Time of Setting Influenced by Inclusion of Fly Ash and Chemical Admixtures


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Title: Time of Setting Influenced by Inclusion of Fly Ash and Chemical Admixtures

Author(s): Tarun R. Naik, Shiw S. Singh, and Bruce W. Ramme

Publication: Special Publication

Volume: 199


Appears on pages(s): 393-414

Keywords: AEA; fly ash; gypsum; HRWRA; paste; retarder; time of setting; water reducer

Date: 6/1/2001

This investigation was performed to establish the effects of pozzolanic and chemical admixtures on setting behavior of cement paste at normal consistency. An ASTM Class C fly ash was used as a pozzolanic and cementitious admixture. Mixtures were proportioned to contain fly ash in the range of O-l 00% by mass of the cementitious materials using a cement replaced by fly ash in a proportion of 1: 1.25. One source of ASTM Type I cement was used. The effects of five admixtures, air-entraining agent (AEA), water reducer, retarder, high-range water-reducer (HRWRA), and hemihydrate gypsum (CaSO,. 1/2H2O) on setting characteristics of pastes, were investigated. Both initial and final setting times remained essentially the same or were slightly delayed up to 20% cement replacement with respect to the 0% fly ash mixture. Beyond this range, the times of setting were generally accelerated. Increased rate of setting occurred at cement replacement levels of 40 % and above irrespective of type of chemical admixtures used.