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All FAQs

  • What is the difference between PLC and traditional portland cement?
    PLC, portland-limestone cement, is a similar product to traditional portland cement. Both materials are based on clinker, which is produced by firing a specific combination of inorganic ingredients like rock and clay in a large kiln. Clinker is ground into a fine powder and blended with gypsum to make portland cement. Limestone can also be added to the cement to make the finished product. Portland cement can contain up to 5% ground limestone, whereas portland-limestone cement can contain from 5% to 15% ground limestone with the clinker. In the US, portland cement is the most common binder (glue) used to make concrete and PLC is made from the same ingredients as portland cement in slightly different proportions.
  • Is PLC specified as a Type IL or a Type GUL?
    That depends where you are. The US standard for blended cement is ASTM C595, which designates “portland-limestone cement” as Type IL (identical requirements are found in AASHTO M 240). In Canada, there is a different standard for cementitious materials for use in concrete, CSA A3001, which designates “general use limestone cement” as Type GUL, and also designates a blended cement version of it as Type GULb.
  • Is the handling and placing of PLC concrete different than “regular” concrete?
    No, mixes made with PLC are handled in the same way as traditional portland cement mixes. Mix designs are tested to demonstrate how PLC affects performance, and proportions may be adjusted during the testing stage. Ready-mix producers have generally found they do not need to change concrete proportions when PLC is substituted for traditional portland cement at a 1:1 replacement level. Fresh and hardened properties of concrete are similar whether the binder is portland cement or portland-limestone cement.
  • Should architects change their plans when using PLC?
    No. The only change an architect needs to consider when allowing PLC is to include it in their project specifications (if they don’t already have provisions for it).
  • How long has ground limestone been used in cement?
    Known additions of ground limestone to cement go back decades in Europe: the 1960s in Germany, the 1970s in France, and the 1990s in the UK. Canada began allowing small amounts of limestone additions as far back as 1983. The U.S. standard for portland cement (ASTM C150) allowed small amounts of limestone additions starting in 2004, and that is still the case today. The term “portland-limestone cement” is not an absolute, as different countries apply or allow different limits for limestone content via the cement standards that they use.
  • Why do mill test reports for PLC (Type IL), and other blended cements that meet ASTM C595 or AASHTO M 240, not report potential Bogue phase compositions (C3S, C2S, C3A, and C4AF) as are reported for ASTM C150 and AASHTO M 85 portland cements?
    The primary utility of reporting Bogue phase compositions was to establish performance of a portland cement for characteristics like sulfate resistance or heat of hydration. Assumptions inherent in the Bogue equations make the calculations irrelevant and inaccurate for blended cements, whose performance is characterized by other tests. For more information, see IS791.
  • What does that acronym stand for?
    Many industry groups are mentioned on this site, as are abbreviations for some technical terms. Here is a list of acronyms along with what each one stands for: AASHTO – American Association of State Highway and Transportation Officials ACI – American Concrete Institute ACPA – American Concrete Pavement Association AIA – American Institute of Architects ASTM International – formerly, American Society for Testing and Materials CAC – Cement Association of Canada CSA – Canadian Standards Association DOT – Department of Transportation, usually associated with each state. For example, Colorado DOT MIT CSHub – Massachusetts Institute of Technology Concrete Sustainability Hub NCMA – National Concrete Masonry Association NRMCA – National Ready Mixed Concrete Association OPC – ordinary portland cement PCA – Portland Cement Association PCI – Precast/Prestressed Concrete Institute PLC – portland-limestone cement
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