# Characterization and Reactivity of Natural Pozzolans from Guatema
## 3 Results and Discussion
### Pozzolanic Activity
#### 3.2.3 Thermogravimetric Analysis  
This part is subdivided into two parts: (a) hydrated lime pastes cured at 20 \({}^{\circ}\)C and 40 \({}^{\circ}\)C, tested for curing times of 7, 28, and 90 days with a 1:2 CH/VP weight ratio; and (b) cement pastes cured at 20 \({}^{\circ}\)C for 28 and 90 curing days using a control paste (only cement II) and the pastes with the 25% replacement (either T or R). **(a) Hydrated lime/pozzolan (CH/VP) pastes**  
To calculate the hydrated lime fixation (fixed lime), the calcium hydroxide dehydroxylation mass loss was measured and corresponded to the reaction:  
\[Ca(OH)_{2}\to CaO+H_{2}O\uparrow\]  
The fixed lime content was in accordance with the calcium hydroxide initially dosed in the sample. Therefore, Equation (3) was used to calculate the percentage [31]:  
Figure 7: Electrical conductivity loss at 60 \({}^{\circ}\)C for pozzolans. \[\text{{Fixed line}}\ \ (\%)=\frac{CH_{O}-CH_{P}}{CH_{O}}*100 \tag{3}\]  
where  
\(CH_{O}\):the initial amount of calcium hydroxide present in the paste;  
\(CH_{P}\): the amount of calcium hydroxide present in the CH/VP paste for a given curing time. The amount of calcium hydroxide present in the paste was calculated by stoichiometry with Equation (4):  
\[\text{{CH}}_{\text{P}}=\frac{H}{PM_{H}}*PM_{CH} \tag{4}\]  
where  
\(H\): loss of mass due to the calcium hydroxide dehydroxylation present in the paste;  
\(PM_{H}\): water molecular weight;  
\(PM_{CH}\): calcium hydroxide molecular weight. Furthermore, the combined water in the formed hydrates (CSH, CAH, and CASH) was calculated, which indicates the associated amount of water with hydration products, to simultaneously provide an approximation of the percentage of the formed hydration products. Figure 8: _Cont._  
The water percentage associated with the hydrates (\(P_{H}\)) present in the paste was calculated using Equation (5):  
\[P_{H}=P_{T}-P_{CH} \tag{5}\]  
where  
\(P_{T}\): the total percentage of mass loss;  
\(P_{CH}\): percentage of mass loss due to lime dehydroxylation. The DTG curves for the 1:2 CH/VP pastes after 7, 28, and 90 days at the 20 \({}^{\circ}\)C and 40 \({}^{\circ}\)C curing temperatures are presented in Figures 9 and 10 for the T and R samples, respectively. A predominant peak from the dehydroxylation of calcium hydroxide was observed for both pozzolans on the DTG curves at the 20 \({}^{\circ}\)C curing temperature, regardless of the number of days, and was thus higher than the hydrate decomposition peaks (CSH, CAH, and CASH). It can be concluded that, at this temperature, the CH/VP mixtures took considerable time to consume calcium hydroxide via the pozzolanic reaction. The reaction had already begun because the peaks corresponding to CSH, CAH, and CASH had clearly developed at 28 and 90 days. The peaks corresponding to hydrates rose to 40 \({}^{\circ}\)C as a result of the increasing pozzolanic reaction rate. At this curing temperature, most of the calcium hydroxide had been consumed after 90 days, thus demonstrating the relationship between the increase in the curing temperature and the pozzolanic reaction. Table 6 presents the values of total mass loss, dehydroxylation of calcium hydroxide loss, lime fixation percentages, and combined water in hydrates (\(P_{H}\)) for all the mixtures, which were calculated from the aforementioned equations in the introduction to this subsection. No significant differences in the behavior of both pozzolans were found. Figure 8: Pozzolanicity test results for CEM II/A-L 32.5N and the 15%, 25%, 35%, 45%, and 55% replacements with pozzolans T and R: (**a**) 8 days and (**b**) 15 days of testing. [PERSON] and [PERSON] [31] studied a lime-natural pozzolans system with different ratios between both materials. They obtained a greater lime fixation value than the present research work (80% lime fixation at 90 curing days at ambient temperature). The thermogravimetry values confirmed VP reactivity for long curing times.