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Journal of Cleaner Production 67 (2014) 139e146

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Journal of Cleaner Production

journal homepage: www.elsevier .com/locate/ jc lepro

Green Bambusa Arundinacea leaves extract as a sustainable corrosioninhibitor in steel reinforced concrete

Salawu Abdulrahman Asipita a, Mohammad Ismail a,*, Muhd Zaimi Abd Majid a,Zaiton Abdul Majid a, CheSobry Abdullah b, Jahangir Mirza c

aUTM Construction Research Centre, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 UTM, Johor Bahru, Johor, MalaysiabCollege of Business Technology Management Building, Universiti Utara Malaysia, 06010 UUM Sintok, Kedah DarulAman, MalaysiacResearch Institute of Hydro-Quebec, 1840 Lionel Boiled, Varennes, Quebec, Canada J3X 1S1

a r t i c l e i n f o

Article history:Received 24 January 2013Received in revised form8 December 2013Accepted 12 December 2013Available online 21 December 2013

Keywords:Green corrosion inhibitorSustainabilityMorphologyCorrosionSteel reinforcement

* Corresponding author. Tel.: þ60 75531757; fax: þE-mail addresses: mohammad@utm.my, mohamma

0959-6526/$ e see front matter � 2013 Elsevier Ltd.http://dx.doi.org/10.1016/j.jclepro.2013.12.033

a b s t r a c t

The experimental studies carried out on water permeability resistance and microstructure of reinforcedconcrete treated with Bambusa arundinacea as green corrosion inhibitor, are reported in this article. Theeffectiveness of Bambusa arundinacea as green corrosion inhibitor was compared with that of calciumnitrite and ethanolamine inhibitors. Concrete mix was designed for a compressive strength of 30 MPawith a 0.45 water-to-cement ratio (W/C) which was chloride contaminated. Inhibitors addition was 2% byweight of cement. The specimens were subjected to various tests, namely; compressive strength test,durability (permeability using initial surface absorption test (ISAT) and field emission scanning electronmicroscopy (FESEM)) for 360 days exposure. Water absorption values of steel reinforced concrete in thepresence of Bambusa arundinacea inhibitor were generally less than 0.25, 0.17, 0.1 and 0.07 mL/m2 s after10 min, 30 min, 1 h and 2 h, i.e., as required by ISAT standard for low permeability concrete. This mightpossibly be due to the presence of residual alkalinity of potassium hydroxide (KOH) in the concrete. KOHis adequate for passivation and reduction of permeability, which serves as a chemical water barrier orhydrophobic agent that stabilizes calcium silicate hydrates.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

There is a growing demand for biodegradable and less toxiccorrosion inhibitors to combat corrosion of steel reinforcement inconcrete especially in a saline environment (Abdulrahman andIsmail, 2012). Most of the conventional inhibitors that weredeveloped to combat this endemic problem are highly toxic tohuman beings and has the potential to degrade the environment.For instance, they can cause temporary or permanent damage tohuman organs, such as kidney or liver (Raja and Sethuraman, 2008).Inhibitors’ toxicity, according to Abdulrahman and Ismail (2012), ismeasured as LD50 and LC50. The former is a chemical which isconsidered lethal for 50% of animals in 24 h exposure time. Thelatter also has lethal properties in air or water and is known to kill50% of test population. Inhibitor biodegradation, or biological ox-ygen demand (BOD), should, at least, be 60%. The BOD is a measureof inhibitor persistence duration in the environment.

60 75566157.dutm@gmail.com (M. Ismail).

All rights reserved.

Recent studies on green inhibitors have shown that they aremore effective and highly environmentally benign compared toorganic and inorganic inhibitors used in chemical and petro-chemical industries. Among the numerous organic compounds thathave been tested and applied industrially as corrosion inhibitors,the non-toxic ones are now far more strategic (Boonsong et al.,2012; Abdulrahman et al., 2011a).

The known hazardous effects of most synthetic organic in-hibitors and restrictive environmental regulations have compelledand motivated researchers to focus on the need to develop cheap,non-toxic and environmentally benign natural products as corro-sion inhibitors. These natural organic compounds are either syn-thesized or extracted from aromatic herbs, spices and medicinalplants. Plant extracts are viewed as an incredibly rich source ofnaturally synthesized chemical compounds, which can be extractedby simple, inexpensive procedure. Moreover, they are also biode-gradable in nature. The use of these natural products such asextracted compounds from leaves or seeds as corrosion inhibitorshas beenwidely reported by number of authors (Ismail et al., 2011;Abdulrahman et al., 2011b; Ten et al., 2012; Chen et al., 2013;Behpour and Mohammadi, 2012; Negm et al., 2012).

0102030405060708090

100

Com

pres

sive

Str

engt

h (M

Pa)

Variables

7 Days

28 Days

90 Days

180 Days

360 Days

Fig. 1. Compressive strength results.

S.A. Asipita et al. / Journal of Cleaner Production 67 (2014) 139e146140

It is, therefore, imperative to deploy corrosion inhibitor inconcrete structure exposed to harsh environments which is eco-friendly. Consequently, exploitation of Bambusa arundinaceagreen inhibitor, an innovative product with new research direction,is necessary in order to ascertain the compatibility and suitability tosteel reinforced concrete. It is a step in the right direction tominimize the risk posed by organic and inorganic inhibitors toenvironment and sustainability.

2. Experimental

2.1. Materials

Ordinary Portland Cement (OPC) was used in this research. Thechloride was added into the concrete as magnesium chloride(MgCl2) of analytical grade reagent. The MgCl2 concentration usedwas 1.5% by mass of cement, while the corresponding chlorideconcentration was 0.94%. Coarse aggregates (quartzite origin) ofsizes 20 mm and 10 mm were used in the ratio of 1.78:1 to satisfythe overall aggregate grading requirements, in accordance withASTM C192 and Pradhan and Bhattacharjee (2009).

Land quarried sand satisfying BS 882:1992 was used as fineaggregate. The sand has a fineness modulus of 2.5. Tap water wasused for the preparation of specimens. All the concrete mixes weredesigned for similar workability with slump of 30e60 mm. Thewater content was kept constant at 230 kg/m3 for the desiredslump in all the mixes to have similar workability. The fresh density

Fig. 2. FESEM/EDX of as-rec

of concrete was then obtained as per guidelines specified by Britishmethod of mix selection (DOE) to be 2380 kg/m3.

2.2. Hardened concrete tests

Concrete cubes of size 100�100� 100mmwere prepared usingcement, sand and coarse aggregates in ratio of 1:1.2:2, at W/C of0.45. Inhibitor admixtures, namely calcium nitrite, ethanolamineand green B. arundinacea in the amount of 2% by mass of cementwere added. The concrete cubes were demoulded after 24 h ofcasting and subjected to water curing for 7, 28, 90, 180 and 360 d.They were then tested for compressive strength using MS EN12390-8:2012, ASTM C109 and method used by Mefteh et al.(2013). The water absorption test by ISAT was used to determinethe concrete permeability using BS 188-208: 1996 and MS EN12390-3:2012 procedures.

2.3. Metals analyzer by inductively coupled plasma-massspectrometry (ICPMS)

All reagents used were of analytical grade purity, and highquality water was obtained using a Milli-Q system (Millipore,Bedford, MA, USA). Approximately 2 g of Bambusa arundinaceawasaccurately weighed and transferred to a Teflon container contain-ing 5 mL of 65% nitric acid (HNO3) (Merck, Darmstadt, Germany)and 1 mL of 30% hydrogen peroxide (H2O2) (Merck, Darmstadt,Germany) were then added. After initial digestion process, deion-ized water was added to adjust the final volume to 25 mL. Allspecimens were diluted and filtered before analysis, using 0.45 mmfilters (Hydropinilic PVDF Millipore Millex-HV). Standard metalsolutions were prepared daily from 1000 mg/L stock (Merck,Darmstadt, Germany) in 2% HNO3 Suprapur grade (Merck). To avoidspecimens contamination, all PTFE materials (Teflon vessels, pi-pettes, micropipette tips, and auto sampler cups) were firstimmersed in freshly prepared 15% v/v pro analysis HNO3 (Merck)for 24 h. The PTFE materials were then rinsed thoroughly withdoubled distilled deionized water and finally dried in a dust freearea before analyzing.

2.4. Preparation of plant extracts

Fresh leaves of Bambusa arundinacea (Indian Bamboo) werewashed under runningwater, shade-dried and ground into powder.The extractionwas carried out using Soxhlet extraction process. 3 gof pulverized specimens were placed in a porous container and

eived steel specimens.

Fig. 3. FESEM/EDX of control steel specimen.

S.A. Asipita et al. / Journal of Cleaner Production 67 (2014) 139e146 141

continuously extracted using condensed solvent (ethanol). Theextracts from Soxhlet apparatus were rotary-evaporated to expelthe ethanol.

2.5. Surface analysis

Field Emission Scanning Electron Microscopy (FESEM) was usedfor the micro-structural analysis of the embedded steel/paste andpaste/aggregate interfaces of concrete. The analysis was performedusing GEMINI FESEM, which utilizes extremely low magnetic fieldoutside the objective lens enabling investigation of magnetic ma-terials and devices with an accelerating voltage of 30 kV. Theanalyzer was fitted with Energy Dispersive X-ray detector (EDX) forelemental analysis. The fractured concrete specimens used forsurface morphology examination were platinum coated to clearaway superfluous electrons, whereas steel specimens were scanneddirectly as-removed from concrete. Three points (two from outeredges and one at the centre) were collected for chemical elementalcomposition and the average values of each point are reported inthe following section.

3. Results and discussions

3.1. Concrete strength

Compressive strength values of specimens that have been curedfor 360 days are given in Fig. 1 for 1.5% MgCl2 additions. Thespecimens’ compressive strength increased with time regardless of

Fig. 4. FESEM/EDX of contaminated

type of corrosion inhibitors added. However, addition of 2% ofCa(NO2)2 inhibitor to the concrete mix increased the early strength(28 days) followed by a decrease in long term strength. These re-sults are in agreement with earlier studies reported by Ann et al.(2006) and De Schutter and Luo (2004). Ca(NO2)2 inhibitor addi-tion to concrete influences the hydration process of cement paste.

Addition of inhibitors accelerates and stabilizes the formation ofcrystal phase of Ca(OH)2. This leads to increase in the diameter ofmicro pores in the hardened cement paste and thus increases theconcrete permeability. Conversely, Bambusa arundinacea inhibitorincreased the strength of chloride contaminated specimen by 30%.When compared with Ca(NO2)2 and C2H7NO inhibitors, theBambusa arundinacea inhibitor showed superior strength. Mean-while, additions of MgCl2 salt have no detrimental effects on theconcrete’s compressive strength at the early age of hydration; infact it increases the strength. This might be the result of calciumchloro-aluminate formation due to chloride that was chemicallybonded by reactions with C3A compound of the Portland cement asreported by Poursaee et al. (2010).

Chloride ions might have reacted with hydrated tricalciumaluminate (C3A) hydrate to form chloro-aluminate(C3A.CaCl2.10H2O) which may contain 75e90% chloride accordingto Indrajit et al. (2011) study. Since it has exceeded the chloridethreshold level, the protective passive layer would be destroyed asin the case of chloride contaminated specimens. In general, thechloride threshold is taken to be 0.15% of the soluble chloride byweight of cement. So, 0.94% chloride has far exceeded thecommonly accepted corrosion threshold in this work.

steel specimen (1.5% MgCl2).

Fig. 5. FESEM/EDX of 2% Ca(NO2)2 additions to steel reinforcement incorporating 1.5% MgCl2 in concrete.

S.A. Asipita et al. / Journal of Cleaner Production 67 (2014) 139e146142

3.2. Micro-structural investigation

Field emission scanning electron microscopy (FESEM) was usedto study the steel/paste and paste/aggregate interfaces of concrete.The concrete was contaminated with MgCl2 salt and exposed toseawater on wet and dry cycles by dotted point approach for 12months. FESEM enables small-area contamination spots to beexamined at electron accelerated voltage compatible with energydispersive X-ray spectroscopy. It produces clearer and less electro-statically distorted images with spatial resolution that are 3e6times better than the conventional SEM. Additionally, the

Fig. 7. FESEM/EDX of 2% Bambusa arundinacea additions to s

Fig. 6. FESEM/EDX of 2% C2H7NO additions to steel rei

elemental compositions resulting from the admixture chloride ionswere monitored by Energy Dispersive X-ray (EDX). The FESEM/EDXmicrographs are presented in Figs. 2e11. The elemental composi-tional analysis is also summarized in Tables 1 and 2.

3.2.1. Chloride-induced micro structural changes in reinforcedconcrete

The formation of corrosion products in the embedded reinforcedsteel/concrete interface specimens are shown in Figs. 2e7. Asreceived specimen structure (Fig. 2) shows normal iron carbidestructure of ferrite in pearlite matrix unaffected by corrosion, while

teel reinforcement incorporating 1.5% MgCl2 in concrete.

nforcement incorporating 1.5% MgCl2 in concrete.

Fig. 9. FESEM/EDX of 2% Ca(NO2)2 additions to concrete incorporating 1.5% MgCl2.

Fig. 8. FESEM/EDX of contaminated concrete specimen incorporating 1.5% MgCl2.

S.A. Asipita et al. / Journal of Cleaner Production 67 (2014) 139e146 143

control specimen without chloride contamination shows crackinitiations (Fig. 3). Figs. 4 and 5 contain interconnected cracksthrough the voids with large volumes, as a result of large quantitiesof dissolved oxygenwhich reacted with iron to form expansive ironoxides and oxychloride complexes.

Koleva et al. (2011) reported that dissolved oxygen is a majorfactor contributing to the natural corrosion of steel reinforcementin concrete. The oxygen levels for 1.5% MgCl2 contaminated spec-imen as well as C2H7NO2 and Ca(NO2)2 inhibited specimens arehigh as confirmed by EDX, compared to the control specimens(Table 2). As a result, the formed cracks tend to connect with other

Fig. 10. FESEM/EDX of 2% C2H7NO additions

existing cracks thereby forming a percolating network, which inturn promotes further ingress of chloride ions into the concretepaste. Similarly, Fig. 6 contains a denser corrosion product scalewith pronounced cracks as a result of high chloride observed in theEDX.

The chloride reacts with iron oxides to form a complex ironoxychloride, 3Fe(OH)2. FeCl2, which is lamellar in nature, and inconformitywith a similar observationsmade by Koleva et al. (2011).The lamellar crystal is responsible for volumetric expansion thatdecomposes to produce akaganeite [Fe3þ(O,OH,Cl)], goethite(a-FeOOH) and lepidocrocite (g-FeOOH); which eventually cause

to concrete incorporating 1.5% MgCl2.

Fig. 11. FESEM/EDX of 2% Bambusa arundinacea additions to concrete incorporating 1.5% MgCl2.

S.A. Asipita et al. / Journal of Cleaner Production 67 (2014) 139e146144

depassivation of film layer, similar to the one observed by Kolevaet al. (2008). Conversely these initially formed goethite and lep-idocrocite are transformed into more stable high-valent oxides(mainly hematite (Fe2O3) and magnetite (Fe3O4)). These two high-valent oxides thus formed a product layer adherent to the steelsurface as a result of hydrophobic effect of Bambusa arundinacea.This is due to its pore blocking effects which prevented the for-mation of differential aeration of cells. These cells promote corro-sion on the steel surface as a result of oxygen level and chloride ionsin the mix (evident in Table 1) and are also shown in the photo-micrographs presented in Fig. 7. Additionally, the lower value ofdouble layer capacitance Cdl of Bambusa arundinacea could also beassociated with its adsorption mode. This confirmed its adsorbedmolecules paralleled tometal surface, and decreased the number ofsurface active sites, as previously observed by Abdulrahman andIsmail (2012).

3.2.2. Chloride-induced micro structural changes in hydrationproducts of bulk concrete

A FESEM observation in Fig. 8 indicates that chloride might havereacted with aluminous phases and calcium hydroxide Ca(OH)2crystals in the cement paste forming platy crystal. The micrographsshown in Fig. 8 have revealed that the C-S-H intermixedwith crystalsof MgCl2 showing ettringite as the white background suggest a

Table 2Summary of Energy Dispersive X-ray spectroscopy (EDX) results for concrete paste speci

Specimens Element average weight (%)

C O Al Si Cl

Control 6.40 53.68 0.49 34.33 e

1.5% MgCl2 contaminated 11.06 55.67 1.00 3.79 e

2% Ca(NO2)2 8.74 54.46 2.68 10.85 0.322% C2H7NO 5.81 53.61 0.32 35.95 e

2% Bambusa 6.25 51.44 2.16 31.93 e

Table 1Summary of Energy Dispersive X-ray spectroscopy (EDX) results for embedded metal/co

Specimens Element average weight (%)

C O Al Si

As-received 3.49 32.56 4.89 e

Control 6.21 35.89 0.85 1.831.5% MgCl2 contaminated 7.16 45.06 3.83 2.762% Ca(NO2)2 7.20 46.47 3.29 8.032% C2H7NO 3.70 26.28 e e

2% Bambusa 6.01 34.24 0.39 0.96

possible formation of Friedel’s salt (3CaO$Al2O3$CaCl2$10H2O) underchloride ingress. Koleva et al. (2007) have reported that when NaClcomes in contact with free tricalcium aluminate (C3A), it will lead toFriedel’s salt formation. In this case, the reaction that precedes theformation of Friedel’s salt is:

MgCl2(aq) þ 3CaO$Al2O3$6H2O(s) þ Ca(OH)2(s) þ 4H2O /

3CaO$Al2O3$CaCl2$10H2O(s) þ Mg(OH)2(aq).

Therefore, to compensate for the above phenomenon, anequivalent amount of alkali ions would be required for the poresolution, i.e., be absorbed into solid phases. The main ions in thepore solution of a cement paste system are: OH-, Kþ, Naþ and Ca2þ.Hence, to improve the effects of ettringite and Friedel’s salt for-mations at the interfacial transition zones (ITZ) between cementpaste and aggregates, the introduction of inhibitors are supposed toboost the cations at these zones. Figs. 9 and 10 show the effect of 2%addition of calcium nitrite and ethanolamine inhibitors to thecontaminated concrete paste. The micrograph further revealed thepresence of ettringite at the ITZ (seen as the bright white back-ground). Only Fig. 11 shows the boosting effect of Bambusa arun-dinacea. This is a result of noticeable amount of Kþ ions present asconfirmed by EDX and ICPMS with a compacted pore structures(Table 3).

men at W/C ¼ 0.45.

Ca/Si ratio

Ca Mg Na K Fe S

4.46 0.34 0.30 e e e 0.1324.61 2.66 0.39 0.48 e 0.33 6.4924.69 0.52 1.22 0.51 e e 2.284.00 0.08 0.10 0.14 e e 0.115.75 0.22 0.86 1.39 e e 0.18

ncrete interface specimens at W/C ¼ 0.45.

Cl Ca Mg Na K Fe S

e e e e e 59.05 e

e 6.37 e e e 48.85 e

1.31 21.72 e e e 17.24 0.930.97 26.48 0.58 e e 6.99 e

25.45 e e e e 44.57 e

e 7.26 e e e 51.15 e

Table 3Inductively Coupled Plasma Mass Spectrometry (ICPMS) analysis result of Bambusa arundinacea green inhibitor.

Element Pb Hg Cu Zn As Fe Mg Ni Cd Cr Co Na P Se Al Ag Ba K Ca

Result(ppm)

1.933 0.001 0.434 41.634 8.265 7.543 38.916 0.695 0.013 4.273 0.004 45.986 12.063 0.031 11.796 0.052 0.321 629.212 132.875

S.A. Asipita et al. / Journal of Cleaner Production 67 (2014) 139e146 145

The variations in chemical compositions and morphology ofC-S-H in the concrete paste could also be attributed to the effects ofCa/Si ratios. The typical Ca/Si ratio of C-S-H in hydrated Portlandcements is about 1.8. The surface charge on C-S-H depends on itsCa/Si ratio; its surface charge is positive at higher Ca/Si ratio, andbecomes negative at Ca/Si ratio lower than 1.2 or 1.3. From Table 2and Figs. 8 and 9, it could be seen that the Ca/Si ratios are above thenormal acceptable limits for contaminated specimen as well ascalcium nitrite inhibited specimen. On the other hand, the Ca/Siratio for specimens containing Bambusa arundinacea is 0.18 (muchlesser than the lower limits of 1.2) due to the alkali metal incor-porated in the C-S-H as evidenced from EDX analysis (Fig. 11).

In concrete, pseudo capacitance arises due to the adsorption ofOH-, Kþ, Naþ and Ca2þ ions on the reinforcement surfaces.Vedalakshmi et al. (2009) suggested that if double layer capaci-tance is absent, then there will be no frequency dependence.However, corrosion current density (Icorr), which representsinstantaneous rate of corrosion at the particular time of voltagemeasurement is dependent on frequencies most widely reported asan indication of the corrosion performance of steel in concreteaccording to Raafat et al. (2011).

3.3. Water permeability

The permeability of concrete plays a critical and significant rolein controlling the properties of concrete as well as the serviceabilityof reinforced concrete. It is usual practice to simultaneously assessthe water permeability and durability characteristics. Water ab-sorption in concrete is influenced heavily by the paste phase. It isprimarily dependent on the extent of interconnected capillaryporosity in the paste.

The absorption characteristics, which indirectly reflect thepermeability, are shown in Fig. 12. It can be observed that the ab-sorption rate of concrete modified by adding Bambusa arundinaceagreen inhibitor is the lowest as compared to others. This can beattributed to the reduced chloride ion diffusivity which reducesinternal transition zone (ITZ) percolation. It also enhances thecement hydration which is due to internal curing effects from theinhibitors, thereby leading to reduced capillary pores. Althoughthere is general improvement in other inhibitors, such as Ca(NO2)2

Fig. 12. Water absorption characteristics of concrete, W/C ¼ 0.45.

and C2H7NO, they could not meet ISAT standard limits for lowpermeability. In case of Bambusa arundinacea green inhibitor ab-sorptions, it is generally less than 0.25, 0.17, 0.1 and 0.07 mL/m2 safter 10 min, 30 min, 1 h and 2 h, i.e., the set ISAT standard for lowpermeability.

This might be possible as a result of residual alkalinity of KOHpresent in the concrete. KOH is adequate both for passivation andreductionof permeability,which serveas a chemicalwater barrierorhydrophobic agent. This hydrophobic agent combines with Ca(OH)2in cement paste to form an insoluble hydrophobic salt which mightbe similar to the action of calcium stearate emulsion as previouslyreported by Gaidis (2004) as shown in the following equation.

2C4H9-fatty carboxylate þ Ca(OH)2 ¼ 2C4H9OH þ Ca(fattycarboxylate)2

This hydrophobic salt precipitates and covers the pore wall orblocks it entirely with a layer that resists further water penetration(geometric blocking effect).

4. Conclusions

The focus of this research work was generally aimed at devel-oping a sustainable, environmentally benign and eco-friendlycorrosion inhibitor from plant extracts (Bambusa arundinacea),and comparing its effectiveness with the conventional inhibitors(calcium nitrite and ethanolamine) for steel reinforcement inconcrete. Bambusa arundinacea may be considered a better sub-stitute for nitrite and amine-based corrosion inhibiting admixturesfor durable concrete structures due to its hydrophobic effects,viability, versatility and eco-friendliness. Also it exhibited goodadsorption characteristic as it stabilizes calcium silicate hydrates(C-S-H) gel that prevent calcium hydroxide conversion to calciteand carbo-aluminate phases. The following main conclusions canbe drawn from this study:

� The pore blocking effects of Bambusa arundinacea prevented theformation of differential aeration of cells that promote corrosionon the steel surface as a result of oxygen level.

� Addition of 2% calcium nitrite and ethanolamine inhibitors tothe chloride contaminated concrete paste could not reduce theeffects of ettringite and Friedel’s salt formations at the InterfacialTransition Zones (ITZ) between cement paste and aggregates.

� Only Bambusa arundinacea inhibitor could buffer the porestructures as a result of noticeable amount of potassium (Kþ)ions present (confirmed by EDX and ICPMS results).

Acknowledgments

The authors are thankful for the financial assistance given byConstruction Research Alliance, Research Management Centre,Universiti Teknologi Malaysia (UTM), Johor Bahru, Johor, Malaysiaand Federal University of Technology Minna, Nigeria.

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