Diary found in empty campus blocks (5)
I believe the answer is:
clogs
'blocks' is the definition.
(clogging is a kind of blocking)
'diary found in empty campus' is the wordplay.
'diary' becomes 'log' (I've seen this before).
'found in' is an insertion indicator.
'empty' suggests removing the centre.
'campus' with its centre taken out is 'cs'.
'log' going into 'cs' is 'CLOGS'.
(Other definitions for clogs that I've seen before include "Wooden shoes" , "11 across shoes" , "Wooden-soled shoes" , "Sabots" .)