Real force applied to concrete (7)
I believe the answer is:
factual
'concrete' is the definition.
('factual' can be similar in meaning to 'concrete')
'real force applied' is the wordplay.
I cannot really see how this works, but
'real' could be 'actual' ('actual' can be similar in meaning to 'real') and 'actual' is found within the answer.
'force' could be 'f' (symbol used in Physics e.g. f=ma) and 'f' is found within the answer.
No letters remain.
This explanation may well be incorrect...
'to' is the link.
Can you help me to learn more?
(Other definitions for factual that I've seen before include "Based on things known to be true" , "Based on real events" , "Relating to reality" , "Related to the truth" , "like a TV documentary?" .)