# Characteristics of Ordinary Portland Cement Using the New Colloidal Nano-Silica Mixing Method
## 3 Results and Discussion
### Thermal Analysis  
The results of thermal analysis of the 0% CNS and 50% CNS specimens are showed in Figure 7. The TG/DTG results for the 0% CNS specimen are presented in Figure 7a. The weight loss in the temperature range of 50 \({}^{\circ}\)C-200 \({}^{\circ}\)C [58] or 120 \({}^{\circ}\)C-145 \({}^{\circ}\)C [2] was due to the water loss of the C-S-H gel. The weight loss observed at 80 \({}^{\circ}\)C-130 \({}^{\circ}\)C [59] or 110 \({}^{\circ}\)C-150 \({}^{\circ}\)C [60] was due to the water loss of ettrinigite. As the age gradually increased to 1-, 3-, and 28-days, weight loss also increased. This indicates that the formation of ettrinigite and C-S-H gel were increased with the increasing age.  
At 100 \({}^{\circ}\)C-200 \({}^{\circ}\)C [61], the weight loss of gypsum was confirmed. This was supported by the gypsum peak observed in the XRD of Figure 5a. In Figure 5a, the gypsum peak showed a larger peak height at 28-days than at 3-days. In Figure 7a, 28-days shows more weight loss than 3-days. This means that the hydration of OPC particles continues to 28-days.  
The weight loss at 400 \({}^{\circ}\)C-450 \({}^{\circ}\)C [62] is due to the water loss of portlandite. In the 0% CNS specimen, as the age increased, the weight loss rate of portlandite also increased. This indicated that the cement particles were continuously hydrating after the initial hydration stage and that the weight loss at 665 \({}^{\circ}\)C-800 \({}^{\circ}\)C [63] or 720 \({}^{\circ}\)C-760 \({}^{\circ}\)C [64] was due to the water loss of calcite.  
Figure 7b shows the results of TG/DTG analysis of the 50% CNS specimen. The weight loss of C-S-H gel was observed at 50 \({}^{\circ}\)C-200 \({}^{\circ}\)C [58] or 120 \({}^{\circ}\)C-145 \({}^{\circ}\)C [64]. Water loss of ettrinigite was also observed at 80 \({}^{\circ}\)C-130 \({}^{\circ}\)C [59] or 110 \({}^{\circ}\)C-150 \({}^{\circ}\)C [58]. However, the weight loss of gypsum (100 \({}^{\circ}\)C-200 \({}^{\circ}\)C [61]) observed in Figure 7a did not occur. Unlike the 0% CNS sample, the weight loss rate due to water loss of portlandite observed at 400 \({}^{\circ}\)C-450 \({}^{\circ}\)C [62] was similar at 1-, 3-, and 28-days. Further, the weight reduction rate of portlandite in the 50% CNS specimen was less than that of the 0% CNS specimen. This indicates that most of the portlandite was consumed in hydration and that pozzolanic reacted during the early stage of hydration (initial 24 h). This is consistent with the observations of [PERSON] et al. [28] that colloidal nano-silica rapidly forms the C-S-H gel within 12 h. Therefore, the replacement of CNS with the weight of mixing water accelerates the hydration of cement particles, and this phenomenon is mostly completed during the initial 24 h.  
Figure 7: _Cont._When the CNS is replaced by the mixing water weighing method of this study, portlandite is rapidly consumed before 1-day to form a dense hydration reaction matrix. Therefore, it is a mixing method that can improve the mechanical performance sufficiently compared with the PNS and binder weight substitution method used in the previous research.