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CLEAR CHOICE

Concrete is the most common building material in the world.

Its popularity is due to its simplicity: Concrete is a simple mix of paste, water, and mineral aggregates that join together to harden into a strong material. This process is the foundation of all concrete materials, such as pipes or culverts. Let’s look at the process in more depth.

What is Concrete?

The key component of concrete is in the paste. This paste is typically composed of Portland cement and water. Note that while "cement" and "concrete" are often used interchangeably, they’re quite different. Cement is an ingredient used to make concrete.

Portland cement is the most common choice of cement used for concrete mixing and is composed of the following minerals:

  • Calcium
  • Silica
  • Alumina
  • Iron

All together, these minerals form the basis of the concrete mixture. However, it’s only when water is added that the mixture comes to life.

Adding Water to Cement

Soon after cement and water are combined, a chemical reaction known as “hydration” occurs. During this process, a node forms on the surface of each cement particle. This node grows and expands until it links with other expanding nodes in the mixture.These links join together and cause the paste to harden into a rock-like mass, giving it the strength associated with concrete materials.
The character of the concrete depends on the quality of this paste. The quality of the paste, in turn, depends on the ratio of water to cement; the less water used, the higher the quality of the concrete—provided that the concrete is properly placed and cured.
Typically, a high-quality concrete mix will have the following ratios:

  • 10-15 percent cement
  • 60-75 percent aggregate
  • 15-20 percent water

Does the type of water used matter for concrete quality?
Somewhat. A good rule of thumb is that any drinkable water with no noticeable taste or odor may be used as mixing water for concrete.
Conversely, water that is unsafe to drink due to high amounts of chlorides, sulfates, alkalis, or solids should be avoided, as these impurities will affect the quality of the finished concrete.

Aggregates and Curing

The amounts of aggregate used in a concrete mixture depend on the desired thickness, and purpose, of the concrete. Typically, a continuous gradation of particle sizes is desirable for efficient use of the paste, and the aggregates should be clean and free from any impurities that could affect the end product.
After the mixture has been laid, the curing process begins.
This occurs when the exposed concrete surfaces begin to sufficiently harden to resist marring.
Concrete surfaces are cured by applying steam or water. The longer the concrete is kept moist, the more durable it will become. Most of the hydration and strength gain take place in the first month, but hydration continues at a slower rate for many years. This means that, remarkably, concrete actually gets stronger as it gets older.

Precasting

Unlike concrete that is filled on-site, Precast Concrete Products are cast in a factory.
These products benefit from tight quality control only possible within a production plant. Precast concrete pipe is produced in stable conditions under rigid production standards and testing specifications. This means that precast concrete structures can be mixed, tested, and cured at optimal standards to create durable, long-lasting concrete products.

Contact the Canadian Concrete Pipe & Precast Association for Industry Updates