BIBECHANA Vol. 22, No. 3, December 2025, 223-236 ISSN 2091-0762 (Print), 2382-5340 (Online) Journal homepage: http://nepjol.info/index.php/BIBECHANA Publisher:Dept. of Phys., Mahendra Morang A. M. Campus (Tribhuvan University)Biratnagar Advancement of plant-based inhibitor acquired from Elaeocarpus aungustifolius Blume leaves to control carbon steel corrosion in simulated concrete pore solution Madhab Gautam1,2, Dhruba Babu Subedi1, Yuvraj Paudel1 Kamal T. Kunwar Magar1, Nootan Prasad Bhattarai1,∗, Jagadeesh Bhattarai1,∗ 1Central Department of Chemistry, Tribhuvan University, Kirtipur 44618, Kathmandu, Nepal 2Department of Chemistry, Tribhuvan M. Campus, Tribhuvan University, Tansen 32500, Palpa, Nepal ∗Corresponding author. Email: bhattarai_05@yahoo.com[JB], neutan08@gmail.com[NPB] Abstract The extraordinary compressive strength of concrete makes it one of the most popular building materials, second only to water. However, early reinforcement corrosion is a common problem with concrete structures reinforced with carbon steel (CS). This issue underscores the signifi- cance of understanding corrosion-retarding systems that incorporate inhibitors. This research evaluates the effectiveness of leaf extract from Elaeocarpus angustifolius Blume (LEEA) as an inhibitor in an aqueous saturated calcium hydroxide electrolyte that simulates a concrete pore solution (SCPS) with a pH level exceeding 11.5. The objective is to evaluate the corrosion- inhibiting capacity of LEEA at 500-4000 ppm in SCPS to reduce the corrosion of reinforcing carbon steel (RCS) at 298K over four months or more using gravimetric weight loss (GrWL) and electrochemical polarization (ECP) techniques. GrWL and ECP methods yielded the max- imal inhibition efficiencies of 93.9% and 81.7%, respectively, at 4000 ppm LEEA in SCPS. The results of ECP experiments demonstrated that the corrosion current density (CCD) de- creased with increasing LEEA concentrations. This observation indicates that LEEA exhibits a significant inhibitory effect in the SCPS environments. Phyto-compounds (PCs), including polyphenols, alkaloids, and flavonoids found in LEEA, can inhibit both cathodic and anodic (i.e., mixed) processes by promoting the best-fitting Langmuir adsorption isotherm model on the RCS surface. Surface analyses confirmed the corrosion-inhibiting effectiveness of LEEA in enhancing concrete's anti-corrosion properties through a protective layer on RCS. Keywords Corrosion-resistant film, phyto-inhibitor, polarization, reinforcement corrosion, polarization. Article information Manuscript received: April 28, 2025; Revised July 28, 2025; Accepted: August 3, 2025 DOI https://doi.org/10.3126/bibechana.v22i3.78028 This work is licensed under the Creative Commons CC BY-NC License. https://creativecommons. org/licenses/by-nc/4.0/ 223 http://nepjol.info/index.php/BIBECHANA bhattarai_05@yahoo.com neutan08@gmail.com https://doi.org/10.3126/bibechana.v22i3.78028 https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ Madhab Gautam et al./ BIBECHANA 22 (2025) 223-236 224 1 Introduction The most widespread structural building material is reinforcement concrete because of its affordabil- ity, mechanical strength, and adaptability [1]. The reinforcement concrete structures' durability is af- fected by their alkaline nature of interspersed pore solution, which has a pH of around 12-14 [2]. As a result, cement paste's hydration produces a thin, passive, and stable oxide film [3] that firmly sticks to the RCS surface to prevent early corrosion deteri- oration. The RCS corrosion deterioration describes the premature degradation of reinforced concrete structures caused by electrochemical processes on the CS surface brought on by ambient dampness, high temperatures, carbonated conditions, and the ingress of vicious ions such as sulfates and chlo- rides [4]. It is the most prevalent issue in hostile (urban or industrial) and coastal environments [5]. Corrosion causes concrete structures to crack, spall, and weaken, which causes reinforced concrete foun- dations to collapse too soon [6]. The reinforcement corrosion presents significant challenges and should be managed effectively in time [7]. Synthetic waterproofing compounds are utilized for long periods as preventive concrete ad- mixtures to mitigate corrosion of RCS [8]. Un- fortunately, a considerable number of these syn- thetic compounds have the potential to harm liv- ing beings and contribute to environmental con- tamination [9]. It underscores the viability of uti- lizing plant-based green extracts as an alternative approach for corrosion prevention in reinforcement concrete infrastructures [10]. Secondary metabo- lites such as alkaloids, phenols, flavonoids, and oth- ers derived from plant waste—encompassing leaves, roots, stems, and bark—are particularly relevant in this context. These compounds exhibit distinc- tive aromatic systems, unsaturated -systems, and lone pairs of electrons associated with heteroatoms [11]. Such characteristics facilitate the formation of physical and chemical adsorption layers that dis- rupt corrosion reactions at the interface between corroded RCS and the concrete mix that incorpo- rates plant extracts, thereby demonstrating signifi- cant corrosion-inhibiting properties [12]. Nepal ranked the world's second-richest coun- try in forest resources after Brazil, and is home to a diverse range of flora and fauna [13]. How- ever, many forest products in Nepal have been un- derutilized. Research into their potential as envi- ronmentally friendly corrosion inhibitors for rein- forced concrete (ReC) is still in its early stages. Some studies have documented the use of Nepalese plant-based corrosion inhibitors to control the cor- rosion of mild steel (MS) in various electrolytes. For instance, the leaves of Callistemon citrinus have been tested on MS in NaCl [14], while extracts from Areca catechu and Laurus nobilis have been studied in a 0.5M NaCl solution [15]. Addition- ally, Aegle marmelos has shown effectiveness on MS in bioethanol [16], and a range of plants including Acacia catechu, Terminalia arjuna, Aegle marme- los, Catharanthus roseus, Callistemon citrinus, and Laurus nobilis have all been evaluated on MS in acidic electrolytes [17]. Researchers have also explored Vitex negundo on aluminum and copper in biodiesel and its blends [18]. Further studies have involved Aegle marmelos and Catharanthus roseus in both bioethanol and its blends [16], extracts of Vitex negundo and Catha- ranthus roseus on MS for waterproofing applica- tions [11], and the stem extract of Tinospora cordi- folia on aluminum and copper in biodiesel-based fuels [19]. More recent studies have examined leaf extracts of Mangifera indica [20] and Psidium gua- java [21] on MS in concrete beams and slabs. On- going efforts continue to identify new and effective green inhibitors for ReC infrastructure, including the endemic plant species Elaeocarpus angustifolius Blume from Nepal, as a potential green inhibitor. In this context, it is meaningful to mention herein that in the domain of materials science, two synthetic and commercial waterproofing agents, along with the methanolic extract of Mangifera in- dica leaves, had exhibited notable anti-corrosion properties, thereby warranting their recommenda- tion for the protection of reinforced mild steel (RMS) infrastructures [20]. The corrosion resis- tance of 1000 and 2000 ppm concentrations of M. indica extracts applied to RMS within con- crete surpasses that of equivalent concentrations of the commercial waterproofing agents. This en- hanced performance was evidenced by shifts in half- cell potential (HCP) values toward more noble di- rections (i.e., < 10 % corrosion probability re- gions). Such findings suggest that plant-based anti- corrosive concrete admixtures may provide greater advantages than the utilization of conventional wa- terproofing chemicals [20]. Hence, this study aimed to present a rationale for the integration of plant- derived metabolites from Elaeocarpus angustifolius Blume leaf as effective anti-corrosive additives in ferroconcrete formulations. Elaeocarpus angustifolius Blume, commonly known as the bead tree or rudraksha, is a well- known medicinal plant recognized for its vari- ous pharmacological and ethno-medicinal proper- ties [22]. The name comes from Greek, where "carpus" means fruit and "eleaeo" refers to olive, which reflects the olive-like appearance of the tree's fruits [22]. The Elaeocarpus family includes over 360 species worldwide, with 26 species identified in Nepal alone [16]. Among these, E. angusti- folius Blume—also referred to as Elaeocarpus gan- itrus Roxburgh and E. sphaericus Gaertner—is an Madhab Gautam et al./ BIBECHANA 22 (2025) 223-236 225 evergreen tree notable for its ornamental, stony en- docarp, known as Rudraksha [23]. According to Hindu mythology, the Rudraksha tree has sprouted from the tears of Lord Shiva, and its fully devel- oped blue fruits are often referred to as "blueberry beads" [24]. The rudraksha tree is a large, evergreen, decid- uous tree with a spreading crown that can grow to 50 and 200 feet [25]. Its leaves are simple, alter- nate, and oblong-lanceolate, measuring 10-15 cm long. The underside of the leaves has a dull, fi- brous texture, while the upper surface is bright green [26]. This tree is well-known for its spiri- tual and therapeutic benefits, as it produces beads with segmented ridges, believed to possess electro- magnetic properties capable of dispelling negative energy [27]. Research indicates that methanolic leaf extracts of the rudraksha tree (E. ganitrus) exhibit significant analgesic effects and contain al- kaloids, tannins, and flavonoids [28]. Additionally, methanolic leaf extracts of E. sphaericus are rich in phytoconstituents such as saponins, alkaloids, phe- nols, flavonoids, sterols, and carbohydrates; how- ever, they do not contain amino acids or proteins [29]. Because the leaves of this medicinal plant have a high phenol and flavonoid content and contain many classes of bioactive secondary metabolites, the bioactivity tests showed that the leaves might be a potential source of antibacterial, antibiotic, an- tioxidant, anti-diabetic medications [30], and other purposes like as anti-corrosive agents. However, a considerable quantity of leaves from this plant acts as debris without deriving any industrial or monetary benefits. While a limited number of studies have underscored the corrosion-inhibitory properties of the leaf extract [16] and seed ex- tract [31] in aggressive electrolytes, there has yet to be an investigation into their efficacy in mitigat- ing corrosion in ReC. According to what we know, the methanolic leaf extract from the Elaeocarpus aungustifolius Blume plant was not considered a corrosion inhibitor for reinforced carbon steel in SCPS/reinforcement concrete in literature, which is why the present research is considered novel. Therefore, this study aims to evaluate the effec- tiveness of leaf extracts from the Elaeocarpus an- gustifolius Blume plant (LEEA) as environmentally friendly corrosion inhibitors in simulated concrete pore solutions (SCPS) with a pH level higher than 11.5. The primary objective is to assess the viabil- ity of LEEA as a green corrosion inhibitor within this context. The research investigates the ability of LEEA to reduce the corrosion of carbon steel (CS) in SCPS utilizing gravimetric weight loss (GrWL) and potentiodynamic polarization (PoP) methods. The findings may contribute to plant-derived green inhibitors designed to mitigate corrosion in concrete reinforcement. 2 Materials and Method AR grade methanol and calcium carbonate were employed for the preparation of LEEA and satu- rated Ca(OH)2 solution, respectively. They were with a purity of 98%. Elaeocarpus aungustifolius Blume leaves, as illustrated in Fig. 1(a), were iden- tified with voucher code RDP-01 and deposited at the Department of Plant, National Herbarium and Plant Laboratory in Godavari, Lalitpur, after be- ing collected from the Tribhuvan University Cam- pus premises close to the Central Department of Environmental Sciences, TU-Kirtipur, Nepal. The collected leaves were placed in a shady area until completely dried and ground in an electric grinder to make leaf powder, as in Fig. 1(b). About 400 grams of leaf powder of Elaeocarpus aungustifolius Blume were taken in 2000 mL conical flasks with 800 mL of methanol, as described elsewhere [32]. After being tightly sealed in the conical flask and thoroughly shaken, they were kept for 2 weeks or more with regular shaking, as shown in Fig. 1(c). Following the shaking procedure, the supernatant mixtures were kept for a few hours to separate the supernatant using filtration. Excess methanol in the filtrate was removed using a rotary evapora- tor (IKA®RV 10 digital V, Germany) and water bath at 40°C, as illustrated in Fig. 1(d). Then, the semi-solid leaf extract of Elaeocarpus aungustifolius Blume (LEEA) was stored at 4°C. The saturated calcium hydroxide [Ca(OH)2] solution, with a pH of approximately 12±0.5, was used to prepare the SCPS. Figure 1: Photos illustrating the different stages of the LEEA preparation: leaves of Elaeocarpus aun- gustifolius plant (a), dried leaves powder (b), leaf- powder dipped in CH3OH (c), and a solvent evap- orator machine (d). For the GrWL approach, fifteen thermo- mechanically treated carbon steel (CS) specimens, designated as 500CS (NBS marked 500 XD series), were meticulously prepared. As previously outlined in other studies, the surface preparation involved using silicon carbide paper with grits ranging from 200 to 2000 [15]. The average diameter and length of each of the 500CS pieces were 1.13 cm and 2 cm, respectively. A 5-digit micro-balance (BM-252; A&D Weighing Co., Japan) with an accuracy of Madhab Gautam et al./ BIBECHANA 22 (2025) 223-236 226 0.00001 grams was initially used to record care- fully the weight of each 500CS piece (abbreviated as W0). The composition (wt.%) of the 500CS pieces is roughly 98% Fe, with trace C, Mn, S, and P, as described elsewhere [33]. Out of the 15 sample pieces, three 500CS pieces were immersed in three 100 mL beakers contain- ing 50 mL of SCPS without LEEA (controlled SCPS). Similarly, twelve 500CS pieces were dipped in twelve beakers containing 50 mL SCPS with 500- 4000 ppm LEEA for 2802 hours to estimate the corrosion rate (CoR). For this, the weight of each 500CS specimen after being exposed to it for t times (indicated as Wt) was recorded after 7, 14, 28, 43, 60, 90, and 117-day immersion in each SCPS variant. The corrosion rate (CoR) for each sam- ple in the SCPS with LEEA concentrations rang- ing from 500 to 4000 ppm and in the SCPS with- out LEEA (control SCPS) was calculated using the formula provided in equation (1), as described else- where [34]. Additionally, the estimated surface cov- erage () and corrosion inhibition efficiency [CoIE) were calculated using equations (2) and (3), respec- tively, as given in Ref. [35]. CoR(mm/y) = ∆W (g) × 87600 A (cm2)× ρ (gcm−2)×t (hrs.) (1) θ = CR(control) − CR(LEEA) CR(control) (2) % CoIE =CR(control) - CR(LEEA) CR(control) ×100 (3) Where, W = Wo-Wt Furthermore, electrochemical analysis was performed through potentiodynamic polarization (PoP) experiments using an Iquant 64 potentiostat (Model No.: IFC 101-32240) with a three-electrode system, as outlined in the literature [36]. The slopes of the anodic and cathodic polarization curves, de- rived from formulas (4) and (5), were used to calcu- late the corrosion potential (Ecor), corrosion current density (icor), the corrosion rate (CoR) based on icor or weight loss, and the corrosion inhibition effec- tiveness (CoIE) based on icor and weight loss [37]. Consequently, icor-based CoR was determined us- ing Tafel plots of both the anodic and cathodic curves [38]. CR(icor) = 0.13 × icor × E ρ (4) %InE(icor) = icor(control)-icor(LEEA) icor(control) ×100 (5) Where, = 7.86 g/cm³, is density and E = 55.85, equivalent weight of 500CS pieces. The inhibitory activity of the phyto-compounds (PCs) from LEEA is demonstrated using Langmuir adsorption isotherm [39, 40]. The linear fit plot of this isotherm allows us to estimate Gads, using equation (6), as illustrated in literature [41]. CLEEA = 1 Kads + CLEEA (6) In this case, Kads = adsorption equilibrium con- stant, which helps determine the free energy change of adsorption (Gads) value, as described in previous literature [42]. The phytochemical tests [32, 43] of LEEA were conducted to decide the presence (+) or absence () of various phytochemicals in LEEA. The FTIR spectra were recorded in the wavenumber range of 400-4000 cm¹ using the ATR mode (IR Affinity- 1S, Shimadzu Corp., Japan) to confirm the pres- ence of functional groups in LEEA in addition to the phytochemical tests. PCs with their elec- tronic properties identified using UV-Vis spec- tra recorded by a UV-Visible spectrophotome- ter (SPECORD®200 PLUS, Germany) across the wavelength range of 200 to 800 nm. Furthermore, a high-performance quadrupole time-of-flight mass spectrometer (XEVO G2-XS QTOF, IIT Ropar, Punjab, India) was employed to identify the distinct PCs in LEEA through liquid chromatography-mass spectrometry (LC-MS, Waters Corp., USA). The study examined the morphological and compositional modifications of the 500CS samples behind 2802 hours in control-SCPS and SCPS with 500 to 4000 ppm LEEA, using a scanning elec- tron microscope (SEM-Thermo Fisher Scios Field Emission, USA, 10 kV), equipped with energy- dispersive X-ray spectroscopy (EDAX Octane Elect EDS/EDX detector, USA, 30 kV). It captured the surface images of the 500CS pieces submerged in control SCPS and SCPS with 500-4000 ppm LEEA using white light interferometry (WLI) with a NewView-9000 from Zygo Corp. 3 Results and Discussion The phytochemical tests confirmed that phenols, flavonoids, alkaloids, terpenes, saponins, glycosides, and carbohydrates are present in the LEEA as the main PCs, as summarized in Table 1, constituted heteroatoms and unsaturated electrons and/or aro- matic compounds [28]. These findings align with existing literature [30]. The PCs from LEEA con- tribute to forming a diffusion-barrier passive layer on the surface of immersed 500CS pieces through the adsorption phenomenon, which aids in control- ling corrosion and is consistent with previous stud- ies [44]. The UV-Vis analysis revealed distinct peaks as- sociated with various functional groups of LEEA- PCs, thereby confirming the electronic transitions present in the extract, as illustrated in Fig. 2(a). The UV-Vis spectra of LEEA show absorption peaks at 472 nm, 503 nm, 535 nm, 606 nm, and 664 nm, suggesting the existence of aromatic or con- jugated unsaturated systems [45]. Previous study reported that the UV-Vis peaks at 472 nm and 535 nm indicated the presence of terpenoids [46]. The peaks at 606 nm and 664 nm are identified as chloro- phyll [47]. Consequently, PBEs exhibit a strong anti-corrosive effect due to their richness in sec- ondary metabolites (SMs). However, UV-Vis anal- Madhab Gautam et al./ BIBECHANA 22 (2025) 223-236 227 ysis presents challenges in identifying specific con- stituents corresponding to these absorption peaks [48]. Therefore, it is essential to complement UV- Vis findings with other analytical techniques [49], such as FTIR, GC/MS, or UHPLC/MS, to charac- terize the plant extracts, as discussed in the next sections. Table 1: Tests for phyto-compounds (PCs) in LEEA PCs Result PCs Result Alkaloid ++ Saponin + Phenol +++ Tanine − Flavonoid ++ Terpenoid ++ Glycoside + Carbohydrate − Note: Signs +, ++, +++ indicate abundance, while the sign − indicates absence. Figure 2: (a) UV-Vis and (b) FT-IR spectrum of LEEA. The results of functional groups, as shown in Fig. 2(b), are confirmed in the PCs of LEEA by FTIR analysis. The presence of nitrogen (N), sul- fur (S), and oxygen (O) heteroatoms and functional groups like phenols, carboxylic acids, and amines, distinguished by their abundance and degree of unsaturation was verified by FTIR spectra's val- ues [50]. Phenolic, alcoholic or amines compounds are indicated by a peak at 3345 cm¹, which cor- respond to the O-H or N-H stretching vibrations found in aromatic compounds [51]. An FTIR peak at 2922 reflects the asymmetric stretching of C-H vibrations. Other notable peaks include those asso- ciated with carbonyl C=O groups at 1708 cm¹ and C=O or C=C stretching at 1605 cm¹ [52], as well as C=C-C aromatic stretching at 1456 cm¹ [53]. These findings signify the presence of various func- tional groups, including alcohols, amines, ketones, acids, and unsaturated compounds. Furthermore, peaks ranging from 1260 to 1380 cm¹ confirm that all plant extracts contain aro- matic rings [54, 55]. A significant peak at 1200 cm¹ indicates C-N stretching vibrations, suggest- ing the presence of secondary or tertiary amines in the LEEA [56]. Moreover, a peak at 1020 cm¹ corresponds to O-H or C-H bending vibrations in aromatic compounds [57]. These findings are con- sistent with prior studies [58]. Therefore, the re- sults of the FTIR analyses support the potential application of the LEEA as an effective anticorro- sive admixture in concrete formulations to mitigate the corrosion of reinforcement. The FTIR analysis confirms the presence of di- verse functional groups in the examined LEEA, en- hancing our understanding of its chemical compo- sition. These groups are responsible for inhibit- ing the corrosion of reinforcement metals in con- crete infrastructures. Using mass bank matching, the LC-MS analysis of the LEEA reported eight PCs mainly, including phenols, terpenoids, alka- loids, and flavonoid functional groups. These an- ticipated PCs, which assumed to be present in the extract are listed in Table 2 and shown in Fig. 3, are verified from phytochemical testing, UV-Vis, FTIR, and LC-MS analyses. Table 2: Major compounds present in LEEA analyzed from LC-MS analysis S.N. Retention Time (min) Molecular For- mula & Weight (g/mol) Name of Compounds Types of Com- pounds 1 1.853 C18H17NO3 (295.1) DP-Oxazole Acid Alkaloids 2 4.238 C12H18ClNO2S (275.1) Dimethenamid Alkaloid 3 4.864 C21H22O10 (432.4) Apigenin-7-O-glucoside Flavonoids 4 5.219 C21H20O11 (448.1) Kaempferol-3-O-glucoside Flavonoid 5 5.659 C30H52O (428.7) Epifriedelanol Terpenoids 6 6.149 C20H21NO4 (339.1) Canadine or Papaverine Alkaloid 7 8.000 C15H12O3 (240.1) 4’-Hydroxyflavone Flavonoid 8 9.498 C15H11O6 + (287.2) Cyanidin Flavonoid Madhab Gautam et al./ BIBECHANA 22 (2025) 223-236 228 Figure 3: Structural formula of PCs assumed to be present in LEEA identified with LC-MS technique. These studies demonstrated that LEEA has a potent anti-corrosive impact on concrete reinforce- ment corrosion. It allows the chemicals in LEEA to attach to the CS specimens dipped in SCPS, either physically through weak interactions like Van der Waal interactions and/or chemically through ionic or co-covalent bonding [59]. The corrosion rate (CoR) of immersed CS in both control SCPS and SCPS with LEEA con- centrations was estimated using the weight loss method, and the results are plotted in Fig. 4(a). The CoR of the CS in SCPS with 1000 ppm LEEA is lower than that in the control SCPS with 500 and 2000-4000 ppm LEEA, indicating that LEEA effectively inhibits the corrosion of CS in SCPS with 1000 ppm LEEA. As shown in Fig. 4(a), the CoR of sample specimens immersed in SCPS con- taining 500, 2000, and 4000 ppm of LEEA ranged from 0.0013 to 0.0069 mm/y. In contrast, the CoR in SCPS with 400 ppm LEEA was approxi- mately 0.0017 mm/y. The 1000 ppm LEEA addi- tion to the SCPS displayed the highest corrosion resistance. Consequently, the corrosion-inhibiting efficiency was about 95% in the SCPS with 1000 ppm LEEA, as illustrated in Fig. 4(b). It demon- strates the enhanced corrosion inhibition effect of 1000 ppm LEEA in SCPS. Figure 4: Variations of CoR (a) and CoIE (b) of CS immersed in SCPS without (control) and with 500-4000 ppm LEEA. These findings indicate the formation of a sta- ble and anti-corrosive passive film at the 1000 ppm LEEA concentration, in contrast to the other con- centrations of 500, 2000, and 4000 ppm LEEA. Also, it might be a result of the formation of a per- sistent adsorption layer. Over time, more phyto- compounds (PCs)-based inhibitor molecules may have been adsorbed onto the CS surface, which could cause the extract to desorb somewhat from the CS surface [60]. The dissolution of PCs ad- sorbed from LEEA inhibitors in the SCPS by the generation of a chelate between the iron atoms of CS pieces and the heteroatoms of phytoconstituents present in LEEA inhibitor may be the cause of the decrease negligibly in inhibition for 2802 hours im- mersion [61]. The corrosion inhibition of CS specimens en- riched with increasing amounts of LEEA. The in- stability of the CS specimen in the control SCPS, which does not contain LEEA, may be attributed to the break of early-formed layers of CS across the metal-layer interface. This detachment can in- crease the corrosion rate over extended immersion times [62]. The lower CoR of CS in SCPS con- taining LEEA concentrations ranging from 1000 to 4000 ppm is due to beneficial phytochemicals such as polyphenols, alkaloids, and flavonoids in LEEA. These compounds facilitate the formation of a thin passive coating film on the surface of 500CS through the adsorption of complex polyphenols or hetero- aromatic chemicals [63]. According to qualitative examinations, the LEEA retains a variety of flavonoids, alkaloids, phe- nols, and terpenoids. The PCs function as key parts of the phyto-molecular interactions with the cor- roded surfaces of CS specimens in the SCPS, elu- cidated by the adsorption isotherm model, such as the Langmuir isotherm. The molecular interaction between the corroded CS and PCs of LEEA is due to heteroatoms and highly conjugated aromatic - electrons in the PCs [64]. Overall, the use of LEEA as a promising inhibitor for CS in SCPS at different immersion times, as demonstrated by the stabiliza- tion of the highly concentrated extract to the SCPS. Langmuir adsorption isotherm, illustrated in Fig. 5 is utilized to investigate the adsorption of LEEA’s PCs onto the CS piece in SCPS across var- ious immersion periods. It assessed the corrosion inhibition mechanism of LEEA on rusty CS speci- mens in SCPS with changing LEEA concentrations. It is meaningful to mention herein that for the lin- ear Langmuir isotherm plot, the estimated CoR was based on the gravimetric weight loss (GrWtL) method. Figure 5 shows a linear relationship with a very high coefficient of determination (R²) that tends to unity. However, the slope is not equal to one (i.e., 1.284-1.431), indicating a fit not only to the Langmuir monolayer adsorption isotherm. In corrosion inhibition studies, the standard adsorp- Madhab Gautam et al./ BIBECHANA 22 (2025) 223-236 229 tion Gibbs energy is frequently estimated through linear regression of the Langmuir isotherm, as out- lined in equation (6). Figure 5: Langmuir isotherm plots for CS spec- imens in SCPS with different concentrations of LEEA at different immersion times. In this adsorption isotherm model, the slopes of the corresponding straight lines must adhere to the requirements of the Langmuir isotherm, which stipulates a slope of unity. This theoretical frame- work enables relatively precise estimations of the standard adsorption Gibbs energy based on exper- imentally determined surface coverage. However, a deviation in the slope from unity to values ranging from 1.284 to 1.431, as illustrated in Fig. 5, suggests non-Langmuir adsorption phenomena, which may indicate the presence of multi-site adsorption or sur- face heterogeneity [65]. Additionally, the thermo- dynamic analysis, based on G°ads values, suggests that the adsorption in this condition is spontaneous and involves electrostatic interactions, characteris- tic of physisorption [66]. The negative values of G°ads further support the favorable spontaneous na- ture of the adsorption process of PCs on the im- mersed CS surface. We have tested other adsorp- tion isotherm models like Temkin, El-Awady, and Freudlich adsorption models [67]. They did not fit with R² values comparatively much lower than that of the Langmuir isotherm plots. Consequently, the Langmuir adsorption isotherm demonstrates the best fit compared with the Temkin isotherm. These outcomes align with conclusions from earlier research notifying identical adsorption behaviors of PCs on corroded steel specimens in acidic environ- ments [66]. Based on the experimental results from weight loss tests, as discussed above, the corrosion inhibi- tion efficiency and mechanism of LEEA adsorption onto corroded carbon steel (CS) have already been investigated. Besides, the corrosion inhibition ki- netics of LEEA on the CS surface in SCPS, both with and without LEEA, can be examined using potentiodynamic polarization (PoP) analysis. The corrosion potential (Ecor) values shifted to more negative (cathodic) directions without significant changes in anodic current density as a function of LEEA concentrations, as depicted in Fig. 6. In ad- dition, the cathodic current density (icath) and cor- rosion current density (icor) decreased with LEEA concentrations in SCPS, indicating the suppression of cathodic reactions on CS in the given conditions, even though there is no consistent shifting of Ecor. These electrochemical properties are rendered by a protective passive film formation on the surface of the corroded CS in the SCPS with 500-4000 ppm LEEA. Figure 6: Plots obtained PoP for CS immersed in SCPS with (a) 500 ppm, (b) 1000 ppm, (c) 2000 ppm, and (d) 4000 ppm LEEA including control SCPS. The corrosion rate and inhibition efficiency were determined using the corrosion potential (Ecor), corrosion current (icor), and Tafel slopes of the an- ode (anod) and cathode (cath) from potentiodynamic polarization (POP) curves through the Tafel ex- trapolation method, as shown in Fig. 6 and also summarizes in Table 3. Increases in aond and cath, driven by LEEA in SCPS, indicate improved polar- ization resistance (Rp) predominantly by cathodic reduction reactions. A higher cath suggests hin- dered reduction processes, while an increased anod points to slower CS dissolution and potential passi- vation [68]. Madhab Gautam et al./ BIBECHANA 22 (2025) 223-236 230 Table 3: Corrosion current (icor) and inhibition efficiency (icor-based/GrWtL-based CorIE) calculations for CS immersed in SCPS without and with 500–4000 ppm LEEA, obtained from GrWL and PoP approaches LEEA (ppm) Ecor (mV) icor (A/cm2) βanod (mV/dec) βcath (mV/dec) Rpol (kΩ·cm2) icor-based CorIE (%) GrWtL-based CorIE (%) Blank -428.4 7.301 2.54 6.33 0.04 – – 500 -596.1 3.808 9.58 14.67 2.06 47.8 59.9 1000 -545.2 2.576 7.86 17.83 3.22 64.7 94.1 2000 -512.1 1.946 11.09 18.89 7.43 73.4 81.1 4000 -507.4 1.569 12.29 17.39 9.31 78.5 77.3 Ultimately, this trend reflects the formation of a passive layer, enhanced Rp, and decreased corrosion rates [69]. In literature, the CoIEs of 4000 ppm leaf extracts of Tagetes erecta [37] Zizi- phus budhensis [33], and Sisamum indica [46] were 73.78%, 81.48%, and 81.7% (icor-based), and 67.81%, 91.22%, and 93.9% (GrWL-based), respec- tively. In contrast, a 4000 ppm LEEA exhibited in- hibition efficiencies of 81.7% (icor-based) and 93.9% (GrWL-based), indicating the LEEA has shown al- most the same corrosion-inhibiting efficiency for re- inforced concrete as other plant extracts reported in the literature. We investigated the morphological changes of CS sample surfaces after a 2802-hour immersion in SCPS with 4000 ppm of LEEA, compared to SCPS under control conditions. The CS specimen im- mersed in control SCPS exhibited a severely cor- roded surface with several corrosion-related flaws, as shown in Fig. 7(a). The significant corrosion observed was due to the prolonged exposure to the control SCPS, which facilitated the interaction of hostile ions with the CS surface through existing surface flaws [70]. In contrast, the SEM micro- graphs of the pieces immersed for the same dura- tion in SCPS containing 4000 ppm of LEEA, shown in Fig. 7(b), displayed LEEA's remarkable anti- corrosive effectiveness. The samples have smooth surfaces with minimal corrosion-related flaws and few corrosion products. The protective adsorption layers, created by LEEA, act as a barrier against hostile ions, reducing their ability to penetrate the surface [71]. Figure 7: SEM micrograph for the adsorption layer formed over CS pieces after immersion for 2802 hours in (a) control SCPS and (b) SCPS with 4000 ppm LEEA. The EDS examination demonstrated a notable decrease in Fe from 98.37% to 61.69% in the CS sample at control-SCPS after 2802 hours, alongside an increase in O-content to 33.13%, indicating sig- nificant corrosion product formation. Conversely, samples with 4000 ppm LEEA for 2802 hours at SCPS displayed reduced corrosion, with 72.63% Fe and 22.38% O, as shown in Table 4. These re- sults align with Verma and Khan [72], demonstrat- ing minimal rust formation and corrosion-resistant properties on the CS surface. Thus, LEEA effec- tively inhibits iron dissolution in SCPS, acting as a corrosion-preventive agent. Table 4: EDX elemental analysis of immersed CS pieces in control SCPS and SCPS with 4000 ppm LEEA after 2802 hours immersion Specimens Fe (wt.%) O (wt.%) Ca (wt.%) Si (wt.%) Misc. (wt.%) Fresh CS specimen 98.37 – 0.17 0.40 1.08 CS immersed for 2802 hrs in control SCPS 61.69 33.13 3.34 1.84 – CS immersed for 2802 hrs in SCPS with 4000 ppm LEEA 72.63 22.38 3.12 1.87 – The white light interferometry (WLI) technique, known for its high sensitivity in corrosion studies, was employed to assess surface roughness and mor- phology. This method provides rapid and accurate three-dimensional (3D) and 2D topographic analy- sis of corroded metal surfaces, offering precise lat- eral and vertical resolution without physical con- tact [73]. Figures 8(a) and 8(b) display the 2D and 3D profiles of the CS specimens after 2802 hours of immersion in 2000 ppm LEEA at SCPS. The surface roughness (SR) measured 7.059 m, lower than the 8.510 m recorded for specimens immersed in SCPS without the plant extract [33]. It repre- sents a 17.05% reduction in surface roughness when LEEA is present, indicating its effectiveness in min- imizing corrosion [74]. These results are consistent with SEM analysis, further confirming the superior performance of LEEA as a corrosion inhibitor for immersed CS samples. Madhab Gautam et al./ BIBECHANA 22 (2025) 223-236 231 Figure 8: 2D and 3D WLI images of the CS spec- imen after immersion for 2802 hrs in SCPS with 2000 ppm LEEA. The results show LLEA has strong corrosion- inhibiting properties in SCPS environments typical of reinforced concrete, supported by SEM/EDS and WLI assessments. A graphical representation (Fig. 9) to elucidate the corrosion-inhibiting mechanism attributed to the adsorption of plant-derived PCs from LLEA on CS in SCPS, both in the absence of the inhibitor (control) and with concentrations of LLEA ranging from 500 to 4000 ppm under am- bient conditions. This illustration aims to clarify the distinguished inhibiting effect of LLEA within SCPS or concrete environments, as demonstrated in Fig. 9, by following the steps below. Figure 9: A diagrammatic representation shows the adsorption mechanism of 4'-hydroxyflavone onto 500CS in SCPS with 2000 ppm LEEA at ambient conditions. i. The electrostatic interaction occurs between protonated PCs of LEEA and the positively charged Fe2+ ions from CS, facilitating phys- ical adsorption [75]. ii. Coordination bonding between lone pairs (non-bonding electrons) on hetero-atoms like O or N in PCs and the unoccupied d-orbitals of Fe-atoms in the immersed CS specimens may result in chemical adsorption [41]. iii. The aromatic ring and the empty d-orbitals of the Fe-atoms in the RCS interact with -electrons to facilitate chemical adsorption [44]. iv. The d-electrons of Fe-atoms of corroded CS specimens and the vacant anti-bonding molec- ular orbitals of the PCs components of LEEA undergo chemical adsorption, resulting in donor-acceptor interactions or retro-donation [36]. The analysis of multiple adsorption sites indi- cates that the phytochemicals (PCs) obtained from the LEEA are suitable for forming a passive adsorp- tion layer on the surface of CS specimens, serving effectively as corrosion inhibitors. This study ex- plores the plant-based inhibitors for the first time in concrete admixtures to prevent the corrosion of CS in SCPS, highlighting their environmentally friendly properties. 4 Conclusions This study demonstrates that first-time use of LEEA effectively prevents the corrosion of CS spec- imens in simulated concrete pore solution (SCPS). Results from gravimetric weight loss (GrWL), potentiodynamic polarization (PoP), and surface analysis like SEM/EDS and WLI confirm the for- mation of a protective surface layer that slows down the corrosion rate of 500CS in SCPS containing 500- 4000 ppm LEEA as a concrete admixture. The optimal inhibition efficiencies achieved were 93.9% (measured by GrWL) and 78.5% (measured by PoP) at 4000 ppm LEEA in SCPS at room tem- perature. The PoP measurements indicate that the cathodic reaction primarily governs the effective- ness of LEEA as a significant corrosion inhibitor. The Langmuir adsorption isotherm suggests that the LEEA-based PCs create a homogeneous, single- layer protective coating on the surface of the cor- roded CS through physical adsorption. This study established that the initial applica- tion of LEEA significantly mitigates the CS speci- mens when exposed to SCPS. The findings obtained from GWL, PoP, and surface analysis techniques- SEM/EDS and WLI confirm the formation of a protective surface layer. This layer effectively re- duces the corrosion rate of 500-grade carbon steel (500CS) within LEEA concentrations ranging from 500 nd 4000 ppm at SCPS, as a concrete admix- ture. The maximum inhibition efficiencies recorded were 93.9% (as determined by GWL) and 78.5% (as determined by PoP) at a concentration of 4000 ppm LEEA in SCPS at ambient temperature. Ad- ditionally, the PoP measurements suggest that the cathodic reaction predominantly influences the effi- cacy of LEEA as a corrosion inhibitor for concrete environments. Furthermore, the Langmuir adsorption isotherm indicates that LEEA-based protective coatings form a uniform, single-layer protective film on the Madhab Gautam et al./ BIBECHANA 22 (2025) 223-236 232 surface of corroded carbon steel through physical adsorption. Compared to the 500CS sample im- mersed in controlled SCPS without LEEA, surface analysis using SEM/EDS and WLI revealed that the surface of the CS remained smooth after im- mersion for about four months or more in LEEA at SCPS. The extract (500-4000 ppm LEEA) is de- rived from the leaves of Elaeocarpus angustifolius, which are typically discarded and thus readily avail- able at minimal or no cost. It not only ensures cost-effectiveness but also promotes environmental sustainability. The non-toxic and eco-friendly na- ture of the extract enhances its suitability for large- scale applications in real-world infrastructure with- out posing any risks. Acknowledgments The authors acknowledge Mr. Madhusudan Dhakal (IMR-CAS in Shenyang, China) for arranging WLI and Dr. M.A. Fickenscher (University of Cincin- nati, USA) for providing SEM/EDS facilities. The authors also thank Mr. R.D. Pandey for his as- sistance in identifying plant species and prepar- ing LEEA. MG acknowledges the University Grant Commission (UGC-Nepal) for awarding his Ph.D. research grants (Award No.: PhD-78/79-S&T-03). Author contributions MG, NPB & JB planned the experimentations; specimen preparation, practical works, and data ex- amination by MG, DBS, YRP, and KTKM; ana- lyzed the data and results overview by MG, NPB, and JB; documented the manuscript draft by MG and NPB, and did the conclusive edits by MG and JB. All authors read and consented to the final manuscript. Conflict of interest The authors assert that they hold no conflicts of interest Data availability statement Upon appeal, the corresponding author(s) will sup- ply data to reinforce their conclusions. References [1] S.S. Ubayi, A. Ahmad, E. Ahmad, B.S. Abubakar, S. Dulawat, M. Nuhu, U.S. Ibrahim, and A. Ibrahim. A review on the im- pact of jute fiber reinforcement on mechanical properties of concrete. International Journal of Engineering Science, 1:13–34, 2024. [2] S. Yousuf, P. Shafigh, and Z. Ibrahim. 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