2011 Volume 65 Issue 1 Pages 153-160
The mass transport properties and the durability of cement concrete are controlled by their microstructure which includes several different kinds of pores, and thus the characterization of the shape and size distribution of pore is important for prediction of durability of cement concrete. This paper describes the quantitative determination of pore-size distribution of microstructure in hardened cement paste by thermoporometry. The conventional determination method for pore-size distribution, such as nitrogen gas adsorption（NGA）and mercury intrusion porosimetry（MIP）have a disadvantage that the sample must be dried. The drying results in significant alteration of the smaller pores, and this has led to doubt about the validity of NGA and MIP data. In contrast, thermoporometry does not require the drying of sample, so it seems to be an ideal method to quantify the microstructure of hardened cement pastes. Thermoporometry is based on a thermodynamic equilibrium type from latent heat - temperature relations to occur with freeze, fusion of the water in a pore. Low-temperature scanning calorimetry is used to monitor latent heat associated with freezing of the pore water and melting of the ice in pore. The results of thermoporometry for MCM-41 indicates that considering the effect of non-freeze water on the thermodynamic conditions of liquid and solid transformation, the accurate prediction equation of the size and shape of finer pore, of which radius few nano-meters or less, can be given. The thermoporometry study for hardened cement pastes shows that the pore structure in hardened cement pastes is ink-bottle type with two different entry pores. Furthermore, MIP destroys the microstructure of hydration hydrates, so it is difficult to quantify the size of entry pore.
