It really looks to me that the lower foundation was poured, or mixed I should say because, it looks like it was mixed in a potable cment mixer, the mix was poor with too much sand and gravel. Then the block was added on top. The resulting joint has leaked over the years and caused the poured concrete to deteriorate. Adding a bonding agent and resurfacing may help as far as appearance but you may have to attack the exterior below grade to actually stop water from entering. I would get a lisenced mason over there to take a look.