عنوان: نقش سنگدانه گرانیتی در تخریب سد بتنی

نویسنده (گان): فرناندز

مجله/کنفرانس: بولتن زمین شناسی مهندسی و محیط زیست - جلد 74

تاریخ انتشار: 2015

صفحات: 12 صفحه (195 تا 206)

فرمت فایل: PDF (زیپ شده)

حجم فایل: 2.96 مگابایت

Role of granitic aggregates in the deterioration of a concrete dam

A concrete dam was built on the early 1970s in the Douro River about 70 km from the estuary in the Atlantic Ocean, at Porto city. According to other studies developed in Portugal and some reports in the literature, granitic aggregates can be potentially reactive in concrete. The study of the concrete was, therefore, focused on the assessment of the deterioration of concrete by alkali-silica reactions and also on the influence of the conditions of exposure on concrete deterioration processes. The site inspection permitted the identification of signs of deterioration in those structural elements of the dam which were more exposed to the environmental conditions, but not on the dam body. Concrete cores were obtained by drilling and petrographic analysis was performed in order to identify possible products resultant from internal reactions. Products of alkali-silica reaction and sulfate attack were detected on thin-sections of the concrete collected from the thinner structural elements exposed to the external environmental conditions. Their qualitative composition was assessed under a scanning electron microscope and by energy dispersive spectrometry. The study confirmed the occurrence of alkali-silica reactions with granitic aggregates in which very scarce microcrystalline silica was identified. The deterioration was influenced by the environmental conditions of exposition.

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عنوان: تشخیص تشکیل تأخیری اترینگایت در سازه های بتنی

نویسنده (گان): مایکل توماس و همکاران

مجله/کنفرانس: مجله تحقیقات سیمان و بتن – جلد 38

تاریخ انتشار: 2008

صفحات: 7 صفحه (841 تا 848)

فرمت فایل: PDF (زیپ شده)

حجم فایل: 1.45 مگابایت

Diagnosing delayed ettringite formation in concrete structures

Abstract

There has been a number of cases involving deteriorated concrete structures in North America where there has been considerable controversy surrounding the respective contributions of alkali–silica reaction (ASR) and delayed ettringite formation (DEF) to the observed damage. The problem arises because the macroscopic symptoms of distress are not unequivocal and microscopical examinations of field samples often reveal evidence of both processes making it difficult to separate the individual contributions. This paper presents the results of an investigation of a number of concrete columns carrying a raised expressway in North America; prior studies had implicated both DEF and ASR as possible causes of deterioration. Although the columns were not deliberately heat-cured, it is estimated that the peak internal temperature would have exceeded 70 °C and perhaps even 80 °C, in some cases. The forensic investigation included scanning electron microscopy with energy-dispersive X-ray analysis and expansion testing of cores extracted from the structure. Small-diameter cores stored in limewater expanded significantly (0.3 to 1.3%) and on the basis of supplementary tests on laboratory-produced concrete specimens it was concluded that expansion under such conditions is caused by DEF as the conditions of the test will not sustain ASR. In at least one column, DEF was diagnosed as the sole contributory cause of damage with no evidence of any contribution from ASR or any other deterioration process. In other cases, both ASR and DEF were observed to have contributed to the apparent damage. Of the columns examined, only concrete containing fly ash appeared to be undamaged. The results of this study confirm that, under certain conditions, the process of DEF (acting in isolation of other processes) can result in significant deterioration of cast-in-place reinforced concrete structures.

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