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(Concrete Mix Design as per ACI 211.1)
To begin, perform moisture correction on the fine and coarse aggregates, then adjust the free water in the mix design accordingly. Also, adjust the quantity of superplasticizer along with the water in the mix design.
Produce 3-4 cubic meters of concrete to monitor plant variations.
Prior to batching: a) Double-check the mix design calculations, b) ensure that there is no residual water in the plant mixture and transit mixture, and c) ensure that the admixture is well stirred in the tank.
Incorporate chilled water into the mix (for hot weather conditions).
Initiate mixing as per the mix design and allow sufficient time (120 seconds per 2 cubic meters) for all components to blend effectively.
Following batching: Retrieve a printed copy of the batch sheet and compare ingredient variations with the mix design according to ASTM C94 standards. Deviations of + or - 1% for Cement, 2% for Aggregates, and 3% for both Water and Admixture from the design values are acceptable.
7. Extract a fresh concrete sample, assess the initial slump and temperature, observe concrete bleeding and segregation, and document all particulars in the trial mix sheet. Repeat these steps every 30 minutes and continue until the necessary retention period is reached. If the mixture fails to meet retention and workability criteria, then modify the admixture dosage in the following trial, consider altering the chemical admixture, or reevaluate the design through laboratory trials.
8. Verify the air content within the mixture, ensuring it remains below the specified percentage of air as designated in the mix design.
9. Examine the unit weight or bulk density of both the fresh and hardened concrete. Ensure that the outcomes align with the intended unit weight from the design.
10. Obtain cylinders to assess the necessary strength at intervals of 1 day, 3 days, 7 days, 14 days, and 28 days (if fly ash or ggbs is used, also assess at 56 and 91 days). The strength at 1 day (>16%) is crucial for comprehending concrete setting time and the behavior of the admixture.
11. Prior to aggregate selection, assess the potential for Alkali-Silica Reaction (ASR). Additionally, create concrete specimens for the water permeability/penetration test and the Rapid Chloride Permeability Test (RCPT) if specific durability requirements are in place.
12. If all criteria are met, repeat the trial a minimum of three (03) times to ensure consecutive and consistent results. To attain uniform trial outcomes, employ the same batch of cement and admixture for all trials.
Note: All ingredients must undergo testing by an independent laboratory. Approval of material sources is essential before conducting plant trials, and the Batching Plant must be calibrated.
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