Durability and performance in service

The problem with bonded joints is that most of the load is transmitted through the edge zones, and it is these which come under environmental attack first. In fact, the load becomes progressively borne by the inner region of the joint but, nevertheless. 

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D. R. Askins and H. S. Schwartz, Durability of adhesive bonded honeycomb sandwich in accelerated adverse environments, in Materials and Processes in Service Performance, p. 329, SAMPE, Azuza, Calif. (1977). 

To ensure a painted part meets its intended service need, work must be carried out in advance of commercialization to ensure the appearance, physical properties, durability, and performance of the painted part can meet desired expectations. In the developmental stage, usually molded plaques are painted, examined, and tested to the specification appropriate for the part service. This usnaUy inclndes exposure under conditions that will likely be encountered during the service. Both accelerated and real-world exposure testing is undertaken at this time. In addition, often panels are tested to failure in conjnnction to a known control. Failure mode analysis is important and can be a lengthy and tedions process becanse not only do we need to consider all the elements the... 

Durability. The term "durable" has several meanings, but in the present context it is used to describe an asphalt that possesses the necessary chemical and physical properties required for the specified pavement performance, being resistant to change during the in-service conditions that are prevalent during the life of the pavement. 

The laboratory operator is offered many choices in selecting utility outlets. A careful study will need to be made in order to select those that give the best combination of performance, durability, safety, and cost for service in a particular laboratory. 

Whether a new material or design is put into service before its durability has been proved will depend on the risks, cost and timescale involved. In many applications it is simply not possible to perform product trials in service. However, by performing such trials and testing the product at intervals it may be possible to estimate product lifetime and to detect potentially serious problems before they occur. 

The increasing use of high-performance fibrous composites in critical structural applications has led to a need to predict the lifetimes of these materials in service environments. To predict the durability of a composite in service environment requires a basic understanding of (1) the microscopic deformation and failure processes of the composite (2) the significance of the fiber, epoxy matrix and fiber-matrix interfacial region in composite performance and (3) the relations between the structure, deformation and failure processes and mechanical response of the fiber, epoxy matrix and their interface and how such relations are modified by environmental factors. 

The outdoor durability of epoxy bonded joints is very dependent on the type of epoxy adhesive, specific formulation, nature of the surface preparation, and specific environmental conditions encountered in service. The data shown in Fig. 15.19, for a two-part room temperature cured polyamide epoxy adhesive with a variety of fillers, illustrates the differences in performance that can occur due to formulation changes. Excellent outdoor durability is provided on aluminum adherends when chromic-sulfuric acid etch or other chemical pretreatments are used. 

The emphasis in this book is on the service abilities of novel concretes and protective compounds for various environments, such as those involving water, pollutants, acid, and alkali substances. The book draws on much of the excellent research already performed on the durability and corrosion resistance of these materials. 

Paving Trials. A number of sand-asphalt-sulfur test pavements were constructed in Canada without rolling the mixes. The pavements were designed so that mix durability and field performance variables could be evaluated under actual in-service conditions. 

A number of test pavements have been constructed to evaluate mix durability and field performance variables under in-service conditions. While the results are promising, a longer test period is necessary before conclusive results are obtained. 

Requirements specified in this way are deemed-to-satisfy rules. Such rules cannot be used to quantify the performance of the structure in general, specific effects of additional measures (for instance increasing the cover to the steel), or the consequences of sub-standard practice (for example using a higher w/c). In this respect it is important to note that EN 206 also allows the use of alternative performance-related design methods with respect to durability that consider in a quantitative way each relevant deterioration mechanism, the service life of the element or structure, and the criteria that define the end of the service life. Such methods should draw a picture of the characteristics that the concrete must possess to protect the reinforcement for the service life requested from a predictive model of the corrosion attack. These refined methods (as opposed to standard methods) may be based on long-term experience with local practices in local environments, on data from an established performance test method for the relevant mechanism, or on the use of proven predictive models. 

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