This article will answer the question “Why precast concrete?” and will cover topics about precast concrete such as its definition and the manufacturing process it undergoes from engineering design to shipment. The specific cases when the use of precast concrete is not practical for a project will also be discussed in this blog post.
Why Precast Concrete?
The use of precast concrete is recommended for large-scale construction projects whose design permits repetitive units of large building blocks. The space of the construction site is also a determining factor of choosing precast concrete as a base building material. When the location is impractical for onsite concrete preparation, concretes are much better prepared in a manufacturing facility. In addition, precast concrete offers a consistent and reliable quality control because it is prepared in a highly regulated and controlled environment. The product of quality is simply incomparable compared to its onsite concrete counterpart.
Construction projects that utilize precast concrete are buildings or skyscrapers, railways, skyways, bridges, and so on.
What is Precast Concrete?
Precast concrete is a concrete product that is poured and formed in a reusable concrete mold in a manufacturing site (away from construction or project site). The mold is designed to produce repetitive units of these products which are all cured in highly controlled conditions in order to achieve the design properties before being shipped to the location of the project.
Precast concretes are often made with steel reinforcements, although there are cases when the design requirement simply dictates a plain one – or maybe a prestressed version. In other words, the variety of precast concrete products generally depends on the purpose and requirement of the customer.
There are numerous advantages of using precast concrete some of which are the following:
- Precast concrete is designed to have remarkable thermal resistance so it will have the expected stability and integrity at both hot and cold environments.
- The quality is simply outstanding. Because precast concrete is manufactured in a controlled environment, the parameters that affect its quality are strictly monitored and regulated. Equipment for quality testing is available and standardized in a manufacturing setup, so the validity of quality compliance is intact.
- Precast concrete may be reused to some extent which could contribute to the global movement for the greener construction industry.
- The form or mold used in the preparation of precast concrete products are totally reusable without significant negative effect on the quality of a batch. The reusability of molds results in consistent measurements of the precast concrete.
- They have high resistance against high impact loading, and generally have impressive strength, durability, and reliability.
Why Not Use Precast Concrete?
While precast concrete is advisable to large-scale projects, it is also important to note that there are cases when the use of this building product is not the most practical option. For example, in terms of logistics aspect, precast concrete needs to be transported to the construction site in a timely and organized manner since the space available in the project area is limited.
Precast concrete manufacturing facilities are limited. With that in mind, if the distance of the manufacturing site from the construction site is economically impractical, it is best to look for alternatives to precast concrete. Furthermore, the utilization of precast concrete is complementary to a need for construction equipment such as cranes specific for heavy weight building blocks. If the budgetary provision is limited, then precast concretes may not be the best option for the project.
Lastly, the contribution of skilled contractors in the utilization of precast concrete is significant to the success of the project. The scarce skill set of labor force in the project location may overseas recruitment which could also take a toll in the budget of the project.
How is Precast Concrete Produced?
As mentioned, precast concrete is manufactured in a production facility wherein standard methods and procedural compliance is a requirement. For this reason, the process of producing precast concrete is straightforward and standardized.
As with any construction project, structural engineers need to come up with a design that will suffice the requirement of the project. This includes extensive analysis of the product’s mechanical properties in relation to the variation in production parameters such as water-cement-ratio, temperature, pH, and so on. Engineering drawings and specifications are done in this step to clearly visualize the product in a scaled in detailed version. The current technology in the design industry makes use of state-of-the-art engineering design software to come up with engineering solutions in an accurate and timely manner.
When the design is final and approved by the client. The next step is usually the manufacturing of reinforcements to be used in the building block. The reinforcing material to be used, the method of splicing, as well as the specific details of how the mesh and cage are to be organized depend on specifics written in the final design. Because precast concretes are units made of repetition, the skill required from the labor force is consistency from the routine work.
After creating all the reinforcements required, sealing of the mold or form is done next. It is imperative that all openings are enclosed to prevent any leak during concrete pouring. Next to sealing, reinforcements are installed inside the form accordingly.
Concrete Preparation and Pouring
The manufacturing of fresh concrete mixture for precast is optimized to meet the design requirements as well as the economic constraint of the production. For example, the consumption of water in concrete preparation may be minimized to some extent without compromising the strength of the final concrete. Furthermore, it is important to note that the quality of the concrete batch is also regularly monitored at this stage of the production. The flowability or workability as well as the coarseness of the mixture is strictly monitored and regulated to attain the desired quality.
Fresh concrete is then poured gradually inside the form and will be allowed to settle for a while. Complete sealing of the form is verified from the absence of any leak in the form.
Curing and Stripping
When the form is filled and sealed, precast concrete undergoes the curing and stripping process. Compared to onsite concrete pouring, the conditions in the manufacturing facility is controlled and regulated in favor of the curing requirement. Some of the curing parameters like temperature may be adjusted in order to optimize and to hasten up the process. This process as well as the curing conditions are still dependent on the design finalized by the engineers of the project.
When the concrete is completely cured, the form is carefully and strategically stripped off the product. The mold is cleaned from any debris or concrete left-over to be used again on the succeeding batch. Meanwhile, the newly stripped precast concrete is transferred to a storage area in the production facility and will be shipped depending on the requirement and timeline of the project.
This blog post answered the question “Why precast concrete?” Precast concrete was defined as a concrete product that is routinely manufactured in a controlled environment using non-disposable form and mold. It was clearly pointed out that precast concrete is recommended for specific cases such as large-scale projects that require repetitive unit blocks like buildings as well as construction areas that do not have enough space for conventional concrete production.
Furthermore, the manufacturing process of precast concrete was also discussed in this article. It was mentioned that the process starts with an engineering design that distinctly defines all relevant properties and attributes of the concrete product. The formation of molds and cage are processed next and will proceed to concrete preparation at predefined conditions before pouring it to the created cage and form. Curing will be executed next in a highly regulated area to attain the design quality parameters of the product and will then be stripped off from its form when it is completely cured. Shipment then proceeds after.
For any questions and suggestions about this article, please feel free to submit your thoughts in the comment section below.
Frequently Asked Questions (FAQs): Why Precast Concrete?
Is precast concrete stronger?
Compared to concrete casted onsite, precast concrete has higher durability, integrity, and reliability because it is precisely manufactured in a controlled environment. The parameters of fresh concrete are strictly monitored and regulated to follow the engineering design, so the quality is consistent and remarkable.
Is precast concrete safe?
Yes, precast concrete is safe. Each repeating unit of precast concrete is carefully manufactured in a controlled environment, so each attributes and mechanical properties that relate to safety are within design standards.
Does precast concrete have rebar?
Yes, precast concrete may be manufactured with reinforcements to attain the design requirements of the project. Although, it is important to note that besides being reinforced, precast concrete may also be produced as plain concrete and prestressed concrete.
Is precast concrete sustainable?
Yes, precast concrete is sustainable compared to concrete poured on site. The amount of raw material, energy, and time wasted on precast concrete are minimal due to strict compliance to the product design. The manufacturing parameters are controlled which allow a significant decrease in the utilization of water compared to conventional methods.
Are hollow blocks better than precast?
In most aspects, precast concrete is way better than hollow blocks. The durability and ductility of precast concrete is incomparable to hollow blocks.
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