What is the appropriate mixing ratio of sand, cement and aggregates in the construction of a reinforced concrete column?

It all depends on the load-bearing

• 1 means are binding materials (cement)
• 1.5 means are fine aggregate (sand)
• 3 means are coarse aggregate( stone chips)

1 ratio sand3 aggragates5 ratio of cement

Its depend upon the mix requirement and fine to coarse curve as per ASTM finally for the Columns it is prefer to have fine mix rather than coarse mix

check grade of concrete specified for column, after knowing the grade of concrete you know required characteristics strength.. now you can follow guidelines for concrete mix to design concrete for particular strength, whatever you are doing take help of locally available concrete professional. 

Defend on design strength of column