Similarities and Differences in Shale, Aggregate Mixes and Concrete Containing Fly Ash
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SIMILARITIES AND DIFFERENCES IN SHALE, AGGREGATE MIXES AND CONCRETE CONTAINING FLY ASH PETROS E. ZENIERISa and JOAKIM G. LAGUROSb a. Standard Testing and Engineering Company, Oklahoma City, Oklahoma 73105 b. School of Civil Engineering and Environmental Science, The University of Oklahoma, Norman, Oklahoma 73019, U.S.A.
Received 28 October, 1988; refereed ABSTRACT Fly ash technology has been very effective in providing stability in roadway base courses composed either of shale or aggregate materials, and also in partly replacing Portland cement in concrete. X-ray diffractometry and scanning electron microscopy observations indicate that there are certain similarities among these three types of mixes concerning the hydration process; on the other hand, there is evidence of distinct differences in the hydration products which are found to act either as a filler, a chemical agent, or both. Fly ash suppresses the intensity of the clay minerals in shale, speeds up the hydration process in concrete and acts partly as a filler in aggregate mixes. The net practical result is strength development which varies not only in terms of the maximum level attained, but also in regard to its rate. The conversion of ettringite to monosulfoaluminate proceeds at a rate which is considered high in concrete, moderate in aggregate mixes, and moderate to low in shale. X-ray diffraction analyses help to identify other dissimilarities in the minerals produced. The modification which takes place in the fabric and the matrix of the mixes is morphologically the same; in contrast, the growth of crystallites at the "particle"/fly ash interface is explicitly different. Preliminary quantification of matrix changes resulting from new hydration products is also explored.
INTRODUCTION The state of Oklahoma has an abundant supply of high quality Class C fly ash. The research relative to its utilization has been focused on its ability to stabilize expansive Oklahoma clays derived from shales, to replace cement in concrete and to cement/strengthen aggregate road bases. The present comparative study is primarily based on the findings of four research projects undertaken by the University of Oklahoma and sponsored by the Oklahoma Department of Transport (ODOT) and FHWA. Two projects dealt with the effects of fly ash stabilization of shales, covering the range of pre- to post-construction phases of laboratory and field evaluation [1-3]. A third project [4] was devoted to the study of the reaction products of fly ash concrete, while the fourth and most recent project dealt with the feasibility of using fly ash as a binder in coarse and fine aggregate mixes [5,61. The common evaluator of the four studies was the use of X-ray diffractometry (XRD) and scanning electron microscopy (SEM) to identify reaction products and study their morphology.
FLY ASH The fly ashes used in the studies were collected from various plants within the state. Little variation was observed between their physical and chemical properties (Table I), and all of them were classified as C
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