Some Properties of Pozzolanic Cements Containing Fly Ashes

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Title: Some Properties of Pozzolanic Cements Containing Fly Ashes

Author(s): U. Costa and F. Massazza

Publication: Special Publication

Volume: 79

Issue:

Appears on pages(s): 235-254

Keywords: blended cements; calcium hydroxides; compressive strength; fineness; flexural strength; fly ash; heat of hydration; --. portland pozzolan cements; rheological properties; setting (hardening).

Date: 5/1/1983

Abstract:
Properties of pozzolanic cements made by mixing 30% of fly ashes with 70 wt. % of portland cements are studied as a function of fineness. The fineness of the two components ranged between 3260-6940 and 3520-8190 cm2/g (Blaine) respectively. The reaction between fly ash and lime released by clinker silicates becomes apparent after seven days. Combined calcium hydroxide increases with fineness. Replacing 30% clinker + gypsum by fly ash causes a decrease in 1 day-mortar strengths by about 50%. This decrease is recovered in the following days as from 14-28 days the strength of bl ended cements exceeds 70% of that of control cements. Early mechanical strengths of mortars are affected more by the fineness of portland cement than that of fly ash. The opposite occurs for strengths at long ages. Till 7 days fly ash reduces the heat of hydration considerably less than strengths. Yield value and plastic viscosity of cement paste increase when fly ash is ground. The stren gth and h eat of hydration results suggestthatpozzolanic reaction begins before what supposed on the basis of calcium hydroxide conten t of the pastes.