Analysis of Pore Structure Using Thermoporometry with Water and Cyclohexane

【Author】

Tomoaki Sugiyama;Daiki Atarashi;Masahiro Miyauchi;Etsuo Sakai;

【Abstract】

<正>Typically,mercury intrusion porosimetry(MIP) is used to measure the pore size distribution in hardened cement,but this method has a number of disadvantages.It uses mercury,a dangerous material,and the process imposes a high load of 200 MPa on a sample;in weak materials,this can result in the deterioration of the pore structure.Thermoporometry is emerging as a novel alternative analytical approach for characterizing pore structures:thermoporometry is a calorimetric method that determines pore size based on the reduction of the melting or crystallization point of a liquid confined in a pore.Hardened cement has a wide range of pore sizes,from approximately 2 run to 200 nm;it is necessary to analyze the melting or freezing behavior of water at temperatures of approximately -0.1℃when measuring the largest pores,but such measurements are difficult to perform accurately using differential scanning calorimetry.The reduction in the melting point of cyclohexane is larger than that of water,and it is therefore suitable for measuring larger pores.This study investigated the melting behavior of freeze water and cyclohexane in porous silica,and suggested a method that combines the melting behaviors of freeze water and eyclohexam to measure the pore size distribution.Hardened ordinary Portland cement and cement paste deteriorated using sulfuric acid were measured using thermoporometry, and the results were compared with those from MIP. Porous silica with a homogeneous pore size distribution and ordinary Portland cement were used. The water-to-cement ratio in the hardened cement was 0.5;it was cured in moist air for one day, the molds were removed,and the specimens were then cured at 20℃for 28 days.The hardened cements were immersed in a 5%sulfuric acid bath for 7 days.The melting temperature was measured for the freezing water and cyclohexane frozen in the pores,using differential scanning calorimetry.The pore ste distributions were calculated based on the melting behavior,and compared with the results from MIP. It was found that water was suitable for the measurement of pores smaller than 15 nm,and cyclohexane was suitable for the measurement of pores larger than this.The pore structure of hardened cement could be analyzed using this new method.In addition,this method has the potential to allow the measurement of the pore structure of hardened cement deteriorated by sulfuric acid.However,MIP could not measure the pore structure,and the deteriorated sample collapsed when the pressure was approximately 0.1 MPa. Originality The originality of this paper lies in the approach to the analytical method,which combines the melting behaviors of water and cyclohexane,since the range of radii that can be analyzed differ for each liquid.In addition,we demonstrate the measurement of hardened cement deteriorated by sulfuric acid,which cannot be achieved using the conventional methods,because the pore structure collapses under high loads.

【Keywords】

thermoporometry;;mercury intrusion porosimetry;;pore size distribution;;cyclohexane;;water

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