Hi Chris - yes i wish i could have suggested it too, as i know how much enjoyment & satisfaction there can be in a project, thats what dissapppoints me so much with ur project to date. u obviously put a lot of time into plans approvals, costings etc & in most cases its the pouring of the slab that gets us all excited cos ur on the way & watch it grow, unfortumately this has'nt gone to plan for u to date, but if u get the professional help ur planning now, i'm confident that with ur resillience once u have fixed up the slab u will get much more satisfaction as u progress.
i'll just relay a little story i was told by an engineer about concrete strength, he said in USSR when they started building more modern cheap multi level flats, the concrete & reo was that "minimal" in standards that occupants hated living there becos floors all "dipped" into the middle of the unit, so badly that if anything fell off the table it would roll to centre of the room!!!!
they had a lot of trouble with residence not wanting to live in the structures, so to recify the problem they simply poured a slurry of concrete into each room & trowelled off to flat finish - no strength just cosmetic - but it overcame the resistance!
regardless of ur worries, ur slab is on flat ground, single level, has right reo & good thickness, if engineers r at all worried they will make suggestions to improve, the main thing is for u to be confident to continue.... it will get better from here cheers tony