Crushed concrete moisture issue

[powerslave42]

I'm perfoming a modified proctor on some crushed concrete to be used as fill and all of the moistures are coming out to within about +/- 1 % of each other (about 14%), reguardless of the apparent moisture content. This seems too high to begin with, adding that to the fact that they're all coming out the same. This is the second such set of problems with 2 different samples from different locations. I have also tried both oven and microwave methods to obtain the results. Any ideas?

 

[jdonville]

powerslave42 (I like the Iron Maiden reference),

What MCs are you trying to run your proctor points at?

Jeff

 

[Scienceguy57]

Are there many fines in the crushed concrete? Sounds kind of like you're getting the wave action of a clean sand which would require a relative density. Or maybe your sample came in from the field past optimum and you need to dry it out to get below optimum and then go from there.

 

[powerslave42]

We do always dry the material at room temp. under fans before running the proctor, then add water to achieve points about 2% apart. How dry or how wet just depends on a visual evaluation. (e.g. 12 lbs material adding .24 lbs water is 2%) no point had more than .96 lbs water added and the all came out the same. Thanks for the replys!

up the irons \m/

 

[powerslave42]

Oh and yes there are alot of fines (similar to ODOT 304s. I don't know what they are called outside ohio) but I'm not familiar with relative density. We do run alot of sand and have problems with that sometimes too, but maybe that is another can of worms...

 

[Scienceguy57]

Relative density tests (ASTM D4253) are used for cohesion-less soils like a poorly graded sand with little or no fines for another way of determining what the optimums are. SPs don't display a normal moisture to density relationship so doing a proctor on them doesn't yield a good curve with a peak for optimum determinations. Doing a proctor on them produces a "wave" in the dry densities with multiple optimums. Your fines should be providing some cohesion unless they're actually just fine sand and not -200 silts and clays. You might try a #200 wash if you haven't to determine your % fines. Crushed concrete still has some un-reacted cement in it and that may provide some cohesion. When you extrude the soil from the proctor molds, what's it like? Does it just fall apart or is fairly solidified? Your problem still seems different though since your M% are all coming out the same. With a proctor on a SP you’d still get varying M%s. How long do you let your sample sit before you pop it in the oven? I wonder if maybe the concrete was from a mix design with an accelerating admixtures and some of your water is reacting with the cement even before you pop it in the oven. Weird problem…