Successful Rome's engineering and infrastructure

Exactly. It's the "Legio I Italica". It works as a counterbalance for the Pretorian Guard pretty much like the professional bureaucracy works as a foil to the army at large. And vice versa, of course.

Also i wonder would Roman concrete see early reinforced concrete as with no fall of Rome the making of Roman concrete is not forgotten like OTL after when the use of cement gradually returned.

Very much so. ITTL Europe-plus loses nothing of the technological, cultural, and socio-economic achievements of Greco-Roman civilization at its apex and doesn't have to reinvent them nor crawl itself out of the pit of manorialism and feudalism for the better part of a millennium, nor it suffers two millennia of fratricidal wars and the Arab world remains a resource rather than a threat. It keeps all of them and can keep building on them and integrating with new insights that were in its potential and ideas of Asiatic civilizations being shared over a fully-functional Silk Road. Therefore, its natural evolutionary pattern in these circumstances seems a direct jump from Roman Principate to a combo of High Middle Ages & Islamic Golden Age with no manorialism, feudalism, or division of Europe and the Med, then Renaissance, and eventually industrialization, only a half millennium or so earlier. Of course, the sophisticated Asiatic civilizations stand to gain as much as Roman Europe-plus from the Silk Road proto-globalization circuit. If Rome can get early efficient access to Hindu mathematics and the Four Chinese Inventions, China and India can get Roman concrete and engineering just as easily. This is one reason why I expect success of Rome likely boosts Chinese East Asia into being the superpower twin of Roman Europe-plus. The outcome of India is critically reliant on whether different circumstances in the rest of Eurasia can drive it to political unity in time to avoid being swallowed by the Romans when they achieve global reach. If it does, it can certainly become the third superpower. If not, Roman Europe-plus can certainly do what the Muslims and the British did, only with much better chances of lasting assimilation. If Rome remains strong and absorbs all of Europe and the Med, Persia doesn't stand a chance in the long term. The Romans shall eventually harness enough resources from their empire to eat them alive. Now if Persia could somehow achieve a fusion with India, it would be another matter entirely.

As promised, the main successful Rome TL I was revising is now posted. Go and enjoy it, most issues discussed in this thread are addressed there to the best of my ability.

It is always a pleasure since your questions and arguments are always constructive, kind, and helpful. Feel free to make more now that you have the entire ATL frame of reference I was relying upon for my answers. I may even post the modern Rome snapshot as an appendix to the main TL in the near future if I can revise it to my satisfaction.