Macropores, concrete

The cement paste formed by the hydration reactions always contains interconnected pores of different sizes, as shown in Figure 1.2. The pores can be divided into macropores, capillary pores and gel pores. The interlayer spacing within C-S-H gel pores) have a volume equal to about 28 % of the gel and dimensions ranging from a few fractions of a nm to several nm. These do not affect the durability of concrete and its protection of the reinforcement because they are too small to allow significant transport of aggressive species. The capillary pores are the voids not filled by the solid products of hydration of hardened cement paste. They have dimensions of 10 to 50 nm if the cement paste is well hydrated and produced... 

The steep increase of the water permeability above approximately 25 % porosity (corresponding to a wjc ratio of 0.45 with a degree of hydration of 75 %, Figure 1.6) is the background of the specified values in the codes of practice for high quality concrete. For instance. Table 1.2 shows the relationship between water/cement ratio and degree of hydration in order to achieve segmentation of the macropores in a paste of Portland cement. 

Different active components and the catalytic reactions have different requirements on the pore structures of activated carbon. Therefore, it should balance the proportion of the macroporous, mesopores and microporous by the concrete conditions in order to optimize the performances of catalyst. 

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