Showing papers in "Key Engineering Materials in 2014"

Effect of Sisal Fiber Hornification on the Fiber-Matrix Bonding Characteristics and Bending Behavior of Cement Based Composites

Abstract: Cycles of wetting and drying can change the microstructure of vegetable fibers through a mechanism known as hornification, which modifies the polymeric structure of the fiber-cells resulting in a higher dimensional stability. In the present work the influence of hornification on the sisal fiber-matrix bond adhesion as well as in the sisal fiber dimensional stability and mechanical behaviour under direct tension was evaluated. Furthermore, cementitious composites reinforced with randomly dispersed hornified sisal fibers were developed and characterized under bending loads. The results show that the tensile strength and strain at failure of the hornified sisal fibers were increased by about 5% and 39%, respectively, whereas the modulus of elasticity was reduced by 9%. The fibers also presented higher dimensional stability with the hornification process. The fiber-matrix bonding was improved and the pull-out resistance of the fibers submitted to ten cycles of wetting and drying was increased by about 40% to 50%. The higher fiber-matrix bond strength contributed to an increase in the ductility and post-cracking behaviour of the composite. The fracture process was characterized by the formation of multiple cracks with the hornified sisal fibers presenting a higher ability to bridge and arrest the cracks.

Confinement of Masonry Columns with PBO FRCM Composites

Abstract: The overarching goal of this work is to provide a fundamental understanding of the behavior of solid brick masonry columns confined with fiber reinforced cementitious matrix (FRCM) composites. FRCM is a newly-developed type of composite material comprised of a cementitious inorganic matrix (binder) and embedded fibers that are usually bundled to improve the bond between the matrix and the fibers. Compression tests were carried out to investigate the influence of the FRCM confinement and the brick patterns on the load-carrying capacity of the confined columns. Compression tests were conducted on brick masonry columns with different brick configurations. Digital image correlation measurements on the surface of the composite and on the surface of the brick for the control specimens were attempted in order to understand the role of the mortar joints and the arch effect across the section of the columns due to the confinement. The experimental results indicate that FRCM composites can effectively increase the load-carrying capacity of brick masonry columns and the failure mode could be different from the one observed for masonry columns confined with fiber-reinforced polymer (FRP) composites.

Experimental Analysis of the Bond Behavior of Glass, Carbon, and Steel FRCM Composites

Abstract: In recent decades, the construction industry has witnessed a rapid growth of interest in strengthening and retrofitting of existing reinforced concrete (RC) and masonry structures. Fiber reinforced polymer (FRP) composites have gained great popularity, and several studies are now available in the literature on their use in strengthening and retrofit applications. Promising newly-developed composite materials are represented by the so-called fiber reinforced cementitious matrix (FRCM) composites. FRCM composites are comprised of high strength fibers embedded within a cementitious matrix that is responsible for the stress transfer between the existing structure and the strengthening material. FRCM composites are still in their infancy, and very limited results are available in the literature on RC and masonry strengthening applications. This study presents an experimental campaign conducted on different FRCM composites comprised of glass, carbon, or steel fibers embedded within two different cementitious matrices and applied to concrete prisms. The single-lap direct-shear test was used to study the stress-transfer mechanism between the FRCM composite and the concrete substrate. Two different composite bonded lengths were investigated. Debonding occurred at the matrix-fiber interface for some of the composites tested and at the concrete-matrix interface for others. This work contributes to the study of the bond behavior of FRCM composites, which represents a key issue for the effectiveness of FRCM composite strengthening.

The Influence of Fiber Treatment on the Mechanical Behavior of Jute Textile Reinforced Concrete

Abstract: In the present work a natural textile reinforced concrete (TRC) was developed and mechanically characterized. A fabric made of jute, a natural occurring fiber, was used as reinforcement in a fine grained cementitious matrix with a low content of calcium hydroxide. Tensile tests were performed on TRC reinforced with 3 and 5 layers of jute fabric. The mechanical tensile tests were coupled with image analysis in order to measure the crack spacing and the results were correlated with the applied tensile strain. Various stages of loading corresponding to initiation, propagation, distribution, opening, and localization of a crack system in the specimen are discussed. In order to improve the fiber-matrix interface the jute fabric was treated with a polymer based coating.

Energy - absorption and efficiency diagrams of rigid PUR foams

Abstract: Polyurethane (PUR) foam materials represent a class of materials widely used for impact protection and energy absorption. This paper presents a characterization of different rigid PUR foams under compressive impact loading by means of energy absorption and efficiency diagrams. Compressive properties were investigated on cubic specimens on the foams’ rise direction at room temperature with a loading rate of 3.09 m/s for three different closed-cell foams with densities of 100 kg/m3, 160 kg/m3 and 300 kg/m3 respectively. Experimental results show that the compression modulus, yield stress and plateau stress increase with density. Most of the energy is absorbed in the plateau region because of the cell deformation associated with this phenomenon, allowing greater absorption of impact energy at nearly constant load. Authors have found that both the energy absorption and efficiency diagrams are consistent and present similar results for studied foams.

Non-Destructive Techniques and Monitoring for the Evolutive Damage Detection of an Ancient Masonry Structure

Abstract: In the present article non-destructive testing evaluation of the existing damage evolution has been applied to some buildings of the medieval town of Craco (Matera, Italy) and, in particular, to the Normand tower Actually the little town of Craco is totally abandoned as a consequence of the activation of the landslide motions of its soil depth Nevertheless, the Normand tower still stands because it is located on a stable and stiffer foundation ground The tower was built in the XII century It is 20 m tall and has a symmetric square plan, with dimensions 11 m x 11 m; it was built for defense against enemy attacks Inside the tower a cistern in reinforced concrete was placed in 1949 It is not connected to the structural walls of the tower; however it represents an obstacle for installing the damage detection equipment and sensors In this article a preliminary study on the masonry structure of the Normand tower is carried on A finite element numerical model has been developed and a modal analysis has been performed The final aim of the research is to find out the evolutionary stage of the cracks and to propose a possible retrofit of the tower

Durability performance of fly ash based one-part geopolymer mortars

Abstract: Environmental concerns regarding the high CO2 emissions related to the production of ordinary Portland cement (OPC) led to research efforts on the development of eco-efficient alternative binders. Geopolymers constitute promising inorganic binders alternative to OPC which are based on aluminosilicates by-products and alkali activators. The geopolymerization technology of aluminosilicates is a complex chemical process evolving dissolution of raw materials, transportation, orientation and polycondensation of the reaction products. Classical two part geopolymers could become more eco-efficient with a lower CO2 footprint if sodium silicate usage is avoided. Besides current geopolymeric mixes can suffer from efflorescence originated by the fact that alkaline or soluble silicates that are added during processing cannot be totally consumed during geopolymerisation. Therefore, new and improved geopolymer mixes are needed. One-part geopolymers (sodium silicate free) were first proposed in 2007. However, very few papers were published on these materials. This paper presents experimental results on the durability performance of one-part geopolymers concerning water absorption, penetration of chloride, carbonation resistance and resistance to acid attack. Hydration products results assessed by FTIR spectra are also presented.

Comparison between Wrought and EBM Ti6Al4V Machinability Characteristics

Abstract: Electron Beam Melting (EBM) is attracting large interest among the manufacturers of surgical implants as a near-net shape technology. Titanium alloy Ti6Al4V is widely used in the biomedical field thanks to its high biocompatibility, corrosion resistance and mechanical properties. The chemistry and microstructural features of EBM Ti6Al4V indicate lower machinability in comparison with wrought Ti6Al4V. Aim of the paper is to present a comparison between the machinability of wrought and EBM Ti6Al4V in semi-finishing external turning, by quantifying the effects of the cutting speed and the feed rate. Tool wear, surface integrity, chip morphology and microstructural analysis have been used to compare and assess the machinability of Ti6Al4V delivered in the two conditions.

Microwave Heating of Steel Slag Asphalt Mixture

Abstract: In this research, the potential of using steel slag asphalt mixture as a self-healing material was investigated by means of microwave heating. The microwave heating rate and thermal conductivity of asphalt mixtures were tested respectively. The result shown that, the heating rate of steel slag asphalt mixtures is approximately two times faster than limestone asphalt mixtures. While its thermal conductivity is slightly lower. It is concluded that microwave heating can be used to promote self-healing of steel slag asphalt mixture.

Investigation of a New High Sensitive Micro-Electromechanical Strain Gauge Sensor Based on Graphene Piezoresistivity

Abstract: A new strain gauge based on graphene piezoresistivity was fabricated by a novel low cost technique which suits mass production of micro piezoresistor sensors. The strain gauge consists of a monolayer graphene film made by chemical vapor deposition on a copper foil surface, and transferred to Si/SiO2 surface by using a polymethyl-methacrylate (PMMA) assisted transfer method. The film is shaped by laser machine to work as a conductive-piezoresistive material between two deposited electrical silver electrodes. This method of fabrication provides a high productivity due to the homogeneous distribution of the graphene monolayer all over the Si/SiO2 surface. The experimentally measured gauge factor of graphene based device is 255, which promises a new strain gauge sensor of high sensitivity.

Magnesium Oxysulfate Fibercement

Abstract: Recently the use of alternative binder has been verified in several applications like roofing, sheets, panels and refractory. Thus, in this work the authors show results of some properties of Magnesium Oxysulfate Cement reinforced by fibers, specially traction in flexion and durability. MOS cement are formulated and governed by reactions like acid-base between magnesium oxide and magnesium sulfate solution. Some properties as abrasion resistance can be until 1.5 times that of Ordinary Portland Cement. Furthermore its compressive and transverse strengths are also higher than OPC. In the USA and Europe the major use of MOS cement is in the manufacture of lightweight insulating panels. In order to evaluate MOS cement properties, it was analysed two different matrices reinforced by polymeric and cellulose fibers. Calcium carbonate was employed as filler. Tests showed good mechanical behaviour, durability, and the possibility of using MOS fibercements as an alternative for non-asbestos products.

Comparing the Environmental Impact of Stabilisers for Unfired Earth Construction

Abstract: Buildings account for approximately one third of the total worldwide energy emissions, of which approximately a quarter can be attributed to the embodied energy of the building. Current UK legislation for low-energy homes is only concerned with operational energy. Embodied energy, and carbon, is not currently considered but over the design life of an average building is expected to make a significant contribution to the total whole life energy used. Earthen building materials contribute to reduce energy consumption in use through their passive regulation of temperature and humidity. In addition, there can also be significant embodied energy savings compared to other materials. Traditional methods of earthen construction, using locally sourced materials and manual labour require minimal energy for the transport and construction. A greater uptake of earth construction is likely to come from modern innovations such as industrialised manufacture. Extruded fired brick manufacturing processes has the potential to produce a high quality, low cost and low energy product suitable for the mainstream construction sector in both developed and developing nations. By not firing the extruded clay bricks, an embodied energy saving of 86% can be achieved, compared to fired clay, and 25% compared to concrete blocks. However, there are limitations to the structural use of unstabilised earth bricks due to the loss of strength under high moisture content conditions. The use of traditional and novel stabilisation methods can be adopted to address the concerns over strength and durability. Cement and lime are widely used in some countries, but both significantly increase material embodied energy and carbon and can inhibit passive humidity regulation. The paper presents results from a study of the embodied energy of various stabilisers used for unfired clay materials. The Global Warming Potential (GWP) is a measure of the equivalent carbon dioxide that allows for the relative weightings of damaging greenhouse gasses. Both the embodied energy and the GWP figures of various stabilisers are compared and discussed. The conclusion of the work is that there is a maximum quantity of stabiliser than should be used. Typically the quantities of stabiliser are quoted as the amount that gives the maximum strength, but this should take account of not only strength but the environmental impact of achieving the improvement.

Identification of the Modal Properties of a Building of the Greek Heritage

Abstract: In this paper, the experimental modal identification analysis of the public building “San Giacomo” in Corfu (Greece) is illustrated. It represents the unique example of a structure built utilising carves stones inside the city of Corfu. The building has a rectangular plan shape with dimensions 24.75 x 14 m, and height 9 m; all the floors are made by wood. The monitoring system consists of several elements properly connected: the units of acquisitions or piezoelectric accelerometers (in total 18 installed on the different walls) with a sensitivity of 1000 mV/g; the data acquisition system or DAQs positioned at each monitored level; the laptop with an acquisition software; the cables that connect all elements to each other. The paper describes the phases of the investigations, the technical details of the performed in-situ tests, the first identified frequencies of the building by means of the classical methods of Operational Modal Analysis (OMA) and the comments about the acquired data.

Confinement Effectiveness in Eccentrically Loaded Masonry Columns Strengthened by Fiber Reinforced Cementitious Matrix (FRCM) Jackets

Abstract: .The paper is devoted to the analysis of the effectiveness of the Carbon Fiber Reinforced Cementitious Matrix (C-FRCM) as confinement system of the masonry and the characterization of the structural response of masonry column confined by C-FRCM jackets, accounting for all geometrical and mechanical involved parameters. At this aim, tests on confined masonry column under eccentric axial load were carried out. Five masonry column having an overall length of 650 mm, with rectangular cross-section, 250 x 250 mm, were eccentrically loaded until collapse; two specimens were un-confined and used as control specimens, two specimens were confined with one layer of C-FRCM and one specimen was confined with two layers of C-FRCM. The eccentricity values considered were e/H=0and e/H=0.20, being H the height of the section. Failure modes and load-strain diagrams were considered to analyze test results and to evaluate the effectiveness of the confinement both in terms of strength and ductility.

New Die Concept for Self-Pierce Riveting Materials with Limited Ductility

Abstract: Lightweight materials, such as aluminum die castings, are used more and more for automotive applications. Due to the limited weldability, joining these materials by self-pierce riveting has been established. The challenge in this regard is that these materials, especially new high strength aluminum die castings, have a limited ductility, while the joining processes locally induce large plastic deformations. Consequently, joining by forming of these materials can be accompanied by cracks, which develop during the forming operation. This paper shows the experimental and numerical investigation of a new die concept for self-pierce riveting materials with limited ductility. At the new tool concept the riveting die is separated and a movable die element is used. This element allows that the parts are superimposed with compressive stresses during the self-pierce riveting process. In the paper it can be shown, that in contrast to the conventional process crack-free joints can be generated by using the new tool concept. Determination of the joining parameters and the die design was supported by simulative investigations. Additionally, the new and the conventional self-pierce riveting process are compared on the basis of results from the experimental investigations.

Dry Masonry Strenghtening through Basalt Fibre Ropes: Experimental Results against Out-of-Plane Actions

Abstract: One of the most important characteristics that historical masonry should have is that of a monolithic behavior. Without these basic feature, no structural analysis could be considered reliable. If this characteristic is absent, strengthening bearing masonry giving it a transversal monolithic behavior is one of the first retrofitting actions to do so as to improve its seismic performance. Hence come out the idea to develop a new consolidation technique specially formulated for historical masonry. Stitching masonry through continuous flexible elements is an innovative technique, able to connect the several masonry components and to attribute to it a monolithic behavior according to the principles that govern the intervention on existing buildings: minimal intervention, compatibility, reversibility, respect of authenticity, matter conservation, control of the visual impact and possibility of recognizing the intervention. Basalt fibers ropes of 4 mm of nominal diameter (declared by manufacturer), have been used in this experimental program as continuous flexible element. The technique has been already tested and proved to be effective for improving the behavior against “in-plane” actions. Good results has been obtained also excluding synthetic adhesives (resins), with an enhancement about reversibility. In this paper, the results of an experimental campaign aimed to evaluate the technique effectiveness against “out-of-plane” loads are presented. Reinforced and unreinforced brick masonry specimens have been tested simulating vertical bending mechanism activation to evaluate the stitches contribute.

Effect of Aggregate Type on the Concrete Matrix/Aggregates Interface and its Influence on the Overall Mechanical Behavior. A Numerical Study.

Abstract: This paper investigates the effect of siliceous, limestone and plastic aggregates on the compressive behavior of concrete. Firstly, the matrix/aggregates interface is characterized using a scanning electronic microscope. Compressive test is then simulated on a 3D numerical concrete using finite element method. The influence of the matrix/aggregates interface quality is quantified. The results give a new insight and help on the understanding of the contribution of the nature of the aggregate on the overall mechanical behavior of concretes.

Insulating and Strength Properties of an Aerogel-Incorporated Mortar Based an UHPC Formulations

Abstract: With the increasing attention towards energy-efficient and zero emission buildings, improvement to concrete properties is becoming more and more significant in construction and building sectors One such area is to enhance the thermal properties, while maintaining maximum strength of the material Here, attempts were made to address this challenge by formulating mortar composites with low thermal conductivity while targeting a minimum compressive strength of 20 MPa at 28 days For this purpose, aerogel was utilized in an ultrahigh performance concrete (UHPC) formulation to create new aerogel-incorporated mortar (AIM) It was found that AIMs possessing 50 vol% aerogel registered a compressive strength of 20 MPa, while displaying a thermal conductivity of ~ 055 W/(mK) By adding more aerogel to reach 70 vol%, while the thermal conductivity of the concrete decreased by ~ 20 %, a sharp decrease in strength to 58 MPa was observed This represents only 1/30 of the original strength of the UHPC mortar Further addition of aerogel till 80 vol% showed negligible compressive strength, attributing to the imbalance of the particle-matrix ratio in the mortar system, causing a decrease in adhesion of the binder-aggregates

Influence of Process Parameters on Distribution of Shear Strain through Sheet Thickness in Asymmetric Rolling

Abstract: Materials with ultrafine grain structure and unique physical and mechanical properties can be obtained by methods of severe plastic deformation, which include asymmetric rolling processes. Asymmetric rolling is a very effective way to create ultrafine grain structures in metals and alloys. Since the asymmetric rolling is a continuous process, it has great potential for industrial production of ultrafine grain structure sheets. Basic principles of asymmetric rolling are described in detail in scientific literature. Focus in the well-known works is on the possibility to control the structure of metal sheets. However the systematic data on the influence of the process parameters (e.g., ratio of rolls velocity mismatch, reduction per pass, friction and diameter of rolls), and the shear strain rate required to achieve a significant grain refinement in asymmetric rolling are lacking. The influence of ratio of rolls velocity mismatch, reduction per pass, friction and the rolls diameter on the distribution of shear strain through the sheet thickness in asymmetric rolling has been studied in DEFORM 2D. The results of the study will be useful for the research of evolution of ultrafine grain structure in asymmetric rolling.

Durability Analysis for FRP and SRG Composites in Civil Applications

Abstract: In this study, an effort was made to develop an experimental protocol to study the effects of accelerated ageing on composite materials based on bamboo and steel fibers. The physic-mechanical properties of different types of steel and bamboo fibers were investigated. Specimens were subjected to environmental agents. Mechanical and physical tests were used to measure the retained properties and to observe the causes of damage and strength reduction. The experimental data showed that resin properties may strongly influence the durability of FRP reinforcement, environmental combined cycles did not take to significant damage of conditioned specimens; steel fibers are sensitive to alkaline attack when resin does not provide adequate protection to fibers.

Carbonation Resistance of High Volume Fly Ash Concrete

Abstract: The cement industry is responsible for a large part of the global environmental problems: is the largest consumer of natural resources; the most responsible for the emission of greenhouse gases, including about 1.8 Gt of CO2; and requires huge amounts of energy, corresponding to between 12 and 15% of industrial energy use. The cement is also not used in the most appropriate manner, since 40% of the consumption of concrete is due to the renovation and repair of buildings, making concrete structures inefficient because its durability is relatively low. However, in the future, concrete can and should evolve in order to improve its eco-efficiency, with a smaller amount of cement in its composition, replacing it with high quantities of mineral additions, particularly fly ash. Nevertheless, current technology may not allow this type of concrete to be very efficient, because its long-term durability may be compromised. In fact, with increasing dosage of pozzolanic mineral additions, alkali paste components are consumed in the reaction leaving it vulnerable to concrete carbonation which may compromise the passivation layer needed for steel rebar protection against corrosion. This article explores a promising approach to mitigate this problem, which consists in the careful addition of hydrated lime in the concrete composition, highlighting the synergy of its components, significantly enhancing its carbonation resistance. It is proposed, therefore, to manufacture a concrete with high volume of fly ash, low cement content and high service life period: an efficient and sustainable concrete. In this context, an experimental campaign was developed with the aim of characterization of pastes behavior with high fly ash content, in particular with respect to its durability. The results will be presented and properly analyzed.

Influence of Sample Thickness and Capping on Characterization of Bedding Mortars from Historic Masonries by Double Punch Test (DPT)

Abstract: For determination of compressive strength of bedding mortar used in historic masonries, a promising moderately-destructive technique is double punch test (DPT). DPT consists of loading prismatic samples of mortar (about 4×4×1 cm3) by means of two circular steel platens (typically 2 cm diameter) and then calculating mortar compressive strength as the ratio of the failure load to the cross section of the circular platens. In this study, the influence of mortar sample thickness and mortar sample capping on the reliability of results obtained by DPT was systematically investigated. The influence of sample thickness was assessed by comparing DPT results obtained for samples with 5, 10, 15 and 20 mm thickness with compressive strength determined by testing reference 4 cm-side cubes. Different mortars were considered (cement, lime-cement, natural hydraulic lime), in order to investigate a wide range of mortar mechanical characteristics. The influence of surface capping was evaluated on a lime-cement mortar by comparing compressive strength determined on reference cubes with strength obtained by DPT on proper samples, without capping and after capping with rubber, gypsum and cement. The results of the study indicate that sample thickness substantially influences mortar compressive strength determined by DPT, which may vary by up to three times depending on sample thickness. A good estimation of the actual mortar compressive strength was obtained when samples with thickness similar to the loading platens diameter were tested, which suggests that choosing the size of the loading platens for DPT based on the thickness of mortar joints under investigation may be an effective way for obtaining reliable estimations. As for the influence of surface capping, in those cases where no mortar sample regularization is possible, because of the poor quality of the mortar, the results of the study indicate that sample capping actually seems necessary in order to avoid significant underestimations of mortar compressive strength. Considering the higher practicality offered by gypsum with respect to rapid-setting cement for surface capping, the use of gypsum seems preferable.

High Temperature Fatigue Tests of a Cu-Be Alloy and Synthesis in Terms of Linear Elastic Strain Energy Density

Abstract: The present paper summarises the results from uniaxial-tension stress-controlled fatigue tests performed at different temperatures up to 650°C on Cu-Be specimens Two geometries are considered: hourglass shaped and plates weakened by a central hole (Cu-Be alloy) The motivation of the present work is that, at the best of authors’ knowledge, only a limited number of papers on these alloys under high-temperature fatigue are available in the literature and no results deal with notched componentsThe Cu-Be specimens fatigue data are re-analyzed in terms of the mean value of the Strain Energy Density (SED) averaged over a control volume Thanks to the SED approach it is possible to summarise in a single scatter-band all the fatigue data, independently of the specimen geometry

Effect of Oxidation on Sliding Wear Behavior of NiCrSiB-TiB2 Plasma Sprayed Coatings

Abstract: The main goal of this work is to study dry sliding wear behavior of NiCrSiB-TiB2 plasma sprayed coating against NiCrSiB coating. NiCrSiB-based powders with 10, 20, 40 wt.% TiB2 particles content were deposited on steel substrates by plasma spraying. The structure of NiCrSiB-TiB2 coatings consists of Ni-based matrix and TiB2 and CrB grains. Among the coatings studied, the NiCrSiB-20wt.%TiB2 shows excellent wear-resistance. The worn surfaces were observed using scanning electron microscopy and Auger electron spectroscopy to determine the wear mechanisms.

Boron Containing Nano Hydroxyapatites (B-n-HAp) Stimulate Mesenchymal Stem Cell Adhesion, Proliferation and Differentiation

Abstract: Osteoporosis (OP) is a systemic metabolic disease identified with decrease of bone mineral density and deterioration of microstructure leading to fragility fractures in elderly. Boron (B) is assumed to stimulate osteoblasts. Hydroxyapatite (HAp) is clinically used to conduct bone regeneration and improves implant integration. Nano(n)-HAp expands the surface area for cell adhesion and may improve bone regeneration and tissue integration. The objective of this study was to examine the adhesion, proliferation and differentiation of B-n-HAp with mesenchymal stem cells (MSC’s). Human bone marrow derived MSC’s phenotype was assessed using scanning and transmission electron microscopy after combining with B-n-HAp and n-HAp. Cell adhesion and proliferation potential of these ceramics was examined with the real time cell analysis (xCELLigence, Roche Applied Science and ACEA Bioscience, USA) system and adipogenic-osteogenic differentiation was analyzed with morphological and quantitative methods. MSC’s adhesion and proliferation rates (cell index, 4.50) were higher than controls (cell index, 4.00). Adipogenic and osteogenic differentiation potential of MSC’s remained unchanged in the presence of B-n-HAp ceramics. In conclusion, B-n-HAp stimulates MSC’s adhesion, proliferation and differentiation and has a potential to regenerate bone tissue.

Elastic properties of thermo-hydro-mechanically modified bamboo (Guadua angustifolia Kunth) measured in tension.

Abstract: Guadua angustifolia Kunth (Guadua) was subjected to thermo-hydro-mechanical (THM) treatments that modified its microstructure and mechanical properties. THM treatment was applied to Guadua with the aim of tackling the difficulties in the fabrication of standardised construction materials and to gain a uniform fibre density profile that facilitates prediction of mechanical properties for structural design. Dry and water saturated Guadua samples were subjected to THM treatment. A densified homogenous flat sheet material was obtained. Mechanical properties of small clear specimens of THM modified Guadua were evaluated by testing in tension and compared to the results of the same test on a control specimen. Samples were tested in the elastic range to determine values for Modulus of Elasticity (MOE) and Poissons ratio. There was a significant increase in the tensile MOE values (parallel to the direction of the fibres) for densified samples. MOE values measured were 16.21 GPa, 22.80 GPa and 31.04 GPa for control, densified dry and densified water saturated samples respectively. Oven dry densities for these samples were 0.54 g/cm3, 0.81 g/cm3 and 0.83 g/cm3. Despite a 50 % reduction in the radial Poissons ratio for the water saturated sample, no further variation in the Poissons ratio as a result of densification was observed for control and densified dry samples. This paper presents the results of the first phase of a study focussed on the manufacturing of flat Guadua sheet (FGS) by THM treatment and the characterization of its mechanical properties. The achievement of a dimensionally stable FGS by THM modification, with a uniform density and achieved with reduced labour effort during manufacture, will be of key importance for the development of structural applications, and could have a significant impact in the bamboo industry. The final aim of the research at the University of Bath is the development of Cross Laminated Guadua (CLG) panels using THM modified and laminated FGS glued with a high performance resin.

Seismic Retrofitting by FRP of a School Building Damaged by Emilia-Romagna Earthquake

Abstract: A school building, located in Bomporto (Modena, Italy) and hit by the Emilia-Romagna Italian earthquake in 2012, has been investigated in the paper. The seismic vulnerabilityof the building has been evaluated by means of non-linear static analyses, which have been carriedoutthrough the 3MURI calculation program. The comparison between the damage state producedby the earthquake and the simulation results put in evidence the reliability of the numerical analysis.On the basis of the detected seismic deficiencies of the damaged building, a structuralreinforcement intervention of masonry walls has been designed by means of either FRP strips orsteel ones. Finally, a parametric analysis by varying the material and the geometrical configurationof the FRP intervention (width and spacing of the strips) has been performed with the purpose toidentify, through a cost-to-benefit comparison, the optimal retrofitting solution.

IR Thermography and Resistivity Investigations on Ni-Ti Shape Memory Alloy

Abstract: The shape recovery efficiency of Ni-Ti shape memory springs has been investigated upon the application up to 6 X 105 thermo-activation cycles. The hysteretic behaviour of the Martensitic-Austenitic phase transition has been characterized by resistivity measurements and infrared thermography. A loss in the recovery efficiency of the original shape has been observed and has been ascribed to functional fatigue leading to the formation of the R phase upon sample heating. Nevertheless, one way shape memory effect was found to exhibit an asymptotic stable behaviour which makes possible the realization of Ni-Ti actuators able to operate for a relative large number of activation cycles.

Sol-Gel Synthesis and Characterization of SiO2-CaO-P2O5-SrO Bioactive Glass: In Vitro Study

Abstract: Bioactive glass of the type CaO–SrO–P2O5–SiO2 was obtained by the sol-gel processing method. Three samples containing 0 mol%, 5 mol% and 10 mol% of SrO were synthesized. The obtained bioactive glasses were characterized by the techniques such as, X-ray diffraction (XRD) and scanning electron microscope (SEM) and the effect of SrO/CaO substitution on in vitro biological properties of the synthesized glasses were evaluated and biocompatibility of the samples was measured using MTT assay. The results showed that incorporation of Sr in the obtained glass network did not result in any structural alteration of it due to the similar role of SrO compared with that of CaO. In vitro experiments with human osteosarcoma cell lines (MG-63) and MTT assay indicated that bioactive glass incorporating 5 mol% of Sr in the composition is non-toxic and revealed good biocompatibility.

Effect of Colloidal Nano-Silica on the Mechanical and Durability Performances of Mortar

Abstract: s. The mechanical and durability properties of cement mortars with colloidal nanosilica (CNS) were investigated experimentally. Reference mortar with a low water-to-cement ratio of 0.30 was used in this study. The influence of CNS was evaluated by adding 0.5, 1.0, 1.5 and 2.0% of CNS by weight of cement. CNS was first stirred in the mixing water for 2 minutes before added to cement and sand. Superplasticizer was used to maintain the same flowability. Results showed that the compressive strength consistently increases with higher dosage of CNS at all the curing ages, due to both hydration acceleration and pozzolanic reaction. With the increase in CNS, the migration coefficient and water sorptivity consistently decreased; with 2% of CNS, the migration coefficient and water sorptivity were reduced by 45% and 30% respectively in comparison with the reference mortar. The improved durability could be explained by the reduction and refinement in the porosity, which can be attributed to nanofiller effect and pozzolanic reaction of nanosilica. Furthermore, the addition of CNS could reduce the drying shrinkage by densifying the microstructure in the cement paste, which has not been reported previously.