Eco‐Friendly Binder for Pavement Applications: Strength and Microstructure Analysis of Geopolymer Made From Fly Ash, Bagasse Ash, and Calcium Carbide Residue

This research investigates the development of an eco‐friendly geopolymer binder for pavement applications using fly ash mixed with waste materials, including bagasse ash and calcium carbide residue. These blended precursors were used as raw materials, activated with 5 M sodium hydroxide, a binder‐to‐solution ratio of 1:0.75 by weight, and a sodium hydroxide‐to‐sodium silicate ratio of 1:0.5. Compressive strength tests were conducted at 7 and 28 days under ambient curing. Microstructural characterization was performed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and x‐ray diffractometry (XRD), while the 3D pore and void structures were analyzed using x‐ray tomographic microscopy (XTM). The results revealed that the geopolymer contained high Si, Al, and Ca contents, making it suitable as a binder. The mix with 100% FA had the lowest pore volume and highest compressive strength. SEM and EDS mapping confirmed the formation of geopolymer gel, along with unreacted materials. Mixes with 85%–100% fly ash, and those with 40%–60% bagasse ash and calcium carbide residue, and 0%–20% fly ash, achieved compressive strengths of 30–40 MPa. The microstructural densification, indicated by reduced porosity observed through XTM, was identified as a key factor influencing the strength performance of the geopolymer binder. These findings suggest that optimized fly ash blended with waste materials (bagasse ash and calcium carbide residue) can produce a geopolymer binder with satisfactory strength, offering sustainable solutions for pavement applications.