Characterization of the cellular structure of foamed cement using x-ray computed tomography

X-ray;Computed tomography;Foamed cement;Three dimensional characterization

Clark, Jamie V ; Lange ; David A.

关键词: X-ray;    Computed tomography;    Foamed cement;    Three dimensional characterization;   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/99121/CLARK-THESIS-2017.pdf?sequence=1&isAllowed=y

美国|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

The primary objectives of this thesis were to investigate and quantify the cellular structure of foamed cement samples at varying densities as well as to demonstrate X-ray computed tomography (CT) as a valuable three dimensional (3D) characterization technique for the investigation of cementitious materials. Three replicate samples were taken from four foamed cement mixes with target densities of 300, 400, 500, and 600 kg/m3, making 12 samples in total. The quantitative analysis included bulk volumetric properties of all 12 samples. One sample from each target density was further investigated to determine the air bubble size distributions that comprise the cellular structure of foamed cement. Following the quantitative analysis, 3D tetrahedral meshes were also created for one sample in every target density. In the analysis of the bulk volumetric properties, the X-ray CT data showed an increase in percent air volume with a decrease in density. The X-ray CT data showed good repeatability as the coefficients of variation calculated for each sample set were low at 6.64, 1.01, 1.81, and 2.17% for the 300, 400, 500, and 600 kg/m3 samples, respectively. The X-ray CT calculated densities were all found to be slightly lower than those measured of the original 4 x 8 inch cylinders from which the X-ray CT samples were extracted. To check the validity of these results a one sided t-test was performed with alpha equal to 0.05 for each set of samples. The alternative hypothesis was that the X-ray CT calculated densities should match the measured density values. The results of the t-test confirmed the null hypothesis with all t-values falling well below the critical value of 2.920. This revealed that from a statistical standpoint the X-ray CT calculated densities are not significantly different from the measured density values.In the analysis of the air bubbles size distributions of the foamed cement samples, the median bubble diameter followed no discernible trend and were fairly similar at 71.68, 87.06, 79.52, and 86.72 μm for 300, 400, 500, and 600 kg/m3 samples, respectively. An investigation of bubble volume fractions also showed that the cellular structure for all four samples are comprised of bubbles of similar size, despite their varied densities. The majority of the bubbles fell between 100 and 200 μm in diameter for each sample. The 300 and 500 kg/m3 samples had a higher number of bubbles comprising their cellular networks than the 400 and 600 kg/m3 samples. This was reflected in the bubble volume fraction data as an increase in the percent of smaller air bubbles ranging from 50 to 100 μm in diameter. Following the quantitative analysis, tetrahedral meshes were created for the foam cement samples to show the potential for using X-ray CT data in finite element analysis (FEA). These meshes are directly compatible with finite element softwares such as COMSOL Multiphysics Modeling Software and Abaqus Unified FEA.