Crushed Granite vs. Crushed Limestone for Base

[ChuckI]

At first I thought someone was trying to split hairs when I received this question from the field, but now I'm not so sure:

For shallow foundations/Slabs/Pads - I've called out 6" of a no. 610 crushed limestone, per the soils report. It's a well-graded aggr base and the existing subgrades are fat clays (pi about 45). The area is North portion of Louisiana, south of Shreveport. Outdoor industrial site.
I was advised from the field that the 610 in the area is crushed granite, not limestone as in the dwg notes, so they want to know how to proceed.
Granite is a harder rock, so I was thinking no issue, but I'm wondering if permeability (bathtub effect) is a big difference when comparing granite fines vs limestone fines.

I'm a civil/structural engr, and we have a good geotech that I've left a message with, but he's out-of-pocket for a day or two.

Any Opinions?

 

[Ron]

Because of the high calcium content, crushed and graded limestone tends to hold to together nicely and for the long term will actually hydrate into a stronger mass. That does not happen with granite.

Both make excellent base materials. Limestone is likely less permeable, because of the cementation that ultimately occurs.

 

[cvg]

Limestone is far more reactive if you have low ph soils / water, Granite is less so. crushed granite may be "decomposed granite" which is highly weathered rock that disintegrates into mainly sand. crushed granite quarry rock that is not decomposed is more competent material.

 

[oldestguy]

Assuming the supplier has good quality control, fine.

However, decomposed granite can be found alongside very decomposed granite that is a fat clay. You might see if they have any tests for LL and PI, just to be sure.

 

[cvg]

we do not allow DG under structures, only competent, crushed quarry stone. around here, DG is used for landscaping

 

[ChuckI]

Thanks for the quick feedback.
That's about where I was going with it for the most part. The granite is definitely a good base in general. I'll give them the go-ahead on ordering, but will still be interested to see what our geotech has for input. I'll ask them to provide the test results from the supplier for that material.

 

[BigH]

Just wondering what the LA Abrasion test value or the Micro-Deval value?