[TowerTalk] concrete strength for 18m heavy duty tiltover

[Jim Thomson]

Date: Wed, 31 Aug 2016 16:05:19 +1200
From: Simon Lewis <zl4plm at outlook.com>
To: "TowerTalk at contesting.com" <TowerTalk at contesting.com>
Subject: [TowerTalk] concrete strength for 18m heavy duty tiltover

Just about to order 4 m3 of concrete for the new base for my 18m hd tiltover tower 
Whats the std strength of concrete normally thrown into the base of these...
I can get from 20 - 50 mpa  Of course stronger = more $ 
Std strength seems to be about 25 

Cheers

Simon  ZL4PLM

## 

20 mpa =  2900 psi
25 mpa =  3625 psi
30 mpa =   4350 psi
35 mpa =   5075 psi
40 mpa =   5800 psi

I used   8 cubic yards of 30 mpa on my trylon freestanding tower base,
and   17 cubic yards of 35 mpa on my UST crankup tower.
Local town uses 40 mpa for city sidewalks.  Basement walls on new homes use
a min of 30 mpa concrete.

30 mpa is not much more $$  than 20 mpa....and a helluva lot stronger..like 50% stronger.
The stronger 35+ mpa concrete  doesnot end up with all the hair line cracks like 20-25 mpa.

You are only buying 4 cubic meters to start with.  Its a one shot deal, you dont get a 2nd chance.
I would suggest  using 30-35 mpa and be done with it.  And dont forget the rebar, dont go cheap on that. 
Concrete has a lot of compression strength, but very little tensile (stretching) strength, hence the rebar.

A tower base is one thing, but a fold over tower  puts a huge stress on the base.  
Dont forget to rent the concrete vibrator!  Rake it across fast, and you will see the concrete level drop asap.
By using a vibrator, the air pockets and voids will all be eliminated.   I would not use aggregate bigger than
.375 inch.  Dont over vibrate, if you do, the aggregate will sink.  

Jim   VE7RF