Mechanical performance of low cement reactive powder concrete (LCRPC)

The possibility of producing a reactive powder concrete (RPC) with low cement content was aimed in the scope of this study. Cement was replaced with class-C fly ash (FA) up to 60% for this purpose. Three different curing conditions (standard water curing, autoclave curing and steam curing) were applied to specimens. Two series of RPC composites were prepared with bauxite and granite aggregates. Mechanical properties such as compressive strength, splitting tensile strength, flexural strength and fracture energy of composites were investigated. Test results showed that, compressive strength of 200 MPa can be reached with low cement by using high-volume fly ash. Thermally treated specimens showed compressive strength beyond 250 MPa and high volume fly ash RPC have superior performance. Furthermore, compressive strength values reached up to 400 MPa with external pressure application during setting and hardening stages.     

Mechanical performance of low cement reactive powder concrete (LCRPC)

The possibility of producing a reactive powder concrete (RPC) with low cement content was aimed in the scope of this study. Cement was replaced with class-C fly ash (FA) up to 60% for this purpose. Three different curing conditions (standard water curing, autoclave curing and steam curing) were applied to specimens. Two series of RPC composites were prepared with bauxite and granite aggregates. Mechanical properties such as compressive strength, splitting tensile strength, flexural strength and fracture energy of composites were investigated. Test results showed that, compressive strength of 200 MPa can be reached with low cement by using high-volume fly ash. Thermally treated specimens showed compressive strength beyond 250 MPa and high volume fly ash RPC have superior performance. Furthermore, compressive strength values reached up to 400 MPa with external pressure application during setting and hardening stages.     

Role of microwave radiation in curing the fly ash geopolymer

Fly ash geopolymer requires rather long heat curing to obtain reasonable strength development at an early age. However, the long heat curing period limits the application of the fly ash geopolymer. High strength development and a reduction in heat curing duration have been considered for energy saving. Therefore, this research proposed a process using 90-W microwave radiation for 5 min followed by conventional heat curing for high-calcium fly ash geopolymer. Results showed that the compressive strengths of geopolymer with microwave radiation followed by conventional heat curing were comparable to those of the control cured at 65 °C for 24 h. Microwave radiation gave the enhanced densification. In addition, SEM images showed that the gels formed on the fly ash particles owing to the promoted dissolution of amorphous phases from fly ash. This method accelerated the geopolymerization and gave the high compressive strength comparable to the conventional curing.     

Environmental effects on the mechanical and thermomechanical properties of aspen fiber–polypropylene composites

The mechanical properties of newly developed aspen fiber–polypropylene composites (APC) were experimentally explored and numerically predicted at the temperatures and humidity that are typical for domestic housing applications. The mechanical properties of APCs with five different fiber-loadings were evaluated at the room temperature, 4 °C, and 40 °C. Environmental effects on the mechanical properties of APCS were experimentally quantified after conditioning the APCs with two different fiber-loadings in the following temperature and humidity for over 7000 h: (1) hot/dry at 40 °C and 30% relative humidity (RH), (2) hot/wet at 40 °C and 82% RH, (3) cold/dry at 4 °C and 30% RH, and (4) cold/wet at 4 °C and 82% RH. The tensile moduli, flexural moduli, and the flexural strength increased as the woodfiber content increased in the composites. However, the tensile strength decreased as the fiber content increased. The tensile strength was shown to slightly improve with an addition of a coupling agent between the aspen fibers and polypropylene. The simple empirical micromechanics Halpin–Tsai model for randomly distributed short fiber reinforced composites was employed to predict the homogenized elastic moduli of APC, by optimizing the interfacial model parameter. Scanning electron microscopy (SEM) micrographs confirmed that an addition of the adhesion promoter maleated anhydride polypropylene (MAPP) between the aspen fibers and polymeric matrix improved the interfacial bonding.     

Characterisation of mechanical and thermal properties of epoxy grouts for composite repair of steel pipelines

The mechanical and thermal properties of the grouts are critical to their potential application as infill materials in structural repair. In this paper, the mechanical and thermal behaviour of five epoxy based grouts were investigated to identify their prospects as a component of the composite repair for steel pipelines. The compressive strength and stiffness of the grouts are found to be 52–120 MPa and 1.7–11 GPa, respectively. The tensile, flexural and shear strengths of the grouts are found to be within the ranges of 11–32, 27–53, and 13–30 MPa, respectively. The tensile and flexural moduli range within 3–17, and 4–13 GPa, respectively. Thermal analysis of the grouts suggests that the glass transition temperature (T_g) within 60 and 90 °C which also provide the thermal applicability limits for the grouts in the composite repair of steel pipes. The development of compressive properties of three selected grouts over 28 days period was also investigated as well as the effect of the addition of coarse fillers.     

Evaluating the effects of multi-walled carbon nanotubes on the mechanical properties of chopped strand mat/polyester composites

In this research, the influence of adding multi-walled carbon nanotubes at various contents on the mechanical properties of chopped strand mat/polyester composites was investigated. Initially, the effect of the sonication time on the dispersion of carbon nanotube at the highest weight ratio (0.5 wt.%) was inspected. To achieve this goal, a new technique based on scanning electron microscopy, which utilizes the burn-off test, was introduced to visualize the dispersion state of carbon nanotubes. Subsequently, the effect of addition of multi-walled carbon nanotube on the tensile and flexural properties of the fiber reinforced composites was studied. The results of mechanical tests showed that adding only 0.05 wt.% carbon nanotube enhanced the flexural strength of the hybrid composite by 45% while the tensile strength was not changed significantly. Improvements in the tensile and flexural moduli were also observed. Moreover, theoretical relations between the tensile, flexural and compressive moduli based on the classical beam theory were employed to determine the effect of carbon nanotube on the compressive modulus of composites. The theoretical result showed 31% enhancement in the compressive modulus.     

Influence of fibre type on flexural behaviour of self-compacting fibre reinforced cementitious composites

This paper investigates the flexural properties of self-compacting fibre reinforced cementitious composites that contain high fly ash volume. Seven types of fibres were compared at the same volume fraction and in similar matrices containing high-volume fly ash and having a high compressive strength of around 85 MPa at 28 days. Third-point bending test was conducted on beam specimens to obtain their load–deflection curves, and investigate their fracture behaviour, flexural strength, deflection and toughness. The results showed that using straight steel and micro-polyvinyl alcohol fibres produced composites demonstrating stable deflection-hardening with multiple-cracking phenomenon. This behaviour resulted in high flexural strength, along with large maximum deflection and toughness values, which are important for applications in cementitious composites. This study indicates that fibres with both sufficiently high aspect ratio and high tensile strength are necessary for achieving deflection-hardening in self-compacting cementitious composites with high-strength matrices containing high-volume fly ash.     

Size-scale effects of silica on bis-GMA/TEGDMA based nanohybrid dental restorative composites

The present study focuses on the effect of size-scale combination of silica on the mechanical and dynamic mechanical properties of acrylate based (50% Bis-GMA and 50% TEGDMA by weight) composites with an aim to overcome the conventional problem of high-volume fraction filling of acrylate based composites, typically used in restorative dentistry. Two classes of light-cured composites based on the size-scale combination of silica (7 nm + 2 μm; 14 nm + 2 μm) as the filler were prepared. FTIR spectroscopy revealed functionality and interactions whereas morphological investigations concerning the state of distribution and dispersion of nano- and micro-silica has been carried out by SEM–EDX Si-dot mapping. The dynamic mechanical properties, compressive, flexural and diametral tensile strengths were characterized. Micromechanical analysis of viscoelastic storage moduli following Kerner composite model has revealed an enhancement in the reinforcement efficiency of the nanohybrid composites based on the filler size-scale combination of 14 nm + 2 μm with 10 wt.% nanofiller loading. The compressive strength of the micro-filled composite (with 2 μm silica only) was found to remain comparable to that of the nanohybrid with 5 wt.% of 7 nm silica and 10 wt.% of 14 nm silica filled composites. Diametral tensile strength has been observed to be influenced by the size-scale combination and extent of nanofiller loading. The effective volume fractions in the composites validating the experimentally determined DTS were calculated following Nicolais–Narkis model. Our study demonstrates the conceptual feasibility of exploring the optimization of size-scale combinations of filler for enhancement in reinforcement efficiency by manipulating the volume fraction of filler induced immobilized polymer chains by resorting to the principle of micromechanics.     

Physical and mechanical characterization of Fiber-Reinforced Aerated Concrete (FRAC)

Fiber-Reinforced Aerated Concrete (FRAC) is a novel lightweight aerated concrete that includes internal reinforcement with short polymeric fibers. The autoclaving process is eliminated from the production of FRAC and curing is performed at room temperature. Several instrumented experiments were performed to characterize FRAC blocks for their physical and mechanical properties. This work includes the study of pore-structure at micro-scale and macro-scale; the variations of density and compressive strength within a block; compressive, flexural and tensile properties; impact resistance; and thermal conductivity. Furthermore, the effect of fiber content on the mechanical characteristics of FRAC was studied at three volume fractions and compared to plain Autoclaved Aerated Concrete (AAC). The instrumented experimental results for the highest fiber content FRAC indicated compressive strength of approximately 3 MPa, flexural strength of 0.56 MPa, flexural toughness of more than 25 N m, and thermal conductivity of 0.15 W/K m.     

Electromagnetic shielding effectiveness of aluminum alloy–fly ash composites

The cenosphere and precipitator fly ash particulates were used to produce two kinds of aluminum matrix composites with the density of 1.4–1.6 g cm⁻³ and 2.2–2.4 g cm⁻³ separately. The electromagnetic interference shielding effectiveness (EMSE) properties of the composites were measured in the frequency range of 30.0 kHz–1.5 GHz. The results indicated the EMSE properties of the two types of composites were nearly the same. By using the fly ash particles, the shielding effectiveness properties of the matrix aluminum have been improved in the frequency ranges 30.0 kHz–600.0 MHz and the increment varied with increasing frequency. The EMSE properties of 2024Al are in the range −36.1 ± 0.2 to −46.3 ± 0.3 dB while the composites are in the range −40.0 ± 0.8 to −102.5 ± 0.1 dB in the frequency range 1.0–600.0 MHz. At higher frequency, the EMSE properties of the composites are similar to that of the matrix. The tensile strength of the matrix aluminum has been decreased by addition of the fly ash particulate and the tensile strength of the composites were 110.2 MPa and 180.6 MPa separately. The fractography showed that one composite fractured brittly and the other fractured in a microductile manner.     

Effect of formulation variables on the mechanical properties of compression-moulded phlogopite/LLDPE composites

Phlogopite is a flaky mineral with outstanding chemical, thermal and electrical resistance and is also flame resistant. These properties make it a candidate for combining it with a polymeric binder to produce a composite board. It is the purpose of the present study to investigate the influence of particle size, percentage binder and the binder modification technique, on the mechanical properties of composites comprising small amounts of binder, by means of a statistically designed experiment. The results were also evaluated by means of the analysis of variance. Percentage binder was found to be the most important controlled variable determining the mechanical properties of the composite and the following other conclusions were drawn: particle size and modification technique contributed significantly only towards the flexural stress at yield; 20% linear low density polyethylene (LLDPE) modified with 200 mmol acrylic acid per 100 g LLDPE were found to be optimal; phlogopite particle size between 180 and 250 μm results in the highest tensile and flexural moduli.     

Manufacture and characterisation of thermoplastic composites made from PLA/hemp co-wrapped hybrid yarn prepregs

PLA/hemp co-wrapped hybrid yarns were produced by wrapping PLA filaments around a core composed of a 400 twists/m and 25 tex hemp yarn (Cannabis sativa L) and 18 tex PLA filaments. The hemp content varied between 10 and 45 mass%, and the PLA wrapping density around the core was 150 and 250 turns/m. Composites were fabricated by compression moulding of 0/90 bidirectional prepregs, and characterised regarding porosity, mechanical strength and thermal properties by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). Mechanical tests showed that the tensile and flexural strengths of the composites markedly increased with the fibre content, reaching 59.3 and 124.2 MPa when reinforced with 45 mass% fibre, which is approximately 2 and 3.3 times higher compared to neat PLA. Impact strength of the composites decreased initially up to 10 mass% fibre; while higher fibre loading (up to 45 mass%) caused an increase in impact strength up to 26.3 kJ/m², an improvement of about 2 times higher compared to neat PLA. The composites made from the hybrid yarn with a wrapping density of 250 turns/m showed improvements in mechanical properties, due to the lower porosity. The fractured surfaces were investigated by scanning electron microscopy to study the fibre/matrix interface.     

Compaction of fly ash–aluminum alloy composites and evaluation of their mechanical and acoustic properties

The density and elastic moduli of green compacts can be determined by ultrasonic method with the help of pre-prepared diagrams. In this way, pressing conditions can be taken under control easily. In this study, fly ash particles were used as fillers in an aluminum alloy matrix material. The weight fractions of fly ash in the composites were in the range of 5–30%. The resulting composites were compacted at pressures ranging from 63 MPa to 316 MPa. It was observed that the green density increased with increasing compacting pressure and decreased with increasing weight percent of fly ash particles resulting in lightweight composites. The green compact composites were also tested using an ultrasonic non-destructive evaluation method. Results showed that ultrasonic velocities are a strong function of the density and the fly ash fraction in this material and could be potentially used to predict the density and the fly ash fraction as well as the elastic moduli of the metal matrix composite.     

Thermal and mechanical behaviour of sisal/phenolic composites

This research proposes the development of polymeric composites reinforced with natural fibres to become stronger the damaged timber structures and proposes thermal and mechanical characterization of these composites. Fibres with larger structural applications are glass and carbon fibres but the use of natural fibres is an economical alternative and possesses many advantages such as biodegradability, low cost and is a renewable source. Woven sisal fabric was submitted to heat treatment before moulding and the influence of moisture content of fibres on the composites behaviour was observed. The paper presents mechanical characterization by tensile and flexural strength of woven sisal fabric composites, with and without thermal treatment (at 60 °C for 72 h) on the fabric, thermal characterization by TGA and the manufacturing process by compression moulding. Experimental results show to sisal/phenolic composites a tensile strength and a flexural strength value of 25.0 MPa and 11.0 MPa, respectively, independent to the use of sisal fibres with or without thermal treatment.     

Influence of palm oil fuel ash on ultimate flexural and uniaxial tensile strength of green ultra-high performance fiber reinforced cementitious composites

This study focuses on the measurement of the ultimate flexural and tensile strength of GUSMRC, a new class of green ultra-high performance fiber reinforced cementitious composites (GUHPFRCCs) in which 75% of the volume contains ultrafine palm oil fuel ash (UPOFA). This green concrete is currently under development at the Universiti Sains Malaysia (GUSMRC). The main objective of this study is to investigate the potential of UPOFA as a partial binder replacement for the ultimate flexural and uniaxial tensile strength of GUSMRC mixtures. Results showed that UPOFA enhances the flexural and uniaxial tensile responses of fresh UHPFRCCs. The highest flexural and uniaxial tensile strength values at the 50% replacement level after 28 days were at 42.38 MPa and 13.35 MPa, respectively, indicating the potential of utilizing UPOFA as an efficient pozzolanic mineral admixture for the production of GUSMRC with superior engineering properties.     

Study on mechanical properties of fly ash impregnated glass fiber reinforced polymer composites using mixture design analysis

This paper describes the mechanical behavior of fly ash impregnated E-glass fiber reinforced polymer composite (GFRP). Initially the proportion of fiber and resin were optimized from the analysis of the mechanical properties of the GFRP. It is observed that the 30 wt% of E-glass in the GFRP without filler material yields better results. Then, based on the optimized value of resin content, the varying percentage of E-glass and fly ash was added to fabricate the hybrid composites. Results obtained in this study were mathematically evaluated using Mixture Design Method. Predictions show that 10 wt% addition of fly ash with fiber improves the mechanical properties of the composites. The fly ash impregnated GFRP yields significant improvement in mechanical strength compared to the GFRP without filler material. The surface morphologies of the fractured specimens were characterized using Scanning Electron Microscope (SEM). The chemical composition and surface morphology of the fly ash is analyzed by using Energy Dispersive Spectroscopy (EDS) and Scanning Electron Microscope.     

Thermomechanical properties of bio-based composites made from a lactic acid thermoset resin and flax and flax/basalt fibre reinforcements

Low viscosity thermoset bio-based resin was synthesised from lactic acid, allyl alcohol and pentaerythritol. The resin was impregnated into cellulosic fibre reinforcement from flax and basalt and then compression moulded at elevated temperature to produce thermoset composites. The mechanical properties of composites were characterised by flexural, tensile and Charpy impact testing whereas the thermal properties were analysed by dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The results showed a decrease in mechanical properties with increase in fibre load after 40 wt.% for the neat flax composite due to insufficient fibre wetting and an increase in mechanical properties with increase fibre load up to 60 wt.% for the flax/basalt composite. The results of the ageing test showed that the mechanical properties of the composites deteriorate with ageing; however, the flax/basalt composite had better mechanical properties after ageing than the flax composite before ageing.     

Investigations on the fabrication and the characterization of glass/epoxy,carbon/epoxy and hybrid composites used in the reinforcement and the repair of aeronautic structures

This paper reports the fabrication and the characterization of glass/epoxy, carbon/epoxy and hybrid laminated composites used in the reinforcement and/or the repair of aeronautic structures. These composites were manufactured by the hand lay-up process. Their physical, thermal and mechanical behaviors are discussed in terms of moisture absorption, thermal stability, tensile strength, elastic modulus, flexural strength, flexural modulus and abrasive wear resistance. The impact of hygrothermal aging on the mechanical properties of each composite group has been also investigated.The main results indicated that after water immersion, all composites showed significant moisture absorption especially for glass/epoxy composite. Thermogravimetric analysis showed that the hybrid composite presented the best thermal stability behavior while the glass/epoxy composite the bad behavior. The mechanical properties of the carbon/epoxy composites, in the bulk material, were considerably higher than those of the glass/epoxy; the hybrid structure presented intermediate mechanical properties. The same trend was also observed in terms of wear properties. Finally, a deleterious effect on the strength of all composites due to hygrothermal exposure was established. However, carbon/epoxy composites seem to be less susceptible to aging damage after 90 days at 90 °C.     

Ductile unidirectional continuous rayon fibre-reinforced hierarchical composites

Endless rayon fibres (Cordenka®) were used to reinforce polyhydroxybutyrate (PHB) nanocomposites containing 2.5 wt.% nanofibrillated cellulose (NFC) to create truly green hierarchical composites. Unidirectional (UD) composites with 50–55% fibre volume fraction were produced using a solvent-free continuous wet powder impregnation method. The composites exhibit ductile failure behaviour with a strain-to-failure of more than 10% albeit using a very brittle matrix. Improvements at a model composite level were translated into higher mechanical properties of UD hierarchical composites. The Young’s moduli of rayon fibre-reinforced (NFC-reinforced) PHB composites were about 15 GPa. The tensile and flexural strength of hierarchical PHB composites increased by 15% and 33% as compared to the rayon fibre-reinforced neat PHB composites. This suggests that incorporation of NFC into the PHB matrix binds the rayon fibres, which does affect the load transfer between the constituents resulting in composites with better mechanical properties.     

Mechanical,thermal expansion,and flammability properties of co-extruded wood polymer composites with basalt fiber reinforced shells

Basalt fiber (BF) filled high density polyethylene (HDPE) and co-extruded wood plastic composites (WPCs) with BF/HDPE composite shell were successfully prepared and their mechanical, morphological and thermal properties characterized. The BFs had an average diameter of 7 μm with an organic surfactant surface coating, which was thermally decomposed at about 210 °C. Incorporating BFs into HDPE matrix substantially enhanced flexural, tensile and dynamic modulus without causing a noticeable decrease in the tensile and impact strength of the composites. Micromechanical modeling of tensile properties for the BF/HDPE composites showed a good fit of the selected models to the experimental data. Compared to neat HDPE, BF/HDPE composites had reduced linear coefficient of thermal expansion (LCTE) values. The use of the pure HDPE and BF/HDPE layers over a WPC core greatly improved impact strength of core–shell structured composites. However, the relatively less-stiff HDPE shell with large LCTE values decreased the overall composite modulus and thermal stability. Both flexural and thermal expansion properties were enhanced with BF reinforced HDPE shells, leading to well-balanced properties of core–shell structured material. Cone calorimetry analysis indicated that flammability performance of core–shell structured composites was improved as the BF content increased in the shell layer.