Key Words: Steel Wool, Polypropylene, Fibre, Impact, Flexural,Strength 1. INTRODUCTION
International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page1609 COMPARATIVE STUDY OF MECHANICAL PROPERTIES OF STEEL WOOL AND POLYPROPYLENE FIBRE REINFORCED CEMENT MORTAR COMPOSITES Shodolapo Oluyemi Franklin1, a , Khadija Salim Mronga2 1Senior Lecturer, Department of Construction Engineering, Gaborone University College, Mmopane, Botswana Formerly, Department of Civil Engineering, University of Botswana, Gaborone, Botswana 2 Formerly, Department of Civil Engineering, University of Botswana, Gaborone, Botswana aCorresponding Author *** Abstract – In the current study a comparative analysis of the mechanical strength of steel wool and polypropylene fibre reinforced cement mortar slabsispresented.Forthiswork two fibre contents of 0.75 % and 2 % of the cement mass were used. A total of 60 slabs including the control specimens, of dimensions 300 mm x 300 mm x 20 mm was cast and tested at 14 and 28 days after curing. Impact strength tests were conducted on 30 specimens, while the remaining slabs were subjected to flexural strength tests. In either case, 3slabswere utilized to obtain mean values per test parameter. It was found that the unreinforced slabs had very low impact resistance after the initial cracking. Furthermore, there was little difference between the impact load resistanceofthesteel wool fibre reinforced slabs and the control specimens. In contrast the polypropylene fibre reinforced slabs performed significantly better as regards impact load resistance and the distribution of crack patterns. With reference to flexural strength, both types of fibre reinforced specimens exhibited similar behaviour and response. However, as far as toughness corresponding to the recorded deflections at failure was concerned, it was concluded that the steel wool mortar composites were relatively tougher than their polypropylene counterparts.
Althoughsteelfibresfirstcameintobeinginmoderncivil engineering,syntheticfibresparticularlypolypropylenehave becomeincreasinglypopular.Infactbothtypesoffibresare nowverywidelyused(Naamanetal.[2]) Inrecentdecades there have been numerous studies conducted on fibre reinforcedconcretecomposites.Thesehavebeensuccinctly summarizedbyZollo[3],ACICommittee544[4]andBrandt [5], amongst others. More recent works are those due to Mobasher[6],Uddin[7],Singh[8],Naaman[9]andfinally theRILEM FIBpublications([10],[11])onfibrereinforced concrete. A survey of the literature reveals that arguably more studies have been carried out on fibre reinforced concrete composites, in comparison to fibre reinforced cement mortars. It is for this reason and to highlight the benefits of using synthetic fibres, more especially polypropylenefibres,thatthepresentinvestigationhasbeen conducted.The emphasisis ontheutilization of materials sourced locally or at least within the Southern African region.Astudyoftheimpactandflexuralstrengthsofsteel woolandpolypropylenefibrecementmortarcompositeshas beenattempted.
Cement mortars have been universally employed for a varietyofpurposeinbuildingandcivilengineering,ranging fromplastering,rendering,repairofdamagedconcrete,floor levellingandfillingorpatching Theseusesnotwithstanding, itiscommonlyacceptedthatcementmortarshaveseveral limitations including delayed hardening, quite low tensile strengths, high drying shrinkage as well as relatively low chemical resistance. It is for these reasons that in recent decadescementmortarcompositeshavecomeintofavour. Suchcompositescomprisecement,sand,waterandfibres. Withreferencetothelatter,bothnaturalandartificialfibres are employed to enhance flexural strength, impact resistance, ductility and toughness. According to Ramakrishna and Sundararajan [1], the fibres are also important in reducing the bleeding, shrinkage and permeabilityofthecementitiousmatrixinthefreshstate.
2.1 Materials, Mix Proportions and Casting
The steel wool fibres utilized were purchased locally. Theywereofveryfinegradeandhadelasticmodulusof200 GPaandlowcarboncontent.Diametersrangedfrom6.35μm to8.89μm,andtensilestrengthswereintherange200 300 MPa.Thepolypropylenefibreshaddiameter18micronsand fibrelengthsof12mm.Theypossessedhighacidicresistance and100%alkaliresistance.Thecementusedwasmasonry
2. EXPERIMENTAL PROGRAMME
In this section the basic characteristics of the major materials utilized, the manner in which the mix proportions were chosen as well as some details regarding casting of the composite specimens are arepresented.Inadditionthetestingproceduresadoptedoutlinedtosomedegree
AClass1mortarasspecifiedbySANS1090:2002[13]was used.Themixhadacement sandratioof1:1.6.Thewater cement ratio was deduced by trial mixes, theaim being to achieve a medium workability mix that would be kept constant for all the proposed tests on flexural and impact strengths. A water cement ratio of 0.47 was ultimately adopted, and this was maintained for the casting of all 60 slabs,eachbeingofdimensions300mmx300mmx20mm. All parameters were kept constant except for the varying fibre percentages. The cast specimens were vibrated by means of a vibrating table for a specified period and subsequentlycoveredinwethessianfor24hours.Theywere thereafterde mouldedandthenimmersedinatemperature regulatedwaterbathcontainingcleanpotablewater. Ofthe 60slabscast,30werecuredfor14dayswhiletheremaining wascuredfor28dayspriortotesting.Thecompositionofthe mortarmixusedfortheexperimentalprogrammeisshown inTable1. Table 1: Mortarcompositionforcastingthreeslabs content (%) Procedures
Fig. 1:Sampleofsteelwoolfibres
Theflexuralstrengthfortheslabswasdeterminedusinga one point loading system by means of a 150 kN capacity flexural testing machine. The specimens’ were placed in positionsupportedontwooppositeedges.Theloadfromthe flexuraltestingmachinewasappliedataslowrateandthe dialgaugereadingswererecordedsimultaneouslywiththe loadcausingdeflections.Theexperimentalset upforthetest isshowninFigure4.
cementMC12.5XrequiredtoproduceaClass1mortaras specified in Fulton’s Concrete Technology [12], with a minimum28daycompressivestrengthof12.5MPa.Thesand constituentinmortarisbyfarthemajorconstituentofsand cement mixes and has a significant influence on their performance.Consequently,naturalsandwasemployedas thiswasgenerallyroundedandidealforgoodworkability. Thesandmettherecommendedgradingformortarsandsas specified inFulton’sConcrete Technology[12]. Samplesof the steel wool fibre and the polypropylene are shown in Figures1and2respectively.
International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page1610
The cured samples were tested immediately after they hadbeenremovedfromthecuringtankandhanddriedwith paperrollordrycloth.Boththeimpactstrengthandflexural strength tests were carried out on the steel wool and polypropylene fibre reinforced specimens with fibre variationsof0%,0.75%and2%at14and28daysafter curing.Fortheimpacttests,asolidsteelmetalballweighing 440gwasdroppedfromaheightof330mmuntothetest specimens.Theballwasallowedtofirstrolldownagently inclined slope before it fell, in order to maintain the same force(orenergy)foreachdrop.Theinclinewassominimal thattheextradistancetheballrolledpriortofallingvertically wasdeemedinsignificant.Theballwasalsopositionedsuch thatitlandedexactlyatthecentreofeachtestslab;thelatter wassimplysupportedonallfouredges.Thenumberofblows it took to observe the first crack (which was ascertained visuallyandcheckedforaftereachdrop),andthenumberof blows it took for ultimate failure of a specimen were recorded.Ultimatefailurewasdefinedinthiscontextaswhen thecrackwentrightthroughthethicknessoftheslab.The testset upfortheimpacttestingisshowninFigure3.
(g)Sand (g)Cement (ml)Water (g)Fibre 0 7800 5025 2400 0 0.75 7800 5025 2400 38 2.0 7800 5025 2400 101 2.2 Testing
Fig. 3:Impactstrengthtestset up
Fibre
Fig. 2:Sampleofpolypropylenefibres
Ithadbeenobservedthat2outofevery3specimensof theunreinforcedcementmortarslabsdevelopedcracksprior to placement in the curing tanks. These were identified as shrinkagecracksbecausetheywerehairlineshaped,random, multiple, meandering in the concrete, and formed a discontinuouspattern.Notwithstanding,thevariationofthe numberofblowswithfibrefraction forfirstcrackingandfor ultimate failure at 14 and 28 days, for the steel wool and polypropylene fibres are shown in Figures 5 and 6.The resultsindicatedaretheaveragevaluesforthreeslabtests.
Fig. 5: Variationofnumberofblowswithfibrefraction Fig. 6: Variationofnumberofblowswithfibrecontent
The residual impact ratio for the unreinforced cement mortarslabsneverexceeded1.2forboththe14dayand28 day tests. In respect of the steel wool fibre specimens the rangewas1.3 2.3,whichatmostwasapproximatelytwice
International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page1611 Fig. 4:Flexuralstrengthtestset up 3. RESULTS AND DISCUSSION Inthissectiontheresultsoftheimpactandflexuralstrength tests are presented, together with the crack patterns observed during loading. In addition cogent observations anddeductionsaremade 3.1 Impact Strength Tests
For the steel wool fibre specimens, there was little deviationbetweentheirimpactloadresistancesandthoseof the unreinforced mortar slabs, although in the former, no shrinkagecrackswereobservedattheinitialstages.There wasnotmuchvariationbetweenthe14and28dayscuring testresults,althoughforthe2%fibrefraction,thenumberof blows required from first cracking doubled, in order to produceultimatefailure. Withregardstothe14or28daystest,theintroductionof polypropylene definitely enhanced the mortar quality because0.75%ofpolypropylenereinforcedmortarresisted atleast13dropsofthesteelball(or17.2Joules)beforeinitial cracking was observed. After this crack, at least 100 additionalblowscausedultimatefailure.Thiswasonaccount of the superior matrix the fibres created. They assisted in holdingthemortartogetherbydistributingtheshockloading evenly through the slab. This can be seen from the crack patternswhicharediscussedatalaterstageinthepresent section. However, an increase in the polypropylene fibre content to 2 % did not increase the amount of energy requiredtoinitiateacrack.Forboththe0.75%and2%fibre contents, the impact resistance after initial cracking was significantly high, since it took from 132 to 153 Joules to causeultimatefailureintheslabs.
Forthe100%mortarslabs(or0%fibrecontent),6blowsof the steel ball (equivalent to 7.92 Joules) caused initial cracking at 14 days. The longer curing period of 28 days resultedinverylittleextra resistanceto impactloadingas only a single extra blow (or 1.32 Joules) was required to initiatethefirstcracking.Forthe28daystest,8blowsintotal wereneededtoproduceultimatefailure.Thisimpliesthat unreinforced mortar slabs have relativelyverylowimpact resistanceaftertheinitialcrack.
3.2 Crack Patterns
Fig. 7:Failurepatternforunreinforcedslab
Fig. 10: Load deflectioncurves steelwoolslabsat28days
3.3 Flexural Strength Tests
Fig. 9:Cracksforpolypropylenefibreslab
TypicalcrackpatternsatfailureareshowninFigures7to 9.Fortheunreinforcedslabstheinitialcracksappearedat thebottomacrosstheslabspecimens.Applicationoffurther impactloadingcausedthecracktolengthenandwidenuntil it went right through the slab depth, resulting in ultimate failure. The steel wool reinforced slabs had crack patterns thatresultedin3to4brokenpieces.Thecracksformedwere more like those of their polypropylene counterparts, but werenotasmany. Forthepolypropylenereinforcedslabs,thecrackpatterns werequitedifferentfromthoseoftheunreinforcedslabs.The initialcrackatthebottomoftheslabswasextremelysmall and hair line, requiring close visual inspection to spot. Multiple cracks would form around the struck region and widenslightly,meanderingtowardstheslabedges,asfurther impactloadingtook place.Thefailedslabwouldconsistof multipledismantledslabpieces.
Fig. 8:Crackpatternforsteelwoolfibreslab
International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page1612 that of the unreinforced mortar slabs; this was certainly unimpressive. The polypropylene specimens in contrast exhibitedexcellentcharacteristics,sincetheresidualimpact ratioswereintherange6.4 9.1.
Load deflectioncurvesforthesteelwoolfibrereinforced specimensandtheunreinforcedmortarslabsat28daysare shown in Figure 10; the 14 days test results are not presented Theunreinforcedslabwithstoodaforceofabout 2.1kNwithacorrespondingdeflectionof2.1mmforthe14 days test. The 28 days test produced a slight increase in ultimateloadtoabout2.32kN;thisgaverisetoincreased deflectionsbyabout0.53mm.The0.75%steelreinforced mortarslabexhibitedabout1.31kNmoreloadresistanceat 14 days than the unreinforced slab. An increase in steel contentto2%resultedinabout1.89kNloadresistanceat14 days. The 28 days test produced an increase in load resistance but resulted in a decrease in deflection in the range0.75 0.81mm.Onthewholethesteelwoolfibreslabs had increased load resistance over the unreinforced specimensby1.31 1.89kNat14days,and0.94 1.23kNat 28days.Consideringthefactthattheseslabswereof20mm thicknessandsubjectedtoonecentralpointloading,these increaseswereconsideredsignificant.
REFERENCES
thepolypropylenereinforcedslabsweremorevaried, widespreadanddevelopedthanthoseforthesteelwool fibrereinforcedspecimens.
[8] H. Singh, “Steel Fibre Reinforced Concrete Behaviour, Modelling and Design”, 1st Edition, Springer Transactions in Civil and Environmental Engineering, Singapore,2017,172pp.
Fig. 11:Load deflectioncurvesforpolypropfibreslabs Calculationsfortoughnessindicatedthatthesteelwool fibre reinforced mortars were tougher than the polypropyleneequivalents.At28daysatoughnessofupto 5.07Joulesand3.71Jouleswasobtainedforthesteelwool andpolypropylenefibrereinforcedslabsforthe0.75%fibre fraction.Forthe2%fibrefractionat28daystherespective values were 3.95 Joules and 4.94 Joules respectively. As expected, the unreinforced slabs exhibited the least toughnessof2.60Joulesat28days.
[6] CementB.Mobasher,“MechanicsofFibreandTextileReinforcedComposites”,CRCPress/Taylor&Francis,USA, 2012,473pp.
ACKNOWLEDGEMENT
[1] G.RamakrishnaandT.Sundararajan,“ANovelApproach toRheologicalandImpactStrengthofFibre Reinforced Cement/Cementitious Composites for Durability Evaluation”,Chapter17inDurabilityandLifePrediction in Biocomposites, Fibre Reinforced Composites and Hybrid Composites, Woodhead Publishing Series in CompositeScienceandEngineering,M.Jawad,M.Thariq andN.Saba(Eds.),2019,pp.389 406.
The study reported herein is the culmination of the experimental work carried out in the Materials and StructureslaboratoriesoftheCivilEngineeringDepartment attheUniversityofBotswana,Gaborone.Theauthorshereby expresstheirthankstotheChiefTechnicalOfficerMr.John Kennedy,aswellasthetechnicalstaffMs.Botshomanyane andMr. Thatayaone Moreengfor theirassistance. Special thanks are extended to Prof. Goitseone Malumbela (presentlyatBotswanaInternationalUniversityofScience and Technology) for the coordination of the final year undergraduate projects during the period the laboratory investigationwascarriedout.
4. CONCLUSIONS
International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page1613
Load deflection curves for the polypropylene fibre reinforcedspecimensat28daysareshowninFigure11.The behaviouroftheseslabswereratherdifferentfromthatof thesteelwoolspecimens,inthesensethatforthe14days test,anincreaseinfibrecontentfrom0.75%to2%resulted inadecreaseintheloadcapacityfrom3.69kNto2.85kN. However for the 28 days test, the trend was reversed; an increaseinfibrecontentfrom0.75%to2%resultedinan increasein failureloadfrom3.25kN to3.54kN.This was ratheroddandcouldbeduetopoormixingandspreadingof the0.75%polypropylenefibrefractionthroughoutthemix, orsomeotherunknownfactors.
The present investigation was intended to be a comparativestudyofthemechanicalstrengthofsteelwool and polypropylene fibre cement mortar slabs. For this purpose,atotalof60slabsweretestedunderconditionsof impactstrengthandflexuralstrengthloadings.Basedonthe experimental work carried out, the following conclusions maybedrawn.
(2) The steel wool andthe polypropylene fibre reinforced slabshadcomparableflexuralstrengths.Thetoughness ofthesteelwoolfibredslabswasmuchhigherthanthe polypropylene fibre specimens for the 0.75 % fibre fraction.Howeverforthe2%fibrecontent,thesituation wassomewhatreversed.
(1) Slabsreinforcedwithpolypropylenefibres withstood thehighestamountofimpactblowsaftertheinitialcrack, upuntoultimatefailure.Inaddition,thecrackpatternsin
[2] A. Naaman, T. Wongtanakitcharoen and G. Hauser, “Influence of Different Fibres on Plastic Shrinkage CrackingofConcrete”,ACIMaterialsJournal,Vol.102, No.1,2005,pp.49 58. [3] R.F. Zollo, “Fibre Reinforced Concrete: An Overview after30YearsofDevelopment”,CementandConcrete Composites,Vol.19,1997,pp.107 122. [4] ACI Committee 544, “State of the Art Report on Fibre Reinforced Concrete”, ACI 544.1R 96, American ConcreteInstitute,FarmingtonHills,Michigan,2002,66 pp.
[5] A.M. Brandt, “Fibre Reinforced Cement Based (FRC) Composites after over 40 Years of Development in BuildingandCivilEngineering”,CompositeStructures, Vol.86,2008,pp.3 9.
[7] N. Uddin (Ed.) ”Developments in Fibre Reinforced Polymer (FRP) Composites for Civil Engineering”, 1st Edition, Woodhead Publishing Series in Civil and StructuralEngineering,2013,558pp.
International Research Journal of Engineering and Technology (IRJET) e ISSN: 2395 0056 Volume: 08 Issue: 12 | Dec 2021 www.irjet.net p ISSN: 2395 0072 © 2021, IRJET | Impact Factor value: 7.529 | ISO 9001:2008 Certified Journal | Page1614 [9] A. Naaman, “Fibre Reinforced Cement and Concrete Composites”,1st Edition,TechnoPress,USA,2017,765 pp. [10] RILEM FIB,“FibreReinforcedConcrete:Improvements and Innovations”, Proceedings of International Symposium on Fibre Reinforced Concrete, P. Serna, A.Liano Torre,J.R.Marti VargasandJ.Navarro Gregori (Eds),21 23September,Valencia,Spain,2020,1164pp. [11] RILEM FIB,“FibreReinforcedConcrete:Improvements and Innovations II”, Proceedings of International Symposium on Fibre Reinforced Concrete, P. Serna, A.Liano Torre,J.R.Marti VargasandJ.Navarro Gregori (Eds),20 22September,Valencia,Spain,2021,979pp. [12] G. Owens (Ed.), “Fulton’s Concrete Technology”, 9th Edition,CementandConcreteInstitute,Midrand,South Africa,465pp. [13] SANS1090:2002,“AggregatesfromNaturalSources Fine Aggregates for Plaster and Mortar”, 2.01 Edition, SABS Standards Division, Pretoria, Republic of South Africa,2002.