Either pretend that the circle is infact a square, then you can make collision detection alot easier, otherwise if you want you can keep the position of the ball by using the centeral point, and then check if the block is within or equal to the radius of the circle.

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Ballistic Programs

Probably the fastest way, assuming your blocks are uniform, would be to first check the ball''s center.y+radius (or whatever your variable names are) against the bottoms of the bricks. For each row, you check to see if the ball''s top ''edge'' is higher the bottoms of bricks. Then for each of those rows, check to see if the ball''s bottom ''edge'' crosses the top plane of that row. (Basically using the ball as a square for primary collision detection) Here''s where it can get a little tricky, first, check if the ball is contained entirely horizontally within each piece. If the ball''s left and right edges are contained within the piece, you have a collision. If not, probably the best way would be to check to see if the corner points of the two potential colliding bricks are contained in the circle.
(If distance(circle.center, brick.cornerpoint) <= radius)

it''s early, and this may be way off, but just a thought.