Flexural behavior of geopolymer composites reinforced with steel and polypropylene macro fibers

Like ordinary Portland cement concrete, the matrix brittleness in geopolymer composites can be reduced by introducing appropriate fiber reinforcement. Several studies on fiber reinforced geopolymer composites are available, however there is still a gap to understand and optimize their performance. This paper presents the flexural behavior of fly ash-based geopolymer composites reinforced with different types of macro steel and polypropylene fibers with higher aspect ratio. Three types (length-deformed, end-deformed and straight) of steel fibers and another type of length-deformed polypropylene fiber with optimum fiber volume fraction of 0.5% are studied. The effects of different geometries of the fibers, curing regimes (ambient cured and heat cured at 60 °C for 24 h) and concentration of NaOH activator (10 M and 12 M) on the first peak strength, modulus of rupture and toughness of the geopolymer composites are investigated. The quantitative effect of fiber geometry on geopolymer composite performance was also analyzed through a fiber deformation ratio. The compressive strength, splitting tensile strength and flexural toughness are significantly improved with macro fibers reinforcement and heat curing. The results also show that heat curing increases the first peak load of all fiber-reinforced geopolymers composites. End-deformed steel fibers exhibit the most ductile flexural response compared to other steel fibers in both heat and ambient-cured fiber reinforced geopolymer composites.     

Characterisation of cotton fibre-reinforced geopolymer composites

This paper describes the physical, mechanical and fracture behaviour of fly-ash based geopolymer reinforced with cotton fibres (0.3–1.0 wt%). Results show that the appropriate addition of cotton fibres can improve the mechanical properties of geopolymer composites. In particular, the flexural strength and the fracture toughness increase at an optimum fibre content of 0.5 wt%. However, as the fibre content increases, the density of geopolymer composites decreases due to an increase in porosity and tendency of fibre agglomeration.     

Effect of fabric orientation on mechanical properties of cotton fabric reinforced geopolymer composites

This paper presents the thermal, mechanical and fracture behaviour of fly-ash based geopolymer composites reinforced with cotton fabric (0–8.3 wt.%). Results revealed that fly-ash based geopolymer can prevent the degradation of cotton fabric at elevated temperatures. The effect of cotton fabric orientation (i.e., horizontal or vertical) to the applied load on flexural strength, compressive strength, hardness and fracture toughness of geopolymer composites is also investigated. The results showed that when the fabrics are aligned in horizontal orientation with respect to the applied load, higher load and greater resistance to the deformation were achieved when compared to their vertically-aligned counterparts.     

碳纤维复合材料在超临界正丁醇中降解的反应动力学

采用超临界正丁醇在KOH作用下从碳纤维/环氧树脂（CF/EP）复合材料中回收高性能CF。分析了反应温度和反应时间对CF/EP复合材料中EP降解率的影响,研究了回收CF增强聚丙烯（PP）复合材料的力学性能;分析了降解液相产物组分,研究了EP固化体系在超临界正丁醇中的催化降解历程,建立了降解动力学模型,通过解算动力学参数建立了催化降解动力学方程。结果表明:反应温度和反应时间与EP的降解率呈明显的正相关性;与原CF增强PP复合材料相比,回收CF增强PP复合材料的拉伸强度下降9.2%,弯曲强度下降20.9%,弯曲模量下降10.9%,冲击强度下降7.4%;CF/EP复合材料降解反应主要为EP固化体系分子链段中C—C、—O— 等线性链段的断裂以及交联部位C—N的断裂;CF/EP复合材料催化降解的反应级数为2,反应活化能为165.2 kJ·mol-1,指前因子为3.62×1013 min-1,建立的动力学方程可解决反应温度和反应时间不可预估的问题。      

Effects of fibre content on mechanical properties and fracture behaviour of short carbon fibre reinforced geopolymer matrix composites

Geopolymer matrix composites reinforced with different volume fractions of short carbon fibres (C_f/geopolymer composites) were prepared and the mechanical properties, fracture behaviour and microstructure of as-prepared composites were studied and correlated with fibre content. The results show that short carbon fibres have a great strengthening and toughening effect at low volume percentages of fibres (3·5 and 4·5 vol.%). With the increase of fibre content, the strengthening and toughening effect of short carbon fibres reduce, possibly due to fibre damage, formation of high shear stresses at intersect between fibres and strong interface cohesion of fibre/matrix under higher forming pressure. The property improvements are primarily based on the network structure of short carbon fibre preform and the predominant strengthening and toughening mechanisms are attributed to the apparent fibre bridging and pulling-out effect.     

Thermal and mechanical properties of cotton fabric-reinforced geopolymer composites

As natural fibres, cotton fabrics (CF) offer good opportunities as reinforcement material for geopolymer composites as they have good intrinsic mechanical properties. This article presents thermal and mechanical properties of CF-reinforced geopolymer composites containing up to 4.1 wt% CF. Thermo-gravimetric analysis was conducted to characterise their thermal performance and their mechanical properties, such as flexural strength, fracture toughness, flexural modulus and impact strength were evaluated. Results show that the enhancement of mechanical properties was achieved at an optimum fibre content of 2.1 wt%. Results of thermal analysis show that fly-ash based geopolymer can prevent the degradation of cotton fabric at elevated temperatures.     

Effects of light crude oil contamination on the physical and mechanical properties of geopolymer cement mortar

Fly ash and oil contaminated sand are considered as the two waste materials that may affect environment. This paper investigated the suitability of producing geopolymer cement mortar using oil contaminated sand. A comparison between physical and mechanical properties of mortar produced using geopolymer and Ordinary Portland Cement (OPC), in terms of porosity, hydration and compressive strength, was conducted. The results showed that heat curing can increase the compressive strength of geopolymer mortar up to 54% compared to ambient curing situation. The geopolymer mortar with 1% of light crude oil contamination yielded a 20% higher compressive strength than OPC mortar containing sand with a saturated surface dry condition. Furthermore, the formation of efflorescence decreased as the level of oil contamination decreased. Moreover, the heat curing method increased the kinetic energy and degree of reaction for geopolymer cement mortar, which cause an increment of the density of the pore system and improving the mechanical properties of the resulting composites. From the results of this study, it was demonstrated that geopolymer mortar has the potential of utilizing oil contaminated sand, and reducing its environmental impacts.     

钢纤维增强粉煤灰地质聚合物单轴受压过程的声发射特性

为探索纤维增强地质聚合物宏观力学行为与细观损伤演化特征之间的关联,对不同纤维体积掺量(纤维与拌合物的体积比)的钢纤维增强粉煤灰地质聚合物复合材料进行了单轴压缩试验.基于声发射技术,对试样压缩过程的声发射行为进行监测,研究了纤维体积掺量对地质聚合物单轴受压破坏行为及声发射特性的影响.结果表明:地质聚合物的强度、延性、声发射波形的上升斜率及平均频率均随纤维掺量的提高而增大,试件破坏形态由脆性灾变逐渐向延性破坏转变;在破坏前期,纤维体积掺量为0及0.5%的试件的声发射撞击率及能量释放率(简称能量率)都保持在较高水平,最终导致试件出现灾变破坏;而2.0%的纤维体积掺量使得声发射撞击率及能量率在应力-时间曲线的拐点处达到峰值,随后缓慢下降,最终导致试件呈现延性破坏;因此,仅依据声发射撞击率及能量率的快速上升来预测灾变破坏的发生,有时可能会出现谎报的情况.     

Geopolymerization of a silica residue from waste treatment of chlorosilane production

A silica residue from waste treatment of chlorosilane production was used together with solid sodium aluminate to test its applicability for the production of one-part geopolymers. The blend was activated with water and cured at 70 °C. The degree of reaction and strength were determined after 1, 3, and 7 days. The reaction products were analyzed by XRD and SEM/EDX. Until the third day of curing the degree of reaction of the residue reached 51 % and the strength was 8.9 MPa. The reaction product was identified as geopolymer containing zeolite A. Thus, the results confirmed that the residue may be used in the production of geopolymers. However, after 3 days of curing no further progress of reaction was observed and the strength slightly decreased, which was attributed to changes in the structure of the geopolymeric gel. It was further observed that even harsh vacuum drying left some water (presumably zeolitic water and surface hydroxyl groups) in the geopolymer.     

Synthesis and tribological behavior of metakaolinite-based geopolymer composites

Metakaolinite-based geopolymer composites containing 5%–30% (volume fraction) scalelike graphite, polytetrafluoroethylene (PTFE), and molybdenum disulfide (MoS₂), respectively, were synthesized in the presence of a compound activator composed of aqueous NaOH and sodium silicate at room temperature. The tribological behaviors of the resulting composites sliding against AISI-1045 steel were investigated on an MM-200 friction and wear tester, and the bending strength and compressive strength of the composites were determined on a universal materials tester. Moreover, the worn surfaces of the composites were analyzed by means of scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray photoelectron spectroscopy (XPS), which was aimed to reveal the wear mechanisms of the composites. It was found that all the three kinds of the tested solid lubricants contributed to greatly decrease the friction and wear of the composites, and they were also able to remarkably reduce the fluctuation of the friction coefficient. This was attributed to the formation of a lubricating film containing higher content of the detached solid lubricant particulates and the oxidized product Fe₂O₃ of the counterpart steel wear debris. The metakaolinite-based geopolymer was dominated by severe adhesion wear, while its composites filled with the solid lubricant particulates were characteristic of mild adhesion, scuffing, and delamination.     

Infrared infiltration and properties of SCS-6/Ti alloy composites

Liquid infiltration processes are seldom used in the fabrication of titanium matrix composites primarily because of severe interfacial reactions during processing. To minimize fibre-matrix interfacial reactions, a rapid infrared manufacturing (RIM) process has been developed. In this study, SCS-6 fibre reinforced titanium matrix composites were fabricated by the RIM process. Experimental results indicate that composites prepared by the RIM process exhibit small interfacial reaction zones and superior mechanical properties compared to diffusion bonded composites. Interfacial reactions during processing in this composite system have been investigated. Microscopic analyses showed that the carbon-rich coating present on SCS-6 fibres partially dissolved in the alloy during infiltration without forming a continuous reaction product. A physical model has been proposed to explain the dissolution mechanism of the carbon-rich coating. The dissolution rate of the coating at the processing temperature of 1300 °C was calculated to be 1.4×10^–6 cm s^–1.     

活性填料在先驱体转化法纤维增强陶瓷基复合材料中的应用 II——复合材料的制备及其表征

将活性填料Al应用到吉林碳纤维(JC)和M40JB纤维增强先驱体转化SiC陶瓷基复合材料的制备中。研究表明,经过7个周期的致密化处理,当复合材料素坯中不含活性填料时,JC增强复合材料比M40JB增强复合材料有更高的弯曲强度,因此,JC纤维更适合用作先驱体转化陶瓷基复合材料的增强纤维;当复合材料素坯中含有活性填料Al时,由于Al与碳纤维发生碳化反应,使纤维受损,在纤维与基体之间形成不良的界面结合,导致复合材料的强度发生退化。图象分析表明,M40JB与Al的反应层厚度约为0.94 μm。为了防止碳纤维与Al发生反应,应对碳纤维进行适当的表面处理。     

Microstructure and mechanical properties of cast (Al–Si)/SiCp composites produced by liquid and semisolid double stirring process

Abstract

A stirring process containing two steps, i.e. liquid and then semisolid stirring, was used to produce SiC particle reinforced aluminium matrix composites. The major advantages of this process are that full wetting of SiC particles by molten aluminium can be readily achieved at relatively low stirring rates, and undesirable Al₄ C₃ is not formed at the Al/SiC interface due to lower processing temperatures. Cast Al–Si matrix composites reinforced with 15 and 20 vol.-%SiC particles were produced in the present work. The mechanical properties of the composites were evaluated under the conditions of investment mould casting and heat treatment. For the composites obtained without employing semisolid stirring, the aggregation of SiC particles observed in the microstructure of composites resulted in quite poor mechanical properties. Observations and analyses indicated that some Al/SiC interfaces were very clean, and a reaction product of spinel MgAl₂O₄ was also found at some Al/SiC interfaces. Silicon dioxide (SiO₂ ) was found to exist on the surface of as purchased and 250°C dried SiC powders. This SiO₂ is involved in the spinel reaction at the interface between the SiC particles and the matrix in the present Al/SiC composites.     

Fibre reinforcement and fracture response in geopolymeric mortars

The inorganic polymeric cement called geopolymer or PSS, has been studied in recent years as a binder for mortar and concrete. The present work reports the fracture toughness studies in mortars made of PSS cement matrix reinforced by wollastonite microfibers (Ca(SiO₃)). K_I‐curves for PSS cement composites were determined according to the superposition asymptotic assumption and compared with reference Portland cement (PC) composites. The maximum toughness gain occurs in both composite systems with V_f = 2%. For higher fibre volumes (3 and 5%), K_I values decrease, due to an increase in porosity. Microstructural analyses showed that toughening mechanisms, as debonding and pullout of the fibers, are more common in PSS cement composites than in the reference PC composites. The difference of toughness between PSS and PC cement (0% of fibers) is about 80%. This demonstrates the high performance of these geopolymeric materials.     

Mechanical and thermal properties of lightweight geopolymer composites

This research has investigated the properties of thermally insulating geopolymer composites that were prepared using waste expanded polystyrene as lightweight aggregate. The geopolymer matrix was synthetized using metakaolin and an alkaline activating solution. To improve its mechanical properties, this matrix was modified by the addition of an epoxy resin to form an organic-inorganic composite. Moreover, in order to reduce drying shrinkage marble powder was used as an inert filler. The materials obtained were characterized in terms of physico-mechanical properties, thermal performance and microstructure. The geopolymer expanded polystyrene composite have improved properties compared to Portland cement-based materials, with higher strengths and lower thermal conductivity. The research demonstrates the manufacture of sustainable lightweight thermally insulating geopolymer composites using waste expanded polystyrene.     

颗粒增强铜基复合材料的研究进展

为了研究颗粒增强相对铜基复合材料的性能的影响,对不同类型铜基复合材料的特点及其制备方法进行对比分析,探讨了颗粒相的生成机制,重点论述了颗粒增强相的类型及铜基复合材料的制备工艺.结果表明在铜基体中引入纳米分散相进行复合,可以使铜合金的力学性能得到极大改善,其中机械合金化和原位复合化学反应获得的纳米陶瓷颗粒在铜基复合材料中效果最佳;反应喷射沉积成型法、液相反应原位生成法和机械合金化法在制备纳米粒子增强铜基复合材料方面有着良好的应用前景.     

Analysis of geopolymer concrete columns

Ordinary portland cement (OPC) has been traditionally used as the binding agent in concrete. However, it is also necessary to search for alternative low-emission binding agents for concrete to reduce the environmental impact caused by manufacturing of cement. Geopolymer, also known as inorganic polymer, is one such material that uses by-product material such as fly ash instead of cement. Recent research has shown that fly ash-based geopolymer concrete has suitable properties for its use as a construction material. Since the strength development mechanism of geopolymer is different from that of OPC binder, it is necessary to obtain a suitable constitutive model for geopolymer concrete to predict the load–deflection behaviour and strength of geopolymer concrete structural members. This article has investigated the suitability of using an existing stress–strain model originally proposed by Popovics for OPC concrete. It is found that the equation of Popovics can be used for geopolymer concrete with minor modification to the expression for the curve fitting factor, to better fit with the post-peak parts of the experimental stress–strain curves. The slightly modified set of stress–strain equations was then used in a non-linear analysis for reinforced concrete columns. A good correlation is achieved between the predicted and measured ultimate loads, load–deflection curves and deflected shapes for 12 slender test columns.     

低频电磁场下原位合成Al-Zr-O系复合材料机制研究

为研究低频电磁场下铝基原位复合材料的合成机制,以A356-Zr(CO3)2反应组元制备出Al-Z-O系复合材料,在低频旋转电磁场条件下原位合成了微米级颗粒增强铝基复合材料.研究表明:当感应线圈内输入电流150A,频率4Hz时,对应磁场强度为0.25T,X射线衍射结果显示基体中增强相为Al3Zr和Al2O3;SEM观察该条件下合成的复合材料凝固组织发现,生成的增强颗粒细小,粒径1~2μm,而且在基体中均匀弥散分布.对原位反应的热力学和动力学过程分析表明:反应的关键环节是高温铝液和ZrO2固液相间反应,电磁场力作用加大了反应体系的混合对流运动,提高了传热传质和物质扩散速度,并促进了颗粒在基体中的弥散分布.     

Tensile properties and microstructures of Al composite reinforced with BN particles

Al–4.5 wt% Mg alloys reinforced with and without BN were fabricated by pressureless infiltration method and then their tensile properties and microstructures were analyzed. Since the spontaneous infiltration of molten metal occurred at a temperature of 800 °C for 1 h under nitrogen atmosphere, it was possible to fabricate the Al composites reinforced with BN and control alloy without BN. A large increase in strength in the case of the control alloy is related to the in situ formation of AlN particles as well as grain size refinement. In the composite reinforced with BN, additional AlN was formed by the interfacial reaction of the BN and Al melt as well as AlN by the in situ reaction. In addition, the grain size in the composite reinforced with 7.5 vol% BN further decreased to about 4.0 μm and exhibited approximately 3.5 times reduction in the grain size of the commercial alloy. Consequently, a further strengthening in the composite resulted from both the BN artificially added and AlN formation (by the in situ reaction and interfacial reaction) and grain refinement.     

Mechanical properties of soil buried kenaf fibre reinforced thermoplastic polyurethane composites

A study on mechanical properties of soil buried kenaf fibre reinforced thermoplastic polyurethane (TPU) composites is presented in this paper. Kenaf bast fibre reinforced TPU composites were prepared via melt-mixing method using Haake Polydrive R600 internal mixer. The composites with 30% fibre loading were prepared based on some important parameters; i.e. 190 °C for reaction temperature, 11 min for reaction time and 400 rpm for rotating speed. The composites were subjected to soil burial tests where the purpose of these tests was to study the effect of moisture absorption on the mechanical properties of the composites. Tensile and flexural properties of the composites were determined before and after the soil burial tests for 20, 40, 60 and 80 days. The percentages of both moisture uptake and weight gain after soil burial tests were recorded. Tensile strength of kenaf fibre reinforced TPU composite dropped to ∼16.14 MPa after 80 days of soil burial test. It was also observed that there was no significant change in flexural properties of soil buried kenaf fibre reinforced TPU composite specimens.