Chemical and Physical Properties of Cement Paste and Concrete Containing Fly Ash After Hydrothermal Exposure

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Title: Chemical and Physical Properties of Cement Paste and Concrete Containing Fly Ash After Hydrothermal Exposure

Author(s): J. Kropp, J. Seeberger, and H. K. Hilsdorf

Publication: Special Publication

Volume: 91

Issue:

Appears on pages(s): 201-218

Keywords: cement pastes; chemical analysis; concretes; fly ash; hydration; hydrothermal reactions; microcracking; physical properties; porosity; strength.

Date: 2/1/1986

Abstract:
Concrete subjected to elevated temperatures may suffer considerable loss in strength due to the development of microcracks or phase transformations in the matrix. The prevailing mechanism depends on the type of aggregate as well as on the moisture content of concrete. Experiments on different hydrated cement systems showed that under hydrothermal conditions phase transformations in neat cement paste lead to an increase in porosity and reduction in strength. In cement pastes containing fly ash or ground quartz in sufficient amounts, gel-like compounds are formed in pozzolanic reactions during hydrothermal exposure. An increased specific surface area as well as an increase in strength is observed. Concrete exposed to hydrothermal conditions is affected by these phase transformations of the matrix; a loss in strength can be prevented by addition of fly ash or ground quartz. Due to a higher shrinkage of the modified matrix which causes increased microcracking these concretes, however, show a loss in strength when drying during temperature exposure.