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Concrete under high temperature conditions is a topic of wide interest for applications in several engineering fields, from nuclear to civil as well as building engineering.

Fiber reinforced cementitious matrix (FRCM) composites represent a promising alternative to the use of fiber reinforced polymer (FRP) composites for strengthening existing structures. FRCM composites are comprised of a high-strength fiber net (textile) embedded within an inorganic matrix, which is responsible of the stress-transfer between the composite and the substrate. FRCM composites comprising one layer of fiber are generally reported to fail due to debonding of the fibers from the embedding matrix. However, depending on the FRCM material employed, failure at the matrix-substrate interface, interlaminar (delamination) of the matrix, and fiber rupture may also occur. When stitch-bonded textiles are employed, i.e. textiles where longitudinal and transversal bundles are firmly connected, the interlocking between fibers and matrix plays a key role in the matrix-fiber stress-transfer mechanism and failure generally occurs due to cracking of the matrix. In this paper, the bond behavior of FRCM-masonry joints comprising one layer of a carbon stitch-bonded textile embedded within a lime-based matrix is studied by means of single-lap direct-shear tests of FRCM-masonry joints. A mesoscale three-dimensional finite element approach, which accounts for the matrix-fiber bond behavior and matrix-textile interlocking, is adopted to study the formation and propagation of the matrix cracks in the FRCM strip that eventually led to failure of the FRCM-masonry joints. The finite element analysis was carried out by using a dynamic explicit approach, which allowed for overcoming convergence difficulties associated with severe nonlinearities of the model. [ABSTRACT FROM AUTHOR]

The use of recycled concrete aggregates is very attractive from the point of view of reducing concrete production costs and of sustainability. A peculiar origin of such aggregates is that of demolitions of pre-existing concrete buildings. Scope of this work is to analyse the challenging aspects of recycled aggregates modelling in concrete mixtures and to define a procedure to cope with them. Particularly, numerical analyses dealing with the mechanical behaviour of concrete mixtures made of natural and recycled aggregates are here performed at the meso-scale level, distinguishing between concrete paste and aggregates themselves. Some compelling issues for the modelling phase are addressed, i.e.: i) the correct reproduction of recycled aggregates within the concrete samples, which involves both the acquisition of the external geometry of the aggregates and their random disposition in the sample, ii) the characterization of the mechanical constitutive law of the composite. An elastic-plastic-damaged formulation is adopted for representing the constitutive behaviour of mortar and cement matrix; the procedure is calibrated and validated so proving its predictability features when describing damage triggering and spreading within concrete samples subjected to compressive loads. [ABSTRACT FROM AUTHOR]

A three-dimensional coupled thermoelectromechanical model for electrical connectors is here proposed to evaluate local stress and temperature distributions around the contact area of electric connectors under different applied loads. A micromechanical numerical model has been developed by merging together the contact theory approach, which makes use of the so-called roughness parameters obtained from experimental measurements on real contact surfaces, with the topology description of the rough surface via the theory of fractal geometry. Particularly, the variation of asperities has been evaluated via the Weierstrass-Mandelbrot function. In this way the micromechanical model allowed for an upgraded contact algorithm in terms of effective contact area and thermal and electrical contact conductivities. Such an algorithm is subsequently implemented to construct a global model for performing transient thermoelectromechanical analyses without the need of simulating roughness asperities of contact surfaces, so reducing the computational cost. A comparison between numerical and analytical results shows that the adopted procedure is suitable to simulate the transient thermoelectromechanical response of electric connectors. [ABSTRACT FROM AUTHOR]

A deep understanding of concrete at the mesoscale level is essential for a better comprehension of several concrete phenomena, such as creep, damage, and spalling. The latter one specifically corresponds to the separation of pieces of concrete from the surface of a structural element when it is exposed to high and rapidly rising temperatures; for this phenomenon a mesoscopic approach is fundamental since aggregates performance and their thermal properties play a crucial role. To reduce the risk of spalling of a concrete material under fire condition, the inclusion of a low dosage of polypropylene fibres in the mix design of concrete is largely recognized. PP fibres in fact evaporate above certain temperatures, thus increasing the porosity and reducing the internal pressure in the material by an increase of the voids connectivity in the cement paste. In this work, the contribution of polypropylene fibres on concrete behaviour, if subjected to elevated thermal ranges, has been numerically investigated thanks to a coupled hygrothermomechanical finite element formulation. Numerical analyses at the macro- and mesoscale levels have been performed. [ABSTRACT FROM AUTHOR]

The application of fibre reinforced polymer (FRP) composites as an external reinforcement for concrete columns has proved to be an efficient method of confinement for strengthening and retrofitting existing structures needing a performance enhancement. In recent years, many different numerical models have been proposed to evaluate the behaviour of FRP confined concrete, also focusing on different constitutive laws for concrete. In this paper, a damage model has been developed to simulate and predict the response of concrete columns under uniaxial loading, externally confined with carbon FRP (CFRP) jackets, mainly focusing on the role of cross-section shape and internal steel bars in the strengthening intervention efficiency. Particularly, the constitutive behaviour of concrete has been here formulated via a modified Mazars’ damage law, which allows to evaluate the three-dimensional confinement effects in the columns during monotonic axial compression loads. Many analytical models included in the design codes as well as previously developed numerical models do not relate the external FRP jackets performances to the internal steel reinforcements: the present study pursues this task, trying to understand the mechanisms from a detailed model. Its overall good agreement with experimental results gathered from literature proves the correctness of the suggested formulation. [ABSTRACT FROM AUTHOR]

In recent years experimental investigations have demonstrated that the risk of spalling for a concrete material under fire conditions is drastically reduced by using a low dosage of polypropylene fibres in the mix design. This effect can be explained by considering the increase in voids connectivity within the cement paste and in concrete porosity due to polypropylene evaporation above certain temperatures. In this work the complex mechanism of polypropylene contribution on concrete behaviour under thermal conditions has been numerically evaluated through a coupled hygro-thermal–mechanical finite element formulation. [ABSTRACT FROM AUTHOR]

Lung toxicity mediated by multiwalled carbon nanotubes (MWCNT) has been widely demonstrated and recently associated with induction of carcinogenic asbestos-like effects, but the chemical features that drive this toxic effect have still not been well elucidated. The presence of metals as trace contaminants during MWCNT preparation, in particular iron (Fe) impurities, plays an important role in determining a different cellular response to MWCNT. Our goal was to clarify the mechanisms underlying MWCNT-induced toxicity with correlation to the presence of Fe impurities by exposing murine alveolar macrophages to two different MWCNT samples, which differed only in the presence or absence of Fe. Data showed that only Fe-rich MWCNT were significantly cytotoxic and genotoxic and induced a potent cellular oxidative stress, while Fe-free MWCNT did not exert any of these adverse effects. These results confirm that Fe content represents an important key constituent in promoting MWCNT-induced toxicity, and this needs to be taken into consideration when planning new, safer preparation routes. [ABSTRACT FROM PUBLISHER]

Abstract: In recent years FRP (Fiber Reinforced Polymer) technology has been developed to repair damaged concrete structures. This work proposes to investigate the complex mechanism of stress–strain evolution at the FRP interface until complete debonding as well as when long-term loads are accounted for. The study has been performed by means of a fully three-dimensional approach within the context of damage mechanics, to appropriately catch transverse effects and normal stresses, developing a realistic and comprehensive study of the delamination process. The adhesion properties have been reconstructed through a contact model incorporating an elastic-damaged constitutive law, relating inter-laminar stresses acting in the sliding direction. A F.E. research code (FRPCON3D) has been developed, including a numerical procedure accounting for Mazars’ damage law inside the contact algorithm. The code is also able to describe the delamination process when considering the effects from different concrete surface preparations. Additionally, it has been upgraded to describe the long-term behaviour of composite structures by means of two visco-elastic formulations: (i) Bažant’s B3 law has been considered for the concrete component, where creep effect is composed by three different terms, i.e. the elastic part, basic creep and drying creep; (ii) for FRP’s fibres and matrix a micromechanical approach has been implemented. The numerical results have been calibrated and validated against available experimental evidences. [Copyright &y& Elsevier]

This work discusses the numerical and physical models developed for the design of a membrane roof for the Baptist Church of Fortaleza as well as the fabrication and construction of the actual membrane, comparing results of the models with those of the real structure. The roof area amounts to about 2,900 m2, a national record for flexible border membranes and, to the writers' knowledge, the first case of a fully computer-assisted design process within Brazil. The paper initially outlines procedures to form finding, stress analysis, and patterning, and then focuses on the physical models developed to validate them. Finally, construction of the actual membrane is described, and comparison is made with the previous numerical and physical models. Determination of the mechanical properties of the fabrics used to construct the membrane is also briefly discussed. Additionally, analyses of the geometric configuration and definition of the structural response of typical connectors of such a tension structure, collecting and distributing stresses coming from sails and anchoring cables and elements acting to transfer loads to the foundations, are developed. Unilateral contact is considered to develop among the aforementioned connector and the cable/rings welded to the slabs and the redance, imposing localized directional variations to the cable; furthermore, geometric (large strains) and material nonlinearities are accounted for. [ABSTRACT FROM AUTHOR]

Karyomegalic interstitial nephritis is a rare, but perhaps an "underdiagnosed" condition. Peculiar nuclear changes characterize it, involving mainly tubular cells along with glomeruli and blood vessels. Herein, 3 bioptically proven new cases of patients with chronic renal failure are discussed. The first case had a recently diagnosed karyomegalic nephritis, which, to date, still does not required dialysis. The other 2 (brother and sister) required dialysis 4 and 1 years after diagnosis. Karyomegalic changes are found not only in the skin and liver biopsies of the male, in skin and duodenal biopsies of the male, in skin and liver biopsies of the female and in the urine cells of both patients. The date reported in this study emphasize the usefulness of pathologic investigation of both tissue and urine samples in the identification of this disease. Moreover, as karyomegalic interstitial nephritis is strongly suspected to have a genetic background, its identification may well not only be of clinical relevance, due to its ominous outcome, but may also bear eugenetic value. [ABSTRACT FROM AUTHOR]

Electron microscopy defined classic patterns of hereditary glomerular disease long before genetics revealed an underlying specific mutation. Genetic analysis is now easier to perform in clinical practice but an earlier optimism that genetics would predict disease severity and phenotype is challenged. The classic paradigm is Alport nephritis in which only a subset of mutations may predict glomerular abnormalities and disease severity. Interpretation of ultrastructural pathology of monogenetic diseases like Alport nephritis is complicated when the proband is the first family member to be diagnosed or there is discrepancy between clinical presentation and ultrastructural changes. In this review the authors have selected a dozen cases representative of common monogenetic glomerular diseases as a platform to discuss the utility of diagnostic electron microscopy in the era of molecular genetics. The emphasis is on genotype/glomerular phenotype correlations. [ABSTRACT FROM AUTHOR]

• Proposal of a new cohesive contact algorithm for ITZ in Concrete Materials. • Detailed discussion of the theoretical framework. • Characterization of ITZ strength related to the roughness of the aggregates surface. • Numerical experimental comparisons to describe the behavior of ITZ. The capability of modelling damage evolution in concrete materials represents a topic of relevance for improving the design of concrete structures and for the recovery of existing components. The present work aims to investigate the collapsible behaviour of the Interfacial Transition Zone (ITZ) around coarse inclusions, by using a new cohesive contact law able to take into account the coupling between normal/peeling and shear stresses, specifically calibrated to take into account the roughness of various aggregate types. A series of numerical analyses have been carried out considering different material inclusions and distributions within concrete samples, so proving the capabilities of the proposed formulation. [ABSTRACT FROM AUTHOR]

• In-depth understanding of the mechanical behavior of concrete. • Proposal of a procedure that combines 3D image techniques with FE modelling. • Exact geometric reconstruction of concrete at meso-level via the use of X-ray CT. • Adoption of an upgraded elasto-plastic damage model for the cement paste. • Sound prediction of damage triggering and evolution under generic stress states. The increasing attention to numerical issues related to material modeling is still a strong incentive to develop sound mechanical models that can explain material behavior up to failure. A procedure to handle a robust geometric meso-scale reconstruction of concrete materials is here proposed, based on X-ray Computed Tomography (CT-scan or X-ray CT). This study applies X-ray CT on ordinary concrete made with limestone aggregates. In this case the technique allows to acquire the overall inner geometry and distribution of the aggregates and also voids, thanks to the difference in material density of the components. Solid models have been generated with such technique and discretized in space to be numerically studied via the Finite Element (FE) method. The numerical results are compared with uniaxial compression tests on the same scanned specimens. For the numerical analyses a specific non-associated elasto-plastic constitutive behavior, coupled with damage, is developed for the cement matrix, whereas the coarse aggregates are treated as elastic. The mechanical characteristics of the components are gathered through a specific experimental campaign. The study confirms that a predictive simulation of damage triggering and evolution in concrete under generic 3D stress states requires the characterization of the continuum at a meso-scale level. Comparisons between numerical and experimental results proves the soundness of the proposed constitutive description to evaluate the brittle behaviour of cementitious materials and to satisfactorily simulate damage triggering under generic 3D stress states. [ABSTRACT FROM AUTHOR]

We describe the occurrence of renal Encephalitozoon (Septata) intestinalis infection in a 35-year-old AIDS patient who died with disseminated tuberculosis. The patient did not complain of specific symptoms involving the kidney or lower urinary tract during life, but at autopsy, light microscopic examination of the kidney revealed numerous small round or oval bodies in the tubules and tubular cell cytoplasm that were interpreted as intracellular protozoa. Transmission electron microscopy of tissue retrieved from paraffin-embedded samples identified these organisms as microsporidia belonging to the Encephalitozoonidae family, but did not allow definitive identification of the species of infecting parasite. This was made possible only by means of Southern blot hybridization after the polymerase chain reaction, which recognized the micro-organism as E. intestinalis. [ABSTRACT FROM AUTHOR]

BACKGROUND: The aim of this multicentre collaborative study was to compare the progression of renal disease in children and adults with Henoch-Schönlein purpura (HPS) nephritis selected on the basis of IgA-dominant renal deposits and biopsy material available for review. METHODS: The analysis was performed in 152 patients (95 adults and 57 children < 16 years old at diagnosis) with a follow-up (> or = 1 year up to 20 years (4.9 +/- 3.4 years in adults and 4.8 +/- 3.9 years in children). RESULTS: Renal histology and clinical presentation were similar in both age groups: crescents were found in 36% of adults and 34.6% of children (in only 2.7% of adults and 1.9% of children involving > 50% of glomeruli), nephrotic-range proteinuria in 29.5% of adults and 28.1% of children and functional impairment in 24.1% of adults and 36.9% of children. The outcome was similar for both age groups (remission, 32.5% of adults and 31.6% of children; renal function impairment, 31.6% of adults and 24.5% of children). Endstage renal disease was observed in 15.8% of adults and in 7% of children. Renal function survival at 5 years was not significantly different in the two groups (85% in adults and 95% in children) and at 10 years it was approximately 75% in both groups. None of the children died and adult survival was 97% at 5 years. In adults at presentation, renal function impairment (P < 0.02) as well as proteinuria higher than 1.5 g/day (P < 0.02) and hypertension (P < 0.001) were negative prognostic factors. Multivariate analysis stressed the main statistical relevance of proteinuria (relative risk 2.37, P < 0.02). Conversely, in children no definite level of proteinuria, hypertension or other data were found to be associated with poor prognosis. CONCLUSIONS: Among patients with a clinical presentation which warrants renal biopsy, HSP nephritis has a similar prognosis in children and adults. The evolution is more predictable in adults than in children. [ABSTRACT FROM PUBLISHER]

Background. The renal minimal lesion disease induced in rats by adriamycin (ADR) is generally thought to be consequent to a direct cytotoxic effect of this drug on glomerular epithelial cells. Only recently an altered synthesis of mediators, including reactive oxygen species and monocyte-macrophage cytokines, has been hypothesized. Methods. A mouse strain (nude) bearing a congenital thymic aplasia is a suitable experimental animal to evaluate the role of immune reactions in the development of ADR nephropathy, provided mouse susceptibility to its toxic effect. Therefore, experimental mice were divided into three groups (G) each receiving adriamycin 7.5 mg/kg b.w.: GA (15 heterozygous nu/O mice with normal immune system); GB (15 homozygous nu/nu athymic mice); GC (15 homozygous nu/nu mice which were also splenectomized, irradiated, and treated with anti-asialo Gml antibody to abolish NK and decrease macrophage activity). All animals were maintained under pathogen-free conditions. Urinary proteins, albumin and TNF-α excretion were measured. Results. After 14 days the proteinuria was 43.8± 1.7 μg/min in GA, 30.2±2.9 μg/min in GB (P<0.05) and 12.2±2.8 μg/min in GC (GA vs GC, P<0.0001; GB vs GC, P<0.05). Albuminuria gave a similar profile. TNF-α urinary excretion was significantly higher in GA (17.3±3.2 mU/min) than in GB (5±0.6 mU/min, P<0.001) and GC (3.2±0.9 mU/min, P<0.001). A significant correlation was found in GA between urinary TNF-α and protein losses (r2=0.63 P<0.0001). Kidney tissue homogenates failed to show in each experimental group any evidence of mRNA encoding for TNF-α, which was detectable in peripheral mononuclear cells from GA and GB, but undetectable in GC mice. Segmental effacements of glomerular epithelial cell foot process were observed by electron-microscopy in GA only, while they were minimal in GB and absent in GC. Iron colloidal staining for anionic sites on frozen sections always showed a normal pattern. Conclusions. Nude mice bearing cellular immunity deficiency are protected from proteinuria following ADR toxicity. An impaired synthesis and release of lymphomonocyte mediators including TNF-α could be envisaged. [ABSTRACT FROM PUBLISHER]

• Proposal of a new non-local three-invariant elastoplastic constitutive model. • Detailed discussion of the theoretical framework. • Non-local integral type regularization based on a Search-Sphere iterative procedure. • Soundness of constitutive model tested through numerical 1D and 3D examples. • Results depend on internal length; speed improvement via the radius of the sphere. Within the framework of infinitesimal elasto-plasticity for describing concrete behaviour, this paper proposes a new non-local constitutive model. Particularly, a non-local integral-type regularization technique is applied to the three-invariant Menétrey-Willam model, here modified by the inclusion of a non-associated flow rule. The resulting model allows for taking into account the role of the intermediate principal stress and the Lode parameter, as well as to control inelastic dilatancy. A regularization scheme is hence introduced to circumvent strain localization and resolve the incapability of objectively describing localized material failure. One- and three-dimensional Finite Element analyses are developed to prove the soundness of the novel implemented regularized scheme and the upgraded response with respect to a local approach. [ABSTRACT FROM AUTHOR]