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An Even Closer Look at Portland Cement
Editor’s note: In response to feedback from the Portland Cement Association, notes have been added to the digital version of “A Close Look at Portland Cement” to clarify that, after fabrication, most of the silica in portland cement may be amorphous silica, not crystalline.

Recently, The Synergist published “A Close Look at Portland Cement: Respirable Crystalline Silica and Other Hazards of a Familiar Substance" by Veronica Stanley (February issue). The Portland Cement Association’s Occupational Health and Safety Committee, including Certified Industrial Hygienists, reviewed the article with concern. 
The article contains factual inaccuracies and misleading claims, and reflects an incomplete understanding of portland cement’s physical composition, its widespread and safe use in commerce, and the extensive measures taken by cement manufacturers and downstream users to minimize hazards in the workplace.  Most notably, the article states that “after fabrication, portland cement may have about 25 percent silica-containing material.” This attempt to link the term “silica-containing material” to the presence of crystalline silica is misleading. Portland cement production chemically transforms any silica-containing materials at temperatures in excess of 1450°C to calcium silicates—a separate class of compounds with completely different physical, chemical, and hazard characteristics. Indeed, as acknowledged later in the article, NIOSH defines portland cement as containing less than 1 percent crystalline silica, contradicting the article’s assertion. ASTM standards, in turn, limit the presence of insoluble residues, including crystalline silica, to no more than 1.5 percent. In practice, typical levels of crystalline silica fall below 0.2 percent.  The article correctly identifies that OSHA specifically excluded portland cement from the hexavalent chromium standard, determining that whatever traces of this metal might be found in some portland cement, workers would not be exposed to levels approaching the final rule’s permissible exposure limit. The article failed to note, however, that the rule’s preamble also addressed concerns with dermal exposure to portland cement by workers who might be allergic to hexavalent chromium, finding that the personal protective equipment already recommended for those working with wet cement and wet concrete would also protect those allergic to hexavalent chromium.  In a similar vein, the article suggests the presence of “other heavy metals of concern” and that concentrations of such metals vary geographically and with adjustments “to produce colors.” While it is true that any mineral mined from the ground may have varying compositions by area or region, it is incorrect to create the inference that portland cement contains these metals at harmful levels. Also, adjustments are not made during the cement manufacturing process to produce colors; portland cement as manufactured is either naturally gray or white in color. In addition, the article notes that “at least 22 different solid phases of portland cement have been identified, some of which are not stable.” While the existence of 22 different solid phases may be true, the “stability” of those phases is totally unrelated to health and safety issues, and any suggestion to the contrary is misleading at best. We appreciate the ability to respond to this article and to address some of our concerns. The cement industry is deeply committed to ensuring both workplace and product safety and is working collectively to monitor and address potential hazards associated with its products and to develop and maintain robust data supporting its efforts. PCA and its member companies are prepared to help OEHS professionals, researchers, and the public have an accurate understanding of our materials, products, and hazards. Stephen J. Robuck Sr. Director, Government Affairs Portland Cement Association