The World of Concrete: Advantages and Limitations
November 16, 2011
Did you know that concrete is the most commonly used construction material in the world and that around 7.5 billion cubic meters are cast every year worldwide. What makes concrete so popular? Why does it get used so much?
One of the reasons it gets placed into so many situations is because of what it is: artificial rock. However, it has one big advantage over rock because its first stage is fluid or plastic. That means that in this stage, with a little help, it conforms to the shape or form of whatever it gets poured into. If some reinforcement is added it can take on structural properties that rock can’t match. So we can say that along with it being really strong, concrete has sculptural qualities and can mirror a wide range of textures and finishes that can be incorporated into the mold.
This ability to take on almost any shape is an important component of why it is so often used in the built environment around us, but it’s also its ability to act like rock that really makes it desirable for many situations. Concrete lasts a long time, has very low maintenance requirements and mostly just needs to be kept clean. Concrete doesn’t burn, decompose or rot, and is not a tasty snack for insects or rodents. It also happens stands up to pretty much anything Mother Nature can throw at it. So like rock it’s stable, solid and unchanging.
But before we get an unrealistic picture of concrete, we should probably talk about some of its limitations or shortcomings. Interestingly enough many of these are weaknesses of rock as well. One of the primary concerns is that concrete is weak in tension. Basically what that means is that it doesn’t stand up well to pulling forces and that’s why reinforcement is used, usually steel which is really strong in tension. Concrete also has low ductility, which means that it doesn’t bend very much before it breaks. Other things like wood or steel can bend quite a bit and still retain much of their strength before they finally break. Concrete is brittle and when a force or weight greater than it can take is applied, it doesn’t bend very much before it breaks. In fact you have to use very sophisticated scientific equipment to see that it bends at all. Concrete also has a very low strength to weight ratio. This is great if you are building a dam but a very challenging problem when you’re building something like a bridge.
Concrete can also have some unsightly elements to it, like that it has a tendency to crack. If designed properly this generally isn’t a problem for how concrete functions but it can detract from how it looks and in some applications this is really important. Concrete is also susceptible to staining and efflorescence. Both of these relate to the fact that even though concrete looks solid and impervious, at a very small scale it is porous and the poorer the quality of the concrete the more porous it is. So these pores or spaces can be filled with very fine particles of dirt or they can allow liquids to soak into the top layer of the concrete making these stains very hard to remove.
But in spite of these limitations, the combination of strength, durability and artistic potential is helping to keep concrete at the forefront in an ever widening array of uses. With research being conducted into every conceivable facet of concrete to help overcome some of its weakness and find new uses, its popularity isn’t likely to diminish any time soon.