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.