Abstract

The purpose of the present study is to evaluate pore structure of hardened cement paste immersed in sodium sulfate solutions and to experimentally examine the relation between the change of pore structure and hydration products. Cement paste specimens were immersed in sodium sulfate solutions and ion-exchanged water for two weeks. Since oxygen gas can pass through the pores having micro scale, it is possible to evaluate the effect of the pore structure on the oxygen transport in cement pastes. Thus, the oxygen diffusion coefficient (DO2) of the specimens after immersion were measured, and the pore volume and the pore size distribution were also measured. In addition, the phase compositions of the specimens were acquired. As a result, DO2 of the specimens immersed in the sodium sulfate solutions decreased as compared to the specimens immersed in the ion-exchanged water. The tortuosity of the specimens immersed in the sodium sulfate solutions increased due to decreasing of the pore volume having a diameter larger than 20 nm. There was a correlation between the volume of ettringite and the pore volume having a diameter larger than 20 nm. According to the above results, it was considered that the decreasing of DO2 in the case of sulfate immersion can occur as a result of the complication of the pore structure owing to filling of the pores by ettringite

Abstract

Cemented sand is a common way for soil stabilization or ground improvement. Tortuosity is an important parameter that has a significant impact on flow and transport characteristics of porous media and related to permeability and diffusion coefficient. This study aims to quantitatively investigate the tortuosity of the cemented sand with different cement content using X-ray computed tomography (CT) based random walk simulation. The cemented samples were scanned using microCT and converted to 3D pore space through image processing. Random walk simulation was applied to the reconstructed 3D pore space to calculate the tortuosity. Higher cement content gave an increase in tortuosity and a decrease in porosity. This indicates that the addition of cement makes pore space more tortuous and decreases both permeability and diffusion coefficient which are being treated as important parameters for durability of construction materials.