Influence of steel and PP fibers on mechanical and microstructural properties of fly ash-GGBFS based geopolymer composites

In this study, experimental investigations were carried out to estimate the mechanical and microstructural properties of polypropylene (PP) and steel fiber reinforced geopolymer mortar. Two industrial by-products are used as binders to produce the geopolymer composites, i.e., fly ash (FA) and ground granulated blast furnace slag (GGBFS). Different percentages of PP and steel fibers are used in geopolymer mortars to find the mechanical properties such as compressive, splitting tensile and flexural strengths were investigated to understand the strength behavior. However, the compressive elastic modulus values were estimated through the proposed equation based on the compressive strength of the fiber reinforced geopolymer composite samples. Moreover, to understand the geopolymeic reaction, microstructural studies, i.e., scanning electron microscopy (SEM), were conducted. The experimental results revealed that the addition of PP fibers up to 2.0% (volume fraction) enhanced the flexural properties of geopolymer mortar samples. The compressive strength of the steel fiber-reinforced geopolymer composite reached a maximum of 2.5% volume fraction, being a 13.26% improvement over the control mix. The flexural toughness index of the PP and steel fiber reinforced composites improved with increasing the fraction. However, steel fiber reinforced geopolymer samples are shown better flexural toughness compared to PP fibers. The SEM analysis of the geopolymer control mix achieved a good degree of geopolymerization and both the fibers yielded a considerable interfacial bonding with the geopolymer paste.     

High-flexural-strength of geopolymer composites with self-assembled nanofiber networks

Natural-fiber-reinforced geopolymer composites are environmentally friendly materials that have garnered considerable attention. In practice, the drying shrinkage and uneven dispersion of fibers in geopolymers result in low flexural strength, which limits the use of large-scale composites. In this study, high-flexural strength geopolymer composites with self-assembled nanofiber networks were hybridized using in situ polymerization. Composites with different fiber contents were evaluated via morphology and mechanical strength assessments. A mixed nanofiber and geopolymer solution was created to achieve uniform dispersion, and then the geopolymers were optimized at the nanoscale level using a bottom-up approach to achieve self-assembled nanofiber networks with good interfacial bonding. Due to the water retention properties of the nanofibers and subsequent gel material, the networks facilitated internal curing of the geopolymers, thus preventing drying shrinkage. This ultimately reduced the weight loss and increased the density of the composites. In addition, high flexural strength properties were observed in composites with a fiber content of 0.5%, due to the combination of fiber reinforcement and porosity. Thus, this work introduces new considerations for geopolymer applications.     

Microstructure and mechanical properties of a metakaolinite-based geopolymer nanocomposite reinforced with carbon nanotubes

The preparation and mechanical behavior of metakaolin-based geopolymer nanocomposite reinforced with multi-walled carbon nanotubes are presented in this study. In this work, Multiwall carbon nanotubes (MWCNTs) were added to the metakaolin-based geopolymer paste at 0, 0.5, or 1 wt% concentration. For each specimen, the mechanical properties were tested at the age of 7, 14 and 28 days. TEM and FESEM were employed to evaluate the dispersion quality of MWCNTs within the metakaolin geopolymer matrix and determine their strengthening mechanism. The test results showed that the addition of about 0.5 wt% MWCNTs increased the compressive and flexural strength by as much as 32% and 28%, respectively. Based on these results, the MWCNTs can act as effective bridges to minimize and limit the propagation of micro cracks through the metakaolin-based geopolymer nanocomposite under the conditions of homogenous dispersion and good bonding between the MWCNTs and the surrounding metakaolin-based geopolymer paste.     

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.     

Reaction kinetics and mechanical properties of a mineral-micropowder/metakaolin-based geopolymer

In this study, metakaolin was partially replaced with mineral micropowder to prepare a mineral-micropowder/metakaolin-based geopolymer was prepared under alkali activation, and the compressive and flexural strengths of various geopolymer specimens were determined. Geopolymer reaction kinetics were examined using the Johnson-Mehl-Avrami-Kolmogrov model, and the effects of the mineral-micropowder content on the properties and structure of the metakaolin-based geopolymer were investigated. Results revealed that micropowder addition significantly influenced the mechanical properties, microstructure, and reaction heat of the geopolymer. At a powder content of 30 wt%, the polymer exhibited superior mechanical properties; furthermore, the compressive and flexural strengths of the specimens cured for 28 d were 58.3 MPa and 12.6 MPa, which were 24.1% and 40% higher than those of the control group, respectively. Meanwhile, the geopolymer setting time was significantly reduced because the presence of calcium in mineral micropowder promoted the geopolymerisation reaction. Therefore, the formation of a multi-gel phase considerably enhanced the geopolymer structure.     

香蕉纤维的表面改性及其增强环氧树脂复合材料的性能研究

采用硅烷偶联剂(A-174)偶联、高锰酸钾接枝和乙酰化包覆等3种方法对香蕉纤维进行表面改性,制备了改性香蕉纤维增强环氧树脂复合材料,测试其拉伸、弯曲、压缩、冲击等力学性能。结果表明,偶联、接枝、包覆等表面改性均能明显改善香蕉纤维与基体树脂的相容性,提高复合材料的力学性能,其中偶联改性的效果最好。当改性香蕉纤维含量为10wt%时,与未改性的香蕉纤维比较,复合材料的拉伸强度、弯曲强度、压缩强度分别提高了1.8、1.0、2.6倍;随着纤维含量的增加,复合材料的力学性能明显提高。     

Performance evaluation of basalt fiber-reinforced geopolymer composites with various contents of nano CaCO3

High carbon footprint of cement production is the major drawback of plain cement concrete resulting in environmental pollution. Geopolymer composites paste can be effectively used as an alternative to Portland cement in the construction industry for a sustainable environment. The demand for high-performance composites and sustainable construction is increasing day by day. Therefore, the present experimental program has endeavored to investigate the mechanical performance of basalt fiber-reinforced fly ash-based geopolymer pastes with various contents of nano CaCO₃. The content of basalt fibers was fixed at 2% by weight for all specimens while the studied contents of nano CaCO₃ were 0%, 1%, 2%, and 3%, respectively. The compressive strength, compressive stress-strain response, flexural strength, bending stress-strain response, elastic modulus, toughness modulus, toughness indices, fracture toughness, impact strength, hardness, and microstructural analysis of all four geopolymer composite pastes with varying contents of nano CaCO₃ using scanning electron microscopy (SEM) were evaluated. The results revealed that the use of 3% nano CaCO₃ in basalt fiber-reinforced geopolymer paste presented the highest values of compressive strength and hardness while the use of 2% nano CaCO₃ showed the highest values of flexural strength, impact strength, and fracture toughness of composite paste. The SEM results indicated that the addition of nano CaCO₃ improved the microstructure and provided a denser geopolymer paste by refining the interfacial zones and accelerating the geopolymerization reaction.     

In Situ Processing of Graphene/Leucite Nanocomposite Through Graphene Oxide/Geopolymer

Graphene/leucite nanocomposites (rGO/leucite) were prepared through in situ reduction of graphene oxide/geopolymer (rGO/KGP) composites. The effects of rGO on the microstructure and mechanical properties with respect to the geopolymer matrix after the high‐temperature treatment were investigated systematically. The results show that GO is first partially reduced in the geopolymeric solution and then completely under the post high‐temperature treatment. The rGO sheets undergo no interfacial reactions with the matrix even after thermal treatment. The rGO/geopolymer composites fully transform to rGO/leucite composites after being treated at 1000°C for 30 min in an argon atmosphere. Significant improvements in mechanical properties were achieved through rGO reinforcement giving flexural strength, elastic modulus, and fracture toughness of 91.1 MPa, 60.5 GPa, and 2.04 MPa·m^1/2, increased by 120%, 8%, and 1.5%, respectively, compared with the leucite matrix alone.     

Characteristics of murta bast fiber reinforced epoxy composites

The growing global concern over environment protection has led to the application of natural fiber reinforced polymer composites as alternative materials in manufacturing sectors. Various natural fibers are therefore being explored for reinforcement of polymer matrices. In the present work, murta bast fibers of varying length and weight percent are mixed randomly with the epoxy matrix and the composites are prepared from these mixtures by using the hand lay‐up method. The composites are characterized on the basis of density, thermal gravimetric analysis, infrared spectroscopy, scanning electron microscopy, tensile strength, flexural strength, compressive strength, impact strength, and Rockwell hardness studies. Tensile, flexural, and compressive moduli of the composites are also determined. The tensile strength of the composite was analyzed in the light of the different analytical models. Composites containing 30 weight % fibers of length 25 or 35 mm have the optimum mechanical properties. Murta bast fiber has the characteristics to become a good natural material for reinforcement. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44142.     

Low-energy impact behavior of ambient cured engineered geopolymer composites

Engineered geopolymer composite (EGC) is a new kind of fiber reinforced geopolymer composite with tensile strain-hardening behaviors. This paper was intended to investigate the low-energy impact behaviors of EGC. To further reduce the carbon footprint and material cost of EGC, the feasibility of developing ambient cured EGC with cheap local PVA fiber was discussed according to the micromechanics-based analytical models. The compressive, tensile and impact tests of EGC, engineered cementitious composites (ECC), pure geopolymeric matrix and cementitious matrix were conducted and compared. It was found that the EGC specimens have similar tensile behaviors with ECC and the ultimate tensile strain of EGC can be as high as 7.5%. Under impact load, it was found that the PVA fibers could effectively restrict the crushing and spalling of geopolymeric matrix. Also, the dissipated energy of pure geopolymeric matrix is 3.8 times higher than that of cementitious matrix, indicating that it is recommendable to develop impact-resistant material based on geopolymeric matrix. The influences of NaOH molarity on the impact behaviors of EGC and geopolymeric matrix were discussed. It was found that the impact-resistance of EGC improved with the increase of NaOH molarity, while the threshold of NaOH molarity for geopolymeric matrix was recommended as 12 mol/L. Even though the compressive strength of EGC is lower than ECC, it can be concluded that EGC could have comparable or even higher impact-resistance than ECC under different low-velocity impact conditions.     

Mechanical properties and prediction of fracture parameters of geopolymer/alkali-activated mortar modified with PVA fiber and nano-SiO2

Properties of fly ash (FA) and metakaolin (MK) based geopolymer/alkali-activated mortar modified with polyvinyl alcohol (PVA) fiber and nano-SiO₂, including workability, compressive strength, flexural performance, elastic modulus and fracture property were tested in this study. PVA fiber content varies from 0 to 1.2%. Nano-SiO₂ content is 0 and 1%. Adaptive neuro-fuzzy interfacial systems (ANFIS) method was used to establish the artificial intelligence (AI) model to predict the fracture parameters of geopolymer/alkali-activated mortars. The inputs of ANFIS models include PVA fiber content, nano-SiO₂ content, compressive strength, flexural strength, elastic modulus, critical crack mouth opening displacement, crack load and peak load. The outputs of ANFIS model include critical effective crack length, initiation fracture toughness, unstable fracture toughness, and fracture energy. Experiment results showed that PVA fiber addition enhanced the mechanical properties especially the compressive strength and fracture performance, but decreased the workability. 0.8%–1.0% was considered as the optimal content of PVA fiber. Addition of 1% nano-SiO₂ shows a slight improvement on both workability and mechanical properties of the mortar no matter how much fiber is added. Based on the ANFIS algorithm and 42 sets of experimental data, the trained models were proved to have high accuracy with root mean square error (RMSE) under 0.15, mean absolute error (MAE) under 0.01, and coefficient of determination (R²) over 0.85. The ANFIS model established in this study combined the fracture properties with the basic mechanical properties of geopolymer/alkali-activated composites, which can provide a new method to assess the fracture performance of geopolymer/alkali-activated mortars modified with PVA fiber and nano-SiO₂ in the future.     

Investigation of brucite-fiber-reinforced concrete

Laboratory experiments were made on the brucite-fiber-reinforced concrete composites. Effects of brucite fiber grades and the dosage on flexural strength, compressive strength, impact strength, sulfate corrosion resistance and the slump, cohesiveness, as well as the water retentiveness were also investigated. Different water reducers were tested. The particle-size characteristics of brucite fibers, the densities of the concrete, and the viscosities of the fiber/water-reducer suspensions were also measured. Results show that proper addition of brucite fibers in concrete can improve the mechanical properties, especially the flexural strength. In the test, the optimum quantity was about 0.5 wt.% of concrete. With the dosage increase of brucite fibers in concrete, the fluidity and the density of the concrete decrease. The performance of the concrete strengths is the collective interactions of the fiber reinforcement and the density reduction. The aspect ratio and the surface area of brucite fibers are the important affecting factors to the workability and the mechanical properties of the fiber concrete. Larger aspect ratios and smaller surface areas benefit the reinforcement. Water reducers with lower fiber suspension viscosities are favorable in improving the workability and strengths of the brucite fiber concrete.     

聚甲醛纤维增强砂浆的力学性能和干燥收缩试验研究

本文研究了不同长度聚甲醛(POM)纤维单掺和混掺对砂浆流动度、抗折强度、抗压强度、弯曲韧性及干燥收缩的影响,并通过扫描电镜观测了其微观结构。研究发现,砂浆流动度随POM纤维长度和掺量增大而下降,混掺纤维比单掺对砂浆流动度的影响更小。POM纤维能有效提高砂浆的抗折强度,但掺量超过0.6%(体积分数,下同)时增强效果减弱,与未掺纤维试样相比,0.6%掺量的6 mm纤维对试样28 d抗折强度提升最高,为14.67%,抗压强度随纤维掺量增加而降低。12 mm纤维比6 mm及混掺对试样弯曲韧性提升更明显,最大提高49.43%。纤维的掺入可显著降低试样的干燥收缩率,且随纤维掺量增加,试样90 d干燥收缩率先减小后增大。与未掺纤维试样相比,0.6%掺量的6 mm纤维试样90 d干燥收缩率下降最多,为27.39%。混掺POM纤维在掺量0.6%以上时仍可显著提升砂浆的抗折强度并减小干燥收缩率。     

Preparation and mechanical characterization of chicken feather/PLA composites

Green composites, a bio‐based polymer matrix is reinforced by natural fibers, are special class of bio‐composites. Interest about green composites is continuously growing because they are environment‐friendly. This study describes the preparation and mechanical characterization of green composites using polylactic acid (PLA) matrix including chicken feather fiber (CFF) as reinforcement. Extrusion and an injection molding process were used to prepare CFF/PLA composites at a controlled temperature range. CFF/PLA composites with fiber mass content of 2%, 5%, and 10% were manufactured. The effects of fiber concentration and fiber length on mechanical properties of CFF/PLA composites have been studied. Mechanical properties of composites were investigated by tensile, compression, bending, hardness, and Izod impact testing. The results of experiments indicated that Young's modulus, compressive strength, flexural modulus, and hardness of the PLA reinforced CFF composites are higher but tensile strength, elongation at break, bending strength and impact strength of them are lower than pure PLA. The results indicate that these types of composites can be used for various applications. POLYM. COMPOS., 38:837–845, 2017. © 2015 Society of Plastics Engineers     

The Properties of Woven Kenaf and Betel Palm (Areca catechu) Reinforced Unsaturated Polyester Composites

The use of woven betel palm and kenaf lignocellulosic fibers as a reinforcing phase in unsaturated polyester was reported. The morphology, physical properties, and mechanical properties of the natural fibers and resulting woven composites were evaluated. Kenaf fibers exhibit higher tensile properties than betel palm fibers due to the higher amount of cellulose content. From the morphology observation, it is found that the alkaline treatment of the fibers effectively clean the fiber surface and increase the fiber surface roughness. Comparison between treated and untreated woven betel palm and kenaf composites at 7 vol% of fiber content was carried out. Interestingly, untreated woven kenaf composites exhibit comparable flexural strength with those of untreated woven betel palm composites. However, untreated kenaf composites exhibit superior flexural modulus to those of betel palm composites. In general, mechanical properties of the woven composites made from alkali-treated fibers were superior to the untreated fibers.     

净水功能型透水混凝土的组成设计研究

为净化雨水和补充地下水,设计了一类净水功能型偏高岭土基地聚合物透水混凝土。通过研究壳聚糖掺量、碱激发剂模数与碱当量对偏高岭土基地聚合物浆体力学、吸附特性的影响,制备了一种可用于透水混凝土的高吸附性浆体材料。基于此,进一步探讨了透水混凝土骨料堆积孔隙率、浆集比(P/A)等体积结构参数对其净水、透水与力学性能的影响。结果表明:随着壳聚糖掺量的增加,偏高岭土基地聚合物的强度呈先提高后降低的趋势,Pb²⁺的吸附量呈增大趋势;随着骨料堆积孔隙率的增大,透水混凝土的力学和净水性能均减弱,透水性增强;随着浆集比的增大,透水混凝土力学与净水性能增大,透水性减小。最终设计出净水、透水与力学性能协调的透水混凝土,其28 d抗压强度、透水系数和Pb²⁺去除率分别为20.1 MPa、0.67 cm/s和90.5%。     

SiC fiber reinforced geopolymer composites,part 1: Short SiC fiber

In this paper, short SiC fiber (SiC_sf) reinforced geopolymer composites (SiC_sf/geopolymer) were prepared and effects of fiber contents and lengths on the microstructure and mechanical properties of the composites were investigated. In-situ crack growth was carried out to study the fracture behavior and toughening mechanism of the composites. The results showed that SiC_sf/geopolymer composite developed weak interfacial bonding state through mechanical interlocking rather than chemical interfacial reaction. The presence of SiC_sf not only enhanced both flexural strength and work of fracture, but also prevented the catastrophic failure as seen in neat geopolymer. When fiber content was 2.0 vol% with length of 5 mm, the composite obtained the highest flexural strength and work of fracture, which were 5.6 and 63 times as high as those of neat geopolymer, respectively. In-situ crack growth together with fractographs showed that toughening mechanisms of the composite included formation and propagation of microcracks, crack deflection, fiber debonding and significant pulling-out.     

The Influence of the Material Structure on the Mechanical Properties of Geopolymer Composites Reinforced with Short Fibers Obtained with Additive Technologies

Additive manufacturing technologies have a lot of potential advantages for construction application, including increasing geometrical construction flexibility, reducing labor costs, and improving efficiency and safety, and they are in line with the sustainable development policy. However, the full exploitation of additive manufacturing technology for ceramic materials is currently limited. A promising solution in these ranges seems to be geopolymers reinforced by short fibers, but their application requires a better understanding of the behavior of this group of materials. The main objective of the article is to investigate the influence of the microstructure of the material on the mechanical properties of the two types of geopolymer composites (flax and carbon-reinforced) and to compare two methods of production of geopolymer composites (casting and 3D printing). As raw material for the matrix, fly ash from the Skawina coal power plant (located at: Skawina, Lesser Poland, Poland) was used. The provided research includes mechanical properties, microstructure investigations with the use of scanning electron microscope (SEM), confocal microscopy, and atomic force microscope (AFM), chemical and mineralogical (XRD-X-ray diffraction, and XRF-X-ray fluorescence), analysis of bonding in the materials (FT-IR), and nuclear magnetic resonance spectroscopy analysis (NMR). The best mechanical properties were reached for the sample made by simulating 3D printing process for the composite reinforced by flax fibers (48.7 MPa for the compressive strength and 9.4 MPa for flexural strength). The FT-IR, XRF and XRD results show similar composition of all investigated materials. NMR confirms the presence of SiO₄ and AlO₄ tetrahedrons in a three-dimensional structure that is crucial for geopolymer structure. The microscopy observations show a better coherence of the geopolymer made in additive technology to the reinforcement and equal fiber distribution for all investigated materials. The results show the samples made by the additive technology had comparable, or better, properties with those made by a traditional casting method.     

Mechanical properties of pineapple leaf fiber-reinforced polyester composites

Pineapple leaf fiber (PALF) which is rich in cellulose, relatively inexpensive, and abundantly available has the potential for polymer reinforcement. The present study investigated the tensile, flexural, and impact behavior of PALF-reinforced polyester composites as a function of fiber loading, fiber length, and fiber surface modification. The tensile strength and Young's modulus of the composites were found to increase with fiber content in accordance with the rule of mixtures. The elongation at break of the composites exhibits an increase by the introduction of fiber. The mechanical properties are optimum at a fiber length of 30 mm. The flexural stiffness and flexural strength of the composites with a 30% fiber weight fraction are 2.76 GPa and 80.2 MPa, respectively. The specific flexural stiffness of the composite is about 2.3 times greater than that of neat polyester resin. The work of fracture (impact strength) of the composite with 30% fiber content was found to be 24 kJ m⁻². Significant improvement in the tensile strength was observed for composites with silane A172-treated fibers. Scanning electron microscopic studies were carried out to understand the fiber-matrix adhesion, fiber breakage, and failure topography. The PALF polyester composites possess superior mechanical properties compared to other cellulose-based natural fiber composites. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1739–1748, 1997     

Novel eco‐friendly biodegradable coir‐polyester amide biocomposites: Fabrication and properties evaluation

Biocomposites are prepared from a cheap, renewable natural fiber, coir (coconut fiber) as reinforcement with a biodegradable polyester amide (BAK 1095) matrix. In order to have better fiber‐matrix interaction the fibers are surface modified through alkali treatment, cyanoethylation, bleaching and vinyl grafting. The effects of different fiber surface treatments and fiber amounts on the performance of resulting bio‐composites are investigated. Among all modifications, cyanoethylated coir‐BAK composites show better tensile strength (35.50 MPa) whereas 7% methyl methacrylate grafted coir‐BAK composites show significant improvement in flexural strength (87.36 MPa). The remarkable achievement of the present investigation is that a low strength coir fiber, through optimal surface modifications, on reinforcement with BAK show an encouraging level of mechanical properties. Moreover, the elongation at break of BAK polymer is considerably reduced by the incorporation of coir fibers from nearly 400% (percent elongation of pure BAK) to 16‐24% (coir‐BAK biocomposites). SEM investigations show that surface modifications improve the fiber‐matrix adhesion. From biodegradation studies we find that after 52 days of soil burial, alkali treated and bleached coir‐BAK composites show significant weight loss. More than 70% decrease in flexural strength is observed for alkali treated coir‐BAK composites after 35 days of soil burial. The loss of weight and the decrease of flexural strength of degraded composites are more or less directly related.