As the title suggests. If roman concrete supposedly has the capabilities to mend tiny cracks via chemical reaction, why isn’t it used with modern reinforcements to seal the pathways to the steel beams to protect it from oxygen and elements and prevent corrosion? Are there any major downsides to hot-mixed concrete, is it not as good as the studies make it out to be, or is it simply not viable due to cost and manufacturing process/storage requirements?
Very simply, because Roman concrete’s magical properties are somewhat overstated by urban legend.
There are a few factors here. For one thing, the only examples of Roman construction still standing today are those which were wildly overbuilt and which happened to have particularly strong materials, because everything else has long since crumbled due to errosion and earthquakes and scavanging. This in turn means that we are *only* seeing the absolute strongest examples of Roman concrete ever poured; not every batch was this good, and not every building was built this strong (in fact, only a small number of each were). This is related to the old maxim that any engineer can build a bridge that stands, but it takes a really good engineer to build a bridge that *barely* stands. Modern mathematics and technology has made us much, much better engineers than the Romans, which ironically means we tend to build things that are much less durable (but also vastly cheaper).
Another important factor here is that Roman concrete isn’t really *that* mysterious in terms of chemical properties. We’re well aware of how to make similar concrete, and we’ve been aware for a long time (though we only recently got confirmation of what exactly the Romans were doing), but we actively choose not to. The main reason we choose not to is modern construction has other techniques available to it, most notably steel reinforcement, which makes it better to mix concrete with a different set of tradeoffs than what the Romans had to do. Modern concrete sets a lot faster and is a lot stronger than Roman concrete under compressive forces (which are the only forces modern concrete has to withstand, specifically because of reinforcement).
There’s more that goes into all of this, but the tldr is that we *could* make Roman concrete if we wanted to, and we’ve been able to do it for a long time (even though we didn’t know for certain that it’s what the Romans were doing), but we choose not to because the concrete mixtures we’re using today are much better than what the Romans were using *within the context of modern construction*. Additionally, we *could* build things to stand for thousands of years, the way the Romans built a few of their works, but doing so is wildly expensive and probably completely unnecessary: after all, it’s not like the *Romans* are benefitting from the fact that the Pantheon is still standing. So we don’t tend to overbuild anything to that extent because no one wants to pay for it.