Effect of iron on mineral composition of quaternary phase clinker and its hydration properties

Abstract

The present task is to investigate the influence of iron on the mineral composition and microstructure of the phase Q (C20A13M3S3, in the text below C = CaO, A = Al2O3, M = MgO, S = SiO2, F = Fe2O3) clinker and its hydraulic property by using XRD, Rietveld refinement, BSE, isothermal calorimeter, DSC, non-evaporable water content and compressive strength measurements. Results reveal that incorporating 4% of iron leads to the formation of the accompanying minerals which are spinel (MA), gehlenite (C2AS) and tetracalcium aluminoferrite (C4AF), and 6% of iron results in the formation of 15.3% of monocalcium aluminate (CA). Additionally, the lattice parameters of phase Q change with the doped-iron content which could be due to Ca2+ and Si4+ being substituted by Fe3+. Although the formation of C4AF coating layer around the clinker grains inhibits the hydraulic activity of clinker within the first 1 day, it has no adverse impacts on the later-age (28 days) hydration and is favorable to improve the 28-day compressive strength. The formation of CA accelerates the hydration of clinker, shortens the time span of the acceleration and deceleration periods, and may influence the hydration reaction of phase Q. Considering compressive strength, the threshold limit of iron incorporated into phase Q raw meal is found to be 4.0 mass%, beyond which an obvious decrease in 28-day compressive strength is detected.