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All you need to know about prestressed concrete

All you need to know about prestressed concrete

The construction industry has got a boon in the form of prestressed concrete. It is getting the exposure and fame for quite some time now, but its widespread benefits and advantages are not known to many. There are many questions in the mind of even the experts in the field of construction. This is why we thought of putting together all the important information related to prestressed concrete in this blog article today.

Check if these questions ever crossed your mind!

  1. Is there a specific method of controlling the camber of prestressed concrete element under a specific prestressing force?

The most common and widely used method to control the camber of prestressed concrete element is using haunch with variable pedestals to overcome the unnecessary camber. This should be bore in mind that this method also has some restrictions that must be considered.

  1. How does prestressed concrete differ from reinforced concrete?

Prestressed concrete is also a type of reinforced concrete. Prestressed concrete is actually a compound of high-resistance steel and concrete. The stress has a counter-impact and the opposite of the stresses resulting from the loads affecting the structural element ultimately increases its capability to endure all types of loads affecting it. While reinforcement steel bars embedded in the concrete bear the tensile loads in reinforced concrete, the responsibility to bear the loads lies on the pre stressed cables or tendons encased within the concrete.

  1. What are the types of prestressing?

Prestressing is of basically two types – Pre-tensioning and Post-tensioning.

Pre-tensioning: Here, the tendons are tensioned against some abutments before the concrete is placed. The tension force is released after the hardening of concrete. The tendon tries to attain its initial length, which the concrete doesn’t allow because of the bond between them. In this way, a compression force is induced within the concrete.

Post-tensioning: In this method, metal or plastic ducts are placed inside the concrete before casting. The tendons are placed after the hardening of the concrete. The tendons are placed inside the ducts, stressed and hardened after the concrete hardens and attains enough strength.

  1. What are the applications of prestressed concrete?

Prestressing concrete can be used in the construction of bridges, RCC roads, precast electrical poles, railway concrete sleepers, etc.

  1. What are the advantages of prestressed concrete?

Prestressed concrete members have numerous advantages that include high durability, easy transportation because of smaller size of the sections, and their ability to do away with cracks.

Do you have any question regarding prestressed concrete that you would want to ask us? Do let us know and our experts would be happy to help.

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Why Precast Concrete Technolgy is a Boon

Why Precast Concrete Technology is a Boon

Humanity has been using concrete for centuries; the strength and durability just can’t be ignored. Add to this the effectiveness and added benefits of precast concrete and it’s nothing less than a boon for the construction industry. So what are the benefits that precast concrete has in the offering for you? Let’s discuss.

7 Benefits of Precast Concrete

    1. Easy installation: Precast is not dependent upon weather conditions because it is prepared off-site in a covered environment. Off-site manufacturing and on-time delivery of precast concrete makes way for an on-time delivery of a project.
    2. Better quality: Since the precast structures are prepared off-site and are not affected by dirt, dust, humidity, fluctuating temperatures and other such conditions, they exhibit better quality. In addition, precast structures undergo effective monitoring and curing that helps get high-quality structures that see off harsh environment conditions over larger spans of time.
    3. Cost-effective: Concrete precast structures extent the life-cycle of a building. They also help the cause by making best use of available space, wasting less space in the process. All these factors make precast concrete the best available and a cost-effective option for building structures that last various decades.
    4. Weather and fire-resistant: Whatever be the weather condition, precast concrete structures have the capability to withstand the chilliest of conditions to the harshest of heat waves. In addition, they are also fire-resistant to the level that they do not melt and additional fire-proofing is not required.
    5. Long life and low-maintenance: Precast concrete structures can last for over a century, thereby reducing the life-cycle cost of the projects. The quality is consistent, there are less leakages and cracks, and hence the overall maintenance cost is low too. The structures are strong and sturdy for their entire lifetime.
    6. Noise reduction: Owing to the dense and sturdy nature of precast concrete, the buildings made out of them are essentially sound-proof to a great extent. This is the reason precast concrete becomes a great choice for commercial buildings, residential complexes and official organizations where noise-reduction is a necessity. The high thermal mass of the prestressed concrete precast structures allow high level of sound insulation and work as sound barriers against urban noises and noise from the roads.
    7. Recyclable: Did you know that the precast cement structures are also recyclable? They can be crushed and reused for construction fills and road-bases. This makes way for further savings while having less impact on the environment.

In addition to having all these amazing properties, precast concrete has a lot to offer. Did we tell you about the water-tight property of the structures made out of precast concrete? The minimal on-site activity requirement and the enhanced speed of construction further make it a perfect choice of the engineers.

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Principles of Prestressing

Basic Principles of Concrete Prestressing and its Types

Let’s get back to the basics

A homogenous concrete beam has very low flexural strength and bends under the effect of heavy-weights and with the passage of time. In order to do away with this deficiency of the concrete structures, the beams are provided with steel reinforcements near the bottom to take care of the tensile stresses. Yet, a considerable part of concrete below the neutral axis merely maintains the reinforcement in position, but its tensile strength is neglected in the computation for the flexural strength.
This is where prestressing comes in! Tensile stresses are applied to the tensile reinforcement before applying the external loads, resulting in the generation of compressive stresses in the concrete of the beam. Generally, the tensile stresses instigated by the loads are totally counteracted or absorbed by the compression stresses in the concrete, as a resultant of prestressing.

Principle of prestressing

The most significant principle of prestressing is to counterpoise the stress generated in the tension-bearing portion of a beam generated due to loading. In prestressing technology, prestressed tendons provide a clamping load that generates a compressive stress to balance the tensile stress that the concrete compression member would have else experienced owing to the bending load. Simply put, the internal pressure is the tensile stress produced when a pre-tensioned rod is included between the concrete in order to keep the rod from returning to its original position. Chemical bond between the concrete and the steel makes the process possible.
In order to better understand the functioning of prestressing, consider a scenario. Take a rubber band, stretch it a little and put some weight on it; the rubber band sags considerably. Now, stretch the rubber band further, as much as you can (without breaking it) and place the same load on it. This time, the rubber band sags very less (almost negligible). This is the exact same case with prestressing.
Basically, there are two main types of prestressing:

  1. Pre-tensioning
  2. Post tensioning

Let’s discuss both the types of prestressing in brief.
Pre-tensioning: Usually done with precast, pre-tensioning involves tensioning tendons against some abutments before pacing concrete. After the concrete hardens, the tension is released and the tendons try to shrink back to their original lengths. Quite obviously, this isn’t possible as the concrete resists the tendons getting back shorter because of the bong between them. Thus, a compression force is induced in the concrete.

Post-tensioning: On the other hand, metal or plastic ducts are placed inside the concrete before casting. In this process, the tendons are tensioned after the concrete is hardened and has enough strength. The tendon is placed inside the duct, is stressed, and anchored against the concrete. Grout may be injected into the duct later. This can be done either as a precast or cast-in-place.

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Precast Concrete for Homeland Security

What is Prestressed Concrete?

Prestressed concrete is fundamentally concrete in which internal stresses of an appropriate distribution and scale are introduced so that the stresses resulting from the external loads are countered to a preferred extent. As it is evident from the name, it is a form of concrete which is stressed by means of compression before supporting any design load beyond its own weight. The compression is produced in concrete by tensioning the high tensile strength “Tendons” located in or adjacent to the concrete mass.
The basic functioning of prestressed concrete is in a manner that high-strength steel tendons in the concrete members induce compressive strength that balances tensile stresses levied in the member during service. There are many added benefits of using prestressed concrete and it has numerous advantages over the traditional reinforced concrete structures.

Advantages of Using Prestressed Concrete (PSC) over Reinforced Concrete (RCC):

  1. Since there is no tensile crack, prestressed concrete is more durable than reinforced concrete. PSC is also resistant to the effect of shocks and stresses.
  2. Improved shear resistance among the PSC members reduces the principle tensile stress.
  3. In PSC, the section of members can be reduced to use the smaller sections for longer periods of time. Also, this makes transportation easier.
  4. Prestressed concrete offers excellent fire resistance elegance, high corrosion-resistance, and adaptability, and also boasts of low maintenance costs.
  5. Prestressed structures are lighter in weight than reinforced structures.
  6. PSC requires lesser quantity of materials as compared to RCC. Thus, the material cost is less.
  7. The reinforcement in prestressed concrete stays unaffected from external factors and hence, longevity is much better than RCC.
  8. The dead weight of P.S.C. is much less compared to what is required for R.C.C. It is 1/3rd of its RCC equivalent.
  9. PSC structures are stiffer owning to lesser deflections.
  10. The deformation in prestressed members is very much less than reinforced concrete member. As in the case of reinforced beam, the deflection is just about 25% of an equivalent RCC beam.
  11. PSC structures have better fatigue strength.
  12. Prestressed concrete is a better option for structures that need to retain water for long.

It has been proved that structures made out of prestressed concrete have better durability and longevity; the cost of construction is also on the competitive side. However, expert supervision, skilled labour-force and specialist construction tools are required in order to go forward with a construction involving PRC.

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