Truth about Truth, whether it is about mathematics or any other sciences must be the same always. So I didn't consider mathematics here. If we verify mathematics closely we can understand that it deals with abstract ideas though it seems to be concrete.
From a very lower level we can say truth is concrete. They (most facts) exist for a short time; our senses help to perceive so. But truth is/must be immutable.
Since these concrete 'things' undergo changes, we cannot treat them as truth. So the only thing we can do is to imagine that. That means, we can only say that truth is abstract.
But when in the case of the Ultimate Truth, it is beyond these two. The Ultimate Truth transcends concreteness and abstractness. It can't exclude your self/our self. The proof is, Truth can be realized. And there were/are many living examples who realized the Truth.
Sometimes we say 'Now I understand the truth'. Since understanding is a mental process only, we can't say so actually. The greatest wonder is, we (most men) are ignorant about that--the thing that is beyond concreteness and abstractness. We can think only of a concrete thing or an abstract thing.
If Truth is abstract,
'Concreteness produced from Abstractness'....There is something illogical. Then we will be compelled to say every thing is abstract.
You will get some explanations from this article.