Civil Engineering Graduate Seminar
Thursday, October 31, 4:00 pm, 641 Dow
Speaker: Xiao Sun
Title: Effects of Internal Curing on Permeability of Interface Transition Zone in Cement Mortar
Due to its high porosity, prewetted lightweight aggregate (LWA) is widely used as the internal curing medium to supply water for hydration or to mitigate moisture lost induced by self-desiccation or evaporation, thereby enhancing the sustainability of infrastructure. This research focuses on the pore structure and transport physical properties of the interface transition zone (ITZ) in cement mortar with internal curing. Mortar samples with and without LWA were made with the same water-cement ratio, which was 0.35. After curing for 28 days, the samples were polished, vacuum impregnated with fluorescent dye and cut into thin sections. The microstructures were characterized through scanning electron microscopy (SEM) imaging technique to exam the real differences of ITZ pore structure between two types of mortar. From those images, the two-dimensional digital samples contain pores, cement particles and fine aggregates were generated in micron scale. Based on the same porosities, the three-dimensional digital microstructures were generated using 3D image reconstruction technique. The permeability analysis was conducted on the 3D reconstructed pore microstructure. The permeasolver code developed by Dale Bentz and Nicos Martys at NIST was applied. The finite-difference method was conducted based on image pixels with artificial compressibility relaxation algorithm to solve the Stoker equation. Once the solution of the average velocity at four different depths converges to a fixed value, the permeability can be obtained from Darcy equation based on that velocity. A comparison of permeability between samples with and without internal curing was made. This study will demonstrate the effect of internal curing on the pore microstructure and transport properties at ITZ.
Xiao Sun is a second year PhD student of Michigan Tech. He works as a Research Assistant for Dr. Dai. His previous research topic is the microstructure and transport properties of concrete material. He received his undergraduate and graduate studies of fluid mechanics and hydraulic concrete structure from the universities in China.