Effects of siliceous iron tailings powder on performances of interface transition zone in concrete

Abstract

At the meso-level, the interface transition zone (ITZ) is an important part of concrete and is closely related to the macroscopic properties of concrete. In this paper, the influences of siliceous iron tailings powder on concrete ITZ have been researched, in order to better reveal the mechanism of the powder as an auxiliary cementitious material in concrete. Based on XRD, SEM, hardness test and numerical simulation, the Ca(OH)2 (CH) crystal orientation, calcium-silicon ratio (Ca/Si), porosity, microhardness and elastic modulus of ITZ have been explored, and the results are as follows. When water-to-binder ratio (w/b) is 0.38 and 0.48, iron tailings powder increases the complexity of CH crystal orientation in the ITZ, but the effects of w/b and hydration age on the CH crystal orientation index with and without iron tailings powder are similar. The Ca/Si of ITZ blended with iron tailings powder is lower than that of benchmark group with the same w/b. The porosity in ITZ first decreases with the distance from aggregate surface, and stabilizes at about 40 μm, and the ITZ porosity in groups of iron tailings powder is less than that in the reference group at the same w/b and the same age. The microhardness and elastic modulus of ITZ decreases by mixing the iron tailings powder, and microhardness increases with the distance from aggregate surface, and at last stabilized at also about 40 μm, and elastic modulus increased with the decrease of w/b and the extension of hydration age. The findings show that incorporation of iron tailings powder has some degree of improvement on the microscopic structure of ITZ, but does not reduce its size, and the thickness of ITZ both with and without iron tailings powder are all 40μm. In particular, the variation law of pore in IZT needs to be studied more comprehensively and in-depth in the future.