CA was retained by AES Puerto Rico to work on developing and evaluating alternatives for the utilization of coal combustion by-products from the production of electricity by AES in their plant in Guayama, Puerto Rico. Among the many alternatives developed, the use of the by-product for producing unbound granular fill and base material for highway construction and in flowable fill applications in construction were found to be promising. CA performed materials characterization as well as trial mixes and mock-up placements for this application. The evaluation and analysis of the strength development properties and chemical and mineralogical examination of samples at different ages and different exposure conditions was done in collaboration with Texas A&M University. Of great importance in this materials research project was the development of the necessary guidelines for ensuring the dimensional stability of the material while in service.