Thanks guys, Exactly as I suspected but still improper and even though it hasn't failed YET, If and when it does,My report will indicate that they were installed improperly.
Now about the material aspect of using concrete for flue liners. I would think that heat from combustion would crack the blocks, That is why clay flue liners are used. They have been fired to 850 some odd degrees higher than the heat that would ever go through them so cracking woould not be an issue.
So were these blocks a failed design or are they still used and do they hold up to the heat?