PLC stands for portland-limestone cement. It’s been developed over decades to help address the sustainability of cement and concrete. As we’re all aware, sustainability has become a hot topic across the globe. Climate change events worldwide make it hard to ignore the need to reduce environmental impacts. One of the most urgent is to develop more efficient operations with lower CO2 and other greenhouse gas (GHG) emissions. To address this issue, manufacturing industries across the world are finding new ways to ‘green’ their operations and shrink their carbon footprints. Many are setting up paths to carbon neutrality.
For its part, cement manufacturers have committed to reaching carbon neutrality by 2050. This is important because cement is the most important ingredient in concrete manufacturing and concrete is everywhere. Concrete is the most used material on the planet (besides water) and its flexibility and versatility allows us to build many of the durable structures, roads, and other infrastructure on which our modern society depends upon.
The Environmental Protection Agency (EPA) estimates cement manufacturing accounts for 1.25% of US carbon emissions. Globally, it is estimated that cement manufacturing accounts for as much as 5 to 8% of worldwide carbon emissions. Given the large amount of cement that is used around the globe, even a small reduction in the CO2 footprint of cement will have a major impact on our overall carbon emissions.
This is where PLC cement comes in - it is engineered with a higher limestone content than our traditional portland cement to reduce the carbon footprint. Traditional portland cement is made up of clinker that is ground to a fine powder with some other minor ingredients to improve the performance of the cement. When we mix the powder with water, it reacts through the cement hydration process to form the glue that holds the concrete together. Portland cement can also contain up to 5% of unfired ground limestone in addition to the clinker. PLC allows the ground limestone to be increased to up to 15%. This reduces the carbon footprint of the concrete by up to another 10%, even more when other cementitious materials like slag cement or fly ash are mixed into concrete.
So, you may ask, if PLC has an additional 10% limestone, how can it work as well as regular portland cement? Good question - the key is that the cement producers optimize the production of PLC so it performs the same as or better than traditional portland cement. Primarily, this involves grinding the PLC to a finer consistency than portland cement and optimizing the chemistry of the finished product. (Fineness is shown on the mill certification as the ‘Blaine’ value, and PLC is on average 100 m2/kg higher than traditional portland cement.) This causes the cement to react faster and more thoroughly which compensates for the lower clinker content. The higher fineness also leads to a more tightly packed mix, even at the cement-sized particles and smaller range. That also helps improve concrete strengths. As I said earlier, cement producers design the PLC to have similar strength gain characteristics as the base portland cement so that PLC is a 1:1 replacement for portland cement. The cement producers have also found that PLC typically allows using the same dosage of fly ash and slag cement as traditional portland cement.
Because PLC is manufactured with the same clinker as the portland cement it replaces, it has similar characteristics such as set time, strength gain profile, workability, and overall color profile that you are used to. In many cases, it will also be slightly lighter in color (due to the lower clinker content and finer grind) so you may notice brighter colors in your pigmented architectural units and it may even allow you to slightly lower your overall pigment content.
While the PLC is designed to be a ‘drop in’ for the portland cement it replaces, it’s always good practice when you change cements to verify its performance in your particular concrete products manufacturing facility. Your ACM Technical Services Team is always available to help you with this process.
In short, there is nothing to fear in moving to PLC cements. They should give you the performance you are used to while helping to reduce the carbon footprint of your concrete products. Also, if you are developing Environmental Product Declarations, EPDs, for your products, shifting to PLC can help you demonstrate a reduced carbon footprint of your products.
While PLC cements are a very important step towards carbon neutrality of concrete, it is not by any means the only step along the path. For more information on PLC cements visit PLC: Greener Cement | Home , and for more information on the roadmap to carbon neutrality of concrete visit Roadmap to Carbon Neutrality (cement.org).
Want to know more about cements? - check out our Concrete 101 Cement Video