On Mon, 11 Jul 2005 19:05:03 GMT, Nick Hull wrote:
In article ,
RoyJ wrote:

Problem with concrete blocks is that they crumble at unexpected times
and do it in a total failure mode.

If that were really true no one would use them for the foundation of
their house.

Not really. In their intended use, the loads are very evenly
distributed. Setting the weight of part of a car on a small point on
the block is a very different stress.

In fact, when the ground slides and concrete block
foundations crack, they almost invariably crack in a zigzag line of the
mortar. If you are afraid to go under a vehicle PROPERLY supported by
concrete blocks, how do you get the courage to go into your house and
how do people manage to live & sleep in mobile homes supported by the
flimsiest of concrete block stacks?

Well, put it this way. When we block up a car for an extrication in the
firefighting world, we use wood cribbing. Cranes, as mentioned, use
wood cribbing. Cement block for building, wood for cribbing. If
there's a standard material for a purpose, why not use it?
The load that a house puts on block is very even, and all compression.
If your car puts a point load on the concrete, it puts a tension load on
either side of that contact, and concrete stinks in tension.

Since it's a matter of putting your body under it, I'll go with what has
been used for a few millennia, myself.