Shotcrete and Bonding Agent 1

[Engrman]

I was called in to look at a 5 yr old commercial structure, one story 60'x84' with a basement. Flat site except for west side which slopes up (vehicle traffic surcharge on east and south sides). Wood framed roof and walls, 2-1/2" conc. slab on mtl deck and bar joists at ground level. Basement slab is SOG. Floor-to-floor hgt = 11'-0". Soils report says at rest EFP = 45pcf. The fdn wall is 8" thick reinf w/ #4 at 24" oc, centered (d=4"). Not surprisingly, every wall has a mid-height horizontal crack. The engineer who designed it has had his license revoked for other, even worse designs. My plan is to shotcrete a sister wall on the inside. I need bond btwn existing and new. I am specifying the existing surface to be roughened to proper amplitude but is there a additive that can be used to increase bond? Maybe a latex modifier?

 

[SlideRuleEra]

Bonding agents that work with shotcrete are manufactured, here is a link to a typical product

http://www.targetproducts.com/catalog/specsheets/polymer.pdf

...but they may not really be needed. See Question & Answer #6 and #29 at this link

http://www.shotcrete.org/ASAfaqs.htm#Q6

http://www.SlideRuleEra.net

 

[BigH]

Agree with SRE on his second paragraph. We recently used the wet mix method using accelerator at the nozzle and sprayed on rock using less than ideal spraying techniques. Did some coring for the interface and it was excellent bond.

 

[Engrman]

Thanks SRE and BigH. Good info.

 

[BigH]

Engrman - just a reminder: you'll want to be sure you have the concrete scaled (cleaned) well before you spray.

 

[Jabson]

City of Seattle has learned alot using shotcrete in sturcural aplications, and we have found that the bond between exisiting roughened concrete and new shotcrete is exceptional, and does not require additional bonding agents. The shotcrete paste is literally 'blasted' into the microcracks in the exisiting concrete, with bond tests exceeding expectations.

 

[BigH]

Jabson - good backup case history - thanks!