[tminima]

I noticed that the two bars were breaking differently under the hydraulic press. One was crumbling and the other (manufactured) was exploding. There was no mention of this effect in the video. It couldn't be the due to force because in the 2nd half the manufactured bar broke at a lower force. Could this factor has consequences on how manufactured sand concrete behaves with natural phenomenon (hurricanes, earthquakes, fires, etc.)

[ars]

Exploding means it was keeping its integrity for longer (i.e. not compressing), and then releasing it when it couldn't anywhere.

Crumbling means it was falling apart.

A paper book will explode in a press because it does not have any way to compress and release any of the force on it, until it releases all of it in one shot.

[kamray23]

Putting stress on the concrete requires force, and causes the concrete to deflect. Force over displacement is work, and energy can't be lost to nothingness by just breaking the concrete. Thus, the concrete releases the stored up energy as kinetic energy of its fragments.

Stronger concrete requires more stress to cause it to fail, and as such it takes more force to break it. There is logically more energy because of the higher force, so more energy gets released.