Mechanical properties of geopolymer concrete exposed to dynamic compression under elevated temperatures

Through adoption of a self-designed high temperature SHPB apparatus herein, an experimental study is made on the mechanical properties of geopolymer concrete (GC) exposed to dynamic compression under elevated temperatures. As the results have turned out, the weight loss is remarkable within temperature ranges from room temperature to 200 °C as well as from 600 °C to 800 °C. The dynamic compressive strength of GC grows higher at 200 °C than at room temperature, but suffers a dramatic drop at 800 °C. The critical strain is higher at elevated temperature than that at room temperature. At 200 °C and 600 °C, respectively, its energy absorption property is superior to that at room temperature. However, at 400 °C and 800 °C, respectively, it is inferior to that at room temperature. The strain rate effect of the dynamic increase factor (DIF) obtained from test data can reflect the inherent nature of GC. The DIF assumes a linear relationship with the logarithm of strain rate.     

Effects of high-temperature heat treatment on the mechanical properties of unidirectional carbon fiber reinforced geopolymer composites

Unidirectional carbon fiber reinforced geopolymer composite (C_uf/geopolymer) is prepared by a simple ultrasonic-assisted slurry infiltration method, and then heat treated at elevated temperatures. Effects of high-temperature heat treatment on the microstructure and mechanical properties of the composites are studied. Mechanical properties and fracture behavior are correlated with their microstructure evolution including fiber/matrix interface change. When the composites are heat treated in a temperature range from 1100 to 1300 °C, it is found that mechanical properties can be greatly improved. For the composite heat treated at 1100 °C, flexural strength, work of fracture and Young's modulus reach their highest values increasing by 76%, 15% and 75%, respectively, relative to their original state before heat treatment. The property improvement can be attributed to the densified and crystallized matrix, and the enhanced fiber/matrix interface bonding based on the fine-integrity of carbon fibers. In contrast, for composite heat treated at 1400 °C, the mechanical properties lower substantially and it tends to fracture in a very brittle manner owing to the seriously degraded carbon fibers together with matrix melting and crystal phases dissolve.     

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.     

SiC fiber reinforced geopolymer composites,part 2: Continuous SiC fiber

In this paper, unidirectional SiC fiber (SiC_f) reinforced geopolymer composites (SiC_f/geopolymer) were prepared and effects of fiber contents on the microstructure and mechanical properties of the composites in different directions were investigated. The XRD results showed that addition of SiC_f retarded geopolymerization process of geopolymer matrix by weakening the typical amorphous hump. SiC_f in all the composites were well infiltrated by geopolymer matrix, but microcracks which were perpendicular to the fiber axial direction were noted in the interface area due to the thermal shrinkage of matrix during the curing process. With the increases in fiber contents, although Young's modulus of the composites increased continuously, flexural strength, fracture toughness and work of fracture increased at first, reached their peak values and then decreased. And when fiber content was 20 vol%, the composites showed the highest flexural strength, fracture toughness and work of fracture, which were 14.2, 15.2 and 81.6 times as high as those of pristine geopolymer, respectively, indicating significant strengthening and toughening effects from SiC_f. Meanwhile, SiC_f/geopolymer composites failed in different failure modes in the different directions, i.e., tensile failure mode in the x direction (in-plane and perpendicular to the fiber axial direction) and shear failure mode in the z direction (laminate lay-up direction).     

Effects of fiber contents on the mechanical and microwave absorbent properties of carbon fiber felt reinforced geopolymer composites

In this paper, phosphate-based geopolymer composites are studied and the effects of different carbon fiber felt contents (from 20?vol% to 40?vol%) on the phase composition, microstructure, mechanical properties and microwave absorbent properties from 2?GHz to 18?GHz frequency band of the composites were systematically investigated. The results indicate that with the increase in carbon fiber felt contents, flexural strength and Young's modulus of the composites gradually increased. The fracture mode of the composite changed from brittle failure to ductile failure with the presence of carbon fiber felt. It was mainly due to the micropore deformation as well as fibers pulling-out and the crack deflection, which consumed most fracture energy. However, microwave absorbent performance tended to increase at first and then decreased as the carbon fiber felt content ramping up. When the content of carbon fiber felt in the composite was 26.7?vol%, the composite showed the best microwave absorbent performance and the reflection loss reached to ??59.3?dB. It is mainly attributed to the Debye polarization of the carbon fibers and the interface polarization between fibers and the matrix.     

Synthesis and mechanical properties of lightweight hybrid geopolymer foams reinforced with carbon nanotubes

A lightweight hybrid geopolymer foams reinforced with carbon nanotubes (CNTs) was exploited by adding the CNTs into geopolymeric matrix through hydrogen peroxide method. The synergistic effects of nanotubes and foaming agent on the phase evolution, microstructure, and mechanical properties were investigated. After introduction of nanotubes, the geopolymer foams reinforced with CNTs (CNTs/KGP) still showed amorphous structure. Porosity of the foams increased with the H₂O₂ content and decreased with the increase in CNTs content. The addition of CNTs (1-9 wt%) in foams refined the distribution of pore size from 523 to 352 μm. Compression strength of the CNTs/KGP samples elevated with the increasing content of CNTs, which was contributed to the crack propagation and bridging of CNTs in foams. The CNTs/KGP foams with considerable porosity show potential applications in adsorption, filtration, membrane supports, other industries, etc     

Coefficient variation of the mechanical properties of carbon fiber during carbonization

The approaches of the development for carbon fibers are how to improve their mechanical properties and to reduce the cost of the production as well as to maintain or to control the stability of their properties, i.e., the reproducibility. The coefficient variation of the mechanical properties immediately influenced the reproduction. In this paper, the effect of the operating conditions during carbonization on the coefficient variation of the properties for carbon fiber is discussed.     

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.     

高低温老化对碳纤维复合材料芯棒结构性能的影响

采用拉挤工艺制备了碳纤维增强环氧树脂基复合材料芯棒,并对其进行高低温人工加速老化试验,以及对老化前后碳纤维复合材料芯棒的横截面、外观颜色和密度进行了测试和分析。结果表明,高低温老化使芯棒颜色加深,主要对芯棒的外层产生一定的影响,内部结构没有明显变化;老化后芯棒的密度比老化前减小约2.5%,并且不同老化周期对芯棒的密度基本不变。     

Development of lightweight aggregate geopolymer concrete with shale ceramsite

This paper developed a lightweight aggregate geopolymer concrete (LAGC) with shale ceramsite. 18 groups of LAGC specimens with 3 sand ratios (30%, 40% and 50%) and 6 aggregate contents (10%, 20%, 30%, 40%, 50% and 60%) were prepared. A series of static tests (dry density test and uniaxial compression test) and dynamic tests (ultrasonic pulse velocity test) were performed to achieve the dry density, compression strength and P-wave velocity. The effects of sand ratio and aggregate content on the dry density, compression strength and P-wave velocity were discussed. Two optimal mix proportions for the LAGC were proposed. The results show that the dry density and P-wave velocity increase as sand ratio increases. The compressive strength increases then decreases as sand ratio increases. In addition, the dry density and compressive strength decrease as aggregate content increases. The P-wave velocity increases as aggregate content increases. The LAGC with the sand ratio of 30% and aggregate contents of 30% reaches the dry density of 1378.0 kg/m³ and compressive strength of 18.5 MPa. The LAGC with the sand ratio of 30% and aggregate contents of 40% reaches the dry density of 1348.0 kg/m³ and compressive strength of 16.8 MPa. Both of the proportions satisfied the engineering requirements, which are recommended for the potential application in the construction.     

Thermal and mechanical properties of fiber reinforced high performance self-consolidating concrete at elevated temperatures

This paper presents the effect of temperature on thermal and mechanical properties of self-consolidating concrete (SCC) and fiber reinforced SCC (FRSCC). For thermal properties specific heat, thermal conductivity, and thermal expansion were measured, whereas for mechanical properties compressive strength, tensile strength and elastic modulus were measured in the temperature range of 20–800 °C. Four SCC mixes, plain SCC, steel, polypropylene, and hybrid fiber reinforced SCC were considered in the test program. Data from mechanical property tests show that the presence of steel fibers enhances high temperature splitting tensile strength and elastic modulus of SCC. Also the thermal expansion of FRSCC is slightly higher than that of SCC in 20–1000 °C range. Data generated from these tests was utilized to develop simplified relations for expressing thermal and mechanical properties of SCC and FRSCC as a function of temperature.     

大丝束碳纤维复合材料力学性能研究

本文研究了大丝束碳纤维(48K)复合材料的常规力学性能及耐湿热性能，并与小丝束碳纤维(T300．3K)复合材料进行了对比，研究结果可为大丝束复合材料在航空器的次承力件或非承力件的应用提供技术基础。     

Dynamic mechanical and morphological properties of polycarbonate/multi-walled carbon nanotube composites

Dynamic mechanical and morphological properties of the polycarbonate (PC)/multi-walled carbon nanotube (MWNT) composites were studied by dynamic mechanical thermal analysis (DMTA) and X-ray diffractometry, respectively. For the without annealed PC/MWNT composites containing the higher content of the MWNT (≥7.0 wt%), double tan δ peaks were observed, which could be explained by the phase separation morphology model. For the annealed PC/MWNT composites, a broad single tan δ peak was observed. From the X-ray diffraction of the annealed PC/MWNT composites, it was observed that more regular structure of the PC was obtained, which was consistent with the result of the thermal analysis of the annealed PC/MWNT composites. From the dynamic mechanical properties, thermal analysis, and X-ray diffraction of the annealed PC/MWNT composites, it is suggested that PC/MWNT composites show a broad single tan δ peak and partially crystalline structure of the PC in the PC/MWNT composites by annealing.     

Effect of PDMS content on waterproofing and mechanical properties of geopolymer composites

The present study mainly studies the effect of polydimethylsiloxane (PDMS) content on the waterproofing and mechanical properties of geopolymer composites. Firstly, hydrophobic modified geopolymer composites (HM-GC) were prepared by adding PDMS during the mixing process. Secondly, the surface wettability characteristics, water absorption, uniaxial compressive and tensile properties of HM-GC were investigated. The effect of PDMS content on the waterproofing and mechanical properties was further discussed. Finally, considering the waterproofing and mechanical properties, the optimal PDMS content was proposed. The results showed that with increasing PDMS content, the contact angle of geopolymer composites rapidly increase at first and then stabilizes. The geopolymer composites with 4% and 5% PDMS content exhibit overhydrophobic surface wettability. In addition, the water absorption gradually decreases with increasing PDMS content, indicating an improvement in the waterproofing ability. The incorporation of PDMS can enhance the compressive properties of geopolymer composites while reducing the tensile properties. Comprehensively considering the waterproofing and mechanical properties, it is reasonable to select 4% as the optimal PDMS content used in practical marine engineering.     

PANI/PP复合纤维对沥青混凝土力学性能的影响

以聚苯胺/聚丙烯(PANI/PP)复合纤维为导电相材料,采用非连续密级配制备了PANI/PP复合导电纤维沥青混凝土,采用马歇尔试验法对沥青混凝土的力学性能进行了测试。结果表明:随着PANI/PP复合纤维掺量的增加,PANI/PP复合导电纤维沥青混凝土的稳定度、流值、空隙率均有增大趋势,复合纤维的质量掺量为0.8%时,沥青混凝土稳定度可增加近50%,流值增加100%。复合纤维的质量掺量为0.2%~0.8%时,纤维在沥青混凝土中分散均匀性好。     

Chemo-mechanical properties of carbon fiber reinforced geopolymer interphase

Geopolymers, as a potentially environmentally friendly alternative to Portland cement, are increasingly attracting attention in the construction industry. Various methods have been applied for customizing the properties of geopolymers and improving their commercial viability. One of the promising methods for refining the properties of geopolymers such as their toughness is the use of short fibers. The effectiveness of a high-strength short fiber in the geopolymer matrix is largely dependent on the interfacial bonding between the fiber and its surrounding matrix. While the importance of this interfacial chemistry is highlighted in the literature, the characteristics of this bonding structure have not been fully understood. In this paper, we aim to investigate the bonding mechanism between the carbon fiber and metakaolin-based geopolymer matrix. For the first time, the existence and nature of the chemical bonding at the interfacial region (interphase) between carbon fiber and geopolymer matrix has been revealed. X-ray pair distribution function computed tomography (PDF-CT), field emission-scanning electron microscopy imaging, and nanoindentation techniques are employed to discern the chemo-mechanical properties of the interphase. PDF-CT results show the emergence of a new atom–atom correlation at the interfacial region (around 1.82 Å). This correlation is a characteristic of interfacial bonding between the fiber and its surrounding matrix, where the existence of chemical linkages (potentially ^VAl-O-C) between fibers and the matrix contributes to the adhesion between the two constituents making up the composite. Due to such chemical bonding, the nanomechanical properties of the interfacial region fall between that of the carbon fiber and geopolymer. The combination of advanced techniques is proved useful for enhancing our understanding of the interfacial chemistry between fibers and the binding matrix. This level of knowledge facilitates the engineering of composite systems through the manipulation of their nanostructure.     

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.     

短切碳纤维及碳纤维布增强硅橡胶复合材料的制备及力学性能

将短切碳纤维(CF)、白炭黑和甲基乙烯基硅橡胶(VMQ)共混后,与碳纤维布(CFC)复合制备VMQ复合材料.考察了CFC层数对复合材料的拉伸性能、邵尔A硬度、耐磨性能及动态力学性能的影响.结果表明,随着CFC层数的增加,复合材料的扯断伸长率基本不变,拉伸强度逐渐升高.与仅添加10份(质量,下同)CF的复合材料相比,加入...     

炭纤维增强水泥基复合材料(CFRC)的电磁性能

炭纤维增强水泥基复合材料(Carbon Fiber Reinforced Cement Composites,CFRC)是新发展起来的一种电磁屏蔽材料,它是防止电磁污染的防护性功能材料之一。本文阐述了炭纤维增强水泥基复合材料的制备成型工艺;分析了炭纤维掺入量和长度、水灰比和密实成型制备工艺、炭纤维分散性、养护龄期、外加剂、炭纤维表面化学气相沉积(CVD)处理等因素对CFRC力学性能、导电性能、压敏性能及电磁性能的影响。合适的炭纤维掺入量和长度、炭纤维的均匀分散、合理的水灰比和炭纤维表面处理是影响CFRC导电性能和电磁性能的主要因素。CFRC对电磁波的屏蔽效果除利用屏蔽效能从反射电磁波角度衡量外,亦可从吸收电磁波角度利用反射率进行评价。     

Tribological behavior of carbon fiber reinforced ZrB2 based ultra high temperature ceramics

The tribological behavior of ultra-high temperature ceramic matrix composites (UHTCMCs) was investigated to understand these materials in friction applications. Samples consisting of pitch-based randomly orientated chopped carbon fiber (CF) reinforced ZrB₂-10 vol% SiC were prepared (ZS). The tribological behavior was tested on a self-designed dynamometer, coupling the UHTCMC pads with either carbon fiber reinforced carbon−silicon carbide (C/C-SiC) or steel disks, with two applied contact pressures (1 and 3 MPa) and the surface microstructures were analyzed to unravel the wear mechanisms. Even at high mechanical stresses, tests against the C/C-SiC disk showed stable braking performance and wear. The abraded material from a steel disk formed a stable friction film by fusing together harder pad particles with abraded steel, which reduced wear and stabilized the braking performance. The high values of coefficient of friction obtained (0.5–0.7), their stability during the braking and the acceptable wear rate make these materials appealing for automotive brake applications.