It's more than just the fuel used to fire it. The limestone itself
gives off CO2 as it gets cooked. It's a fundmental chemical process
that is required to turn the limestone into cement.
There are some cement plants that use alternative fuels. Old tires
is one example. Tires burn at a very high temperature. Keeps them
out of landfills. The key is having proper pollution controls on the
furnace. Combustion of tires, natural gas, oil, or whatever fuel
still gives off CO2, though.
Another factor to consider in the strawbale comparison. How much
extra fertilizer does a farmer need to use because the straw doesn't
compost in the field providing nutrients for the next crop? Chemical
fertilizers aren't exactly CO2 friendly. There is no free ride.
Don't get me wrong. I like strawbale construction too. It makes a
great deal of sense if you have source of bales close to your
building site, like in most rural areas. Live off the land!
Adobe builders apply that principle in the southwest.
Same principle applies to papercrete. Used paper is a plentiful
cheap resource available in urban areas. Build with the resources
close to your site! Paper is everywhere. It was transported for
other uses first, so now it's cheap and easy to find for our uses.
Most importantly. Arguing about who is "greener" between strawbale
and papercrete is a pointless exercise. The best way to green a
structure as far as CO2 is concerned is to build a super energy
efficient one. It pays CO2 dividends for decades to come and is less
expensive over time. The small differences in CO2 emission during
the construction process pale in comparison to the kilotons or
megatons of extra CO2 that are produced providing the extra energy
for inefficient structures (even if they are up to "code") over their
life span. Note: I'm talking megaTONS. That millions of tons.
Trillions of pounds! Why quibble of a few POUNDS for a bag of
cement? Makes no sense!
--- In papercreters@yahoogroups.com, Mikey Sklar <sklarm-yahoo@...>
wrote:
>
> When Portland cement is being made from limestone, natural gas or
> propane is used to heat the limestone. White portland would have a
> even higher CO2 footprint as it is cooked longer.
>
> On Aug 8, 2007, at 9:21 AM, "slurryguy" <slurryguy@...> wrote:
>
> > Does clinker outgas CO2 as it is getting fired? How much?
> >
> > I'm not disagreeing with your overall point. I actually agree.
> >
> > --- In papercreters@yahoogroups.com, Mikey Sklar <sklarm-yahoo@>
> > wrote:
> >>
> >>
> >> I have been tormented by a few local adobe and straw bale
builders
> >> for my use of Portland cement. They point out to me that by using
> >> a high energy product that I am destructive to the environment. I
> >> had my doubts and decided to run some numbers this evening about
> >> just how much CO2 was being produced to create a bag of portland.
> >> The answer I came to was less than 26lbs of CO2 per 94lb bag of
> >> portland. I suppose I can now point out to the so called green
> >> builders who are hauling straw bales or pre made adobes from
across
> >> state boarders that their CO2 footprint is orders of magnitude
> > larger
> >> than my own.
> >>
> >> - portland cement 4,700,000 million btu per ton
> >>
> >> - convert btu's per ton to one bag of Portland (94lbs)
> >> * 1 ton 2000lbs
> >> * 2000 / 94 = 21.28
> >> * 4700000 / 21.28
> >> * 22,0864.66 btu's per bag
> >>
> >> - convert btu's of natural gas to pounds of CO2
> >> * 1 million BTUs (NG) will produce 117.08 pounds of CO2
> >>
> >> - convert btu's per ton of portland to pounds of CO2
> >> * 4,700,000 / 1,000,000 = 4.7
> >> * 4.7 * 117.08
> >> * 550.276 lbs of CO2 per ton of Portland made from Natural Gas
> >>
> >> - convert lbs of CO2 per ton of Portland to bag of Portland
> >> * 550.276 / 21.28
> >> * 25.86 lbs of CO2 per bag of Portland
> >>
> >> When we consider that jet fuel, diesel, and car fuel all produce
> >> about 20 lbs of CO2 per gallon we can see that a bag of Portland
> >> is producing the same amount of CO2 as driving 20 miles in your
> >> truck.
> >>
> >> If you want to bring yourself to neutral on CO2 for your Portland
> >> usage. Consider that the average tree will absorb 26lbs of CO2
per
> >> year.
> >>
> >> Keep in mind that we humans on average exhale over 2lbs of CO2
per
> >> day.
> >>
> >
> >
> >
> >
> >
> > Yahoo! Groups Links
> >
> >
> >
> >
>
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