In response to ever-increasing market demand for sustainable building solutions, Lafarge North America has recently introduced a new portland-limestone cement (PLC) commercial offering in Canada. Widely used in Europe for over 25 years, PLC is a new category of cement that provides performance similar to conventional portland cement with up to 10 percent less CO2 emissions.
Approved for use by the Canadian Standards Association, the National Building Code of Canada, and the British Columbia, Ontario, and Quebec Building Codes, PLC is produced by inter-grinding portland cement clinker with between 6 percent and 15 percent limestone. Based on a number of trials, considerable testing and Lafarge’s approach to PLC, the new GUL cement with as much as 15 percent limestone—well below the 35 percent limit in Europe—will achieve comparable performance to regular portland cement in terms of concrete workability, set time, durability and all ages of concrete strength development.
According to Daniel Héroux, ing., P.Eng., Lafarge's LEED green associate technical services engineer, cement, feedback from the field indicates little to no change noticed in concrete mix basics like workability, set time or compressive strength. "From a workabiliy standpoint, we've had positive comments that it's 'easier to finish,' most likely a result of PLC being ground to a higher Blaine versus traditional portland cement," he explains.
"The set time was recently tested in lab conditions comparing our GU and GUL—PLC version of GU—products at various temperatures for our time-sensitive Chronolia mixes (at 22°C, 10°C and 5°C). The results were about 4 percent quicker, or 15 minutes earlier, for the GUL mixes at 22°C, and similarly at 10°C and 5°C," he continues. "The compressive strengths were equivalent, with the PLC mixes having a slight advantage with higher strengths at one day and three day. Again, most likely the result of the higher Blaine.
"The additional limestone in a portland-limestone cement has an important quality in that it is interground with the clinker in the final stages versus simply being added at the ready-mixed plant as you might with some SCMs [supplementary cementing materials]. With limestone being comparatively softer than clinker, the results are indicative that the limestone portion ultimately grinds finer than the clinker portion. This results in a better packing density for the final product and can help contribute to strength.”
Because of these performance similarities and the significant sustainability advantages, Lafarge will start the transition from regular portland cement to PLC this year. Customers in British Columbia, Ontario and Quebec are currently being supplied PLC from Lafarge’s plants in Richmond, British Columbia, and Bath, Ontario. Product introduction to other provinces will occur as additional testing and updates to local building codes are completed, which is expected by the end of 2012.
With the potential to bring about a 10 percent reduction in greenhouse gas emissions, the production of PLC at Lafarge’s Richmond and Bath cement operations alone is expected to reduce CO2 emissions by 160,000 metric tons annually, equivalent to taking more than 30,000 cars off the road. In addition, concrete containing combinations of PLC and varying levels of supplementary cementing materials (up to 50 percent) will permit further reductions in the carbon footprint.