Glass transitions of hygrothermal aged pultruded glass fibre reinforced polymer rebar by dynamic mechanical thermal analysis

The changes that can occur in glass fibre reinforced polymer (GFRP) composites with ageing can affect its application, performance and lifetime. Hygrothermal ageing (i.e. accelerated ageing by moisture absorption and temperature change) is a very useful technique to evaluate durability as well as development of GFRP composites in a reasonable timeframe. Dynamic mechanical thermal analysis (DMTA) is essentially able to detect all changes in the state of molecular motion in polymer composites as temperature is scanned. In this work, pultruded GFRP rebars were accelerated aged in an alkaline aqueous environment at 60 °C for 1, 2, 3, 4 and 6 months to evaluate the changes in glass transition of viscoelastic GFRP rebars by DMTA. Five different glass transitions in an average temperate range from 110 to 165 °C were observed at storage modulus, loss modulus and damping factor traces of DMTA. It was also found that glass transition temperature (T_g) of the aged samples changed up to maximum 6 °C compared with that of controlled sample. This change in T_g with ageing time was believed to be due to moisture absorption by rebars.     

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.     

Influence of alkali treatment and fibre length on mechanical properties of short Agave fibre reinforced epoxy composites

Composites based on short Agave fibres (untreated and alkali treated) reinforced epoxy resin using three different fibre lengths (3 mm, 7 mm and 10 mm length) are prepared by using hand lay up and compression mould technique. The materials were characterized in terms of tensile, compressive, flexural, impact, water absorption properties and machinability behaviour. All mechanical tests showed that alkali treated fibre composites withstand more fracture strain than untreated fibre composites. As evidenced by the dynamic mechanical analysis (DMA) tests, the thermo-mechanical properties of the composite with alkali treated Agave fibre were considerably good as alkali treatment had facilitated more sites of fibre resin interface. The machinability and atomic force microscope (AFM) studies were carried out to analyze the fibre–matrix interaction in untreated and alkali treated Agave fibre–epoxy composites.     

Effect of UV and water spraying on the mechanical properties of flax fabric reinforced polymer composites used for civil engineering applications

The lack of data related to durability is one major challenge that needed to be addressed prior to the widespread acceptance of natural fibre reinforced polymer composites for engineering applications. In this work, the combined effect of ultraviolet (UV) radiation and water spraying on the mechanical properties of flax fabric reinforced epoxy composite was investigated to assess the durability performance of this composite used for civil engineering applications. Specimens fabricated by hand lay-up process were exposed in an accelerated weathering chamber for 1500 h. Tensile and three-point bending tests were performed to evaluate the mechanical properties. Scanning electron microscope (SEM) was used to analyse the microstructures of the composites. In addition, the durability performance of flax/epoxy composite was compared with synthetic (glass and carbon) and hybrid fibre reinforced composites. The test results show that the tensile strength/modulus of the weathered composites decreased 29.9% and 34.9%, respectively. The flexural strength/modulus reduced 10.0% and 10.2%, respectively. SEM study confirmed the degradation in fibre/matrix interfacial bonding after exposure. Comparisons with other composites implies that flax fabric/epoxy composite has potential to be used for civil engineering applications when taking its structural and durability performance into account. Proper treatments to enhance its durability performance will make it more comparable to synthetic fibre reinforced composites when considering as construction building materials.     

Repair of damaged RC columns using fast curing FRP composites

In this study, two fast curing resins were used to repair pre-damaged RC columns. They were 1.5-hour heat activated curing prepreg and 20-min ultraviolet curing resin. A 24-hour curing epoxy was also used for comparison purposes. A total of 24 steel reinforced φ 152.4 mm×609.6 mm small-scale concrete columns were designed, cast, cured, surface prepared, and pre-damaged. The damaged samples were repaired using the three types of E-glass fabric reinforced resins. An accelerated conditioning using boiling seawater and ultraviolet radiation was also conducted to investigate the hygrothermal durability of the repaired samples. Uniaxial compression test was conducted on both control samples and conditioned samples. The test results and cost/benefit analysis results show that the two fast curing resins can replace the currently used long-time curing resins in repairing damaged RC columns.     

Mechanical properties of poly(butylene succinate) (PBS) biocomposites reinforced with surface modified jute fibre

A biocomposite was originally fabricated with biodegradable polymer PBS and jute fibre, and the effects of fibre surface modification on characteristics of jute fibre and mechanical properties of the biocomposite were evaluated in this paper. The experimental results show that surface modification can remove surface impurities and reduce diameter of jute fibres. Regarding the mechanical properties of biocomposites, it is observed that the biocomposites with jute fibres treated by 2% NaOH, 2 + 5% NaOH or coupling agent, respectively, an optimum in mechanical properties can obtain at fibre content of 20 wt.%, which exhibit an obvious enhancement in mechanical strength and modulus compared to the ones with untreated jute fibre. Furthermore, surface modification also exhibits less effects on flexural properties compared to tensile properties and more on flexural or tensile modulus than on the strength.     

Fire behaviour of reinforced concrete beams strengthened with CFRP laminates: Protection systems with insulation of the anchorage zones

This paper presents experimental and numerical investigations about the fire behaviour of reinforced concrete (RC) beams flexurally strengthened with carbon fibre reinforced polymer (CFRP) laminates. The main objective was to assess the efficacy of different fire protection systems and to evaluate the viability of their use in floors of buildings. Fire resistance tests were conducted on an intermediate scale oven to investigate the behaviour under fire (ISO 834) of loaded CFRP-strengthened RC beams. The fire protection systems comprised calcium silicate boards and layers of vermiculite/perlite cement based mortar, with thicknesses of 25 mm and 40 mm, applied along the bottom soffit of the beams that was directly exposed to fire. In addition, the anchorage zones of the CFRP laminates were highly thermally insulated in order to evaluate the benefits of this particular constructive detail. Member deflection and temperatures throughout the midspan section were measured and recorded during the tests. When the strengthening system was left unprotected in the exposed length of the beam, the CFRP laminate anchorage debonded after about 23 min. When the above mentioned fire protection materials were applied in the exposed length of the beams, the strengthening system debonded after between 60–89 min (25 mm thickness) and 137-167 min (40 mm). Two-dimensional finite element thermal models of all beams tested were also developed in order to predict the evolution of temperatures in the materials. The calculated temperatures compared reasonably well with those measured in the tests.     

Bond analysis of corroded reinforced concrete beams under monotonic and fatigue loads

This study investigated the fatigue bond behaviour of corroded steel reinforced concrete beams. Nine beams (152 × 254 × 2000 mm [6 × 10 × 78.74 in.]) were constructed and tested. Bond failure occurred in all the beams. The variables in this test series were: the type of load applied (monotonic or repeated loading), the repeated load range, whether the reinforcement inside the beam was corroded or not, and whether a carbon fibre reinforced polymer (CFRP) repair method was used or not. The fatigue life of the beams varied linearly with the range of applied load with a very shallow slope. Corroding the beams to a low corrosion level decreased the fatigue bond strength by about 30%. Corrosion caused the concrete in between the lugs of the reinforcing bars to be partially crushed due to the formation of the rust products from the corrosion process. This reduced the strength of the concrete keys and increased the rate of slip in the bar under repeated loading.     

Improvement of ternary recycled polymer blend reinforced with date palm fibre

This paper investigates the study and preparation of date palm fibre reinforced recycled polymer blend composites. This is the first paper which describes the recycled polymer ternary blends of (1) recycled low density polyethylene (RLDPE), (2) recycled high density polyethylene (RHDPE) and (3) recycled polypropylene (RPP). The date palm fibre reinforced composites (C_D00) were prepared by maintaining constant weight% of fibre of 20 wt% without any fibre treatment. Maleic anhydride (MA) was used as the compatabilizer (1 and 2 wt%) and the effect of compatabilizer on the blend matrix composites was studied. The mechanical, thermal, morphological properties, water absorption and chemical resistance properties were evaluated for these composites and also studied for pure blend matrix (C₀₀). Date palm fibre improved the tensile strength and hardness of recycled polymer blend matrix. Further improvement was achieved with 1% MA (C_D1), which showed that 1% MA treated composites (C_D1) had higher tensile strength, modulus and hardness properties. Thermal stability and water absorption were improved by 1% MA. These improvements were demonstrated at the nanoscale level by the decrease in roughness appearing in Atomic Force Spectroscopic Microscopy analysis indicating that flow is better under this concentration. The SEM analysis also showed that the fibre matrix adhesion improved by adding 1 wt% (C_D1) of MA. The melting and crystallisation temperatures of the blends did not change with the addition of date palm fibre and MA, indicating that the additives did not influence the melting and crystallisation properties of the composites. The chemical resistance test results showed that these composites are resistance to all chemicals but more weight gain observed in solvents. 2 wt% of MA (C_D2) caused poor adhesion between the polymer chains and fibres as well as polymer chain scission.     

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.     

Electrophoretic bilayer deposition of zirconia and reinforced bioglass system on Ti6Al4V for implant applications: An in vitro investigation

The physical, chemical and biological properties of the bioglass reinforced yttria-stabilized composite layer on Ti6Al4V titanium substrates were investigated. The Ti6Al4V substrate was deposited with yttria stabilized zirconia — YSZ as the base layer of thickness ≈ 4–5 μm, to inhibit metal ion leach out from the substrate and bioglass zirconia reinforced composite as the second layer of thickness ≈ 15 μm, which would react with surrounding bone tissue to enhance bone formation and implant fixation. The deposition of these two layers on the substrate was carried out using the most viable electrophoretic deposition (EPD) technique. Biocompatible yttria-stabilized zirconia (YSZ) in the form of nano-particles and sol gel derived bioglass in the form of micro-particles were chosen as precursors for coating. The coatings were vacuum sintered at 900 °C for 3 h. The biocompatibility and corrosion resistance property were studied in osteoblast cell culture and in simulated body fluid (SBF) respectively. Analysis showed that the zirconia reinforced bioglass bilayer system promoted significant bioactivity, and it exhibited a better corrosion resistance property and elevated mechanical strength under load bearing conditions in comparison with the monolayer YSZ coating on Ti6Al4V implant surface.     

Geometry and restraint effects on the bending behaviour of the glass fibre reinforced polymer sandwich slabs under point load

The behaviour of structural glass fibre reinforced polymer (GFRP) composite sandwich slab was investigated under static point load. In this paper, the effects of dimensions aspect ratio, skin fibre orientations, overall thickness, boundary restraints, and boundary conditions on the static behaviour of the GFRP slab were presented. It was found that the ultimate load of the fibre composite sandwich slab is reducing with increasing panel dimension aspect ratio. The experimental results also showed that the fibre orientation of the skin has an effect on the failure mode and stiffness of the slab. As expected, the flexural stiffness of 18 mm thick slab is higher than the 15 mm thick slab. Finally, the restraint conditions did not affect much on the failure load and stiffness of the one-way and two-way slab systems.     

Structural performance of shear-critical RC deep beams with corroded longitudinal steel reinforcement

The effect of corrosion of longitudinal reinforcement on the structural performance of shear-critical reinforced concrete (RC) deep beams was experimentally investigated. A total of eight medium-scale reinforced concrete beams were constructed. The beams measured 150 mm wide, 350 mm deep and 1400 mm in length. The test variables included: corrosion levels (0%, 5%, and 7.5%), existence of stirrups and FRP repair. Six beams were subjected to artificial corrosion whereas two beams acted as control un-corroded. Following the corrosion phase, all beams were tested to failure in three point bending. The test results revealed that corrosion of properly anchored longitudinal steel reinforcement does not have any adverse effect on the behaviour of shear critical RC deep beams. Corrosion changed the load transfer mechanism to a pure arch action and as a result the load carrying capacity was improved. A strut and tie model was proposed to predict the failure loads of shear-critical RC deep beams with corroded longitudinal steel reinforcement. The predicted results correlated well with the experimental results.     

Quasi-static and dynamic mechanical elastic moduli of alkaline aged pultruded fibre reinforced polymer composite rebar

Due to the increased use of glass fibre reinforced polymer composite (GFRP) rebar in concrete structures, the durability performance of GFRP rebar has been an important research topic in recent years. This paper presents elastic modulus of alkaline environment (pH ≈ 13) aged pultruded GFRP rebar as evaluated by three different methods, namely, quasi-static tensile, quasi-static flexural and dynamic mechanical thermal tests. It was found that elastic modulus of the GFRP rebar samples did not change significantly due to exposure in alkaline environment at 60 °C for 1, 2, 3, 4, 6 and 14 months when compared with that of control sample. Elastic modulus was found to be in the range of 52.5–56.5 GPa irrespective to testing methods and ageing time. In addition, it was estimated from the long time projected results that quasi-static tensile, quasi-static flexural and dynamic mechanical moduli will be retained by about 93%, 95% and 85%, respectively, after 100 years in alkaline environment at 60 °C. Microscopic analysis indicated that quasi-static tensile and flexural failure was mainly due to matrix cracking and shear failure of fibre/matrix interface.     

Comparative study of fluoride conversion coatings formed on biodegradable powder metallurgy Mg: The effect of chlorides at physiological level

The development of a biodegradable metallic implant demands a precisely defined degradation profile and adequate mechanical properties. Mg has been proposed for this purpose but it has an excessively high corrosion rate and insufficient yield strength. In the present work pure Mg mechanically reinforced by a powder metallurgy (Mg(PM)) route and treated with KF was used. The effect of chlorides, at the physiological level, on four fluoride conversion coatings (F-CC) formed on Mg(PM) was evaluated comparatively. The behavior of Mg(PM) during fluoride treatments (0.01 M–0.3 M fluoride-containing solutions) before and after the addition of chlorides (8 g L^? 1 NaCl) was investigated by conventional corrosion techniques and by scanning electrochemical microscopy (SECM) complemented with SEM observations and EDX analysis. Results showed that the composition and the microstructural characteristics of the F-CCs as well as their corrosion behavior change with KF concentration and immersion time. Treatments in the 0.01 M–0.1 M KF range prove to be effective to protect Mg(PM) against corrosion in the absence of chlorides while higher KF solution concentration (0.3 M) adversely affects the corrosion resistance of this metal. In the presence of chloride ions the F-CCs progressively lose their fluoride content and their corrosion resistance at a rate that depends on the treatment conditions. Such temporary corrosion protection is appropriate for biodegradable implants.     

Mechanical properties of a degradable phosphate glass fibre reinforced polymer composite for internal fracture fixation

This paper reports on the mechanical properties and pH upon degradation of phosphate glass fibre reinforced methacrylate-modified oligolactide. Phosphate glass fibres of the composition 51.04 P₂O₅–21.42 CaO–25.51 Na₂O–2.03 SiO₂ (mol%) were produced by a crucible spinning technique. Fibres were embedded into a matrix of a degradable organic polymer network based on methacrylate-modified oligolactide; samples with and without addition of CaCO₃ for pH control were produced. pH during degradation in physiological NaCl solution could be increased to up to 6.5 by addition of 20 wt.% calcium carbonate to the fibre composites. pH in Tris buffer solution was about 7.11. Mechanical properties of dry specimens were investigated during 3-point bending tests and gave elastic moduli in the range of cortical bone (15 to 20 GPa). However, addition of calcium carbonate decreased tensile strength of the fibre composites and resulted in brittle fracture behaviour, while CaCO₃-free composites showed a fibrous fracture mode. Control of pH and degradation is a requirement for obtaining a fracture fixation device with degradation properties matching in vivo requirements. Results show that addition of CaCO₃ is suitable for controlling the pH during degradation of metaphosphate glass polymer composites.     

Influence of alkali treatment on the interfacial and physico-mechanical properties of industrial hemp fibre reinforced polylactic acid composites

The focus of this work was to produce short (random and aligned) and long (aligned) industrial hemp fibre reinforced polylactic acid (PLA) composites by compression moulding. Fibres were treated with alkali to improve bonding with PLA. The percentage crystallinity of PLA in composites was found to be higher than that for neat PLA and increased with alkali treatment of fibres which is believed to be due to the nucleating ability of the fibres. Interfacial shear strength (IFSS) results demonstrated that interfacial bonding was also increased by alkali treatment of fibres which also lead to improved composite mechanical properties. The best overall properties were achieved with 30 wt.% long aligned alkali treated fibre/PLA composites produced by film stacking technique leading to a tensile strength of 82.9 MPa, Young’s modulus of 10.9 GPa, flexural strength of 142.5 MPa, flexural modulus of 6.5 GPa, impact strength of 9 kJ/m², and a fracture toughness of 3 MPa m^1/2.     

Effect of water absorption on the mechanical properties of hemp fibre reinforced unsaturated polyester composites

Hemp fibre reinforced unsaturated polyester composites (HFRUPE) were subjected to water immersion tests in order to study the effects of water absorption on the mechanical properties. HFRUPE composites specimens containing 0, 0.10, 0.15, 0.21 and 0.26 fibre volume fraction were prepared. Water absorption tests were conducted by immersing specimens in a de-ionised water bath at 25 °C and 100 °C for different time durations. The tensile and flexural properties of water immersed specimens subjected to both aging conditions were evaluated and compared alongside dry composite specimens. The percentage of moisture uptake increased as the fibre volume fraction increased due to the high cellulose content. The tensile and flexural properties of HFRUPE specimens were found to decrease with increase in percentage moisture uptake. Moisture induced degradation of composite samples was significant at elevated temperature. The water absorption pattern of these composites at room temperature was found to follow Fickian behaviour, whereas at elevated temperatures it exhibited non-Fickian.     

Properties of medium density fibreboard (MDF) from kenaf (Hibiscus cannabinus L.) core as function of refining conditions

The objective of this study was to evaluate physical and mechanical properties of medium density fibreboard (MDF) panels made from kenaf core as function of fibre geometry and refining conditions. Raw material was prepared by using pressure levels of 3, 5 and 7 bar at two heating times, namely 3 and 5 min. The length and width of the fibres were determined employing image analyser. Experimental samples with a target density of 700 kg m⁻³ were produced with 12% of urea formaldehyde as a binder. Physical properties such as swelling in thickness (TS) and water absorption (WA) of the panels in addition to their mechanical properties including modulus of rupture (MOR), modulus of elasticity (MOE) and internal bonding (IB) were evaluated based on MS 1787:2005. Based on the test results, low digestion pressure produced longer fibre length and panels made from these fibres had higher TS with MOR and MOE than those of the others panels. However, the IB properties of samples were low. Panels made from shorter fibre resulted in contradict properties found above. The ideal properties of the samples were found for the panels made having fibre length of 0.81 mm and aspect ratio of 23.4. Such sample had 14.6%, 63.2%, 30.3 MPa, 3619 MPa and 0.66 MPa for TS, WA, MOR, MOE and IB, respectively.     

Effect of surface functionalization on mechanical properties and decomposition kinetics of high performance polyetherimide/MWCNT nano composites

In this investigation, Polyetherimide (PEI) reinforced with multi-walled carbon nanotube (MWCNT) using novel melt blending technique. Surface of MWCNTs are modified by acid treatment as well as by plasma treatment. PEI nano composites with 2 wt% treated MWCNT shows about 15% improvement in mechanical properties when compared to unfilled PEI. The thermal decomposition kinetics of PEI/MWCNT nano composites has been critically analyzed by using Coats – Redfern model. The increase in activation energy for thermal degradation by 699 kJ/mol for 2 wt% MWCNT implies improvement in the thermal properties of PEI. Studies under Fourier Transform Infrared Spectroscopy (FTIR) and Transmission Electron Microscopy (TEM) depict significant interfacial adhesion with uniform dispersion of MWCNT in polymer matrix due to surface functionalization. 0.5 wt% chemically modified MWCNT shows typical alignment of MWCNT. There is a significant improvement in mechanical properties and thermal properties for surface functionalized MWCNT reinforced.