Robustness of corroded reinforced concrete structures

Short Term Scienti c Mission, COST ACTION TU-0601The deterioration of existing structures has been a growing concern in the last decade. Signi cant attention has been paid to the deterioration of bridges, since signi cant costs in repair and replacement are expected in the next decades. At the same time structural robustness seems to be an emergent concept related to the structural response to damage. At the present time, robustness is not well de ned and much controversy still remains around this subject. This report intends to be a contribution to the de nition of structural robustness especially in the analysis of reinforced concrete structures subjected to corrosion. To achieve this, rst of all, several proposed robustness de nitions and indicators and misunderstood concepts will be analyzed and compared. From this point and regarding a concept that could be applied to most type of structures and damage scenarios, a robustness de nition is proposed. To illustrate the proposed concept, some example of corroded reinforced concrete structures will be analyzed using nonlinear analysis numerical methods based on a continuum strong discontinuities approach and isotropic damage models for concrete. Finally the robustness of the presented examples will be assessed and compared

Laccase-catalysed protein-flavonoid conjugates for flax fibre modification

The introduction of flavonoid compounds into proteins can improve the natural properties of proteins, being promising products which essentially require antioxidant property. The oxidative conjugation of protein–flavonoids was processed by laccase catalysis resulting in the synthesis of biologically functional polymers. The new reaction products were detected in terms of sodium dodecyl sulfate polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionisation-time of flight mass spectra, showing a greater molecular weight formation. Their characterisations were further carried out in terms of UV–Vis spectroscopy, photon correlation spectroscopy, differential scanning calorimetry and Fourier transform infrared (FT-IR) spectroscopy analysis. In addition, their application of protein–flavonoid conjugates onto flax fibres was exploited to supplement a suitable microorganism environment of protein-possessed fibres. The anchoring of conjugates onto cationised fibres was successfully performed by ionic interaction with negatively charged proteins. The level of anchoring efficiency was quantified in terms of measuring colour strength (k/s) and fluorescence microscopy analysis. The conjugates onto fibres presented acceptable durability in terms of washing resistance and the surface became hydrophilic when α-casein–catechin was applied (lower contact angle 48°). By the anchoring of protein–flavonoid conjugates onto flax fibres, the final products with new colour generation and antioxidant activity (>93%) were obtained

Possibilities for recycling cellulases after use in celllase processing - part I: effects of end-product inhibition, thermal and mechanical deactivation, and cellulase depletion by adsorption

Preliminary recycling experiments with cellulase enzymes after cotton treatments at 50°C showed that activity remaining in the treatment liquors was reduced by about 80% after five recycling steps. The potential problems of end-product inhibition, thermal and mechanical deactivation, and the loss of some components of the cellulase complex by preferential and or irreversible adsorption to cotton substrates were studied. End-product inhibition studies showed that the build-up of cellobiose and glucose would be expected to cause no more than 40% activity loss after five textile treatment cycles. Thermal and mechanical treatments of cellulases suggested that the enzymes start to be deactivated at 60°C and agitation levels similar to those used in textile processing did not cause significant enzyme deactivation. Analysis of cellulase solutions, by fast protein liquid chromatography, before and after adsorption on cotton fabrics, suggested that the cellobiohydrolase II (Cel6A) content of the cellulase complex was reduced, relative to the other components, by preferential adsorption. This would lead to a marked reduction in activity after several treatment cycles and top-up with pure cellobiohydrolase II would be necessary unless this component is easily recoverable from the treated fabric

Effects of temperature on the cellulose binding ability of cellulase enzymes

The effects of high temperatures on catalytic activity and binding abilities of crude Trichoderma reesei cellulases in solution and adsorbed to a cotton fabric were studied. Above optimum temperature of 50 degrees C, catalytic activities were severely diminished but the binding behaviour was not found to be adversely affected. In order to verify possible applications of cellulases adsorbed to cotton fabrics as anchors for textile finishing purposes, we also checked the binding abilities after ironing. Previous ironing of cellulase adsorbed fabrics increased dyeability with an acid dye, but dye fastness was poor. Desorption of cellulases from cotton fabrics increased from pH 5 to pH 10. Dry ironing of fabrics resulted in less desorption, whereas wet ironing inhibited desorption at pH 5 and only 11% of protein were desorbed at pH 10. Ironing of the fabrics diminished enzyme activity of desorbed cellulases. Wet ironing resulted in complete denaturation of the proteins and no cellulolytic activity was found. The presence of water during thermal treatment of cellulases was found to be essential for complete denaturation and unfolding of the proteins. Dry heat only resulted in partial denaturation. Fluorescence measurements of cellulases adsorbed to cotton fabrics showed after ironing a significant shift in tryptophan fluorescence to higher wavelengths. This indicates unfolding and denaturation of the enzymes and revelation of more hydrophobic amino acids to the surface, which enables increased hydrophobic interactions with the fabric. (C) 1999 Elsevier Science B.V. All rights reserved

Possibilities for recycling cellulases after use in cotton processing - part II: Separation of cellulases from reaction products and released dyestuffs by ultrafiltration

The adsorption and activity of a total cellulase (Trichoderma reesei) was measured and compared on undyed and dyed cotton fabrics. Recovery of enzymes from the reaction mixture and by desorption from the cotton substrate was evaluated. About 80% of the initial protein could be recovered. The removal of released products (soluble reducing sugars and dyes) from the treatment liquor and subsequent concentration of cellulase proteins was performed using an ultrafiltration membrane. Strong protein-dye interactions made it impossible to separate efficiently the dyes from the enzymecontaining treatment liquors. The use of surfactants did not enhance cellulase desorption from cotton fabric. Although anionic surfactants have a deactivating effect on cellulases, this effect seems to be reversible, since after ultrafiltration the cellulase activity was similar to that of enzymes desorbed with buffer only. Humicola insolens cellulases were shown to be much more sensitive to anionic surfactant than T. reesei cellulases. The use of cellulases that bind reversibly to cellulose is suggested for achieving more efficient cellulase recycling and for reducing backstaining by dye-cellulase complexes

Effects of agitation level on the adsorption, desorption, and activities on cotton fabrics of full length and core domains of EGV(humicola insolens) and CenA (cellulomonas fimi)

The activities (at pH 7 and 50 degrees C) of purified EGV (Humicola insolens) and CenA (Cellulomonas fimi) were determined on cotton fabrics at high and low levels of mechanical agitation. Similar activity measurements were also made by using the core domains of these cellulases. Activity experiments suggested that the presence of cellulose binding domains (CBDs) is not essential for cellulase performance in the textile processes, where high levels of mechanical agitation are applied. The binding reversibilities of these cellulases and their cores were studied by dilution of the treatment liquor after equilibrium adsorption. EGV showed low percentage of adsorption under both levels of agitation. It was observed that the adsorption/desorption processes of cellulases are enhanced by higher mechanical agitation levels and that the binding of cellulase with CBD of family I (EGV) is more reversible than that of CBD of the cellulase of family II (CenA). (C) 2000 Elsevier Science Inc. All rights reserved

The scope of preserved procedural memory in amnesia

The finding that patients with amnesia retain the ability to learn certain procedural skills has provided compelling evidence of multiple memory systems in the human brain, but the scope, defining features and ecological significance of the preserved mnemonic abilities have not yet been explored. Here, we tested the hypothesis that subjects with amnesia would be able to learn and retain a broad range of procedural skills, by examining their acquisition and retention performance on five novel experimental tasks. The tasks are based on real-world activities and encompass a broad range of perceptual–motor demands: (i) the weaving task involves weaving pieces of fabric from woollen strings, using a manual weaver’s loom; (ii) the geometric figures task consists of tracing geometric figures with a stylus as they move horizontally across a touch screen monitor; (iii) the control stick task involves tracking a sequence of visual target locations using a joystick control; (iv) the pouring task consists of pouring 200 ml of water from a watering can into a series of graduated cylinders, from a point 20 cm above the cylinders; and (v) the spatial sequence task involves learning an ordered sequence of pushing five spatially distributed buttons without visual guidance. Ten chronic and stable amnesic subjects (nine with bilateral medial temporal lobe damage due to herpes simplex encephalitis or anoxia, and one with thalamic stroke) and 25 matching normal comparison subjects were tested on three occasions: initial learning at time 1; retention at time 2 (24 h later); and retention at time 3 (2 months later). Despite impaired declarative memory for the tasks, the amnesic subjects demonstrated acquisition and retention of the five skills; their learning slopes over repeated trials were comparable with those of comparison subjects. These findings indicate that preserved learning of complex perceptual–motor skills in patients with amnesia is a robust phenomenon, and that it can be demonstrated across a variety of conditions and perceptual– motor demands. The comparability of the tasks employed in this study with real-world activities highlights the potential application of this memory dissociation in the rehabilitation of patients with amnesi

On the robustness to corrosion in the life cycle assessment of an existing reinforced concrete bridge

Management of existing structures has traditionally been based on condition assessment, based on visual inspections, disregarding the susceptibility of different structural types to aging and deterioration. Robustness, as a measure of the effects of unpredictable damage to structural safety can be a complementary information to the results of inspection. Although robustness has mostly been used to evaluate the consequences of extreme events, a similar framework can be used to investigate the result of aging, allowing a better understanding of the potential effects of deterioration and allowing a better allocation of available maintenance funding. In this work, a probabilistic structural robustness indicator is used to quantify the susceptibility of structures to corrosion. The methodology is exemplified through a case study comprising an existing reinforced concrete bridge deck, heavily damaged due to reinforcement corrosion, and finally demolished due to safety concerns. Robustness measures the bridge deck safety tolerance to reinforcement corrosion. The principal effects of corrosion, including loss of area and bond between concrete and steel are modelled using a non-linear finite-element model, coupled with a Response Surface Method to compute the bridge reliability as a function of the corrosion level, and finally used to assess robustness. Results show that the redundancy of the bridge allows significant redistribution of loads between elements with different corrosion levels. As a result, the bridge presents significant robustness and tolerance to reinforcement corrosion

Desorption of cellulases from cotton powder

Cotton fabrics were treated with three different Trichoderma reesei cellulase preparations (total crude – TC, endoglucanase enriched – EG-rich, cellobiohydrolase enriched – CBH-rich) using mechanical agitation to produce cotton powder. Desorption of cellulase enzymes from the cotton powder was then performed by washing with buffer. After 3 washings most of the protein was desorbed from the cotton powder and the amount of sugars released in the latter washings was negligible. TC and CBH-rich preparations produced a finer cellulose powder than EGs. The desorption process caused a decrease in degree of polymerisation (DP) specially for the cotton treated with EGs and a marked increase in polydispersity (Pd ) for all preparations