Study on the Alkali-Activated Mechanism of Yellow River Sediment-Based Ecological Cementitious Materials

As one of the key components in geopolymer systems, the activator significantly influences the properties of cementitious materials. This study investigates the effects of key activator parameters, specifically alkali equivalent and activator modulus, on the setting time, workability, hydration characteristics, compressive strength, and splitting tensile strength of Yellow River sediment-based slag eco-friendly cementitious materials. Tests such as setting time, slump, flowability, hydration heat, and strength were conducted to evaluate these effects. Additionally, X-ray diffraction (XRD), differential thermal analysis (DTA), mercury intrusion porosimetry (MIP), and scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) tests were conducted to investigate the mechanisms and variations in microstructural properties. The results indicate that the alkali equivalent and activator modulus significantly affect the setting time, workability, reaction process, and strength of Yellow River sediment-based eco-friendly cementitious materials. An excessively high or low alkali equivalent and activator modulus result in either insufficient or excessive activation, adversely affecting the densification process of the hardened matrix. When the alkali equivalent is 5% and the activator modulus is 1.2, the matrix demonstrates superior flowability, well-regulated and sustained heat evolution during hydration, and achieves compressive and splitting tensile strengths of 61.68 MPa and 4.37 MPa, respectively. Under optimal alkaline conditions, slag dissolution, hydrolysis of silicon-oxygen and aluminum-oxygen tetrahedra, and the formation of low-calcium calcium silicate hydrate (C-S-H) and calcium aluminum silicate hydrate (C-A-S-H) phases are effectively promoted, leading to the development of a wrinkled three-dimensional polymeric gel structure. This structure fills the matrix pores, optimizes the pore structure, and contributes to strength development.