concrete vs. Cement: A True Understanding Helps Build Better Walls and Fences

With our experience building precast concrete walls and fences in California, we feel quite comfortable with a good understanding of the concrete and cement business. In general, “concrete” and “cement” are not the same thing. Sidewalks and foundations are made of concrete, not cement, although cement is a vital and significant ingredient in concrete. Other ingredients may include gravel or crushed stone (also known as aggregate), sand, water, and other performance-enhancing additives. The trucks you see with the rotating container that most people call concrete mixers are actually concrete mixers.

Cement in concrete is known as Portland cement, because Joseph Aspdin, an English mason credited with the invention, felt that its color was almost the same as limestone quarried on the Isle of Portland. Aspdin obtained a patent for cement as early as 1824. He used to heat limestone and clay in a kiln until parts of the mixture fused together, then grind the burned and dried result to a fine powder. Adding water to the powder produced a workable paste and started a chemical process, called hydration, in which the water bonded with compounds of calcium, silicon, aluminum, and iron, causing everything to combine into a stiff mass. Wet Portland cement doesn’t just “dry out,” hydration transforms it into a chemically distinct material, which continues to get stronger over time.

Although concrete is very difficult to crush, it is actually quite easy to break it apart. One way to compensate for this tensile weakness (meaning it’s easy to break) is to add steel reinforcing rods, known as rebar, which generally hold the concrete in place when it cracks. Concrete reinforced with rebar should crack, Meyer explained. “That may sound funny to the layman,” he said, “but the reason is that if it didn’t crack, you wouldn’t need the steel. The engineer’s challenge is to keep the cracks small, so instead of having a few big cracks, we have many small cracks.

Another way to reinforce the cement is by adding threadlike fibers of steel, polypropylene, polyolefin and other sample materials. Therefore, by adding polypropylene fibers to the mix, the risk of such failures can be reduced, as the fibers melt at high temperatures and leave voids that act as relief valves for steam.