Years ago my wife was helping her dad mix concrete... ranch was too remote for any concrete truck... so they opened multiple bags of concrete on top of the gravel brought from town, and dumped water into the back of the old 2 1/2 ton grain truck.... so my wife would speed forward, slam on the brakes, after the mix settled down, put the truck in reverse, speed backwards and slam on the brakes... and repeat.... once her dad though they had a good mix, they dumped it into the project