07 October 2010

How Firm a Foundation

Got up really early this morning.  They were going to get started around 05:30 and I wanted to watch so I took half a day vacation from work.  When I got there a cement truck was leaving and this is what I saw.
Everyone standing around.  It looked as if  most of the foundation poured and they were waiting for the rest of the trucks to arrive and finish up. 

I walked around and checked everything out, nodding my head in approval as I went along.   Had to make sure everything looked satisfactory you know; like I would be able to tell. 

I practiced what little Spanish I knew and asked around for el jefe.  This is Roberto.

This is the first time I have watched the foundation being poured and C. had told me about this new cable system that they were using in lieu of all of the rebar.  Roberto was very kind and answered any questions I had.  Especially about all of this business...

See these cables?  They're contained in a purple heavy duty plastic sheath to keep the cables from corroding.  I guess the sheaths come in other lovely colors, but I like the purple, don't you?

Instead of the traditional rebar reinforcement that is normally used when pouring a slab, we are having a Post-Tensioned concrete slab poured.  A post-tensioned slab puts the slab in tension after the concrete has cured.  It minimizes cracking and makes a stronger foundation.

After testing the soil in our area the geotechnical guys come up with specifications for our slab.  The plastic sheathed cables are laid out in the same grid that rebar normally is.  They are held secure and kept at a certain depth by positioning tools called "chairs".  The cables are run through the forms like this.

The concrete is poured and after it has hardened to 75% of its strength,

the cables are pulled, or post-tensioned, with a hydraulic jack to a force of 25,000 psi; then the ends of the cables are anchored and the concrete is left to harden completely.  I'm disappointed I wasn't able to get back out to the site to watch that part, but a girl's gotta work, you know!

After my education from Roberto the rest of the trucks came rolling in.  They brought in 13 trucks in all. 

All of those guys just standing around earlier came alive and started working like a hive of bees.

 The guy in the white hoodie seemed to be the communicator with the truck drivers on which way to move the big chute that the concrete came pouring out of.

 The last of the 13 trucks backing into position

Whew!  I got really tired watching these guys work.  They did not stop for the rest of the time I was there.  They have a really hard job and I was very impressed.

And I thank them for our foundation!

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