Hot Stops and Hot Starts As a Plant Inspector it is your responsibility to insure all AC mixtures purchased by Caltrans meet the minimum specification. When a plant operator performs a hot stop, the proportioning of the aggregate, dust and asphalt binder no longer meet our tolerances. If the aggregate and asphalt binder drop above or below the approved production rates established during the CT 109, proportioning error is know unknown. If the drum is left full of aggregate, the hot asphalt binder can drain out of the spray bar and over asphalt the aggregate still in the drum. All AC mixtures with unknown proportions or adequate temperatures should be rejected and not sent to the silo.