How many of us understand what a pozzolan is and how it works?
I know that there are a lot of our members that know this subject
very well. They probably won't get much from this post, however, we
also have members that may not understand it as clearly. This post
is targeted to them.
I don't claim to be the ultimate expert. However, I do enjoy trying
to help others break through seemingly complicated technical terms
with everyday language so anyone can understand on a basic level what
something is and how to use it.
I'll try to simplify pozzolans for anyone that might be confused.
Start by thinking chemistry. Don't let that scare you away. We all
deal with chemistry on a daily basis. Chemistry is all about
molecules and combining them together and taking them apart in
chemical reactions. Fire, for example, is a chemical reaction where
oxygen is combined with a fuel (usually something that has carbon in
it) and gives off heat (and usually carbon dioxide). We all use fire
everyday in some form. We might cook with it, or use it inside a car
engine. Our own bodies use our breathing to take oxygen out of the
air and chemically react that oxygen with carbon in the food we eat
to give us energy. See, YOU ARE a chemistry lab and didn't know it.
Pozzolans are chemicals that react with stuff inside cement.
Specifically pozzolans like to get friendly with "Calcium
Hydroxide". Pozzolans like to try to turn Calcium Hydroxide into a
hard rock like substance.
Probably the most common way you might see nearly pure calcium
hydroxide is to look at lime plaster. Slaked lime plaster
predominantly is concentrated Calcium Hydroxide and water. So, if
you mixed a pozzolan with slaked lime, you'd get a interesting
chemical reaction. In a way, pozzolans speedily turn the lime back
into something like the limestone that it was made from to begin with.
Cement contains some of the same stuff as lime plaster, but has a few
other goodies added to it. It's the lime portion of the cement that
gets all happy and "rocks out" when pozzolans show up.
Examples of common pozzolans are:
fly ash - the most common pozzolan, is a waste product captured
out of the smoke stacks of coal burning power plants
silica fume - a chemical given off during the production of other
chemicals
metakaolin - a form of a kind of white clay, "kaolin". If the
clay has become rock, it's called kaolinite. Kaolin, is also known
as "china clay". Yes, those fancy china plates everyone gives as
gifts at weddings, those are usually made from kaolin. It has lots
of very common uses, like in many paper products, particularly glossy
papers. Metakaolin is formed when Kaolin clay is heated in a kiln
like furnace. (similar to the cement making process)
Each of these materials reacts with lime to make a rock like
substance.
What's the point? Why use pozzolans?
In concrete, pozzolans enhance concrete, making it stronger. They
also can make it more difficult for microscopic water or other things
to pass through it. This is good for things like concrete bridges
that get salt dumped on them in the winter as ice melt. The salt can
seep inside the concrete and rust out the rebar weakening the
structure.
Why use pozzolans in papercrete?
Pozzolans will react with the lime component in cement whether it is
in concrete, or papercrete. This will create more rock inside the
tangle of paper fibers. At this point, there isn't much technical
data publicly available to prove exactly how pozzolans change the
performance of papercrete. It probably makes them stronger, and
allows someone to use less cement, but we don't have that exact data
for papercrete yet.
I hope some find this explanation helpful.
Now you can Ponder the Point of Picking Pozzolans and Poke fun at my
Puns and Pepper my Propensity for Pounding Powerful alliteration too.
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/papercreters/
<*> Your email settings:
Individual Email | Traditional
<*> To change settings online go to:
http://groups.yahoo.com/group/papercreters/join
(Yahoo! ID required)
<*> To change settings via email:
mailto:papercreters-digest@yahoogroups.com
mailto:papercreters-fullfeatured@yahoogroups.com
<*> To unsubscribe from this group, send an email to:
papercreters-unsubscribe@yahoogroups.com
<*> Your use of Yahoo! Groups is subject to:
