Lightweight Aggregate (IM-03)
Today, most lightweight aggregate is produced by rapidly heating clay or shale to high temperatures, which causes it to expand or bloat. This "puffed" rock is widely used to make lightweight concrete and building blocks. About half as heavy as conventional blocks and cements, they save money because less steel is needed and so transportation and labor costs are less. Lightweight cement is more flexible and has good acoustical and thermal properties. Other lightweight aggregates used are porous volcanic rocks, diatomaceous earth, various slags and cinders.
Our Hoosier State Beneath Us: Industrial Minerals