Dear reader we are discussing about ASTM specification for fine aggregate for concrete. In case of concrete mix design, the designer assumed some parameter like fineness modulus (as relevant in this post) etc. They assume a fineness modulus for concrete proportioning considering a source of fine aggregate available in desired location.
Now do you think, assumed fineness modulus can be maintained throughout the full shipment for particular grade of concrete for desired member? We know concrete proportioning is changed significantly depending on strength, workability, durability etc.
To explain this topic we have to know about base fineness modulus. We have discussed about fineness modulus, base fineness modulus are determined from former tests, but if there have no data from previous test, it is measured taking average values of fineness modulus of first ten aggregate samples on the sequence. When less than ten samples are tested, average is taken from all preceding fineness modulus values.
Specifier or purchaser continues shipment of desired fine aggregate from a selected source, only when difference between fineness modulus and base fineness modulus is within 0.20. They have authority to reject or approve fine aggregate depending on base fineness modulus.
But when shipment from a source, however, has to continue, depending on difference between two values, suitable adjustment should be conducted in mix proportioning to maintain desired properties of concrete.