amartial artist learns to deliver higher force than average people. But that much is not sufficient to break a pile of concrete. What he does actually is he strikes the piles in a very short time in a very small area. Since, impulse, I = F × t and this implies F = I//t. t becoming very short the force becomes very large. And as the area is small a tremendous is pressure is generated by his hand on the brick which exceeds the breaking stress and finally it breaks.
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When an amount of force is delivered with in a very short duration of time, then it makes a lot of IMPACT on the surface of the body.  This is called impulse.

Impulse defined as   Force * time duration

The time duration is usually less than 1/10 th of a second.

This  impulse is equal to change of momentum of the person's hand giving impulse. 

IT is the same principle that is making a cricket ball fly with very high speed. It is given an impact during 0.1 sec or less by the cricket bat.

Regarding the breaking down of tiles, he hits at the center of a tile. That point requires least impact, as it is most distant from either support.  The force of the hand is spread over a thin surface area of the side of the palm.  The load per unit area / width on the tile is very high.

Every material has an elastic property yield strength and ultimate strength. If the stress (force /area) is higher than these limits, the material reaches a breaking point or Fracture point.
Then it breaks at the point where the strain is maximum.

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