AFAIU, the original Interstate Highway System was all concrete. These days states usually resurface heavily trafficked segments with asphalt (of various varieties) atop the old concrete. Apparently, at least as of 2006 60% of the system was still concrete pavement: https://pubs.usgs.gov/fs/2006/3127/2006-3127.pdf Which is not surprising as IME long segments of the IHS are often still concrete pavement, especially in the South and West; it's only in urban areas where asphalt surfacing seems ubiquitous.
I'm not sure how new segments are built today, but they may very well still use concrete underlayment, or at least something more substantial than loose aggregate. Road tech these days is way more complicated than just concrete v. asphalt. I would guess that for remote segments, and given the load requirements, it may still be cost effective to keep using concrete surfacing.
I'm not sure how new segments are built today, but they may very well still use concrete underlayment, or at least something more substantial than loose aggregate. Road tech these days is way more complicated than just concrete v. asphalt. I would guess that for remote segments, and given the load requirements, it may still be cost effective to keep using concrete surfacing.