API 686 Preparation for Grout

[Alexthegreat]

Hi All,

A contentious one I have seen multiple time on projects is the application of API 686, 3.6.2 "A minimum of 25mm of concrete must be removed in this chipping process". Previously we have engaged concrete consultants who wrote memorandums explaining that the intention should be to get rid of laitance to the requirement of the grout supplier surface roughness in order to achieve the grouts properties as stated.

However i see in ACI 351.1 Cl 6.2.3 that this 25mm for epoxy grout and 6mm for cementitious grout is not only for laitance but to manage the thermal expansion of the epoxy grout.

Does anyone have evidence this is required? typically here in Australia we scabble and grout without thinking too hard.

 

[HTURKAK]

AFAIK , the concrete surfaces should be chipped to a roughness that produces aggregate exposure and almost half of that exposed aggregate should shear.
Epoxies have a much higher coeff. of thermal expansion and concrete has a tendency to restrain the expansion of the epoxy and causes severe shear stresses at the interface when temperature changes . If necessary, peripheral dowels should be provided to grab the epoxy grout and avoid the edge lift .
IMO,the concrete surfaces should be chipped to provide a minimum of 25 mm thk. epoxy grout thk.



According to the grace of God which is given
unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon. . . .
I Corinthians 3:10

 

[Alexthegreat]

How have you chipped the concrete surface down in the past? I have come from jobs with mechanical dynamic equipment like compressors which are 6mx20m in size so it is completely impractical to chip that much concrete down and also the flowability of the grout would be a major concern if we were to leave it super granular (if we use a 20mm stone concrete stay 10mm variability of roughness). In the past we have just used a 5 Head Scabbler to mill down the surface to rough finish (approx. 5-10mm depth but the surface is maybe 3-5mm variability). We always leave concrete 30mm down from equipment base plate height so you end up with 20-40mm thick grout depending on how accurately the concrete was finished, how accurately the equipment was installed and if any adjustments to equipment was required.

 

[HTURKAK]

I do not have any idea if the concrete is new freshly poured , old or , contaminated .My suggestion would be ,

- If the concrete would be fresh , the surface will be well-brushed and washed down with very high pressure water in order to remove all excess laitance and fine aggregate to facilitate the exposing of the coarse aggregate. ( Just for info. using WOMA pressure pump

https://www.woma-group.com/en/

)

- If the concrete is old , the concrete surfaces should be chipped with a chisel point in a handheld chipping gun.( again for info .(

https://www.prent.nl/producten/mach.../hakhamer/rodcraft-hakhamer-6-joule-rc-5305/)

Just saying.


According to the grace of God which is given
unto me, as a wise masterbuilder, I have laid the foundation, and another buildeth thereon. . . .
I Corinthians 3:10