If you’ve been keeping up with this blog, you’re probably well on your way to becoming an expert in all things cement. This week, we’re taking a look at how cement is made, following its journey from rock quarry to build site.
Cement is usually made out of limestone, clay and sand. These rocks contain the four primary elements necessary for making cement: calcium, silicon, iron and aluminum.
The first step in cement production is to mine the raw material from a rock quarry. The limestone rocks are fragmented into moveable pieces by setting off explosives in holes bored into the rocks. The rocks are then broken down by large crushers, transforming boulders into small chunks measuring about 1.5”.
Next, the rocks are brought to a lab that analyzes their exact chemical components so that an accurate proportion of limestone to clay can be established. The mix is usually 80% limestone and 20% clay. At this point, the mix is ground up into a fine powder by a series of heavy rollers. The mix is still considered “raw” until it passes through the kiln.
After moving through a pre-heating chamber, the raw cement mix is heated to 1450°C (2642°F). This kicks off a series of chemical reactions, releasing carbon dioxide from the mixture and creating the final cement product: calcium silicate. The kiln’s ultra high heat causes the calcium silicate to harden into small lumps or nodules, known as clinker.
The clinker is cooled before entering the final grinding phase. The clinker enters a rotating ball mill that uses steel balls to break the clinker into another very fine powder. When making Portland cement (the most common), gypsum is also added.
Some cement is packaged into bags, but it’s typically shipped in bulk quantities. When the cement is ready to hit the road, we step in. Every day, we load powder cement into dry bulk trailers and transport this crucial building material to construction sites across the country.