Floor slabs on expansive slag fill

[valleyboy]

I've been asked to look at a project where a number of floor slabs within a property have heaved. On excavation of trial pits, it appears that the floor slabs are founded on a slag fill.

I am aware from limited research that these fills can be expansive, and my gut feeling is that this is the culprit. The slag has numerous steel inclusions, and also contains some free lime - it appears that it is a steel slag. I am going to schedule some lab testing to confirm the type of slag and its expansive potential.

The internal partions are constructed off the slab and have suffered limited movement also.

One solution would be to demolish the internal walls, remove the fill, and reconstruct, which is a costly and disruptive option.

Another solution may be to use heave protection materials usually used as a clay heave precaution such as this stuff:-

http://www.vencel.co.uk/products/fo...=Clay_Heave_Protection_-_Claymaster&nav=nav_1

I wondered whether anyone has used these products successfully in this scenario or has any views?

VB

 

[fattdad]

If I recall correctly, the Hotel Roanoke (Roanoke, Virginia) had a problem just like this. You may want to check this out (if you can find details).

The most likely scenario for this heaving is the mineral ettringite. For the case that the slab was "stabilized" with free lime and to the extent that there is sulfur in the slag materials in the presence of water ettringite will form.

You may notice that the heave in the slab is greater where the slab has less loading on it. For example, at the partition walls (if they are carrying any load) the slab may show less settlement. Similarly at the foundation walls.

I'd recommend a level survey throughout the entire slab.

We had a very similar case where we had to underpin the foundation wall, demo the slab and remove/replace the subbase with clean fill.

These cases are usually riddled with lawyers and getting details can be difficult.

I'd recommend some chemical testing to fully evaluate. There are mineral tests (scanning microscope, spectrometry) and chemical analyses that can help with this.

Swell testing may show nothing depending on whether the ettringite has fully formed. Then again, if there is remaining potential (i.e., more water to come. . . ) then you may see something. You can use a simple odometer with a 1/4 tsf seating load to set up the test. Let it run for at least 30 days.

Go to fatt-dad.com for a link to my email if you want more information. I may be better able to help off line.

f-d

¡papá gordo ain’t no madre flaca!