Exploring the Use of Plant Extracts from Leaves, Bark, and Roots of Boswelia dalzelia as Corrosion Inhibitors on Low-Carbon Steel Embedded in Concrete as Reinforcement When Subjected to Chloride and Acidic Environment

Abdulrazak Akilu ^1,*, Muhammad Sani Abdullahi ¹, Auwal Jaji Aliyu ²

1. Department of Pure and Applied Chemistry, Kaduna State University, Kaduna, Nigeria

2. Department of Armament Engineering, Air Force Institute of Technology, Kaduna, Nigeria

* Correspondence: Abdulrazak Akilu

Academic Editor: Emanuele Brunesi

Special Issue: Corrosion Characterization and Sustainable Protection in Advanced Materials

Received: December 01, 2025 | Accepted: April 06, 2026 | Published: April 16, 2026

Recent Prog Sci Eng 2026, Volume 2, Issue 2, doi:10.21926/rpse.2602005

Recommended citation: Akilu A, Abdullahi MS, Aliyu AJ. Exploring the Use of Plant Extracts from Leaves, Bark, and Roots of Boswelia dalzelia as Corrosion Inhibitors on Low-Carbon Steel Embedded in Concrete as Reinforcement When Subjected to Chloride and Acidic Environment. Recent Prog Sci Eng 2026; 2(2): 005; doi:10.21926/rpse.2602005.

© 2026 by the authors. This is an open access article distributed under the conditions of the Creative Commons by Attribution License, which permits unrestricted use, distribution, and reproduction in any medium or format, provided the original work is correctly cited.

1. Introduction

The use of steel reinforcement in concrete has become a common practice in the construction of structures and infrastructure because of its excellent properties compared with other construction materials in terms of strength, fire resistance, and durability [1]. Reinforced concrete represents a very successful combination of materials, not only from a mechanical point of view but also from a chemical perspective, because the hydrated cement can provide excellent protection against corrosion. This chemical compatibility allows for the composite behavior of reinforced concrete and is the basis of its high durability. The composite action occurring in the steel–concrete bond may be unlimited over time while steel remains passive. The study of the conditions leading to reinforcement corrosion is of high importance because corrosion may significantly affect the load-bearing capacity of reinforced concrete [2]. Corrosion damage to reinforcing steel is an electrochemical process with anodic and cathodic half-cell reactions [3]. In the absence of corrosive species, the anodic dissolution reaction of iron is balanced by the cathodic oxygen reduction reaction.

The corrosion behavior of reinforcement in concrete has been investigated for organic and inorganic inhibitors. The organic inhibitors were extracted from Azadirachta Indica (neem) and Ruta Graveolens plants, and the inorganic inhibitors used were sodium nitrate and ethylenediaminetetraacetic disodium dehydrates. The inhibitors were added during concrete mixing, and the reinforced concrete specimens were immersed in hydrochloric acid (HCl), sodium chloride (NaCl), and magnesium sulfate (MgSO₄) solutions to induce corrosion. The corrosion resistance of the reinforcement was evaluated using weight-loss measurements and a half-cell potentiostat. The results of the inhibitors studied showed that Azadirachta indica has superior corrosion inhibition efficiency compared with the other inhibitors in acid and chloride solutions. Ethylenediaminetetraacetic disodium dehydrate exhibited good corrosion inhibition efficiency in the sulfate solution. It was also observed that the efficiency of inhibitors depends on the exposure environment [4].

This research will explore the use of extracts from the leaves, bark, and roots of Boswelia dalzelia as corrosion inhibitors for steel rods embedded in concrete as reinforcement when subjected to chloride and acidic-environments. Boswelia dalzelia exhibits strong antioxidant and metal chelating properties, which are important characteristics for corrosion inhibition because they can suppress electrochemical oxidation [5]. This plant is also available in West Africa, particularly Nigeria. For that reason, it is a cost-effective and sustainable source of green corrosion inhibitors.

2. Materials and Methods

2.1 Materials

Steel rods, Measuring cylinder, Filter paper, Separating funnel, 500 ml Beakers, Digital multimeter (Model: DT 9205A), Cement (Portland cement), Sand, Aggregate, Water and Organic inhibitors (Boswelia dalzelia).

2.2 Chemicals

Methanol, sulphuric acid, calcium chloride, and copper sulfate (CuSO₄).

2.3 Methods

2.3.1 Sampling

Three different parts; leaves, bark, and root of Boswelia dalzelia, were collected from various locations in the Zaria local government to ensure sample representativeness. The samples were separated by plant part and sent to the laboratory for pretreatment.

2.3.2 Pretreatment of the Samples

The samples were washed and dried, then ground into a fine powder using a mortar and pestle.

2.3.3 Preparation of the Standard Solutions

(CaCl₂ 1.0 M). One molar solution of CaCl₂ was prepared by measuring 111.00 g of calcium chloride using a weighing balance. The measured CaCl₂ was carefully poured into a 1 L volumetric flask, a small amount of distilled water was added, and the flask was swirled until the calcium chloride was completely dissolved. The flask was filled to the mark [6].

(H₂SO₄ 1.0 M). One molar H₂SO₄ was prepared by measuring 55.55 ml of concentrated H₂SO₄ and pouring it into a volumetric flask containing 500 cm³ distilled water. The flask was filled with distilled water up to the mark.

(CuSO₄ 1.0 M). One molar solution of CuSO₄ was prepared by measuring 159.60 g of copper sulfate. The measured CuSO₄ was carefully poured into a 1 L volumetric flask, and a small amount of distilled water was added and swirled until the copper sulfate dissolved to the mark. This solution was used as a copper-copper reference electrode in the half-cell container [7].

2.3.4 Extraction of Plant Samples

One hundred grams of the powdered leaves were measured and dissolved in 1000 mL of methanol at room temperature for 24 h, and they were filtered using filter paper. The extracts were recovered by filtration and stored at 40°C in a rotary vacuum evaporator. The same process was performed for the pre-treated (powdered) bark and root samples [8]. 15 g of each organic extract was used as an inhibitor in each concrete prism, based on the composition ratio of cement, sand, and aggregates [9].

2.3.5 Preparation of Reinforced Concrete Prisms

Reinforced concrete prisms of size 200 × 70 × 70 mm were prepared using cement, sand, and aggregates in a ratio of 1:2:3. A reinforcement bar of diameter 8 mm and length 200 mm was embedded while casing at a distance of 40 mm from the prism and allowed to dry before testing began. In addition, based on the concrete prism composition, 15 g of each inhibitor was added during mixing. Seven concrete prisms were prepared, six of which contained 15 g of the inhibitor each from the root, leaves, and bark of plant A (i.e., Boswellia dalzelia), and were immersed in acid and chloride solutions separately, while the remaining solution served as a control [10].

2.4 Characterization

2.4.1 Scanning Electron Microscopy Analysis

Surface analysis of the reinforcing bars by scanning electrode microscopy was carried out on Phenom X MVE 0987612. The surface morphology of unprotected (i.e. control samples) and protected (i.e. treated samples) reinforcement bars was analyzed after removal from the concrete prism using a crushing machine. Scanning was performed at magnifications of 350, 500, and 1000 to obtain clearer images, and the instrument was operated at 15 kV.

2.4.2 Potential Difference Measurement

The corrosion potential of the reinforced prisms was measured using a half-cell potentiometer at an interval of 2 weeks up to 12 weeks [11]. The electrical potential of a point on the surface of the steel reinforcing bar was measured by comparing its potential with that of the copper– copper sulfate reference electrode on the surface [12]. Practically, this was achieved by connecting a wire from one terminal of a voltmeter to the reinforcement and another wire to the copper sulfate reference electrode [13].

3. Results and Discussion

3.1 Surface Analysis

The results of surface analysis were obtained by scanning electron microscopy, and the images are presented below:

Surface analysis of the reinforcing bars by scanning electrode microscopy was carried out on Phenom X MVE 0987612. The surface morphology of unprotected and protected reinforcement bars was analyzed at a magnification of 350 and operated at a voltage of 15 KV. Scanning electron microscopy revealed that the plant extract adsorbed on the surface of the steel reinforcing bars increased their smoothness, thereby reducing corrosion attack [Figures 1(C), (D)]. Scanning electron microscopy images of unprotected or control reinforcing bars in acid and chloride show severe corrosion attack in Figures 1(A), (B) which is due to the absence of inhibition species according to the findings of [14]. The SEM images also demonstrate that the plant extract possesses significant corrosion-inhibition capability for steel reinforcement in aggressive acid and chloride environments. The uninhibited samples exhibited severe surface degradation with pronounced pitting and corrosion product formation, whereas the inhibited samples showed comparatively smoother morphologies with evidence of protective film formation.

Figure 1 SEM images of (A) unprotected reinforcement treated with acid solution, (B) unprotected reinforcement treated with chloride solution, (C) protected reinforcement treated with acid solution, and (D) protected reinforcement treated with chloride solution, scanned at 350×.

3.2 Potential Difference

The half-cell potential measurements were averaged over three readings for each measurement, and the resulting values were plotted as a function of time in Figure 2 and Figure 3.

Figure 2 Potential difference vs. Time in (weeks) for concrete treated with leaves, bark, and roots of BD plants in acid solution.

Figure 3 Potential difference vs. Time in (weeks) for concrete treated with leaves, bark, and roots of BD plants in chloride solution.

The inhibition impact is assessed by the magnitude of the negative value of the measured potential difference [15]. The greater the magnitude of the negative values, the greater the probability of corrosion. Electrode potential values greater than -200 mV are considered low (10% risk of corrosion), which is safe according to corrosion/civil engineers, whereas values less than -350 mV but greater than -450 mV are considered to be high risk (90% risk of corrosion), which is unsafe, and values less than -500 mV are considered to be severe corrosion, which is dangerous [16]. The potential difference values obtained were within less than -200 mV for the past 12 weeks, which showed the efficiency of the BD leaf extract in acid medium, whereas the values for BD bark and BD root extracts were above -300 mV (Figure 2), which is 90% risk and are not considered to be effective inhibitors. The efficiency pattern of the extract from BD leaves, bark, and root in acid shows the following pattern: leaves > bark > root extracts. This probably shows that among the components of leaves, certain compounds are more effective in corrosion inhibition and are not found in bark and root extracts [17].

The measured potential difference for the samples treated with leaf and bark extracts exceeds 200 mV, indicating a 10% corrosion risk and is considered safe by corrosion engineers [18]. For the sample treated with root extract, the magnitude of the measured potential obtained is less than 250 mV and greater than -350 mV (Figure 3) and is considered an intermediate risk of corrosion, i.e., moderately safe according to corrosion engineers [3]. The efficiency pattern of the extract from BD leaves, bark, and root extracts in chloride shows the following pattern: bark > leaves > roots.

4. Conclusion

Based on the results of the experimental investigation into the effect of green inhibitors on concrete reinforcement in acid and chloride media, it can be concluded that SEM and electrochemical potential measurements consistently demonstrate that the plant extract possesses significant corrosion-inhibition capability for steel reinforcement in aggressive acid and chloride environments. The uninhibited samples exhibited severe surface degradation with pronounced pitting and corrosion product formation, whereas the inhibited samples showed comparatively smoother morphologies with evidence of protective film formation. The potential differences over time further confirmed improved electrochemical stability in the presence of the inhibitor, with the sample containing leaf extracts showing the highest protection efficiency, followed by bark and root samples. The inhibition mechanism is attributed to the adsorption of bioactive compounds onto the steel surface, forming a barrier that suppresses corrosion reactions. Overall, the plant extract can be considered an effective, environmentally friendly corrosion inhibitor for reinforced steel in corrosive media.

Author Contributions

Abdulrazak Akilu: Conducted the laboratory analysis and manuscripts write-up. Muhammad Sani Abdullahi: Interpreted the experimental results. Auwal Jaji Aliyu: Conducted the data analysis and review the manuscripts.

Competing Interests

The authors have declared that no competing interests exist.