I appreciate this reasonable and clear explanation of the use of cement in papercrete. I have to admit I haven't carefully read the technical things that have appeared here. My eyes tend to glaze over at such things, although I admit the information may be interesting (?). Anyway, I look at mixing papercrete like making bread. If you have the basic things that make it what it is then you can add and experiment all you want. Maybe it was here that you saw cellulose insulation added to the mixer. It was quick and easy but would get expensive if used all the time.
At the risk of being redundant I must repeat - the beauty of papercrete is it's elemental simplicity and inexpensiveness. For an $11 investment for a bag of cement I can have a good portion of a wall. If I can't get cement or can't afford it I can use clay soil. If can't get newspapers I can use cardboard or junk mail from the post office.
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To: papercreters@yahoogroups.com
From: Spaceman@starship-enterprises.net
Date: Fri, 3 Jun 2011 07:40:44 -0600
Subject: Re: [papercreters] Re: Papercrete mix design
Periodically we seem to get concrete folks on here who proceed to tell us how we are doing it all wrong and you can't mix concrete like we do. Well, the thing is that papercrete is NOT concrete and they are not very similar. Papercrete often is used in a liquid state, thin enough to pump, and has no slump at all. With concrete the amount of water is absolutely critical to the final strength of the concrete. That does not apply to papercrete.
Most often it is the mixer that is pulping the paper in a water bath. You have to use enough water to mix, and then the bulk of the water is drained off. The mixing methods used for concrete do not apply here. I have only seen expensive cellulose insulation (dry fiber) used for papercrete once, and it was simply dumped into the mixer along with water, cement, pumice, etc., and all were mixed together. Normally this wet mix is put into forms or molds where the extra water rapidly drains away, leaving a soft material that will finally develop some firmness after a few minutes of draining. Molds can often be removed within a few minutes of filling. Depending on the thickness, the mix, the temperature, the wind, this material may take days or weeks to dry out and become hard.
A few weeks ago I looked at trying some cellulose insulation in a concrete mixer but backed off when I realized the final product would cost more than $10 a cubic foot. Not to mention that buying a product like that would negate the green/recycling aspect of using paper destined for the landfill. If there were a cheap source of pulverized paper then it would be possible to mix with less water, but exact ratios could be thrown off by humidity since paper absorbs moisture well. There might be a wide range of water content that would be mixable since the fibers are absorbent. I think papercrete mixes are like cooking - recipes are a starting guide but need to be adjusted for real conditions.
spaceman
All opinions expressed or implied
are subject to change without notice
upon receipt of new information.
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On 6/3/2011 5:59 AM, Johan wrote:
Hi everybody, nice question folks. A good method in concrete mixing to obtain consistency is the slump test whereby a prismatic shape tin container without a bottom is filled with the concrete/pc mix. The tin is then removed upwards and the height of the material that it has slumped to is measured. This is then recorded and compared to the height of the tin as a percentage including the details of this particular mix i.e. cement type and brand and possible batch # in one column with amount used by volume or weight. The next column contains type of sand/paper used and preferably weighed dry. Record the amount of water used because too much water weakens the strength of the concrete/pc. I have the details somewhere and will post it as soon as I have found it, but the point is that even if there is no current standards for pc you can record your own slump heights results for own use. The point of the exercise is to obtain consistency and being able to record your experiments with various mixes for different applications.
Just another point of interest is that the addition of slaked lime (not agricultural lime) will give the mix a nice buttery working consistency and it will strengthen the material more over a longer period after the cement has reached it full strength.
Slag cement also increases strength after Portland cement has stopped but for all these additives you must remember it does not reach its maximum strength as fast as when you did not use it. It needs time as in years to develop full strength.
When concrete is mixed in a drum mixer, the stone is added first, then follows some of the measured amount of water just to coat the stone followed by the cement and then only the sand and final water left over. I would assume that the dry paper is shredded first followed by some water, then the cement followed by final water allocated for the mix. Please inform me if it is different. Finally I apologies for any incorrect English since it is not my home language.
Regards
Johan Van Tonder
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