## 5 Micro-Properties of the Cemertitious Materials with RP
### Pore Structure  
The pore structure of cement-based materials has a crucial role in determining many qualities, such as mechanical strength and durability. Furthermore, the permeability and diffusivity of cement-based material are contingent upon pore characteristics, including porosity, pore size, pore tortuosity, and pore connectedness ([PERSON] et al., 2019; [PERSON] et al., 2020; [PERSON] et al., 2020; [PERSON] et al., 2020). The pore distribution of cementitious materials can be assessed using MIP or BET tests ([PERSON] et al., 2020). In addition to these two methods, nuclear magnetic resonance (NMR) is a recently developed technology that has found extensive applications in cement-based materials ([PERSON] et al., 2020). In general, concerning the effects of pore size on the performance of paste, pores in paste were categorized into four groups according to [PERSON]'s ([PERSON] et al., 2020) pore size grading theory, i.e., harmless pores (\(<\)20 nm), less harmful pores (20-50 nm), harmful pores (50-200 nm), and more harmful pores (\(>\)200 nm) ([PERSON] et al., 2019; [PERSON] et al., 2020; [PERSON] et al., 2020; [PERSON] et al., 2020; [PERSON] et al., 2020). In some cases, a different pore size classification is used in which pore types are divided into hydrated phases (gel) porosity, i.e., gel pores (0-10 nm), fine capillary pores (10-50 nm), middle capillary pores (50-100 nm), and large capillary pores (100-10,000 nm) ([PERSON] et al., 2019; [PERSON] et al., 2020; [PERSON] et al., 2020); [PERSON] et al. (2020). 146,147,169,294,303]. It has been reported that pores smaller than 50 nm are associated with creep and shrinkage, whereas pores larger than 50 nm are believed to be associated with strength and permeability [56; 59; 169; 303]. Regarding the pore structure, general comments can be made as follows, with exceptions: As RP is involved and RP content increases, porosity increases [45; 72; 84; 97; 98; 127; 129; 131; 140; 141; 145; 164; 192; 193; 205; 217; 245; 253; 295; 303]. Figure 15 presents the porosity variations for mechanically treated RP. The presence of greater RP content results in a proportional increase in the pore size and pore volume [45; 59; 71; 84; 98; 129; 164; 192; 197; 203; 205; 235; 245; 253; 296; 303; 304] as presented in Figure 16.  
Figure 16: Average pore diameter (nm) for mechanically treated RP utilized in cement-based materials (%) [45; 59; 244; 294]. Figure 15: Porosity variation (%) for mechanically treated RP utilized in cement-based materials (%) [35; 72; 98; 152; 179; 193; 244; 294]. The presence of greater RP content results in an increase in the percentage of larger pores as presented in Figure 17[71, 78, 98, 131, 146, 164, 192, 205]. It should also be noted that the high fineness of RP can enhance the hydration reaction of cement paste and increase the density of concrete by filling the pores [52, 71, 176, 192]. The increase in porosity following the incorporation of RP can be attributed to an agglomeration of finer particles within the cement matrix [78, 98, 146, 192, 303]. It can also be explained by stating that the presence of untreated RP reduces the formation of new hydration products and has a negative effect on the pore structure of the produced cementitious materials [8, 56, 101, 129, 140, 164, 179, 192, 193, 250, 293]. [PERSON] et al. [98] stated that the overall porosity of the mortar increased significantly, particularly when the dose of RCP was above 20%. [PERSON] et al. [295] stated that the average pore diameter slightly decreases as the incorporation of GCP increases from 10% to 30%. [PERSON] et al. [192] observed that when replacing 30% of the cement with RFP, there is a decrease in hydration products and an increase in pore structure. [PERSON] et al. [179] stated that substituting 20% RCP results in a higher cumulative pore volume compared to the reference paste. [PERSON] et al.