# Characterization and Reactivity of Natural Pozzolans from Guatema
## 3 Results and Discussion
### Pozzolanic Activity
#### 3.2.3 Thermogravimetric Analysis
**(b) Cement/pozzolan (PC/VP) pastes**  
In these systems, the PC reaction with water showed a sequence of processes that produced hydration cementing products (Ettringite, CSH, CAH, and CASH) and portlandite. In the presence of pozzolanic materials, this released portlandite can form new hydration products, such as some of those formed during cement hydration. It is essential to note that two reactions simultaneously occurred: cement hydration and the pozzolanic reaction. Fixed lime depends on calcium hydroxide, which produces hydration in the control paste. Therefore, by calculating the fixed lime percentage in cement pastes, Equation (6) could be used [32]:  
\[\textbf{{Fixed~{}Line}}\left(\%\right)=\frac{\left|CH_{\text{C}}*C_{\%} \right|-CH_{P}}{\left|CH_{\text{C}}*C_{\%}\right|}*100 \tag{6}\]  
where  
\(CH_{\text{C}}\):the amount of CH in the control pastes for a given curing time;  
\(CH_{\text{P}}\): the amount of CH present in the paste with the volcanic pozzolan at the same curing time;  
Figure 10: DTG curves for the 1:2 CH/R pastes after 7, 28, and 90 days at curing temperatures of: (a) 20 \({}^{\circ}\)C and (b) 40 \({}^{\circ}\)C.  
Figure 9: DTG curves for the 1:2 CH/T pastes after 7, 28, and 90 days at curing temperatures of: (a) 20 \({}^{\circ}\)C and (b) 40 \({}^{\circ}\)C.  
The corresponding TG curves were analyzed. The total mass loss, portlandite dehydroxylation mass loss, and combined water in hydrates were obtained. Table 7 summarizes these values, and also the Ca(OH)\({}_{2}\) present in the reacted pastes and the fixed lime percentages, which were calculated from the aforementioned equations in the introduction to this subsection. The results obtained with the analysis of the PC/VP pastes showed a negative fixed lime percentage at 28 days, which indicates that the pozzolanic additions acted as a filler for that curing time and accelerated cement hydration [33]. This behavior is typical of FA pastes at early curing times. Therefore, pozzolan particles are useful primarily as a nucleating agent, where cement hydration products are precipitated. In this way, cement continues to hydrate and the amount of portlandite present in the matrix increases. At 90 days, the fixed lime values were positive. This suggests a significant contribution of the pozzolanic reaction. It also means that the pozzolanic reaction is slow and its chemical effects are evident for long curing times. The percentage of water associated with hydrates for the control paste and the pastes with the 25% replacements at 28 days of curing at 20 \({}^{\circ}\)C indicated that pozzolan acted as a filler for a short period of time. For this reason, all the pastes had similar combined water contents in the cementing hydrates. For longer curing times (90 days), the significant \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Total Loss**} & **Ca(OH)\({}_{2}\)** & \multirow{2}{*}{**CH\({}_{P}\)**} & \multirow{2}{*}{**Fixed Lime**} & **H\({}_{2}\)O in** \\  & & & **Loss** & & \\ \hline T 20 \({}^{\circ}\)C 7d & 7.06 & 5.23 & 21.51 & 31.28 & 1.83 \\ T 40 \({}^{\circ}\)C 7d & 10.53 & 3.57 & 14.70 & 53.04 & 6.96 \\ T 20 \({}^{\circ}\)C 28d & 10.32 & 4.10 & 16.88 & 46.09 & 6.22 \\ T 40 \({}^{\circ}\)C 28d & 11.55 & 1.39 & 5.72 & 81.73 & 10.16 \\ T 20 \({}^{\circ}\)C 90d & 11.84 & 2.79 & 11.47 & 63.35 & 9.05 \\ T 40 \({}^{\circ}\)C 90d & 14.88 & 1.24 & 5.12 & 83.65 & 13.64 \\ R 20 \({}^{\circ}\)C 7d & 9.95 & 5.99 & 24.65 & 21.25 & 3.96 \\ R 40 \({}^{\circ}\)C 7d & 10.17 & 3.22 & 13.22 & 57.75 & 6.95 \\ R 20 \({}^{\circ}\)C 28d & 10.62 & 4.09 & 16.82 & 46.25 & 6.53 \\ R 40 \({}^{\circ}\)C 28d & 15.16 & 1.40 & 5.75 & 81.61 & 13.76 \\ R 20 \({}^{\circ}\)C 90d & 12.58 & 2.83 & 11.64 & 62.81 & 9.75 \\ R 40 \({}^{\circ}\)C 90d & 18.16 & 1.23 & 5.05 & 83.87 & 16.94 \\ \hline \hline \end{tabular}
\end{table}