Technical Questions

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What tests are necessary or desirable in making a series of trial mixtures to arrive at a suitable mixture for a particular job?

Q. What tests are necessary or desirable in making a series of trial mixtures to arrive at a suitable mixture for a particular job?

 

A. The bulk density, air content, and temperature of the freshly mixed concrete and the hardened properties specified should be determined. With this information and the known quantities of each material used, the corrected batch quantities and the w/ cm should be calculated and tabulated. Slump tests may be made and observations recorded with regard to workability—tendency to segregate, harshness, or over-mortaring. On the basis of the corrected quantities, the proportions to use for the second trial batch can be estimated. A complete record of all trial batches will be invaluable for reference when changing the mixture to meet new conditions on the job. The record should show the actual quantities batched into the mixer and the necessary corrections to the basis of saturated-surface-dry aggregates; also, it should show the w/cm as corrected for total water, including surface water introduced with the aggregates.

 

References: SP-1(02); ACI 211.1-91

Topics in Concrete: Mixture Proportioning; Testing

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