A question for you concrete experts....

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dun":1lzytock said:
I owuld ask someone that does concrete work and go by his recommendations. If your construction guy is a concrete man, that would be good enough for me. But I tend to trust people.

not to change the sugject but i notice that "dun" lives in Mo Ozarks. I live in California although my Grandma & Grandpa are from Bakersfield MO. I was curious if you them. Elvis Cotter and Agnes Howard. My Great Grandma was Alphie Cotter. and on the other side is my great grandma and grandpa Myrtle Howard and Pete Howard.I remember growing up and all the trips we took back to Videt. My mom was born in Ott.
 
upfrombottom":xey9gi90 said:
novatech":xey9gi90 said:
So what exactly did you find technical?
Steel for beams should be no less than 5-#5 with stirrups at 2 ft. The slab should have a minimum of #3 at 18" oc each way. Concrete should be pored 4' thick. These sizes are minimum.
If you have ever parked in a modern parking garage it was probable built wit precast panels that are hollow and only about 4" thick. The exterior and interior beams are what give the main structural strength

novatech":xey9gi90 said:
With a BS in structural Engineering I would think you should have a lot more than something like this to contribute.
With all these unknowns how can one possibly know what the foundation design should be?

The first thing I was taught in college by a very respected engineer was:" State only what you believe to be fact and be prepared to defend it, because as a professional you will be challenged."

I actually typed a long and drawn out response to the original question soon after it was posted based on my engineering education . Then I sat and read my response with my common sense education. The latter made me delete it.
upfrombottom wrote:
As has been stated, concrete can't withstand the stress of tension, that is the reason for steel in the concrete. But contrary to what most believe, the greatest stress on concrete is at the surface whether bottom or top. The problem with steel is its deterioration from oxidation and it must have a good covering of concrete to protect it. The horizontal center of a slab is the most neutral part of that slab and ideally the steel should be placed toward the edge where the greatest tension occurs i.e. the top and bottom. The best solution for surface tension is fibermesh. Its noncorrosive nature allows its placement where it is needed most.
So why would you think that anything anybody else wrote was any more technical than what you wrote. And by the way what you wrote may have been informative to many on the boards not only to the man that asked the question. How were the responses any more technical than the question asked? No I do not think the man is building a parking garage. It was just an example of how well designed and placed concrete can have tremendous strength. My main point through out has been that there are to many unknowns for proper design. There are tremendous differences in the soils where the concrete will be placed. The loads being placed upon it will make a difference. Will he be using a light tractor or an 40,000 lb articulated loader. He ask a question because he is concerned. He does not want it to fail and have to do it again.
All things considered, this project is a silage bunker, being built by a farmer, whose main concern will be cost and functionality.
This is the exact attitude that has caused more failures than anything else. Have you ever considered the cost of concrete removal and replacement?

The suggestion of using fiber would probably the best and most economical over all. If expansion joints were used beams may not even be necessary. That is on the ground that I think he may have. On the ground I have it would snap like a cracker. Also he may want to check out post tension. Even though he would likely have to use an out side contractor the price would be less tan re bar at the price of steel theses days.In my book you should have posted the first draft that you deleted. It may have pointed out the fact that there is a lot more to concrete than just pouring some off the cuff, arm chair design that may or may not work. Not only for the man that asked the question but for others that may have projects they are thinking of doing. I think your knowledge may be appreciated and used. If it only helped one person think it is still a gain in my book. Sharing knowledge is what these boards are all about.
 
O.K. Mr. nova I won't argue your point about my opinion maybe helping someone, then again I
really wasn't in the mood for an argument over my opinion and am not so sure I am now, but, nevertheless I will offer one.

As far as thickness adding strength, it actually does. The strength that it adds is called shear strength. The thinner the slab, the less the shear force it can withstand. In most cases 4 inches can withstand the shear placed on it by a common automobile, but can't withstand the force of heavy machinery. Shear force is what causes a lot of potholes in roadways. So how would a person design a parking garage with a concrete slab of 4 inches? Well the easiest solution is to lower the ceiling and narrow the entrance so that nothing larger than a common automobile can enter.

There has been a great deal of research done trying to find a replacement for the component in concrete that adds the most to the cost, that being Portland cement. There are some that are used to reduce the amount of cement necessary to achieve the desired strength. One of those is fly ash, a waist product of coal burning power plants. Fly ash does not reduce the designed strength of concrete but it does significantly increase the curing time it takes to reach that strength. The fly ash will also increase the working time of concrete which is also desirable in most instances.

The tensile strength of the concrete itself is considered to be zero. Most can't understand how a slab lying flat on the ground can have tension force applied to it by driving a vehicle across it. A very easy way to understand it is to hold a pencil by the ends and with your thumbs push up on the center of it until it bends. The top of the pencil is in tension and the bottom is in compression; meaning your stretching the top fibers and compressing the bottom fibers. Since concrete has a great deal of compression strength and no tensile strength it will fracture or crack on the side in tension. By pushing or bending the pencil in the opposite direction the compression and tension will be reversed and it should be easily understood how the horizontal center of the pencil is the most neutral or has the least amount of tension applied.

Steel is the most common material used to resist the tensile forces that are placed on the concrete. Fibermesh is also a great reinforcement material but it should not be totally relied upon for its strength. I can remember doing an experiment in the laboratory using fibermesh compared to concrete wire. The tensile strength of the concrete with mesh was actually a little stronger than the concrete using common wire. As far as using wire compared to rebar it depends on the loads being applied to the concrete. Number 3 rebar or 3/8 rebar ( the diameter of rebar is commonly measured in 1/8 inch increments and specified by the number of eighths) put on 18 inch centers gives about 2 times the strength of the concrete wire and it also adds shear strength. If you use concrete wire and add fiber, you can easily get the same results and in most cases at a cheaper cost.

Based on all the variables that would have to be known to engineer a design for Mr. whitewing, I won't give a professional opinion, but I will suggest this, go to your concrete supplier and ask them to help you. I don't know the regulations that they have to follow there, but they do have formula's that they go by to design the strength of concrete and if you are not up to doing the job yourself, they can recommend someone reputable that can.

One thing that I forgot to add is moisture barrier. All concrete has air pockets and in instances where it is subject to freezing temperatures, an air entraining admixture is put in the mix to increase the amount of pockets. Concrete will wick moisture into the air pockets and if subjected to freezing temperatures it will crumble under the pressure or tension placed on it. The admixture is added to increase the number of pockets to allow a place for the expanding moisture to go. Lack of air entrainment is what causes surface spalding. So in my opinion all slabs that are to be used for storage of a material that is to remain dry should have a moisture barrier under it.
 
Wow, you guys really know your stuff and have given me some great ideas.....I really appreciate the time put into these responses.

Also, after reading some of the comments, I realized that this particular thread had zero pics of my silo. Sorry, that's my fault because I posted them in another thread but will also add them here. This is an in-ground silo, a trench basically that will have an entrance point and an exit on the far end. It's supposed to slope gradually downhill but I've not actually verified that yet. I suspect I need to do so before starting.

Freezing? No problem here...the lowest I've ever seen it is about 60F. Water table? In my area I think it's at about 300 feet. :D Having said that, when it rains, it pours. Looking at the soils I'm working with in this particular hillside, I'd say the majority of the material is red clay, say 70% or so, 25% sand and the remainder would be gravel.

Now the pics:

100_2676.jpg


100_2678.jpg


100_2681.jpg
 
From what I can see in the pics it seems like good non-expansive soil. There seems to be enough clay to bind it well when compacted. There is way to much to use a plate compactor. I would employ some one with road compaction equipment to do this or just rent the equipment. As dry as the soil is water is going to have to be applied for proper compaction. The use of steel at today's prices may be cost prohibitive. Fiber Mesh should do you a good job if expansion joints are used. I also feel that beams would not be necessary.(Assuming heavy equipment will not be used on top of it.) Again, you may want to talk to a post tension company in your area and get a price to compare with. (If there is one)
How do you intend to address the side walls? When the bunk is full there should be no problem. When it is not you may get some cave inns especially where there is a lot of gravel in the foreground of the pic. A very good positive slope away from to bunker for drainage will help. Even better if you can compact it too.
You mentioned that when it rains it is usually very heavy. Going back to the pic., showing the gravel in the foreground, it comes close to the surface with a small layer at the top. When the rains come this will act as a drain so to speak allowing water to travel down and for an underground spring, thus putting water into your silo. Not good and should be addressed. This may be to technical, sorry. But I think it should be sealed if it was me building it. I would dig it out a compact clay into it.
As an added note, not only for you but other that may be reading this, concrete is not poured it is placed. Most subcontracted concrete want to water down the concrete so it will flow. This make there job easier but also make for weaker concrete. Concrete should be placed with not more than a 5" slump. Again this may be technical but it is important. Google up slump on concrete.
I am not a design engineer and my recommendations are only an opinion.
For any of you that think that I am going overboard on this, I would like you to consider this. As cattlemen we are all concerned with longevity of our cattle that may produce for 20 or so years if we are lucky. So why shouldn't we be just as concerned about concrete which should last 20 or more lifetimes, wither it be a sidewalk, driveway silo floor, or multi story building. If you don't think so I would like you to meet my friend, Mr. Jackhammer.
 
novatech":1mir4mv5 said:
From what I can see in the pics it seems like good non-expansive soil. There seems to be enough clay to bind it well when compacted. There is way to much to use a plate compactor. I would employ some one with road compaction equipment to do this or just rent the equipment. As dry as the soil is water is going to have to be applied for proper compaction. The use of steel at today's prices may be cost prohibitive. Fiber Mesh should do you a good job if expansion joints are used. I also feel that beams would not be necessary.(Assuming heavy equipment will not be used on top of it.) Again, you may want to talk to a post tension company in your area and get a price to compare with. (If there is one)
How do you intend to address the side walls? When the bunk is full there should be no problem. When it is not you may get some cave inns especially where there is a lot of gravel in the foreground of the pic. A very good positive slope away from to bunker for drainage will help. Even better if you can compact it too.
You mentioned that when it rains it is usually very heavy. Going back to the pic., showing the gravel in the foreground, it comes close to the surface with a small layer at the top. When the rains come this will act as a drain so to speak allowing water to travel down and for an underground spring, thus putting water into your silo. Not good and should be addressed. This may be to technical, sorry. But I think it should be sealed if it was me building it. I would dig it out a compact clay into it.
As an added note, not only for you but other that may be reading this, concrete is not poured it is placed. Most subcontracted concrete want to water down the concrete so it will flow. This make there job easier but also make for weaker concrete. Concrete should be placed with not more than a 5" slump. Again this may be technical but it is important. Google up slump on concrete.
I am not a design engineer and my recommendations are only an opinion.
For any of you that think that I am going overboard on this, I would like you to consider this. As cattlemen we are all concerned with longevity of our cattle that may produce for 20 or so years if we are lucky. So why shouldn't we be just as concerned about concrete which should last 20 or more lifetimes, wither it be a sidewalk, driveway silo floor, or multi story building. If you don't think so I would like you to meet my friend, Mr. Jackhammer.

:shock: Definitely no "friend" of mine... :lol:
 
Nova, this project actually started a couple of years ago but because of drought at my place I never finished it. What little pasture production I had was rapidly and completely consumed by my animals so I didn't make the effort or incur the expense. This past year we had near-normal rainfall and I got a firsthand look at just how much material my pastures can produce in short order. That's why I want to complete the project before the rains fall again.

During heavy rainfalls this past "winter", the walls held up amazingly well and I'm confident that once full of material, I'll have little problem with the structural stability of the walls. Also, there will be a thick plastic sheet between the walls and the material in the silo. This sheet of plastic will actually cover a few feet of the concrete floor on both sides, run up the walls, and then be flapped over the material in the silo to prevent air intrusion from damaging the material within. It'll be held down with used tires.
 
So all you need is a slab that heavy equipment can operate on. Not too hard to do.
The most important thing is a good tight compaction on the soil. An easy way to check that is to "proof roll it" That is take a loaded dump truck and drive it back and forth across it and check for pumping. Pumping? You will know it when you see it. Just watch the soil under the tires and if it moves up down under load and springs back up it is pumping. If your soil is well compacted most any thickness of concrete will work but to be safe use 5 inch. It is a lot cheaper to buy concrete now than patching later. I would thicken it along the edges a little.
Reinforcement: number 4 bars at one foot spacing both ways mid slab will be fine. If it fails from equipment load it will be short span flexure but most likely shear, so placement is not a big deal. You could get away with 6 inch by 6 inch 10 gauge welded wire if your soil is "very well" compacted and not saturated while you are working on it. But I would feel much better with a rebar mat.
Fiber reinforcement: I have never liked it and tell most folks it is a waste of money. There is no substitute for steel.
Use 3,000 PSI concrete and keep it wet for a week or two while it cures. Place plastic under it if for no other reason than to keep the water from seeping out of the concrete while it cures. You don't want concrete to dry and shrink. You want it to hydrate and cure.
 
Wow!!! Was just thumbing around & came across this thread......'bout blew my mind reading all of this - From all the posts here (& all the bickering back & to), I'm going to place my head on the chopping block and offer my opinion as I may be the only contractor that has actually built a significant number of inground bunkers to post to this.
Sub-base conditions are site specific & must be addressed accordingly, but in "general" this formula will work anywhere - Remove all pumping material & replace w/ suitable backfill - If sub-base holds up a backhoe w/ front bucket full of dirt without the front tires making tracks, compaction is ok - Spread 3-4" screenings over entire site - We stack 2' x 6' concrete waste blocks in a staggering pattern on the screenings up both sides above the original ground line, you can go 4 high with backfill on the outside & increase capacity vs floor area - Fine grade interior area - Chalk a concrete placement line 6" high down the inside of ea waste block wall - Roll out @ least a 6 mil poly vapor barrier - Place a mat of #4 rebar 12" OC ea way on top of concrete bricks allowing for a break for expansion joints in a basically square pattern, I don't like to get any bigger than 30' x30' - Mark these joint locations on the waste block wall for reference later- Roll out 6" x 6" #10 wire mesh solid over rebar on top of bricks & secure w/ tie wire - On entrance & exit ends, dig a 12" deep x 18" wide footing & place 4 #4 rebar crosswise by securing to stakes - Hire a pump truck to place 4000 psi concrete w/ a max of 5" slump (if you request no flyash your concrete provider should oblige, we hardly ever use flyash) - Have plenty of help to place & finish - Topcoat w/ a sealer as soon as you get off finish work - Next morning saw control joints about 2" deep in previously marked locations...........Built many of them over the years, never seen one fail in any way - Never had a complaint from a customer - May not be the "absolute cheapest" way to build one, but if you don't want to build it but once, it works.
 
chenocetah":3sybficv said:
Wow!!! Was just thumbing around & came across this thread......'bout blew my mind reading all of this - From all the posts here (& all the bickering back & to), I'm going to place my head on the chopping block and offer my opinion as I may be the only contractor that has actually built a significant number of inground bunkers to post to this.Sub-base conditions are site specific & must be addressed accordingly, but in "general" this formula will work anywhere - Remove all pumping material & replace w/ suitable backfill - If sub-base holds up a backhoe w/ front bucket full of dirt without the front tires making tracks, compaction is ok - Spread 3-4" screenings over entire site - We stack 2' x 6' concrete waste blocks in a staggering pattern on the screenings up both sides above the original ground line, you can go 4 high with backfill on the outside & increase capacity vs floor area - Fine grade interior area - Chalk a concrete placement line 6" high down the inside of ea waste block wall - Roll out @ least a 6 mil poly vapor barrier - Place a mat of #4 rebar 12" OC ea way on top of concrete bricks allowing for a break for expansion joints in a basically square pattern, I don't like to get any bigger than 30' x30' - Mark these joint locations on the waste block wall for reference later- Roll out 6" x 6" #10 wire mesh solid over rebar on top of bricks & secure w/ tie wire - On entrance & exit ends, dig a 12" deep x 18" wide footing & place 4 #4 rebar crosswise by securing to stakes - Hire a pump truck to place 4000 psi concrete w/ a max of 5" slump (if you request no flyash your concrete provider should oblige, we hardly ever use flyash) - Have plenty of help to place & finish - Topcoat w/ a sealer as soon as you get off finish work - Next morning saw control joints about 2" deep in previously marked locations...........Built many of them over the years, never seen one fail in any way - Never had a complaint from a customer - May not be the "absolute cheapest" way to build one, but if you don't want to build it but once, it works.
When you assume such thing you know you are usually just making an A$$ out of U :lol:
you gave good info but in WW's circumstance alot of what you suggested is out of the question
because of his limited availabilty to products or services
 
By the way Mr Cowman, my post did address within it's content WW's concerns - The post was not meant in as much as an absolute answer to WW's situation as it was to provide some common sense information to other cattle farmers who might read this forum & may have benefitted from that rather than the senseless yayaing yall so-called engineers or whatever yall are had been doing on here - I maintain that I was correct in being the only poster that publicly admitted that I had actually built silo bunkers, & quite a few of them at that - You state that you have been involved with 100,000's of yds of concrete.....In my 50+ yr career I can measure the slabs I've done in Sq Miles - I have no desire to, nor will I be, drug into a childish bickering of nonsense - Your last post was a window into your empty hollow soul - May God have Mercy on you.
 
I am not a engineer and most of theconcrete I have laid was designed by one, but there are silage slabs that have been down for a number of years, OK more than I havebeen around for that have not cacked but been erroded by the corrosive nautre of the silage it's self. In order to remady this problem Ashphelt, or Tarrmacadam has been used as this is less prone to being eaten away.

In light of this some new pads are now just built with Ashphelt floors.

Newer concrete has not stood up to the corrosion like older stuff has.
 
It might be a good idea to get a concrete contractor in your area who knows the ground and the expectations for your area . As far as the silage being corrosive you can spray it with a membrane to stop it . I'm actually a concrete contractor . However I can't tell you what's best for your area. Soil reacts to weight water etc. Your sub foundation is just as important as your slab .
 
JSCATTLE":3kpuxr2m said:
It might be a good idea to get a concrete contractor in your area who knows the ground and the expectations for your area . As far as the silage being corrosive you can spray it with a membrane to stop it . I'm actually a concrete contractor . However I can't tell you what's best for your area. Soil reacts to weight water etc. Your sub foundation is just as important as your slab .

That is why it is important to have soil studies done before foundation design and to determine how the pad should be built.
 

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