Durability mechanics of concrete and concrete structures—Re-definition and a new approach –

This paper gives a summary of the activities of the Working Group on Durability Mechanics (WG3) within the Japan Concrete Institute (JCI) Technical Committee on Time Dependent Behavior of Cement-Based Materials (JCI-TC061A). A re-definition of and new approach to durability mechanics is proposed for establishing systematic prediction and evaluation of the time-dependent behavior of concrete materials and structures. The chemo-mechanical deterioration of cementitious materials over time due to chemical reaction, environmental action, and external load, are described by physicochemical models of reaction, transport, fracture and their coupling. Furthermore, the performance of concrete structures over time is also discussed. In addition, the outlines of several representative research projects on durability mechanics will be introduced. 2 PROPOSED RE-DEFINITION OF “DURABILITY MECHANICS” The Working Group on Durability Mechanics within the Japan Concrete Institute (JCI) Technical Committee on Time Dependent Behavior of CementBased Materials has proposed the following redefinition of durability mechanics based on the proposal of Coussy & Ulm (2001) in order to systematize each deterioration factor so as to lead finally to the prediction and evaluation of the structural performance of concrete structures: “Durability Mechanics for concrete structures is one of the academic disciplines of Engineering Mechanics for the systematic prediction and evaluation of time-dependent behavior of concrete materials and structures, in which the chemo-mechanical deterioration of cementitious materials over time due to chemical reaction, environmental action, and external load, can be described by physicochemical models of reaction, transport, fracture and their coupling, and the performance of concrete structures over time can be also predicted by constitutive models of deteriorating materials.” 3 SUMMARY OF ACTIVITY OF WG 3.1 Approach to durability mechanics Figure 1 shows the approach to materialization of durability mechanics of WG3. The cause, mechanism and coupling effect in the process of timedependent deterioration of concrete and concrete structures are systemized, including the effects of environmental action and external load. As a preliminary step to the materialization of the concept of durability mechanics, a flow diagram describing the process of deterioration has been prepared by reordering related information. Next, a framework of the time-dependent processes of 1) production, change and consumption of substances, 2) transport of substances, 3) material and structural properties, and 4) their interaction, named “Mandala for durability mechanics,” has been made. Then, the element models describing phenomena resulting in deterioration and the prediction methods for each deterioration processes are summarized. Finally, examples of the interaction between materials property and structural performance as well as modeling and simulation of structural performance are introduced. 3.2 Mandala for Durability Mechanics Figure 2 shows the Mandala, which is a figure describing the whole system of durability mechanics. This figure includes the process before casting, because the quality of construction strongly affects the quality of hardened concrete. However, this paper focuses on the phenomena after casting because of the limited number of theoretical approaches evaluUnderstanding of mechanism of deterioration process for building prediction method

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