Towertalk
[Top] [All Lists]

Re: [TowerTalk] Concrete

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Concrete
From: David Gilbert <xdavid@cis-broadband.com>
Date: Mon, 26 Aug 2019 14:48:25 -0700
List-post: <mailto:towertalk@contesting.com>

"Slump" is a common term in the concrete industry and there is a spec for it.  Usually it is measured by putting a truncated cone of it on a flat surface and measuring how many inches the top of the cone sags.

And yes, it is essentially a measure of how much water was used in the mix, although the Portland cement content also has some influence.  It takes VERY little water to facilitate the chemical reaction that creates hard concrete, but water is also normally necessary to make the stuff flow where you want it to go so it is a tradoff.  I've seen videos of machines laying concrete for highways, and that stuff is so stiff that they essentially pack it into place.  They can get 10,000 PSI out of it that way, though.

Excess water in concrete diminishes the ultimate strength of the concrete.  Whatever water that isn't needed for the chemical reaction ultimately goes away, leaving microscopic voids that diminish the overall compressive strength since air doesn't hold up much unless it is moving.  It is possible to get concrete with the spec'd amount of Portland cement that still never meets rated strength simply because either the driver or the concrete company decided to make their job easier.

Some Google searching can give you charts of compressive strength versus both water content and amount of Portland cement per cubic yard, but most of us don't have much ability to check what we're actually getting.  Other than the slump test, that is.  You can find charts for that as well.

73,
Dave   AB7E



On 8/26/2019 2:12 PM, Michael OBrien wrote:
  When I put in my UST HDX-555 some 20 years ago, I hired a contractor I knew 
to dig the foundation with a backhoe and construct the rebar cage as per UST 
instructions.

He also ordered the concrete. But when the truck arrived, he insisted upon checking 
something that was new to me -- the "slump" of the concrete.

The driver wasn't happy about it, but (as I recall) they placed a hefty blob of concrete 
on a slanted board and then timed its travel down the incline. Whatever, the batch didn't 
pass the "slump" test.

After conferring with the company office by phone, the driver took that load of concrete 
to another construction site. A different truck was dispatched, and the concrete it 
delivered was judged to be acceptable, "slump"-wise.

I'm guessing that "slump" has something to do with how much moisture is in the 
concrete mix. I had never before, and have never since, heard the term used. But it was 
important to my contractor that day.

Mike K0MYW






      On Monday, August 26, 2019, 2:26:10 PM CDT, Bob Shohet, KQ2M 
<kq2m@kq2m.com> wrote:
Mac,

Thank you for noticing my error.  It was not 20 sq. yds, it was 20 cubic yds.  That’s what I paid for and 
what I received.  I actually used ~ 18.5 cubic yds for the two tower bases and six guy anchor holes – the 
“extra” was what was dumped in the depression at the edge of my driveway.

I don’t recall the size of the truck or if they had to make more than one trip, 
but t was a HUGE truck.

For perspective, because of the boulders and other debris in several of the holes, what would start out as a 3’ x 
4’ x 4’ hole became more like 4’ x 5’ x 6’ as a removed boulder or piece of 
construction debris (steel cables, sheetrock, broken piece of wood, barbed wire, etc.) would tear out a chunk of the dirt 
wall and require re-straightening by the backhoe and enlarging the hole in the process.

Bob,  KQ2M


From: Mac
Sent: Monday, August 26, 2019 3:07 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Concrete

Humm ?  a 20 Sq yd concrete truck  ..  ??

that's a very big and very heavy truck , more to the point, they don't
make emm that big ...

mac/mc  w5mc

On 8/26/2019 1:15 PM, Bob Shohet, KQ2M wrote:
I used a different method which I will mention here just it case it may be 
helpful for a TT reader.

My qth is on irregular and jagged ledge – in some spots the ledge is at or just below the surface (like 
an iceberg) in other spots, as little as 1’ away, the dirt extends down for 4’ or more feet.  
You can’t predict where it is; you can only dig and see where it actually lies.

My house sits in a small “valley” about 10 – 15’ below the top of the ledge which starts less than 15’ from the 
ends of the house.  Coming from the street down my driveway facing my house, you could almost imagine this as a “U” with the 
middle part of the “U” flat and very elongated.

Both of my towers are on the top of the ledge with no way to get there other than to climb up at a very steep 
angle > 30 degrees.  This made it impossible to get a large concrete truck, with 20’ sq yds of 
concrete, up to the tower base.  And even if it made the first base, it could never get through the dense 
woods and over the boulders to get to the second base 110’ feet away.  It was a challenge.

I decided to hire an experienced person with a SMALL backhoe.  We proceeded by having the large concrete truck drive to the base 
of the ledge, extend its concrete pouring chute to the top of the ledge and then pick up that chute and place it in the 
“scoop” of the small backhoe.  (We had discovered that only a small backhoe could navigate the boulders and jagged 
ledge (although not without tearing and blowing out two backhoe tires in the process!))  The concrete truck then poured the 
concrete through the chute into the scoop of the backhoe filling it ~ 1/2 way.  The chute was taken out and the backhoe proceeded 
VERY slowly with the sloshing concrete and then poured it into slowly and carefully into the tower base and guy anchor holes (already 
strengthened with a cage or rebar and metal ties – previously made by N1MM and myself).  At each hole another employee of 
the concrete company worked with a concrete trowel, level and other tools to move and spread the concrete and level it properly.  
We repeated this process many times over a  2 1/2 hour period so that we could fill in both tower bases and six guy anchor holes.

It was a slow and painstaking process but it produced outstanding results.  No concrete 
was lost or spilled, the concrete filled all the holes and spread and leveled beautifully and 
the highly complex and challenging terrain was overcome.  We even had ~ 1 yard of 
concrete left over which I had them dump into a depression in the driveway over an underground 
stream and which successfully filled and stabilized a mini-sinkhole.  :-)

This was in 1998 and cost ~ $1,050 cash for all the concrete, delivery, labor and 1/2 hour of 
overtime.  I had calculated that doing it all myself with renting a mixer, buying all the concrete mix, 
and other chemicals, would have cost at least $400 and consumed at least two full days.  I’m not 
sure if it would even have been possible to get the mixer through the woods and over the boulders to the two 
tower bases, and guy anchor holes on the ledge in the forest, but I do know that the labor would have been 
backbreaking – probably almost as bad as the weeks of chainsawing that I had to do in order to clear 
the dense forest for the tower locations.  I know that I would not have had results as good as having 
the professionals do it. There has been no issue with any of the concrete in the past 21 years.

I would also add that the pros know the temperature range that the concrete will set best at as well as the chemical 
composition of the concrete to give the best “pour” and “set”.  I certainly would 
not have known that.  For that information and knowledge alone to ensure the safety and the longevity of my 
installations, it was worth every penny!


73

Bob, KQ2M


From: k7lxc--- via TowerTalk
Sent: Monday, August 26, 2019 1:11 PM
To: towertalk@contesting.com ; xdavid@cis-broadband.com
Subject: Re: [TowerTalk] Concrete

   What size is your tower base?? In my opinion, mixing your own for a
typical tower base is not a cost effective undertaking unless you have some 
insurmountable access issue that prevents you from bringing in a mixer truck.
       I agree. I've poured dozens of tower bases and every base plan I've ever 
seen calls for 3kpsi concrete. The labor involved in buying, transporting, mixing and pouring 
a base yourself doesn't usually pencil out compared to having it delivered.

       And if there is an access issue, hire a line pump to get the mud in the 
hole. It'll pump up to 400 feet which should solve most problems.

Cheers,Steve    K7LXCTOWER TECH -Professional tower services for amateur and 
commercial
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk


_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
<Prev in Thread] Current Thread [Next in Thread>