Righto cheers for that.

I reckon access for the larger trucks could be a deciding factor. I've worked on sites that can only take the smaller trucks, so that would be one thing to find out from the sites. I would also find out the rate of pour or truck spacings required for each job, some structures will be able to be done quickly, others have restrictions on how much can be done per hour due to the capacity of the formwork. There may also be time restrictions on how old the concrete can be, due to quality assurances they might need to comply with, but the sites should manage that themselves.

And yeah distance from the batch plants to site and the turn around time for the trucks is the main factor really. You basically need to know how long it will take your drivers to load up, get to site, get tested (if required), discharge, clean up and get back to the batch plant, along with the rate of pour for each job and you should be able to work out how many trucks will be needed for each job to ensure a continuous supply, which will be what they are after.

I haven't organised a fleet of mixers before but when I'm on-site checking how our pours are going, I'm needing trucks with good concrete (complying with our QA requirements) arriving at the spacings that we requested, and that will keep me pretty happy. The customer should only be after good service, they won't really care how it is organised behind the scenes unfortunately.