Autoclaved Cement-Based Products Containing Fly Ash


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Title: Autoclaved Cement-Based Products Containing Fly Ash

Author(s): Thorkild Bach

Publication: Special Publication

Volume: 91


Appears on pages(s): 291-312

Keywords: autoclaved products; autoclaving; fly ash; gypsum; hemihydrate; plasticizers; Portland cements; silica; strength.

Date: 2/1/1986

The use of autoclaving processes in producing cement-based products is well established. The main reason for using autoclaving processes is often to increase production rate and/or to decrease sensitivity towards variations in humidity, such as reducing moisture movements. The latter effect is mainly believed to be caused by an improved crystallinity of the finished material. The use of fly ash as the siliceous component in the base mixture is also well known. However, the crystallinity is ignored by the use of a noncrystalline base material, such as fly ash. From productions of autoclaved cement-based products utilizing silica sand it is known, that additions of small amounts of gypsum to the base mixture may improve strength and reduce moisture move-ments. This paper deals with the production of autoclaved materials utilizing fly ash and gypsum or its derivatives. Materials produced are characterized according to their density and strength-characteristics as well as to their crystallinity. The use of gypsum or its derivatives may cause significant improvements in strength as well as in crystallinity, but the op-timum design is closely related to the actual production process as well as to the chemical properties of the base materials and to the physical properties of the fly ash.