Light weight concrete with lava rock agregrete

Mars_3

Hello wallies, Ive got a question for ya. I have a infloor system in a house that is set up for hard wood floors with sleepers on 12" on center. the application is poord infloor with 1/2" tube stapled down 6" on center tubing placement. 2 x 4 sleepers. The contractor decided to use light weight concrete with a aggregrated of volcanic rock instead of the standard gypcrete. If Im reading Siggys article from 11-99 P @ M Magazine right Im in trouble. Any input would be helpful concerning light weight concrete in this application. This is the main floor and has a finished basement below.