## 6 Fresh-State Properties in Cementitious Matrices with RP
### Setting Time  
Setting time refers to the duration it takes for a mix to progressively lose its fluidity and plasticity due to the hydration process, ultimately reaching a specific level of strength [102]. The setting time is a crucial parameter used to evaluate the initial behavior of cementitious materials [13; 65; 102; 118; 293]. In literature, the most used standards for this purpose are GB/T 1346-2011 [310], GB 175-2007 [319], ASTM C187-16 [320], ASTM C191-19 [321], BS EN 196-3: 2005 [322], and JC/T 727-2005 [323]. The inclusion of RP has a dual effect on the setting time. On one side, the inclusion of RP reduces the quantity of hydration products in the mix, thereby prolonging the setting time. Conversely, RP particles function as nuclei for crystallization, thus facilitating the formation of hydration products and reducing the time it takes for the material to crystallize [98; 102; 295; 297; 114; 293]. Some scholars stated that RP tends to decrease the setting time due to the presence of small particles, which have a nucleation effect [35; 65; 78; 114; 118; 293; 297]. [PERSON] et al. [114] observed that the usage of wet-grinded RP (WGRP) decreased the time interval between the first setting and final setting time of PC pastes. [PERSON] et al. [324] and [PERSON] et al. [35] reported that an optimal quantity of RP (30%) enhances the flowability and reduces the setting time of cement. However, some scholars have come to the opposite conclusion, stating that the mix exhibited an increase in both the initial and final setting time compared to the reference [62; 71; 72; 84; 98; 140; 147; 179; 203; 208; 213; 222; 295; 324]. Figure 30 presents setting time (initial and final) of mechanically grinded RP. [PERSON] et al. [72], [PERSON] and [PERSON] [62], and [PERSON] et al. [84] argued that the delays were attributed to the reduction in C\({}_{3}\)A and C\({}_{3}\)S, which enhance the hydration reaction, as the proportion of WCP increases. [PERSON] [213] stated that the setting time is prolonged in cement batches having more than 3% of NS, due to the accumulation of NS particles. [PERSON] et al. [140] also examined the effect of NS on the early hydration properties of RCP-cement-based materials. They reported that the addition of 30% RCP (without NS) resulted in a prolongation of both the initial and final setting time of the cement paste. However, contrary to [PERSON] [213],  
Figure 29: Spreading diameter (mm) versus CO\({}_{2}\) activated RP percentage (%) [61; 130; 180; 262]. [PERSON] et al. [140] stated that the inclusion of NS decreased both the initial and final setting times. They explained this phenomenon by mentioning the nucleation effect of NS, which offers numerous nucleation sites for the precipitation of cement hydration products, hence expediting the hydration process. [PERSON] et al. [71] stated that, adding FA and SF to RCP pastes, the setting time was significantly reduced. They argued that this can be ascribed to the fact that the inclusion of FA and SF can enhance the hydration process of cement, resulting in the formation of many flocculent C-S-H gels, so the cement loses its plasticity and experiences a significant reduction in setting time. [PERSON] and [PERSON] [208] also reached identical findings and stated that the setting time increases as the FA ratio increases. On the other hand, [PERSON] et al. [147] obtained contradictory outcomes by using FA and SF. They reported that, as the amount of WCRP content increased, the initial setting time of pastes initially increased and later decreased, whereas the final setting time of pastes increased but the addition of FA and SF to the WCRP paste resulted in a significant decrease in the setting time. Regarding the effect of chemical activation on he setting time, [PERSON] et al. [325] stated that the setting time of the paste decreased substantially with the increased amount of alkali activator. They explained that within an alkaline environment, the amorphous structure present in GGBS will gradually undergo destruction and decomposition.