Strength, Mineralogy, Microstructure, and Statistical Analysis of Alkali-Activated Sugarcane Bagasse Ash–Eggshell Lime Pastes

Abstract

Portland cement production is an energy-intensive process, and more sustainable substitutes are needed, e.g., alkali-activated binders originated from industrial wastes. Thus, this paper analyzes the combination of sugarcane bagasse ash (SCBA) and hydrated eggshell lime (HEL) as precursors for an alkali-activated binary system, a combination, to our best knowledge, not studied in past research. The mechanical and microstructural behavior of the SCBA-HEL alkali-activated pastes has been discussed through unconfined strength tests, and x-ray fluorescence, x-ray diffraction (XRD), Fourier transform infrared spectroscopy, and scanning electron microscopy (SEM) and energy-dispersive detector (EDS) microstructural analysis. In addition, an analysis of variance was applied to investigate the impact of a three-factor combination, i.e., SCBA/HEL ratio, NaOH concentration, and water/binder ratio (W/B), on the paste’s compressive strength. The highest compressive strength is associated with 80% of SCBA and 20% of HEL (ratio equals 4), 1 M molarity, and W/B relation of 0.8 (2.61% of Na2O). A C─ (N)─ A─ S─ H gel is observed in the form of an amorphous hump through the XRD pattern. SEM images show that the material synthesized from alkali-activation has a cementing effect, with a structure less dense and more porous than that of conventional cementing materials. The EDS display areas are rich in Ca, Si, Na, and Al. The bands found for the alkali-activated paste are consistent with vibrations characteristic of C─ A─ S─ H and N─ A─ S─ H gels.