The inhibition synergism of some plant extracts and common inorganic inhibitors to enhance the corrosion control of the embedding steel bars in concrete

Project Information

NATCON

Grant agreement ID: 892074

DOI

10.3030/892074

Project closed

EC signature date 28 March 2020

Start date 11 January 2021

End date 10 January 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 86 466,24

EU contribution

€ 86 466,24

Coordinated by

UNIVERSIDAD CARLOS III DE MADRID
Spain

Periodic Reporting for period 1 - NATCON (The inhibition synergism of some plant extracts and common inorganic inhibitors to enhance the corrosion control of the embedding steel bars in concrete)

Reporting period: 2021-01-11 to 2022-01-10

Summary of the context and overall objectives of the project

Corrosion of reinforcements often limits the durability of reinforced concrete structures, because of chloride ions or as a result of carbonation. Corrosion of reinforcement has huge economic implications as well as social issues including endangering the safety of people who are working in industries. Corrosion inhibitors control the corrosion of steel reinforcements without significantly changing the concrete properties. The environmental toxicity of the synthesized corrosion inhibitors has resulted in the search for finding green corrosion inhibitors with lower amount of toxic compounds. The corrosion inhibitors extracted from the plant products are inexpensive, readily available and renewable. Most parts of plants such as leaf, fruits peel, etc., are rich of the compounds that give them the capability to be used as corrosion inhibitor for various substrates in different electrolytes. NATCON project aims to examine the synergistic effect of some plant extracts and common inorganic inhibitors to enhance the corrosion control of the embedding steel bars in concrete.

The objective of NATCON is the development of synergistic organic natural inhibitors (from plants) and inorganic ones for construction (concrete) applications. NATCON has a clear novelty, as inhibitors prepared from plant extracts have been scarcely tested in strongly alkaline environments as those that can be found in the pores of concrete. More than synergy with traditional inorganic inhibitors (nitrites), NATCON has tried to evaluate the performance of natural inhibitors both in solution and in mortar.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

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).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

- Plant extracts provided desirable corrosion inhibition for steel rebar in chloride-polluted concrete pore solution.

- Electrochemical data indicated the most adequate plant extract concentration, obtaining very high corrosion inhibition efficiencies (e.g. higher than 80% for licorice) in solution.

- Surface analysis detected the presence of plant extracts on the oxide/hydroxide surface.

- DFT indicated that plant extracts can be considered promising inhibitors of steel corrosion in alkaline electrolyte.

- Synergism between a selected plant extract (liquorice) and traditional sodium nitrite was proven in chloride-contaminated solutions simulating those found in concrete pores.

- Licorice extract provided desirable corrosion inhibition for steel rebar also in chloride-polluted mortars.

- EIS results indicated the influence of plant extract concentration (within the range studied) when evaluating inhibition in mortars.

- In the range evaluated, mechanical strength of mortars is not affected by the addition of the extract, even although slight changes in porosity can be found in some cases.

- Synergism of liquorice with traditional sodium nitrite was proven in mortar too.


The project is finished.

Licorice efficiency in chloride-contaminated, concrete pore-simulated solution