RESILIENT PROPERTIES AND MICROSTRUCTURE OF MODIFIED FLY ASH-STABILIZED FINE-GRAINED SOILS

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 (M sub r) 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 10 to 15. Specimens obtained from the field were also evaluated through an M sub r test program, and the results were compatible with those for laboratory-made samples. Finally, a microstructure 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.