Is it permissible to study the subject of "Construction Economics," 90% of whose calculations rely on Riba-based interest, and which is useful in evaluating alternatives and financing projects?

There is no harm in studying Riba (usury/interest) for someone who does not intend to act upon what is forbidden, because the means share the rulings of their ends. Therefore, there is no harm in studying this subject, provided one has good intentions and dislikes Riba in their heart.