Effects of Accelerated Curing Procedures on Nature and Properties of Cement and Cement-Fly Ash Pastes

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Title: Effects of Accelerated Curing Procedures on Nature and Properties of Cement and Cement-Fly Ash Pastes

Author(s): K. Mather

Publication: Special Publication

Volume: 95

Issue:

Appears on pages(s): 155-172

Keywords: accelerated curing; cement pastes; compressive strength; consistency; curing; electron microscopes; fly ash; hydration; portland cements; pozzolans; x-ray diffraction.

Date: 10/1/1986

Abstract:
Bars (25 mm square) of normal-consistency paste made using Type I and Type II portland cements and pastes consisting of 70 percent cement and 30 percent of a Class F fly ash, by solid volume, at the same water-to-solids ratio, were stored under four temperature regimes: the three accelerated curing regimes given in ASTM: C 684 (warm-water, boiling-water, and autogenous) and at 23 + 1.70~. Modified-cube compression tests were made and samples of the paste examined by X-ray diffraction and scanning electron microscopy at the end of accelerated curing and at 3, 7, 28, 91, 180, and 365 days. Coefficients of determination for the regression equations average approximately 0.9 for the warm-water, 0.8 for the boiling-water regimes, and were about 0.6 for the autogenous regime. The boiling-water method affects the nature of the hydration products that are present especially by degrading the crystallinity of the ettringite. The autogenous method does not provide uniform acceleration. It was concluded that the warm-water method was to be preferred. It is now used by the Corps of Engineers. The degradation of the ettringite in the boiling water regime was accompanied by the production of hydrogarnet. The micrographs of one-day old pastes cured by all relevant regimes show very large amounts of empty space in spite of the pastes having water-to-solids ratios of 0.23 and 0.25 by mass.