Hi Robert,
Thank you for your e-mail and mix design. I'll definitely try it out! May I ask you a few clarifying questions?
You mentioned clay in your mix design, and I just wanted to verify, you're talking about regular clay from the ground, right? Have you done any experimenting with metakaolin clay? I copied below a section from Eli Sutton's 3/3/07 e-mail about metakaolin clay. It seems like a very cool additive, but I don't know what cost it adds to a mix, and as it is formed through the thermal de-hydroxylation of kaolin clay (heating up the clay to drive off the water), it does release CO2 into the atmosphere.
Also, you mentioned using lime. I'm assuming you're referring to hydrated lime, right? Are you using it dry, out of the bag? or are you slacking it first?
Since lime is cheaper than borax, and hydrated lime has a pozzalonic effect and apparently inhibits mold, why do people use Borax? In your mix, Robert, I'm assuming the clay and sand content creates the flame resistance, so again, borax probably isn't needed. Borax users, why have you chosen to use borax instead of hydrated lime? Inquiring minds want to know!
warmest regards,
Eric
except from Eli Sutton's 3/3/07 post:
- "In a conversation with Clyde Curry (Eve's Garden, Marathon TX), he told me about metakaolin, a calcined clay mined in SC. The product is sold as Power Pozz (Advanced Cement Technologies. 435 Martin Street, Suite 2040. Blaine, WA 98231 http://www.metakaolin.com/ ) and is very cool stuff. It has a high pozzolanic activity, meaning it sets up like cement but by a different, yet complementary, chemical reaction. As I understand it, when portland hydrates and sets it releases Calcium hydroxide (lime), the metakaolin reacts with the free lime and hardens as well so you have two reactions happening simultaneously. Set time is increased dramatically--I am able to turn a block after about 24hrs as opposed to three days without the Power Pozz. Another virtue of the stuff is that it decreases water permeability by reducing the pore size in the cured concrete. I'm hoping (I haven't tested this because I don't have a dry/cured block yet) that this will actually slow water penetration into the block. I'm especially interested in trying the Power Pozz in stucco--our first line of defense.
- We are planning to make special blocks for the first two courses, the most vulnerable to water penetration and those carrying the most load. In addition to the Power Pozz we will be adding sand to the mix to increase compressive strength, and BlockTite (Euclid Chemical), a liquid admixture that reduces water permeablity. I think a good stucco design is the most important step we can take to prevent water problems, in additon to wide overhangs and meticulous attention to sealing openings in the walls. Here in Moore, TX, about 50 miles south of San Antonio, we have low rainfall and medium humidity so I'm not terribly concerned about humidity issues, but want to take every precaution possible to avoid problems with mold."
- We are planning to make special blocks for the first two courses, the most vulnerable to water penetration and those carrying the most load. In addition to the Power Pozz we will be adding sand to the mix to increase compressive strength, and BlockTite (Euclid Chemical), a liquid admixture that reduces water permeablity. I think a good stucco design is the most important step we can take to prevent water problems, in additon to wide overhangs and meticulous attention to sealing openings in the walls. Here in Moore, TX, about 50 miles south of San Antonio, we have low rainfall and medium humidity so I'm not terribly concerned about humidity issues, but want to take every precaution possible to avoid problems with mold."
- "Metakaolin
- Metakaolin is produced by calcination of kaolin (clay mineral) at 650-800°C. Kaolin is the by-product of oil sands operations. Metakaolin is a highly reactive pozzolan with a high specific surface, which makes it very suitable as a cementing material in concrete. Metakaolin particles are nearly 10 times smaller than cement particles, which results in a denser, more impervious concrete. Using metakaolin in concrete increases the durability of concrete (i.e. resistance to chemical attacks, sulphate, ASR expansion, and freeze-thaw cycles). Metakaolin also enhances several mechanical properties (i.e. early-age compressive strength, and flexural strength) of concrete. "
- Metakaolin is produced by calcination of kaolin (clay mineral) at 650-800°C. Kaolin is the by-product of oil sands operations. Metakaolin is a highly reactive pozzolan with a high specific surface, which makes it very suitable as a cementing material in concrete. Metakaolin particles are nearly 10 times smaller than cement particles, which results in a denser, more impervious concrete. Using metakaolin in concrete increases the durability of concrete (i.e. resistance to chemical attacks, sulphate, ASR expansion, and freeze-thaw cycles). Metakaolin also enhances several mechanical properties (i.e. early-age compressive strength, and flexural strength) of concrete. "
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