[TowerTalk] Concrete

Mon Aug 26 18:23:15 EDT 2019

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 at 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 at 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 at contesting.com ; xdavid at 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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>>> TowerTalk at contesting.com
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