ASTM Subcommittee C09.24 on Supplementary Cementitious Materials has two ballot items open until May 28, 2017. American Coal Ash Association’s Technical Committee has reviewed both items and prepared recommendations for ACAA members who participate on the ASTM subcommittee.
Is the proposed new “Standard Specification for Natural Pozzolans Used in Cementitious Mixtures.” Currently, fly ash and natural pozzolans are both included in Standard C 618. If this ballot moves forward and is approved by the C09 main committee, then class N (assigned to natural pozzolans) would be removed from C 618 making the specification exclusively for fly ash. The Technical Committee asks members to review the proposed specification to ensure a fair technical comparison with fly ash and other pozzolans.
Is related to a proposed change to C 1697, Specification for Blended Supplementary Cementitious Materials, that would include ground calcium carbonate in the pool of materials that can be blended under this specification. Several researchers have attributed benefits, such as higher early strengths, to ground calcium carbonate in concrete. For this reason, ground calcium carbonate is currently allowed to be inter-ground with portland cement clinker to produce portland-limestone cement that may contain up to 15 percent calcium carbonate. Ground calcium carbonate meeting ASTM C 1797 – Standard Specification for Ground Calcium Carbonate and Aggregate Mineral Fillers for use in Hydraulic Cement Concrete – can also be specified for use in concrete (not as a part of portland-limestone cement.) Thus, a natural progression would be to allow the material to be blended with supplementary cementitious materials, which would be another way to include ground calcium carbonate in concrete. While the change makes sense, the challenge is integrating the other subcommittee initiative of allowing the blending of off-spec materials. Since at this point the language of the two potential changes hasn’t been harmonised, the Technical Committee recommends abstaining on this ballot.