Acceptable moisture content of granular fill 1

[Alan CA]

Hi everyone,

What's the maximum acceptable moisture content (humidity) of granular fill under concrete slab on-grade?
I know it may differ from code to code, but what's generally the maximum that we shouldn't accept?

 

[dik]

Determine it using a Proctor test... it should give you the optimum value.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Do you feel any better?

-Dik

 

[Alan CA]

Thank you for your answer. But isn't there a range to determine if test results are acceptable or too high for granular under slab?

 

[Eric C.]

The results of a Proctor test should give you the range. As dik said, the Proctor test will give you the optimum moisture content to achieve the maximum dry density. If your specification requires, for example, that the granular fill is to be compacted in such a manner as to achieve 95% of the maximum dry density then you should be able to look at the Proctor test curve for your project and determine the moisture content range, to the left and right of optimum, that is required to achieve the 95% compaction.

Alternatively, I have also seen some project specifications state that the moisture content of fill material is to be +- 2% of optimum at placement.

 

[Alan CA]

Thank you very mich Eric and dik. I appreciate your input

 

[TigerGuy]

I think we are all presuming you are referring to an aggregate base with some fines content. You have already received great information on that approach.

I typically recommend a free-draining aggregate directly beneath slabs, which doesn't really require a set range of moisture.

 

[Alan CA]

Thank you TigerGuy. I prefer the same but as the code allows for granular fills with fine content, we don't always see clear crushed stones under slabs so we need to deal with it

 

[EireChch]

Earthworks: A Guide 2nd Edition (Geotechnical and Environmental) Hardcover – 16 Jan. 2015
by Paul Nowak (Author)

The above book is one of the best references for earthworks.

I can’t remember what the range is but I would guess the max water content for a good quality granular fill with less that 10% fines is approx 15%

Also I would never refer to moisture content or water content as humidity, doesn’t make sense tbh