Mechanical Response of Cement-Stabilized Pond Ash during Repeated Loading Based on Shakedown Concept

Pond ash is a byproduct obtained from the combustion of coal in thermal power plants. It can be used as an alternative to conventional granular materials in compacted subgrade or subbase layers in pavements. The properties can be further enhanced by the addition of small doses of cement. Typically, the modulus parameters required for the design of pavements are based on resilient modulus models. Such models presume that the material attains a shakedown response in every loading sequence and the resilient modulus (M_R) can be defined. However, it is not very clear whether a nonconventional material such as pond ash or cemented pond ash attains shakedown within 100 cycles of each sequence as stipulated in the resilient modulus test protocol. The number of loading cycles required to reach the shakedown limit is explored in this study. There are two sets of experiments conducted: the conventional resilient modulus tests with 100 cycles in each sequence and repeated load triaxial tests with 10,000 cycles for three confining pressures (41.4, 27.6, and 13.8 kPa) at a deviator stress of 69 kPa. The effect of cement dosage (2% and 3%), compaction condition (standard and modified Proctor compaction), and water content (optimum moisture content (OMC), OMC−2%, and OMC+2%) were studied. The shakedown theory is explained in terms of permanent deformation increment per cycle, dissipated energy, and tangent modulus. The resilient modulus is defined as the tangent modulus of the material which has attained shakedown. The cemented pond ash did not strongly correlate to confining pressure and hence, a constant value of the resilient modulus may be used.