Concrete is the most widely used construction material in the world. Even some statistics mentioned that concrete is the secondly consumed material on earth and the first is water. Look on your house, street, or anywhere and you will find concrete some where.
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What is Concrete?
Concrete is a man-made material (of course) that has the appearance of stone. Do you know that “concrete” is coming from a latin word “concretus”, which has a deep meaning of “growing together”.
Engineers define concrete as a composite material made of coarse granular material (called the aggregate or filler) embedded in a hard matrix of material (the cement or binder) that fills the space between the aggregate particles and glues them together.
An easier definition would be “concrete is a composite material that consists basically of a binding medium in which are embedded the aggregate particles”
We mentioned that concrete is a composite material. So, what is a composite material?
A composite material is a material that is made of two or more components; each component has different properties that the other. The overall properties of the composite material is different from the properties of each of is components.
Basic Components of Concrete
Any normal concrete mixture will have three basic components (also called ingredients):
- Portland Cement
- Fine Aggregates (sand)
- Coarse Aggregates (gravel or crushed stone)
All these compounds are mixed together to produce the concrete in the from we all know. The hard medium that we talked about earlier is coming from the reaction of the cement and water [Hydrated Cement Paste].
Portland cement + water + fine aggregate + coarse aggregate → Concrete
Fig. 1: Concrete materials
Applications of Concrete
The popularity of concrete is because of two points:
- concrete is used for many many different structures, such as dams, buildings, pavements, frames, bridges, much much more than any other construction material.
- Concrete has the highest consumption today in construction more than any other construction material.
Look at the following images for wonderful structures built with concrete:
- Tall buildings; for example, the columns of the International Finance Centre in China were build with high strength concrete
- Dams; for example, the Three Gorges dam which used 22 million m3 of concrete for construction.
- In addition, concrete has been widely used in other applications including but not limited to: airport runways, tunnels, highways, pipelines, and oil platforms.
For your information, if concrete were a material that people eat, everyone in the world would have 2 tons each year to eat.
So, what made concrete so popular to this degree? To answer this question, let us look at the following advantages of the material.
Advantages (Pros) of Concrete
- Cheap: compare the cost of concrete with any other construction material and you will find concrete cheaper. It is inexpensive in terms of the cost of production compared to other materials. As we mentioned earlier, concrete is made with cement, water and aggregate. Compared with steels, plastics, and polymers, concrete ingredients are cheaper and readily available all over the world.
- Hardens at normal temperature: cement can react at room temperature with water to produce the hardened cement paste. In other words, concrete does not need special requirements for its production.
- Versatile: fresh concrete (concrete at mixing) flows like a liquid. That is why it can be poured in almost any formwork with any shape or size.
- Energy efficient: the energy consumption for producing a ton of plain concrete is 450–750 kWh and reinforced concrete is 800–3200 kWh. This is very low when compared with the energy required for producing the same amount of steel (8000 kWh)
- Resists water efficiently: Water damages wood and rusts steel. For concrete, water can be actually a cause for increasing its strength. Concrete can withstand water actions with much damage. Thus, concrete is ideal for building water-related structures such as dams, tanks, pipelines, etc.
- Resists heat: what happens to wood and steel in case of fire? Yep, wood burns and steel melts. How about concrete? It can resist the fire for 2-6 hours. Is this enough time to rescue the people in there? yes, it is in most cases. That’s why for steel structures we add a protective layer of concrete on steel.
- Reduces waste of other industries: other materials that are water from some industries can be used to replace a proportion of cement. For example, fly ash, slag and silica fume.
- Works well with reinforcing steel bars: concrete and steel have close thermal expansion coefficients so they can work well together. Concrete protects steel from rust while steel provides the necessary tensile strength that concrete lacks. Good team right?
- Less maintenance needed: concrete in normal conditions does not need coating or painting as protection for weathering, while for a steel or wooden structure, it is
necessary. These coatings will usually need replacement within a few years, making the cost of maintenance less for concrete structures than wood and steel.
Limitations of Concrete
Similar to anything in world, concrete has some drawbacks. We would rather call them limitations instead of disadvantages since there is always a way to overcome the limitations.
- Quasi-brittle material: Concrete is a quasi-brittle material. It fails suddenly in tension without giving a large deformation as a warning sign. Ductile materials such as mild steel deforms a lot before failure so they give sufficient warning for people to act before failure. Thus, usually, concrete has to be used with steel bars to form “reinforced concrete”, in which steel bars are used to carry tension and the concrete carries compression.
- Low tensile strength: concrete is great in compression. It can carry compression loads very good. However, for tension, it is ability is 1/10 of its compression ability. In other words, tensile strength of concrete is only about 1/10 of its compressive strength for normal-strength concrete, or lower for high-strength concrete.
- Formwork is required: fresh concrete is flowable and requires a formwork to hold its
shape and to support its weight. Formworks are not cheap; they are labor intensive and time-consuming.
- Long curing time: concrete needs to be cured with water after casting to continue gaining strength. The design index for concrete strength is the 28-day compression
strength. It is not feasible sometimes to cure concrete that much period.
- Concrete cracks: even reinforced concrete elements crack on the tension side. Cracks in some cases can be a cause of reducing the ability of concrete to resist detrimental substances in the environment.