Uniaxial tensile response of microfibre reinforced cement composites

Microfibre reinforced cement composites reinforced with high volume fractions of carbon, steel and polypropylene fibres were tested in uniaxial tension. Composites investigated included those with only one type of fibre (mono-fibre composites) and those with two or more types of fibres (hybrid-fibre composites) in the same mix. Considerable strengthening, toughening and stiffening of the host matrix due to microfibre reinforcement were observed. In the hybrid-fibre composites, different fibres appear to act as additive phases; i.e., they maintain their individual reinforcing capabilities. The composites were also impact tested in uniaxial tension using a newly designed instrumented impact machine. When compared with static test results, considerable sensitivity to stress rate was noted; composites were found to be stronger and tougher under impact and the improvements were more pronounced at higher fibre volume fractions. The potential of these composites for use in thin sheet products and other similar applications is recognized, and the need for continued research is stressed.     

Synthesis and evaluation of liquid amine‐terminated polybutadiene rubber and its role in epoxy toughening

Epoxy resin is widely used for coatings, adhesives, castings, electrical insulation materials, and other applications. However, unsolved problems still remain in its applications. The main problem is low toughness: cured epoxy resin is rather brittle, with poor resistance to the propagation of cracks derived from the internal stress generated by shrinkage in the cooling process from cure temperature to room temperature. The objective of this study was to improve the flexibility and toughness of diglycidyl ether of bisphenol A based epoxy resin with a liquid rubber. For this purpose, amine‐terminated polybutadiene (ATPB) was synthesized. The product was characterized by Fourier transform infrared and NMR spectroscopy and elemental analysis. ATPB‐modified epoxy networks were made by curing with an ambient‐temperature curing agent, triethylene tetramine. We varied the epoxy/liquid rubber compositions to study the effect of toughener concentration on the impact and thermal properties. Higher mechanical properties were obtained for epoxy resins toughened with 1 phr ATPB. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2446–2453, 2005     

Carbonation in concrete infrastructure in the context of global climate change – Part 1: Experimental results and model development

There is nearly unanimous consensus amongst scientists that increasing greenhouse gas emissions, including CO₂ generated by human activity, are effecting the Earth’s climate. Increasing atmospheric CO₂ emissions will likely increase the rates of carbonation in reinforced concrete structures. However, there is a lack of reliable models to predict the depth of carbonation as a function of time.To address this deficiency, a numerical model involving simultaneous solution of the transient diffusion and reaction equations of CO₂ and Ca(OH)₂ was developed. The model successfully includes the effects of variations in various properties such as porosity, humidity, temperature, atmospheric CO₂ concentrations and chemical reaction rates.The applicability of the model was confirmed after calibration using data from accelerated carbonation experiments, and the model is used to evaluate the possible effects of climate change by inputting various future climate scenarios in Part 2.     

Poly(ethylene oxide)/clay nanocomposite: Thermomechanical properties and morphology

Poly(ethylene oxide) (PEO)/clay nanocomposites were prepared by a solution intercalation method using chloroform as a solvent. The nanocomposites were characterised by X-ray diffraction (XRD), differential scanning calorimetry (DSC), hot-stage polarized optical microscopy (POM), Fourier transform infrared spectroscopy (FT-IR), tensile analysis, dynamic mechanical analysis (DMA) characterisation techniques. Formation of nanocomposite was confirmed by X-ray diffraction (XRD) analysis. A decrease in PEO crystallinity in case of nanocomposite, was confirmed by a decrease in the heat of melting and spherulite size as indicated by DSC and POM studies, respectively. Improvement in tensile properties in all respect was observed for nanocomposites with optimum clay content (12.5 wt%). DMA studies indicate an increase in loss peak temperature and broadening of loss peak as a result of clay intercalation.     

Hybrid fiber reinforced concrete (HyFRC): fiber synergy in high strength matrices

In most cases, fiber reinforced concrete (FRC) contains only one type of fiber. The use of two or more types of fibers in a suitable combination may potentially not only improve the overall properties of concrete, but may also result in performance synergy. The combining of fibers, often called hybridization, is investigated in this paper for a very high strength matrix of an average compressive strength of 85 MPa. Control, single, two-fiber and three-fiber hybrid composites were cast using different fiber types such as macro and micro-fibers of steel, polypropylene and carbon. Flexural toughness tests were performed and results were extensively analyzed to identify synergy, if any, associated with various fiber combinations. Based on various analysis schemes, the paper identifies fiber combinations that demonstrate maximum synergy in terms of flexural toughness.     

Impact resistance of fiber reinforced wet-mix shotcrete Part 2: plate tests

In Part 1 of this paper, data on impact resistance of fiber reinforced wet-mix shotcrete obtained by testing beam specimens was presented. Ten different types of commercially available fibers were investigated. It was argued that since shotcrete in many applications is loaded dynamically, slow-rate static tests are not sufficient for a comprehensive characterization of its in-place performance. mance. It was also demonstrated that shotcrete is a highly stress-rate sensitive material, and its performance under impact is very different from that predicted by the slow-rate, quasi-static tests. From a standardization point of view, proper characterization of toughness and energy absorption capability of fiber reinforced shotcrete remains a challenge before the industry. Both beam and plate specimens are prescribed, but little understanding exists of the correlation, if any, between these two specimen geometries. In this paper, the same ten fiber types, tested in Part 1 using beam specimen, were investigated using plate specimens. As before, both static and impact tests were performed. Plate tests showed similar toughness enhancement due to fiber reinforcement, but the relative improvements between fiber types are not necessarily in agrcement with those indicated in the beam tests. Plate specimens were also found be less sensitive to changes in the rate of loading from static to dynamic. Considering these issues, and realizing that in practice shotcrete is often loaded in bi-axial bending, the use of plate specimens rather than beam specimens for the characterization of toughness of fiber reinforced shotcrete is recommended.     

BEM and FEM analysis of planar moving cracks in creeping solids

Applications of the boundary element method (BEM) and the finite element method (FEM), to the analysis of two-dimensional problems of moving cracks in creeping bodies, is the subject of this paper. In the absence of an acceptable crack growth law valid under small scale transient as well as extended steady state creep conditions, the computer simulations are carried out here for crack extension at prescribed constant speeds. It is shown here that the BEM is most effective for the analysis of transient crack growth under small scale creep conditions while the FEM appears to be best suited for the study of crack growth under conditions of extensive creep throughout most of the structure. These two methods, therefore, tend to complement each other for this class of problems. It is felt that the numerical methods presented here can, in conjunction with experiments, be very useful for the evaluation of existing crack growth laws as well as for the development of new ones.

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Résumé Le sujet du mémoire est l'application de la méthode par valeurs aux limites (BEM) et de la méthode par éléments finis (FEM) à l'analyse de problèmes bidimensionnels de fissures en extension dans des composants soumis à fluage.En l'absence d'une loi d'extension de fissure qui soit applicable tant sous des conditions de fluage transitoire à petite échelle que de fluage stable généralisé, on procède aux simulations per calcul on considérant le développement d'une fissure à des vitesses constantes fixées.On montre que la méthode BEM est plus efficace pour analyser la croissance d'une fissure de fluage en régime transitoire à une petite échelle, tandis que la méthode FEM convient le mieux pour étudier la croissance d'une fissure dans des conditions de fluage s'étendant à l'ensemble du composant.Dès lors, les deux méthodes tendent à se compléter pour cette classe de problèmes. On estime que les méthodes numériques qui sont présentées ici, peuvent être très utiles, en association avec des essais, pour évaluer les lois existantes en matière de propagation de fissures, ainsi que pour en développer de nouvelles.

     

Preparation of Adrenochrome Hydrogel Patch, Gel, Ointment, and the Comparison of Their Blood Coagulating and Wound Healing Capability

The aim of this study is to make an effective blood coagulant and wound healing agent, which on its topical application on ruptured skin would help in instant coagulation of blood and ongoing healing of wound. The hydrogel has been prepared by mixing 28% w/v gelatin and 21% w/v PVA in distilled water, and heated to 40°C followed by addition of a blood coagulant at a lower temperature. Beeswax, alcohol, liquid paraffin, and adrenochrome were mixed, triturated, and heated accordingly to prepare adrenochrome ointment. Polyvinyl alcohol and glycerin were mixed and heated and the drug was added at a lower temperature, and stored at 4-5°C to form adrenochrome gel. Gelatin alone has cell adhesion property. Adrenochrome is a blood coagulant. Therefore, gelatin with adrenochrome in hydrogel has a synergistic effect in wound healing. To evaluate the efficacy of these three different formulations, incisions were made on the backs of three mice and simultaneously adrenochrome containing hydrogel patch, gel, and ointment were applied on the wound and observed at regular intervals for half an hour to examine the rate of blood coagulation and kept under observation for 2 days to study the rate of wound healing. The efficacy of all these three formulations was compared to appraise the most effective blood coagulating and wound healing agent.     

Study of impact properties and morphology of 4,4′‐diaminodiphenyl methane cured epoxy resin toughened with acrylate‐based liquid rubbers

Randomized carboxyl poly(2‐ethylhexyl acrylate) (A‐1) and randomized epoxy poly(2‐ethylhexyl acrylate) (B‐1) rubbers were synthesized in the form of liquid rubber by a solution polymerization technique. The liquid rubbers A‐1 and B‐1 were characterized by ¹H NMR and IR spectroscopic analysis, non‐aqueous titration, viscosity measurements and gel permeation chromatography. The liquid rubbers A‐1 (M?_n = 3900 g mol^?1), B‐1 (M?_n = 4100 g mol^?1) and a (1:1) mixture of A‐1 and B‐1 were pre‐reacted with epoxy resin separately and the modified epoxy networks were made by curing with high temperature curing agent. The modified epoxy networks were evaluated by unnotched Izod impact testing. The morphology and toughening behaviour were analysed by scanning electron microscopy. Optimum properties were obtained with the mixture of A‐1 and B‐1. Copyright © 2003 Society of Chemical Industry