Implications of pre-formed microcracking in relation to the theories of DEF mechanism |
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Authors: | SO Ekolu MDA Thomas |
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Affiliation: | a Department of Civil Engineering, University of Toronto, 35 St. George Str, Toronto, ON, Canada M5S 1A4 b Department of Civil Engineering, University of New Brunswick, P.O. Box 4400, Fredericton, N.B., Canada E3B 5A3 |
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Abstract: | Microcracks were induced in cementitious systems by freeze-thaw action and by alkali-silica reaction. These mechanisms often co-exist with delayed ettringite formation in concretes. Mortars and concretes were subjected to a heat treatment cycle consisting of a pre-set period of 4 h at 23 °C followed by accelerated curing at 95 °C. To isolate the mechanical effects of induced microcracking, heat-cured specimens were subjected to varied prescribed damage induced by freeze-thaw or alkali-silica reaction prior to the onset of delayed ettringite formation. It was found that inducement of pre-formed microcracks led to an earlier onset of expansion due to delayed ettringite formation. Initially, microcracks enhanced ultimate expansion until a certain relatively high extent of microcracking was reached. Thereafter, ultimate expansion decreased with any further increase in microcracking. This report gives support to the paste expansion theory. |
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Keywords: | Delayed ettringite formation Microcracking Steam-curing Alkali-silica reaction Freeze-thaw |
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