Management And Control Of Concrete Mixing Plant Production Systems

The management and control process includes various aspects such as raw materials, mix design and control, production, transportation control, and delivery inspection and sampling. Currently, many ready-mix concrete plant managers lack professional knowledge and quality awareness, and do not have sufficient understanding of the concrete industry and concrete products.  Equipment selection and professional configuration are inadequate, measuring instruments are inaccurate, and some even fail to conduct any inspections, or even use volume ratios for measurement. They are unfamiliar with modern computer-based office methods and treat concrete production as a traditional, simple, and ordinary building material, solely pursuing profit maximization without seriously implementing standards and specifications, engaging in fraudulent practices and substituting inferior materials for quality ones, ultimately leading to compromised concrete quality and engineering quality accidents.

1. Control of Raw Materials: The quality of raw materials directly affects the quality of concrete. Strict screening and inspection of materials upon arrival are crucial. Substandard raw materials must not be allowed into the mixing plant.

2. Cement: Ready-mix concrete should primarily use cement from large-scale rotary kiln cement manufacturers with guaranteed quality and good reputation in the local area. During procurement, strict control should be exercised to ensure that all three certificates for the cement are complete, and according to regulations, concrete setting time, stability, and strength indicators should be re-tested in batches to ensure cement quality. 1.1.2 Coarse and Fine Aggregates: High-quality sand and gravel should be used to mix concrete. Using larger aggregate sizes can improve concrete strength. While the unit price of sand and gravel may increase, the concrete strength and strength guarantee rate are significantly improved. Therefore, under the same strength and strength guarantee rate, the amount of cement and admixture components can be reduced, and the cost of concrete mixed materials is often lower than using inferior sand and gravel.

3. Water: Drinking water is generally used for mixing ready-mix concrete. If non-drinking water sources are used, they should be tested beforehand or regularly to ensure compliance with regulations. If they meet the standards, further concrete tests should be conducted to determine their suitability.

4. Admixtures: The types of mineral admixtures include: ground fly ash, ground slag, ground natural zeolite, and silica fume and their composites. To ensure the effective content of admixtures, the concentration of liquid admixtures should be strictly tested. When changing the type of admixture, the residue in the admixture storage tank and measuring instruments must be thoroughly cleaned. Currently, most expansion agents used are in powder form and require large dosages.  Ideally, a dedicated silo should be used for the expansion agent, along with cement and mineral admixtures, and all should be cumulatively measured within the same metering system. Various chemical admixtures should be sampled and tested in batches according to relevant standards to verify their main physical properties in concrete.  Adaptability tests should also be conducted with different types and batches of cement and mineral admixtures. 1.2. Mix Proportion Design and Control: The scientific mix proportion design of ready-mixed concrete reflects the technical strength of concrete production. Operators should prioritize serving the next process. Mix proportion design should consider the difficulties at the construction site. Concrete production should carefully study the mix proportion design based on the problems reported by the construction unit, find patterns through experiments, and make the mix proportion more scientific and reasonable to ensure smoother construction. Concrete is characterized by the diversity of materials and the series of strengths. Generally, based on the cement strength grade, coarse and fine aggregate gradation, and admixture type, several water-cement ratios with appropriate intervals can be initially designed for a series of mix proportion tests. The water-cement ratio corresponding to the selected concrete strength is determined, and the mix proportion is adjusted and trial-mixed. If the workability of the concrete mixture after trial mixing meets the requirements, it can be selected as the final mix proportion. To control the concrete mix proportion, a sample of the concrete mixture should be taken once per shift for each concrete mix proportion for concrete mix proportion analysis testing.

5. Production and Transportation Process Control: Technical personnel input the construction mix proportion into the mixing control computer. For each mix proportion, a trial batch should be mixed first to measure the slump of the concrete mixture and observe its cohesiveness and water retention, evaluating whether its workability meets the requirements. If it does not meet the requirements, adjustments should be made until it does. After approval by the operator and technical personnel, formal mixing and production can begin.

6. Metering: Metering is a critical link. In addition to reliable equipment and regular inspections, operators and quality control personnel should strengthen monitoring, analyze printed reports, and investigate and eliminate the cause of any errors that exceed the allowable range or show continuous or stable positive or negative deviations.

7. Mixing: Mixing is the core link of the entire production process. Any small error or mistake in this link will cause problems for subsequent processes. The names and specifications of various raw materials should be clearly marked on the control panel in the control room. Clear and concise markings on the control panel facilitate identification by workers. Simultaneously, strengthen the professional skills training of workers and cultivate the habit of verification and self-correction.

8. Transportation:  Based on site conditions, reasonably allocate vehicles and control departure times to avoid vehicle congestion while ensuring a continuous supply of concrete and guaranteeing the quality of concrete construction. Before loading the concrete, any accumulated water in the mixer drum must be drained. The drum must be kept rotating continuously during transportation to maintain the workability of the concrete. The time of entry into the pump should be controlled according to the temperature and concrete properties.  Adding water arbitrarily during transportation and pumping is strictly prohibited.

9. Delivery Inspection: After the concrete is delivered to the construction site, its type, grade, and quantity should be confirmed according to the delivery order, and a delivery inspection should be carried out according to regulations. To adapt to changing conditions, the slump and retardation time of the concrete mixture should be controlled, and measures such as adding retarders and secondary addition of water-reducing agents should be taken as needed. The scope of secondary addition of water-reducing agents must be determined to ensure uniform distribution of the admixture.