Effect of the Ti-extracted residue on compressive strength and microstructural properties of modified cement mortar

The Ti-extracted residue is a metallurgical solid waste and its utilization is limited in cement-based materials due to its high amount of chloride salts. In this study, the washed and unwashed Ti-extracted residues were used to replace high-quality supplementary cementitious materials, and the compressive strength and microstructural properties of the prepared specimens were studied. Incorporating the Ti-extracted residue in the cement paste can increase the early compressive strength due to the acceleration effect of the chloride salt on the hydration process, but the washed Ti-extracted residue reduced the later compressive strength due to its lower reactivity. Meanwhile, the Ti-extracted residue with its hydraulic and pozzolanic effects contributed to the formation of the C-S-H gel with a low Ca/Si ratio, which resulted in the consumption of calcium hydroxide and the lowering of the indentation modulus and hardness of the C-S-H gel. In addition, the leaching test demonstrated that the washed Ti-extracted residue was harmless to the environment, and the chlorine ion of the Ti-extracted residue can be physically and chemically bonded. Therefore, the washing method is an effective way to remove the soluble chlorine of the Ti-extracted residue and decrease its potential risk to environment. This research finding facilitated the recycling of the Ti-extracted residue as supplementary cementitious materials in cement-based materials.