Here is the URL to the website which describes what is being done at DCA:

https://www.flyreagan.com/dca/project-journey

Here is the construction advisory page:

https://www.flyreagan.com/dca/construction-advisories

I think this construction runs through the end of 2021. If it ends up like the Metro extension to IAD, construction will go on for years after the scheduled completion. I think the part of the project that is furthest along is the new AA commuter plane concourse to replace the infamous bus gate 35X (on the opposite side of the "new" north terminal from where DL is).