I believe the building didn’t explode, it shrunk.
The explosives are placed alongside the store of faux-Pym particles. We don’t know how Pym particles are stored, but they seem to be inert while in containment. Once the explosives go off, their containers are destroyed, and the Pym particles are spread throughout the building. But they’re out of containment, and so they almost immediately activate and start shrinking the building. This gives the appearance of the building imploding, and explains why there’s no wreckage left.
(I saw the film a week ago and my memory is somewhat sketchy, so details may be inaccurate)