Carbon fiber reinforced composites from industrial waste for microwave absorption and electromagnetic interference shielding applications

Lightweight materials with hybrid microstructures are getting great attention in the area of electromagnetic wave absorption. In the present study, carbon fiber and fly ash reinforced composites are prepared by mixing them with ground granulated blast furnace slag, followed by compaction and sintering at 1000 °C under an argon atmosphere. Akermanite-gehlenite was observed to be the primary crystalline phase present in the prepared samples. Porous composites are obtained with the addition of fly ash and carbon fiber as they inhibit densification. The resultant microstructure has homogeneous carbon fiber dispersion and uniform fly ash anchoring on the matrix phase. This enhanced interface polarization, defect polarization, electron transportation, and impedance matching characteristics of the composites. Hence, the developed composites' microwave absorption and electromagnetic interference shielding properties exhibited an outstanding performance at low thickness with a reflection loss value of ?41.24 dB and total shielding effectiveness of 42.29 dB at the X-band.     

PVA纤维类型对应变硬化地聚合物基复合材料力学性能的影响

本文对比分析了4种不同聚乙烯醇(PVA)纤维分别在不同配合比地聚合物基体中的增韧作用,为利用国产无表面涂油PVA纤维制备应变硬化地聚合物基复合材料(SHGC)提供实验数据。主要研究矿渣与粉煤灰的比例、碱溶液的浓度、纤维尺寸以及纤维表面特性等因素对地聚合物基复合材料抗压和直接拉伸性能的影响。结果表明,经过7 d室温养护,含矿渣的地聚合物基体和复合材料的抗压强度均高于30 MPa,而纯粉煤灰地聚合物基体和复合材料的抗压强度较低,为12~15 MPa。表面涂油PVA纤维SHGC的延展性普遍高于无表面涂油PVA纤维SHGC。然而,通过调节地聚合物基体配合比,可以提高无表面涂油PVA纤维的增韧效果。当粉煤灰质量分数为33%时,无表面涂油PVA纤维SHGC的极限拉伸应变达1.44%,与表面涂油PVA纤维SHGC相当。在纯粉煤灰的情况,4种PVA纤维复合材料均呈现出稳定的多缝开裂和应变硬化特征。     

粉煤灰对PVA纤维/水泥基体界面作用及复合材料拉伸性能的影响

本文研究了粉煤灰掺量对基体强度、聚乙烯醇(PVA)纤维/水泥基体间界面作用以及无表面修饰PVA纤维应变硬化水泥基复合材料(SHCC)拉伸性能的影响。结果表明,随着粉煤灰掺量的增加,基体的28 d抗压强度在18~93 MPa内呈下降趋势。单轴拉伸试验结果表明,掺入20%(质量分数,下同)和50%粉煤灰对SHCC的影响不明显,随着粉煤灰掺量增至67%和80%,SHCC的多微缝开裂和应变硬化特征呈增强趋势,极限应变值也相应增大,最高达7.2%,并且具有轻质特性。单纤维拔出试验结果显示,高掺量粉煤灰不仅可以降低PVA纤维与基体间的化学黏结作用,还能减弱界面摩擦作用,从而有效抑制了PVA纤维在拔出过程中出现过早断裂,显著提高了无表面修饰PVA纤维SHCC的延展性。     

Improving compressive strength of fly ash-based geopolymer composites by basalt fibers addition

In this study, ASTM Class C fly ash used as an alumino-silicate source was activated by metal alkali and cured at low temperature. Basalt fibers which have excellent physical and mechanical properties were added to fly ash-based geopolymers for 10–30% solid content to act as a reinforced material, and its influence on the compressive strength of geopolymer composites has been investigated. XRD study of synthesized geopolymers showed an amorphous phase of geopolymeric gel in the 2θ region of 23°–38° including calcium-silicate-hydrate (C-S-H) phase, some crystalline phases of magnesioferrite, and un-reacted quartz. The microstructure investigation illustrated fly ash particles and basalt fibers were embedded in a dense alumino-silicate matrix, though there was some un-reacted phase occurred. The compressive strength of fly ash-based geopolymer matrix without basalt fibers added samples aged 28 days was 35 MPa which significantly increased 37% when the 10 wt%. basalt fibers were added. However, the addition of basalt fibers from 15 to 30 wt% has not shown a major improvement in compressive strength. In addition, it was found that the compressive strength was strong relevant to the Ca/Si ratio and the C-S-H phase in the geopolymer matrix as high compressive strength was found in the samples with high Ca/Si ratio. It is suggested that basalt fibers are one of the potential candidates as reinforcements for geopolymer composites development.     

Microstructure,dielectric and piezoelectric properties of 0–3 lead free barium zirconate titanate ceramic-Portland fly ash cement composites

Piezoelectric ceramic – Portland cement composites have been developed for sensor application in concrete structures to overcome the acoustic matching problem that may occur for piezoelectric ceramic or polymers with concrete. Pozzolanic materials such as fly ash are commonly used in concrete to enhance durability. The objectives of this research were to investigate the effects of fly ash addition on the physical properties, dielectric properties and piezoelectric properties of 0–3 barium zirconate titanate ceramic– Portland cement composites. The results showed that the dielectric constant of these composites decreased when the fly ash content in the composite increases. However, the piezoelectric coefficient (d₃₃) value of BZT–PC composite with fly ash 10% by volume was found to be similar to that of BZT–PC composites.     

玄武岩纤维增强粉煤灰水泥浆体的耐久性及缺陷分析

采用环境扫描电镜和能谱仪表征了玄武岩纤维的耐酸碱腐蚀性能。通过玄武岩纤维的抗弯增强效果和相对动弹性模量的变化情况评定了玄武岩纤维在水泥基体中的耐久性。用XCT（X-ray computed tomography）研究了玄武岩纤维对掺或不掺粉煤灰的水泥浆体内部缺陷的尺寸与分布的影响。结果表明：玄武岩纤维的耐酸腐蚀性能优于耐碱腐蚀性能;粉煤灰的掺入能显著提高玄武岩纤维增强水泥的后期抗折强度提高率和相对动弹性模量增长速率;粉煤灰和玄武岩纤维的掺入均使基体内部总的缺陷体积分数增大,但粉煤灰掺入玄武岩纤维水泥浆体明显降低了尺寸在0.007～0.01mm3内的缺陷数量。     

Properties of high-volume fly ash concrete incorporating nano-SiO2

This paper presents a laboratory study on the properties of high-volume fly ash high-strength concrete incorporating nano-SiO₂ (SHFAC). The results were compared with those of control Portland cement concrete (PCC) and of high-volume fly ash high-strength concrete (HFAC). Assessments of these concrete mixes were based on short- and long-term performance. These included compressive strength and pore size distribution. Significant strength increases of SHFAC compared to the high-volume fly ash high-strength were observed as early as after 3 days curing, and improvements in the pore size distribution of SHFAC were also observed. In this work, the hydration heat of nano-SiO₂ fly ash cement systems was also studied in comparison to the fly ash-cement systems and to the pure cement systems. In addition, the weight change of fly ash incorporating nano-SiO₂, fly ash, and nano-SiO₂ alone after immersed in saturated lime solution was also studied.     

Hybridization effect of basalt and carbon fibers on impact and flexural properties of phenolic composites

In this study, the impact and flexural properties of woven basalt fiber/phenolic (BFP), woven carbon fiber/phenolic (CFP) and woven basalt/woven carbon hybrid phenolic (BCFP) composites are investigated. The hybridization effect of woven basalt and woven carbon fibers on the impact energy absorption and flexural properties is investigated for various weight ratios of basalt/carbon hybrid fibers such as 1:0, 0.83:0.17, 0.68:0.32, 0.61:0.39, 0.34:0.66 and 0:1. It is found that the impact properties of the composites are strongly improved when the basalt fiber increased. Impact energy absorption of CFP composite showed a regular trend of increase with increasing weight ratio of basalt fiber in hybrid fiber composite. The lowest impact energy absorption values are found for the composites with weight ratio 0:1 (CFP), with average of 70 kJ/m². Corresponding values for energy absorptions are obtained for 0.83:0.17, 0.68:0.32, 0.61:0.39, 0.34:0.66 basalt/carbon weight ratio in hybrid composites. The impact energy absorption of hybrid composites (BCFP) shows the highest value with an average of 219 kJ/m², when the weight ratio of 0.83:0.17 is used. Finally, the impact energy absorption of BFP composites with the weight ratio of 1:0 shows the highest value of 268 kJ/m². The experimental evidence shows that the hybrid composites based on combinations of stiff carbon fibers and tough basalt fibers have good flexural properties and therefore, they can be used as promising materials in a number of engineering sectors such as the protective structures.     

Utilization of rice husk ash in green natural fiber-reinforced cement composites: Mitigating degradation of sisal fiber

This study aims to explore a novel approach to improve the durability of sisal fiber in cement composites by using by-products of biomass power plant: rice husk ash (RHA). The effects of two RHAs on the fiber's degradation were investigated indirectly by testing flexural behavior of sisal fiber-cement composite beams and directly by means of uniaxial tensile properties, thermal decomposition, crystallinity indices and microstructures of embedded fibers, after exploring up to 30 wetting and drying cycles. Allowing the distinction between pozzolanic activities, the efficiency of RHA was compared with two fly ashes and combinations of two clay minerals (metakaolin and nanoclay) with a cement substitution level of 30 wt.%. The durability of composites was improved considerably by incorporating RHA owing to the mitigation of fiber's degradation: the ultimate tensile strength and cellulose fraction of embedded fibers were improved by 384% and 45%, respectively. Fine RHA and the combination of metakaolin and nanoclay yield similar efficiency in mitigating degradation of sisal fiber, and are better than the coarse RHA and fly ashes. The correlations between cement hydration and sisal fiber degradation were analyzed. The results indicate that degree of hydration, calcium hydroxide content and alkalinity of the cement matrix play decisive roles in alkali attacks and mineralization of fiber's cell walls.     

Mechanical characterization of lightweight engineered geopolymer composites exposed to elevated temperatures

In this study, the effect of different factors, such as PVA fibers (2% by total volume) and precursor type (slag, fly ash, or a combination of both), on the behavior of green lightweight engineered geopolymer composites (LEGC) and lightweight engineered cementitious composites (LECC) after exposure to temperatures up to 800 °C for 1 h is investigated. Expanded glass granules were used as lightweight aggregate instead of silica sand to reduce the spalling tendency and density of the composite. The flowability, density, color change, mass loss, spalling resistance, residual mechanical properties (compressive strength, stress-strain diagram, tensile stress-strain diagram, load-deflection response, failure mode), and microstructural analysis (by scanning electron microscopy) were investigated before and after exposure to thermal deterioration. The findings pointed out that the dry density, compressive strength, fiber bridging stress, strain capacity, maximum load, and maximum deflection of the developed mixtures before exposure to fire deterioration were in the range of 1703–1883 kg/m³, 16.66–64.11 MPa, 2.66–4.97 MPa, 2.40–3.33%, 1573–4824 N, and 2.92–5.53 mm respectively. It's worth mentioning that the substitution of 50% slag in the lightweight EGC mixture demonstrated the optimal tensile strain capacity and deformation capacity and further enhanced both ultimate tensile strength and flexural strength of fly ash-based EGC (FA-EGC) mixtures. After heat exposure, both LEGC and LECC composites demonstrated strain hardening behavior and deflection hardening behavior up to 300 °C of heat treatment, while after exposure to a temperature of 300 °C and above, both deflection hardening behavior and strain hardening behavior are dramatically damaged. This is attributable to the melting of the PVA fibers. Also, the microstructural analysis showed that incorporating fly ash into lightweight EGC mixtures can effectively reduce the melting point of PVA fibers and further improve the fire resistance of EGC mixtures.     

Thermal,mechanical, and surface properties of poly(vinyl alcohol) (PVA) polymer modified cementitious composites for sustainable development

This study aimed to investigate the effect of poly(vinyl alcohol) (PVA) polymer on the thermal, mechanical, and surface properties on cementitious composites for sustainable development. Thermal properties of the PVA‐modified cement paste, including thermal insulation and energy absorption ability, were first studied and correlated with the porosity and microstructures. The experimental results indicated that the thermal conductivity of cement paste can be greatly reduced by 42.9% with 2.0 wt % addition of PVA due to the more porous structure. However, at the same time, more thermal energy can be captured and concentrated at the surface of cement paste with the increasing amount of PVA, causing an increased thermal load and a negative effect on thermal insulating efficiency of cement paste. The contradictory effect of PVA on thermal properties of cement paste should be balanced before it is used as a foaming modifier to fabricate cementitious composites with thermal insulation. In addition, the contact angle measurement revealed that PVA can be used as an effective additive to improve the hydrophobicity of cement‐based materials. Only 3.0% PVA can turn the surface nature from hydrophilicity to hydrophobicity for cement paste, which benefited to the development of self‐cleaning cementitious composites. Finally, the mechanical properties of the PVA‐modified cement paste, especially for the tensile strength that has been rarely reported, were investigated and correlated with its thermal and surface properties. Due to the compensative effects of irregular packing, formation of PVA films and microcracks, tensile strength of cement paste can be improved by 23.5% with a small scarifying of the compressive strength by adding 2.0% of PVA. In conclusion, the PVA‐modified cement‐based materials with lower thermal conductivity, hydrophobic surface nature and enhanced mechanical properties have a great potential to satisfy the high requirements in developing sustainable infrastructure. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46177.     

Influence of tragacanth resin on the thermal and mechanical properties of fly ash-cement composites

This study was aimed to search the possibility of usage of the thermal power plants fly ashes, cement and tragacanth composites in concrete or plaster by investigating their thermal insulation characteristics. The fly ash used in the experiments is supplied from Af?in Elbistan Thermal Power Station. Portland cement (KPC 325) with resin is used as binding and 24 specimens are prepared depending on the percentage of fly ash and tragacanth. In all fly ash, tragacanth and binding mixture, the weight percentages of fly ash are taken as 0, 10, 20, 30, 40 and 50%. The amount of the resin in the mixture is 0.5, 1 and 1.5% of the weight of the total cement and fly ash.

24 samples were prepared and tested to find out the effects of resin on thermal and mechanical properties of fly ash and cement composites. Whereas fly ash percentage increased from 0% to 50%, i) thermal conductivity and compressive strength decreased 19.37–28.62% and 7.66–16.55% respectively as the porosities of the samples increased 18.91–28.62% with the effect of artificial pores generated by 1.5% resin other than the pores generated by fly ash. ii) the new produced samples can be used as partition walls, floorings, ceiling concretes, briquettes or bricks and plaster.     

Dielectric regulation of high-graphitized fine ash wrapped cube-like ZnSnO3 composites with boosted microwave absorption performance

Intrinsic dielectric properties and tuning conductivity play important roles in microwave absorption. Novel multi-interfaced ZnSnO₃@ fine ash (ZSFA) composite was successfully synthesized by coating cube-like ZnSnO₃ particles with highly graphitized gasification fine ash. After hydrothermal reaction and Ostwald ripening process, fine ash was tightly wrapped around the assembly of ZnSnO₃ particles. Related electromagnetic parameters and dielectric dissipation ability were discussed with different mass additions. Owing to the strong polarization relaxation, special conductive network, and multi-interface structural design, the as-synthesized ZSFA exhibited adjustable dielectric loss behaviors and efficient microwave absorption ability. When 50% mass added, the maximum reflection loss value of the obtained ZSFA-2 is ?47.8 dB at 2.5 mm thickness, showing the enhanced dielectric loss ability. Meanwhile, the widest effective absorption bandwidth (RL ≤ ?10 dB) can cover 7.0 GHz (11.0–18.0 GHz) at a thickness of only 2.2 mm, which included the entire Ku band. This unique pure dielectric composite exhibited high-performance electromagnetic wave attenuation property and broadband frequency response, thereby providing a new approach to the production of a superior microwave absorber.     

Properties of concrete incorporating high volumes of class F fly ash and san fibers

The results of an experimental investigation to study the effects of replacement of cement (by mass) with three percentages of fly ash and the effects of addition of natural san fibers on the slump, Vebe time, compressive strength, splitting tensile strength, flexural strength and impact strength of fly ash concrete are presented. San fibers belong to the category of “natural bast fibers.” It is also known as “sunn hemp.” Its scientific (botanical) name is Crotalaria juncea. It is mostly grown in the Indian subcontinent, Brazil, eastern and southern Africa and some parts of the United States (Hawaii and Florida). A control mixture of proportions 1:1.4:2.19 with W/Cm of 0.47 and superplasticizer/cementitious ratio of 0.015 was designed. Cement was replaced with three percentages (35%, 45% and 55%) of class F fly ash. Three percentages of san fibers (0.25%, 0.50% and 0.75%) having 25-mm length were used.The test results indicated that the replacement of cement with fly ash increased the workability (slump and Vebe time), decreased compressive strength, splitting tensile strength and flexural strength and had no significant effect on the impact strength of plain (control) concrete. Addition of san fibers reduced the workability, did not significantly affect the compressive strength, increased the splitting tensile strength and flexural strength and tremendously enhanced the impact strength of fly ash concrete as the percentage of fibers increased.     

Fabrication of High Performance Fly Ash/Mica/Poly(ether-ether-ketone) Hybrid Composites

This paper deals with the preparation and characterization of poly(ether-ether-ketone) (PEEK) fly ash mica hybrid composites containing filler 5:15, 10:10 and 15:5 fly ash mica combinations loading. The performances and properties of the resulting 20 wt% loading of fly ash mica/PEEK hybrid composites were examined. The resulting hybrid composites of 20 wt% fly ash and mica with varying combinations exhibit the optimum improvement of mechanical properties and dielectric strength. MDSC showed the decrease in the crystallization temperature (Tc) with varying combinations of fly ash and mica. The morphology of fly ash/mica/PEEK hybrid composites was studied by SEM.     

Electromagnetic and microwave absorption properties of FeSiAl and flaky graphite filled Al2O3 composites with different FeSiAl particle size

The increasing electromagnetic interference problems have drawn much attention to microwave absorbing materials. To satisfy the needs of practical application, FeSiAl and flaky graphite filled Al₂O₃ composites were sintered by hot-pressing for microwave absorption application. The effect of FeSiAl particle size on the electromagnetic and microwave absorption properties was investigated in the X-band (8.2–12.4 GHz). The results show that the dielectric properties enhance significantly with increasing FeSiAl particle size, which is attributed to the increased interfacial polarization and conductance loss. As a result of the favorable impedance matching and appropriate electromagnetic attenuation, the reflection loss (RL) of the composites filled with 25–48 μm flaky FeSiAl achieves -15.2 dB at 10.6 GHz and the effective absorption bandwidth (RL < -10 dB) is 1.2 GHz in 10.0–11.2 GHz with a matching thickness of 1.0 mm. It indicates that FeSiAl and flaky graphite filled Al₂O₃ composites are potential candidates for thin-thickness microwave absorbing materials, and the microwave absorption properties can be enhanced by adjusting absorbent particle size.     

纳米粒子和PVA纤维增强水泥基复合材料抗裂性能研究

采用两种纳米粒子(纳米SiO2和纳米CaCO3),通过水泥基复合材料抗裂性能试验,探讨了PVA纤维和纳米粒子单掺和复掺两种情况下PVA纤维用量、纳米材料种类和用量对水泥基复合材料抗裂性能的影响.研究结果表明,在PVA纤维增强水泥基复合材料中掺入纳米SiO2,可以显著提高水泥基复合材料抗裂性能,而且在本文试验纳米粒子掺量范围内,水泥基复合材料抗裂性能随着纳米SiO2掺量的增加不断增强;在纳米SiO2水泥基复合材料中掺入PVA纤维,可以提高水泥基复合材料的抗裂性能,当纤维体积掺量不大于1.2%时,PVA纤维体积掺量较大的纳米水泥基复合材料具有较高的抗裂性能;纳米CaCO3与纳米SiO2均能增强水泥基复合材料的抗裂性能,纳米SiO2的增强效果略优于纳米CaCO3.     

Effect of filler–fiber interactions on compressive strength of fly ash and short‐fiber epoxy composites

Compressive properties of epoxy composites reinforced with fly ash and fibers, which have differing aspect ratios, are studied. Retention of strength and modulus are observed for a greater range of fiber volume fractions following fly ash introduction into the system. A slight decrease in density was also observed when fly ash content was higher, making these composites with materials of differing aspect ratio bearing reinforcement systems suitable in weight specific applications. The investigations showed that strength decrease is larger in fiber‐bearing samples compared with only ash‐bearing samples. This decrease was ascribed to the tendency of fibers to bunch. When the ash filler was introduced, this tendency of fibers to cluster appears to be reduced, resulting in increased strength and modulus. Further attempts are made to analyze these interactions of fibers and fillers through observations made on the surfaces of failed samples by scanning electron microscopy. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 836–841, 2003     

Uncured and cured state properties of fly ash filled unsaturated polyester composites

Physical properties of fly ash filled unsaturated polyester composites in both uncured and cured states have been studied with special reference to the effect of degree of loading, nature of filler surface, and surface treatment of filler. The effect of filler surface on curing and oil absorption characteristics of filler were also examined. In the uncured state, sedimentation rate test and viscosity measurement for fly ash reinforced composites were performed. For cured fly ash filled unsaturated polyester composites, tensile properties decreased with the addition of fly ash particles whereas surface treatment led to improved mechanical properties and resistance to swelling. In terms of dynamic mechanical thermal analysis, effects of both filler and surface treatment on loss factor (tan δ) were discussed. Tan δ value and damping temperature range increased to the 15% fly ash addition. The composite having 15% unsilanized fly ash was found to have the highest tan δ and damping temperature range together with maximum performance in terms of tensile properties and swelling behavior. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1128–1136, 2000     

Heat evolution of high-volume fly ash concrete

In this paper, the results of a laboratory investigation conducted with heat evolution of high-volume fly ash (HVFA) concrete are presented. Heat evolution of concrete was studied by measuring the temperature increase in concrete under adiabatic curing condition. Characteristic of heat evolution of fly ash concrete was found to be strongly dependent on the replacement level of fly ash and dosage of superplasticizer used to maintain workability. It was also found that using fly ash as cement replacement resulted in a reduction on the maximum temperature rise. Increasing the replacement level of fly ash caused lower temperature rise in concrete. Superplasticizer caused a delay in peak temperature rise time; this is taken as an indicator that high-dosage superplasticizer used in concrete caused retardation in hydration of cement. Concretes having similar ingredients showed similar peak temperature rise whether they are superplasticized or not.