BYU is working with several institutions to modify existing standards for use of fly ash in concrete production. This quarter we summarized the current state of the relevant ASTM standard and proposed modifications. This summary appears below. We are also working with institutions in Europe and with ISO committees on similar issues.
The current ASTM standard describing specifications for fly ash used in concrete production is C618, which was most recently modified in 1999. The complete specification and title of the standard is "C618-99 Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Concrete."
The currently defined scope of the standard is as follows: "This specification covers coal fly ash and raw or calcined natural pozzolan for use as a mineral admixture in concrete where cementitious or pozzolanic action, or both, is desired, or where other properties normally attributed to finely divided mineral admixtures may be desired, or where both objectives are to be achieved."
This standard is under the jurisdiction of ASTM Committee C09 on Concrete and Concrete Aggregates, Subcommittee C09.24 for Ground Slag and Pozzolanic Admixtures. The Subcommittee Chairman is Scott Schlorholtz, Iowa State (515/294-8761; e-mail:firstname.lastname@example.org). A technical contact for the subcommittee is Jenny Hitch, ISG Resources Inc., (702) 228-5085 email: email@example.com. The specific issues associated with slag and pozzolanic materials as they relate to alkali-silica reactions are being investigated by C09.24 and C09.26, the latter being the Subcommittee on Chemical Reactions. People interested in this may contact Joint Task Group Chairman Michael Thomas, University of Toronto (416/978-6238; e-mail: firstname.lastname@example.org), Subcommittee C09.26 Chairman Leslie Struble, University of Illinois (217/333-2544; e-mail: email@example.com), or Scott Schlorholtz. However, the issues of most direct concern to the biomass-coal cofiring community are being handled within C09.24 and are summarized here.
The general issue is that C618, within strict interpretation, pertains only to fly ash derived from coal. Cofiring generally results in mingling coal and biomass fly ash, resulting in fly ash that can not strictly comply with the standard. There are many other processes that result in the same problem that have nothing to do with cofiring (ammonia injection, SO3 injection for improved precipitator performance, carry over from sulfur scrubbers, calcite-derived material from calcite injection for sulfur control, etc.). The subcommittee for Ground Slag and Pozzolanic Admixtures (C09.24) is actively investigating all of these issues and is striving to modify C618 to accommodate the whole range of activities.
The subcommittee last met in New Orleans, LA, December 6-8, 1999. A new, more comprehensive standard had been proposed but was not accepted, and the bulk of the discussion centered on strategic approaches to the modifications rather than the modifications themselves. A primary objection to the new standard was that the existing C618 should be revised rather than creating a new standard. No consensus was reached during this discussion. Subcommittee C0924 is currently pursuing two parallel paths, one that involves development of a new standard and one that involves revisions of the current standard. These are being drafted now and will be balloted (by mail) between now and the next meeting of the subcommittee (June 19-21).
International and other regional standards feature the same limitations and are also being readdressed. We are cooperating with CEN and ISO to coordinate the US domestic and international revisions. However, none of these standards are likely be be modified and accepted soon, although there is mounting evidence that fly ashes from wood-derived biomasses have no deleterious effects on concrete. Fly ashes from cultivated or herbaceous biomass are generally less appropriate for concrete applications.