## 3 Results and Discussion  
### Isothermal Calorimetry  
Figure 2 shows the heat release rate and accumulated hydration heat of the adhesives kept at a temperature of 20 \({}^{\circ}\)C for 72 h. nS0 represents the paste without nanoparticles. nS2 and nS4 represent pastes containing nano-silica doped with 2 wt.% and 4 wt.% cement, respectively. Cement hydration involves the initial (pre-induction) period, induction period, acceleration (post-induction) period, deceleration period, and diffusion period [26]. As shown in Figure 2a, the main heat flow peaks appeared in the order of nS0 \(>\) nS2 \(>\) nS4. The PCE used in this study delayed the binder hydration kinetics in all UHSC systems with its dosage. In the induction period, the appearance of the main hydration peak was delayed and the peak heat flow rate values were suppressed because of the addition of PCE. This behavior occurred because the surface of cement and nS particles was adsorbed by PCE molecules. The surface dissolution and product nucleation sites were inhibited by this adsorption of PCE molecules, resulting in suppression of the hydration kinetics in the induction period [27]. In addition, it can be clearly observed that there were three peaks for nS2 and nS4. The first peak represents a dissolved peak of tricalcium aluminate. The second peak represents an exothermic peak of C\({}_{3}\)S and other topochemical reactions, and the last peak represents sulphate-type-AFm and C\({}_{3}\)A rehydration. The formation of three peaks was due to the following three reactions. The first peak, representing initial hydration on the cement particle surface, mainly involved tricalcium aluminate (C\({}_{3}\)A). However, since the paste was stirred outside the bottle, the first peak was not captured entirely. The second peak was due to the consumption of C\({}_{3}\)S and other topochemical reactions [28], resulting in the formation of calcium silicate hydrate (C-S-H) and calcium hydroxide (CH). The third distinct peak was due to the formation of sulphate-type-AFm (monosulphate) or due to secondary hydration of C\({}_{3}\)A with ettringite [29]. This is similar to the experimental results of a previous study [10]. The appearance of monosulphate depends on the gypsum content. After the depletion of gypsum, and AFt is unstable and AFt begins to change into AFm. If the gypsum is depleted in the first 3 days, monosulphate can be formed. The three peaks were still observed in the nS0 specimens. However, due to the proximity of the second and third peaks to each other, the two peaks could not be easily distinguished. Figure 2b shows the cumulative heat accumulation curve of all UHSCs for 72 h at 20 \({}^{\circ}\)C. It can be observed that as the nano-silica was added, the heat released from UHSCs increased significantly, indicating an increase in the hydration phase formation relative to the amount of binder. For example, compared with the heat released from nS0 (145 J/g) at 3 days, nS2 (160 J/g) and nS4 (170 J/g) were observed to increase approximately by 10% and 17%, respectively. It is worth noting that, in the initial period, the amount of heat released from nS2 and nS4 was greater than that from nS0 because of the nucleation effect of nano-silica which promotes cement hydration [30]. However, in the acceleration period, the heat released from nS0 was greater than that from nS2 and nS4. This behavior occurred, because the higher PCE content reduces binder hydration [31], resulting in a decrease in the heat flow rate, making the cumulative heat of the nS0 the highest. Finally, in the deceleration period anddiffusion period, the heat release from nS4 was the greatest, followed by nS2, and the heat release from nS0 was the lowest. The setting time was determined by the first derivative of the heat release rate curve of the specimen [22]. Figure 3 is a typical plot of the first derivative of the heat release rate curve from the original isothermal calorimetry test data.