Concrete has been the most popular building material for millennia. It’s used to make not just buildings, but dams, sidewalks, roadways, different types of walls and bridge decks. Concrete is so ubiquitous that it’s easy to take for granted. Yet concrete is a fascinating material. Here are six things most people probably don’t know about concrete:
1. Concrete is not Cement
It’s easy to get concrete and cement mixed up. Concrete is made of cement when cement is mixed with water, sand and gravel. Cement itself is a fine, gray powder. Most cement used to make concrete is Portland cement. Portland cement is a hydraulic cement, which means it hardens under water. It gets its name because it’s the same gray color as the stone found on the Isle of Portland in the United Kingdom.
2. The Longer Concrete Stays Wet, the Stronger it Is
A chemical reaction between the cement and water that goes to make concrete makes it strong. So, the longer the cement is allowed to stay wet, the stronger it is. This is why builders don’t want concrete to dry out too fast, and try to keep it moist for at least three days.
3. Very Cold Temperatures Keep Concrete From Hardening
Cold weather slows down the rate at which concrete hardens. Concrete that’s being poured on wintry days needs to be protected, because ice crystals in the cement can impair its ability to harden properly and make it weaker than it should be. When concrete is protected from the outside air, the heat that’s generated from making it prevents it from freezing.
4. The Ancient Romans Used Concrete
Concrete is so durable that some of the concrete structures the ancient Romans built are still around today. The Pantheon is one of these structures. Its dome is the largest in the world made of unreinforced concrete. To make the cement, the Romans mixed slaked lime with a type of volcanic ash called pozzolana. People forgot how to make cement after the fall of the Roman Empire, but the skill had been revived by the 18th century.
Other structures made largely out of concrete include:
- The Hoover Dam
- The Panama Canal
- The Three Gorges Dam
The creation of the Erie Canal called for great amounts of cement. In 1818, the engineer Canvass White found enough rock in Madison County, New York to be able to make a natural hydraulic cement. A great deal of this cement was used to create the Erie Canal.
5. Concrete Gets Stronger Over the Years
If concrete is mixed, poured and cured properly, it grows stronger as time passes. This strengthening can last for decades. This is because the calcium hydroxide in the cement absorbs carbon dioxide and turns into calcium carbonate. Calcium carbonate, or CaCO3, is found in rocks such as marble and limestone and doesn’t dissolve in water.
6. Concrete Can be Made to Imitate Other Materials
New technologies make it possible for concrete to mimic other, more costly materials. These include stone such as granite or travertine, ceramic tile, porcelain, wood, cobbles, brick or leather. Concrete can be used for floors and countertops in residences or office buildings. It can be polished until it glistens or has a matte finish. It can be stained, dyed, stamped and made to incorporate objects from sea glass to seashells to family crests to integral sinks and trivets. Shingles and siding for houses can be made of concrete, or fiber cement. They are made in ways that make them resemble traditional wood shingles and shakes. Their attractiveness, durability and fire and weather resistance makes them valuable.