Pet Peeve Time
Okay I gotta get this off my chest. I've been pouring concrete for over 20 years and it still makes me twitch when someone calls it "cement." Cement is an INGREDIENT in concrete. Calling concrete "cement" is like calling a cake "flour." My dad used to correct people on this all the time and now I'm turning into him. So let's set the record straight.
What's In Concrete
Concrete is basically four things mixed together:
- Portland cement - the gray powder. This is the binder, the glue that holds everything together. It's made from limestone and clay fired in a kiln at crazy high temperatures. Named after Portland, England because some guy in the 1800s thought it looked like Portland stone. Not from Portland, Oregon - I've had people ask.
- Aggregate - rocks and sand. The coarse aggregate is gravel or crushed stone, usually 3/4 inch or so. The fine aggregate is sand. This makes up about 60-75% of the mix by volume. It's the bulk, the skeleton.
- Water - activates the cement. And what most people don't realize - the cement doesn't "dry," it CURES. It's a chemical reaction called hydration. The cement particles react with water and form crystite bonds that get stronger over time. Concrete at 28 days is stronger than concrete at 7 days.
- Admixtures - these are the special sauce. Accelerators to make it set faster, retarders to slow it down (big deal in Florida heat), air-entraining agents, water reducers, fiber mesh. Different jobs need different admixtures.
Nerd Stuff
Since we're nerding out anyway:
- Concrete is the second most consumed material on Earth after water. Think about that.
- The Romans used concrete. The Pantheon's dome? Concrete. Still standing after almost 2000 years.
- Standard concrete reaches about 75% of its strength in 7 days and full design strength at 28 days. But it actually keeps getting stronger for years after that, just very slowly.
- The water-to-cement ratio is THE most important factor in concrete strength. Too much water = weak concrete. This is why you never add water to the truck to make it flow easier, even though it's tempting.
So What's Cement Then?
Cement is just the powder. You can buy bags of Portland cement at any hardware store. By itself it's useless for building anything. You need the aggregate and the right amount of water to make concrete. Now you know, and you can correct your neighbors. You're welcome.
Questions about concrete? Yeah I could literally talk about this all day. (941) 374-8674.