(179c) The Impact of pH Variations on Early-Stage Hydration Kinetics and Microstructural Evolution of Ye’Elimite"

The reactivity of ye'elimite, a key mineral in calcium sulfoaluminate (CSA) cement, is intricately linked to the pH levels within the pore solution. Variations in pore solution pH directly influence the dissolution-precipitation kinetics of ye'elimite, yet the impact of pH on ye’elimite hydration kinetics, particularly at the early stage, remains uncertain. This study examines how pH variation affects the early-stage hydration characteristics and microstructure of ye'elimite in cementitious systems. By adjusting the pH levels of ye'elimite paste using dilute nitric acid and dilute sodium hydroxide, we investigated changes in mineralogical composition through X-ray diffraction (XRD) analyses, microcalorimetry studies, and scanning electron microscopy (SEM), revealing insights into hydration kinetics and microstructural evolution. The results demonstrate a clear relationship between pH and ye'elimite reactivity. Lowering the pH with dilute nitric acid significantly enhances ye'elimite reactivity, leading to increased formation of hydration products like ettringite and monosulfate. Conversely, elevated pH levels result in incomplete ye'elimite reaction despite some observed reactions. This study enhances our understanding of pH-dependent reactivity in ye'elimite-based cementitious systems, with implications for optimizing cement formulations to tailor early-stage properties and microstructure for improved construction material performance.