In the production process of precast concrete components, the correct selection of concrete type and its proportion plays a decisive role in improving production efficiency and ensuring product quality.
Different types of precast concrete components have different requirements for concrete due to their differences in use, structural shape, and use environment.
Whether it is a load-bearing wall panel and beam column, or a decorative facade, each prefabricated component needs to be accurately selected to ensure the concrete mix ratio according to its characteristics and usage conditions to ensure its strength, durability, and appearance quality. Therefore, when designing the concrete mix ratio, the first task is to clarify the specific purpose of each prefabricated component and its usage environment, to accurately set the various performance indicators of the concrete.
Let's explore some common concrete types and their ideal applications to help you better understand their unique properties and benefits.
Wet Poured Concrete
Wet-cast concrete is commonly used in the production of various precast concrete components such as wall panels, TT panels, beams, columns, and stairs. These products are usually produced in molds. The pouring process is carried out using a traditional hopper and then compacted by vibration.
The common compressive strength range of wet-cast concrete is 20-60 MPa. It has good mechanical properties and is suitable for the production of load-bearing components. However, with the development of technology, self-compacting concrete (SCC) has gradually become the preferred material for modern factories because it can be automatically compacted without vibration, which greatly simplifies the production process.
Applicable scenarios
Components that require traditional vibration forming, such as wall panels, beams, columns, etc.
Dry Mix Concrete
Dry-mix concrete is mainly used in the production of hollow-core slabs, and the key point lies in the stability of freshly mixed concrete.
In addition, the adhesion between the prestressed steel strands and the concrete is also crucial. This requires good compaction and the right concrete mix.
The advantage of dry-mixed concrete is that it can achieve high compressive strength at a lower cement dosage.
For this type of concrete, the amount and quality of its binder directly affect the performance of the concrete, especially the early strength (i.e., demoulding strength), so special care is required.
The demoulding time of precast components produced with dry-mixed concrete is usually 5 to 24 hours.
Applicable scenarios
Hollow-core slabs and other components that require rapid demoulding.
Self-compacting concrete
Self-compacting concrete is an innovative type of concrete that can be poured and compacted without vibration.
It has good fluidity, can fill the formwork, and achieve complete compaction even in the case of dense reinforcement. Moreover, the hardened white compacted concrete has a dense and uniform texture and has the same engineering performance and durability as traditional vibrated concrete.
In recent years, the application of self-compacting concrete in the precast concrete industry has been rapidly promoted. It is particularly suitable for the production of complex geometric shapes and thin precast concrete components, especially when conventional concrete is difficult to compact.
In addition, self-compacting concrete has the significant advantage of reducing noise and vibration.
Applicable scenarios
Complex structures, thin-walled components, and prefabricated components with dense steel bars.
High Strength and Ultra-High Performance Concrete
High-strength ultra-high-performance concrete is widely used in the production of various precast concrete components. High-strength concrete is usually fiber-reinforced and is suitable for high-rise buildings, especially in earthquake-prone areas.
Due to its excellent mechanical properties, high-strength concrete is used in structures that are subject to high mechanical and chemical loads, such as industrial floors, sewage treatment plants, and hydroelectric power plants.
Applicable scenarios
High-rise buildings, heavy-load structures, and earthquake-resistant design projects.
External facade concrete
Facade concrete is a special application area, and its surface appearance is often the main factor in determining the mix ratio.
Especially for colored concrete, the cleanliness of its production and transportation equipment is particularly important. Mixers and transport hoppers must be cleaned regularly, and many factories also set up facade concrete mixing plants.
Cement is usually white or gray, or a mixture of the two. In facade concrete, common additives such as fly ash are generally not recommended because they may cause uneven color and easily affect its durability, especially in cold climates.
Applicable scenarios
Building facades, decorative components, and colored concrete projects.
FAQ
Q: Dry-cast concrete: what is it best for?
A: Dry-cast (dry-mix) concrete is commonly used for hollow-core slabs and similar production lines where compaction stability and early strength for demolding are critical.
Q: Do you always need air entrainment for durability?
A: Not always. It depends on the environment. For cyclic freeze–thaw exposure, air entrainment is commonly required, and the needed air content depends on exposure severity and aggregate size.
Q: Can I add air entrainment to dry-cast hollow-core mixes?
A: Be careful. Some hollow-core specifications state air-entraining admixture shall not be added, noting that it is not effective in dry mix concrete.
Q: Wet-cast vs SCC: which one should you choose?
A: If your element is simple and vibration is easy, wet-cast is stable and economical. If you have dense reinforcement, thin walls, complex shapes, or surface defect pain, SCC is often the better production choice because it can fill formwork with little/no vibration and improve surface quality.
Conclusion
In the production of precast concrete components, different types of concrete have their characteristics and are suitable for different application scenarios.
Choosing the right type of concrete can not only optimize the production process but also improve the performance and aesthetics of precast components. Understanding the characteristics and applications of each type of concrete can help make wise decisions in design and production, thereby achieving the best construction results and lasting structural quality.