In order to obtain quickly the influences of blast furnace slag and water-binder ratio on the leaching behavior of cement-based material and its corrosion resistance in water environments, an accelerated calcium leaching experiment on a slice specimen with slag-cement pastes in 6M NH 4 Cl solution was carried out. Using the saturation-drying weighing method, X-ray diffraction (XRD) and the scanning electron microscope (SEM/EDS) measurement, the influences of water-binder ratio and slag content on the porosity, phase composition, microstructure morphology and Calcium-Silicon ratio of slag-cement pastes in the process of calcium leaching were analyzed. Results show that, compared to cement pastes without slag, the slag-cement paste with the appropriate slag content has a low rate of microstructure deterioration and a good leaching resistance. The optimum slag contents in slag-cement pastes are respectively 40% and 50% corresponding to the low and high water-binder ratio. The porosity, Calcium-Silicon ratio and microstructure morphology of slag-cement pastes exhibit small change in the process of accelerating leaching, and this indicates that the slag-cement pastes with the optimum slag content can provide the best performance of calcium leaching resistance in the soft-water environment.
In order to apply shape memory alloy (SMA) damper for effective control of cable vibration under external excitations, motion equations and corresponding state equation of the system made up of SMA dampers and a cable are described based on Hamilton Principle, and the system's optimization problems based on the linear quadratic regulator (LQR) active control algorithm are investigated to obtain the optimum cable vibration control effects and control forces. According to the equivalency between SMA damper optimum passive control effects and LQR active control effects, the optimal design principle and methods of SMA damper for cable vibration control are proposed. Utilizing the above optimal methods, a SMA damper is designed to control vibration of a practical cable under white noise excitations, and its control effects are compared with the LQR active control effects by numerical simulation. Results show that the cable vibration responses under both LQR active control and SMA damper optimum control are obviously less than those without control, and SMA damper optimum control effects are approached to the LQR active control effects. This may indicate the effectiveness of the supposed SMA damper optimum design methods for cable vibration control.
Tortuosity is an important parameter for characterising the transport behaviours of cement-based materials. Based on some basic assumptions obtained by scanning electron microscope observations, this paper presents a twodimensional geometrical model for the tortuosity of transport paths in hardened cement pastes. The proposed model is expressed as a function of porosity, cement hydration degree, shape factor of cement particles and water/cement (w/c) ratio. In order to validate the proposed model, mercury intrusion porosimetry (MIP) tests on 30-day-cured cement paste samples with different w/c ratios were conducted to determine microstructure properties such as porosity, tortuosity and pore size distribution. The tortuosities of the samples from the proposal model were compared with those from the MIP tests and the results show good agreement. The present work can provide a basis for modelling the tortuosity of transport paths in mortar and concrete in order to numerically analyse the transport behaviours of concrete materials and structures.
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