Q.: We are storing and batching our own cement and aggregates and mixing our own concrete for a large job. Some portland cement has now been stored 5 months in the silos. There isn't any testing laboratory nearby and we wonder if there is a simple test to determine whether the cement is still good. It still flows freely and is not lumpy.
A.: You have probably already made the simplest test; the fact that the cement is free-flowing and free of lumps means that it is most likely still good. Cement can be stored for an indefinite number of years if it is kept dry enough.
If you must make a more definitive test, your best bet would probably be to have a testing laboratory make a test of compressive strength on mortar cubes using ASTM method C 109. The strength should meet the requirements of ASTM C 150.