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Magnesium oxychloride cement (MOC) is an eco-friendly cementitious material with a fine prospect in construction and protection engineering. A full understanding of the time-dependent rheological behavior of MOC paste is crucial to many applications. In this study, the shear flow curves of MOC pastes with various H 2 O/MgCl 2 molar ratios were tested at different reaction times. The setting process of MOC paste was characterized by the time evolution of storage modulus (G′). Results indicate that the rise of the H 2 O/MgCl 2 molar ratio reduces the dynamic yield stress and plastic viscosity while leading to a more prominent shear-thinning behavior. The formation of crystalline 5-phase greatly accelerates the development of rheological parameters. The evolution of G′ reveals that the setting process of MOC paste includes five stages, which are governed by the gradual rigidification of 5-phase linkages among particles and the dynamic evolvement of electrostatic repulsion induced by the ionic composition changes of interstitial solution. Moreover, the rise of the H 2 O/MgCl 2 molar ratio is found to weaken the mechanical efficiency of 5-phase in the setting process. • The impact of 5-phase crystallization on the rheological properties of MOC paste was investigated. • The setting process of MOC paste was characterized by the growth of storage modulus. • The evolution of storage modulus derives from the 5-phase linkage formation and the changing electrostatic repulsion. • The rise of H 2 O/MgCl 2 molar ratio weakens the mechanical efficiency of 5-phase during setting. [ABSTRACT FROM AUTHOR]

Air bubble stability in cementitious materials in low air pressure (AP) environments is influenced by the Ostwald ripening process, which causes coarsening behavior of air bubbles. This research reports the enhancement of air bubble stability in low AP via the adoption of rheology and surface tension methods. Besides, the evolution of air bubbles during the cement early hydration process is proposed. It was found that incorporating viscosity-modifying agents (VMAs) and shrinkage-reducing admixtures (SRAs) resulted in improving air bubble stability by 37.7 % and 23.4 %, upon undergoing AP change from 100 to 60 kPa. Calculation of air bubbles via ripening equations under low AP revealed that VMA induced a notable decrease in the effective diffusion flux within fresh cement mortar, leading to a reduction of 9.8 % in air bubble ripening within 120 min. Conversely, SRAs were primarily aimed at reducing the initial dimensions of air bubbles. [ABSTRACT FROM AUTHOR]

The influence of pumping on the rheological properties of self-consolidating concrete (SCC) is widely recognized, but there is still limited understanding of its behavior within the pipeline. In this study, we propose a novel approach using equilibrium distances to investigate the evolution of rheological properties along the pipeline. Full-scale horizontal pumping circuits spanning 328 m were established to assess the axial development of SCC's rheological properties. Thirteen mixtures, with water-to-cement (w/c) ratios ranging from 0.22 to 0.27, were pumped at discharge rates varying from 5.77 to 12.69 L/s. Our findings show that for pumping setups and material studied, both the w/c ratio of SCC and the discharge rate significantly affected the influence of rheological equilibrium distances on pressure loss gradient changes. In all tested samples, viscosity values required the entire length of the pipeline to reach post-pumping levels, while yield stress values rapidly achieved their fully developed state upon entering the pipeline. Importantly, the predicted pressure loss displayed a strong correlation with experimental measurements, with an accuracy of 89.42% across all tested mixtures. Our predictive model showed an average improvement of 4.6% in accuracy compared to the linear approach, with the most significant enhancement observed in samples with higher w/c ratios. This research sheds new light on the behavior of SCC during pumping and provides valuable insights for optimizing the pumping process. • The equilibrium distance of rheology is introduced to describe SCC flow behavior along the pipeline. • Horizontal pumping circuits spanning 328 m is used. • Factors affecting the equilibrium distance of rheology are discussed. • The prediction accuracy of the model is validated. [ABSTRACT FROM AUTHOR]