Mechanical properties and hydration mechanism of high-volume ultra-fine iron ore tailings cementitious materials

Abstract

• A blended low-carbon cementitious materials containing high-volume mine solid waste activated ultra-fine IOT is designed. • IOT2 has higher pozzolanic activity and better dense filling effect. • IOT2 can consume more portlandite produced from cement hydration to form more rigid hydration products. • The increase of later compressive strength owes to the synergistic action of the improvement of hydrates and filler effect. Iron ore tailings (IOT) are a type of mining solid waste and cause many environmental and safety problems. The aim of this paper was to investigate the effect of high-volume ultra-fine IOT on the mechanical properties and hydration mechanism of cementitious materials. To obtain ultra-fine particles, IOT was processed via grinding in water, and the particle characteristics were characterized using a laser particle-size analyzer, scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FT-IR) and inductively coupled plasma (ICP). The influence of the IOT particle size (D50 = 47.63 μm, 4.32 μm, 1.09 μm), substitution percentage (30 %, 40 %, 50 %), and hydration age (1 d, 7 d, 28 d) on the compressive strength of mortar specimens were also studied. The results show that ultra-fine treatment enhances the hydration activity of IOT particles and has a positive effect on the mechanical properties of cementitious materials. The addition of IOT increases the setting time and reduces the hydration heat at early hydration stage; however, the ultra-fine treatment can minimize this problem and meet the requirements of practical engineering applications. Compared with raw IOT, the ultra-fine IOT exhibits more remarkable filling effect and hydration activity. They can consume a large amount of portlandite, which is produced by cement hydration to form densified calcium silicate hydrate gel and accelerate the development of strength. This study provides a design method and experimental data support for the preparation of a kind of low-carbon cementitious materials.