Status of ASTM and Other National Standards for the Use of Fly Ash Pozzolans in Concrete
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STATUS OF ASTM AND OTHER NATIONAL STANDARDS FOR THE USE OF FLY ASH POZZOLANS IN CONCRETE RICHARD M. MAJKO American Fly Ash Company, 606 Potter Road, Des Plaines, IL Received 9 November,
60016
1986; refereed
ABSTRACT The Subcommittee of ASTM that is responsible for pozzolan specifications, (C09.03.10) is currently revising C 618, the standard specification, and C 311, the standard test methods. It is no small task. It is generally considered that dividing fly ashes into two classifications (Class F and Class C) is no longer acceptable. The Subcommittee has reached the tentative conclusion that one class of fly ash pozzolan is more appropriate and less ambiguous, provided it is accompanied by an optional table outlining the appropriate limits for sulfate resistance, heat of hydration, hydraulic properties, etc. That is, the engineer need specify only a fly ash pozzolan. If the engineer needs more than a "general purpose" fly ash he calls for special characteristics from the optional requirement table. Any major revision in the C 618 specification challenges the Subcommittee to look for better and more useful test methods in C 311. The committee is looking at C 1012 for a sulfate resistance procedure, conduction calorimetry as a heat of hydration method, and better methods to evaluate pozzolanic activity. The committee is aware of the limited usefulness of hydrated lime or sodium hydroxide in evaluating pozzolanic activity. Perhaps a more suitable term, i.e. the activity index with cement, is more appropriate. Fly ash properties that need to be evaluated include water reduction, activation by lime and alkalies, hydraulic or self-cementing properties and pozzolanic activity. Any test that tends to compensate for0 a fly ash's lower reactivity (i.e., accelerated thermal curing at 350C or 65 C) probably leads to misleading results. A critical look at the national standards of other countries might allow the committee to take a visionary yet practical approach toward a new fly ash specification. INTRODUCTION The classification of fly ash into two classes of mineral admixtures as is done by ASTM C 618 may no longer be useful or appropriate. The French use the term silico-aluminous (much like Class F), Silico-calcic (much like an intermediate grade Class F/C), and sulfo-calcic (like Class C), to classify fly ashes [1]. Some fly ashes appear to be strictly pozzolanic; that is, they react slowly over time with lime and alkalis. Other ashes are very hydraulic and rather quickly form calcium aluminate hydrate and ettringite. Another (intermediate) class, is weakly hydraulic forming ettringite, calcium aluminate, and hydrated gehlenite [1]. It does not appear useful to classify fly ashes by their hydraulic properties. For example, in the 1960's (before there was a Class C fly ash designation), the American Fly Ash Company sold a hydraulic Class F fly ash produced from Southern Illinois bituminous coal. It was not particularly pozzolanic (high iron content and a coarse size distribution) yet it set up rapidly. With every passin
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