Foamed glass gravel was invented in the early 20th century, by the Soviets no less, and started being used more in the 80s. It is a "boring" technology. (Source: https://www.glavel.com/foam-glass-aggregate-guide/)
Also it was used for a temporary repair to get the road open again while a permanant repair was made using more conventional roadbuilding.
If you know something is a temporary repair and time is the most important consideration, you can take risks or shortcuts (crushed stone wasn't available) because you know it's not a permanent fix.
If you know something is a temporary repair and time is the most important consideration, you can take risks or shortcuts (crushed stone wasn't available) because you know it's not a permanent fix.