Effect of carbon fibres on the mechanical properties and corrosion levels of reinforced portland cement mortars

The changes in mechanical properties of portland cement mortars due to the addition of carbon fibres (CF) to the mix have been studied. Compression and flexural strengths have been determined in relation to the amount of fibres added to the mix, water/binder ratio, curing time and porosity. Additionally, the corrosion level of reinforcing steel bars embedded in portland cement mortars containing CF and silica fume (SF) have also been investigated and reinforcing steel corrosion rates have been determined. As a consequence of the large concentration of oxygen groups in CF surface, a good interaction between the CF and the water of the mortar paste is to be expected. A CF content of 0.5% of cement weight implies an optimum increase in flexural strength and an increase in embedded steel corrosion.

Mechanical Properties and Durability of CNT Cement Composites

In the present paper, changes in mechanical properties of Portland cement-based mortars due to the addition of carbon nanotubes (CNT) and corrosion of embedded steel rebars in CNT cement pastes are reported. Bending strength, compression strength, porosity and density of mortars were determined and related to the CNT dosages. CNT cement paste specimens were exposed to carbonation and chloride attacks, and results on steel corrosion rate tests were related to CNT dosages. The increase in CNT content implies no significant variations of mechanical properties but higher steel corrosion intensities were observed.

Structure and mechanical properties of sodium and calcium caseinate edible active films with carvacrol

Edible active films based on sodium caseinate (SC) and calcium caseinate (CC) plasticized with glycerol (G) at three different concentrations and carvacrol (CRV) as active agent were prepared by solvent casting. Transparent films were obtained and their surfaces were analysed by optical microscopy and scanning electron microscopy (SEM). The influence of the addition of three different plasticizer concentrations was studied by determining tensile properties, while Fourier transformed infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) were used to evaluate the structural and thermal behavior of such films. The addition of glycerol resulted in a reduction in the elastic modulus and tensile strength, while some increase in the elongation at break was observed. In general terms, SC films showed flexibility higher than the corresponding CC counterparts. In addition, the presence of carvacrol caused further improvements in ductile properties suggesting the presence of stronger interactions between the protein matrix and glycerol, as it was also observed in thermal degradation studies. FTIR spectra of all films showed the characteristic bands and peaks corresponding to proteins as well as to primary and secondary alcohols. In summary, the best results regarding mechanical and structural properties for caseinates-based films containing carvacrol were found for the formulations with high glycerol concentrations.

Temperature influence on the physical and mechanical properties of a porous rock: San Julian's calcarenite

This work discusses the results from tests which were performed in order to study the effect of high temperatures in the physical and mechanical properties of a calcarenite (San Julian's stone). Samples, previously heated at different temperatures (from 105 °C to 600 °C), were tested. Non-destructive tests (porosity and ultrasonic wave propagation) and destructive tests (uniaxial compressive strength and slake durability test) were performed over available samples. Furthermore, the tests were carried out under different conditions (i.e. air-cooled and water-cooled) in order to study the effect of the fire off method. The results show that uniaxial compressive strength and elastic parameters (i.e. elastic modulus and Poisson's ratio), decrease as the temperature increases for the tested range of temperatures. A reduction of the uniaxial compressive strength up to 35% and 50% is observed in air-cooled and water-cooled samples respectively when the samples are heated to 600 °C. Regarding the Young's modulus, a fall over 75% and 78% in air-cooled and water-cooled samples respectively is observed. Poisson's ratio also declines up to 44% and 68% with the temperature in air-cooled and water-cooled samples respectively. Slake durability index also exhibits a reduction with temperature. Other physical properties, closely related with the mechanical properties of the stone, are porosity, attenuation and propagation velocity of ultrasonic waves in the material. All exhibit considerable changes with temperature.

Controlled rippling of graphene via irradiation and applied strain modify its mechanical properties: a nanoindentation simulation study

Ripples, present in free standing graphene, have an important influence in the mechanical behavior of this two-dimensional material. In this work we show through nanoindentation simulations, how out-of-plane displacements can be modified by strain resulting in softening of the membrane under compression and stiffening under tension. Irradiation also induces changes in the mechanical properties of graphene. Interestingly, compressed samples, irradiated at low doses are stiffened by the irradiation while samples under tensile strain do not show significant changes in their mechanical properties. These simulations indicate that vacancies, produced by the energetic ions, cannot be the ones directly responsible for this behavior. However, changes in roughness induced by the momentum transferred from the energetic ions to the membrane, can explain these differences. These results provide an alternative explanation to recent experimental observations of stiffening of graphene under low dose irradiation, as well as paths to tailor the mechanical properties of this material via applied strain and irradiation.

Effects of Fe addition on the mechanical and thermo-mechanical properties of SiC/FeSi2/Si composites produced via reactive infiltration

Remaining silicon in SiC-based materials produced via reactive infiltration limits their use in high-temperature applications due to the poor mechanical properties of silicon: low fracture toughness, extreme fragility and creep phenomena above 1000 °C. In this paper SiC–FeSi2 composites are fabricated by reactive infiltration of Si–Fe alloys into porous Cf/C preforms. The resulting materials are SiC/FeSi2 composites, in which remaining silicon is reduced by formation of FeSi2. For the richest Fe alloys (35 wt% Fe) a nominal residual silicon content below 1% has been observed. However this, the relatively poor mechanical properties (bending strength) measured for those resulting materials can be explained by the thermal mismatch of FeSi2 and SiC, which weakens the interface and does even generate new porosity, associated with a debonding phenomenon between the two phases.

Effects of infiltration pressure on mechanical properties of Al–12Si/graphite composites for piston engines

In this work results for the flexural strength and the thermal properties of interpenetrated graphite preforms infiltrated with Al-12wt%Si are discussed and compared to those for packed graphite particles. To make this comparison relevant, graphite particles of four sizes in the range 15–124 μm, were obtained by grinding the graphite preform. Effects of the pressure applied to infiltrate the liquid alloy on composite properties were investigated. In spite of the largely different reinforcement volume fractions (90% in volume in the preform and around 50% in particle compacts) most properties are similar. Only the Coefficient of Thermal Expansion is 50% smaller in the preform composites. Thermal conductivity of the preform composites (slightly below 100 W/m K), may be increased by reducing the graphite content, alloying, or increasing the infiltration pressure. The strength of particle composites follows Griffith criterion if the defect size is identified with the particle diameter. On the other hand, the composites strength remains increasing up to unusually high values of the infiltration pressure. This is consistent with the drainage curves measured in this work. Mg and Ti additions are those that produce the most significant improvements in performance. Although extensive development work remains to be done, it may be concluded that both mechanical and thermal properties make these materials suitable for the fabrication of piston engines.

Mechanical, thermal and colorimetric properties of LLDPE coloured with a blue nanopigment and conventional blue pigments

Purpose – This research deals with a new kind of nanopigment, obtained from the combination of organic dyes and layered nanoclays, that the authors call nanoclay-colorant pigment (NCP). Whilst they have already been employed in inks and coatings, to date these nanopigments have not been used as pigments for polymers. The existing lack of knowledge surrounding them must be redressed in order to bridge the gap between current academic studies and commercial exploitation. Therefore, the main purpose of this paper is to examine the hitherto unknown aspects of the NCP, which relate specifically to their applicability as a new type of colorant for polymers. Design/methodology/approach – A blue NCP has been prepared at the laboratory according to the patented method of synthesis (patent WO0104216), using methylene blue and montmorillonite nanoclay. It has then been applied to a thermoplastic polymer (linear low-density polyethylene – LLDPE) to obtain a coloured sample. Furthermore, samples with the same polymer but using conventional blue colorants have been prepared under the same processing conditions. The mechanical, thermal and colorimetric properties of these materials have been compared. Findings – The thermal stability of the sample coloured with NCP is reduced to some extent, while the mechanical strength is slightly increased. Moreover, this sample has better colour performance than the conventionally pigmented samples. Originality/value – In this paper, a blue NCP has been synthesised and successfully employed with polyethylene and the obtained sample shows better colour performance than polyethylene with conventional pigments.

Self-sensing properties of alkali activated blast furnace slag (BFS) composites reinforced with carbon fibers

In recent years, several researchers have shown the good performance of alkali activated slag cement and concretes. Besides their good mechanical properties and durability, this type of cement is a good alternative to Portland cements if sustainability is considered. Moreover, multifunctional cement composites have been developed in the last decades for their functional applications (self-sensing, EMI shielding, self-heating, etc.). In this study, the strain and damage sensing possible application of carbon fiber reinforced alkali activated slag pastes has been evaluated. Cement pastes with 0, 0.29 and 0.58 vol % carbon fiber addition were prepared. Both carbon fiber dosages showed sensing properties. For strain sensing, function gage factors of up to 661 were calculated for compressive cycles. Furthermore, all composites with carbon fibers suffered a sudden increase in their resistivity when internal damages began, prior to any external signal of damage. Hence, this material may be suitable as strain or damage sensor.

Influence of thymol and silver nanoparticles on the degradation of poly(lactic acid) based nanocomposites: thermal and morphological properties

Biopolymers, such as poly(lactic acid) (PLA), have been proposed as environmentally-friendly alternatives in applications such as food packaging. In this work, silver nanoparticles and thymol were used as active additives in PLA matrices, combining the antibacterial activity of silver with the antioxidant performance of thymol. The combined action of both additives influenced PLA thermal degradation in ternary systems. DSC results showed that the addition of thymol resulted in a clear decrease of the glass transition temperature (Tg) of PLA, suggesting its plasticizing effect in PLA matrices. Slight modifications in mechanical properties of dog-bone bars were also observed after the addition of the active components, especially in the elastic modulus. FESEM analyses showed the good distribution of active additives through the PLA matrix, obtaining homogenous surfaces and highlighting the presence of silver nanoparticles successfully embedded into the bulk matrix. Degradation of these PLA-based nanocomposites with thymol and silver nanoparticles in composting conditions indicated that the inherent biodegradable character of this biopolymer was improved after this modification. The obtained nanocomposites showed suitable properties to be used as biodegradable active-food packaging systems with antioxidant and antimicrobial effects.

Structure, gas-barrier properties and overall migration of poly(lactic acid) films coated with hydrogenated amorphous carbon layers

Hydrogenated amorphous carbon (a-C:H) films were grown on a poly(lactic acid) (PLA) substrate by means of a radiofrequency plasma-enhanced chemical vapour deposition (rf-PECVD) technique with different deposition times (5, 20 and 40 min). The main goal of this treatment was to increase the barrier properties of PLA, maintaining its original transparency and colour as well as controlling interactions with food simulants for packaging applications. Morphological, chemical, and mechanical properties of PLA/a-C:H systems were evaluated while permeability and overall migration tests were performed in order to determine the effect of the plasma treatment on the gas-barrier properties of PLA films and their application in food packaging. Morphological results suggested a good adhesion of the deposited layers onto the polymer surface and the samples treated for 5 and 20 min only slightly darkened the PLA film. X-ray photoelectron spectroscopy revealed that the structural properties of the carbon layer deposited onto the PLA film depend on the exposure time. PLA/a-C:H system treated for 5 min showed the highest barrier properties, while none of the studied samples exceeded the migration limit established by the current legislation, suggesting the suitability of these materials in packaging applications.

Fire-resistance, physical, and mechanical characterization of particleboard containing Oceanic Posidonia waste

In this work, particleboards manufactured with Oceanic Posidonia waste and bonded with cement are investigated. The particleboards are made with 3/1.5/0.5 parts of cement per part of Posidonia waste. The physical properties of bulk density, swelling, surface absorption, and dimensional changes due to relative humidity as well as the mechanical properties of modulus of elasticity, bending strength, surface soundness, perpendicular tensile strength and impact resistance are studied. In terms of the above properties, the best results were obtained for particleboards with high cement content and when the waste “leaves” are treated (crushed) before board fabrication, due to internal changes to the board structure under these conditions. Based on the results of fire tests, the particleboard is non-flammable without any fire-resistant treatment.