[Greenbuilding] Crushing Clay

[RT]

On Wed, 03 Aug 2011 16:55:44 -0400, natural building  
<naturalbuilding at shaw.ca> wrote:

>  tried the "dissolve-all-of-the-clay-to-make-a-minimally-wet-clay-slip"  
> approach at a fairly early stage in the process but it was totally  
> unworkable.

> The ratio of water to clay necessary to achieve the optimum Proctor 
> (compressive strength) is in the region of 30 - 35% by weight (water to  
> clay)and resulted in a ridiculously sticky mixture that was impossible  
> to thencombine evenly with the aggregate.It just turns into a large ball  
> covered in gravel.

The "minimally-wet" stipulation mentioned earlier was intended as an  
attempt to address the issue of excessive shrinkage (and possibly  
shrinkage cracking) after the mixture has been placed in the forms.

However, I don't think that for clay mixes, there is any issue similar to  
the critical water:cement ratio that affects the strength of the final  
product as would be the case for concrete where the water is apportioned  
like a chemical formula for hydration of the cement.
ie I don't think that there are any chemical changes going on in the clay.  
Molecular structure changes perhaps.

That is to say, I strongly suspect that one could make a soupier clay slip  
than would be implied by the 30-35% water: clay ratio you mention (for  
ultimate compressive strength).

ie Perhaps one makes the slip as soupy as is required to facilitate  
reasonable workability and then set the mud aside (perhaps covered if  
necessary to control moisture loss rate) to let it dry out to the desired  
moisture content to reach the 30-35% water: clay ratio  (maybe days, maybe  
weeks "curing" time) before placing in the forms for tamping ?

The term "unworkable" is pretty subjective too.

ie One of the most common mistakes that novices make when mixing  
cementitious mortars without the aid of a mechanical mixer is that they  
don't do enough mixing of the properly-proportioned mix and finding that  
it's too difficult to work with, add water to the mix to make mixing  
easier when in fact, what they should have done is mix longer with more  
elbow grease.

I know that a clay soil that seems fairly dry and hard and not amenable to  
being worked, will eventually turn into a pliable and plastic material  
when "kneaded" with sufficient (very high) pressure, not unlike what  
happens during the floating and trowelling processes in concrete finishing  
... a process of compaction that amongst other things, brings water to the  
surface.

I'm wondering if the unworkable, large, gravel-covered ball you mention  
was worked only by hand or were mechanical means tried as well ? (Like  
maybe something similar to an institutional-sized bread dough mixer ... or  
a herd of cows  ... or [ ] ?)




-- 
=== * ===
Rob Tom
Kanata, Ontario, Canada
< A r c h i L o g i c  at  Y a h o o  dot  c a >
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