Characterization and Performance Evaluation of Angular-Shaped Fly Ash Aggregates for Pavement Base and Subbase Applications

This study presents the results of an extensive laboratory investigation on the characterization of angular-shaped fly ash aggregates (FAAs) and their potential as an innovative alternative to natural stone aggregates for pavement materials. The FAAs were produced by curing fly ash blocks in hot water and crushing them into the required sizes of coarse aggregates. The characteristics of the FAAs were correlated with the specifications of the Indian Road Congress. The experimental program comprised experiments such as particle size analysis, heavy Proctor compaction, California bearing ratio (CBR), and repeated load triaxial tests. The performance of two distinct types of FAA in the pavement base and subbase layers was assessed using repeated load triaxial tests at various stress levels. The CBR test results met the criteria for base and subbase layer materials. The resilient modulus (Mr) values of FAA ranged from 105 to 180 MPa, which reveals its practicality compared to natural stone aggregates. Additionally, the fit of various existing models for the observed resilient modulus and permanent strain data was examined, and the model parameters for FAA in the best-fitting model were identified. Finite-element analysis indicated that the pavement’s service life using FAA as the base material was approximately 15% longer than that of a pavement with a natural aggregate (NA) base layer. Results also demonstrate that the FAA would perform satisfactorily and fulfill the requirement of pavement material. The angular shape and rough surfaces of the proposed FAA are beneficial for better interlocking and result in higher frictional capabilities and low permanent deformation. A comprehensive cost analysis indicates that using FAA for constructing flexible road pavement reduces material costs by 50% compared to using NA. The use of FAA decreases natural aggregate consumption and encourages the usage of waste material in the construction industry.