How long is 'Many years"?
These blocks would be produced in backyard or
workshop settings without ideal conditions. With limited controls, I think these homemade blocks would not have the same tolerances, strengths and longevity. Blocks produced commercially, in optimum controlled conditions, last for decades. Concrete is tough stuff. Environmental conditions and how it is used will impact the longevity of the block. Freezing and thawing conditions can have the greatest impact, all you need is a small crack which water can get into and disintegration can start.
My father poured some concrete steps in the mid 70s. They are still there today holding up fine. They'll probably be there another 50 years.
My uncle poured a short concrete wall around the same time. It cracked and fell apart in a few years.
These homemade blocks have many applications.
Would I use them to build a
shelter for livestock? sure.
Would I use them to build a home which children would live in? perhaps not.
These blocks are a fabricated material. They need to be proven and tested before one can place faith in their integrity. If they are packed tight, made from a proven recipe, allowed to cure, and placed well, I think they could be used for simple construction. A tool shed, livestock shelter, and containment walls would fit the bill. Multi-story construction would demand proven materials.