A Successful Plant Trial for Concrete Mix Design as per ACI 211.1: How to do?

 

Recently we’ve done a successful plant trial for concrete mix design as per ACI 211.1 in our project which is one of the top megaprojects of Bangladesh. In this article, I tried to write down all the necessary things need to be done to achieve success for executing this type of work activities.

1) At first, we need to do moisture correction of fine and course aggregate accordingly to adjust the free water in the mix design. If it exceeds the quantity limit of superplasticizer as per ACI 211.1, then we need to adjust the amount of superplasticizer with water in the mix design. 

2) Then we need to produce atleast 3-4 cubic meters of concrete to observe the plant variations. 

3) Before Batching:

We should do the followings:
A) recheck the mix design calculation,

B) Make sure there is no remaining water in the plant mixture and transit mixture

C) Also admixture tank stirrer well.

4) For hot weather conditions, we must Use chilled water in the mix. 

5) Then we can Start mixing according to the mix design. Proper time (120s/2cum) should be given to all ingredients for well blending. 

6) After Batching: 

6) Now We should take out the print copy of the batch sheet to check the ingredients variations with mix design according to ASTM C94 (for Cement 1%, Aggregate 2%, Water and Admixture 3%, can be accepted + or – from the design value)

7) Fresh concrete sample should be taken to check the initial slump and temperature. We must observe the bleeding and segregation of the concrete, and record all the details in the trial mix sheet. We need to do the same after every 30min and up to the required retention period. If it is not meeting the retention and workability requirements, then adjust the admixture dosage in the subsequent trial or change the admixture or review the design again by lab trial.

8) Air content in the mix should be checked and it should be below whatever amount of air % is considered in the mix design. 

9) It is compulsory to check the unit weight or bulk density of the fresh concrete and the hardened concrete accordingly to match the results with the designed unit weight. 

10) To check the required strength in 1-day, 3-day, 7-day, 14 day & 28 day, Taking cylinders is very crucial (if used fly ash or ggbs then check 56 & 91 day strength), 01-day strength (>16%) is significant for understanding the concrete setting time and the admixture behavior. 

11) We should make some specimens for the water permeability/penetration test and chloride reactivity test (if there are concrete durability requirements). 

12) If everything meets our requirements, then we need to do the same trial at least three (03) times to check the consecutive and consistent result. To get the same trial result, need to use the same batch of cement, and admixture for all trials. 

NB: All ingredients should be tested by the independent laboratory, materials source approval must be required before performing the plant trial, and Batching Plant must be calibrated.