Portland-Limestone Cement and Sustainability
Portland cement manufacturers have developed a modified formulation of their most important product to respond to growing calls for reducing embodied carbon associated with construction. Portland-limestone cement (PLC) is a blended cement with a higher limestone content, which results in a product that works the same, measures the same, and performs the same, but with a reduction in carbon footprint of 10% on average.
Sustainability encompasses many aspects designed to improve construction practices, including: more efficient use of natural resources, better thermal performance of structures, and reduced environmental impacts, with a focus on embodied carbon. One area of growing concern to environmental leaders is CO2 emissions. Like all building materials, portland cement has an environmental footprint, and it’s often described in terms of greenhouse gas (GHG) equivalents. Cement is made by grinding clinker—the main energy intensive ingredient—to a fine powder. Producers know that replacing some of the clinker in portland cement with ground limestone offers benefits, the most important being that it reduces the embodied CO2 of the cement.
Modifying a concrete mix design to replace higher carbon materials with lower carbon ingredients is an effective strategy to reduce its environmental footprint. Whereas the U.S. standard for portland cement allows for up to 5% of clinker to be replaced by limestone, the standard for blended cement allows for 5% to 15% limestone replacement in PLC (Type IL). The same clinker is used to make portland cement and portland-limestone cement, but there is less of it in PLC. And concrete mixes designed with PLCs are compatible with all supplementary cementing materials (SCMs), so when you substitute PLC for ordinary portland cement, you can continue to use all the other materials you use to make concrete for an even greater reduction in carbon footprint.
Other than water, concrete is the most-used material on the planet, representing about 50% of all manmade materials by mass. Because society places so much concrete each year, even small changes to its formulation can have dramatic effects on the construction industry’s annual carbon footprint—and benefits everyone on the planet. For instance, if all cement used in the U.S. in 2019 had been converted to PLC (Type IL), it would have reduced CO2 emissions by 8.1 million metric tons, which the U.S. EPA says is the equivalent of taking 1.75 million cars off the road for an entire year.
As a key part of the construction industry, cement manufacturers have already made major contributions to help address global climate change. They recognize that they can play a big role and continue to innovate for better binders with even more favorable environmental performance. PLC is extensively tested, proven technology, readily available through the same supply chain that already successfully serves developers, builders, and contractors. It offers the design community a new way to think about concrete while still offering the resilience and sustainability they’ve come to expect from it.
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