(Just in case you need to get up to speed)
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), also known as Type 1L cement, is a blended cement with a higher limestone content, which results in a product that is produced to work the same, measure the same, and perform the same, but with a reduction in its carbon dioxide (CO2) 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 or CO2 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 one being that it reduces the embodied CO2 of the cement.
Modifying a concrete mix design to replace higher CO2 emission materials with lower ones is an effective strategy to reduce its environmental footprint as long as the performance of the concrete is not compromised. 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 1L). 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 mainstream supplementary cementing (or cementitious) 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.
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 it benefits everyone on the planet. For instance, if all cement used in the U.S. in 2019 had been converted to PLC (Type 1L), 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.