A certified batching plant. Ask whether the plant is computer-controlled and load-cell based — this is what keeps batch-to-batch variation low.
Documented mix design. A supplier should be able to tell you the grade, admixtures and water-cement ratio for your specific order, not just "standard mix."
A slump test on delivery. Workability should be checked at the point of pour, not assumed from the batching plant reading alone.
Realistic delivery windows. Concrete has a limited working time after batching. A supplier who can't commit to a delivery window close to your pour time is a risk to your schedule.
A QA-QC team you can actually reach. If a question comes up mid-pour, you want a lab and engineering team who will pick up the phone — not a call centre.
