To help prevent unfortunate deaths and accidents associated with open mine shafts, the United States Bureau of Mines (USBM) has developed a method for sealing abandoned shafts using lightweight and conventional reinforced concrete. Because the seal's primary material is concrete, the USBM method represents an untapped potential market for ready mixed concrete.
In addition to providing a new market for ready mixed concrete use, promoting and coordinating the sealing of abandoned mine shafts can help ready mix suppliers enhance their images as concerned members of the community.
The engineered shaft seal designed by the USBM features lightweight concrete with a wet density of about 45 pounds per cubic foot as its key material component. A reinforced concrete cap designed for a 5 psi live load was constructed over the lightweight concrete seal to provide structural integrity. A platform of steel beams and 5/16-inch steel plate was suspended by heavy chains which were attached to two steel beams that laid across the concrete footings of the shaft. This plate supported the entire mass of foam concrete.