Environmental Sustainability by Bulk Utilization of Fly Ash and GBFS as Road Subbase Materials

The underutilization of fly ash, in contrast with its generation, and scarcity of natural aggregates paved the way to unconventional construction approaches, thereby ensuring environmental stability by preserving valuable land from huge waste dumps and protecting fast depleting natural aggregate resources. In this work, fly ash stabilized with lime and granulated blast furnace slag (GBFS) are studied to assess their utility as a subbase material in flexible pavements. Laboratory investigations were carried out to determine compaction characteristics, unconfined compressive strength, California bearing ratio (CBR), shear strength parameters, and elastic modulus to obtain optimum mixtures of fly ash-lime (FAL) and fly ash-GBFS (FAG), respectively. Both optimum mixes satisfied the minimum strength criteria stipulated by the Indian Road Congress (IRC) for a material to be used as a subbase layer in a flexible pavement. To validate the feasibility of construction, service life, and cost efficiency of pavement constructed with these mixtures, six different test sections were constructed with FAL and FAG in the subbase layers and compared with one constructed with conventional granular subbase (GSB). Proper quality control was maintained throughout the construction of test sections by carrying out field dry density, lightweight deflectometer (LWD), and field CBR tests on the finished subbase layers. On the basis of the initial structural evaluation of pavement sections by a falling weight deflectometer (FWD) test, it was found that both FAL and FAG can effectively replace conventional GSB.