Bricks and cinder blocks are relatively easy to break since, as with most martial arts breaking, they are broken by exploiting their weakness, not their strengths. The strength of bricks and blocks come from their compression strength when stacked. They are not intended to be supported at the ends while having force applied to the midpoint of the span. Bricks and blocks gain strength from their aggregate, not from their base material. Bricks contain sand, cinder blocks contain cinder (smaller in size than sand), and concrete may contain anything from sand, to gravel, to rebar.
Sometimes there is a confusion about the differences between something that is hard and something that is brittle. Something may be hard not be brittle, such as steel. Hit steel with a hammer and nothing happens. Something may be hard but also be brittle, such a diamond. Hit a diamond with a hammer and the diamond shatters. Bricks and cinder blocks are brittle.