Concrete batching plant is one of the core links of construction projects. The efficiency and uniformity of its mixing process directly determine the quality of concrete. However, the mixing time is not fixed, but is affected by a combination of factors. In construction projects, reasonable control of mixing time is the key to ensuring the strength and durability of concrete.
Different projects and construction conditions have different requirements for the time of concrete mixing. Therefore, understanding the factors affecting the mixing time and arranging the mixing time reasonably can not only improve the efficiency of the project, but also effectively reduce the waste of resources.
The proportion of concrete, the type and amount of admixtures can directly affect the mixing time. Different types of concrete have different requirements for mixing time. For example, high-performance concrete may require longer mixing time to ensure that the components are fully mixed and evenly mixed. When adding more cement or finer aggregates, it takes longer to ensure full mixing and even mixing.
The type and capacity of the mixer are important factors affecting the mixing time of concrete. Common types of mixers include forced mixers and self-falling mixers. Forced mixers usually require shorter mixing time and can mix concrete more quickly. Self-falling mixers, by comparison, require longer time to ensure the uniformity of concrete.
Because small-capacity mixers mix less each time, operators may need to load and unload more frequently, which usually takes longer; large-capacity mixers can mix more concrete at one time, so the time required for each mixing is relatively short. In addition, high-performance mixers can also shorten the mixing time because they usually have higher mixing efficiency and better mixing uniformity.
Ambient temperature and humidity will also affect the mixing time. In hot weather, water evaporates faster, which may lead to a decrease in its workability and require longer mixing time; in low-temperature environments, the water in concrete is easy to freeze, and it may take longer to complete uniform mixing during the mixing process.
The mix design of water-cement ratio, sand ratio, and admixtures will affect its workability and setting time. A lower water-cement ratio or the use of retarders will prolong the setting time of concrete and require a longer mixing time.
Before mixing, the length of time for raw material preparation, inspection and preheating depends on the automation level of the cement batching plant and the proficiency of the operator; in the actual mixing process, the mixing time of different formulas and models will vary, and the best time can be determined through experiments; after mixing, the length of the processing time also depends on the automation level and operating specifications of the mixing station, such as the outbound detection and adjustment of concrete and the cleaning of precast concrete batching plant.
Various countries and regions have made clear regulations on the mixing time of different types of concrete. For standard concrete mixes, the mixing time is about 2 to 5 minutes. If a forced mixer is used, the concrete may be fully mixed and evenly mixed within 2 minutes; my country’s “Concrete Structure Engineering Construction Quality Acceptance Code” stipulates that the mixing time of ordinary concrete should not be less than 90 seconds. For concrete that requires high strength or special performance, it may be necessary to determine the best mixing time through trial mixing to ensure that its performance meets the requirements.
The structure, mixing method, production capacity and other aspects of belt-type concrete batch plant and concrete bucket-type batch plant are different, resulting in obvious differences in time efficiency, which is mainly reflected in the batching, mixing, unloading and cleaning links.
Take HZS50 and HZS120 as examples for analysis：
| Model | HZS50 bucket batching Plant | HZS50 belt batching plant |
| Mixing time | 1~1.5min | 1.5~2min |
| Batching Time | 2~3min | 2~3min |
| Unloading time | 1~1.5min | 1~2min |
| Cleaning time | 2~3min | 3~5min |
| Model | HZS120 belt batching plant | HZS120 bucket batching plant |
| Mixing time | 2~3min | 2~2.5min |
| Batching Time | 3~5min | 3~4min |
| Unloading time | 2~3min | 1.5~2min |
| Cleaning time | 5~8min | 3~5min |
The length of concrete mixing time is directly related to the uniformity, strength, durability, frost resistance and impermeability of concrete. Insufficient or too long mixing time will have an adverse effect on the quality of concrete; reasonable mixing time can ensure that the various components of concrete are fully mixed, so as to exert their best performance.
The uniformity of concrete refers to the uniformity of the distribution of cement, aggregate, water and other additives in concrete. Too short mixing time will lead to uneven mixing of the various components of concrete, and the cement paste cannot fully wrap the aggregate, resulting in inconsistent concrete strength and performance. Although too long mixing time can improve the uniformity of concrete, it may also lead to aggravated segregation and bleeding. Appropriate mixing time can ensure that the various components of concrete are fully mixed to form a uniform concrete mixture and improve the overall performance of concrete.
Due to insufficient mixing time and incomplete cement hydration reaction, the early and late strength of concrete will be affected. If the cement hydration reaction is incomplete, the cement and aggregate in the concrete cannot be fully combined, which will lead to reduced strength. Too long a mixing time may cause excessive hydration of cement, reduce the bonding force between cement particles and aggregates, and may also cause excessive expansion or destruction of cement crystals, resulting in cracks on the concrete surface, which may cause the soft aggregates to break or fall off, affecting the aggregate gradation of concrete and resulting in uneven strength.
Too short a mixing time may lead to uneven internal components of concrete, which is prone to capillary pores. There are more pores and weak areas inside the uneven concrete, which are easily eroded by the external environment, thus affecting the durability of concrete. The uniform and dense internal structure of concrete can effectively resist the erosion of the external environment and extend the service life of the building. Especially in cold areas or in environments exposed to corrosive media, the durability of concrete is very important.
Too short a mixing time may cause the concrete to be not dense enough, with too many pores, and easily damaged by freeze-thaw cycles. Too long a mixing time may cause the cement to hydrate too quickly, and the structure between cement particles may not be stable enough, reducing frost resistance. To ensure the frost resistance and impermeability of concrete, the mixing time should be kept within a reasonable range to obtain a uniform and dense concrete structure.
Choose an energy-efficient mixing host, such as a forced mixer, which can force mixing through blades to mix concrete more evenly, especially in large-scale production, which can significantly improve mixing efficiency. At the same time, the capacity of the mixer should match the construction scale. It is necessary to select the appropriate mixer capacity according to the specific needs of the project to avoid inefficiency caused by too large or too small equipment. In addition to the mixing host, the concrete mixer plant should be reasonably configured, including the mixing main building, material weighing system, conveying system, etc., to ensure smooth connection of all links and reduce waiting time.
The ratio of cement and water and the particle size of aggregates have a great influence on mixing efficiency. Too much water will cause the concrete to be too thin and difficult to mix, while too little water will cause the concrete to be dry and hard and unevenly mixed. When the aggregate particles are large or the particle size distribution is uneven, the mixing effect will also be poor.
According to the engineering requirements and material properties, the concrete mix ratio is accurately calculated and optimized to ensure the accurate proportion of each component material, cement, aggregate, water, admixture, etc., and reduce the difficulty and time of mixing. By using a high-precision electronic scale to weigh materials, the weighing accuracy is improved and the error is reduced. At the same time, adding admixtures such as high-efficiency water reducer or fluidizing agent can significantly improve the workability of concrete, make concrete easier to flow during mixing, enhance the strength and durability of concrete, and improve the overall construction quality.
Optimizing the operation process of the stationary concrete batching plant can improve the overall production efficiency. It is necessary to comprehensively sort out and optimize the operation process of the mixing station to ensure smooth connection between each process and avoid waiting and stagnation between processes. And adopt an advanced production planning management system, implement 5S management, keep the work site clean and orderly, track production progress in real time, flexibly adjust the production plan, and ensure the efficiency and flexibility of production.
Automation and intelligent technology can effectively improve the efficiency of concrete mixing. By introducing an automated control system, the automated operation of material proportioning, feeding, mixing, discharging and other processes can be realized, reducing manual intervention and improving accuracy and efficiency. Using an intelligent monitoring system, real-time monitoring of key parameters such as temperature, humidity, slump and so on in the mixing process, timely adjusting mixing parameters to ensure stable concrete quality, developing an intelligent diagnostic system to monitor key indicators such as concrete proportion, mixing time and temperature in real time, predicting faults and performing maintenance in advance, thereby ensuring the efficiency and accuracy of the mixing process.
Regularly maintain and service the ready mixed concrete, regularly check the key components of the mixer such as blades, liners, transmission devices, and replace worn parts in time to ensure that the equipment is in the best working condition. Clean up the concrete residue inside the mixer to prevent agglomeration from affecting the mixing effect. Establish an equipment failure early warning mechanism to promptly detect and deal with potential problems and avoid production interruptions caused by equipment failure.
Improving the skills and work efficiency of operators can also help improve mixing efficiency. Regular professional skills training should be conducted for operators of rmc plants to improve their ability in equipment operation, maintenance, quality control, etc., and reduce inefficiency caused by improper operation. Cultivate the energy-saving awareness of operators to avoid unnecessary energy waste. Strengthen safety awareness education to ensure that operators work efficiently under the premise of complying with safety regulations. At the same time, strengthening on-site management to ensure that all links are coordinated and orderly is also the key to improving mixing efficiency.
The time required for precast concrete batching plant to mix concrete is affected by many factors, including concrete formula, mixing equipment performance, operator proficiency, and environmental conditions. Reasonable mixing time can ensure the uniformity, workability, strength and durability of concrete. In order to improve mixing efficiency and quality, construction companies need to start from multiple aspects such as equipment, technology and management. By selecting efficient equipment, optimizing process flow, introducing new technologies and strengthening personnel management, mixing efficiency can be significantly improved while ensuring concrete quality. In actual projects, mixing time should be scientifically controlled according to specific conditions to improve project efficiency.
