A Study on Relationship between Air Permeability of Saturated Mortar and Pore Structure

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This study investigates the air permeability of saturated and non-saturated mortar form the point of view of pore structure in mortar. The results obtained in this study can be summarized as follows.1. The critical pressure at which air flow begins through the specimen is affected by length of specimen, though in unaffected by holding time of pressure.2. The critical pressure of saturated mortar increases due to the decrease of water cement ratio of mortar and the extension of curing period in water. There is an adequate correlation between en U cal pressure an(1 threshold diameter. Threshold diameter is measured by mercury injection curve an(I represents the minimum diameter of pores which are geometrically continuous throughout all regions of the hydrated cement. paste.3. For measurement, of pore size distribution by mercury injection method, pore size distribution of non-saturated mortar is measured by using of frozen sample. Water in pore of mortar evaporates from all pore having diameter of not less than about 1OOnm under generally drying condition. Degree of evaporation of water from pore is approximately proportional to the pore volume of each pore diameter.4. Air permeability coefficient of cement based material is related to the pore structure. The parameters incorporating into the evaluation of air permeability coefficient. are porosity, averaged pore diameter and tortuosity. The concept of critical concentration based on percolation theory is adopted in porosity. Averaged pore diameter is not, anithmetical mean but harmonic mean in consideration for the air flow in pore and the size of pore. Tortuosity is expressed powers of porosity. The air permeability coefficient of concrete is estimated by the method proposed in this study with sufficient. accuracy.