Concrete with Fly Ash and Influence of Alkalinity on Strength, Leaching and Freezing and Thawing of Fly Ash Cement Stabilisations

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Title: Concrete with Fly Ash and Influence of Alkalinity on Strength, Leaching and Freezing and Thawing of Fly Ash Cement Stabilisations

Author(s): A. L. A. Fraaij and J. M. Bijen

Publication: Special Publication

Volume: 221

Issue:

Appears on pages(s): 195-216

Keywords: concrete; fly ash; freezing and thawing; leaching; pH; pozzolanic activity; stabilisations; strength

Date: 5/1/2004

Abstract:
The paper deals with fly ash as the by-product from coal-combustion electricity power plants. This type of fly ash (also classified as ASTM class F fly ash) can be utilized as a raw material in cement production, as a filler material in concrete and as a pozzolanic material that can partly replace cement. This paper examines the use of fly ash in concrete and stabilisations. Fly ash cement stabilisation are used in some road projects and compared to fly ash containing concrete the stabilisation contain a large pro-portion of fly ash relative to the amount of cement. The pH of such mixtures is lower than the pH of the pore water in concrete. The pozzolanic reaction of fly ash with lime needs a sufficient supply of pore water and a high pH because at a low pH the glass of the fly ash will not break down at the molecular level, thus cannot dissolve easily. For enhancement of the pozzolanic reaction, mixtures of fly ash and portland cement have been made with a 2% NaOH solution as mixing water. The stabilisations have been tested on strength, leaching and freezing and thawing durability. The strength increases due to the addition of NaOH. The freezing and thawing durability is investigated with the Fagerlund method and also with a simple freezing and thawing test with thawing under water. The freezing and thawing behaviour however is not improved by the addition of the NaOH solution. Also the leaching of heavy metals and SO4 is not diminished by the addition of the NaOH solution. The use of fly ash cement stabilisations should be under the restriction of protection against rainwater and groundwater, which is easily accomplished in the case of bituminous road constructions.