Testing of Kittson County Bloating Clays as Lightweight Aggregate in Structural Concrete

Abstract

Pleistocene glacial lake clays found in west-central Kittson County, Minnesota, were identified as bloating clays in 1989. One of the primary uses of bloating clays is as lightweight aggregate in structural concrete. Such lightweight structural concrete is used in the construction of high-rise buildings, where the reduced weight allows building higher while reducing the amount of structural steel support. While Minnesota has several different bloating clay deposits, most lightweight aggregate currently used in Minnesota is shipped by barge up the Mississippi River from West Memphis, Arkansas. Among Minnesota's bloating clays are the Cretaceous shales near Springfield in southwestern Minnesota, the Ordovician Decorah Shale of southeastern Minnesota, and the Pleistocene Brenna Formation clays of Kittson County in northwestern Minnesota. The Kittson clays bloat at a lower temperature than the other Minnesota bloating clays and have a unique spherical bloating habit. In addition, the deposit is homogeneous over a large areal extent and thickness and lies within 20 ft. of the surface. The clays would be easily accessible for open pit mining. This project was undertaken to determine whether the Kittson clays, when fired, produced a suitable lightweight aggregate for use in structural concrete. Testing was done according to American Society of Testing Materials (ASTM) standards by an independent testing laboratory. Tests results showed that the Kittson clays meet all ASTM requirements for use as a lightweight aggregate in structural concrete.