Potential Expansion of Slags for Earthworks Fill

[SUGARCANE]

Can anyone help.

We are currently conducting volumetric expansion tests on slag samples on a method which i beleive is based on an American standard (we are in UK). In summary a sample has been compacted into a CBR mould, immersed in a water bath at 80 deg C, swell measured in mm and converted to volumetric based on height of sample.

Could anybody shed light on what limits may be applicable for acceptability and where these references come from. Is the method we are using similar to ASTM D4792. Does anyone have any good net links where I can find further info (there seems to be lots refering to slags use in bituminous materials and concrete aggregates but not much regards its use an earthworks fill).

We know the possible causes for expansion (Free lime & MgO) but haven't tested for these yet (its not our brief), we are mainly interested in appropriate specification limits to which we can refer our consultants to.

Many thanks

 

[cslaude]

I think you are on very dangerous ground here. I don't think you have a good grasp on the project. You should be VERY cautious (and afraid, very afraid).

Slags do not make good earthwork fill materials because they tend to have highly variable chemical compositions and physical properties. (BTW, there are other possible causes for expansion other than MgO and free lime!) You may be able to evaluate those chemical and physical properties of small samples in your lab, but how will you evaluate those properties in the field?

In a typical mass earthwork project, where lots of fill material is brought in from an off-site borrow source, you should get samples of the proposed material and perform laboratory testing to establish the applicable engineering properties of the material (like grain size, atterberg limits, proctor test). If the material is suitable, you should evaluate physical properties of every truckload using simple visually observations. Once every couple of hundred cubic yards of material, or if the visual observations indicate a material change, you should perform laboratory tests. These recommendations are for relatively homogenous soils with that are chemically inert.

There is no practical way to evaluate the composition and physical properties of slags while they are being placed in the field. Even if you could evaluate the chemical and physical properties of each truckload of material brought to the site, it would take some fancy engineering to account for all the possible expansive scenarios presented by the chemicals in the slag. You may be able to tell your consultants what the expansive properties of the slag sample you have in your laboratory are at a particular moisture content and confining pressure, but your consultants may not realize that the expansive properties will change throughout the slag that is placed in the field, and are dependent on moisture content and confining pressure, to name a few variables.

For instance, one supposedly reputable geotechnical engineering firm here in the USA recommended slag material to fill a shopping center site. Even though this firm has offices all over the USA, they did not understand the material they had specified. Their laboratory and field-testing regiments were insufficient even for clean, homogenous fill soil and recklessly inadequate for the material they specified. They did not perform any physical or chemical testing on the slag material prior to construction. One of many problems they encountered was the material beneath concrete floor slabs expanded by varying amounts up to about 8-inches, while the material beneath building footings did not. They did not monitor where the material was placed on site. They did not perform chemical testing on the material brought onto the site. The property owner had to demolish the entire shopping center, remove ALL fill material from the site (some of which was considered hazardous waste, with special, very expensive handling and disposal requirements), and rebuild the shopping center from scratch.

Be happy to talk at length on this subject. I can even address some of the potential environmental problems with using slag as a fill material. But, I’d consider some other material, even fly ash, which tends to be more homogenous, and less chemically reactive.


Christopher S. Laude, P.E.
Carolina Geotechnical Services, P.C.

 

[Focht3]

Even fly ash can be dangerous - and a potential problem. The leachate can contain heavy metals and have a pH of over 12. But I agree with the thrust of [blue]cslaude[/blue]'s post: only recommend the use of a waste product when you thoroughly understand the consequences - and carefully monitor / document the fill.



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[VAD]

What type of slag are we referring to. Blast furnce slags have been used by the railroads as ballast for numerous years and in roadway earthwork fill. Non ferrous slags have a potential for environmental concerns and as such this has to be borne in mind as well as alluded to by cslaude and Focht3.

The Brits have quite a large amount of information on slags and I am wondering if the information reqired by sugarcane could not be readily derived from there through a literature search. Try an internet search.