I seem to be a magnet for exploding concrete ... more on that in a bit.
If you've been following my blog, you know that I've been working on different mixtures of portland cement and a refractory cement, trying to find a balance between insulating and flame-resistant characteristics and durability.
My most recent mix was 10 parts of refractory cement, 7 parts portland cement and 5 parts of water. It turned out to be a lot more durable than the previous mixture (10:4:5) and not as easily scratched or as crumbly. The new mix was a little bit on the wet side, but formed very nicely in my styrofoam mould.
The previous mixture, even after almost a week of curing, was very soft, almost like sculpture's clay, but not as wet. The new mix is much nicer.
I decided to put it to a flame test. I tossed in a small aluminum rivet into one of the depressions and put the propane flame to it. It held up quite nice as the aluminum got to a nice bright glowing red, then *BOOM*, the new mix literally exploded. Good thing I had my welding gloves, full face protection, welding apron on and had the previous slab of concrete sitting on top of it. I guess I'm going to have to heat cure this stuff in an oven for a couple of days to get all the moisture out. You can see from the pictures that the force of the escaping steam was quite strong:
I've got a new mix in the works (7:7:4) which was much drier (and more difficult to mould) that I'm going to cure in an oven before testing it with the flame.
I've been experimenting with different mixes of refractory cement and portland cement. Today, I tried a mix of 10:4:5 (refractory cement, portland cement and water) by weight.
I whipped together a mould out of polystyrene foam (seeing as I've got 'tons' of this stuff lying around now) with a couple of square inserts as an experiment to see how well the concrete will conform to the shape.
After mixing up the two cements with water, I scooped it into the mould. I found that it was a little bit too moist, so next test I'll use less water.
8 hours later: the mix set quite nicely, except it seems to have the consistancy of clay before it's been fired. It can be handled carefully but is easy to mark. I'm going to let it sit overnight in the hopes that it firms up. Tomorrow I'm going to go to a 8:6:4 mix and and see how that turns out.
On the bright side, the cement mix conformed to the mould perfectly.