Welcome to the Forum Broloco:
The sand is probably from the blocks as they are spalling. Rake out any loose residue and fill it back with concrete mix (sackreet) applied as dry as possible and rubbed over with a damp sponge trowel several times while it is curing. This will keep down the cracks around the concrete as it shrinks and cures.
The problem is most likely from too much ground water. You may need to install gutters, fill in with dirt around the outside sloping away from the house, maybe even a French drain at the top of the dirt against the foundation. Anything to get the water away from the house.