Except when the permit requires a slump test and tensile testing of a
cured sample which it did when my towers went up. Total regulatory
overkill for a crank up base that specified 2500psi concrete.
Grant KZ1W
On 8/26/2019 2:48 PM, David Gilbert wrote:
"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
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