Effects of Chlorides on Corrosion of Simulated Reinforced...

Research ArticleEffects of Chlorides on Corrosion of Simulated ReinforcedBlended Cement Mortars

JacksonMuthengiaWachira

Department of Physical Sciences University of Embu Embu Kenya

Correspondence should be addressed to Jackson Muthengia Wachira wachirajacksonembuniacke

Received 8 December 2018 Revised 2 March 2019 Accepted 17 March 2019 Published 27 March 2019

Academic Editor Ramana M Pidaparti

Copyright copy 2019 JacksonMuthengiaWachiraThis is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

Cementitious materials are subject to degradation when subjected to corrosive chloride mediaThis paper reports the experimentalresults on corrosion studies conducted on a potential cementitious material PCDC made from a blend of 55 Ordinary PortlandCement (OPC) Dried Calcium Carbide Residue (DCCR) and an incineration mix of Rice Husks (RH) Spent Beaching Earth(SBE) and Ground Reject Bricks (BB) The experiments were run along 100 OPC Different wc were used Corrosion currentdensities using linear polarisation resistance (LPR) and corrosion potentials measurements versus saturated calomel electrode wereused for the determination of corrosion rates and potentials respectively for simulated reinforcement at different depths of coverin the cement mortars The results showed that PCDC exhibited higher corrosion current densities over all depths of covers andearly attainment of active corrosion than the control cements In conclusion PCDC and OPC can be used in a similar corrosivemedia during construction

1 Introduction

Reinforcing metal in concrete is usually protected by a layerof the iron oxideiron hydroxide and the high concrete pH[1ndash3] The protective layer is a film of the gamma ferric oxides(120574-Fe2O3) iron oxide hydroxide [FeO(OH)] and magnetite(Fe3O4) which prevent Fe2+ from entering into the solutionas well as oxygen from diffusing to the steel surface[4] Thelayer has also been found to be rich in lime with inclusionsof C-S-H gel [5 6] The high electric resistivity of concrete isalso another aspect that helps in corrosion resistance of therebar This acts by reducing the flow of current between thecathodic and anodic sites of the rebar

When reinforced concrete comes into contact with chlo-rides at levels beyond certain critical conditions pittingcorrosion ensues These levels are generally defined in termsof ClminusOHminus threshold of the mortar or concrete This hasgenerally been agreed to be about 06 although some authorshave observed different values [1 7] In an aerated chloridesolution at the critical ClminusOHminus threshold the chloridescause dissolution of the protective layer of the oxides of ironand thus dissolution of the metal in the pit [1 6 8] This

creates charge difference as a result of excess positive metalions forcingClminus ions to rapidlymigrate into the pit giving riseto metal chlorideThe reactions involved are given in (1)ndash(3)They represent that the anodic reaction because corrosion isan electrochemical reaction [9]

Fe (OH)2 + 2Clminus 997888rarr FeCl2 + 2OH

minus (1)

Fe (OH)3 + 3Clminus 997888rarr FeCl3 + 3OH

minus (2)

Fe2O3 + 6Clminus + 3H2O 997888rarr 2FeCl3 + 6OH

minus (3)

The resultant metal chloride undergoes hydrolysis as shownin (4) consequently causing a build-up of the hydrogen andchloride ions that stimulate dissolution of the metal [10]

FeCln + nH2O 997888rarr Fe (OH)n + nHCl (4)

where n = 2 or 3 depending on the oxidation state of FeSince there is limited dissolution of oxygen in the pit

solution the cathodic reduction of dissolved oxygen on themetal surface adjacent to the pit sustains the pit growth Thecathodic site the metal surface is very large compared to the

HindawiInternational Journal of CorrosionVolume 2019 Article ID 2123547 7 pageshttpsdoiorg10115520192123547

2 International Journal of Corrosion

pit size and this makes the pit grow at a fast and an everincreasing rate [11]

The cathodic reactions involved depend on the pH andpotential of the rebar Hydrogen evolution and oxygenreduction are mainly involved [9] Hydrogen evolution doesnot take place unless in condition of cathodic protection orcircumstances with low pH and at conditions where the rebarhas potentials more active than E120579H+H

2

(SHE) Ordinarycorrosion of rebar under chloride initiation involves oxygenreduction as shown by the following [12]

O2 + 4H2O + 4eminus 997888rarr 4OHminus (5)

The mechanical performance of a potential cementitiousmaterial PCDC made from a blend of 55 OrdinaryPortland Cement (OPC) Dried Calcium Carbide Residue(DCCR) and an incineration mix of Rice Husks (RH) SpentBeaching Earth (SBE) and Ground Reject Bricks (BB) hasbeen reported in previous studies However the durabilityof PCDC in corrosive media has not been conducted Thepresent study therefore investigated the corrosion rates andpotentials of PCDC vis-a-vis commercial OPC in simulatedreinforcement at different depths of cover using the testcement mortars

2 Materials and Methods

21 Materials 10 mm by 80 mm mild steel rods whosechemical composition is given in Table 1 (as analysed by theBureau Veritas Consumer Products Services UK LTD) werecut and smoothened on the edges with a smooth fileThe rodswere polished with emery papers 80-600 grit in successionThe resulting metal rods were washed with distilled waterrinsed with acetone and blow dried They were stored in adesiccator that used silica as desiccant

Table 2 shows the various compositions of materials usedin this study

22 Methods

221 Preparation of Simulated ReinforcedMortars 31 sand tobinder (100OPCor PCDC) ratiowas used in preparation ofthe mortar In the initial stages it was presumed that mortarwith 04 05 and 06 wc ratio would be prepared It washowever noted that the amount of water added to correspondwith the above wc ratios could not make consistent pastesThis was because the sand was oven dried Laboratory testsrevealed the oven dried sand would require an amount ofwater corresponding to 0077 percent by weight of sand tocorrelate with non-oven dried sand A 08 wc ratio mortarproved to be the best workable mix with the three cementcategories A lower wc ratio of 073 was also used but thepaste was observed to have a poor workability A higher wcratio of 085 was also prepared A corrected wc ratio aftertaking into account the oven dried sand was found to be 05057 and 062 for 073 08 and 085 respectively To avoidconfusion the later wc ratios have been used in this paper

Six 30 mm by 100 mm by 100 mm high density PVC weremachine cut Six 10 mm hole were drilled through the PVC

blocks From one edge of the blocks two holes were drilled at20 and two more at 15 mm from the other edge A hole wasdrilled through on the remaining edges at 10 mm from theedge Holes with dimensions and distances from the edgessimilar to the PVC block were made on a 05 mm by 100mmby 100 mm polythene sheet The PVC block was lightly spot-oiled with an oil-dump tissue paper The polythene sheet wasplaced on the PVC block and the holes on either matchedThe PVC block plus the polythene sheet were placed at thebottom of a cube mould The polished mild steel rods werecarefully and gently pushed into the PVC block holes Twosuch cube moulds were placed on a vibrating bench Mortarwas carefully shovelled into the cubes and compaction donefor about 30 seconds The mortar was levelled using a troweland vibration continued for about 10 seconds Final levellingwas done The resultant mortar was cured for 24 hours (incase of 073 and 08 wc ratio) and 48 hours (in case of 085wc ratio) after which they were demoulded

On the second day after preparation of individual mortarcubes 6 mm nichrome wires with 5 mm heat shrunktubings were spot welded at about 8 mm from the top sideof the protruding rebar After the sixth day of preparingall the cubes steel reinforcement protector 841 obtainedfrom Flexcrete Technologies Limited (UK) was applied tothe mortars with embedded steel rods This was done byfirst gritting the exposed surface of the rods with emerypaper grade 80 and then deoiling the protruding rebar endswith acetone soaked cloth Steel reinforcement protector wasprepared by mixing 3 1 by volume of cementitious powderto polymer dispersion provided and thoroughly mixing itwith the help of a provided wooden stick to a brushablepaste The resultant paste was thinly applied to about 1 mmwith a 25 mm pure bristles brush on the exposed ends ofthe rebars The steel reinforcement protector 841 paste wassimilarly applied on to the mortar cube to the face with theexposed rebar surface The first coat was allowed to cure forabout 45 minutes before application of a similar second coaton top of the first one After an additional 45 minutes anyvoids were brushed with the steel reinforcement protector841 paste The mortar cubes were allowed to cure overnightThe mortar cubes were cured for an additional 21 days insaturated calcium hydroxide solution After the 28th dayof curing 2-metre insulated copper cables were connectedto the nichrome wire spot welded to the embedded steelrods with the help of joint clips The open ends of the clipswere sealed with silicon based sealant Dow Corning 732The insulated copper cables were labelled with a seven codeidentity as shown in Table 3 All cubes were subjected toone-week alternate wet-dry tank for a period of six monthsThe wet alternate week involved complete immersion of themortar cubes in 35 percent sodium chloride solution

222 Corrosion Current Densities and Potential Measure-ments Corrosion potentials Ecorr were measured usingsaturated calomel electrode (SCE) as reference electrode witha high impedance voltmeter Linear polarisation resistance(LPR) was done using a potentiostat using SCE and graphiterod as reference and counter electrode respectively The LPR

International Journal of Corrosion 3

Table 1 Chemical composition of mild steel

Element ww Method of AnalysisC 018 Combustion AnalysisSi 023 ICPOESMn 077 ICPOESP 0016 ICPOESS 0011 Combustion AnalysisCr 003 ICPOESMo lt002 ICPOESNi 004 ICPOESAl 0032 ICPOESCo lt0005 ICPOESCu 009 ICPOESNb lt0005 ICPOESPb lt002 ICPOESSn lt002 ICPOESTi 0005 ICPOESV lt002 ICPOESW lt002 ICPOESFe BalanceICPOES Inductively Coupled Plasma Optical Emission Spectroscopy

Table 2 Compositions of various materials

Material DescriptionOPC Commercial Ordinary Portland Cement (425 Nmm)PPC Commercial Portland Pozzolana Cement or Blended Cement (325 Nmm)Test Ash A blend of DALS and a calcined mix of RH SBE ground BBPCDC A blend of 55 OPC and 45 Test Ash

Table 3 Description of the insulated copper cables

Material Composition Watercement ratio (wc) Depth of rebar (mm)OP12GL OPC 073 20OP12BL OPC 073 15OP12YL OPC 073 10OP29GL OPC 085 20OP29BL OPC 085 15OP29YL OPC 085 10OP31GL OPC 083 20OP31BL OPC 083 15OP31YL OPC 083 10PC12GL PCDC 073 20PC12BL PCDC 073 15PC12YL PCDC 073 10PC29GL PCDC 085 20PC29BL PCDC 085 15PC29YL PCDC 085 10PC31GL PCDC 083 20PC31BL PCDC 083 15PC31YL PCDC 083 10


0 30 60 90 120 150 180

Monitoring Period (Days)

PC29GLPC29BL

PC29YLLimit Line

minus720minus630minus540minus450minus360minus270minus180minus90

0

Corr

osio

n Po

tent

ial (

mV

SCE

)

Figure 1 Corrosion potential versus time for PCDC at wc of 085

0 30 60 90 120 150 180Monitoring Period (Days)

PC29GLPC29BL

PC29YLLimit Line

0001

001

01

1

10

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )

Figure 2 Log corrosion current densities versus time for PCDC atwc 085

and potential measurements were done for a total of 12 wet-dry cycles which coincided with 168 days Ecorr and LPRmeasurements were done during the wet seasons

In LPRmeasurements the potential wasmanually shiftedfrom Ecorr to plusmn 20 mV in intervals of about 5-8 mV this isbecause at this range no significant noise was expected inthe instrument Corrosion current readings were taken afterstabilisation which took about 45ndash60 seconds A graph ofoverpotentials 120578 versus corrosion current was plotted and itsgradient RP calculated Corrosion current density icorr wasdetermined as per

icorr =52

(SA lowast RP)(6)

where SA is the specific surface area of the rebar approxi-mated from (120587Dh + 120587r2) in which cases D h and r representdiameter height and radius of the rebar respectively Theheight h taken was for the length of the rebar embeddedin the mortar cube 52 mVdecade was taken as the Tafelconstant in all the cases

3 Results and Discussion

31 Corrosion Current Densities icorr and Corrosion Poten-tials Figures 1ndash12 represent the corrosion current densities119894119888119900119903119903 and corrosion potentials Ecorr of the respective sim-ulated reinforced cement mortar at the defined wc versuscuring period Working electrodes that had attained an icorr

0 30 60 90 120 150 180


OP29GLOP29BL

OP29YLLimit Line

minus630minus540minus450minus360minus270minus180minus90

0

Corr

osio

n Po

tent

ial (

mV

SCE

)

Figure 3 Corrosion potential versus time for OPC at wc of 085

00001

0001

001

01

1

0 30 60 90 120 150 180


OP29GLOP29BL

OP29YLLimit Line

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )

Figure 4 Log corrosion current densities versus time for OPC atwc 085

value of greater than or equal to 01 120583Acm2 were consideredto have attained active corrosion [13] Similarly rebars thathad attained Ecorr more active than -270 mV (Vs SCE) weretaken to have attained active corrosion The limit lines inFigures 1ndash12 represent the limits above or below these lines(icorr and Ecorr respectively)

The results showed that the depth of cover was an impor-tant parameter because the rebars at the shallow depth ofcover attained active corrosion earlier than their counterpartsat greater depths of cover This is because the chlorides havelower distance to diffuse and initiate pitting type of corrosionHence there is a lower resistivity due to the reduced concretecover at lower depths of cover

PCDCrsquos rebars exhibited earlier attainment of active cor-rosion compared toOPCsThe inclusion of lime in cements isknown to increase porosity [14 15] PCDC had a significantproportion of lime added in form of DALS This may haveserved to increase porosity of the cement mortar at theinitial stages of curing Upon attainment of active corrosionby the 085 (wc) cements PCDCrsquos rebar registered highericorr than corresponding OPCrsquos rebar Some workers haveattributed the higher corrosion rates by substituted cementsrsquorebars to the lowering of pore pH by the pozzolanic reaction[16] In previous related studies chloride binding abilityand its influence on the rate of corrosion on OPC and itsblended cements of GGBS PFA and SF showed that despitehigher chloride binding ability of blended cements andhigherchloride concentration in OPCrsquos pore solution the corrosion


0 30 60 90 120 150 180


PC31GLPC31BL

PC31YLLimit Line


0

Corr

osio

n Po

tent

ial (

mV

SCE

)


00001

0001

001

01

1

0 30 60 90 120 150 180


PC31GLPC31BL

PC31YLLimit Line

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )


0 30 60 90 120 150 180


OP31GLOP31BL

OP31YLLimit Line

minus420

minus360

minus300

minus240

minus180

minus120

minus60

0

Corr

osio

n Pot

entia

ls (m

VSC

E)


rates of the rebars in OPC were lower than the blendedcements [17] This can be attributed to the higher corrosionrates to a lower OHminus in the blended cements pore solutionThe decline in pore solution OHminus to both dilution factor(lower OPC content) and chemical activity of the pozzolanamaterials may have affected the PCDC cements and hence itsrebars exhibited higher corrosion rates compared to OPCs

At a lower water to cement ratio for example 08there was delay in rebar corrosion initiation time for bothcements compared to the wc of 085 This was due toreduced porosity and hence diffusivity of the chlorides and

0 30 60 90 120 150 180


OP31GLOP31BL

OP31YLLimit Line

0001

001

01

1

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )


0 30 60 90 120 150 180


PC12GLPC12BL

PC12YLLimit Line


0

Corr

osio

n Pot

entia

l (m

VSC

E)

Figure 9 Corrosion potential versus time for PCDC at wc 073

0001

001

01

1

10


PC12GLPC12BL

PC12YLLimit Line

Log

Corr

osio

n Cu

rren

tD

ensit

ies (

Ac

m2 )


0 30 60 90 120 150 180


OP12GLOP12BL

OP12YLLimit Line


0

Corr

osio

n Po

tentia

l (m

VSC

E)



0 30 60 90 120 150 180


OP12GLOP12BL

OP12YLLimit Line

000001

00001

0001

001

01

1

Log

Corr

osio

n Cu

rren

tD

ensit

ies (

Ac

m2 )

Figure 12 Log corrosion current densities versus time for OPC at wc 073

oxygen Lower wc is a well-known factor that reduces thepermeability of concrete and hence diffusivity of aggressiveagents [18]

It was observed that increase in wc ratio increased thepenetration of chloridesThis can be attributed to the fact thatthere is a decrease in porosity within the lime-cement basedmortar as the wc ratio reduced [19] When lime is addedto the PCDC as DALS the effect of reduced porosity due tolower wc ratio must have been experienced in the PCDCThis may have resulted in the increase in initiation time forthe rebars corrosion compared to the higher wc ratio

Increasing wc ratio is also known to increase the oxygendiffusivity into the mortar cubes [20 21] Oxygen diffusion isan important factor that plays a major role in the corrosionof the rebar This is because oxygen is the main cathodicreaction in rebar corrosion At higher oxygen diffusivity thecathodic reaction is high so is the anodic (rebar corrosion)and therefore the corrosion rateOxygen dissolved in the poresolution is important in as far as maintaining the passivity(iron oxides films on the rebar) This prevents the rebar fromcorrosion Sustenance of corrosion (pitting type in this case)is dependent on the sufficient supply of oxygen through thecathodic reaction on the passive film [21]

OPC rebars at 15 and 20 mm depth of cover and wc ratioof 073 did not attain active corrosion as indicated by thecorrosion current densities Observations from the corrosionpotentials (versus SCE) and visual examination of rebarsafter dismantling the cubes indicated that there was activecorrosion of the rebars at the depth of 10mm and a very slightcorrosion on rebars at 15 mm Probably the time interval ofdismantling of the mortar cube and last measurement of therebars may have attained appreciable corrosion for the rebarsat 15 mm depth of cover

Despite poor compaction in both mortars at the wc of073 PCDC exhibited delayed initiation of active corrosionat the 10 mm depth of cover compared to OPCThus delayedactive corrosion was expected for the rebars at the 15 and20 mm depth of cover but the opposite happened PCDCrsquosrebar attained active corrosion while OPCrsquos rebars did notThis could perhaps have resulted from voids around therebars due to poor compactionThis would thus have availeda high chloride ingress at the rebar that would have beensufficient enough to initiate corrosion and hence the observedbehaviour A more insight study on the porosity and hence

permeability would thus be required to provide informationon the same for such low wc ratio of PCDC

PCDCrsquos rebars were observed to have higher corrosionrates and earlier attainment of active corrosion compared toOPCs The reduction of the pore pH due to pozzolanic reac-tion even at low chloride concentration increases iron sol-ubility due to formation of stable chlorocomplex (of Fe2+3+)corrosion products (mainly green rust) These products areeasily oxidised and precipitated as 120573ndashFeOOH (Akagenite) bydiffused oxygen thereby releasing the Clminus This regeneratestheClminus that replenishes the cyclewhich in essence destabilisesthe passive layer Decrease in ClminusOHminus ratio is a contributingfactor to early corrosion initiation phenomenon in blendedcements [22] Perhaps this could be attributed to its high levelof substitution

4 Conclusion

It was generally noted that PCDCrsquos rebars experienced earlyactive corrosion and higher corrosion rates compared tocorresponding OPCrsquos rebars

Data Availability

The data used in this article will be provided upon request

Conflicts of Interest

The author declares no conflicts of interest in this paper

Acknowledgments

The author wish to acknowledge the assistance accordedto this work by Kenyatta University and The University ofManchesterThis work was financially supported by KenyattaUniversity

References

[1] C Alonso C Andrade M Castellote and P Castro ldquoChloridethreshold values to depassivate reinforcing bars embedded in astandardized OPC mortarrdquo Cement and Concrete Research vol30 no 7 pp 1047ndash1055 2000


[2] N Amin S Alam and S Gul ldquoEffect of thermally activated clayon corrosion and chloride resistivity of cement mortarrdquo Journalof Cleaner Production vol 111 pp 155ndash160 2016

[3] M BalonisThe Influence of Inorganic Chemical Accelerators andCorrosion Inhibitors on the Mineralogy of Hydrated PortlandCement Systems Aberdeen University 2010

[4] D M Bastidas A Fernandez-Jimenez A Palomo and JA Gonzalez ldquoA study on the passive state stability of steelembedded in activated fly ash mortarsrdquo Corrosion Science vol50 no 4 pp 1058ndash1065 2008

[5] P Chindaprasirt and S Rukzon ldquoStrength porosity and corro-sion resistance of ternary blend Portland cement rice husk ashand fly ashmortarrdquoConstruction and BuildingMaterials vol 22no 8 pp 1601ndash1606 2008

[6] S A Civjan J M LaFave J Trybulski D Lovett J Lima andD W Pfeifer ldquoEffectiveness of corrosion inhibiting admixturecombinations in structural concreterdquo Cement and ConcreteComposites vol 27 no 6 pp 688ndash703 2005

[7] M U Khan S Ahmad and H J Al-Gahtani ldquoChloride-induced corrosion of steel in concrete an overview on chloridediffusion and prediction of corrosion initiation timerdquo Interna-tional Journal of Corrosion vol 2017 Article ID 5819202 9 pages2017

[8] C Monticelli M Natali A Balbo et al ldquoCorrosion behaviorof steel in alkali-activated fly ash mortars in the light of theirmicrostructural mechanical and chemical characterizationrdquoCement and Concrete Research vol 80 pp 60ndash68 2016

[9] R R Hussain and T Ishida ldquoEnhanced electro-chemicalcorrosion model for reinforced concrete under severe coupledaction of chloride and temperaturerdquo Construction and BuildingMaterials vol 25 no 3 pp 1305ndash1315 2011

[10] K O Ampadu and K Torii ldquoChloride ingress and steel cor-rosion in cement mortars incorporating low-quality fly ashesrdquoCement and Concrete Research vol 32 no 6 pp 893ndash901 2002

[11] M Babaee and A Castel ldquoChloride-induced corrosion of rein-forcement in low-calcium fly ash-based geopolymer concreterdquoCement and Concrete Research vol 88 pp 96ndash107 2016

[12] B Pradhan and B Bhattacharjee ldquoPerformance evaluation ofrebar in chloride contaminated concrete by corrosion raterdquoConstruction and Building Materials vol 23 no 6 pp 2346ndash2356 2009

[13] S Erdogdu T Bremner and I Kondratova ldquoAccelerated testingof plain and epoxy-coated reinforcement in simulated seawaterand chloride solutionsrdquo Cement and Concrete Research vol 31no 6 pp 861ndash867 2001

[14] S Abo-El-Enein G El-kady T El-Sokkary and M GhariebldquoPhysico-mechanical properties of composite cement pastescontaining silica fume and fly ashrdquo HBRC Journal vol 11 no1 pp 7ndash15 2015

[15] M J Mwiti T J Karanja and W J Muthengia ldquoProperties ofactivated blended cement containing high content of calcinedclayrdquo Heliyon vol 4 no 8 Article ID e00742 2018

[16] C Arya N R Buenfeld and J B Newman ldquoFactors influencingchloride-binding in concreterdquo Cement and Concrete Researchvol 20 no 2 pp 291ndash300 1990

[17] C Arya and Y Xu ldquoEffect of cement type on chloride bindingand corrosion of steel in concreterdquo Cement and ConcreteResearch vol 25 no 4 pp 893ndash902 1995

[18] H Yigiter H Yazıcı and S Aydın ldquoEffects of cement typewatercement ratio and cement content on sea water resistanceof concreterdquo Building and Environment vol 42 no 4 pp 1770ndash1776 2007

[19] MMosquera B Silva B Prieto and E Ruiz-Herrera ldquoAdditionof cement to lime-based mortars Effect on pore structure andvapor transportrdquo Cement and Concrete Research vol 36 no 9pp 1635ndash1642 2006

[20] K Kobayashi and K Shuttoh ldquoOxygen diffusivity of variouscementitious materialsrdquo Cement and Concrete Research vol 21no 2-3 pp 273ndash284 1991

[21] R R Hussain and T Ishida ldquoInfluence of connectivity of con-crete pores and associated diffusion of oxygen on corrosion ofsteel under high humidityrdquoConstruction andBuildingMaterialsvol 24 no 6 pp 1014ndash1019 2010

[22] A M Oliveira and O Cascudo ldquoEffect of mineral addi-tions incorporated in concrete on thermodynamic and kineticparameters of chloride-induced reinforcement corrosionrdquoCon-struction and Building Materials vol 192 pp 467ndash477 2018

CorrosionInternational Journal of

Hindawiwwwhindawicom Volume 2018

Advances in

Materials Science and EngineeringHindawiwwwhindawicom Volume 2018


Journal of

Chemistry

Analytical ChemistryInternational Journal of


ScienticaHindawiwwwhindawicom Volume 2018

Polymer ScienceInternational Journal of



Advances in Condensed Matter Physics


International Journal of

BiomaterialsHindawiwwwhindawicom

Journal ofEngineeringVolume 2018

Applied ChemistryJournal of


NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of


High Energy PhysicsAdvances in

Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

TribologyAdvances in



ChemistryAdvances in


Advances inPhysical Chemistry


BioMed Research InternationalMaterials

Journal of


Na

nom

ate

ria

ls


Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom


pit size and this makes the pit grow at a fast and an everincreasing rate [11]

The cathodic reactions involved depend on the pH andpotential of the rebar Hydrogen evolution and oxygenreduction are mainly involved [9] Hydrogen evolution doesnot take place unless in condition of cathodic protection orcircumstances with low pH and at conditions where the rebarhas potentials more active than E120579H+H

2

(SHE) Ordinarycorrosion of rebar under chloride initiation involves oxygenreduction as shown by the following [12]

O2 + 4H2O + 4eminus 997888rarr 4OHminus (5)

The mechanical performance of a potential cementitiousmaterial PCDC made from a blend of 55 OrdinaryPortland Cement (OPC) Dried Calcium Carbide Residue(DCCR) and an incineration mix of Rice Husks (RH) SpentBeaching Earth (SBE) and Ground Reject Bricks (BB) hasbeen reported in previous studies However the durabilityof PCDC in corrosive media has not been conducted Thepresent study therefore investigated the corrosion rates andpotentials of PCDC vis-a-vis commercial OPC in simulatedreinforcement at different depths of cover using the testcement mortars

2 Materials and Methods

21 Materials 10 mm by 80 mm mild steel rods whosechemical composition is given in Table 1 (as analysed by theBureau Veritas Consumer Products Services UK LTD) werecut and smoothened on the edges with a smooth fileThe rodswere polished with emery papers 80-600 grit in successionThe resulting metal rods were washed with distilled waterrinsed with acetone and blow dried They were stored in adesiccator that used silica as desiccant

Table 2 shows the various compositions of materials usedin this study

22 Methods

221 Preparation of Simulated ReinforcedMortars 31 sand tobinder (100OPCor PCDC) ratiowas used in preparation ofthe mortar In the initial stages it was presumed that mortarwith 04 05 and 06 wc ratio would be prepared It washowever noted that the amount of water added to correspondwith the above wc ratios could not make consistent pastesThis was because the sand was oven dried Laboratory testsrevealed the oven dried sand would require an amount ofwater corresponding to 0077 percent by weight of sand tocorrelate with non-oven dried sand A 08 wc ratio mortarproved to be the best workable mix with the three cementcategories A lower wc ratio of 073 was also used but thepaste was observed to have a poor workability A higher wcratio of 085 was also prepared A corrected wc ratio aftertaking into account the oven dried sand was found to be 05057 and 062 for 073 08 and 085 respectively To avoidconfusion the later wc ratios have been used in this paper

Six 30 mm by 100 mm by 100 mm high density PVC weremachine cut Six 10 mm hole were drilled through the PVC

blocks From one edge of the blocks two holes were drilled at20 and two more at 15 mm from the other edge A hole wasdrilled through on the remaining edges at 10 mm from theedge Holes with dimensions and distances from the edgessimilar to the PVC block were made on a 05 mm by 100mmby 100 mm polythene sheet The PVC block was lightly spot-oiled with an oil-dump tissue paper The polythene sheet wasplaced on the PVC block and the holes on either matchedThe PVC block plus the polythene sheet were placed at thebottom of a cube mould The polished mild steel rods werecarefully and gently pushed into the PVC block holes Twosuch cube moulds were placed on a vibrating bench Mortarwas carefully shovelled into the cubes and compaction donefor about 30 seconds The mortar was levelled using a troweland vibration continued for about 10 seconds Final levellingwas done The resultant mortar was cured for 24 hours (incase of 073 and 08 wc ratio) and 48 hours (in case of 085wc ratio) after which they were demoulded

On the second day after preparation of individual mortarcubes 6 mm nichrome wires with 5 mm heat shrunktubings were spot welded at about 8 mm from the top sideof the protruding rebar After the sixth day of preparingall the cubes steel reinforcement protector 841 obtainedfrom Flexcrete Technologies Limited (UK) was applied tothe mortars with embedded steel rods This was done byfirst gritting the exposed surface of the rods with emerypaper grade 80 and then deoiling the protruding rebar endswith acetone soaked cloth Steel reinforcement protector wasprepared by mixing 3 1 by volume of cementitious powderto polymer dispersion provided and thoroughly mixing itwith the help of a provided wooden stick to a brushablepaste The resultant paste was thinly applied to about 1 mmwith a 25 mm pure bristles brush on the exposed ends ofthe rebars The steel reinforcement protector 841 paste wassimilarly applied on to the mortar cube to the face with theexposed rebar surface The first coat was allowed to cure forabout 45 minutes before application of a similar second coaton top of the first one After an additional 45 minutes anyvoids were brushed with the steel reinforcement protector841 paste The mortar cubes were allowed to cure overnightThe mortar cubes were cured for an additional 21 days insaturated calcium hydroxide solution After the 28th dayof curing 2-metre insulated copper cables were connectedto the nichrome wire spot welded to the embedded steelrods with the help of joint clips The open ends of the clipswere sealed with silicon based sealant Dow Corning 732The insulated copper cables were labelled with a seven codeidentity as shown in Table 3 All cubes were subjected toone-week alternate wet-dry tank for a period of six monthsThe wet alternate week involved complete immersion of themortar cubes in 35 percent sodium chloride solution

222 Corrosion Current Densities and Potential Measure-ments Corrosion potentials Ecorr were measured usingsaturated calomel electrode (SCE) as reference electrode witha high impedance voltmeter Linear polarisation resistance(LPR) was done using a potentiostat using SCE and graphiterod as reference and counter electrode respectively The LPR









0 30 60 90 120 150 180


PC29GLPC29BL

PC29YLLimit Line


0

Corr

osio

n Po

tent

ial (

mV

SCE

)



PC29GLPC29BL

PC29YLLimit Line

0001

001

01

1

10

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )




icorr =52

(SA lowast RP)(6)




0 30 60 90 120 150 180


OP29GLOP29BL

OP29YLLimit Line


0

Corr

osio

n Po

tent

ial (

mV

SCE

)


00001

0001

001

01

1

0 30 60 90 120 150 180


OP29GLOP29BL

OP29YLLimit Line

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )






0 30 60 90 120 150 180


PC31GLPC31BL

PC31YLLimit Line


0

Corr

osio

n Po

tent

ial (

mV

SCE

)


00001

0001

001

01

1

0 30 60 90 120 150 180


PC31GLPC31BL

PC31YLLimit Line

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )


0 30 60 90 120 150 180


OP31GLOP31BL

OP31YLLimit Line

minus420

minus360

minus300

minus240

minus180

minus120

minus60

0

Corr

osio

n Pot

entia

ls (m

VSC

E)




0 30 60 90 120 150 180


OP31GLOP31BL

OP31YLLimit Line

0001

001

01

1

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )


0 30 60 90 120 150 180


PC12GLPC12BL

PC12YLLimit Line


0

Corr

osio

n Pot

entia

l (m

VSC

E)


0001

001

01

1

10


PC12GLPC12BL

PC12YLLimit Line

Log

Corr

osio

n Cu

rren

tD

ensit

ies (

Ac

m2 )


0 30 60 90 120 150 180


OP12GLOP12BL

OP12YLLimit Line


0

Corr

osio

n Po

tentia

l (m

VSC

E)



0 30 60 90 120 150 180


OP12GLOP12BL

OP12YLLimit Line

000001

00001

0001

001

01

1

Log

Corr

osio

n Cu

rren

tD

ensit

ies (

Ac

m2 )









4 Conclusion


Data Availability




Acknowledgments


References


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls












0 30 60 90 120 150 180


PC29GLPC29BL

PC29YLLimit Line


0

Corr

osio

n Po

tent

ial (

mV

SCE

)



PC29GLPC29BL

PC29YLLimit Line

0001

001

01

1

10

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )




icorr =52

(SA lowast RP)(6)




0 30 60 90 120 150 180


OP29GLOP29BL

OP29YLLimit Line


0

Corr

osio

n Po

tent

ial (

mV

SCE

)


00001

0001

001

01

1

0 30 60 90 120 150 180


OP29GLOP29BL

OP29YLLimit Line

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )






0 30 60 90 120 150 180


PC31GLPC31BL

PC31YLLimit Line


0

Corr

osio

n Po

tent

ial (

mV

SCE

)


00001

0001

001

01

1

0 30 60 90 120 150 180


PC31GLPC31BL

PC31YLLimit Line

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )


0 30 60 90 120 150 180


OP31GLOP31BL

OP31YLLimit Line

minus420

minus360

minus300

minus240

minus180

minus120

minus60

0

Corr

osio

n Pot

entia

ls (m

VSC

E)




0 30 60 90 120 150 180


OP31GLOP31BL

OP31YLLimit Line

0001

001

01

1

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )


0 30 60 90 120 150 180


PC12GLPC12BL

PC12YLLimit Line


0

Corr

osio

n Pot

entia

l (m

VSC

E)


0001

001

01

1

10


PC12GLPC12BL

PC12YLLimit Line

Log

Corr

osio

n Cu

rren

tD

ensit

ies (

Ac

m2 )


0 30 60 90 120 150 180


OP12GLOP12BL

OP12YLLimit Line


0

Corr

osio

n Po

tentia

l (m

VSC

E)



0 30 60 90 120 150 180


OP12GLOP12BL

OP12YLLimit Line

000001

00001

0001

001

01

1

Log

Corr

osio

n Cu

rren

tD

ensit

ies (

Ac

m2 )









4 Conclusion


Data Availability




Acknowledgments


References


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls





0 30 60 90 120 150 180


PC31GLPC31BL

PC31YLLimit Line


0

Corr

osio

n Po

tent

ial (

mV

SCE

)


00001

0001

001

01

1

0 30 60 90 120 150 180


PC31GLPC31BL

PC31YLLimit Line

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )


0 30 60 90 120 150 180


OP31GLOP31BL

OP31YLLimit Line

minus420

minus360

minus300

minus240

minus180

minus120

minus60

0

Corr

osio

n Pot

entia

ls (m

VSC

E)




0 30 60 90 120 150 180


OP31GLOP31BL

OP31YLLimit Line

0001

001

01

1

Log

Cor

rosio

n cu

rren

t Den

sitie

s (

Ac

m2 )


0 30 60 90 120 150 180


PC12GLPC12BL

PC12YLLimit Line


0

Corr

osio

n Pot

entia

l (m

VSC

E)


0001

001

01

1

10


PC12GLPC12BL

PC12YLLimit Line

Log

Corr

osio

n Cu

rren

tD

ensit

ies (

Ac

m2 )


0 30 60 90 120 150 180


OP12GLOP12BL

OP12YLLimit Line


0

Corr

osio

n Po

tentia

l (m

VSC

E)



0 30 60 90 120 150 180


OP12GLOP12BL

OP12YLLimit Line

000001

00001

0001

001

01

1

Log

Corr

osio

n Cu

rren

tD

ensit

ies (

Ac

m2 )









4 Conclusion


Data Availability




Acknowledgments


References


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls





0 30 60 90 120 150 180


OP12GLOP12BL

OP12YLLimit Line

000001

00001

0001

001

01

1

Log

Corr

osio

n Cu

rren

tD

ensit

ies (

Ac

m2 )









4 Conclusion


Data Availability




Acknowledgments


References


























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




























Advances in



Journal of

Chemistry















Journal of





Volume 2018









Journal of


Na

nom

ate

ria

ls




Effects of Chlorides on Corrosion of Simulated Reinforced...

Documents

Transcript of Effects of Chlorides on Corrosion of Simulated Reinforced...