# Effects of Titanium Gypsum and Flue Gas Desulfurization Gypsum on the Hydration and Mechanical Properties of Anhydrite–Phosphogypsum-Based Supersulfated Cement

## TL;DR

This study examines how different types of industrial gypsum affect the properties of an eco-friendly cement called supersulfated cement, focusing on hydration, strength, and microstructure.

## Contribution

The study systematically compares the effects of titanium gypsum and flue gas desulfurization gypsum on supersulfated cement properties.

## Key findings

- Incorporating 11% titanium gypsum and flue gas desulfurization gypsum reduces sulfate environment and regulates hydration.
- TG2 and FG2 mixtures achieved the highest 28-day compressive strengths of 50.15 MPa and 51.95 MPa, respectively.
- Differences in gypsum dissolution and particle size influence hydration pathways and microstructural development.

## Abstract

Supersulfated cement (SSC) is an environmentally friendly cementitious material with a low clinker content, in which industrial byproduct gypsum serves as the sulfate source, thereby enabling the valorization of solid waste. The hydration process, pore structure, microstructure, and hydration products were investigated using paste samples by means of isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TG–DTG), Fourier transform–infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM), while compressive strength was evaluated using mortar specimens. Compared with ordinary Portland cement (OPC), SSC offers clear advantages in reducing energy consumption and greenhouse gas emissions. In this study, the effects of titanium gypsum (TG) and flue gas desulfurization gypsum (FGD) on the hydration behavior, fluidity, mechanical properties, and microstructural evolution of an anhydrite (AH)–phosphogypsum (PG)-based SSC were systematically investigated. The results indicate that the incorporation of 11% TG and FGD mitigates the strong sulfate environment caused by the rapid dissolution of soluble AH, thereby regulating the hydration process. As the proportion of TG and FGD increased, the cumulative heat release within 72 h gradually decreased. When AH was completely replaced, the cumulative heat release of TG4 and FG4 decreased by approximately 19.7% and 28.6%, respectively. TG and FGD exhibited opposite effects on the fluidity of SSC while both promoting strength development. Among all mixtures, TG2 and FG2 showed the best performance, with the highest 28-day compressive strengths of 50.15 MPa and 51.95 MPa, respectively. Microstructural analysis reveals that differences in particle size distribution and dissolution kinetics among gypsums governed the sulfate release characteristics and slag activation mechanisms, thus leading to distinct hydration pathways, pore structure evolution, and microstructural densification. This study provides a theoretical basis for the efficient utilization of various industrial byproduct gypsums and offers important guidance for the controllable design of SSC performance.