## 3 Fundamental Properties of RP
### Physical and Chemical Properties of RP
#### 3.4.3 Chemical Composition  
To obtain the chemical components of RP, the common method is to use an X-ray fluorescence (XRF) analysis. Figure 8 illustrates the main constituents of RP that have received a mechanical pretreatment, for a specific period, either wet or dry. Figure 7: The maximum and the minimum values of major components of RP. The primary chemical constituents of the RP are SiO\({}_{2}\), calcium oxide (CaO), aluminum oxide (Al\({}_{2}\)O\({}_{3}\)), and ferric oxide (Fe\({}_{2}\)O\({}_{3}\)) [7; 10; 24; 35; 39; 45; 52; 71; 72; 73; 78; 87; 92; 116; 118; 119; 120; 127; 128; 153; 166; 172; 177; 178; 191; 194; 195; 202; 203; 210; 218; 223; 224; 225]. These chemical constituents closely resemble the composition of regular cement [10; 24; 52; 71; 92; 116; 119; 128; 166; 172; 178; 194; 195; 218; 223], FA [24; 71; 87; 116; 119; 194; 218], and GGBS [127; 216] which indicates an optimal distribution of oxides and efficient source to be utilized as SCM in cement-based materials [9; 38; 65]. RP has a significant amount of CaO and SiO\({}_{2}\)[35; 45; 52; 72; 116; 118; 119; 128; 153; 176; 177; 199; 203; 209; 224]. The high content of these two oxides can be attributed to the substantial presence of natural sand (quartz) and natural coarse particles (calcite) in the initial WC [116; 119; 128; 176; 119; 203; 209; 224]. The CaO content in RP is lower than that in cement [10; 35; 39; 52; 71; 82; 87; 92; 116; 166; 172; 203; 218] and higher than that in FA [87; 116; 119; 194; 218]. The CaO content in RP exists as inert CaCO3, whereas the CaO content in cement is in the form of active clinker [194; 199]. The presence of a lower CaO compound can be attributed to the high concentration of siliceous sand and reduced cement component, primarily produced from hydrated cement, existing in the form of C-S-H and CH [39; 116; 128; 193]. The SiO\({}_{2}\) content in RP is higher than both cement [10; 39; 52; 71; 82; 87; 92; 116; 166; 193; 203; 223] and FA [71; 87; 116; 119]. The higher SiO\({}_{2}\) content can be attributed to the fact that RP was produced by grinding WC, and the SiO\({}_{2}\) is mostly present due to the unhydrated cement, C-S-H, and siliceous sand [39; 128; 193]. RP has a lower content of sulfur trioxide (SO\({}_{3}\)), and higher alkali content (potassium oxide (K\({}_{2}\)O) and sodium oxide (Na\({}_{2}\)O)) compared to cement, FA, and GGBS [92]. In addition, RP contains lower amounts of aluminum and magnesium compared to GGBS [216]. There is not an agreement in the literature on the specific ratio of chemical composition in relation to RP, as it varies based on its source and the type of aggregate used in the WC [5; 9; 13; 38; 128; 144; 226]. Some research indicates that RP produced from demolition waste contains more SiO\({}_{2}\)[34; 144; 172; 193] and laboratory-produced RP contains more CaO [144; 227; 228; 229]. A few studies have shown that RP fulfills the necessary criteria of ASTM C618 [230] to be classified as a pozzolanic material, with a composition of Fe\({}_{2}\)O\({}_{3}\)+Al\({}_{2}\)O\({}_{3}\)+SiO\({}_{2}\) above 70% as presented in Figure 9. In addition, it should be also noted that even while certain RP samples may contain more than 70% Fe\({}_{2}\)O\({}_{3}\)+Al\({}_{2}\)O\({}_{3}\)+SiO\({}_{2}\), they may not exhibit pozzolanic activity due to the presence of crystalline particles inside the RP. Nevertheless, the literature indicates that the fine portion of recycled CDW aggregate contains residual anhydrous clinker, which can be recovered through grinding [122]. Consequently, enhancing the added value of recycled materials through physical or chemical methods is essential. It has been demonstrated that grinding \(\alpha\)-SiO\({}_{2}\) in the powder initially converts it into the more stable \(\beta\)-SiO\({}_{2}\), which subsequently transforms into amorphous SiO\({}_{2}\)[183], hence enhancing its activity, and can be used as a cement replacement material [38; 231].