Shamrock Coal Co.'s mine in Asher, Ky., uses conveyor belts to transport mined coal to an outside processing plant. The drives for the conveyors are mounted on 18-foot-wide concrete slabs. Each slab uses about 70 cubic yards of concrete. When the construction of the slabs began, in 1990, workers transported bagged cement and aggregate to the underground jobsite, where it was mixed in a paddle mixer. The costs for each slab was about $28,000.
Tommy Spurlock, Shamrock's maintenance foreman, was given the challenge to find a more efficient and cost-effective method of completing the drive bases. He designed two railcars, each capable of transporting 7« cubic yards of concrete to the jobsite, where it was then pumped out of the cars. The railcars solved one problem and created another. Because of the time taken to transport the concrete 6 miles underground to the jobsite, the concrete would often begin to set in the car or segregate and have poor flow consistency when it arrived on the jobsite. A delay-set admixture solved the setting problem, but the concrete was still segregating and becoming impossible to pump. Finally Spurlock contacted a local admixture distributor, who recommended a pumping and priming aid. The admixture keeps the concrete flowable and also lubricates the pump. With the new delivery system, the same base slab that had cost around $28,000 now can be poured for about $5,000.