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Once excavation was complete we installed reinforcing steel.  The steel is fabricated offsite and delivered in pieces.  The contractors then use wires to tie the steel together  essentially creating a cage of steel bars which are embedded in the concrete adding tensile strength to the grade beams.  Concrete is very strong in compression, but unreliable in tension.  Steel is added to offset this weakeness.  In our case, my contractor installed Visqueen (plastic sheeting) in the trenches prior to laying the steel.  Although this was noted within my engineer’s specifications, I’m not sure it was necessary.  When I came to the site one afternoon, it was already installed and I was a bit offended by the sight.  It seems very environmentally wrong to create a plastic seal in the ground that is permanent and inaccessible.  I suppose it helps to prevent dirt and moisture from the ground from entering into the concrete mix while the beams are curing, however, in the long run it seems that water could be trapped between the sheeting and the concrete.  This would ultimately weaken the concrete over time.  Not sure.  I had to let it go.

Anyways, the engineer visited the site during this phase to insure that the steel was properly installed.  He noticed that some corner bars were missing, and so the contractor had to tie those in at the last second.