Speaker
Description
In this study, the hydration behavior of ternary binder systems composed of calcium aluminate cement (CAC), ordinary Portland cement (OPC), and different types of calcium sulfate sources (C$) was investigated under variable curing temperatures. As calcium sulfate sources, natural gypsum and phosphogypsum, a by-product of the phosphate fertilizer industry, were compared to evaluate their influences on early hydration kinetics, phase formation, and setting properties. To investigate the effect of calcium sulfate sources, the composition of the binder was kept constant at CAC:OPC:C$ = 63:13:24 by mass, and the water-to-binder ratio was fixed as 0.5 across all mixtures. The study was performed at three different curing temperatures: 5℃, 25℃, or 45℃. An isothermal calorimeter was utilized to observe the heat of hydration. Phase evaluation of 1-day, 3, 7- and 28-day-old samples was employed using X-ray diffraction (XRD) and Thermogravimetric analysis (TGA) equipment, providing insights into the mineralogical changes occurring during hydration and curing processes. Scanning electron microscope (SEM) images of the samples of different curing times were taken to observe the microstructure of hydration products. The initial and final setting times were determined with automatic Vicat equipment. Compressive and flexural strengths at 28 days were used to assess mechanical performance. Results show that both calcium sulfate source and curing temperature significantly affect the rate of ettringite formation and strength development. Phosphogypsum tends to delay setting and early hydration but promotes sustained reaction at later ages, particularly under high temperatures. Differences in microstructural evolution and crystalline hydrate phases were evident across curing regimes and C$ types.
Affiliations
Sabancı Technology Center GmbH, Freisinger Landstraße 50 Garching, Munich, Germany, 85748, ozge.demirdogan@sabancibs.com
| Keywords | phosphogypsum, calcium aluminate cement, hydration behavior, curing temperature, XRD |
|---|