Filigree

[MacGruber22]

Not sure how many of you have designed slabs with the Mid-States Filigree system, but something came up that I was not aware of. For those who don't know the system, it is composite CIP concrete on 2" precast prestressed plank. Discrete blocks of insulation are placed on the plank to create somewhat of a concealed waffle slab. It's pretty cool and preferred over PT when compared to conventional CIP plates/flat slabs, where PT is not common in the local market.

Anyways, I learned via their head of engineering that they do not SSD the top of the plank in prep for the CIP topping. And, the oddest thing is that they place the bottom bars directly on the roughened plank without chairs! They insist that the SSD causes problems with bonding and that there is no consolidation/bond issues with placing the rebar on the plank. There are thousands of buildings with this system, so I guess it is working just fine. It is surprising and weird to accept as the EOR/designer of the slab - we have no choice but to go along or we would likely be fired!

What are some thoughts on this?

-Mac

 

[BAretired]

At the risk of sounding unduly ignorant, what is SSD?

BA

 

[Shotzie]

I believe SSD stands for Surface Saturated Dry, meaning that the substrate would be wetted so the surface is dry but the voids below the surface are saturated. It would be to prevent a weak interfacial zone between the substrate and overlay by preventing the substrate from absorbing mix water.

 

[MacGruber22]

Oops. Sorry about that.

Shotzie - therein lies my confusion. Every concrete document that I am aware of requires or recommends SSD for exactly the reason you state. SSD is widely preferred over slurries, bonding agents, etc. For some reason Midstate Filigree says otherwise - dry as a bone. In conversations with their engineer, he says load testing has shown there is no issue. Thus, they do all of this to save time and money.

That explanation is all well and good - But, obviously not all concrete pours are equal. Wind, Temperature, Dewpoint/Humidity, etc strongly dictate plastic properties of concrete. Windy, dry, and hot days are risky for casting, even with use of retarding admixtures and finishing aids to mitigate rapid evaporation.


-Mac

 

[Ingenuity]

This thread507-448887 has some relevant info, more in the SSD 'camp' with research data.

 

[bookowski]

If you’re working with filigree it’s worth reading through the osha report on the tropicana collapse, you can read the executive summary in 5 minutes and it will give you a sense that you should keep an eye on certain things throughout the process.

Not saying filigree is flawed, just worth having this info in mind.

https://www.osha.gov/doc/engineering/2003_10.html

 

[MacGruber22]

Thanks for the links.

-Mac