Permeability and elastic modulus of cement paste as a function of curing temperature

The permeability and elastic modulus of mature cement paste cured at temperatures between 8 degrees C and 60 degrees C were measured using a previously described beam bending method. The permeability increases by two orders of magnitude over this range, with most of the increase occurring when the curing temperature increases from 40 degrees C to 60 degrees C. The elastic modulus varies much less, decreasing by about 20% as the curing temperature increases from 20 degrees C to 60 degrees C. All specimens had very low permeability, k<0.1 nm(2), despite having relatively high porosity, phi similar to 40%. Concomitant investigations of the microstructure using small angle neutron scattering and thermoporometry indicate that the porosity is characterized by nanometric pores, and that the characteristic size of pores controlling transport increases with curing temperature. The variation of the microstructure with curing temperature is attributed to changes in the pore structure of the calcium-silicate-hydrate reaction product. Both the empirical Carmen-Kozeny, and modified Carmen-Kozeny permeability models suggest that the tortuosity is very high regardless of curing temperature, xi similar to 1000. (C) 2011 Elsevier Ltd. All rights reserved.