Tip: See my list of the 
MostThe words “concrete” and “particular” get commonly confused by English learners. Of course, we are not talking about “concrete” in the sense of “made of concrete” (the building material), as in “a concrete wall”. We are talking about “concrete” as in “a concrete example”.
Statistically speaking, if you are reading this, the word you are probably looking for is “particular”, which is about 10x as common as “concrete” in English. It is used to emphasize that you are talking about just a single individual or thing, e.g.
correct Have you already agreed on a particular date?
wrong Have you already agreed on a concrete date?
correct I couldn’t find the particular book you were talking about.
wrong I couldn’t find the concrete book you were talking about.
“Concrete”, being much less common than “particular”, is most commonly used in the sense of “tangible, real” when talking about evidence and proofs:
correct They had just a suspicion; no concrete evidence was found.
unnatural They had just a suspicion; no particular evidence was found.
or in the sense of “not abstract, specific” when talking about examples:
correct It’s too abstract; can you make it a bit more concrete?
unnatural It’s too abstract; can you make it a bit more particular?
