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CEB/FIP Model Code 1990 (MC-1990 [1] Structures 2010 (MC-2010 [5,6,7] BackgroundDurability of concrete structures, and in particular the lack of such, has been in the focus of society in general over the last few decades. Excessive repair needs have challenged our industry. The traditional approach in most national and regional concrete standards is to specify the provisions to ensure a certain design service life by limiting values for material composition and geometry based on the expert opinion of the code committee.There are several weaknesses in this approach: -It is often unclear as to which condition represents the end of the service life.-The required level of reliability for the design is often unclear as well. -The criteria should be based on long-term field experience. Such experience is, however, not normally available for modern materials and design concepts, and concepts with service records > 50 years are seldom in use any more.In 1998 a group of 19 European enthusiasts, all of us with a long record within CEB and FIP, signed a contract with the European Commission to develop a platform for durability design of concrete structures that contained the same elements and philosophy as that of modern structural design. This European network was named "Duranet", and the contract lasted until 2001. At DuraNet's final workshop in Tromsø, Norway, in 2001, attendees from Europe and North America worked out a plan for how to progress to get this methodology standardized and implemented in the industry worldwide (Fig. 1). The obvious environment for this was ISO.Some of us therefore met at the ISO TC-71 meeting in Norway that autumn and presented our visions. TC-71, responsible for concrete-related standardization within ISO, endorsed the initiative, but quite correctly made us aware of the fact that ISO normally starts its work on the basis of existing documents. We therefore agreed to ask the International Federation for Structural Concrete, fib (formed by the merger of CEB and FIP) to work out such a model for a standard. , which came up with a roadmap for how to implement limit state and reliability-based service life design in standards.

Introduction BackgroundLightweight aggregate concrete (LWAC) has potential to offer weight reduction without significantly having to compromise the structural properties. Still, however, this material has not realized its potential as a commonly accepted alternative to normal weight concrete (NWC) or other construction materials. Main reasons for this are somewhat higher material and production costs, a common skepticism related to production properties, design/structural performance and durability, and the lack of sufficient and generally valid guidelines, rules and standards. Furthermore, a dependency on local/national conditions as to materials resources has provided specialized guidelines and standards in a way as to limit an all-European and cross-boarder application and trading with the materials. Another motivation to promote LWAC is that the growing shortage on traditional aggregate resources in great parts of Europe, combined with increasing focus on pollution and waste handling, is forcing the building and construction industry to look for alternative solutions that can combine these issues. Project InformationBased on this background an European consortium was established in 1995 with the aim to run a project within the framework of the Brite EuRam III program. The baseline is an international state-of-the-art and extensive national research in which the consortium partners have played a key role. The project draws on this present knowledge, co-ordinates, validates and utilizes the results in an extended development towards a more generally applicable, European concept for LWA concrete technology.

Durability design and service life modeling of concrete structures rely on environmental exposure classes based on the prevailing deterioration mechanisms. International standard environmental exposure classes, for example, those found in the fib Model Code 2010 and ISO 22965‐1:2007 are predominantly based on European environmental conditions. Although these exposure classes are more suited to the prescriptive design for durability, they may also be adapted to performance‐based design. For more complex design philosophies such as limit state design using partial factors, the generalizations of the standard exposure classes cannot be suitably employed and therefore a more rigorous characterization of the exposure environment is required. The standard exposure classes in the fib Model Code 2010 as well as various national codes from different regions of the world are critically reviewed, and their limitations highlighted. Based on the review, updates to the standard exposure classes for inclusion in the fib Model Code 2020 are proposed. This paper summarizes the work of TG8.8 WP3 (Commission 8: Durability, Task Group 8.8: Common approaches, Working Party 3: Exposure Zones) and represents the view of the Working Party members.