Evaluation of Pore Structure of Hardened Cement Paste Immersed in Sodium Sulfate Solution

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 (D O2) 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, D O2 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 D O2 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.