## 5 Micro-Properties of the Cemertitious Materials with RP
### Hydration Heat Analysis  
The findings of the hydration heat test, which is often used to analyze the early-stage hydration kinetics of cementitious materials, provide a thorough depiction of the chemical reactions occurring in all components inside the sample. The isothermal calorimeter is used to test the hydration heat release of RP [59; 80]. The process of hydrating heat can be categorized into five distinct phases: initial reaction (pre-induction period), induction period, acceleration period, deceleration period (delay period), and stabilization period [59; 65; 80; 140; 144; 147; 179; 201]. Based on the Krstulovic-Dabic model, the hydration of cement pastes with RP can be described by three distinct processes: nucleation and crystal growth, interactions at phase borders, and diffusion. It is important to state that the three processes might happen at the same time, but the rate at which hydration occurs is determined by the slowest process [32]. The inclusion of the RP leads to a decrease in the peak time of the heat of hydration curves, suggesting that the addition of RP enhances the rate at which the paste hydrates due to its dilution effect [65; 83; 84; 98; 101; 129; 138; 140; 142; 144; 152; 201]. The acceleration of cement hydration is typically attributed to the finer particle size and increased surface area available for the nucleation of C-S-H, as seen by the higher specific area of RP compared to cement [32; 83; 101; 118; 127; 142; 163; 293]. At the early stage (the wetting heat is the heat that is generated by a unit mass of initially dry powder upon immersion in water), RP exhibits a greater wetting heat compared to cement because it possesses a more porous structure [38; 59; 129]. Additionally, RP exhibits a smaller particle size and a greater specific surface area, leading to an increased release of heat during hydration due to enhanced interaction with water and a higher number of nucleation sites. Hence, the inclusion of RP can impact the rheological characteristics of cement paste by enhancing the process of cement hydration through improved dissolution and precipitation [38; 59]. Figure 14 presents a summary of the fluctuations in accumulated heat in relation to the reference. A significant increase is observed in the initial phases and at low RP percentages. [PERSON] et al. [32] observed that the addition of RCP with a D50 of 3.0 \(\upmu\)m greatly increased the rate of hydration in cement paste, compared to a larger particle size of RCP measuring 36.1 \(\upmu\)m. [PERSON] et al. [140] suggest that replacing up to 30% by weight of PC with RCP utilizing nano silica (NS) reduces heat flow and accumulated heat. [PERSON] et al. [83] suggest that the utilization of 8% RCP not only decreases the time it takes for a reaction to start but also enhances the amount of heat that is generated. [PERSON] et al. [113] suggest that the heat accumulation in the first 12 h is caused by the ongoing stimulation of cement hydration for 4% RCP with a particle size of 0.249 \(\upmu\)m (D50). [PERSON] et al. [71] reported that when the RCP dosage by weight is 15%, and the substitution rate of other mineral admixtures is 15% by weight, the cumulative heat was the highest among the RCP samples mixed with FA and SF. [PERSON] et al. [144] reported that the RCP-C with a 10% concentration exhibits comparable heat release to CP. According to [PERSON] et al. [35], increasing the proportion of RFP (10-90%)in the blended cement results in a longer period of hydration induction. Additionally, the peak hydration exothermic rate and accumulated heat release show a clear decreasing trend. [PERSON] et al. [147] observed that when the content of WCRP and the content of FA and SF were both 15%, the hydration rate and cumulative hydration heat of the pastes were found to be the highest among all of the samples containing FA and SF. [PERSON] et al. [65] presented that the rate at which heat was produced in pastes containing RP was higher than the rate in cement pastes during the initial 30 min.