In producing precast concrete components, accurate selection of concrete types and proportions is the key to improving production efficiency and ensuring product quality. Due to the significant differences in the purpose, structural shape and use environment of precast concrete components, the specific requirements for concrete performance are also different, and targeted adjustments and optimizations need to be made according to actual conditions.
Whether it is a load-bearing wall panel, beam-column, or a decorative facade, each prefabricated component must accurately select 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 set the various performance indicators of the concrete accurately.
Wet Poured Concrete
Wet-cast concrete is a common process in the production of precast concrete components. It is widely used in the manufacture of various precast components such as wall panels, TT panels, beams, columns, and stairs. These components are usually formed in a mold, poured with concrete through a traditional hopper, and compacted using a vibrating device to ensure the compactness and uniformity of the concrete. The compressive strength of wet-cast concrete is generally between 20-60 MPa, with good mechanical properties, which is very suitable for the production of load-bearing components.
However, with the continuous development of precast concrete technology, self-compacting concrete (SCC) has gradually become the preferred material for modern precast plants. Self-compacting concrete can automatically flow and fill all corners in the formwork without vibration, achieving self-compacting. This material not only simplifies the production process and reduces manual operations, but also improves production efficiency and component quality. It is especially suitable for the production of complex-shaped components or areas with dense steel bars.
Dry Mix Concrete
Dry-mix concrete is widely used in the production of precast components such as hollow-core slabs. The core of dry-mix concrete is to ensure the stability of fresh concrete. In addition, the adhesion between prestressed steel strands and concrete is also extremely critical, which depends on good compaction and precise concrete mix ratio. A major advantage of dry-mix concrete is that it can achieve higher compressive strength with lower cement dosage, but the amount and quality of its adhesive will directly affect the performance of concrete, especially the early strength (demolding strength), so special attention needs to be paid. Normally, the demolding time of precast components produced with dry-mix concrete is generally between 5 and 24 hours.
Self-compacting Concrete
Self-compacting concrete (SCC) is a new type of concrete material that can be poured and compacted without vibration. It has excellent fluidity and can fill the formwork and achieve complete compaction even in areas with dense reinforcement. After hardening, the self-compacting concrete has a uniform and dense texture, and its engineering performance and durability are comparable to those of traditional vibrated concrete.
In recent years, self-compacting concrete has been increasingly used in the precast concrete industry, especially for the production of complex geometries and thin precast components. In these scenarios, traditional concrete often fails to meet the requirements due to its difficulty in compaction, while self-compacting concrete performs well. In addition, self-compacting concrete also has significant environmental advantages and can effectively reduce noise and vibration during construction.
High Strength and Ultra-High Performance Concrete
High-strength and ultra-high-performance concrete are 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 subjected to high mechanical and chemical loads, such as industrial floors, sewage treatment plants, and hydroelectric power plants.
External Facade Concrete
Facade concrete is mainly used for the decoration and protection of building facades, and its surface appearance is a key factor in determining the concrete mix ratio. In particular, colored facade concrete has extremely high requirements for the cleanliness of production equipment. Mixers and transport hoppers must be cleaned regularly, and many factories even set up special facade concrete mixing stations.
The cement color commonly used for facade concrete is white or gray, or a mixture of the two. In the mix ratio, additives such as fly ash are generally not recommended because they may cause uneven color, especially in cold climates, which will affect the durability of concrete. The aggregates used in facade concrete are conventional aggregates, but the amount is usually large, and the color of the exterior wall surface is often achieved by mixing different aggregates. The grading of aggregates depends on the surface treatment process. For example, the depth of the washed concrete surface will limit the particle size of the aggregate.
In order to achieve a specific surface color, pigments can be added, or colored aggregates with white cement as the main component can be selected. In addition, these two methods can be flexibly combined to meet more complex color requirements
