Desenvolvimento de um método de síntese de zeólita tipo A utilizando cinzas volantes de carvão: avaliação do uso como aditivo de mistura asfáltica morna

Abstract

The purpose of this study was to synthesize a zeolite A from fly ash (FA) produced in a thermoelectric plant and to evaluate its potential as a warm asphalt mix (WMA) additive. The conventional hydrothermal route was implemented to synthesize zeolite A, however, specific procedures were necessary to perform the partial extraction of SiO2 and Al2O3 and to remove Fe2O3. The zeolite product was characterized by X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and Scanning Electron Microscopy (SEM). These results confirmed that type A zeolite was the main crystalline phase in the synthesized product. From the X-ray fluorescence (XRF) analysis, it can be confirmed that the ashes are composed mainly of is SiO2, Al2O3, and Fe2O3, respectively. The Cation Exchange Capacity (ECC) of the zeolite was greater than that of FA. The CO2 adsorption-desorption analysis showed a IA type isotherms, suggesting an ultramicroporous material with the main pore diameter around 11 Å. Zeolite A was tested for its potential as a WMA additive. In this way, the asphalt binder (AB) was modified with 1% zeolite A and concentrations of 5 and 10% of fly ash. The softening point, penetration, and rotational viscosity tests were in accordance with the current specifications for asphalt binder. The rheological parameters, obtained in a Dynamic Shear Rheometer, did not show significant differences in the stiffness (G*) for both the unmodified and zeolite-modified binder, but suggest an increase in elasticity (δ) for the modified AB. The performance grade (PG) temperature was 58 °C for the AB samples tested. At this temperature, the Multiple Stress Creep and Recovery (MSCR) test showed results according to the standard. Thermal analysis indicated that the synthesized zeolite retains approximately 17% of the water in its structure, justifying its application as a WMA additive, through the micro-foaming mechanism. The mechanical tests were performed using an unmodified test specimen (TS) and a modified specimen with 0.3% m/m of zeolite A (TS-AB-ZFA), the latter was prepared at WMA temperature. The results of the mechanical tests were similar for both types of TS, reinforcing the potential of zeolite A as a WMA additive. Environmental tests for volatile retention were performed on AB samples modified by fly ash. Thermal volatilization analysis (TVA) and gas chromatography (GC-FID-ECD) systems were used to detect emissions. A significant reduction in the emission of volatiles by the asphalt binder was observed in the presence of ash.