Experimental study on flow properties of blast furnace slag with different alumina contents based on the image measurement method

Abstract

This paper established a novel visualization method for measuring blast furnace slag(BFS) flow properties and investigated the effect of alumina content on the CaO–SiO2–Al2O3–MgO BFS system. The outcomes indicate that elevating Al2O3 concentration in the BFS mixture from 14% to 26% results in a rise of critical flow temperature Tc from 1332.5 °C to 1384.1 °C, leading to a deterioration of BFS flow properties. However, the critical flow velocity Vc of BFS rises from 1.82 mm/min to 2.91 mm/min, representing a 60% increment. BFS with high Al2O3 content was found to be more likely to form high melting point crystals, such as gehlenite, with better crystallization, which is one of the main reasons for the deterioration of BFS flow properties. Fourier Transform Infrared Spectrometer (FTIR) and Raman spectra analysis indicate that the proportional content of simple silicate structures denoted as QSi0([SiO4]4−),QSi1([Si2O7]6−) decreased with increasing Al2O3 content, while those of complex silicate structures, QSi2([Si3O10]8−),QSi3([Si3O9]6−) increased. Furthermore, the Si–O–Al structural unit concentration progressively increased, indicating that the escalation in bridging oxygen within the BFS system raised the polymerization degree of the BFS, leading to a more complex aluminosilicate structure. Notably, the [AlO4]5- tetrahedra content within the BFS has reached saturation at roughly 21%. Further increases in Al2O3 content induced an excess of [AlO6]9−octahedra formation, which generally acts as a network modifier to lower the polymerization degree of the BFS system. However, this effect was not noticeable in this study, which may be attributable to the low basicity (CaO/SiO2 = 0.99) and MgO content (MgO/Al2O3 = 0.21–0.34) of the BFS samples in this study.