Ash reactivity characteristics of diopside powder

Diopside[CaMg(SiO₃)₂] is a common mineral form of calcium magnesium silicate. Apart from dioside quarries, diopside also appears in skarn tailings. Diopside is a novel energy-saving raw material, mainly used in the ceramics industry. Glazed tiles prepared with diopside have the characteristics of low-temperature fast curing, which offers significant advantages to the building materials industry. The results reported in this paper show that the silicate and quartz composition in skarn lead and zinc tailings are likely to participate in the generation of ettringite and C-S-H gel in hydration reactions, respectively. Therefore, lead/zinc tailings can be used as concrete admixtures. As an important component of skarn tailings, the study of the ash reactivity of this type of tailings has great significance for comprehensive utilization in industry, but the relevant literature is incomplete. Paste samples were prepared with diopside, gypsum, and calcium hydroxide in this paper. The ash reactivity of fine-ground diopside was studied and hydration products were investigated using X-ray diffraction, scanning electron microscopy, fourier transform infrared spectroscopy, differential scanning calorimeter and nuclear magnetic resonance. The results show that the compressive strength of the paste prepared from fine-ground diopside can reach 9.83, 12.79, and 18.87 MPa at curing ages of 3, 7, and 28 d, suggesting that fine-ground diopside has good ash reactivity. The hydration products of cement prepared with fine-ground diopside are mainly accounted for by the C-S-H gel. Nuclear magnetic resonance results show that with the deepening of the hydration reaction, the percentage of silicon atoms in the Q² structure state reduces and the Al/Si ratio in the C-S-H gel is lower than that in the original diopside material. With an increasing curing age, a small amount of gypsum and a large amount of Ca(OH)₂ participate in the reaction. The amount of C-S-H gel hydration products increases gradually. The filling effect of the gypsum particles promotes the growth of the tructure's strength with an increasing curing time, although this effect does not alter the chemical reactions. These results will provide sufficient evidence for preliminary judgments of whether skarn tailings possess ash reactivity.