Agreed, maybe an even harder one to go with it so we can use the harder version for bunkers and the normal version for just ordinary buildings.
I've always used breakable metal in all of my builds but just one accidental spark messes up the entire thing, I tried wood but it doesn't react to pressure.
Maybe they can make wood fracture then break under high pressure.

the concrete when in contact with water should harden

What's about Insulator but what conduct electricity? Not wall, because it is big

i really think that we should have heater/cooler

solid objects(not powder) to build rockets cars

THE5
Solid Stone and/or Solid Concrete

Yeah, i had similar thoughts.
We need some element that will be like breakable metal, but not conductive.
Let's call it "concrete". Under high pressure it will crush into stone-powder. Under high temperatures will melt into lava.

[Assuming you mean something like rigid bodies.]
The engine can't do this I am shure.
It would have to calculate the position of one particle dependent on the position of a Parent particle.
It does not seem something like that would be in the code already and coding it into the existing engine would probably result in some extremely slow calculating, unusable cloud of particles that does not behave physically correct at all.

EDIT: This might be one of these suggestions noone realy needs but a Acid-like-Gas would be fun aswell.
( I hope my previous suggestion does not get lost D: )

EDIT2:
I might code these myself but 1stly I don't know what document it is that needs to be changed (see wiki) and 2ndly others shurely can do it way faster.

Can suggestions for current elements go here? I would like a little eye on the stickman so I can tell where he's pointing.

THE5
It's powder.c, and it won't take long to do it yourself.

Add Virus Virus + Stickman =