We have our plants inspected and certified in accordance with the checklist in Section 3 of the National Ready Mixed Concrete Association's Quality Control Manual. This certification includes truck mixer inspection to ensure that there's no appreciable accumulation of hardened concrete in the drum and that the blades are free of excessive wear. However, after the certification, how often should the truck-mixer drums be checked for accumulated concrete and blade wear?
Your drivers are a good resource for determining when concrete buildup or blade wear is a problem. They can visually inspect the inside of the drum during washout at the end of the day. Signs of blade wear include slow discharging or insufficient mixing, even after the required number of revolutions. You should be especially alert for hardened concrete accumulation if the truck is mixing low-slump concrete or concrete containing silica fume.