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It has been suggested that the Stiffness Damage Test ( SDT ) and the Damage Rating Index ( DRI ), mechanical and microscopic tools respectively, can reliably assess the condition of concrete affected by Alkali-Aggregate Reaction (AAR). However, a multi-level characterization of AAR damage through the coupling of the prior tools has never been evaluated so far. This paper presents the overall assessment of twenty concrete mixtures presenting different strengths and incorporating a wide range of aggregate types/natures. Evaluations on both AAR crack development and its influence on the mechanical properties of affected concrete are performed over a multi-level point of view. Results show that strong data envelopes are obtained from each of the test procedures, correlating various critical microscopic and mechanical output parameters with AAR expansion level. Moreover, such assessments allowed the development of comprehensive quantitative data which enables a better understanding/prediction of the material's properties degradation as a function of AAR development. [ABSTRACT FROM AUTHOR]

The Damage Rating Index (DRI), a microscopic and semi-quantitative petrographic tool, is a method that has increasingly been used in North America and Europe because it can answer questions regarding the nature and the degree of damage in concrete affected by deleterious mechanisms such as alkali-aggregate reaction (AAR). This paper presents the results of the condition assessment, using the DRI, of concrete mixtures of different strengths and incorporating different reactive aggregate types (fine versus coarse aggregate) with the aim of verifying both how alkali-silica reaction (ASR) develops against its expansion levels and how the DRI could be used to better quantify damage in concrete due to ASR. [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Civil Engineering is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Abstract: In the framework of the development of generation IV nuclear reactors and fusion nuclear reactors, materials with an improved high temperature (≅650°C) mechanical strength are required for specific components. The 9–12%Cr martensitic steels are candidate for these applications. Thermomechanical treatments including normalisation at elevated temperature (1150°C), followed by warm-rolling in metastable austenitic phase and tempering, have been applied on the commercial Grade 91 martensitic steel in order to refine its microstructure and to improve its precipitation state. The temperature of the warm-rolling was set at 600°C, and those of the tempering heat-treatment at 650°C and 700°C thanks to MatCalc software calculations. Microstructural observations proved that the warm-rolling and the following tempering heat-treatment lead to a finer martensitic microstructure pinned with numerous small carbide and nitride particles. The hardness values of thermomechanically treated Grade 91 steel are higher than those of the as-received Grade 91. It is also shown that the yield stress and the ductility of the thermomechanically treated Grade 91 steel are significantly improved compared to the as-received material. Preliminary creep results showed that these thermomechanical treatments improve the creep lifetime by at least a factor 14. [Copyright &y& Elsevier]

An experimental study is conducted to investigate the shear behaviour and strength of concrete beams made with coarse recycled concrete aggregate. The distinguishing feature of the beams is the manner in which their concrete mixture is proportioned. A new method of concrete mixture proportioning is used wherein recycled concrete aggregate is treated as a two-phase material comprising residual mortar and natural aggregate, and the relative amount and properties of each phase are considered. Using this method, several beams are made of recycled concrete aggregate-concrete and tested to study their serviceability and shear strength. For each beam its load-deflection curve, shear deformations, diagonal cracking load, crack pattern, ultimate shear strength, and failure mode are determined. The results show that the shear performance of reinforced recycled concrete aggregate-concrete beams is comparable, or even superior, to that of beams made entirely with natural aggregates at both the serviceability and ultimate limit states, and the current Canadian Standards Association, American Concrete Institute and Eurocode provisions for shear design can be used without any modification to design recycled concrete aggregate-concrete beams, provided the aforementioned mixture proportioning method is used. [ABSTRACT FROM AUTHOR]

Abstract: A model devoted to the prediction of the high temperature creep–fatigue lifetime of modified 9Cr–1Mo martensitic steels is proposed. This model is built on the basis of the physical mechanisms responsible for damage due to the interaction of creep, fatigue and oxidation. These mechanisms were identified thanks to detailed observations previously reported in part I and part II of this study. These observations led to the distinction of two main domains, corresponding to two distinct types of interaction between creep, fatigue and oxidation. As no intergranular creep damage can be observed in the tested loading range, the proposed modelling consists in the prediction of the number of cycles necessary for the initiation and the propagation of transgranular fatigue cracks. Propagation rate measurements under high stress low-cycle fatigue conditions were carried out to calibrate the Tomkins model used to predict the life spent in crack propagation, whereas the initiation stage is predicted using the model proposed by Tanaka and Mura. The predictions obtained compare very favorably with the experimental creep–fatigue lifetimes. Finally the extrapolations and limits of the model are discussed. [Copyright &y& Elsevier]

Copyright of Canadian Journal of Civil Engineering is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Recent works propose the use of a comprehensive management tool for assessing concrete damage due to alkali-silica reaction (ASR) based on a series of mechanical and microscopic laboratory test procedures, mainly the Stiffness Damage Test ( SDT ) and the Damage Rating Index ( DRI ). However, the use of these procedures for assessing other distress mechanisms other than ASR (i.e. delayed ettringite formation-DEF, freezing and thawing-FT, etc.) has never been performed. This paper presents the assessment of concrete mixtures affected by ASR, DEF and FT (single or coupled), through the use of a multi-level approach (microscopic and mechanical), with the aim of generating a comprehensive management guide for evaluating aging infrastructure. The results show that the ASR proposed approach is suitable for analyzing other distress mechanisms. Moreover, qualitative damage models and quantitative charts linking mechanical responses and microscopic distress features are proposed, which enables an easy comparison among the different damage processes. [ABSTRACT FROM AUTHOR]

Abstract: The 2008–2009 work programme of the European research project on nano-structured oxide dispersion strengthened (ODS) reduced activation ferritic (RAF) steels is being organized along the four following programmatic lines: (1) improve the present generation of nano-structured ODS RAF steels; (2) start the industrial fabrication of the present generation of nano-structured ODS RAF steels; (3) develop an optimised generation of nano-structured and nano-grained ODS RAF steels; (4) investigate the stability of present and optimised generation of nano-structured ODS RAF steels under creep and irradiation. This paper presents the main objectives of current R&D activities being performed within the European research project on nano-structured ODS RAF steels, the main obtained results and the main future activities in the case of the four programmatic lines mentioned just above. [Copyright &y& Elsevier]