sci.physics

Mike H writes:

> One side note that is kind of interesting. When pouring a tunnel and
> runway for the international airport, a local Ready-Mix provider had
> to come up with a way to place the 12" thick concrete pads while
> preventing issues with rapid curing and high heat generation creating
> cracks in the concrete as it cured. Their solution was to replace
> much of the water in the mix with liquid nitrogen.

Say what?!? Unless you're keeping liquid nitrogen under pressure or
in a flask, it's going to turn to gas quite readily and quickly. It
is doubtful that cement will do its chemical reaction with nitrogen
and the aggregate to form concrete.

> They rigged up an
> injector system that allowed a truck to back up to it, and the
> injector would inject liquid nitrogen into the concrete mix. This
> would then be mixed up and discharged into the pad. They only cracked
> the drum on two ready-mix trucks before they had things tweaked just
> right.

Perhaps the story is a bit garbled and the aggregate and cement were
cooled with liquid nitrogen before the water was added to the mix.
Adding liquid nitrogen in any substantial quantity after the water
has been added will result in one big ice cube (which won't mix well).