Preliminary characterization of the Ponca City shale for highway construction purposes, and its amenability to lime, cement, fly ash and conjunctive stabilization were investigated in this study. After numerous screening and evaluation trials it was decided to use 6 percent lime, 14 percent cement, 25 percent fly ash and conjunctively 8 percent cement and 4 percent lime and 18 percent fly ash. The stabilized shale attained a 28-day unconfined compressive strength of 108 psi minimum and its plasticity index was depressed to less than 6 percent. In terms of the strength and plasticity criteria, cement (14%) and conjunctive (8% cement + 4% lime + 18% fly ash) stabilizations were most effective.

Beam action studies were also included and unconfined compressive strength and bending strength values correlated. The correlation equations of the form are helpful in predicting the flexural strength characteristics of stabilized soils and they are considered applicable in the design of multilayered pavement systems.

The strength gain and general amelioration of the plastic shale were further ascertained and explained by X-ray diffraction and SEM studies. X-ray diffractograms show a significant peak reduction in the major clay minerals and that these reductions may explain the strength enhancements. The main reaction products identified were various forms of hydrated and unhydrated forms of calcium alumina and calcium silicate crystals. The SEM micrographs reveal that stabilization reduced the void areas and depict the silt size aggregations of particles, the spiny crystals (Tobermorites), and the alumina and silica gel, that upon hardening, cement the particles and increase the strength characteristics of the shale-stabilizer-water system.