Investigation into the Strength, Hydration, and Microstructural Characteristics of Clinker-Free Cement Composed of...

This study focuses on developing a novel clinker-free cement, specifically comprising phosphorus slag-based cementitious materials (PSCMs), by utilizing lime and industrial byproducts, including granulated electric furnace phosphorus slag and fluidized bed combustion bottom ash. The optimal composition of PSCM was determined by investigating the effects of different proportions of activators (water glass and sodium sulfate) and retarder (potassium fluoride) on the setting time and the mechanical strength of PSCMs. Performance evaluations demonstrated that the compressive and flexural strengths of the optimal PSCM formulation at 28 days were 64.1 MPa and 7.5 MPa, respectively. Notably, concrete prepared with the optimal PSCM exhibited superior freeze-thaw resistance and sulfate resistance compared to Portland cement concrete of equivalent strength grades. The comprehensive characterization of selected PSCM compositions, conducted using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscope-energy-dispersive spectrometry (SEM-EDS), provided in-depth insights into the interrelationship among mechanical properties, durability, and microstructural characteristics. SEM-EDS analysis confirmed that calcium aluminosilicate hydrate and sodium aluminosilicate hydrate are the predominant hydration products of PSCMs. FTIR and TG analyses elucidated the continuous hydration behavior of PSCMs during the curing process, while SEM observations revealed a densely compact microstructure in the hardened PSCM paste.