Crossword Genius

Real obstacle to creating common building material (8,5)

Ross

I believe the answer is:

concrete block

I'm a little stuck... Click here to teach me more about this clue!

'obstacle to creating common building material' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'real' is the wordplay.
I cannot really understand how this works, but
'real' could be 'concrete' (similar in meaning) and 'concrete' is found within the answer.
The remaining letters 'block' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?

I've seen this clue in The Irish Times.
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