peagravel/sand/3/4minus compaction 2

[pdise]

I'm filling in an old mechanics pit appox. 30' x 15' x 4'. It has concrete floor and walls. I will then be pouring back concrete to bring the grade to the same height. What is the best material to use as backfill? Pea gravel, sand, or 3/4" minus? I thought about CDF but the cost is higher than what the owners wanted.

 

[fattdad]

If it's under roof, I'd use No. 57 open-graded aggregate. I'd have in installed in about 18-in thick lifts and compacted with a vibratory plate or small remote controlled roller. If it's not under roof, I'd use No. 21A or 21B dense-graded aggregate, which actually has moisture-density relations and needs to be placed with proper moisture content and compacted in thinner lifts to 95 percent Standard Proctor.

the dense-graded aggregate sheds water so if it rains on the job you wont completly fill all voids with water. The 57 will just take any/all water that falls from the sky!

f-d

¡papá gordo ain’t no madre flaca!

 

[RHTPE]

Geofoam is another possibility, but I have no idea how the cost compares.

I would consider doweling into the existing concrete perimeter for your new slab.


Ralph
Structures Consulting
Northeast USA

 

[hokie66]

What is CDF? I would have thought of liquifill or stabilized sand, but perhaps the owner would think that too expensive also.

 

[RHTPE]

Hokie66,

CDF - I took it to mean 'Controlled Density Fill', which I would have presumed to be the same as CLSM (Controlled Low Strength Material) or Flowable Fill - all being a cementitious material.


Ralph
Structures Consulting
Northeast USA

 

[cvg]

cost of the fill is primarily hauling and compaction. Or if cement is used, than no compaction required. Any granular fill with moderate compaction or any cement stabilized granular material would work. Contrary to common belief, the sand requires some moisture control and compaction. The pea gravel should also receive some compaction, but moisture control is not so critical. If you can drain the bottom of the pit, these two can be flooded / jetted and tamped to consolidate. Contractors often like to use "chips" which is similar to pea gravel. They are cheap and might also work.

 

[hokie66]

Thanks, Ralph. A pet peeve of mine is using acronyms on this site which are area specific and not even findable by search engines.

 

[RHTPE]

Hokie66,

I hope my interpretation of CDF was correct - I was really just guessing. It just kinda fit.

I agree with you about acronyms, even within the US there are regional differences. It's much clearer to at least spell it out completely the first time used in a post.


Ralph
Structures Consulting
Northeast USA

 

[lawayosh]

A flowable, cementitious fill material, whatever the acronym, would seem to be the quickest, easiest and cost effective as well. Something like what we refer to as 1 to 2 sack (90 to 180 lbs of cement per cubic yard) sand/cement slurry. If you are in a real hurry an accellerant could be added as well. The big advantage is no mechanical compaction, just use a vibrator during placement. You also would not have to worry about the slab pour paste and moisture seeping into the subgrade fill material. If hydrostatic head may be a concern, go with 2 sack and place the slurry in two lifts a couple of hours apart.

Yosh