sand vs clay vs crusher dust

[schoolteacher]

I am building a 60 x 100 structural steel building. The building will have a 2' x 2' reinforced concrete foundation. Concrete blocks will will bring the building up to grade. The height of the blocks will be about 2' in the back and 4' in the front. My question is what would be the best material to use to fill with under the slab. Choices are between sand, crusher dust and clay. I can get the crusher dust the cheapest because of a friend at the rock quarry, but is it suitable for compaction.

 

[Ron]

Sand is the better option. It is the least reactive to moisture of the three choices. Crusher dust and clay are more difficult to compact.

 

[schoolteacher]

Thanks Ron for the info. It's interesting that the guys in the office at the Quarry are saying the dust is a better choice. Maybe they are wanting to get rid of dust instead of sand.

 

[Zambo]

Ahh... schoolteacher that would be because it depends on the sand and the quarry dust you have available. Clay in general forget it. But without any further details I agree with Ron, go for the sand.

 

[Ron]

st...ask them for a gradation on the crusher dust. If all of the particles pass a No. 16 sieve and it has more than 10 percent passing a No. 200 sieve, use the sand.

The term "dust" implies rock flour, which is a very fine material, not suitable alone for fill or compaction.

 

[schoolteacher]

They are supposed to be faxing me that info. I will post it as soon as i recieve it. Thanks

 

[concretemasonry]

Gradations do not tell the whole story. Depending on the crushing equipment and the type of rock, you could end up with a lot of flat fines that distort the gradation and compact differently. That will not compact weel and can shift later.

Also, if the rock is limestone, the fines can be cubic and there is an amount of cementing ability in the fine fines that can develop later.

Dick

Engineer and international traveler interested in construction techniques, problems and proper design.

 

[Ron]

CM....there was no indication by the OP that the crusher dust was calcareous. Very fine calcareous materials are bad actors as well. Yes, there is some cementation that occurs from hydration of the carbonates; however, getting compaction in calcareous materials with a high fines content is difficult at best.

Gradation doesn't tell the whole story, as you noted, but it's a good starting point.

 

[Zambo]

Also many types of sand out there.

In some locations "quarry dust" is used as a term for crushed rock fines.

 

[fattdad]

Too many shades of "sand" and also "crusher dust." Either supplier should be able to give gradations and moisture-density relations (i.e., Standard or Modified Proctor). Problem with some sands is that they realize their best compaction at close to saturation moisture content. Crusher dust (some) can be very good for subgrade/subbase below a concrete slab on grade. You can get some good CBR numbers from crusher dust, which correlates to good subgrade modulus values.

No, I'm not taking anything away from Ron and others in their recommendation for sand, I'm just saying crusher dust (what we call No. 10 screenings) can be pretty well graded and very dense when compacted. Around Virginia, much of the No. 10 screenings are the by-product from processing #57 open-graded aggregate. There's a lot of granular material below the No. 10 screen.

f-d

¡papá gordo ain’t no madre flaca!

 

[Ron]

f-d....I agree, just that we don't know what they are calling "crusher dust". Gradation curve necessary.