It certainly is not what became known as "concrete cancer",which is an expansive reaction between high alkali cement and certain silicates in the aggregates.
On the basis of the evidence available I think Mebu's analysis is spot on.
I thought it might be useful to add a little detail on why I believe the evidence is that "concrete cancer" is not the culprit here.
Although I am less specialised than Mebu I can attest that the term "concrete cancer" is used almost exclusively to refer to the reaction he describes, which is generally abbreviated to ASR. The analogy to cancer seems to be used because this is a progressive deep-seated phenomenon in which the concrete undergoes an expansion that causes it to fracture into progressively smaller chunks. The typical appearance of a structure that would arouse suspicions of being subject to ASR can be seen in the attached link. ASR
Unfortunately it would seem that this monument has reached the end of the natural life accorded to it by the particular combination of materials, and maintenance regime in its particular environment. One might speculate that the inconsistency of using concrete in preference to stone to achieve neo-classical details is an indication of a cost pressure which might also have led to economies in expensive cement content and consequent sub-optimum impermeability of the concrete for the environment, which may not have been understood by those commissioning a monument within a budget.
Although repair might be a theoretical option, if funded, it would demand very careful specification and execution to ensure a result even approaching monumental standards of durability. Unfortunately there are many examples where lack of experience by specifiers, inadequate understanding of proprietary repair materials, or sub-optimum workmanship have led to repairs not achieving the expectations of those funding them.
I hope this is a positive contribution to this interesting thread