A comprehensive study on the application of Class F fly ash for stabilizing subgrade soils in Taiwan is presented. Lime (or cement) was used with fly ash to enhance its self-cementing behavior in the study. Laboratory testing included using the plasticity index method to determine the optimum percentages of additive and fly ash. Through a resilient modulus (MR) test program, these percentages were confirmed. A section of test road with treated subgrade constructed on the West Coast Highway has been open to traffic for 40 months to date. A field investigation of this section was part of this study. Results from field California bearing ratio tests indicate that treatment of the subgrade soil had improved its properties by a factor of lO to I 5. Specimens obtained from the field were also evaluated through an MR test program, and the results were compatible with those for laboratorymade samples. Finally, a microstn. icture study is presented showing significant cementitious materials in laboratory and field specimens. Confidence about the future application of Class F fly ash for stabilizing subgrade soils in Taiwan and for handling this problematic waste material is provided.

Fly ash is causing serious disposal problems in Taiwan, where it occurs only in the Class F form as a by-product of electricity generation in thermal power plants. Recently, the use of fly ash as a stabilizer for subgrade soils has been the subject of much research. The project, sponsored by the Taiwan Electric Power Company and the Taiwan Highway Bureau, is recognized as the most complete study on this subject.