Browsing by Author "Hongfang, Sun"

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    3D particle size distribution of inter-ground Portland limestone/slag cement from 2D observations: Characterization and distribution evaluation
    (Construction and Building Materials, 2017-08-30) Sun, Hongfang; Fan, Bing; Memon, Shazim Ali; Cen, Zhuo; Gao, Xiaobin; Lin, Bin; Liu, Bing; Li, Dawang; Xing, Feng; Zhang, Xiaogang; Hongfang, Sun
    Abstract In this research, the particle size distribution (PSD) of different components in inter-ground Portland limestone cement (PLC) and limestone-slag cement (PLC-S) was characterization by using an electron microscopy approach. Firstly, the 2D PSD of limestone, slag, and Portland cement (OPC) was determined by means of image analysis. Based on the 2D data and using a discrete stereology, the 3D size distribution was reconstructed. Finally, the PSD of inter-ground mixtures was assessed by using a compressible packing model. The results showed that the addition of limestone in cement makes the OPC component coarser and distribution broader; meanwhile, the limestone particles were found to be finer than the OPC particles. The addition of both limestone and slag (PLC-S) were found to further broaden the PSD of OPC component and limestone component with the mean size of particles increased in the following order (limestone
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    Investigating drying behavior of cement mortar through electrochemical impedance spectroscopy analysis
    (Construction and Building Materials, 2017-03-15) Sun, Hongfang; Ren, Zhili; Memon, Shazim Ali; Zhao, Diandian; Zhang, Xiaogang; Li, Dawang; Xing, Feng; Hongfang, Sun
    Abstract In this research, electrochemical impedance measurements were taken on cement mortar with different levels of drying. The impedance spectrum was analyzed with equivalent circuit model, through which the drying behavior was investigated. A model considering resistivity distribution along the drying direction was proposed. For drying of mortar, two different schemes (direct drying and ethanol-pretreated drying) were adopted. Moreover, the influence of hydration time of mortar on drying was also evaluated. Test results showed that the proposed model fitted well with both symmetric and asymmetric spectra for different levels of drying. For cement mortar directly dried at 50°C for different durations (1, 4, 24, and 48h), the peak resistivity and drying depth increased with drying time. The ethanol-pretreated mortar showed similar behavior. Moreover, the hydration time of cement mortar was another important factor to influence the drying depth. The proposed model for electrochemical impedance spectrum interpretation provides a low-cost and effective non-destructive approach for understanding the drying behavior of cementitious system.
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    Three-dimensional characterization of steel corrosion embedded in cement paste
    (Construction and Building Materials, 2017-07-15) Sun, Hongfang; Zhao, Diandian; Gu, Yang; Memon, Shazim Ali; Ren, Zhili; Liu, Bing; Zhang, Xiaogang; Xing, Feng; Li, Dawang; Hongfang, Sun
    Abstract In this research, a micro X-ray computed tomography (μCT) technique was used to investigate the distribution of steel corrosion embedded in cement paste non-destructively. An electrochemical method was used to accelerate the corrosion of steels for two designed levels of corrosion (2% and 18%). For μCT observations, two camera lenses (0.4× and 4× camera lenses) were used to globally and locally investigate the tomography of un-corroded steels, corrosion products as well as cracks. The factors affecting the corrosion distribution, such as the immersion depth in NaCl electrolyte as well as the arrangement of cathode position were also investigated. Test results showed that corrosion started at a certain direction by forming pits. For both corrosion levels, the distribution of corrosion products is not significantly related to the position of cathode electrode but related to the distribution of cracks. More corrosion products accumulated at the steel surface where penetrating cracks occurred; whereas in the occluded cracks, the corrosion product was insignificant. Furthermore, the actual corrosion level was found to be related to the immersion depth in NaCl electrolyte. i.e., with the increase in the depth of immersion, the steel corrosion level increased.