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The effect of resting time on the rheological properties of cement suspensions is generally explained by early formed structure and overconsumption of polycarboxylate superplasticizers (PCEs). In this paper, we propose that the influence of resting time on the rheological properties is closely related to size variation of non‐absorbed PCE. To identify this, glass bead suspensions were prepared with various amounts of PCE and ionic solution, and their rheological properties were evaluated at various times. We found that the yield stress increases with time at higher PCE concentrations and higher ionic strength solutions. Adsorbed PCE during resting tends to bridge the particles rather than disperse them. In addition, it was found that hydrodynamic radius of PCE increased with resting time, and depletion forces resulting from non‐absorbed PCE size changes correlate well with the increased yield stress. [ABSTRACT FROM AUTHOR]

The flow around a body of revolution with an appendage controlled by electromagnetic force is calculated by a finite volume method in order to assess the influence of the appendage on the flow and the control effect of the electromagnetic force. The Reynolds number (Re) base on the hull length is 1.0 × 107. An electromagnetic actuator is flush-mounted on the surface of the appendage to generate streamwise eletromagnetic force (Lorentz force) for flow control. The flow around the body at straight course and 6° yaw controlled by Lorentz force is simulated and discussed. The results indicate that the elliptical appendage introduces a complex wake structure and force fluctuation. The wake of the appendage has less influence on the boundary layer of the body at 6° yaw than at straight course. When the Reynolds number is as high as 1.0 × 107, the flow field and dynamic characteristic of the body approximate to the Euler solution. The Lorentz force may suppress the near-wall separation from the appendage effectively and reduce the drag and vibration, especially in the straight course case. [ABSTRACT FROM AUTHOR]

1H spin-lattice relaxometry (T1, longitudinal) of cement pastes with 0 to 0.18 wt % polycarboxylate superplasticizers (PCEs) at intervals of 0.06 wt % from 10 min to 1210 min was investigated. Results showed that the main peak in T1 relaxometry of cement pastes was shorter and lower along with the hydration times. PCEs delayed and lowered this main peak in T1 relaxometry of cement pastes at 10 min, 605 min and 1210 min, which was highly correlated to its dosages. In contrast, PCEs increased the total signal intensity of T1 of cement pastes at these three times, which still correlated to its dosages. Both changes of the main peak in T1 relaxometry and the total signal intensity of T1 revealed interferences on evaporable water during cement hydration by dispersion mechanisms of PCEs. The time-dependent evolution of weighted average T1 of cement pastes with different PCEs between 10 min and 1210 min was found regular to the four-stage hydration mechanism of tricalcium silicate. [ABSTRACT FROM AUTHOR]

In this study, the setting property and mechanical strength of cement pastes containing accelerators (CPCA) with or without superabsorbent polymers (SAPs) were first studied. The early microstructure evolution and water distribution at 7 and 28 days were probed by 1D (T2) and 2D (T1-T2 maps) H1 nuclear magnetic resonance (NMR) relaxometry, and the microstructure was systematically investigated by using mercury intrusion porosimetry (MIP), back-scattered electron (BSE) image and energy-dispersive X-ray spectroscopy (EDX) analysis. Results showed that the SAPs in the cement paste containing accelerators had various influences on setting time and compressive strength depending on the type of accelerators. The presence of SAPs in the cement paste containing alkaline free accelerators could alleviate the decrease of internal relative humidity, promote hydration and help to modify the pore structure. Moreover, it was observed that the SAP cavities could be nicely filled with calcium hydroxide (CH) in the cement paste with alkaline free accelerators. [ABSTRACT FROM AUTHOR]