Would fly ash (by-product of furnaces) be a reasonable substitute for volcanic ash and chunks of volcanic tuff?
The reason I ask is that 20 years ago a professor at UWM (Univrsity of Wisconsin Milwaukee) published a paper on adding fly ash to the concrete mix used in road projects to improve its durability. He estimated that the addition of fly ash (readily available and almost free) would increase a highway’s longevity to 30 years, whereas now they repave about every 5 years and the roads are in poor repair in the meantime. I believe that his idea came from studying Roman roads.
The professor’s suggestion drew no traction and no action from Wisconsin’s road builders. We figure that it is because it threatened the job security of the labor force who likes to repave every 5 years.
We were in Beijing China a while back. It snowed a few inches and suddenly thousands of people with brush brooms, shovels, bicycles with plywood platforms appeared as if out of nowhere and began clearing the snow. I asked an English speaking guy why they didn’t use snow plows and blowers. He responded “but, then, where would these people find work?”
Flyash is mostly oxides, whereas volcanic ash is mostly a mixture of fine silicates and hydrated alumino-silicates; chemicallyand physically, they are different.