CTS (800-929-3030) manufactures cement for flowable fill. The tech data
sheet says it is placed with a "sandy, soupy, pourable" consistency, it
hardens in 1/2 to 2 hours, is a one-sack mix and attains a strength of 1500
to 5000 psi. Their technical data sheet doesn't answer all of your
questions, but their tech. rep. may be able to answer them by phone.