Sorption and Desorption Isotherms of Lightweight Alkali-Activated Materials Modified with Silica Aerogel
Abstract
:1. Introduction
2. Materials and Methods
- (a)
- Using desiccators and weighing cups (desiccator method);
- (b)
- Using a climatic chamber (climatic chamber method).
3. Results and Discussion
4. Conclusions
- The DVS method provided an effective determination of the equilibrium moisture values (w) for all the tested composites at each humidity level (RH).
- For each composite (R0–R3), ten measurement points were obtained in each sorption cycle and each desorption cycle, which provided the possibility of a precise determination of the course of both the sorption isotherms and desorption isotherms.
- All the tested composites exhibited Type III isotherms according to the Brunauer and IUPAC classifications. This type of isotherm occurs when the interactions between the adsorbate molecules are much stronger than those between the adsorbate and the adsorbent. Capillary condensation occurs in the pores of the adsorbent.
- The R0 composite, which did not contain aerogel, had the lowest sorption moisture values w in the entire humidity range tested (0–95%). Increasing the aerogel content led to higher moisture absorption. The R3 composite, with the highest aerogel content, showed the highest values of equilibrium sorption moisture w at all RH levels.
- In the range of the highest relative humidity (RH > 90%), the influence of capillary condensation is clearly visible, leading to an intense increase in the equilibrium sorption moisture w. It is most significant in the case of the R0 composite, with the most compact porosity structure.
- Capillary condensation also affected the course of the desorption isotherms of all the composites, leading to the more intense increase in the equilibrium values of w in the range RH > 80%.
- The desorption trends were similar to the sorption trends at RH > 30%, i.e., the lowest equilibrium values of desorption moisture w were found in the case of the R0 composite and the highest were in the case of the R3 composite.
- In the range of the lowest humidity (RH < 30%), no clear differences were observed between the desorption isotherms of the individual composites. However, in all the composites, there was a significant decrease in equilibrium moisture values w with a decrease in humidity. The changes in this range (RH = 30% → 0%) were much greater than those recorded in the measurements of the sorption isotherms.
- The differences between the sorption and desorption equilibrium moisture w depended on the RH values. The largest differences, ranging from 5% to 7%, occurred at intermediate RH levels. The smallest differences were observed at both the lowest and highest RH levels.
- The hysteresis was most pronounced in the R0 and R1 composites, i.e., those made without the addition of aerogel or with the lowest aerogel content. In the R0 composite, the hysteresis was more pronounced at RH > 50%, and in the R1 composite, the hysteresis was more evident at RH < 50%.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
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Chemical Element Content, wt.% by EDS Analysis | |||||
---|---|---|---|---|---|
Silica Aerogel | GGBFS | Fly Ash-Based Aggregate | |||
Oxygen | 52.27 | Oxygen | 31.96 | Oxygen | 52.06 |
Silicon | 36.48 | Silicon | 11.40 | Silicon | 17.53 |
Carbon | 11.25 | Carbon | 10.01 | Carbon | 6.54 |
Calcium | 37.35 | Calcium | 8.44 | ||
Aluminum | 3.07 | Aluminum | 6.95 | ||
Potassium | 0.66 | Potassium | 3.26 | ||
Magnesium | 2.85 | Magnesium | 1.56 | ||
Iron | 1.21 | Iron | 1.53 | ||
Sulfur | 0.60 | Sodium | 1.38 | ||
Titanium | 0.75 |
Measured RH [%] | R0 w [%] | Measured RH [%] | R1 w [%] | Measured RH [%] | R2 w [%] | Measured RH [%] | R3 w [%] |
---|---|---|---|---|---|---|---|
0.00 | 0.000 | 0.00 | 0.000 | 0.00 | 0.000 | 0.0 | 0.000 |
9.34 | 0.295 | 9.56 | 0.532 | 9.49 | 0.726 | 9.5 | 0.737 |
20.14 | 0.663 | 20.38 | 1.281 | 20.21 | 1.626 | 20.4 | 1.714 |
30.27 | 1.234 | 30.55 | 2.136 | 30.28 | 2.649 | 30.6 | 2.828 |
40.15 | 1.876 | 40.59 | 3.140 | 40.41 | 3.840 | 40.6 | 4.113 |
49.95 | 2.666 | 50.43 | 4.390 | 50.60 | 5.243 | 50.5 | 5.556 |
59.47 | 3.677 | 59.98 | 5.871 | 59.98 | 6.686 | 60.2 | 7.111 |
68.91 | 4.931 | 69.52 | 7.484 | 70.23 | 8.239 | 70.0 | 8.772 |
78.23 | 6.463 | 78.78 | 9.170 | 80.08 | 9.959 | 79.4 | 10.445 |
87.61 | 8.448 | 88.19 | 11.079 | 89.74 | 12.033 | 88.9 | 12.600 |
94.00 | 12.703 | 94.59 | 13.712 | 94.77 | 15.470 | 95.5 | 16.211 |
Measured RH [%] | R0 w [%] | Measured RH [%] | R1 w [%] | Measured RH [%] | R2 w [%] | Measured RH [%] | R3 w [%] |
---|---|---|---|---|---|---|---|
0.00 | 1.798 | 0.00 | 2.228 | 0.00 | 0.948 | 0.0 | 1.492 |
9.49 | 3.638 | 9.66 | 4.327 | 9.47 | 3.141 | 9.9 | 3.824 |
20.30 | 5.370 | 20.53 | 6.385 | 20.33 | 5.223 | 20.9 | 6.070 |
30.44 | 7.238 | 30.72 | 8.644 | 30.49 | 7.762 | 31.2 | 8.728 |
40.48 | 8.387 | 40.84 | 9.974 | 40.53 | 9.240 | 41.3 | 10.454 |
50.24 | 8.800 | 50.65 | 10.420 | 50.40 | 9.691 | 51.4 | 11.048 |
59.87 | 9.507 | 60.22 | 10.866 | 59.93 | 10.177 | 61.0 | 11.611 |
69.31 | 9.794 | 69.71 | 11.391 | 69.49 | 10.910 | 70.6 | 12.221 |
78.59 | 10.160 | 78.99 | 11.947 | 78.92 | 11.841 | 79.9 | 12.950 |
88.06 | 11.521 | 88.30 | 12.803 | 88.44 | 13.773 | 89.3 | 14.411 |
94.00 | 12.703 | 94.59 | 13.712 | 94.77 | 15.470 | 95.5 | 16.211 |
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Garbalińska, H.; Stolarska, A.; Strzałkowski, J.; Ślosarczyk, A. Sorption and Desorption Isotherms of Lightweight Alkali-Activated Materials Modified with Silica Aerogel. Materials 2025, 18, 1338. https://doi.org/10.3390/ma18061338
Garbalińska H, Stolarska A, Strzałkowski J, Ślosarczyk A. Sorption and Desorption Isotherms of Lightweight Alkali-Activated Materials Modified with Silica Aerogel. Materials. 2025; 18(6):1338. https://doi.org/10.3390/ma18061338
Chicago/Turabian StyleGarbalińska, Halina, Agata Stolarska, Jarosław Strzałkowski, and Agnieszka Ślosarczyk. 2025. "Sorption and Desorption Isotherms of Lightweight Alkali-Activated Materials Modified with Silica Aerogel" Materials 18, no. 6: 1338. https://doi.org/10.3390/ma18061338
APA StyleGarbalińska, H., Stolarska, A., Strzałkowski, J., & Ślosarczyk, A. (2025). Sorption and Desorption Isotherms of Lightweight Alkali-Activated Materials Modified with Silica Aerogel. Materials, 18(6), 1338. https://doi.org/10.3390/ma18061338