posted 10 years ago
Good points made by all. I have worked with concrete over the years on small projects, and seen a lot of backyard gardeners do their own thing. From what I have observed and what I have been told, there are 3 variables that will shorten concrete's life significantly. The first, not having the right amount of water in the mix combined with not mixing adequately. Second, not preparing a proper foundation for the project. The third, perhaps a bit distant third, not having the right curing time. In the past couple of decades, sealers have become an important part of the concrete picture - I am guessing rammed earth would also benefit from them as well, but if the foundation is not properly laid, the bricks will crack, and no sealer is going to prevent that from happening.
If I were to undertake such a project, I would certainly consult a PE to give me advice, recommend a soil/mineral mix and give me useful skills to test the mix with, and would also contract out some testing of sample blocks. I have access to free/very cheap equipment rental through friends, so I would be using a big cement mixer to prepare the soil to obtain a very uniform standard.