Use of hardcore in footings

[schiz]

It occured to me that I can reduce the amount of concrete required in my footings by combining it with some decent (i.e. hard) hardcore. A friend (not a builder) thought it would be a bad idea, since the concrete would not then be setting at a uniform rate.

Can anyone here give me the 'scientific' explanation of why I don't want to do this? Looks like I will have way too much of the stuff at the end of the project and will need to pay someone to take it away. So far it's all been washed and the loose bits removed - no crap in there at all.

Any thoughts?

 

[^woody^]

Don't bother.

The hardcore fill will compact, and the building will suffer uneven settlement.

BTW, consider that other people must have thought of doing this, and why is it not common practice?

 

[^woody^]

Don't bother.

The hardcore fill will compact, and the building will suffer uneven settlement.

BTW, consider that other people must have thought of doing this, and why is it not common practice?

 

[Deluks]

It strikes me that trying to save money in the foundations of your house, ie: the bit that holds up the entire building and that might necessitate rebuilding the house should it fail

...is not a smart move.

Build a rockery instead, that's the landscaping sorted then

 

[holmslaw]

The concrete must be in direct contact with the bottom of the trench, also the bottom of the trench must not be tamped down in any way. This means the concrete will completely fill any voids and be in direct contact with the undisturbed ground.

 

[schiz]

BTW, consider that other people must have thought of doing this, and why is it not common practice?

Yeah, I did indeed consider this, hence the post .

The concrete must be in direct contact with the bottom of the trench

This makes perfect sense, but...

also the bottom of the trench must not be tamped down in any way. This means the concrete will completely fill any voids and be in direct contact with the undisturbed ground.

This is the opposite of what I'd expect. Is this because the tamped down earth results in future movement as it redistributes the excess pressure or something?

I've never seen advice to tamp it down, but not seen any advice saying *not* to tamp it, only to ensure that the sides/corners are square and that it doesn't taper in at the bottom.

thanks for the replies.

 

[holmslaw]

This is the opposite of what I'd expect. Is this because the tamped down earth results in future movement as it redistributes the excess pressure or something?

I was surprised too, it is so the concrete is in contact with as much solid ground as possible and forms the exact shape of the bottom of the trench. Therefore the load is spread as evenly as possible on the undisturbed ground.

If you tamp down you make an artificially hard surface that might initially resist the weight of the concrete but could eventually sink due to the weight of the building.

 

[schiz]

 

[Shytalkz]

Don't bother.

The hardcore fill will compact, and the building will suffer uneven settlement.

BTW, consider that other people must have thought of doing this, and why is it not common practice?

How did you come up with that one, Woods?? If he drops some hardcore in the concrete to bulk it up, that's not a problem - and a quite oft used solution when the readymix quantity is a bit short (oh, think there just might be some like that in my barn...!).

So the concrete's possibly not so strong, but so what? You standing on one foot in the bottom of the trench will put about the same pressure on the ground as the building and foundation. It's soil replacement and creating a level base off which to construct, nothing more than that.

Next you'll be telling us you have to scrape the raised bit of soil from between the digger bucket teeth out of the trench bottom .

 

[^woody^]

Err, excuse me ..... please note forum rules about hijacking threads

This thread is about hardcore at the bottom of the trench and not mixing it with concrete. Please start your own thread to discuss this

And I hope you brushed the dust of that MOT first

Regarding the bucket teeth, then by keying the ground it stops the foundations from sliding sideways ... doesn't it?

 

[schiz]

This thread is about hardcore at the bottom of the trench and not mixing it with concrete. Please start your own thread to discuss this

Woody,

I admit I might not have phrased the post as unambiguously as I could, however you have quite some imagination if you thought I meant lining the bottom of the trench with the stuff!

My objective is to dispose of some hardcore, therefore it can go to the bottom, middle or top of the trench.

I consider you'd need to have clean pieces of hardcore (without dirt on them), and rather than just chucking them into the trench you'd want to ensure they are well packed around with the concrete mix, leaving no air gaps, of course.

 

[Shytalkz]

You're changing the post : where does it say in the bottom, he says combine with the concrete? Anyhow, if you put 6" to 9" or so well-compacted type 2 in the bottom and put the concrete footing over it, it wouldn't make a ha'p'orth of difference. Not that a BCO would believe that - it's not in the book, so it can't be done (answer: wait for him to inspect excavations and leave site, then lay the type 2 and concrete).

Dust - additional binder . Some soil went in as well. By accident, I hasten to add...

ETA post refers to Woody, not the one directly above!

 

[Shytalkz]

Schiz: bung it in and tamp it down into the concrete, it won't hurt at all.

 

[^woody^]

Oh, I see, mixing ..... like mixing it together? And not combining like combing the two togther in the trench?

Clear as, well .... grains of soil suspended in a water solution forming a viscous cloud of opaque liquid.

The apology is in the post to norfolk

 

[Shytalkz]

Wells Fargo, I trust?