Showing papers on "Durability published in 1991"

Pressurizable envelope and method

Abstract: An internally pressurizable lightweight high tensile strength multi-layered structure with an outer barrier layer envelope of elastomeric semi-permeable material for use as a cushioning device is provided. The outer barrier layer is bonded, at a multiplicity of sites, to substantially the entire distal surfaces of a double-walled drop-thread linked fabric wherein the filaments are comprised of a highly distorted, long chain, axially orientated crystalline molecular structure which has a low gas permeability. The bond between the barrier layer and the facing fabric is substantially increased by the presence of fibrils and texturizing. The drop threads which are likewise texturized, function as stress averaging members to maintain the composite structure in either a substantially flat or planar or contoured configuration without weldments within the select load-bearing areas. This lightweight product is capable of withstanding very substantial internal inflation pressures, under severe long-term steady state and cyclical compression and flexural fatigue conditions. The product is inflated, pressurized and sealed and maintains the internal inflatant pressure for extended periods of time, generally in excess of the useful life of the overall product, by employing the diffusion pumping phenomenon of self-inflation. The cushioning device can selectively control the rate of diffusion pumping phenomenon by varying the density relationship between the elastomeric semi-permeable material of the envelope and the essentially gas impermeable highly distorted crystalline filament material of the fabric, thus improving the long term performance and durability and reducing the cost, and eliminating some of the disadvantages of the earlier cushioning products. In a limiting case, it is possible to permanently inflate the device using readily available fluids as nitrogen or air.

Durability design and repair of concrete structures: chloride corrosion of reinforcing steel and alkali–aggregate reaction

Abstract: Problems related to the fundamentals of durability design and repair design of concrete structures are discussed with reference to damage caused by chloride corrosion and alkali–aggregate reaction. A unified approach is presented, based on the mechanism of deterioration, which is believed to offer potential for further practical development.

Mechanisms of high durability performance of plain and blended cements

Abstract: In this research, an attempt has been made to study the mechanisms controlling the performance of plain and blended cements against corrosion of reinforcement and ASR. The effect of various compositional and environmental factors, such as C3A and alkali contents, concomitant presence of sulfates, temperature and mode of occurrence of chlorides, on chloride binding and pore solution alkalinity has been studied in plain cements, in an effort to evaluate their influence on mechanism of corrosion resistance. Mechanisms controling resistance to corrosion and ASR of blended cements, formulated using fly ash, blast furnace slag and microsilica have been studied through their effect on chemical environment and physical characteristics of hardened concrete. Results show that high C3A cements have more chloride binding capacity than low C3A cements, explaining their higher corrosion resistance. Increase in curing temperature and alkali content of cement and concomitant presence of sulfates decrease chloride binding capacity in plain cements. Plain cement binds more primary chlorides than secondary external chlorides. Fly ash and slag have little effect on chemical environment of concrete compared to microsilica, which drastically increases aggressivity of the chemical environment. The blending materials bring about significant improvement in the physical structure of concrete through pore refinement, decrease in permeability, chloride and oxygen diffusion and increase in electrical resistivity. These significant improvements in the physical characteristics due to blending materials are responsible for the improved corrosion resistance of the blended cements. Also, the blending materials significantly reduce OH concentration in pore solution. The reduction in the OH concentration and possibly the improved physical structure of blended cements are responsible for their incresed resistance against ASR.

Bituminous seal coats: design, performance measurements, and performance prediction

Abstract: A field study was conducted at the Pennsylvania Transportation Institute's Pavement Durability Research Facility at Pennsylvania State University to determine the effects of specific construction, traffic, and material variables on the performance of bituminous seal coats. As part of the study, the adequacy of existing seal-coat design procedures, quality control procedures, and seal-coat performance measuring techniques was evaluated. The focus of this paper is on the latter evaluation; the effects of the other variables are reported elsewhere. The evaluations were based on actual field measurements and led to numerous recommendations for improvements in seal-coat design methods, equipment calibration, measurement and evaluation of seal-coat performance, prediction of seal-coat life, and the appropriate use of seal coats as a maintenance technique. The recommendations are reported herein. Finally, a definitive pattern of seal-coat macrotexture degradation was identified under this closely monitored field experiment. This finding was used to develop a prediction model for seal-coat life. Aggregate wear rates and embedment rates were measured on two surfaces under closely monitored traffic loading conditions. The wear and embedment rates were used to illustrate the potential of the seal-coat-life prediction model to evaluate the effects of different variables on expected seal-coat life. On the basis of the deficiencies observed in the existing design procedures, updated design charts that use more objective methods of evaluating the existing pavement surface are proposed, as are potential methods for rating the surface.

New developments in catalytic converter durability

Abstract: A number of new developments in the areas of material composition, cell geometry, wall porosity, substrate contour, washcoat formulation, thermal and acoustic insulation, and clamshell and heatshield designs have occurred in recent years to meet the more demanding performance and durability requirements of automotive catalytic converters. This paper reviews the major developments in ceramic and metal substrates, stable washcoat systems, nonintumescent mounting materials, edge-shielded intumescent ceramic mats, ceramic insulation rings, dual can and dual cone packaging designs, and perforated heatshields with convection cooling. These improvements offer higher conversion efficiency, lower pressure drop and extended durability. A brief comparison of ceramic and metal substrate durability, based on laboratory tests, is also included.

Some aspects of durability of high-volume astm class f (low-calcium) fly ash concrete. in: durability of concrete. second international conference. august 4-9, 1991, montreal, canada. volume i

Abstract: Low-calcium fly ash, ASTM Class F, is being increasingly incorporated into portaldn cement concrete as a partial replacement for cement. The replacements commonly used are 15 to 25 percent by weight of cement. This paper presents data on several aspects of durability of this new type of concrete. The aspects discussed include freezing and thawing cycling, resistance to chloride ion diffusion, deicing salt scaling resistance, carbonation, and volume stability. Data on the role of high volumes of fly ash to control alkali-silica reaction in concrete are also presented. It is concluded that, in general, high-volume fly ash concrete has excellent durability characteristics. The only exception is the deicing salt scaling tests, in which the above concrete performs poorly.

Predicting the durability of paving bricks

Abstract: The pore size distributions of approximately 110 bricks removed from existing pavements were measured using mercury intrusion. These distributions were used to calculate a Durability Factor using the method of Maage. This Durability Factor was then correlated with the observed durability performance of the pavements. It was found that all bricks with a Durability Factor greater than 90 exhibited no freeze/thaw durability problems. Further, with very few exceptions, all bricks with a Durability Factor less than 90 were suffering freeze/thaw failures. This procedure is both more accurate and faster for selecting potentially durable bricks than the current use of absorption measurements.

Durability Analysis Using Short and Long Fatigue Crack Growth Data

Abstract: A deterministic method of estimating the fatigue crack growth durability of metallic airframes is presented, with particular reference to a civil transport aircraft.

Interfacial chemistry and adhesion: The role of surface analysis in the design of strong stable interfaces for improved adhesion and durability

Abstract: Durability is a key issue in widening the application of adhesive bonding technology. This paper describes a fundamental study of the adhesion loss in epoxy-steel bonds exposed to water, and the development of steel pretreatments, which significantly enhance durability. XPS studies have revealed two weak links in epoxy/steel bonds, both of which must be improved for optimum performance. They are displacement of the adhesive from the steel and breakdown of the oxide on the metal surface. The former has been addressed by applying monomolecular layers of an aminosilane adhesion promoter to the steel surface. Oxide instability has been remedies by use of a novel and simple treatment that modifies the oxide chemistry to a depth of 2–5 nm. Combining these, results in a joint that loses no strength after 2000 h of water immersion at 50°C, whereas untreated joints lose 68% of their strength after only 400 h. The study shows how careful identification of failure modes, combined with appropriate modification of the substrate surface, can be used to design strong stable interfaces. These modification, which affect only a few molecular layers, have a large impact on both bond strength and durability.

Durability and life prediction of adhesive bonds in severe environments

Abstract: 1. Life Prediction methods may be used to characterize the durability of adhesive bonds of elastomers to rigid substrates. The primary rate determining mechanism of bond failure is considered to be electrochemical in nature, and its rate may be characterized on an Arrhenius basis. 2. Assumption of a single mechanism (and single activation energy) cannot be made across a wide temperature range. Two different regimes were discovered within the temperature range 20 to 90°C for both sea water and oil environments. 3. Durable bonds between elastomers and structural polymer/composites can be formed using normal rubber technology for rubber/metal bonding. In the case of bond durability in iso-octane/toluene at 90°C bonds of HNBR to E-glass composite surpassed those of HNBR to stainless steel. 4. These methods provide a scientific basis for quantitative determination of the life of engineering components in service. Further research is required at present for each new application, but wider use of these ...

Durability of fluoride glasses in water

Abstract: The durability of eight fluoride glasses was tested in liquid water from 25° to 75°C. The studies were done by first growing a corrosion layer and then examining structure and chemistry in cross section with an optical microscope and an electron microprobe. In this way the details of the corrosion behavior could be directly determined. The results indicate that the corrosion process proceeds by a moving boundary, whose penetration rate is diffusion limited.

A study of embankment performance during overtopping

Abstract: : A study was undertaken to determine how embankments behave when overtopped and, based on this knowledge, to predict overtopping performance of different types of embankments (earthen, rock fill, etc.) and to recommend defensive measures that would increase the durability of an overtopped embankment. An experience-oriented approach was taken. Pertinent literature was reviewed. Prototype dams subjected to overtopping, centrifuge modeling of overtopping embankments, and numerical modeling techniques are described.

Influence of Chloride Corrosion on the Durability of Reinforcement

Abstract: This paper deals with the problem of reinforcing steel corrosion in the alkali activated slag mortar exposed to the attack of concentrated chloride solution. The observations of reinforcement in OPC mortars, OPC + SF mortar or OPC + limestone flour mortar were carried out simultaneously.