Showing papers on "Durability published in 2001"

North american design guidelines for concrete reinforcement and strengthening using frp: principles, applications, and unresolved issues

Abstract: Provided is a state of the art report on the North American use of FRP (fiber reinforced polymers) composites in concrete structures. The paper discusses the many reasons for the use FRP bars as internal reinforcement in concrete members to replace conventional rebars. The established fundamental principles for design and construction have been proposed to industry by the American Concrete Industry (ACI). Remarkable attention has focused on strengthening of concrete members with externally bonded FRP laminates or near surface mounted bars. ACI is presently in the process of finalizing the design and construction principles for use in practice. FRP materials are being used in some multi million dollar projects to strengthen parking garages, multi purpose convention centers, office buildings, and silos. An additional area for using these materials in repair/upgrade, the paper discusses the question of durability in relation to application for repair and upgrade.

Review Durability of materials in molten aluminum alloys

Abstract: The durability of metals and ceramics in molten aluminum is a great concern in engineering applications such as die casting, containment of liquid metals and semi-solid processing This paper summarizes related work along with the experimental results from our laboratory Most of the important engineering materials are included Ceramics such as graphite, aluminosilicate refractories, AlN, Al2O3, Si3N4, sialons are characterized as inert in molten aluminum and its alloys The corrosion resistance of metals is generally poorer than that of inert ceramics, although the durability of titanium and niobium is relatively good Factors affecting the material durability in molten aluminum, including the interfacial layers, dynamic agitation, surface coatings and grain size are also discussed

Creep, Shrinkage, and Durability Mechanics of Concrete and other Quasi-Brittle Materials

Abstract: The Proceedings comprise both the invited and contributed papers presented at the Sixth International Conference on Creep, Shrinkage and Durability Mechanics of . . Concrete and other Quasi-Brittle Materials (CONCREEP-6), held at the Massachusetts Institute at Technology, Cambridge, U.S.A., from August 20 to 22, 2001. The tradition of internationai conferences on concrete creep Degan with the conference chaired and organized in Munich in 1958 by Hubert Ruesch. The second conference was held also in Munich. fn 1968, chaired again by Ruesch and or~ by Fol1:er H. Wift:!nann. The third conference followed in Leed!lln.l978, cha1rt:d and organized by Adam Neville. Although theSe three conferences, all held under the auspices of RILBM (International Union of Testing and Research Laboratoriell for Matedals and Structures, Paris), were not considered to oonsHtute any conferenCe Series, the conference held in Evanston}.n 1986 under the sponsorship of the U.s. National Science FO!Jl1dation, which was chaired and organized by Zden~ P. Baf.ant, was labeled as the fourth conference in order to initiate a serieil anchored in a tradition. RILBM was asked to co-sponsor that confeience scieqlifica1ly, and the proceedings, published by John Wiley &:: Sons, U.I<., were dedicated to the memory of Robert L 'Hermite, the founder of RlLEM and a leading early researcher in thefie1d. The acronym CONCREEP was created with the fifth conference, which was held In Barcelona in 1993. It was organizetlby Zden~ P. Bdant and Ignacio Carol, and its proceedings, published by F&:N Spen, London, were dedicated to Adam Neville. . . Pursuant to this long tradition, CONCREEP-6 at MIT presents .agaln the latest results and implementation strategies of creep and shrinkage research at the fnterface of solid mechanics, materials science, experimental mechanics, computational mechanics of . concrete-like materials and structura1 engineering. It is organized with the-scientific c0sponsorship of RILEM, the Am-erican Concrete Institute, and the American Society of Ovil Engineers through the Committee of Material Properties of the Engineeting. Mechanics Division.

Durability of compressed and cement-stabilised building blocks

Abstract: Adequate shelter is a basic human need, yet about 80% of the urban population in developing countries still live in spontaneous settlements as they cannot afford the high cost of building materials. The compressed and stabilised block (CSB) has been identified as a low-cost material with the potential to redress the problem and reverse the shelter backlog. While its other properties are well understood, the durability of the material remains enigmatic. The principal objective of this research was therefore to investigate the durability of CSBs, especially as used in the humid tropics. The thesis examines the interplay between three main factors: constituent materials used (cement, soil, water); quality of block processing methods employed; and the effects of natural exposure conditions (physical, chemical, biological). Through a multi-pronged methodology involving literature reviews, laboratory experiments, petrographic analysis and an exposure condition survey, block properties and behaviour are rigorously investigated. The findings are presented under the two main division of the thesis: Part A and Part B. Part A introduces a review of the literature on the main theoretical concepts of durability and cement-soil stabilisation. It discusses various deterioration modes, and examines in more detail mechanisms of stabilisation using Ordinary Portland cement. Part A also identifies and highlights critical stages of the CSB production cycle, and recommends a strict adherence to proper testing and processing procedures. Part B presents the results of direct investigation methods used. Findings from the fieldwork confirmed that premature deterioration was widespread in exposed unrendered blocks, with defects exhibited mainly as surface erosion and cracking. Quality checks on site materials and practice established an urgent need for improvement through the provision of appropriate standards and codes. Laboratory experiments which compared the properties of traditional blocks (TDB) and blocks improved by the inclusion of micro silica (IPD), established that the latter significantly out-performed the former. A new quick predictive surface test, the slake durability test, which is more reliable and repeatable than existing tests, is proposed. The thesis concludes that it is possible to significantly raise the strength, improve the dimensional stability and wear resistance of CSBs to the extent that they can be safely used in unrendered walls in the humid tropics. This improvement is achieved via better intergranular bonding, reduction in voids and lowered absorption. Using the slake durability test, it is now tenable to freely discriminate, classify, and compare not only blocks but other like materials of any category and storage history as well. New quantitative durability gradings are recommended for future incorporation into CSB standards. The findings are likely to contribute to the widespread use of CSBs. The research, however, also raises a number of new questions which are listed for further work.

Temperature-conductivity relationships for concrete: An activation energy approach

Abstract: The application of electrical techniques for in situ durability monitoring of reinforced concrete structures is now receiving considerable attention.

A design consideration for durability of high-performance concrete

Abstract: Environmental factors, especially the climate, have significant influence on concrete structure. This paper aims to investigate the harmful effects of maritime climate on the durability of concrete structures built in coastal areas. Singly reinforced beam specimens of traditional design and those of densified mixture design algorithm (DMDA) were employed to study the potential problems of concrete structure. Results indicate that cracks on the concrete structure, if go unnoticed, may cause failures. Thus, it is important to know the methodology of achieving high strength and durable concrete in order to avoid formation of cracks in the structural member.

Durability and service life prediction of GFRP for concrete reinforcement

Abstract: In recent years GFRP (Glass Fibre Reinforced Polymers) has emerged as an alternative to conventional steel reinforcement in steel aggressive applications. However, unlike steel GFRP reinforcement deteriorates due to the alkaline environment represented by concrete. This research project aims at determine the long-term environmental influence of concrete on GFRP reinforcement bars. GFRP specimens have been exposed in concrete at different temperatures and the influence of temperature on the tensile strength deterioration rate has been determined using Arrhenius equation. According to preliminary results 18 months in moisture-saturated concrete at 60°C corresponds to 100 years in the same environmental condition but at outdoor temperature (in the south of Sweden).

Consideration of durability of concrete structures: Past, present, and future

Abstract: The paper expresses durability in terms of the expected conditions of exposure as well as of the specified or traditional service life of structure. A brief review of deleterious actions is given. Consideration of durability means how ensuring durability is viewed by designers, and not detailed advice or rules. Thus, the paper reviews the past attitude, which relied on providing strong concrete, it being believed that durability was concomitant with strength. Changes in the properties of cement, in that, with the ‘new’ cements, the same strength as specified heretofore could be achieved at a higher water-cement ratio resulted in structures with a distinctly reduced durability. This led to a re-consideration of mix design procedures, so that both strength and durability are now explicity considered. The future approach has to rely on the use of a range of cementitious materials and admixtures and on a meticulous performance of all operations from batching to curing.

The Tribological Effect of Mechanically Produced Micro-dents by a Micro Diamond Pyramid on Medium Carbon Steel Surfaces in Rolling-sliding Contact

Abstract: In order to evaluate the effects of micro-pockets on the lubrication and the pitting durability of medium carbon steel surfaces, in the present paper, using the roller with a small number of micro-dents marked by a diamond pyramid whose total area was, to minimize the effect of work-hardening, set negligibly small compared to the contact area as the follower in a two-roller testing machine, the pitting durability was tested under poor lubrication conditions and/or severe loading levels. The results successfully demonstrate the effect of such micro-pockets on the pitting durability and scuffing resistance of surfaces in rolling-sliding contact.

Engineered durability for timber construction

Abstract: The application of reliable prediction models is essential for the development of performance-based design procedures. Such models for the durability of timber construction are not available. A review of progress in the development of these models reveals that, while models do exist, they must be calibrated with the performance of real structures before they can be used for design. The development of models for predicting performance of constructions under attack by decay fungi, subterranean termites and corrosion is examined.

Concrete cracking in composite bridges: tests, models and design proposals

Abstract: Concrete cracking affects the durability and the mechanical behaviour of steel concrete composite bridges. The main results of an experimental and theoretical study that focused on the mechanical b...

Relevance of High Temperature Oxidative Stability Testing to Long Term Polymer Durability

Abstract: In polymer degradation and durability studies, as well as predicting shelf-life for medical devices, one is confronted with the need for accurate prediction and difficulties of long term real-time evaluation. Various ways to accelerate the degradation process have met with mixed success. However, recently, in our own studies, a ‘master curve’ like behavior was found to be valid for polypropylene samples studied. Evidently, for samples obeying the master curve, very few data points at high temperatures can be scaled to obtain reasonably accurate estimates on long term durability.

Durability Evaluation of Intumescent Coating for Steel Frames

Abstract: This paper reports on the results of experimental studies on the durability of intumescent coating for steel frames. Intumescent coatings are fireproof materials that provide the thermal insulation of steel structures. They start to foam when the surface temperature reaches about 300°C by heating and form a layer of carbonaceous char 25 to 50 times thicker than at room temperature. However, their durability or long-term fireproofing is not clear. Preliminary accelerated tests and small-scale heat tests were conducted, and it was found that water is the principal environmental factor that affects the durability of intumescent coatings. Another series of accelerated tests and exposure tests was then performed mainly for water resistance. The fire resistance of specimens after degradation was verified in full-scale heat tests. As a result of these tests, a new testing method was proposed for evaluating the durability of intumescent coatings by considering the high-temperature and high-humidity weather conditions of Japan.

Diamonds having improved durability

Abstract: The present invention is directed to a process or method of improving the durability of a diamond-type tool, such as a diamond cutter, by providing the diamond-type tool and treating the surfaces of the diamond-type tool to increase the impact strength and fracture toughness. This treatment is by implanting ions into the surface of the diamond-type tool.

The design of porous asphalt mixtures to performance-related criteria

Abstract: Four laboratory tests, permeability (both vertical and horizontal), particle loss, scuffing and affinity between binder and aggregate, were used to assess porous asphalt samples taken from site with those manufactured in the laboratory. The results indicate that the potential of a mixture to achieve requirements for hydraulic conductivity on site can be assessed from laboratory mixtures, but there was insufficient variation between the samples in the laboratory tests to be able to predict the durability of the material in service. A laboratory design procedure for porous asphalt is proposed which should assist in reducing the current high cost of the material when procured under the current specification clause or, in future, under a performance-related clause. Also, supporting advice on binder selection, aggregate selection, fillers and adhesion agents, aggregate grading, durability and permeability is included. (A)

The Effects of High Temperature Exposure on the Durability of Thermal Barrier Coatings

Abstract: Yttria-stabilized Zirconia (YSZ) coatings deposited by electron beam physical vapor deposition on platinum aluminide and NiCoCrAlY bond coats on single crystal superalloy substrates have been oxidized at temperatures between 1000 and 1200°C in air. The cyclic oxidation lives of the systems with platinum aluminide bond coats were substantially longer than those with NiCoCrAlY bond coats. The thermally grown oxide (TGO) that develops between the bond coat and the TBC during oxidation, as well as the bond coat and the TBC adjacent to the TGO, have been examined in detail using optical metallography, scanning electron microscopy (SEM), and cross-sectional transmission electron microscopy (XTEM). The YSZ is observed to undergo significant amounts of sintering. The TGO grows by the inward diffusion of oxygen and the outward diffusion of aluminum. In some cases, the outward growth component incorporates some of the TBC into the TGO. The depletion of aluminum results in phase changes in the bond coats. Failure of the TBCs occurs after fixed amounts of oxidation which result in increasing amounts of elastic energy being stored in the TGO and YSZ as well as degradation of the TGO-bond coat interface. The fracture path changed as a function of exposure time and temperature with larger amounts of separation occurring at the TGO/BC interface for higher temperatures and longer exposures in dry air. Failure can be accelerated in the presence of water vapor, particularly if spinel formation is induced. Fracture occurs primarily in the oxides, in this case. The fracture surface for systems with platinum aluminide bond coats often contains precipitates, which are rich in refractory metals. These features do not appear to be prevalent with NiCoCrAlY bond coats.

Strength and Durability of Concrete Containing Salts of Alkenyl-Succinic Acid

Abstract: The performance of concrete is judged by many different properties, including durability and strength Admixtures are frequently used to improve these properties Most admixtures provide a positive effect on only one property and, therefore, combinations of admixtures must be used Deterioration due to reinforcement corrosion is likely the most important durability issue with reinforced concrete Corrosion inhibitor admixtures are commonly added to concrete to suppress or delay reinforcement corrosion, and additional admixtures must be added to improve the concrete's freeze-and-thaw resistance This paper presents research on 2 forms of a chemical that improves the durability of concrete in several ways: by improving corrosion resistance; by reducing water penetration; and by providing resistance to freezing and thawing The effect of the chemical on several concrete material properties is also discussed Performance was compared with concrete containing commercial admixtures

Environmental durability studies for frp systems: definition of normal conditions of use of frp for structural strengthening applications

Abstract: This paper presents environmental durability data for both E-glass and carbon wet-lay-up systems subjected to several environmental exposure conditions. Water resistance, salt water resistance, alkali resistance, dry heat resistance, freeze-thaw and UV/condensation are investigated. Tests were performed according to ASTM specifications and the effects of these different environmental exposure conditions were observed, particularly on the tensile and shear properties of the fiber reinforced polymer (FRP) systems. This data should help in defining the "normal" environmental conditions according to which FRP systems should be designed, manufactured, and applied.