Posted on December 18, 2020
There's a new initiative to promote Portland-limestone cement (PLC). The PCA initiative includes the launching of a new microsite, GreenerCement.com. It includes a convenient CO2 calculator. Enter a building size or pavement length to calculate PLC’s impact on a project’s carbon footprint.
Ton for ton, PLC mixtures perform much like ordinary Portland cement (OPC). Tests show that strength, durability and resilience are comparable. What is different is the 10 percent reduction in carbon emissions. The use of SCMs like fly ash or slag reduces a project’s carbon footprint even further.
Calcination accounts for approximately 60 percent of all carbon emissions in cement production. It generates more than 525 kg of CO2 per ton of clinker. Therefore, using less clinker is key to more sustainable concrete. Type IL cements do just that. Portland cement is about 91 percent clinker, while PLC is just 83 percent clinker. Limestone content is up to five percent in ordinary Portland cement (OPC), but as high as 15 percent in PLC.
PLC blends appear in residential, commercial and government projects. Specifiers list PLC concrete for bridges, pavements and a wide variety of structures. Schools, hotels, parking garages are some examples. In 2007, Colorado became the first state to allow the use of PLC concrete for paving. By 2018, there were more than 900 lane miles of PLC paving in Colorado, Utah and Oklahoma combined. Now, thirty state transportation departments permit the use of these blended limestone mixes.
Progress in the Acceptance of PLC
European producers embraced Portland-limestone cement (PLC) decades ago. In the mid-1960s, German producers experimented with PLC for certain specialty applications. They experimented with mixtures including up to 20 percent limestone. By 1990, blended limestone cements were widely used in Germany. In 1992, the United Kingdom followed suit. It allowed up to 20 percent limestone in PLC formulations.
Less than a decade later, 2000 EN 197-1 created CEM II/A-L for blended cements with 6-20 percent limestone. CEM II/B-L is for blends with 21-35 percent limestone. 2008 CSA A3001 included cements containing 5-15 percent limestone. Finally, in 2012, ASTM C595/AASHTO M 240 allowed for Type IL cements with 5-15 percent limestone.
Performance and Reduced Carbon Footprint
How is it possible to add this much limestone to a cement blend without compromising performance? Both physical properties and chemical reactions enhance performance. Limestone grinds finer than the clinker it replaces. This promotes denser particle packing and more even particle distribution,increasing nucleation.
The use of finely milled limestone particles introduces another small, yet positive advantage. It provides more surfaces on which cement hydrates may form. This frees up the clinker grains for extra hydration.
The Market for PLC
In the United States, PLC production is increasing. From 2012 to 2016, producers delivered 2 million tons of PLC. More specifically, Type IL cement production reached 348,000 metric tons in 2013. In 2016, plants produced 890,000 metric tons, an increase of 155 percent in the span of four years.
Intensified pursuit of sustainability goals will further increase demand. The Portland Limestone Cements Market Report forecasts significant market expansion through 2025.
Testing Confirms PLC Performance
One study compared three kinds of PLC. One contained no SCMs. Another consisted of 35 percent slag. The third contained 20 percent fly ash. With all three, compressive strength was actually higher at one, seven and 28 days. At 56 days, the compressive strength of the 20 percent fly ash mix was less. It was still higher in the other two mixes.
A 2009 study demonstrates the long-term performance of PLC pavements. Crews paved the plant yard at a ready-mixed concrete plant with four different mixes. There were Type I and Type IL mixes without SCMs. Crews also placed Type I and Type IL mixes with 25 percent slag.
Another test conducted in Sarnia, ON, relates to the transportation sector. Crews used Type I and Type IL concretes with 25 percent slag to build slip-formed barrier walls. The University of Toronto and third-party labs conducted a battery of tests. The PLC blend performed well, time and again. It demonstrated appropriate compressive strength, flexural strength, linear shrinkage and freeze/thaw durability. It also resisted scaling, a product of the use of deicing chemicals.
Portland-limestone cement has proven viable in a variety of sports-related projects.
Tim Hortons Field - Hamilton, ON
Tim Hortons Field achieved LEED Silver status, in part because of the PLC concrete used. The 23,218-seat stadium replaced Ivor Wynn Field in 2014. It is home to the CFL’s Hamilton Tiger-Cats. It also hosted the 2015 Pan Am Games in soccer. Approximately 14,000 cubic yards of PLC concrete delivered strengths to 5000 psi.
Renovation of Davis Wade Stadium - Starkville, MS
The renovation of Davis Wade Stadium, home of the Mississippi State Bulldogs, is another case. The project included the use of 2400 cubic yards of PLC concrete. Seating increased from 55,000 to more than 61,000. The renovation also provided for premium seating options and social gathering places.
Mattamy National Cycling Centre - Milton, ON
The Mattamy National Cycling Centre is a world-class velodrome. It features a Siberian spruce wood cycling oval suitable for international competition. The $63 million (CAD) facility opened in 2014. The multi-use facility includes an indoor walking/running track. It also features an infield suitable for volleyball, basketball and trade shows. Contractors used 17,000 cubic yards of PLC concrete in the construction of the 139,000 sq-ft facility.
Register for the Webinar
Interested in improved sustainability with PLC? Check with your cement supplier for availability and specific properties. Register for our Portland-Limestone Cement Webinar here.
Please contact PACA if you have any questions or further requests.