Author(s):
J.T. Houston, H.R. Blank, G.W. Kunze
Publication Date
November 1969
Abstract
The wide variations found in the properties of synthetic aggregates made from clay-type materials may be due in large part to differences in the degree of thermal transformation of their constituents resulting from processing in rotary kilns.|In order to study this problem, two different clays were processed in a research rotary kiln under different conditions of temperature and retention time. For each material, firing conditions were planned to yield two groups of aggregates, one heavy (more than 55 Ibs. per cu. ft.) and one light (less than 55 Ibs. per cu. ft.).|The raw clays and the resulting aggregates, as well as a commercial synthetic aggregate for comparison, were investigated by X-ray diffraction, differential thermal analysis (DTA), effluent gas analysis (EGA), and gas chromatography (GC). This combination of methods yielded useful information concerning the extent of the transformation of the clay minerals into new crystalline substances, the elimination of impurities (such as organic matter, carbonates, and sulfur compounds), and the gases responsible for bloating. From this information the poorly burned aggregates could be identified.|Retention time as well as temperature was shown to be important in bringing the thermal reactions to completion. The most effective combination of temperature and retention time depends upon the particular raw material. Firing conditions producing a lightweight aggregate do not automatically insure that the aggregate will be chemically and physically sound.|The effects of the degree of thermal transformation on the engineering properties of these aggregates, and on their behavior in concrete, are discussed in Reports 81-8 and 81.10.
Report Number:
81-9
Link(s):
Document/Product
http://tti.tamu.edu/documents/81-9.pdf
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