You could quantify the scale effect in brittle materials using the models by Prof. Bazant. There is a great deal of research on size effects in quasi-brittle material, I would suggest to start from the following review paper, " Bažant, Z.P., 1999. Size effect on structural strength: a review. Archive of applied Mechanics, 69(9), pp.703-725. "
Lorenzo Del Giudice Many thanks for your reply. If i'm not mistaken, the procedure put forward by Professor Bažant is mostly applicable to flexure-induced tension not direct tension. I was wondering if the procedure can be modified to apply it to direct tension.