What is the limit of silt content in sand for concreting?

first of all take the sample of the sand and insert it into a measuring jar,then add water as per required,then add half spoon salt for better setting time.shake the jar slowly....and wait for 10...

Silt, sand, gravel, pebbles, cobbles, boulders all have sizes nominated in your favourite Dictionary of Geology. And don't forget mud.

Not more than 3%

Actually it changes ratio of cement to the other contents of concrete (Sand and crush). However an optimum percentage of cement sand and crush is decided by trial casting of concrete

Maybe you should rethink the question.... Because all I can think of is "a gag". sorry ;-)