After excavation, the concrete work began. Concrete is composed of Portland cement, gravel, sand,
and water. When freshly poured, concrete is wet
and plastic. But within hours it begins to solidify,
ultimately becoming as hard as rock.
Most people call that process “drying,” but the
concrete crew foreman on my job told me that’s not
really the best choice of words. Concrete does not
simply solidify because excess water has evaporated
from the slurry. Instead, the water reacts with the
cement in a chemical process known as hydration.
The cement absorbs the water, causing it to harden
and bond the sand and pebbles together, creating
the stone-hard material we know as concrete.
FRAMING THE CONCEPT
Prior to the mid-19th century, building was an art
that took many years of apprenticeship to learn.
There were few if any building codes. Quality of work
was based largely on the personal integrity and
craftsmanship of each builder.
For 2,000 years, the most common technique for
building with wood was the method called timber
framing. Buildings of that era still exist; typically
they are barns and homes with huge wooden beams
supporting large open spaces.