Alkali–Aggregate Reaction in Concrete: A World Review

کتاب واکنش قلیایی سنگدانه در بتن: یک مرور در اطلس جهان

Several varieties of concrete were used as construction materials by the Romans. The development of concrete based on hydraulic cement similar to that used at the present time dates from the 19th Century. Since then a great number of technological improvements have occurred, extending the varieties of cements and hence concretes available today. In one form or another, concrete has become an essential and ubiquitous constructional material across the modern world. Along with the technological refinements, a basic scientific understanding of the nature of this material has been developed, including the realisation that certain problems can and do occur, some of which can lead to its premature deterioration and failure. One such problem arises from an injudicious selection of aggregate and cement types when designing and mixing the concrete.

Although the concrete may initially meet all the required specifications of strength development and quality, after several years of service, it has been found that a few concretes begin to expand and crack, necessitating expensive remedial work or replacement. The particular problem involved is referred to as Alkali-Aggregate Reaction (AAR) and constitutes the subject of the present volume. This book updates and replaces the first edition entitled ‘The Alkali-Silica Reaction in Concrete’ (Editor: R.N. Swamy, 1992) and offers a greatly extended world coverage of AAR, including a global review of the problem and some of the possible solutions currently available.

AAR in concrete was first observed and identified in North America during the late 1930s and the first comprehensive scientific investigations describing the reaction and its effects were published by Stanton in December, 1940. Stanton investigated a number of occurrences of expansion and cracking leading to failures in concrete pavements in California, and found that the problem developed only when certain types of mineral components were present in the aggregates, and only when cement alkalis exceeded some minimum threshold percentage concentration. The reaction between the aggregate and the alkali gave rise to the name “alkali-aggregate reaction”. His findings encompassed a great deal of detailed information regarding the nature and practical significance of the reactions taking place, and included early versions of test methods that later became standards, and of methods of preventing or at least mitigating the results of the reactions.

In a recent appreciation, Thomas (2011) suggested that the impact of Stanton’s findings could not be overstated. Prior to his publication, aggregate was considered to be an inert filler, but afterwards it was realized that some aggregates were not suitable for use in concrete without taking special precautionary measures. Of course, Stanton’s findings that cement alkalis could influence the durability of concrete caused great concern for the cement manufacturing companies and perhaps the most disturbing implication of Stanton’s study was that concrete could “fail… even if it is exposed to only normal curing and weathering conditions”. Since this early work a tremendous volume of research into causes, effects, avoidance and possible solutions to the problem of AAR in concrete has been undertaken.

This work has been driven in part by the major costs involved in making good the damage AAR can cause, but also by the world-wide extent of the problem, AAR being found to occur in so many countries (see Figure 1.1). Despite the fact that the actual occurrence of damaging AAR in concrete structures is relatively rare and seemingly spasmodic, the repair or replacement of affected structures involves a major expense for their owners. Most of the research into this problem has taken place since the Second World War, giving rise to an extensive technical literature numbering several thousand research papers and technical reports. An important source of information concerning this work has been in the form of the proceedings of a series of International Conferences on AAR (‘ICAARs’). The first of these was held in Copenhagen in 1974 and the 15th was held in Sao Paolo, Brazil in 2016. In addition, numerous national specifications and guidance documents for avoiding AAR have been published and will be referred to in late chapters of his book.

کتاب واکنش قلیایی سنگدانه در بتن: یک مرور در اطلس جهان

کتاب واکنش قلیایی سنگدانه در بتن: یک مرور در اطلس جهان

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