Straw bale is a very interesting concept, except that all that straw takes up a lot of space, and it needs to be covered anyway. To summarize this brief overview, I have looked at a number of alternatives, and I still favor the approach we have worked out. While there is a wide variation of possible recipes that will all work, it is useful to have a basic understanding of the chemistry involved with the use of lime. The classic way to do this is to combine lime with clay. Other sources of silica are also used, but there seems to be no agreement about the chemistry involved.
Sand is very high in silica, but because of the particle size, it is less significant than clay.
However, I have experimented with mixes higher and lower in sand, and my personal experience is that sand is an essential ingredient in the mix. Mixes with little or no sand are just not as hard or durable as mixes made with plenty of sand. Then there is the question of the silica component in the aggregate, the agricultural waste, weeds, chips, or straw. Hemp hurds are high in silica, and that is probably one of the reasons why the hemp hurds plus lime formula has been such a success in France. My personal experience confirms that hemp hurds perform better than just about any other similar aggregate material.