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Title: Study on Effect of Curing Regimes on Ultra-High- Performance Concrete by Nuclear Magnetic Resonance Spectroscopy

Author(s): Hao Qian, Gaozhan Zhang, Jun Yang, Qingjun Ding, Chundong Geng, and Sudong Hua

Publication: Materials Journal

Volume: 121

Issue: 2

Appears on pages(s): 115-126

Keywords: calcium-(alumino)silicate-hydrate (C-(A)-S-H) gel; curing regime; nuclear magnetic resonance (NMR) spectroscopy; microstructure; ultra-high-performance concrete (UHPC)

DOI: 10.14359/51740372

Date: 4/1/2024

As one of the key factors influencing the hydration process, as well as the microstructure formation and evolution of ultra-highperformance concrete (UHPC), the action mechanism of different curing regimes have been studied to some extent. However, the current knowledge of the underlying mechanisms that control the different effects of different curing regimes is limited. In this study, the composition of hydration products, micromorphology, and migration and evolution of aluminum-phase hydration products of UHPC under three combined curing regimes (standard curing, steam curing + standard curing, and autoclave curing + standard curing) were investigated in depth. Micromorphology observation shows that heat treatment promoted the formation of higher-stiffness hydration products (tobermorite and xonotlite) in UHPC, and the higher the polymerization degree, the higher the Si/Ca ratio of the hydration product. Meanwhile, 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy shows that specimens with higher strength had higher Al[4]/Si and a lower amount of ettringite and AFm at the early curing stage. The elevated curing temperature reduced the formation of ettringite and AFm and allowed more Al3+ to replace Si4+ into the structure and interlayer of the calcium- (alumino)silicate-hydrate (C-(A)-S-H) gel, which increased the mean chain length (MCL) and polymerization degree of the C-(A)-S-H gel. However, the polymerization effect of Al ions is limited, so the provision of the silicon source to improve the Si/Ca ratio of the system is important.