Study of the spent catalysts as internal curing agents on the hydration kinetics and microstructure development of ultra-high performance concrete (UHPC)

Abstract

In this study, the effect of 5–30 % (by mass) of spent catalyst (SC) on the characteristics of ultra-high-performance concrete (UHPC) is investigated, including mechanical properties, volumetric stability, hydration kinetics, and microstructural development. Specifically, scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and low-field proton nuclear magnetic resonance spectroscopy (1H NMR) are employed to clarify the microstructures, while thermogravimetric analysis (TG), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS) are carried out to understand the phase variation. The results obtained show that the samples containing SC and additional water exhibit good mechanical properties, such as a 1.0 %-2.9 % higher compressive strength of UHPC with SC (5–15 %) and additional water compared to SC1 at 60 days. Additionally, SC can also improve the volumetric stability of UHPC. Moreover, the Ca/Si ratio of the hydration products decreases and the Al/Ca ratio increases with the enhancement of SC and additional water content. Furthermore, the water release effect of SC promotes the hydration of cement and pozzolanic reactions, leading to the generation of more hydration products and optimization of the pore structure and interfacial transition zone (ITZ) of UHPC in this study.