63758 2025 eng lecture 0 -- -- -- This study investigates the early hydration of calcium sulfoaluminate (CSA) cement in water (CSAH) and 2M NaOH (CSA2M), both with a liquid/solid ratio of 0.5. Hydration kinetics were assessed using in situ X-ray diffraction, isothermal conduction calorimetry, ultrasonic pulse velocity (UPV) and mechanical strength measurements. The results indicate that in the CSA2M system, the maximum heat release occurs earlier, and UPV measurements reveal a more rapid increase in mechanical stiffness (Figure 1a). The presence of alkalis accelerates the dissolution of ye’elimite and anhydrite, leading to a shorter induction period and faster precipitation of ettringite (Figure 1b-d). The phase refinement confirmed a higher dissolution rate of anhydrite in the alkaline environment, while the formation of ettringite stabilizes within 10 hours. Initial dissolution (0–40 min) increases ion concentration, followed by accelerated ettringite formation (0.6–2.5 h) with rising heat flow and UPV. A secondary acceleration (2.5–4.3 h) occurs only in CSAH. Deceleration (2.5–10 h) leads to further stabilization, with reactions proceeding at a slower rate. At 25 h, CSAH reached 58.3% ettringite and CSA2M 48.2%. These findings contribute to a deeper understanding of the early hydration mechanisms of CSA cement and the impact of alkalis on phase evolution. 3rd International Workshop on Calcium Sulfoaluminate Cements Leeds, UK 23.06.2025 25.06.2025 0 publish false true Luís Urbano Durlo Tambara eng uncontrolled Calcium sulfoaluminate cement eng uncontrolled Ultrasonic pulse velocity eng uncontrolled Early hydration eng uncontrolled Alkali eng uncontrolled In situ XRD Ingenieurwissenschaften und zugeordnete Tätigkeiten 7 Bauwerkssicherheit 7.4 Baustofftechnologie Material Degradationsmechanismen Datei im Netzwerk der BAM verfügbar ("Closed Access") Präsentation