Technical Questions

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How can the adequacy of mixing be determined?

Q. How can the adequacy of mixing be determined?


A. With concrete containing normal-density aggregate and with typical air content and slump, tests on samples taken at different points in the discharge can show the degree of uniformity. With aggregates larger than 37.5 mm (1.5 in.) in nominal maximum size, it may be necessary to also check the uniformity of the mortar and of the coarse-aggregate distribution throughout the batch on samples taken from different points in the discharge. Criteria for mixer performance are given in ASTM C94, which also includes a comparison of 7-day strength tests of each sample. A large variation in air content or slump indicates either an inappropriate sequence of loading materials into the mixer or insufficient mixing.


References: SP-1(02); ACI 304R-00; ASTM C94

Topics in Concrete: Concrete Fundamentals

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