I) SOLUTION TESTING.
I.a) Tested inhibitors and methodology.
Three natural plant extracts were finally developed and tested within NATCON: Urtica dioca (nettles), Glycyrrhiza glabra (liquorice), and Ferula Gummosa. Root from liquorice, leaves from nettles and root from Ferula Gummosa were tested. Synergism with traditional nitrites inhibitors was tested for liquorice, taking into account the results obtained for this inhibitor on its own.
Testing solution (according to UC3M experience) was always 0.3 M KOH + 0.1 M NaOH to deionized water, being solution then saturated with Ca(OH)2 and filtered. 1% (wt.) NaCl was also fixed. In all cases, different extract amounts were evaluated, always with 0.1% (wt.) maximum. Moreover, synergism with traditional nitrites inhibitors was tested for one of the extracts (liquorice, as it was the selected also for mortars). Amount of inhibitor was fixed (0.1% by wt.), and liquorice and sodium nitrite were used in different percentages (100-0, 75-25, 50-50, 25-75, 0-100).
I.b) Characterization techniques.
Different characterization techniques were employed to fully understand inhibitors performance, including:
- electrochemical impedance spectroscopy (EIS),
- polarization curves,
- scanning electron microscopy (SEM),
- Fourier transformed infrared spectroscopy (FTIR),
- X-ray photoelectronic spectroscopy (XPS),
- density-functional theory (DFT) quantum chemical calculations.
II) TESTS IN MORTAR
II.a) Tested inhibitors and methodology.
One natural extract plant was selected to develop mortars within NATCON: root from Glycyrrhiza glabra (liquorice). Again, synergism with traditional sodium nitrite inhibitors was tested for liquorice, comparing the results obtained for the inhibitors alone.
Mortar selected (according to UC3M experience) was Portland cement IV. In all cases, water/cement ratio (L/S) was 0.5 and the cement to standard sand (with 0.08–2 mm of grain size) ratio was 1:3. The amount of CaCl2 was fixed (1.25 % by wt.). Different extract amounts were evaluated, always with 0.2% (wt.) maximum. After curing, testing was developed for 86 days.
II.b) Characterization techniques.
Different characterization techniques were employed to fully understand inhibitors performance, including:
- mortar porosity (Hg intrusion),
- bending and compression strength of mortars,
- electrochemical impedance spectroscopy (EIS).
