How to ensure that the mix ratio of concrete is effectively controlled during construction?

To ensure effective control of concrete mix ratio during construction, it is necessary to start from the whole process of raw material management, mix design, mixing production, construction pouring and quality inspection, and achieve the goal through standardized operation and refined management. The following are specific measures:

 

⛳  I. Raw material quality control

✈️1. Raw material on-site inspection

Cement: Check the brand, strength grade, stability, setting time and other indicators, send for inspection by batch, and strictly prohibit the use of expired or damp cement.
Aggregate (sand, stone): Focus on controlling grading, mud content, mud block content, and needle-like particle content. For example, the mud content of fine aggregate (sand) must be ≤3% (C30-C55 concrete), and the needle-like particle content of coarse aggregate (crushed stone) must be ≤15%.
Admixture: Check the type (such as water reducer, retarder), dosage adaptability, and provide a factory inspection report and retest qualification certificate to avoid the impact of admixture quality fluctuations on mix performance.
Mixing water: Use drinking water or non-drinking water that has passed the test to ensure that there is no pollution such as oil, acidic and alkaline substances.

✈️2. Raw material storage management

- Aggregates of different specifications are stored in separate warehouses and obvious signs are set up to avoid mixing; sand and stone yards need to be hardened and drainage facilities are set up to prevent rainwater from eroding and causing grading changes.
- Cement and admixtures need to be stored in warehouses, moisture-proof and rain-proof, and used according to the "first in, first out" principle to avoid long-term storage and failure.

 

⛳  II. Mix design and approval

✈️1. Adaptability design

- The professional laboratory will design the mix ratio according to the project requirements (such as strength grade, impermeability, durability), raw material characteristics and construction conditions (such as pumping height, pouring temperature).
- At least 3 groups of trial mixes are carried out to adjust parameters such as water-cement ratio and sand ratio to ensure that the workability (slump, cohesion), setting time and strength of the concrete mixture meet the standards.

✈️2. Approval and briefing

- The mix ratio must be approved by the project technical person in charge and the supervision unit before use.
- Before construction, conduct technical briefings to the mixing station and construction team to clarify key parameters such as the amount of each material, mixing time, and slump control range.

 

⛳  Ⅲ . Mixing production process control

✈️1. Calibration of measuring equipment

- The mixing station metering system (such as electronic scales) needs to be calibrated regularly (at least once a month), and zero-point calibration is performed before opening to ensure that the measurement error meets the standard:
- Cement, admixture: ±1%;
- Aggregate: ±2%;
- Water: ±1%.

✈️2. Standardization of mixing process

Feeding sequence: Usually the "secondary feeding method" is used (first feed aggregate, cement, and mineral admixtures, dry mix for 30 seconds, then add water and admixtures, and then mix for 90-120 seconds) to improve the homogeneity of concrete.
Mixing time: Controlled according to the mixer type, the forced mixer should be no less than 60 seconds to ensure that all materials are mixed evenly.
Real-time monitoring of slump: At least 2 tests per shift. If the slump does not meet the requirements (such as the design requirement of 180±20mm), the water consumption or admixture dosage needs to be adjusted. It is strictly forbidden to add water at will.

 

⛳  Ⅳ . Transportation and pouring process control

✈️1. Transportation process management

- Use a mixer truck for transportation. The transportation time should not exceed 1 hour (shortened in summer) to prevent excessive initial setting or slump loss of concrete.
- Keep the tank body rotating at a low speed (2-4 rpm) during transportation to avoid segregation; rotate at a high speed for 20-30 seconds before unloading to make the mixture uniform.

✈️2. Inspection before pouring

- Check the concrete strength grade, impermeability grade and other labels. It is strictly forbidden to mix concrete with different mix ratios.
- Test the slump again. If the slump does not meet the standard due to long transportation time, the water reducer of the original mix ratio can be added for adjustment (the dosage needs to be determined by test). It is strictly forbidden to add water directly.

✈️3. Casting process control

- When casting in layers, the thickness of each layer shall not exceed 500mm (pumping concrete), and the vibration time shall be controlled within 20-30 seconds to avoid segregation or honeycomb surface caused by over-vibration or missed vibration.
- Avoid casting at noon in high temperature season (temperature>30℃), and take insulation measures in low temperature season (temperature<5℃) to prevent the performance of concrete from being affected by temperature.

 

⛳  V. Quality inspection and dynamic adjustment

✈️1. Specimen preparation and inspection

- For every 100 trays (not exceeding 100m³) of concrete with the same mix ratio, make at least one set of standard curing specimens (cubes with a side length of 150mm) to test the 28-day strength; at the same time, make specimens under the same conditions to evaluate the demolding or tensioning strength.
- For concrete with anti-seepage requirements, make one group of anti-seepage test pieces (6 pieces/group) for every 500m³.

✈️2. Data analysis and adjustment

- Establish a statistical analysis account for concrete strength, compare the design value with the measured value, and if the standard deviation of strength for three consecutive groups exceeds the allowable value of the specification, the mix ratio needs to be re-optimized.
- Adjust the construction mix ratio in time according to the fluctuation of raw materials (such as changes in sand moisture content). For example, for every 1% increase in sand moisture content, it is necessary to reduce the amount of water and increase the amount of sand accordingly to keep the water-cement ratio unchanged.

 

⛳  Ⅵ. Personnel training and responsibility system

✈️1. Job training

- Provide professional training for mixing station operators and construction teams to master the key points of mix ratio control, equipment operating procedures and emergency treatment measures (such as slump abnormality adjustment methods).
- Regularly organize technical briefing meetings to convey specification updates or design change requirements.

✈️2. Responsibility to individuals

- Establish a "three-inspection system" (self-inspection, mutual inspection, and special inspection), clarify the person responsible for each process (such as the station manager, tester, and construction team leader), and sign and confirm the implementation of the mix ratio.
- Accountability for illegal operations (such as adding water without authorization and not feeding materials according to the metering) is included in performance appraisal.

 

⛳  Ⅶ . Information management means

- Introduce an intelligent mixing station management system to monitor metering data, mixing time, slump and other parameters in real time, and automatically alarm and lock the equipment when abnormal.
- Use BIM technology to simulate the concrete pouring process, optimize the construction sequence, and reduce the risk of mix ratio failure caused by process problems.

Through the above measures, the full-cycle closed-loop management of concrete mix ratio from "design-production-construction-testing" can be achieved to ensure that the concrete performance meets the design requirements and ensure the safety and durability of the engineering structure.

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