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Effect of the Surface Treatment of Recycled Rubber on the Mechanical Strength of Composite Concreterubber 2014 Materials and Structures

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  ORIGINAL ARTICLE Effect of the surface treatment of recycled rubberon the mechanical strength of composite concrete/rubber L. P. Rivas-Va´zquez  ã R. Sua´rez-Ordun ˜ a  ã J. Herna´ndez-Torres  ã E. Aquino-Bolan ˜ os Received: 9 June 2013/Accepted: 31 May 2014   RILEM 2014 Abstract  In this study, the influence of the additionof tire rubber in concrete was evaluated, to partiallyreplace thefineaggregateofsandparticles.Therubberfibers were also surface treated with different solventsto improve adhesion of the fibers to the concretematrix. Compressive strength, slump test, FourierTransform Infrared Spectroscopy of concrete sampleswere performed at time intervals of up to 28 days. Theresults showed a decrease on mechanical propertyvalues after the addition of tire rubber withouttreatment as well as a decrease of workability. It wasalso observed that the tire rubber treatment withacetone caused an increase of the mechanical strengthof the samples. Keywords  Concrete    Mechanical properties   Composite concrete/rubber 1 Introduction The use of rubber in the construction industry is notnew, various construction industries have usedrubber elements as a fundamental part of structure.This material has been used in the construction of concert halls (as an acoustic absorber), in theconstruction of bridges (buffer), as waterproofing,filling in roads, among others [11]. The addition of rubber is used as a replacement of fine aggregate, tomodify basic properties of concrete, such as theincrease of flexural strength as well as shearstrength, these additions also promote the decreaseof concrete density, by doing so, the thermalconductivity of the concrete decreases [4].Some studies have indicated that the addition of rubber to mortar decreases mechanical properties,compared to the resistance of mortar without rubber.The decrease in mechanical properties is caused byweak chemical interaction between rubber and Port-land cement [10]. Snelson et al. [10] reported that small additions of up to 10 % recycled rubber,combinedwith mortar, causes the decrease inmechan-ical strength due to poor interaction of rubber in fiberform with mortar. At the same time, Ganjian et al. [3]reported mechanical studies have shown that just over5 % of added rubber material can generate significantchanges in the properties of the composite. Fromanother point of view, Toutanji [13] evaluated theincorporationofrubberchipsasareplacementofsand.Theincorporationoftheserubbertirechipsinconcrete L. P. Rivas-Va´zquez    R. Sua´rez-Ordun˜a ( & )   E. Aquino-Bolan˜osUniversidad del Papaloapan, Ferrocarril s/n,C.P. 68400 Loma Bonita, Oaxaca, Mexicoe-mail: rsuarez@unpa.edu.mxL. P. Rivas-Va´zqueze-mail: privas@unpa.edu.mxJ. Herna´ndez-TorresCentro de Investigaciones en Micro y Nanotecnologı´aVeracruz, Calzada Ruiz Cortı´nes No. 455, Col. CostaVerde, C.P. 94294 Boca del Rı´o, Veracruz, MexicoMaterials and StructuresDOI 10.1617/s11527-014-0355-y  exhibited a reduction in compressive and flexuralstrengths.Attempts have been made to improve the mechan-ical strength of the concrete/rubber composite, by theimplementation of different additions or modificationsin the composition of the material. Tangudom et al.[12] state that the addition of bagasse ash silica to theconcrete composite with partial replacement of fineaggregate of rubber tires, result in an improvement inthe dispersive and distributive properties of rubber/ concreteaggregateintherubbermatrix,asindicatedbyan increase in tensile strength and elongation at break.Another approach is to increase the use of rubbermodified cement concrete by developing a cementi-tiouscoatinglayeraroundrubberparticleswithasilanecoupling agent. In this case, the result shows that thecompressive and split tensile strength of the concreteincorporating coated rubber improved by 10–20 %, incomparison to concrete with uncoated rubber [2].Other studies indicate that it is possible to increasethe resistance of rubber/cement composite materialthrough the treatment of rubber in NaOH solutions,however in this respect there is no consensus as towhether or not this method helps to improve theinterfacial adhesion of rubber with mortar [5]. Thenagain, it has been reported the use of magnesiumoxychloride as a binder in cement mixes with rubber[9], produces the surface modification of rubber, withthe intention of increasing the adhesion with cement,as it has been reported by Segre and Joekes [7].Another report by Segre et al. [8] mentions thatexisting additives commonly found in tires, are thosethat during the mixing with cement can migrate andcause the disintegration of phases. Generationincreases the mechanical strength of the material [6].This study raises the possibility of increasing themechanical strength of the concrete/rubber samples,using different solvents which may promote adhesionof the concrete/rubber interface. 2 Materials and methods 2.1 Materials 2.1.1 Cement  The cement used in this study was ordinary Portlandcement (OPC) ASTM type I. The specific gravity of cement used is 3.16. The chemical composition of OPC was determined by the testing method X-rayfluorescence spectrometry (XRF). The chemical com-position of cement used in this experimental study isshown in Table 1. 2.1.2 Water  Clean drinking water was used for concreting; thewater aided in the hydration of the cement, whichresulted in the setting, and hardening of the concrete. 2.1.3 Aggregates Fine aggregate was natural sand obtained in LomaBonita, Oaxaca, Me´xico, with specific gravity andfineness modulus of 1.39 and 1.47, in particular. Thecoarse aggregate used had a maximum size of 25 mm.Grain size distributions for aggregates are given inTable 2 and shown in Figs. 1 and 2. Both the fine and coarse aggregates were air dried to obtain saturatedsurface dry condition to ensure that the water/cementratio is not affected. 2.1.4 Rubber  The material used was provided by the Genbrugercompany, and consists of rubber obtained from theshredding of automobile tires. Powdered rubber usedhas a particle size of less than 1.18 mm. Grain sizedistributions for tire rubber are given in Table 2, and aphotograph of the tire rubber used in this work isshown in Fig. 3.2.2 MethodsThepreparationofconcretesampleswasconductedbythe initial mixing of the components of concretecement, gravel, sand and as a replacement of part of the fine aggregate, waste rubber was used. The mixingwas performed in an electric mixer. After preparingthemixtureofcomponentswascompleted,theprocessto perform the casting in cylindrical molds withdimensions set by the ASTM C873/C873M-10a [1]was carried out. These samples were kept in the moldsuntil they reached a certain consistency, suitable forstripping without breaking (setting: 1 day). The sam-ples were stored in a humid chamber (samples were Materials and Structures  collected at continual time intervals for a period of 28 days, which is the time needed for the concrete toreach its maximum resistance).The resistance of the obtained samples was char-acterized by a compressive strength test. This testingwas performed with the samples processed by inter-vals of 1, 3, 7, 14 and 28 days. The rubber particleswere surface treated with different solvents (ethanol,acetone, and methanol prepared in a 50 % by volumeof a solvent/water ratio). The treatment effect wasevaluated by infrared spectroscopy, and the change incompressive strength of the different samples wasstudied. 3 Results and discussion Figure 4 shows the slump of concrete samplesobtained with different rubber/sand ratio and awater/cement ratio of 0.5, likewise, different solventswere used for the surface of the rubber that wastreated. The resultsclearlyindicated adecrease slump,associated with a decrease in workability of themixture. Furthermore, it was observed that the sam-ples containing surface treated rubber with a solvent,decreased workability with respect to samples thatwere not treated (under the same conditions of therubber content). This result indicates that the surfacetreatment caused some interaction with the wateradded, increasing the viscosity of the mixture anddecreasing the workability. The use of acetone causeda slump in samples containing 10 % rubber by about4 cm, compared to 12 cm obtained with the untreatedsamples. The sample under these conditions was Table 1  Chemical composition of OPC (% by mass)CaO SiO 2  Al 2 O 3  Fe 2 O 3  MgO K  2 O Na 2 O SO 3  MnO LOI62.3 21.4 6.1 2.52 2.6 0.6 0.3 2.0 0.004 2.1 Table 2  Sieve analysis of aggregate typesSieve size (mm) Passing (%)Fine aggregate Coarse aggregate Rubber25.4 100 100 10019 100 99.41 10012.7 100 66.77 1009.5 100 39.17 1004.75 97.96 15.94 1002.38 94.24 0.00 1001.18 85.7 – 99.760.595 62.14 – 98.770.287 13.35 – 55.960.149 3.5 – 28.970.074 0.66 – 1.72 \ 0.074 0.00 – 0.00 160002004006008001000120014001000102030405060708090 Particle Size ( µ m)    C  u  m  u   l  a   t   i  v  e  p  a  s  s   i  n  g   (   %   ) Lower boundUpper boundFine aggregate Fig. 1  Particle size distribution of the fine aggregate 250481216201100102030405060708090100 Particle Size ( µ m)    C  u  m  u   l  a   t   i  v  e  p  a  s  s   i  n  g   (   %   ) Upper boundLower boundCoarse Aggregate Fig. 2  Particle size distribution of the coarse aggregateMaterials and Structures  unworkable, for this reason, the use of a fluidising toimprove workability of the mixture without changingthe water/cement ratio was suggested..Figure 5 shows the test results in compression of concrete samples with additions of rubber which wereadded as a replacement for fine aggregate. In thesesamples,therubberisadded withoutanypretreatment.Asitisobserved,sampleswhich haverubberadditionsdecrease in mechanical strength, which coincides withprevious reports by Snelson et al. [10] and Ganjianet al. [3]. The decrease in the mechanical strength of concrete is thought to be caused due to poor chemicalinteraction between the different phases of theconcrete and rubber, causing little or no adhesion atthe interface of the concrete/rubber.Furthermore, Fig. 6 shows the results of concretesamples with an addition of 10 % surface treatedrubber. The different solvents used, increased Fig. 3  Micrograph rubberparticles and agglomeratesobtained from theautomobile tire shredding 16.504812 130123456789101112 Rubber Aggregate (%)    S   l  u  m  p   (  c  m   ) Rubber treated w/ 50% vol. AcetoneRubber treated w/ 50% vol. MethanolUntreated Rubber Fig.4  Slumptestsofconcretesamplespreparedunderdifferentrubber surface chemical treatments 300481216202428200020406080100120140160180 Setting time (Days)    C  o  m  p  r  e  s   i  v  e   S   t  r  e  n  g   t   h   (   M   P  a   ) 0 % Rubber10 % Rubber20 % Rubber Fig. 5  Graph of compression tests with different concreteaddition of rubber without chemical treatment 300481216202428240020406080100120140160180200220 Setting time (Days)    C  o  m  p  r  e  s   i  v  e   S   t  r  e  n  g   t   h   (   M   P  a   ) Rubber treated w/ AcetoneRubber w/ MethanolRubber w/ EthanolUntreated Rubber Fig. 6  Graph of compression tests with different concreteaddition of rubber treated with different solventsMaterials and Structures

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