In Hong Kong.
Know nothing formal about concrete.
Choose any two.

Email letter should happen sometime for those 'subscribed'- too busy so far.
Having our fares all cancelled one day out and having to rebook whole
trip helped increase the fun level.
Anon.
Snippets - worth what you paid for them Accuracy variable.YMMV.

CO2 increases concrete strength by converting it back to the Calcium
Carbonate it started out as.
Airborne CO2 does this over decades.

Romans made stuff from burned limestone that wasn't concrete. Some
structures made with this still remain. The great discovery was that
adding fly-ash made a vast difference to the properties.

Many Roman structures were concrete with brick being added as facings
for cosmetic appearance. Much of the Colosseum is concrete.

Roman bricks have an aspect ratio that offends my sense of how a brick
should look. Much longer and thinner than the current norm.

WW2 concrete structures will now be around 60-70 years old. Those
remaining here seem very solid but with surface degradation. Load
bearing structures no doubt a different matter.

We have a large road viaduct that carries the busiest section of the
NZ highway system across a city shopping area. Mayhaps 40-50 years
old. It's mechanically worn out and due for replacement. Looks fine to
the uninitiated eye.

Concrete has about zero tensile strength. Pull on the cement glue that
holds all the rocks and sand to eac other and it crumbles. Push on it
and you force the parts together iup to a limit. SO concrete in
tension can be thought of as a means of resisting the tension of the
reinforcing material which does the actual structural work.

Carl and others expert may now tear this apart :-).

    Russell
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist