Q. We are in the preliminary stages of bidding on what designers hope to be a Leadership in Energy and Environmental Design (LEED) structure. We are considering developing a “green” concrete mix design using blended cements. In our research, we discovered there have been recent changes to the ASTM standards for blended cements.
What were these changes?
A. Interest in blended cement products has been increasing, with many producers finding these premixed cements useful in customizing mix designs. Experts define blended cements as “portland-based cements that include supplementary cementitious materials (SCMs), such as ground granulated blast furnace slag, fly ash, or other pozzolans, such as silica fume or meta-kaolin.” Delivered as a premixed blend, producers need to only use one silo in their plant.
Recognizing this increased use, ASTM C 595-06, Standard Specification for Blended Cements, was released in August 2006 with some important changes to nomenclature. The committee responsible for the specification simplified the document, hoping to make it easier to use. The committee also wanted to eliminate a problem with producing cements near the boundaries.
For example, under the previous standard, the old Type IP cement contained between 15% and 40% pozzolan, while a Type I(PM) cement contained between 0% and 15% pozzolan. These definitions made it almost impossible for a manufacturer to produce a blended cement with about 15% fly ash, since as with normal process variation, it would sometimes be classified as a Type IP and sometimes a Type I(PM).
To solve this, the new standard eliminates both classification types. They were replaced by Type IP(X) classification, where the X stands for the nominal percentage of the SCM included in the blended cement. For example, a cement designated as Type IP(20) contains 20% pozzolan by mass.
This change will facilitate communication between the cement suppliers, producers, and engineers for quantifying the amounts of SCM in concrete mixes. It will help producers when considering adding SCMs on projects where the mix may be subject to restrictions on the total amount of SCMs in the concrete.
Here is a summary of the changes found in the new document:Type I(PM), I(SM), I(PM)-A, I(SM)-A, and S were eliminated.New portland-pozzolan cement, Type IP(X), can include between 0% and 40% pozzolans, replacing old Types IP and I(PM).New portland blast furnace slag cement, Type IS(X), can include between 0% and 95% ground granulated blast furnace slag, replacing the old Types IS, I(SM), and S.The letter X stands for the nominal percentage of the SCM included in the blended cements.
This topic was recently covered in the December 2006 edition of Concrete Technology, published by the Portland Cement Association (PCA) and is the source of some of the information contained in our reply.
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