In 2011, a new category of cement called Portland-limestone cement (PLC) was launched in Canada. PLC has a lower carbon footprint and similar performance characteristics as compared to conventional portland cement. It is now approved for use by the Canadian Standards Association(CSA), the National Building Code of Canada (NBCC) and the Ontario, Quebec and British Columbia Building Codes. PLC has been used in Europe for over 25 years.
What is Portland-Limestone Cement?
While regular portland cement may contain up to 5% limestone, PLC is manufactured by intergrinding portland cement clinker with between 6% and 15% limestone. The clinker used to make PLC is the same clinker used to manufacture regular portland cement. The 15% limestone limit applied to PLC in Canada is well below the maximum limit of 35% permitted in European standards.
The performance of PLC is dependent on the quality of the limestone. Accordingly, limestone used in PLC is tested for calcium carbonate content, clay content and total organic carbon content. PLC performance specifications are similar to those of regular portland cement in that it must meet the same physical requirements.
Lafarge's innovative approach to PLC is to achieve as good or better performance when compared to regular portland cement in the areas of workability, set time, and all ages of strength development. Because of these performance similarities, transitioning from regular portland cement to PLC will be seamless for our customers. Lafarge strongly recommends customers perform standard QC checks, such as slump and air content, before and after any cement change.
PLCs are as susceptible to alkali silica reaction (ASR) as are regular GU and HE cements; therefore, industry-accepted mitigation methods (i.e. alkali level control, use of slag and fly ash) are still required with PLC. Regular GU and HE cements as well as PLC are susceptible to sulphate attack in the absence of appropriate supplementary cementitious materials such as slag and fly ash.
Energy Savings and Reduced Emissions
The introduction of PLC to North America represents a proactive step by both the cement and concrete industries to help mitigate climate change. Manufacturing PLC results in up to 10% less CO2 emissions as compared to manufacturing regular portland cement.
Starting in 2011, Lafarge is transitioning its Canadian customers from regular portland cement to PLC. All Canadian Lafarge GU and HE cements will eventually be affected by this change. HS, MS, masonry and mortar, and well cements are not included in this change.
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