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A Guide to Prestressed and Post-stressed Concrete

Concrete undergoes various procedures to attain a certain degree of strength and resistance appropriate for different uses. While reinforced concrete is one of the most widely used construction materials, concrete by itself is much more fragile than expected, having limited use beyond a few applications.

The material performs exceptionally well against compression, but it has low tensile strength and ductility. That’s why it is often reinforced with steel to give it more durability. Still, due to steel’s ductility, it will stretch or bend, making the concrete crack. For this reason, prestressed and post-stressed concrete is crucial to extending its lifespan and making it more durable. 

The Importance of Prestressed and Post-stressed Concrete

Due to reinforced concrete’s cracking potential, it sets off a destructive process referred to as spalling. This phase is exacerbated when water penetrates the cracks in reinforced concrete, damaging the building’s structural integrity in three ways. 

For starters, since liquid fills any space it can reach, it can then freeze when the temperature reaches 0º Celsius. The resulting ice crystals occupy more space than liquid water molecules, pushing the concrete and widening the cracks. Once the ice melts, the crack is more prominent, allowing more water to flow inside to fill the gap, repeating the cycle and multiplying the damage exponentially.

The second way is that the cracks will eventually be large enough for water and air to reach the steel rebar implanted in the reinforced concrete. The exposure will cause the rebar to rust, exposing the interior layers of iron to corrosion. 

The third way is that when the water reaches the reinforced concrete, it may change the environment’s pH balance, catalysing numerous chemical reactions within the concrete. It will result in new crystals, which will physically push the reinforced concrete apart, damaging the material further.

The damage water can inflict on concrete is also why investing in concrete waterproofing is essential. It adds more protective layers to the material, shielding it from moisture and preventing water from penetrating the material and widening the cracks.

The Prestressed Concrete Process

To prevent this cracking, you can stretch the steel rebar before pouring the cement, known as prestressing or pre-tensioning, since it supplies additional tension force to the steel before forming the reinforced concrete. The steel will then continuously pull itself back towards its original shape and pull the surrounding concrete towards itself, resulting in a compression force.

Putting the concrete in this constant prestressed condition reinforces it and makes it more durable since concrete shines when faced with compressive forces. As a result, cracks are less likely to form since the steel pulls the concrete and keeps it together, preventing it from stretching as far as it usually would if the steel were not prestressed. Additionally, cracks that do form will be pulled closed by the force of the steel attempting to revert to its initial relaxed state. It will then restrict the amount of water that can penetrate and corrode the reinforced concrete.

Post-stressed Concrete

Another way to strengthen concrete is to subject it to post-stressing, which involves tightening the steel once the concrete has started to harden. While it seems like it fully sets in hours, it takes approximately a month to cure appropriately and continues hardening and strengthening for at least five more years. 

Conclusion

Prestressed and post-stressed concrete is much more durable than reinforced concrete. It leads to less cracking, even when you use smaller and thinner sections, giving you more support and structure without any of the most recurring problems that reinforced concrete experiences.

Phoenix Reinforcing is a concrete reinforcing business in Queensland offering a full delivery service in reinforcing productions and cage fabrication, building products, decorative concrete products, and many more. We also provide a cement calculator on our website to help you with your estimations. Contact us today to learn more about what we can do for you!

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