The last time I asked about adding glass in something, the answer I got is that adding glass to steel alloy is, for every intent and purpose, impractical. But what about concrete? Is using glass in concrete or mortar more practical?
Here is the scenario--in an alternate Earth, this is the map of Europe:
Marked in brown are the mountain ranges (the Skandies, 18,510 feet above sea level; and the Alps, 22,838 feet above sea level). Marked in red are the uplifts and plateaus that result in the mountain-building. Only the Skandies (Scandinavia) are capable of releasing ash into the atmosphere and settling them to the ground. Not marked but still capable of producing ash are the islands of Corsica, Sardinia, Sicily, Crete and Cyprus. One producer is too far from the Roman Empire for the Romans to mine or collect. The other producer just couldn't produce enough ash for mass-production.
If the Life After People episode "Heavy Metal" were correct, glass is biodegradable, and almost a century after Rhyolite, Nevada, was abandoned, the glass is still in pristine condition.
With that in mind, in an alternate scenario, in the absence of volcanic ash, could glass guarantee the longevity of non-reinforced Roman concrete?