Building a rocket cook stove - can you help?

I want to make several rocket cooking stoves for cooking meals/boiling water in times of an electricity outage.

I'm using 5 gallon buckets, but I might get some slightly larger open head steel drums. I made one from 50/50 portland cement and garden vermiculite and, as you can guess, it is very crumbly and basically falling apart after several firings. I want to move these guys around, store them in the garage, etc. and they need to be durable and ugly - so, cob is out.

Does anyone know which kind of commercial refractory castable would be most suitable for this? I am trying to find a balance of a castable which is abrasion resistant & tough, and also will not crack/break when under temperature. I would think the temperature inside would be relatively low (compared to pizza ovens, and kilns obviously). In the UK I have been looking at kiln suppliers which offer several grades which range in different temperature.. Guessing higher temp rating stuff = softer. I am also thinking of adding 2-3% steel needles to the castable for strength.

2nd question: What ratio of refractory vermiculite should I use in the castable? The stove is much more efficient when there is some insulation.

3rd question: Would I benefit from adding a layer of fire bricks at the bottom/half way up the vertical heat riser? Would this increase the efficiency and also increase some abrasion resistance for feeding the fuel?

Many thanks if anyone can help me with these question marks. Cheers!

Matt Jackson : This is not a shaggy dog story, though it does have some few twists and turns ! While not the lightest example this is a good place to start
for something strong, durable and portable !

Do a google search for Tea Stump Rocket Stove pictures, if you get directed to Stump tea you went wrong ! If you get directed to Tea Stomp Rocket
stoves thats good ! As this project was made for an Elementary Teacher the surface was literally made to look like a disney version of an old tree stump
and the picture shows a large black canning Kettle on top !

After you find the picture described you can click on the picture and a link to E & Es blog will appear and give you a little more information, irregardless
of any thing you might find in the Crap on U-tube, do not include iron/steel in your build Except for the little shelf the wood sets on.

And do not use any Portland cement within the refractory material you mix with the Clay and Sand that Are the primary materials of your build !

This should get you started, and even without lightweight portability as long as you keep it out of the weather, these Rocket stoves will last a long time
burn surprisingly clean~ish, with very little wood, and stand up to marathon burning times ! Hope this helps and is timely, for the Good of the Craft!
Big AL

Matt Jackson : Because the goals of strength, durability and a long useful life are not common characteristics of Insulation and other highly refractory materials,
and then add in the fact that both iron/steel and Concrete are damaged by the temperatures found in the Rocket Stove, every thing we do is a trade-off !

In the column listing of all posted threads, most recent 1st you should see the Rocket Stove Forum Thread ''Fake Fire Brick'' I want you to L@@K at Erica W.s
thread extension of Dec 20th, especially the last 3 paragraphs where she nails the explanation of the most common materials used in Rocket stoves and hi-end
Rocket Mass Heaters ! Big AL

Al. Thanks for the great info. Between your advice and the "Fake fire brick" thread, I feel like I will pretty much be able to avoid the biggest pitfalls in constructing these cook-stoves. If I get good enough results I'll be sure to share the photos here.

Thanks again!