Showing papers on "Durability published in 2009"

Factors affecting strength and durability of densified biomass products.

Abstract: Effectiveness of a densification process to create strong and durable bonding in densified products such as pellets, briquettes, and cubes can be determined by testing the strength (i.e., compressive resistance, impact resistance, and water resistance), and durability (i.e., abrasion resistance) of the densified products. These tests can indicate the maximum force/stress that the densified products can withstand, and the amount of fines produced during handling, transportation, and storage. In this article, the procedures used for measuring the strength and durability of the densified products are discussed. The effects of constituents of the feed such as starch, protein, fiber, fat, lignin and extractives; feed moisture content; feed particle size and its distribution; feed conditioning temperature/preheating of feed; added binders; and densification equipment variables (forming pressure, and pellet mill and roll press variables) on the strength and durability of the densified products are reviewed. This article will help select process parameters to produce strong and durable densified products from new biomass feedstocks or animal feed formulations. Guidelines for developing standards on criteria for the acceptance levels of strength and durability of the densified products are presented.

Polymer Electrolyte Fuel Cell Durability

Abstract: Stack Components- Dissolution and Stabilization of Platinum in Oxygen Cathodes- Carbon-Support Requirements for Highly Durable Fuel Cell Operation- Chemical Degradation of Perfluorinated Sulfonic Acid Membranes- Chemical Degradation: Correlations Between Electrolyzer and Fuel Cell Findings- Improvement of Membrane and Membrane Electrode Assembly Durability- Durability of Radiation-Grafted Fuel Cell Membranes- Durability Aspects of Gas-Diffusion and Microporous Layers- High-Temperature Polymer Electrolyte Fuel Cells: Durability Insights- Direct Methanol Fuel Cell Durability- Influence of Metallic Bipolar Plates on the Durability of Polymer Electrolyte Fuel Cells- Durability of Graphite Composite Bipolar Plates- Gaskets: Important Durability Issues- Cells and Stack Operation- Air Impurities- Impurity Effects on Electrode Reactions in Fuel Cells- Performance and Durability of a Polymer Electrolyte Fuel Cell Operating with Reformate: Effects of CO, CO2, and Other Trace Impurities- Subfreezing Phenomena in Polymer Electrolyte Fuel Cells- Application of Accelerated Testing and Statistical Lifetime Modeling to Membrane Electrode Assembly Development- Operating Requirements for Durable Polymer-Electrolyte Fuel Cell Stacks- Design Requirements for Bipolar Plates and Stack Hardware for Durable Operation- Heterogeneous Cell Ageing in Polymer Electrolyte Fuel Cell Stacks- System Perspectives- Degradation Factors of Polymer Electrolyte Fuel Cells in Residential Cogeneration Systems- Fuel Cell Stack Durability for Vehicle Application- R&D Status- Durability Targets for Stationary and Automotive Applications in Japan

Structural concrete with incorporation of coarse recycled concrete and ceramic aggregates: durability performance

Abstract: The growing difficulty in obtaining natural coarse aggregates (NCA) for the production of concrete, associated to the environmental issues and social costs that the uncontrolled extraction of natural aggregates creates, led to a search for feasible alternatives. One of the possible paths is to reuse construction and demolition waste (CDW) as aggregates to incorporate into the production of new concrete. Therefore, a vast and detailed experimental campaign was implemented at Instituto Superior Tecnico (IST), which aimed at determining the viability of incorporating coarse aggregates from concrete and ceramic brick wall debris, in the production of a new concrete, with properties acceptable for its use in new reinforced and pre-stressed structures. In the experimental campaign different compositions were studied by incorporating pre-determined percentages of recycled coarse concrete aggregates and recycled coarse ceramic plus mortar particles, and the main mechanical, deformability and durability properties were quantified, by comparison with a conventional reference concrete (RC). In this article, these results are presented in terms of the durability performance of concrete, namely water absorption, carbonation and chlorides penetration resistance.

Mechanical and durability characteristics of concrete containing EAF slag as aggregate

Abstract: The present study aims to investigate the opportunity to largely substitute natural aggregates of traditional concrete with Black/Oxidizing Electric Arc Furnace (EAF) slag. Compressive and tensile strength, elastic modulus and durability characteristics (accelerated aging, freezing and thawing, wetting and drying) of concrete containing EAF slag as aggregate according to Fuller’s ideal grading curve were experimentally investigated. This study aims to improve the scarce database of mechanical and durability tests on this type of concrete and give some insights to improve durability properties of concrete made with EAF slag, not only using modern agents and additives, but also working on the actual grading curve of aggregates used, closely connected to the overall durability for any kind of concrete. Concrete made with EAF slag as aggregate showed good strength characteristics since, in normal environmental conditions, strength properties of the conglomerate containing EAF slag are totally comparable (or even better) than those observed for traditional concrete. Conversely, the typical chemical and physical properties of EAF slag, such as the high content in calcium and magnesium oxides inclined to hydration, may be a limit for the durability of the resulting concrete: on one hand the durability can be strongly improved even in critical freezing/thawing environmental conditions by a small amount of air-entraining agent, on the other hand, this conglomerate still remains rather vulnerable to repeated cycles of wetting and drying.

Durability of GFRP Reinforcing Bars Embedded in Moist Concrete

Abstract: This paper presents mechanical, microstructural, and physical characterization of glass fiber-reinforced polymer GFRP bars exposed to concrete environment. GFRP bars were embedded in concrete and exposed to tap water at 23, 40, and 50°C to accelerate the effect of the concrete environment. The measured tensile strengths of the bars before and after exposure were considered as a measure of the durability performance of the specimens and were used for long-term properties prediction based on the Arrhenius theory. In addition, Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy were used to characterize the aging effect on the GFRP reinforcing bars. The results showed that the durability of mortar-wrapped GFRP bars and exposed to tap water was less affected by accelerated aging than the bars exposed to simulated pore-water solution. These results confirmed that the concerns about the durability of GFRP bars in concrete, based on simulated laboratory studies in alkaline solutions, do not properly correspond to the actual service life in concrete environments.

Use of ultrafine rice husk ash with high-carbon content as pozzolan in high performance concrete

Abstract: Rice husk ash (RHA) has been generated in large quantities in rice producing countries. This by-product can contain non-crystalline silica and thus has a high potential to be used as cement replacement in mortar and concrete. However, as the RHA produced by uncontrolled burning conditions usually contains high-carbon content in its composition, the pozzolanic activity of the ash and the rheology of mortar or concrete can be adversely affected. In this paper the influence of different grinding times in a vibratory mill, operating in dry open-circuit, on the particle size distribution, BET specific surface area and pozzolanic activity of the RHA is studied, in order to improve RHA’s performance. In addition, four high-performance concretes were produced with 0%, 10%, 15%, and 20% of the cement (by mass) replaced by ultrafine RHA. For these mixtures, rheological, mechanical and durability tests were performed. For all levels of cement replacement, especially for the 20%, the ultra-fine RHA concretes achieved superior performance in the mechanical and durability tests compared with the reference mixture. The workability of the concrete, however, was reduced with the increase of cement replacement by RHA.

Experimental investigations on the durability of fibre–matrix interfaces in textile-reinforced concrete

Abstract: Changes in the strength and toughness of textile-reinforced concrete with increasing age are determined essentially by the durability of the armouring fibres, the matrix itself, and the bond between the matrix and the fibres. Based on new experimental results, important mechanisms influencing the durability of the fibre–matrix bond are treated in this article and discussed as to their significance. The investigations were conducted on multi-filament yarns of AR-glass which were imbedded in matrices of varying alkalinity and hydration kinetics. The loading capacity of the fibre–matrix bonds was determined in direct tension tests on under-reinforced specimens after they had undergone accelerated aging. Further, the condition of the microstructure between fibre and matrix was ascertained with both image analysis and analytical procedures. It was concluded that measured reductions in the toughness of the composite material could be attributed to the diminishing protective effect of organic polymer sizing on the surface of the filaments as well as to the disadvantageous new formation of solid hydration phases (mainly Portlandite) in the fibre–matrix interface.

Comparative durability evaluation of ambient temperature cured externally bonded CFRP and GFRP composite systems for repair of bridges

Abstract: In recent years externally bonded fiber reinforced polymer (FRP) composites have been increasingly accepted as an efficient means of rehabilitating deteriorating and under-strength concrete structures. In the case of the two primary application procedures – wet layup of fabric and adhesive bonding of prefabricated strips, the efficacy and reliability of the approach intrinsically depends on the strength and durability of bond between the FRP and the concrete substrate. This paper presents results from an extensive 24-month study, involving ten different external strengthening FRP systems, to assess the durability of the bond under environmental exposure conditions including immersion in water, immersion in salt water, ponding at different humidity levels, and exposure to freeze conditions of –18 °C. The FRP systems were characterized through determination of moisture uptake characteristics, tensile strength and modulus of the resins and adhesives, and direct tension pull-off testing of the FRP-concrete assembly. As expected from ambient temperature cure systems, both tensile characteristics and pull-off strength show degradation with time under specific environmental exposure conditions. Differences in bond durability are discussed based on system and exposure type and it is seen that exposure to the −18 °C environment results in the highest level of deterioration overall. The results indicate that the use of wet layup, with appropriately selected resins, and well fabricated composites, may at present have advantages over the use of adhesive bonded systems as related to long-term durability of the FRP-concrete bond. They also suggest that the changes in characteristics in resin/adhesive and bond due to environment exposure induced deterioration need to be considered in design to avoid premature failure.

Assessment and prediction of RC structure service life by means of durability indicators and physical/chemical models

Abstract: This paper presents an approach to assess the durability of RC structures, with respect to chloride-induced reinforcement corrosion. The approach is based on durability indicators (DIs). First, performance-based specifications, which involve solely DIs, are proposed for concrete mix-design. In addition, within the framework of service life prediction, a multi-level modelling concept is presented, where DIs are the main input data of the various models. A multi-level physically-based numerical model of chloride ingress has been developed within this framework, and is summarized in the paper. The model offers currently three levels of sophistication in saturated conditions and one level in non-saturated conditions: level 1 is a simple chloride diffusion model, level 2 is a multi-species model based on Nernst–Planck equation, level 3 involves transport-chemistry coupling, whereas level 4 is a coupled moisture-ion transport model. Examples of application and validation of the model in lab and in field conditions, in particular in the case of wetting–drying cycles, are given in the paper.

Is scientific literature subject to a sell-by-date? A general methodology to analyze the durability of scientific documents

Abstract: The study of the citation histories and ageing of documents are topics that have been addressed from several perspectives, especially in the analysis of documents with delayed recognition or sleeping beauties. However, there is no general methodology that can be extensively applied for different time periods and/or research fields. In this paper a new methodology for the general analysis of the ageing and durability of scientific papers is presented. This methodology classifies documents into three general types: Delayed documents, which receive the main part of their citations later than normal documents; Flash in the pans, which receive citations immediately after their publication but they are not cited in the long term; and Normal documents, documents with a typical distribution of citations over time. These three types of durability have been analyzed considering the whole population of documents in the Web of Science with at least 5 external citations (i.e. not considering self-citations). Several patterns related to the three types of durability have been found and the potential for further research of the developed methodology is discussed.

Modeling of Chloride Concentration Effect on Reinforcement Corrosion

Abstract: : The corrosion of reinforcement is one of the major causes of deterioration of reinforced concrete (RC) structures, considerably affecting their durability and reliability. The rate of reinforcement corrosion is governed by, among other factors, the presence of chlorides on the surface of the steel. The assessment of such deteriorating effects necessitates the development of relevant models and the utilization of advanced simulation techniques to enable the probabilistic analysis of concrete structures. In this article an approach for the assessment of the durability and reliability of RC structures under attack from chlorides is introduced. The field of chloride concentration at different locations in the structure (represented in 2D space by chosen longitudinal or cross sections) is modeled as a function of time by a cellular automata (CA) technique. The results of this simulation are then utilized for the assessment of a steel corrosion prognosis using a probabilistic 1D model at chosen points, although the rate of corrosion is based on experimental results. The concentrations of chlorides and pH levels are reflected in this way. The described approach is applied to an illustrative example showing the feasibility of capturing the effect of chloride concentration on the steel corrosion rate and consequently on the assessment of the service life and/or reliability of the structure.

Mechanical properties and durability of normal and water reduced high strength grade 60 concrete containing rice husk ash

Abstract: This paper reports an investigation on the strength properties, a time dependent property as well as durability characteristics of normal and water reduced high strength concrete (WRHSC), with or without rice husk ash (RHA), designed to produce Grade 60 at 28 days. RHA was ‘added’ or ‘replaced’ at/by 5% - 20% of the cement content. A PCE superplasti-cizer was added to all mixes to provide workability in the range of 150 - 200 mm slump. Based on the initial trial mixes, four high strength concrete mixes were selected for further tests on mechanical properties (compressive strength, tensile splitting strength, flexural strength and static modulus of elasticity), drying shrinkage and durability (water absorption, sorptivity, chemical resistance to MgSO4 solution). Incorporation of RHA increases the strength, reduces the drying shrinkage and improves the durability of concrete compared to conventional OPC concrete.

Assessing the Durability of Engineered Cementitious Composites Under Freezing and Thawing Cycles

Abstract: This paper reports the durability performance of non-air-entrained engineered cementitious composites (ECC) when subjected to freezing and thawing cycles. ECC is a newly developed, high-performance, fiber-reinforced, cementitious composite with substantial benefits both in terms of high ductility under uniaxial tensile loading and improved durability due to intrinsically tight crack width of less than 100 μm. To evaluate the frost durability of ECC, freezing and thawing testing in accordance with ASTM C666 Procedure A was conducted. The mass loss, pulse velocity change, and flexural parameters (ultimate deflection and flexural strength) of specimens subjected to freezing and thawing cycles were determined in the test. In addition, air-void parameters, in accordance with ASTM C457, modified point count method, and pore size distribution obtained by mercury intrusion porosimetry technique were studied. To analyze the influence of micro-fibers and high tensile strain capacity on the freezing and thawing durability of ECC, all of the above-mentioned properties were also investigated for a control ECC matrix (ECC without fibers). After 210 cycles of freezing and thawing, the control ECC matrix specimens were severely deteriorated, requiring removal from the test, but still exhibited better performance than the conventional non-air-entrained concrete, which would fail at much earlier cycles. On the other hand, ECC with fibers without air-entrainment had excellent resistance to cycles of freezing and thawing with minimal reduction in ultimate tensile strength and ductility. The observed superior frost durability of ECC over control ECC matrix in terms of lower weight loss, pulse velocity change, and higher flexural load and ductility can be attributed to the following reasons: Increase of pore volume larger than approximately 0.30 μm in diameter, intrinsically high tensile ductility and strength due to the presence of micro-poly-vinyl-alcohol fibers.

Concrete Durability: A Practical Guide to the Design of Durable Concrete Structures

Abstract: Introduction Pore Structure and Transport Processes Physical Deterioration Mechanisms Deterioration Mechanisms - Chemical Durability performance tests Modelling and predicting the effects of deterioration mechanisms Materials selection for improved durability performance Construction processes for improved durability Design aspects that can reduce risk from deterioration mechanisms Case Studies: durability problems, repair strategies or proper consideration to durability design? Repair Methods Issues related to performance-based specification for concrete Advances in durability design and performance-based specification

Durability design of concrete structures, Part 1: Analysis fundamentals

Abstract: Concrete structures (CS) are designed so that they can satisfy requirements regarding safety, serviceability, durability and aesthetics throughout their design service life. Present design procedures regarding CS required by national or international codes and standards such as Model Code Euro International Committee of Concrete (1993) now Federation Internationale du Beton (FIB), Eurocodes, ACI, RILEM, etc. are predominantly based on strength principles and limit state formulation. The durability aspect is a natural extension of the classical resistance verification where deterioration effects are normally neglected. The reliability is assessed through the given performance that must be delivered within the design service life, the so-called performance-based design. This approach can be adopted for a performance based on service life design. In the recent years design is related to durability through the analysis of carbonation, resistance to chloride ingress, improved freezing and thawing resistance, etc. The review of literature and some recommendations are presented referring to the design of structures aiming to attain greater durability of CS. The accent is put on the theory of reliability, failure probability and service life probability. The basics of this analysis are given through the principles of performances and service life, and deterministic and scholastic methods using the lifetime safety factor.

Vibration Durability Assessment of Sn3.0Ag0.5Cu and Sn37Pb Solders Under Harmonic Excitation

Abstract: In this paper, the vibration durability of both SAC305 and Sn37Pb interconnects are investigated with narrow-band harmonic vibration tests conducted at the first natural frequency of the test, printed wiring board, using constant-amplitude excitation. A time-domain approach, reported by Upadhyayula and Dasgupta (1998, "Guidelines for Physics-of-Failure Based Accelerated Stress Test," Proceedings, Reliability and Maintainability Symposium, pp. 345-357), was adapted in this study for the fatigue analysis. The test board consists of daisy-chained components, to facilitate real-time failure monitoring. The response of the test specimens was characterized, and accelerated fatigue tests were conducted at different loading amplitudes to obtain a mix of low-cycle fatigue (LCF) and high-cycle fatigue data points. The SAC305 interconnects were found to have lower fatigue durability than comparable Sn37Pb interconnects, under the narrow-band harmonic excitation levels used in this study. This trend is consistent with most results from broadband vibration tests by Zhou et al. (2006, "Vibration Durability Comparison of Sn37Pb vs. SnAgCu Solders," Proceedings of ASME International Mechanical Engineering Congress and Exposition, Chicago, IL, Paper No. 13555), Zhou and Dasgupta (2006, "Vibration Durability Investigation for SnPb and SnAgCu Solders With Accelerated Testing and Modeling," IEEE-TC7 Conference on Accelerated Stress Testing & Reliability, San Francisco, CA), and Woodrow (2005, "JCAA/JG-PP No-Lead Solder Project: Vibration Test," Boeing Electronics Materials and Processes Technical Report) and from repetitive mechanical shock tests by Zhang et al. (2005, "Isothermal Mechanical Durability of Three Selected Pb-Free Solders: Sn3.9Ag0.6Cu, Sn3.5Ag and Sn0.7Cu," ASME J. Electron. Packag., 127, pp. 512-522), but counter to findings from quasistatic, LCF, and mechanical cycling studies by Cuddalorepatta and Dasgupta (2005, "Cyclic Mechanical Durability ofSn3.0Ag0.5Cu Pb-Free Solder Alloy, " Proceedings of the ASME International Mechanical Engineering Congress and Exposition, Orlando, FL, Paper No. 81171). Failure analysis revealed two competing failure modes, one in the solder and another in the copper trace under the component. Thus solder fatigue properties extracted with the help of finite element simulation of the test article should be treated as lower-bound estimates of the actual fatigue curves.