Lightweight Concrete Aggregate from South Dakota Shales

The development of South Dakota shales for a lightweight concrete aggregate by the Agricultural Engineering Department of the Agricultural Experiment Station was prompted by several factors. First of all, an abundant supply of various shales is in existence west of the Missouri River in the state. The shortage of the finished product is nationwide, and the need for a good aggregate in farm building is pressing. Also, the existing plants in production are somewhat scattered, which increases the transportation charges and the cost to consumer. At the present time, there is no high quality lightweight aggregate produced in the state. There are a few plants in operation producing a small amount of perlite, froth-like particles of acidic volcanic glass, white to gray in color. A considerable volume of cinders from power plants and furnaces is being used. The tremendous growth of the building block industry in the last 15 years has been one of the outstanding construction developments in America, as product sales multiplied 80 times in the 10 years prior to 1946. During World War II, increased construction brought about a scarcity and restricted use of highly competitive building materials. However, the tremendous growth of the building block industry has not been due to scarcity of other materials alone, since concrete blocks have been utilized more and more in building construction since the depression days of the early thirties. An acute shortage of good lightweight aggregates has existed for approximately eight years. This may be partially attributed to the change-over to various furnace fuels from coal and the increased use of powdered coal, eliminating to a marked degree, clinkers and cinders that have been used in large quantities in the past for concrete aggregates. There also has been an increasing market for precast building units. Using lightweight aggregate concrete in large commercial buildings has augmented the enormous demand for suitable aggregates and also contributed to the market shortage. Private industry and various governmental agencies have undertaken considerable investigation in developing lightweight aggregates from shales, clays, slates, and slag. The Bureau of Mines has published information on the different aspects= of the industry from time to time. Also, a cooperative project has been carried out by the Bureau of Mines, Norris, Tennessee, in conjunction with the Tennessee Valley Authority. Geologists and engineers of the Tennessee Valley Authority have investigated raw materials, procured samples, and estimated manufacturing costs of shales in Tennessee.2 Since the wide range of geological formations over the state makes it impossible to give reliable recommendations as to the possibilities of the raw shale for a concrete aggregate without a careful and detailed laboratory study of the specific shale in question, this research was undertaken. The purpose of this research was to determine the feasibility of obtaining a finished product from raw shales suitable for concrete and concrete block construction which would have as many desirable characteristics as possible. The results are given in this preliminary report