Grout integrity outdoors 1

[JAE]

I've got a steel framework above an existing roof that is expected to support a very large condensing unit. The two main support beams span 40 feet and are W27 beams. The condenser manufacturer had specified a maximum 1/2 inch deflection which resulted in the heavy beams. I specified a 1" positive camber (the minimum camber for that shape) with an expected downward deflection under unit weight of about .7 inches. This would place the unit on a steel support that would be ultimately cambered about .3 inches.

The problem is that now the manufacturer wants the steel to be more level than what is provided (in other words, he's asking for a "flat" surface and doesn't care what the ultimate downward deflection ends up...the 1/2" limit was for wind loads).

What we want to do is remove the unit, and install a more level steel shape, like a tube, atop the beams. The plan is to grout the space between the "flat" tube and the cambered beam after shimming and setting the tube. We would eventually weld side plates from the tube to the top flange to permanently tie everything together.

Would standard, non-metallic, non-shrink grout be appropriate here? The owner has expressed some reservations about whether, over time, the grout would break up with the small flex in the beams and the exposure to freeze-thaw cycles (we're in the midwest U.S.).

Would an epoxy grout or some other product be more appropriate?

 

[Ron]

JAE...I would use an epoxy grout, preferably filled with oven dried sand or with metallic blast grit. Bond between steel and grout will likely break (eventually), but will last longer with epoxy than cementitious.

Note that epoxies have high coefficient of thermal expansion, so thermal fatigue on the bond will likely be a consideration. If shaded, it will help.

Ron

 

[JAE]

Thanks for your reply, Ron.

The thermal expansion issue was a concern with the epoxy grout. This is above a large warehouse-type roof and exposed to midwest temperatures (100 deg F in summer to -10 deg F in winter). One side faces north so would be in the shade. The other is southern exposure...

The metalic grit....I thought of that as I know that metallic grout has a higher ductility than non-metallic. But...does the metallic ingredient rust over time when exposed to the outdoors?