Case Studies in Construction Materials (Jul 2023)
Alkali-activated binders based on technogenic fibrous waste
Abstract
Alkali-activated binders based on technogenic fibrous waste (TFW) were developed. An increase in the specific surface area (Ssp) of TFW makes it possible to change the strength parameters. Thus, at Ssp = 160 m2/kg, the strength of the binder was 1 MPa, at Ssp = 220 m2/kg, an increase in activity by almost 3 times is noted (compressive strength 3.2 MPa). With an increase in the specific surface of the particles, the microstructure of the binder samples is characterized by a higher density, with a small number of cavities not filled with hydration products. Analysis of the microstructure revealed the presence of a denser matrix in all cases compared to the compositions obtained with a lower specific surface area of TFW. The pressed sample has a dense matrix with an increased number of contact zones between particles; TFW fibers are clearly visible over the entire surface under study. When the alkaline activator NaOH is introduced into the system, the solubility of the crystalline phases of pyroxenes (albite, anorthite) and quartz increases, which is noted by a decrease in the intensity of diffraction reflections. The main chemical composition in the binder is represented by oxides of SiO2, Na2O, CaO, MgO, Al2O3. The presence of sodium-calcium hydroaluminosilicate compounds in the synthesized system of compounds is confirmed by differential thermal analysis. The endothermic peak at 733 °C is associated with the decomposition of sodium-calcium hydroaluminosilicates. The exoeffect peak at 900 °C is associated with the crystallization of tobermorite-like compounds C–A–S–H and C–S–H into wollastonite. The presence of hydrosilicate tobermorite-like compounds is also confirmed by microstructural analysis, where almost the entire surface of waste particles is covered with fibrous new growths, which, most likely, belong to calcium silicate hydrates of tobermorite type C–A–S–H.
