WI: Roman concrete recipe survies

What impact would there be on European history if the necessary information and skills for making Roman concrete doesn't die with the empire but is preserved, most likely in some monastery, and continues to remain in use?
 
Imagine the Lombards with concrete! or more likely the early caliphate! They could do some pretty cool stuff!

Better yet, Lombard's stopping Charlemagne due to great concrete fortifications. Concrete fortifications keeping the Arabs in the desert and out of Persia, Syria, and Egypt.
 
Gothic cathedrals don't take centuries to build - the Hagia Sophia in Constantinople was finished in a mere 4 years, which will substantially change the look of many of them from what we are used to - you won't have many of them left unfinished nor would you see the evolution of the gothic style in one structure with e.g. different south and north towers, a high gothic choir and a flamboyant gothic nave etc..

Especially the framework of gothic church windows and the highly decorated spires would have been significantly faster to produce if they could have been cast in concrete instead of the slow and arduous artisanal masonary production of OTL.
 
Correct me if I'm wrong, but didn't Roman concrete depend on a volcanic ash that isn't really available outside the Mediterranean?
 
Correct me if I'm wrong, but didn't Roman concrete depend on a volcanic ash that isn't really available outside the Mediterranean?

Only when making wet-set concrete which the Romans largely used for maritime purposes like piers, dock pilings and the like. The 'standard' (as best as one could use that term in this context) recipe didn't need it for all the other stuff like municipal buildings, fortresses or aqueducts.
 
Better yet, Lombard's stopping Charlemagne due to great concrete fortifications.]

This part is definitely doable as all that would be needed would be purpose-built fortifications in the Alpine passes.

Concrete fortifications keeping the Arabs in the desert and out of Persia, Syria, and Egypt.

I could see these being built but that outcome is unlikely, there's just too much land to cover and the main reason the Caliphate utterly trounced Byzantium and Persia was due to those two empires battering each other bloody for an entire generation. It would, however, have a huge impact on the Middle East long-term if they gain access to concrete early on.
 
This part is definitely doable as all that would be needed would be purpose-built fortifications in the Alpine passes.



I could see these being built but that outcome is unlikely, there's just too much land to cover and the main reason the Caliphate utterly trounced Byzantium and Persia was due to those two empires battering each other bloody for an entire generation. It would, however, have a huge impact on the Middle East long-term if they gain access to concrete early on.

I think the PoD is the Romans and Persians looking at all these awesome fortifications and saying "this fighting each other thing really isn't worth it."
 
I think the PoD is the Romans and Persians looking at all these awesome fortifications and saying "this fighting each other thing really isn't worth it."

They already had some pretty impressive fortifications that were built based on that technology in place. The region had been a battleground between the empires for a good five hundred years by the time the Arabs came on the scene and the presence of older Roman fortifications or newer ones did nothing to deter any of those conflicts.
 
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