Q.: If a truck mixer will be broken down for an extended period, but we can still turn the mixer drum, what can be added to the concrete to completely destroy its set so as to prevent the concrete from hardening in the drum?

A.: The old standby for destroying the set of concrete is ordinary sugar. Many concrete mixer trucks carry a bag of sugar for just such emergencies. For most circumstances 15 pounds of sugar ought to be enough to kill the set of a 10-cubic-yard batch if it can be thoroughly mixed in. It would be best to completely dissolve the sugar before adding it to the mixer. Some companies prefer to carry excess retarder on the truck and add whatever amount they feel sure will be effective. The concrete is wasted but the mixer drum remains usable.