness of the composites. Two machine learning models, shallow artificial neural network (ANN) and the non-linear deep neural network (DNN), are employed to predict the above properties. A parametric study was performed for each model and optimized parameters were identified and later used to predict the properties beyond 40% volume fraction of Cenospheres. The predictions of non-linear DNN demonstrated less slope than shallow ANN and, for mass density, the non-linear DNN had unexpected predictions of increasing mass density with the addition of lighter Cenospheres. Hence, a double-hidden-layer DNN is used to predict the mass density beyond 40%, which provides the expected behavior. Full article

This paper investigates the effects of silica fume, cenosphere, fly ash, and ground slag powder on the rheological properties and mechanical strengths of self-compacting ultra-high performance concrete (UHPC). The mass ratio of each mineral admixture varies from 0% to 15%, while the water-binder ratios are set at 0.18, 0.20, and 0.22. The slump flow and plastic viscosity of fresh UHPC are measured, and the corresponding flexural and compressive strengths of UHPC cured for 3 days and 28 days are determined. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) are employed to elucidate the mechanisms underlying the observed performance changes. The results indicate that the addition of silica fume and mineral powder negatively impacts the fluidity of fresh UHPC but positively affects its plastic viscosity. Conversely, the inclusion of cenosphere and fly ash enhances the fluidity of fresh UHPC while having the opposite effect on its plastic viscosity. Increasing the water-binder ratio improves the fluidity of fresh UHPC but reduces its plastic viscosity. Mechanically, silica fume enhances the strengths of UHPC. In contrast, the cenosphere, fly ash, and mineral powder decrease the strengths of UHPC cured for 3 days but increase those cured for 28 days. UHPC containing silica fume exhibits the most compact hydration products and the lowest content of Ca(OH)₂. Full article

This study aimed to analyze the effects of PVA aqueous solution as a new foaming agent, and the production and characteristics of ultralight foam concrete using a mixed lightweight aggregate of perlite (PL) and cenosphere (CP). In addition, the application of a new high-temperature curing process was proposed to improve the foaming effect of PVA and reduce the weight of concrete. The mixing ratios (s/c) of the PVA solution and OPC were 1.0, 1.5, and 2.0, and the ratio of the PVA solution–OPC–lightweight aggregate (perlite and cenosphere) (s/(c + CP + PL)) was 0.43–1.0. As a result, an ultralight foam concrete with a dry density of less than 1.0 g/cm³, an average pore diameter of 0.1–2.3 mm, and a compressive strength of 1.5–10.5 MPa could be manufactured. From the experimental results, PVA showed sufficient usability as a foaming agent. And the new high-temperature curing process proposed in this study could be suggested as a method applicable to the expansion of pores and lightweight reduction in the manufacture of foamed concrete. The diameter of the foamed pores changed depending on the mixing ratio of CP and PL, and the diameter of the foamed pores increased as the ratio of PL increased. However, an increase in the ratio of CP improved the insulation properties. The increase in the OPC ratio increased the mechanical strength, but increased the dry density and decreased the insulation properties. Therefore, the mixing ratio of CP and PL was an important factor affecting the properties of ultralight foam concrete. From the experimental results, PVA was suggested to have sufficient potential as a new foaming agent, and the new high-temperature curing process proposed in this study is expected to be applicable to the production of foam concrete using PVA. Full article

Fabric-reinforced hybrid polymer composites are present in almost every sector of modern life, and most essential areas of research in recent years have focused on glass–carbon fabric with filler material composites. Fabric and fillers are employed in strengthening polymer composites with the aim of improving their mechanical and tribological properties. The primary objective of this investigation was to investigate thetribological and mechanical properties of unfilled and cenosphere-filled carbon–glass-reinforced polyester composite systems, utilizing two types of fabric (glass and carbon) with cenosphere filler in varying weight fractions (0, 2.5, 5, 7.5, 10, and 12.5 wt.%) for both carbon fabric and the cenosphere. The abrasive wear characteristics were evaluated using a stainlesssteel wheel abrasion tester, utilizing silica sand as the abrasive material. Tests were performed at various distances (360–1800 m) and loads (12 N and 24 N). The results show that the wear rate of carbon–glass fabric-reinforced polyester composites differs significantly, with and without cenosphere fillers. Notably, the unfilled composites exhibit the highest wear volume loss, indicating a substantial improvement in wear resistance with the addition of cenospheres. The results reveal that in carbon–glass fabric-reinforced polyester composites, specific wear rate decreases when more cenospheres are loaded. The wear rate was successfully reduced by cenospheresunder silica sand as an abrasive. Compared to unfilled composites, the mechanical properties of filled composites exhibit superior performance. These variations were explained by examining the worn-out surfaces under an SEM and correlating the features observed with the mechanical properties. Full article

This study investigates the combustion behavior of polycarbonate (PC) and polycarbonate–carbon nanotube (PC-CNT) composites in fluidized bed reactors. The primary objective was to evaluate the influence of carbon nanotubes (CNTs) on the thermal stability and combustion efficiency of PC. Simultaneous thermogravimetric and differential scanning calorimetry (TG-DSC) analyses were conducted under both air and oxygen-deficient conditions to assess decomposition temperature ranges and energetic effects. Additionally, a simultaneous TG-DSC analysis of the samples’ decomposition in a 2 vol.% O₂ atmosphere was carried out to simulate adverse combustion conditions that may occur in some combustion technologies, such as the accumulation of degraded material on the grate. Combustion experiments were performed in inert and catalytic fluidized beds, the latter incorporating Fe₂O₃-coated cenospheres to enhance catalytic activity. The results demonstrated that the presence of CNTs alters the combustion mechanism, reducing energy release in the initial degradation stage while significantly intensifying exothermic effects in subsequent stages. Under oxygen-deficient conditions, both PC and PC-CNT required higher temperatures and extended times for complete decomposition. The catalytic fluidized bed markedly improved combustion efficiency at lower temperatures, achieving up to 90% conversion at 550 °C, compared to inert beds that required 750 °C for similar efficiency. Full article

Binder jetting is the most widely implemented additive technology for the fabrication of sand molds. However, the use of furan binder-jetting technology in the production of molds for vacuum casting is hindered by the thermal destruction of the furan binder accompanied by violent gas emission that occurs during the mold heating process. This investigation explores the potential of using the molds obtained via furan binder jetting 3D printing and further impregnation in colloidal silica binder and sintering. Two distinct sands, proppant and cenosphere, were utilized in the fabrication of the mold components exhibiting different thermal properties. An examination of the structure of the initial sands and samples produced via different impregnation and sintering regimes was conducted via scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray diffractometry, thermogravimetric analysis, and micro computed tomography. Furthermore, the bending mechanical properties and linear shrinkage of the samples were determined. The experimental findings demonstrated that the specific impregnation and sintering regimes examined in this study yielded sufficient mechanical properties for the casting molds and the structure with cristobalite bridges. The mold assembly, composed of proppant and cenosphere sands-based parts, was produced, and impeller nickel-based superalloy castings were fabricated. The findings of this study demonstrate that the utilization of a furan binder-jetting technique, in conjunction with impregnation in colloidal silica binder, is a promising technology for the manufacture of high-melting-temperature alloy casting. Full article

In this study, a microencapsulated phase-change material (PCM) with an n-octadecane core and a fly ash cenosphere shell (ODE/FAC) was prepared and it was used to replace micro silica sand forming a novel kind of heat-stored engineered cementitious composite (HS-ECC). The influence of ODE/FAC content on the mechanical and thermal properties of the resulting HS-ECC was investigated. It turned out that the compressive strength, flexural strength, and tensile cracking strength of HS-ECC gradually decreased as the incorporation content of ODE/FAC increased, while the tensile strength and tensile strain capacity were enhanced. Moreover, the inclusion of ODE/FAC can obviously decrease the thermal conductivity of ECC, which indicates the elevated heat storage capacity. This work is significant because it provided new insights into the design of heat-stored ECC for synergistically improving the tensile properties and thermal energy storage performance. Full article

This study investigated the effect of non-prewetted and prewetted cenospheres (CSs) on the hydration course and physical and mechanical properties of refractory castable mixtures incorporated with nano silica (NS). The fixed amount of 0.1% of NS improves the compressive strength of the refractory castable, containing various proportions of non-prewetted and prewetted CSs (up to 25% in composition). It was found that an increase in CSs slows down the hydration of cement and the early structure formation of refractory castable mixtures. Proportionally, due to the increase in the amount of non-prewetted and prewetted CSs in the composition, the density of the samples decreases from 1875 kg/m³ to 1310 kg/m³ after firing. The amount of CSs varied from 15 to 25% in the composition, increasing compressive strength by up to 5.3% and 8.6% in the case of non-prewetted CSs and by up to 39.2% and 20.5% in the case of prewetted CSs after the drying process. Prewetting CSs provides additional internal water that facilitates cement hydration during drying, promoting the formation of stratlingite (C₂ASH₈), a key hydration product that enhances mechanical properties after firing and promotes the early formation of anorthite. The firing at 800 °C and 1100 °C temperatures decreases compressive strength to a greater extent, as more CSs are in the composition. However, prewetting of CSs leads to significantly less deterioration (up to 32%, compared to compositions with non-prewetted CSs) in the compressive strength of refractory castables. The shrinkage of the refractory castable samples after firing at 1100 °C reached 0.16% in the case of non-prewetted CSs and 0.1% in the case of prewetted CSs. Prewetted CSs in refractory castables relaxes the stresses arising during firing more efficiently and practically compensates for shrinkage processes. Full article

Global coal consumption is continuously increasing. It is still the primary fuel used in power plants. Despite policies in the European Union aimed at reducing coal consumption, there are countries in the world where coal use continues to rise (China and India are the largest consumers of coal). Coal combustion produces waste, 70% of which is fly ash. It consists mainly of SiO₂ and Al₂O₃. Fly ash also includes Fe₂O₃, TiO₂, MgO, K₂O, and CaO. This article describes various methods of using fly ash. Fly ash can be used in the cement industry, as a filler in materials, in zeolite synthesis, in cenosphere separation, in agriculture, in water purification, in road construction as an asphalt filler, and in mine backfilling. An interesting method of using fly ash as a filler in the production of rigid polyurethane foam was also described. The article concerns potential uses in accordance with the principles of a Circular Economy. The environmental, energy, and material aspects are discussed. Full article

The aim of the presented research was to evaluate the impacts of modifications to the technical properties of fly ash-based geopolymer composites, particularly focusing on enhancing the thermal insulation. Through the utilization of a generalized utility function, optimal dosages of additives such as perlite sand, waste perlite powder, and cenospheres were determined. The study aimed to increase the thermal insulation of the composites while maintaining satisfactory compressive and flexural strength. The results indicated that dosages of perlite dust and cenospheres significantly influenced the technical characteristics of the composites; an exception was the flexural strength, for which these modifications did not show a statistically significant effect. The average compressive strength values, except for the mixes with poor workability, were at least 3.5 MPa (RILEM class II). Notably, a balanced dosage of additives, around 75 kg per cubic meter of the mixture in the total mixture, yielded the most favorable outcomes in terms of thermal isolation (0.18–0.24 W/(m·K) and workability (cone immersion 40–70 mm). Additionally, perlite dust emerged as a potentially superior modifier due to its waste origin. However, further analysis considering life cycle parameters including the carbon footprint and water footprint would be necessary to validate this claim. Overall, the study highlights the potential of utilizing perlite-based modifiers to enhance the thermal insulation of geopolymers while addressing environmental concerns. Full article

Noise is a concern in industries like aviation. Existing acoustic materials have limitations in terms of effective broadband sound attenuation and operating conditions. This work addresses these limitations by designing and developing a noise mitigation system using lightweight graded micro-porous material made from Cenospheres and high-char binder. However, Cenospheres are nearly spherical with rough surfaces, so determining the flow properties of sound propagation is challenging, and direct measurements are expensive. We developed a multivariable-fit inverse method to estimate these properties using an experimental absorption coefficient, validated first with smooth-surface glass beads and then applied to micro-porous material. The determined flow properties were used in a predictive acoustic analysis and validated experimentally. It was demonstrated that a microstructurally graded material is needed to optimize both sound absorption and transmission loss. A graded material system designed for turbofan engine acoustic liners (50 mm thick) met the target broadband sound absorption coefficient of ≥0.50 and transmission loss of ≥20 dB above 500 Hz. The study also highlights that larger particles in thicker layers enhance sound absorption, while a graded micro-structure improves overall acoustic performance. This research offers a novel approach for designing a lightweight acoustic material for aviation, marking a breakthrough in passive noise mitigation technology. Full article

With the growing global concerns regarding sustainable development in the building and construction industries, concentration only on the engineering properties of building materials can no longer meet the requirements. Although some studies have been implemented based on the lifecycle assessment of lightweight cement-based materials, very few attempts have been made pertaining to multi-criteria optimization, especially when fly ash cenospheres are used as lightweight aggregates and nano additives are incorporated as modifying admixtures. This investigation utilized cenospheres as fine aggregates to produce green, sustainable, lightweight cement mortar. Multi-walled carbon nanotubes at 0.05, 0.15, and 0.45% were binarily added, together with 0.2, 0.6, and 1.0% of nano silica to improve the mechanical performance. Strength tests were conducted to measure the flexural and compressive behaviors, combined with a cradle-to-gate lifecycle assessment and direct cost analysis to assess the environmental and economic viability. Integrated indexes and the TOPSIS method were adopted to systematically evaluate the mortar mixes and determine the optimal mix. The outcomes show that nano additives worked synergically to enhance the mechanical properties of the mortars. The utilization of cenospheres effectively reduced environmental impacts and improved economic feasibility. Nano additives significantly affected the sustainability and economic viability; in particular, the utilization of multi-walled carbon nanotubes increased the material costs. To minimize the impact of the price of multi-walled carbon nanotubes, it is proposed to binarily use less expensive nano silica. In the multi-parameter optimization, the mix with 0.05% multi-walled carbon nanotubes and 0.02% nano silica was recommended to be the optimal mix. Full article

The current research focuses on the analysis of fly ash cenospheres (FACs), a waste generated in coal-fired power plants, and the possibilities of using them in refractory castables. Cenospheres are micro-scale (~50–400 µm) spherical structures derived from fly ash, predominantly composed of silica and alumina oxides (86.7%). Their distinctive morphology and characteristics make them highly advantageous for a diverse array of applications, notably as lightweight fillers and nondegradable pore-forming agents. Furthermore, cenospheres have the potential to contribute significantly to the performance of refractory castables when incorporated into compositions with calcium aluminate cement (CAC). FAC XRD analysis revealed that FACs mainly consist of mullite along with cristobalite, which forms at higher temperatures. Furthermore, the study examined the impact of FACs on the properties of medium cement castable (MCC), especially durability, when 3%, 5%, and 7% of fine fireclay were replaced by FACs; 5% of FACs were found to reduce the density of refractory castables and decrease the cold crushing strength by approximately 6%, but it increased the resistance to thermal shock by approximately 75% and 43%, depending on the thermal treatment temperature, 950 °C and 1100 °C, respectively, and improved resistance to alkali corrosion. A higher FAC content (7%) does not have any positive effect on the MCC properties tested. Full article