Today, we seek to cement our knowledge with
concrete understanding. The University of Houston's
College of Engineering presents this series about
the machines that make our civilization run, and
the people whose ingenuity created them.
The history of concrete is
pretty skimpy, considering how important it is.
Most accounts start with the use of gypsum plaster
in ancient Egypt. The Greeks used slaked lime, and
the Romans knew how to mix lime with sand and
volcanic tuff to make a real cement. In fact, the
Romans did some pretty fancy concrete work. The
next well-known advance was John Smeaton's
invention of a water-resistant, or hydraulic,
cement while he was rebuilding the Eddystone
Lighthouse in 1756. What we call Portland cement
was invented by another Englishman in 1824.
A Russian historian, Znachko-Iavorskii, tells a
surprising story about concrete and cement. Too
many historians of concrete have studied only
written documents. That's not where the story is.
The concrete itself survives from Roman times right
down through the ages. Znachko-Iavorskii has looked
at old concrete all over the world and found that
it's remarkably variable.
But chiefly he's found so much very good cement and
concrete that's been passed over and forgotten. He
finds highly water-resistant plasters from the 4th
century BC. He finds that egg whites, Cheshire
cheese, and sour camel cream were all used in the
Middle Ages to make cements water-resistant. He
finds a great deal of medieval, and even Roman,
concrete that would easily pass today's standards.
He tells us something historians of technology have
learned the hard way, and only during the last 50
years. The scribes of kings and emperors didn't
write down the means used by craftsmen out behind
the castle. Documentation of ancient technology is
very minimal. The word technology itself is a
modern concept. It literally means the study or
lore of technique. Engineering textbooks -- that
written lore -- are really very new.
Consequently, an art that is as base, and yet as
fundamentally important, as mixing concrete was
learned and forgotten a hundred times. Some of the
ancient hydraulic cements made from local limes in
Kiev, Riga, and St. Petersburg greatly exceed
today's strength standards. Yet it's been a
practice in those regions to bring in expensive
Portland cement, because the potential of native
materials has been forgotten.
Only in very recent times have we written down our
concrete-making techniques and made it possible to
compare, judge, and improve them. By making
concrete work into a technology, we've only
recently jumped to the point where we can do things
with concrete that would've been unthinkable in the
ancient world.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds
work.
(Theme music)
