《Table 4 Electric fluxes of concretes with montmorillonite in the aggregate》

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《Property and Degradation Characteristics of Concrete Prepared with Aggregate Contained Montmorillonite》

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The permeability properties of all concretes were assessed by the electric flux as listed in Table 4.The concrete electric flux is related to the various pores in the concrete.Generally，the higher is porosity，the higher electric flux is available[23].Compared to 30 to40 percent capillary porosity of ordinary cement paste present in hardened concrete，the volume of pores in most natural aggregates is usually under 3 percent and rarely exceeds 10 percent.Therefore，it is always considered that the permeability of aggregate would be much lower than that of the typical cement paste.However，this may not necessarily be the case.The size of capillary pores in aggregate is usually much larger.Most of the capillary porosity in a mature cement paste lies in the 10 to 100 nm range，whereas the pore sizes in aggregate are，on the average，larger than 10μm[2，4].Thus some aggregates with only 10 percent porosity show much higher permeability than the cement paste.Their permeability may be low，but such aggregates are vulnerable to expansion and cracking associated with sluggish moisture movements and the resulting hydrostatic pressure.Montmorillonite has the layer structure and thus appears high porosity.However，it also always implies that its volume can be expanded after the absorbing water.The pores would change to be smaller or be sealed.Thus the porosity decreases and the permeability resistance is improved.Finally，the electric fluxes of all concretes go by this way，and the concretes with montmorillonite in the aggregate have the lower electric flux than the control as shown in Table 4.The electric fluxes of all concretes are more than 1200 C.This result shows that all concretes are dense with low permeability.