[TowerTalk] Grout ad nauseum

[Tower2sell@aol.com]

Gary You added some interesting comments to the discussion so let us go for ad nauseum - ad nauseum.

Your comment about not buying a tower that had grout for strength purposes... Well if you have bought a packed free standing tower you may already have. The reason is that the base plate calculations are seldom included in your design package that is submitted to the building officials. The reason is simple. They don't ask for it (most of the time) Second when they do they get calculations that most likely they wouldn't understand. The main reason is that a lot of companies design with proprietary design methods that they have developed from tests and/or theory. The clue to the situation is what the engineer assumed and that is normally found on the final drawings that either require grout or it doesn’t.


Now for the water. Grout and water don't mix. If you are using a pipe legged tower (as opposed to a solid, round or angle) water can become trapped in the pipe and when it freezes it may rupture the pipe leg. So pipe legged towers are designed with a drainage plate at the bottom. This plate is a sheet metal plate with a drainage channel. So other means may exist such as holes in the pipe at the bottom. Some people try to make a channel in the grout with a rod to drain the water. I've personally seen this broken up into small pieces, probably because the ice expanded sideways and pushed the grout out. As you can see for a pipe legged tower the grout is not its friend.

You point out that we should build foundations with better care so that they are not concaved and trap water. A slight slope from the center in normally specified.


Finally, be kind to your anchor bolts and keep them high, dry and mow the grass and shrubs around them. I received a call from a government agency explaining that they had large tower with severely rusted anchor bolts. Over the years the powers to be did not like the appearance of the anchor bolts and planted shrubs and bushes around the tower with an automatic sprinkler system. The results years later when a CALTRAN structural engineer found them was a life threating situation. I had him find a local engineer who could fix the problem with some epoxied bolts.



>The lesson learned is that watering your tower will not make it grow taller only rust quicker.
 Sorry for late post....been on vacation teaching Boy Socuts ham radio at Boy 
Scout Camp.......

I'll side with Hank......grout does zip for adding strength to tower
bases......free standing or otherwise.

Grout does two things;

1. Cosmetics. Makes the base look nice and keeps garbage from collecting
underneath.

2. Keeps water out. Depending on how the foundation was finished (convex
vs. concave) you can pool water underneath the base plate which will seep
down next to the anchor bolts. Depending on your climate it will either
rust through the bolts or freeze and crack the concrete away from the bolts
which will weaken the foundation.

I would hesitate to buy a tower that required grouting if the expressed
reason was added strength. How would you ever be sure that the grout was
uniformly spread under the plate? What is the developed strength of the
grout?

Gary K7FR P.E.
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