All FAQs

What is the difference between PLC and OPC?


PLC, portland-limestone cement, is a similar product to OPC, ordinary 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, OPC is the most common binder (glue) used to make concrete and PLC is made from the same ingredients as OPC 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 OPC mixes. Mix designs are tested to demonstrate how PLC affects performance, if at all, and proportions may be adjusted during the testing stage. Ready-mix producers have generally found that concrete proportions do not change when PLC is substituted for OPC 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.




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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