LOGNORMAL SIMULATION OF PORE-SIZE DISTRIBUTIONS IN CEMENTITIOUS MATERIALS

The pore size distributions in cement pastes and mortars, over the range of pore sizes determined by high-pressure mercury intrusion porosimetry (MIP), can be described in terms of multimodal distribution by using lognormal simulation. The pore size distribution may be regarded as a mixture of lognormal distributions. Such a mixture is defined by a compound density function: p(x) = SIGMA-f(i)p(x, mu-i, sigma-i), SIGMA-f(i) = 1, where x is the pore diameter, f(i) is the weighting factor of the ith lognormal subdistribution of pore sizes, p(x, mu-i, sigma-i), and mu-i and sigma-i are the location parameter and the shape parameter of the ith subdistribution, respectively. It may indicate that different origins and formation mechanisms exist for pores in different size ranges in cementitious materials. A graphical method is proposed to estimate the parameters for the compound distribution. Applications of this model to prediction of permeability are discussed.