Johan,
I haven't heard of anyone doing slump tests with papercrete (not
that it cannot be done, but with enough water to saturate the paper
and the different kinds of paper, I am not it will work as
consistantly as concrete will for test purposes).
Also, with papercrete, larger aggregate (bigger than sand) is normally
not used from what I understand, and since it needs to be a paper
slurry, the paper and initial water are usually the initial things
added to the mix, followed by cement, then sand (if used) and other
additives. As with all 'crete (con- paper- adobe- dirt-) each
practitioner seems to have their own 'secrete recipe', so there really
are no rules, just guidelines and experience.
I wonder if anyone has done empirical tests on papercrete as to the
effect of water? I know water is very important with concrete and you
need enough to hydrate the cement fully. Since so much is needed to
make a paper slurry, and it becomes
a fairly 'weak concrete' using normal mixes, I would expect that 'to
much' water is available to make the concrete strong.
In concrete there are 'air' entraining additives to reduce the size of
the air bubbles and make the of consistent size. This helps reduce
the need for water and helps with the freeze thaw characteristics (and
with less water to hydrolize the cement or other cementatious
additives (crushed slag or flyash) adds to its strength).
Talking with a friend a few months ago, his company took some cores
from a 75+ year old bridge that was being pulled down for replacement.
They tested the cores and as expected, they keep getting harder for
many years after the concrete is poured. On this bridge it had only
hydrated 75% of the portland cement, so it still had a long way to go
to get to it's ultimate strength. ( Typically 30 day strength is
considered 'full strength' for construction purposes. But concrete
keeps getting harder and harder. After it is initially set, it also
helps concrete to be fully under water to ensure there is enough water
to hydrate the cement. Except for bridge footings, or test samples
that are kept under water to ensure full hydration, it never seems to
happen. )
I like your idea of making sure you use the same units when measuring
(volume or weight). The concrete industry tends to use weight. Small
users (like most of us) tend to use volume just because it is easier
for us. Neither is bad, but consistency is the goal to getting
consistent batches!
I have a professional concrete person friend who mixes things in
different orders (sometimes I think he is just messing with me :) ).
The water before the cement keeps the amount of cement dust floating
around down (a good thing), other than that, any order is OK but you
have to mix it long enough after the last stuff is added to ensure a
homogeneous mixture.
Paper doesn't have to be shredded, but it takes more powerful mixers
to tear paper and make it into a slurry than to take pre-shreaded
paper and make it into the same slurry. To me it makes sense to have
it pre-shreaded if you don't have as strong a mixer just to ensure the
consistantcy we are after.
><> ... Jack
Whatever you do, work at it with all your heart... Colossians 3:23
"You don't manage people; you manage things. You lead people."
"It's easier to ask forgiveness than it is to get permission" — Grace
Hopper, US Navy Admiral
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