Papers by Author: Xin Cheng

Abstract: The effects of wood fiber and polypropylene fiber on the mechanical performance, drying shrinkage and moisture loss of sulphoaluminate cement (SAC) mortar were studied. The experimental results show that wood fiber and polypropylene fiber can both improve the flexural strength of the mortar and reduce drying shrinkage ratio and moisture loss at different ages. Polypropylene fiber can also improve the late compressive strength of the mortar. Adding 0.3% mass fraction of wood fiber, the drying shrinkage ratio and moisture loss of the motar reach minimum values. The drying shrinkage ratio reduces to 0.029% at 28d. Moisture loss reduces to 0.4%. Adding 0.5% mass fraction of polypropylene fiber, the drying shrinkage ratio and moisture loss of the motar also reach minimum values. The drying shrinkage ratio reduces to 0.03% at 28d and moisture loss reduces to 0.39%.

Abstract: A cement based piezoelectric composite sensor using 1-3 cement based piezoelectric composite as sensing element was fabricated. The basic properties of the sensor were mainly investigated. The results indicate that in the frequency range from 0.1 to 40 Hz, the output voltage amplitudes of the sensor increase nonlinearly with increasing frequency of input load under 10 Hz. When the frequency of input load is larger than about 10 Hz, the output voltage amplitudes of the sensor is nearly independent of frequency. There exists an obviously linear relationship between the output voltage amplitude of the sensor and input load amplitude. The output voltage of the sensor is correspond to the complex load very well. The phase difference between the output voltage of the sensor and input load is near zero. Therefore such sensors have a good potential to be used in civil engineering structural health monitoring.

Abstract: Sulphoaluminate cement and Lead Niobium-Magnesium Zirconate Titanate ceramic (PMN) were used as matrix and functional component to fabricate 1-3-2 piezoelectric ceramic-cement composites by dicing and filling method. The influences of base thickness on piezoelectric, dielectric and electromechanical coupling properties of the composites were analyzed and discussed. The results show that with increasing the base thickness, the piezoelectric stain factor d₃₃ increases gradually, while the piezoelectric voltage factor g₃₃ decreases. The relative dielectric factor ε_r decreases initially and then increases, while the dielectric loss tan δ increases initially and then decreases. When base thickness is 0.50 mm, ε_r has the minimum value of 1406. When base thickness is 3.00 mm, tan δ reaches the minimum value of 0.251. With increasing the base thickness, the planar electromechanical coupling coefficient K_p exhibits the decreasing trend, and the thickness electromechanical coupling coefficient K_t and acoustic impedance Z show the increasing trend.

Abstract: The effects of carbonation on structure and properties of steel slag specimens are evaluated by some different testing technologys in this paper. The experimental results of strength and soundness show that the compressive strength of samples is improved 6-8 times due to carbonation, and carbonated specimens have qualified autoclave soundness. Also the carbonation reactions of steel slag and the reason that why strength and soundness improved are analyzed by chemical titration, XRD, TG, SEM and MIP etc. Experimental results indicate that in steel slag specimens, f-CaO, f-MgO, partial C2S and C3S minerals could be carbonated, and 105～110 gram CO2 gas could be sequestrated after carbonating per kilogram of steel slag specimens.

Abstract: Carbon fiber reinforced cement could sense its own temperature based on the temperature resistivity effect. In contrast with Portland cement, sulphoaluminate cement has much better freeze- resistance. As a result, carbon fiber sulphoaluminate cement composite (CFSC) has the superior potential to sense its own temperature than carbon fiber reinforced Portland cement in the negative and positive temperature, especially for the negative temperature range. The temperature resistivity effect of CFSC was discussed in the positive and negative temperature. And the lower and the upper temperature limit of temperature resistivity effect were investigated. The results indicated that temperature resistivity effect of CFSC was related to the hot expansion and the electric carrier activating. And the electric carrier activating was the primary influence factor. Temperature sensors could be made by CFSC based on its good temperature resistivity effect in positive and negative temperature range. Therefore CFSC has the advantage to sense positive and negative temperature by resistivity measurement.