Cimento álcali-ativado a partir de cinza de casca de arroz e cal de casca de ostra hidratada

Abstract

The combined application of hydrated oyster shell lime (HOSL) and rice husk ash (RHA) in alkali-activated binders is still unexplored in the literature. Furthermore, specific comparative studies to understand the chemical and microstructural differences between binders produced from different silica sources remain limited. Therefore, this research sought to fill these gaps by producing an alkali-activated binder based on rice husk ash (RHA), hydrated oyster shell lime (HOSL), and an activated NaOH solution, as well as comparing this binder with another produced from photovoltaic module glass (PMG), HOSL, and an activated NaOH solution. A critical analysis revealed specific limitations and gaps related to the use of HOSL in scientific research, and an experimental design was developed that fixed variables involving different curing times (7, 14, 28, 63, and 91 days), activator concentration (1, 3, 5, 7, and 9M), and different RHA/HOSL arrangements (90/10, 80/20, 70/30, and 60/40). The produced binders were evaluated for their mechanical and chemical behavior through Unconfined Compressive Strength (UCS) tests, Fourier Transform Infrared Spectroscopy (FTIR), and statistics using ANOVA and Tukey's multiple comparison test. Additionally, a comparison between the binders was performed based on microstructural and chemical analyses obtained by Scanning Electron Microscopy coupled with X-ray Energy Dispersive Spectroscopy. (SEM/EDS). The results showed good mechanical behavior in relation to Unconfined Compressive Strength (UCS), mainly for compositions containing up to 30% HOSL and 80% RHA, with molarities between 1 and 5 M. The 80/20 (RHA/HOSL) sample activated with a 3 M solution showed continuous improvement in strength throughout the curing period, going from 0.50 MPa at 7 days to 0.67 MPa at 14 days, 1.20 MPa at 28 days, 3.10 MPa at 63 days, and reaching a peak of 3.94 MPa at 91 days. FTIR and SEM/EDS analyses indicated the formation of C-A-S-H and N-A-S-H gels, with a predominance of hybrid structures of the (N,C)-A-S-H type, responsible for the development of the mechanical properties of the binders. Thus, the cement Alkali-activated binders derived from RHA, HOSL, and NaOH proved effective in terms of mechanical and microstructural properties for application in non-structural installation blocks, class I and II laying and coating mortars, and ceramic bricks and blocks, highlighting the binder as a good substitute for Traditional Portland Cement (OPC) in these cases. Comparisons between binders using RHA or PMG as a silica source demonstrated different phases of gel formation and microstructure evolution, showing that the structural form of silica directly influences the dissolution of precursors, the organization of the silicate network, and the homogeneity of the products formed.