Showing papers on "Durability published in 2007"

Durability of an Ultrahigh-Performance Concrete

Abstract: Significant recent advancements in cement-based, fiber-reinforced composite materials have stretched the bounds of concrete into the realm of ultrahigh-performance concrete (UHPC). The durability of a commercially available UHPC was independently evaluated through six standardized durability tests and the results are reported herein. Regardless of the curing treatment applied, this concrete exhibits significantly enhanced durability properties as compared to normal and high performance concretes. The concrete exhibited minimal damage after being subjected to two times the normal number of ASTM C 666 freeze–thaw cycles. It was innocuous to ASTM C 1260 ASR deterioration, to ASTM C 672 scaling deterioration, and to AASHTO T259 chloride penetration. The ASTM C 1202 Electrical Indication of Concrete’s Ability to Resist Chloride Ion Penetration test result was negligible if any steam-based curing treatment was applied, and was very low otherwise. Steam-based curing treatments significantly enhanced the ASTM C 9...

A review on durability properties of strain hardening fibre reinforced cementitious composites (SHFRCC)

Abstract: This paper reviews and presents various durability properties of strain hardening fibre reinforced cementitious composites (SHFRCC). Published research results show that, due to its tight crack width properties compared to ordinary concrete and ordinary fibre reinforced concrete, SHFRCC significantly resists the migration of aggressive substances in to the concrete and improves the durability of reinforced concrete (RC). It is also reported that, due to the strain hardening and multiple cracking behaviours, SHFRCC meets the tight crack width limits for durability of RC structures proposed by different design codes. Based on the reviewed durability properties it is argued that SHFRCC materials can be used in selected locations of RC structural members to improve their overall durability performances.

Durability of composites for civil structural applications

Abstract: Introduction: The use of composites in civil structural applications. Part 1 Aspects of composite durability: Fabrication, quality and service life issues for composites in civil engineering Durability of composites in aqueous environments Durability of composites in freeze-thaw conditions Durability of composites exposed to ultraviolet radiation Durability of composites exposed to elevated temperature and fire Durability of composites under fatigue loads Creep and time-dependent response of composites Durability of composites due to wear and erosion. Part 2 Applications and monitoring of composites in civil engineering: Fibre-reinforced polymer composite structures and structural component Current applications and durability issues Reinforcement of concrete using fibre-reinforced polymer composites External strengthening of structures using fibre-reinforced polymer composites Rehabilitation of concrete structures using fibre-reinforced polymer composites: Identifying potential defects Structural health monitoring and field evaluation of composite durability.

Long-Term Performance of a Glass Fiber-Reinforced Polymer Truss Bridge

Abstract: In the summer of 2005, after eight years of use as a temporary bridge during the winter, the Pontresina Bridge for pedestrians was transported to the Swiss Federal Institute of Technology Lausanne for a detailed assessment of the structural safety, serviceability, and long-term durability of the bridge. The assessment included a visual inspection, quasistatic testing identical to that performed in 1997, and detailed investigations of material degradation. The visual inspection showed a variety of different local defects and damage such as local crushing caused by impact, local cracks due to inappropriate storage and lifting of the structure, fiber blooming, degradation of cut surfaces, and damage due to vandalism. Comparisons between load tests performed in 1997 and 2005 showed, however, that the structural safety and serviceability of the bridge have not been affected by these local damages. The stiffness of the pultruded shapes remained unchanged, whereas a slight decrease in strength between 13 and 18% was measured, which, however, is not critical when taking into consideration the high effective safety factors. In view of a further service period of 5 years until the next inspection, the visible damages were repaired. This experience showed that the durability is primarily affected by inappropriate constructive detailing and that pultruded glass fiber-reinforced polymer shapes, if correctly manufactured and processed, can offer good long-term performance and durability.

Durability of Soil–Cements against Fatigue Fracture

Abstract: Cementitious stabilization is a common method of ground improvement when weak foundation soils are encountered in practice, and marginal or nonstandard materials such as recycled aggregates are used in civil engineering construction. Long-term durability of stabilized materials becomes an issue, especially when it involves one or more recycled materials with unknown and often questionable properties. The study presented herein investigates the fatigue durability, endurance limit, and damage accumulation process in recycled crushed concrete aggregate stabilized with cement-fly ash mixtures. Results show that the 2 million cycles fatigue endurance limit for the stabilized recycled aggregate was nearly 53% of the static modulus of rupture, indicating that the fatigue strength of this material is quite similar to or better than other traditional cementitious composites. It was also found that the accumulated permanent deformation and the expended fatigue life can be related by a nonlinear power law, and the fatigue damage in this material approximately follows Miner's rule for cumulative damage. Finally, the importance of developing innovative testing methods for durability assessment are highlighted, which include coupled mechanical and environmental loadings to simulate the most damaging field conditions, and accelerated aging and life prediction processes using the Arrhenius time-temperature superposition methods.

Improvement of concrete durability with the aid of bacteria

Abstract: Shortcomings of conventional surface coatings have drawn the attention to alternative treatments for the improvement of the durability of concrete. Promising results of an innovative biotechnology based on microbial carbonate precipitation have lead to research concerning the use of bacteria in or on concrete. In our research groups, first the criteria for the selection of calcium precipitating Bacillus strains were established. Bacillus sphaericus strains capable of the remediation of Euville limestone, by precipitating a dense and coherent calcium carbonate layer and concomitantly inducing a reduction of capillary water absorption, were characterised by a high urease activity, abundant EPS-production, a good biofilm production and a very negative ζ-potential.

Polymer Modified Asphalt Durability in Pavements

Abstract: The project was designed to develop (1) a better quantitative understanding of the relation between laboratory accelerated binder aging and field aging, (2) a test procedure to measure properties of an aged binder that relate to failure on the road and (3) a proposed specification for estimating the relative durability of binders in the presence of oxidative aging. Tests were conducted on original base and polymer modified binders, laboratory compacted mixtures, and pavement aged binders. The project necessarily evolved to a more comprehensive approach to improving pavement service life. Methods for significantly improving pavement durability should be implemented: (1) construct pavements with the lowest possible accessible (interconnected) air voids, consistent with other best construction and mix design practices; (2) use mix designs that have an inherently low decrease in fatigue life with binder oxidation, coupled with an appropriately high initial fatigue life; (3) use binders with a minimum stiffness at the PAV* 16 hour condition (consistent with the appropriate performance grade); (4) use the pavement aging model for pavement design; (5) use binders that have inherently slow hardening rates kinetics; and (6) use modifiers that provide the most reduction in the hardening rate. Items 1 and 2 have a dramatic impact on pave service life but require additional research for the most effective implementation: (1) determine the parameters that govern the decline of mixture fatigue life with binder hardening; (2) determine methods to reliability; and (3) with minimal risk to other construction parameters, achieve very low accessible air voids in pavements.

Aluminum buffer layer for high durability of all-solid-state switchable mirror based on magnesium-nickel thin film

Abstract: Aluminum buffer layer was inserted in all-solid-state switchable mirror based on Mg–Ni thin film to improve its durability. Optical switching speed of the device has been improved because the buffer layer might work to transport electrons and protons promptly as an electrode. Durability of the device was evaluated by cyclic switching test. The device with buffer layer showed three times higher stable durability than that of the device without buffer layer. The authors found that the aluminum buffer layer effectively works to suppress the diffusion of nickel and palladium atoms into the Ta2O5 thin film during cyclic switching test, resulted in high durability.

Primer on Durability of Nuclear Power Plant Reinforced Concrete Structures - A Review of Pertinent Factors

Abstract: The objective of this study was to provide a primer on the environmental effects that can affect the durability of nuclear power plant concrete structures. As concrete ages, changes in its properties will occur as a result of continuing microstructural changes (i.e., slow hydration, crystallization of amorphous constituents, and reactions between cement paste and aggregates), as well as environmental influences. These changes do not have to be detrimental to the point that concrete will not be able to meet its performance requirements. Concrete, however, can suffer undesirable changes with time because of improper specifications, a violation of specifications, or adverse performance of its cement paste matrix or aggregate constituents under either physical or chemical attack. Contained in this report is a discussion on concrete durability and the relationship between durability and performance, a review of the historical perspective related to concrete and longevity, a description of the basic materials that comprise reinforced concrete, and information on the environmental factors that can affect the performance of nuclear power plant concrete structures. Commentary is provided on the importance of an aging management program.

Performance of concrete with binary and ternary cement blends

Abstract: Among the many factors that govern the durability and performance of concrete in service, type of cement receives greater attention. This paper describes the characteristics of cementitious systems required to meet the diverse requirements of strength and durability of concrete and highlights the advantages of part replacement of OPC by fl y ash, granulated slag and silica fume – either singly or in combination in ternary blends. Examples of successful application are cited.

Freeze-Thaw Resistance of Concrete with Marginal Air Content

Abstract: Freeze-thaw resistance is a key durability factor for concrete pavements. Recommendations for the air void system parameters are normally 6% ± 1% total air and spacing factor ≤ 0.20 mm (0.008 in.). However, it was observed that some concretes that did not possess these commonly accepted thresholds presented good freeze-thaw resistance in laboratory studies. A study evaluated the freeze-thaw resistance of several marginal air void mixes, with two different types of air-entraining admixtures: a Vinsol resin admixture and a synthetic admixture. The study used rapid cycles of freezing and thawing in plain water, in the absence of deicing salts. For specific materials and concrete mixture proportions used in this project, the marginal air mixes (concretes with fresh air contents of 3.5% or higher) presented an adequate freeze-thaw performance when Vinsol resin-based air-entraining admixture was used. The synthetic admixture used in the study did not show the same good performance as the Vinsol resin admixture did.

PEMFC Durability Test under Specific Dynamic Current Solicitation, Linked to a Vehicle Road Cycle

Abstract: The Laboratory of Electrical Engineering and Systems (L2ES) is concerned with fuel cell system durability and reliability. Since the lab is predominantly involved in the field of transport applications, one of the objectives is to study PEMFC ageing in different specific environments linked to electric vehicle operation. The first phase of the durability program was devoted to the reference test of a 100 W three cell stack, operated in a stationary regime at roughly nominal conditions for 1,000 hours. The second phase, on which this paper is focused, is dedicated to the durability test of another 100 W stack placed under dynamical current constraints. The current cycle load applied is first computed from a standardized transportation mission profile (time vs. speed of vehicle) and then adapted to the power of the fuel cell tested. The gas supply strategy is defined and the work presented in this paper shows the importance of the gas flow management in providing highly dynamical current profiles. The experimental methodology is based on polarization curves as well as on electrochemical impedance spectroscopy measurements performed regularly throughout the ageing. The experimental results showing the degradation of the fuel cell performances are presented and analyzed.

Effect of Voids on Thermomechanical Durability of Pb-Free BGA Solder Joints: Modeling and Simulation

Abstract: The effect of process-induced voids off the durability of Sn-Pb and Pb-free solder interconnects in electronic products is not clearly understood. Experimental studies have provided conflicting ambiguous conclusions, showing that voids may sometimes be detrimental to reliability, but they may sometimes even increase the reliability of joints, depending on the size and location. Because of the higher level of process-induced voids in Pb-free solders, this debate is more intensified in Pb-free joints. This study presents finite element analysis (FEA) of the influence of void size, location, and spacing on the durability of Pb-free solders. A three-dimensional, global-local, viscoplaslic FEA is conducted for a CTBAG132 assembly under thermal cycling. The displacement result of the global FEA at the top and bottom of the critical ball is used as the boundary condition in a local model, which focuses on the details of a single ball of the CTBGA package under temperature cycling. Parametric study is conducted to model a solder ball with voids of different sizes and locations. The maximum void area fraction modeled is from 1% to 49% of the ball area. An energy-partitioning model for cyclic creep-fatigue damage is used to estimate the damage and to monitor the trends as the size and location of voids are varied. Potential sites for maximum damage and crack initiation are identified. FEA results show that as void size increases up to about /5% of the area fraction of the ball, durability increases. For voids bigger than that, the durability starts to decrease. This study also confirms that as voids are located closer to the damage initiation site and the propagation path, their lifespan decreases.

Durability of All-Solid-State Switchable Mirror Based on Magnesium–Nickel Thin Film

Abstract: An all-solid-state switchable mirror with Mg-Ni thin film was prepared for basic research on a new type of smart window. The device has a multilayer of Mg-Ni/Pd/Ta 2 O5/WO 3 /indium tin oxide/glass and can switch reversibly from a reflective state to a transparent one. The durability of the device was investigated by a cyclic switching test. Though a transmittance change was slightly decreased, the device showed high durability up to 2000 switching cycles. We found that the degradation was related with the damaged surface of Mg-Ni thin film and the diffusion of Ni and Pd atoms into Ta 2 O 5 thin film during a cyclic switching test.

Optical coating with improved durability

Abstract: The invention discloses optical coatings with improved durability, the coating comprising a durability enhancing layer, a nucleation layer and an infrared reflecting layer. The invention also discloses methods of making thin film layers having enhanced durability.