This paper presents an extension of an existing phenomenological model for predicting the evolution of hydration heat of a cemented waste form. The cemented waste form is essentially a mixture of blended cement and homogeneous low- and intermediate-level liquid (simulant) radioactive waste (sludge). The motivation stems from the fact that the existing empirical or phenomenological models are not designed to handle the interaction of a blended cement system with the waste sludge. The main objective of the proposed model is to minimize the number of isothermal or semi-adiabatic experiments (and thus the cost) required to design a promising recipe for conditioning the waste form. The paper demonstrates the capability of the model to successfully predict the evolution of hydration heat for various cemented waste form recipes.