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Re: Crushed Gravel Moisture Content

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On 31 Mar 2005, at 11:58, Michel Blangy wrote:

> Does anyone know what the typical moisture content is of 3/4" clean, crushed
> gravel? How does it vary with temperature and humidity when stored on site
> assuming it is covered?
> 
> Michel Blangy

Michel,

This is a difficult question to answer definitively, given the information that you've
shared.

There are four typical moisture conditions that we group aggregates into.

O.D. - oven dry - the aggregates have been run through an oven heating the
aggregates to about 225°F, there should be no moisture in the rock.

A.D. - Air dry - the aggregates have some pore water absorbed into them, but
are not saturated. (This condition is very difficult to quantify the H2O content)

S.S.D. - Saturated Surface Dry - all absorbed water is in the rock and the surface
of the aggregate has no water film or adsorbed water.

Wet - aggregates are shiny with a water film (adsorbed water) and may have
a difficult to quantify amount of H2O in the pile of agg.

I'm assuming that you are referring to agg. in the A.D. state.  These will usually
have between 0.5-3% water in them.  And yes, temperature and relative humidity (RH)
affect the moisture content of the stockpile.  The warmer it is with a lower RH, the
less H2O in the pile.  The only two conditions that can be counted on when designing
a concrete mix is the O.D. state and the S.S.D. state.  O.D. will 'suck' water like a
sponge reducing the water/cement (w/c) ratio in the mix.  SSD will not subtract or add
water to the designed w/c ratio.

As a general rule, the lighter the aggregate, the more water it can absorb and
the higher the water content will be in the stockpile.

Stockpiles are tricky, because the water content changes as you dig into the 
pile.  If the material was stockpiled in the O.D. state, then the  material on 
the inside will still be closer to the O.D. state than the outer layers of the pile,
which have absorbed some moisture from the air, especially in high RH times.
If the pile was stockpiled in the SSD state, the the outer layers will be drier 
and the inner part of the pile will be nearly SSD.  (Assuming consumption
of the pile fairly soon after stockpiling, not years later)

I hope that all of this helps narrow the question some.


Take care,
Lloyd Pack, P.E.


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