Lately there’s been an issue on the minds of plasterers and the NPC.
As industries look to become more environmentally friendly — and regulators demand it — cement producers have taken notice and looked for ways to reduce their carbon footprint. The solution: Slightly increasing the proportions of limestone in their product.
The production of cement begins with the creation of clinker, which involves melting rock and other minerals in a kiln. These components include limestone. The hard clinker, which forms in lumps, will be ground to create a powder that is mixed with other components to create cement. In addition to the limestone that comes in the clinker, unfired (or uncalcined) limestone is added to the ground clinker.
Reaching the high temperatures needed to melt the minerals takes considerable fossil fuel consumption. In addition, heating the limestone causes a chemical bond to break, releasing carbon dioxide into the atmosphere.
To make the material more environmentally friendly, the cement industry opted to begin adding up to 15% unfired limestone to the mix, rather than the traditional 5%.
“Because we’re not having to burn up to 10% more limestone, we are saving on the fossil fuels that generally are used to burn the rock and other ingredients in a cement kiln,” says Jamie Farny, Director, Environmental Measurement and Metrics for the Portland Cement Association.
This product, called portland limestone cement, is made to standards developed specifically for it. And it is meant to be treated the same as traditional cement.
“Manufacturers in the U.S. will ... optimize or balance its chemistry so that it is designed as a one-to-one swap for portland cement,” Farny says. “We are trying to make it easy for users ... We want the portland limestone cement mix to be pretty much equivalent to a portland cement mix.”
Some have viewed the added, unfired limestone as a filler, but it is an essential component, Farny says.
The limestone does grind into finer particles than the clinker and other ingredients, he added: “They might behave a little bit differently. It could be controlled by admixtures if it was noticeable to an installer. But they seem to be fine under working tools, whether it’s a screed, trowel or anything else. They just seem to perform quite well.”
The finer particles also result in a tighter matrix, he adds.
Portland limestone cements have been used in Europe since the 1960s, and the U.S. standard was published about 10 years ago, Farny says. It has taken a while for the material to be adopted, as cement producers sold their existing stock and tried to figure out how to store this new type of material on top of the traditional product. Among industries that have adopted limestone cements, none have reported changes in how the product must be applied, Farny says.
As the pool-plastering industry looks at the inevitability of using portland limestone cement in their products, professionals want assurances that it won’t compromise the finished product or drastically change application.
“There’s not enough research yet to say with a clear conscience that there are no issues with it,” says NPC Technical Advisor Kent Westfall. “It’s different when you submerge it into a pool. That constant immersion creates a whole different set of parameters that you have to deal with. So when you’re changing a cement that has worked for years, it begs the question what’s going to happen.”
Farny recommends that installers test and monitor the new cement to see how it works in their applications.
NPC Chair Rob Romano has charged the Research Committee with looking into the topic, to determine how it wants to approach this issue and insure the product meets the industry’s needs. In the meantime, it will hold a session on this topic at its conference.