Re: to Al- Comparing kiln building and RMH is really interesting. There's the practical technical science, but then the adaptation of available materials aspect that is very similar in both groups. Plus no one wants to build something that melts down (seen it) or has the fire department breathing down your neck (been there), Of course saving money and recycling where possible is one of the appealing aspects of both to me.
I can really only relate my experiences and observations in firing and kiln building to what people are doing, fire being fire and all. Between college/work/personal experience I've fired or help build about sixty kilns of all types so a broad range. There is a lot of cross over, but a lot of differences too.
I looked at the link you posted. It has good info. But. I know a few people who have made bread ovens- all potters, all data junkies with stop watches, pyrometers and kiln logged tests and the temps are 1000-1400 tops. And compared to a kiln or RMH firebox, more open...cooler burning, although I don't know by how much. Point is not as intense. Also short burns, and much less fire/wear time. So I don't know how helpful for referencing RMH's.
On the other side, kilns are usually built with one potters clay, glazes, and firing temp as driving design considerations. It's about efficiency and cost of firing in relation to the product, both in individual firings and life of kiln.
Ovens and kilns have the same purpose. Raise the temperature to a desired point, then shut it off and let it cool. In the kilns case, as slowly as possible. RMH's are a bit more like a forge or glass furnace for the sustained length of generating heat at such high temps, and using the rushing air as an accellerant.
The potter you refer to Simon Leach? possibly? If so I actually met him- he was on a workshop circuit in the early 90's and did one at Munson Williams in Utica. (near me). Hate to admit it, but I'm not familiar with any kiln-related videos he did, will check it out.
As to others to look at, I think sustained wood firing would come the closest in concept. Especially anagama style kilns; historically and their modern equivalents. And there's as many different opinions and variations as with RMH's but going back to ancient times! US southern groundhog kilns too- also use the earth as mass.
The cement in any mix would definitely not contribute to strength other than when wet as a stiffening agent. Even without any breakdown from heat, 10 % is not anything. Nylon fiber would add more when it's dry, which of course would burn out and be no help when wet. I would not use (any) cement in any mix for the hottest areas. At 2400F, especially in the absence of oxygen, the cement could act as a flux and combine with the clay in the mix and lower the heat tolerance significantly. You can definitely make your own soft firebricks with sawdust but you need use a known fireclay or do very good testing on found clay. Most mixes I've seen like I described are over arched kilns etc. With mine, I had a generic furnace firebrick liner (on their sides for economy!) and my interior temp was max 2150F b/c I was firing local clay and that was it's limit. It was an insulating layer between an outer scavenged mix of red bricks for protection from the elements.
More on real bricks; firebricks (hard or soft) are rated for temp limits. Especially important under their own weight because if overfired will start to melt and slump. They are basically high alumina large-particle clay that doesn't expand much. Here's a good chart for reference: http://www.sheffield-pottery.com/SOFT-BRICKS-Insulating-Firebrick-s/372.htm
Look at the Si:Al ratio for each temp increase. You can similarly get the breakdown on any dry bag of clay you might buy to make your own mixes. Different clays are available in different parts of the country, although you can ship anything. But there's only a few types so regional is fine if it meets the specs you need. In addition to masonry suppliers, potters or schools/colleges near you may order regularly and you can often combine shipping to save if you want to order in bulk. Some found clay is fireclay. More found close to the surface is earthenware which fires red, and contains a lot of different impurities that basically melt it into a glaze at anything over 2000-2100F sometimes a LOT lower. Think of the old Albany slip that was used on antique crocks as a liner glaze. Fired lower as a lump it would be a brick. If that brick was heated to the stoneware temp used in the salt kilns the crocks were fired in it would melt into a puddle. This chart could be useful too for people trying to get a grasp on temperatures and supplies: http://www.ceramicstoday.com/cones.htm
There are recipes around on various pottery sites to make your own kiln furniture. Posts, specialty supports even shelves. Not at all difficult. Probably worth the effort for a few to go in on together if planned out well.
My own next question would be, Why use brick at all vs steel as some I've seen to line the Combustion chamber? Seems expensive. What creates the wear and breaks it down? What do you mean by protect it? Is the softbrick to prevent a buildup of heat within the barrel so it pushes more into the mass? Again, I've seen some that look like they are using hard firebrick... do their barrels put off more initial heat into the room?
Also why does the sand type matter? For sharpness or mineral makeup?
So many variables to take into consideration!