Comparison of Mercury Intrusion Porosimetry and multi-scale X-ray CT on characterizing the microstructure of heat-treated cement mortar

In this contribution, the microstructure features of cement mortar exposed to various temperatures (105 degrees C, 200 degrees C, 400 degrees C, 600 degrees C, 800 degrees C) was investigated by combining Mercury Intrusion Porosimetry (MIP) and multi scale X-ray computed tomography. The influence of exposure temperature and resolution of X-ray CT on the determination of microstructure parameters of heat-treated mortar was focused. Based on results of MIP test, it was found the porosity and pore size increased slightly when the exposure temperature varied from 105 degrees C to 200 degrees C and significant pore coarsening and micro-damage occurred once the temperature exceeded 400 degrees C. Bimodal pore size distribution (PSD) of the heat-treated mortar specimens was observed when the temperature reached 400 degrees C. To interpret the results of MIP test, the microstructure of heat-damaged mortar specimens was imaged using X-ray CT with a reconstructed voxel size of similar to 4.0 mu m(3) and then local volume inside the specimen was focused and scanned with a reconstructed voxel size of similar to 1.5 mu m(3). A method was proposed to select proper threshold based on the MIP results for segmenting the void space from the X-ray CT images. The fracture aperture, 2D/3D fractal dimension, connectivity and tortuosity of the heat-damaged mortar specimens were further determined at different scale. By analyzing the fracture aperture determined from X-ray CT images, it was found the bimodal PSD revealed by MIP test can be associated with the creation of thermal micro-fractures. The fractal dimension increased remarkably when exposure temperature was raised from 400 degrees C to 600 degrees C while it varied slightly from 600 degrees C to 800 degrees C. Linear dependences between the fractal dimension and the volume fraction/tortuosity of micro-scale pores and fractures were found. The scale-dependent fractal properties of the heat-treated mortar were revealed with the capillary pressure data measured by MIP. The fractal dimension of micro-scale pores and fractures measured by MIP exhibited good consistency with that determined based on by X-ray CT images with a reconstructed voxel size of 1.5 mu m(3).