Guide to Diagnosis and Appraisal of AAR Damage to Concrete in Structures

راهنمای تشخیص وارزیابی AAR آسیب به بتن در سازه ها

Diagnosis of damage to concrete in structures caused by Alkali-Aggregate Reaction (AAR) often involves complex processes because of the resemblance of the external characteristics of the damage with those caused by other actions, such as e.g. frost attack or shrinkage. The wide variety of aggregate types used in concrete worldwide, the different reactivity and proportions of the reactive constituents in the aggregates involved and the wide range factors that influence the reaction result in wide variability found in site samples. This makes diagnosis difficult and has sometimes led to subjective or even erroneous  interpretations and conclusions Furthermore, there has frequently been a lack of agreement amongst experts on how to approach the issues of diagnosis and prognosis of AAR damage in structures. The reasons for the differences in opinion include: The wide range and often inconclusive methods used for performing the assessment. The limited number of reliable internationally applicable standard procedures or methodologies for performing the diagnosis and prognosis.
. The inherent variability of aggregate sources and of concrete which make AAR diagnosis from limited sampling dependant on the local composition of
samples selected. The not uncommon occurrences of localised patches of AAR cracking in site concretes, which leads to diagnosis of AAR as a problem, even though the magnitude of the reaction is not sufficient to produce significant problems of serviceability or structural function. . The assessment that is often carried out from core samples without reference to the structure itself. Difficulties in simulating the long term AAR damage in a structure with short term laboratory tests and the translation of the test results to the actual structures. Several national laboratories, private companies and even individuals using
their own procedures, which are very often ‘tailored’ to solve only specific local types of AAR damage, thus limiting their flexibility in use. Over the past few decades, experts in several countries with AAR problems have pooled their resources and expertise to prepare national guidance documents for assessing damage of concrete caused by AAR. The current document presents an international procedure for the diagnosis of AAR damage to concrete in structures. The guidance outlined in this document is based on experiences, recommendations or national guidance of several countries throughout the world where the AAR
problem is well understood and documented [1-10]. Experience in Austria, Australia, Belgium, Canada, Czech Republic, China, Denmark, France, Iceland,
Japan, The Netherlands, New Zealand, Norway, United Kingdom, United States of America and several other countries has been documented in the proceedings of the thirteen ICAAR (International Conferences on AAR) since 1974 in Denmark (see Appendix 1). Like many other causes of damage in concrete, diagnosis and prognosis of AAR in structures relies to a large extent on the judgement and the level of expertise of the personnel involved. A reliable analysis to identify, evaluate and establish the extent of the damage and to make prognosis of its effect on the structure requires a clear and thorough understanding of the mechanisms and processes of damage resulting from AAR. To do so, the effects of AAR need to be considered as part of a complex of structural and ‘non-structural’ actions and deterioration which lead to cracking and damage in the concrete. Complete diagnosis of distress caused by ASR usually involves a series of steps involving multi-disciplinary tests and investigations, performed in a systematic manner. Figure 1 shows an outline flowchart of these interactions relative to the main diagnostic procedures; the complete flowchart showing the place of the diagnosis within an overall investigation and making the links between AAR-6.1 and AAR- 6.2, is presented in appendix 2.

راهنمای تشخیص وارزیابی AAR آسیب به بتن در سازه ها

راهنمای تشخیص وارزیابی AAR آسیب به بتن در سازه ها

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