STRENGTH AND BEHAVIOUR OF CARBON NANOTUBE REINFORCED CEMENT COMPOSITES

STRENGTH AND BEHAVIOUR OF CARBON NANOTUBE REINFORCED CEMENT COMPOSITESRESMA RAJENDRAN NAIRM1 Structural EngineeringRoll No. 141092Guided byDr. Bindhu K R1IntroductionIdea behind nano-science started at a talk entitled Theres plenty of room at the bottom by physicist Richard Feynman in 1959.

Nano-science involves ability to control individual atoms and moleculesSize range 1-100 nanometers(nm)One nanometer is a billionth of a meterA sheet of paper is about 1,00,000 nm thick

22Two main approaches:

Top down approach Materials are deconstructed to nano scaleMaintains original material properties

Bottom up approachMaterials are engineered from atoms through self assemblyMolecular manufacturing

3Large surface areaPhysical, chemical, optical and mechanical properties changeInert materials may become reactive, some may conduct heat or electricity better, some even change colour

4Common Nano materials1. Carbon Nanotubes Cylindrical shapeEfficient thermal conductorsImproves flexural, shear and compressive strength when added to cement compositesAlso improves durability, resistance to corrosion and crack formation

52. Silver nanoparticlesUpon contact with bacteria, viruses, etc., their cellular metabolism is affectedUsed for odour control

3. Titanium Dioxide White pigmentExcellent reflective coatingAdded to paints, cement etc., for its sterilizing propertiesAlso used to remove organic pollutants when applied to outdoor surfaces6Nanotechnology in construction industryConcreteAddition of nano-silica reduces permeability of waterCarbon nanotubes improve compressive strength and flexural strength of cement mortarNano sensors used for damage detection

SteelAddition of copper nano particles reduces surface unevenness of steel Vanadium and molybdenum nanoparticles reduces effects of embrittlement7GlassTitanium dioxide nanoparticles impart self cleansing propertiesBreaks down organic pollutants washed away by rainFumed silica nanoparticles impart fire protection

Structural MonitoringNano-sensors embedded into concrete during construction phaseUsed to monitor structural performance of concrete8Hollow tubular channels formed by single or multiple walls of rolled graphene sheetsEnds capped by half fullerene moleculesWeak inter-planar bonds Allows tubes to slide within one anotherMain force acting is van der Waals force

9Carbon Nanotubes

Atomic structure is based on tube chiralityzigzag shaped zero chiralityarm chair shaped chiral angle of 30

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CNTs have a hollow center therefore it is lightYoungs Modulus 1TPaAverage tensile strength 60GPa Average ultimate strain 12%Density 1.3-1.4g/ccAspect ratio 25,00,000:1No. of walls 3 to 1511Mechanical PropertiesElectric arc dischargeElectric arc passed between two carbon electrodes through an inert gas like argon or heliumHigh temperature causes carbon to sublimate and re-solidify into CNT AdvantagesPurity of 30% by weight can be achievedSingle and multi-walled carbon nanotubes can be produced

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Methods Of SynthesisLaser ablation technique

A pulsing laser is used to vaporize a piece of graphite within an inert gas inside a furnace at 1200CVaporized graphite solidifies onto walls of chamber and forms CNTAdvantageUpto 70% purity by weight may be achieved

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Disadvantages Expensive processContinuous production not possibleAdditional purification processes are necessary

14Chemical Vapor Deposition

CNTs produced by decomposition of a carbon containing gasCarbon based gas with a metal catalyst used as initiatorAdvantagesHigh purity can be achievedLow cost per unit rateContinuous production of CNTs possibleMethod used widely for up-scale to industrial production

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Good dispersionCNTs have increased chances of agglomerating due to strong Van der Waals forcesCauses non uniform stress transfer Uniform alignment of nano-filamentsNano-filaments aligned perpendicular to primary stresses cant efficiently transfer stress along its axis Therefore parallel alignment necessary

16Requirements For A good CNT ReinforcementLarge aspect ratioLarge surface area improves bond between cement and nano-filamentsOptimal bondProper adhesion required to prevent sliding of nano-filaments out of the cement matrix.

17Physical TechniquesUltrasonicationMechanical vibrations are created in the liquid mediumCauses formation and collapse of microscopic bubblesHigh level of energy is released leading to dispersion of nano materials in the liquid

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Dispersion TechniquesChemical TechniquesUse of surfactantsDispersion improved by repulsion between surfactant molecules adsorbed in nano particlesDispersion capability depends on Surfactant concentrationOptimum surfactant to nano- material ratio

19Scanning Electron Microscopy (SEM)SEM scans a focused electron beam over a surface to create an imageElectrons in the beam interact with sample producing varying signals

Main components include:1. A sample chamber Samples are placed hereIncludes translation stage, tilt and rotation devices

20Instrumentation Methods2. A source of electronThese electrons are accelerated to 1-40kv and condensed to a narrow beam

3. A column down which electrons travel Electrons are accelerated down through a combination of lenses and aperturesElectrons hit surface of sample

4. An electron detectorDetects the resulting signals

5. Computers and displays to view the images

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Scanning Tunneling Microscopy (STM)

Works by moving a very sharp metal wire over the required surfaceThe tip is brought very close to the surface Electric voltage is applied to the sample/tip

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Quantum mechanical effect and tunnelingFeed back loop Monitors the tunneling current and positions the tip to maintain a constant currentThese adjustments are recorded by the computerBased on this, surface image can be developed

DisadvantageOnly conducting or semi conducting surfaces can be imaged

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Nur and Vinoth (2014) conducted comparative studies on compressive strength, flexural strength and flow values of cement mortar reinforced with CNTs and Carbon nano-fibres (CNFs)

OPC compressive strength - 24MPa Water cement ratios (w/c) - 0.35, 0.4, 0.45, 0.5Dosage rates - 0.1% and 0.2% CNT/CNFs by weight of sampleSuper plasticizer added in the ratio 0.008 by weight

25Case StudiesCOMPRESSIVE STRENGTH

ASTM C109 test procedure adoptedMortar prepared with 1 part cement and 2.75 parts graded sandAfter sonication, nanoparticles were mixed with cement and sand for 4 min50mm cube cement mortars were preparedCompressive strength of cubes tested at 7, 14, and 28 days using UTM at the rate of 890 to 1800 N/s

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Source: Nur and Vinoth, 2014FLEXURAL STRENGTH

ASTM C348 test procedure followed40mm40mm160mm sample 28 day flexural strength was testedThree point loading test conducted at the rate of 2640110N

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Source: Nur and Vinoth, 2014FLOW TEST

ASTM C1437 test procedure used to obtain the flow value of mortarMortar placed 25mm from bottom of mouldCompacted 20 times in 2 layers, flushed smooth at topFlow mould was removed and flow table dropped 25 times in 15 secondsPercentage increase in base diameter obtained

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Source: Nur and Vinoth, 2014Madhavi et al. conducted studies on strength characteristics and durability of concrete reinforced with multi walled nanotubes in ratios of 0.015%, 0.03% and 0.045% by weight of cement.

W/c ratio of 0.4 was usedCubes of 150150150mm Cylindrical specimens of 150mm diameter and 300mm height were preparedSurfactants at 0.25% by weight of cementSonication was carried out for 30 minutes and stirred by magnetic stirrer

32WATER ABSORPTION TEST

ASTM C6428 followedWater absorption test was carried out at 28 days

33Sl No.% of MWCNT% water absorption% reduction in water absorption1Conventional concrete (0)0.587320.0150.527310.2230.030.502714.4140.0450.48317.76Source: Madhavi et al., 2013SPLIT TENSILE STRENGTHSplit tensile strength tests were carried out as per IS 5816-1999Cylindrical specimen of height 300mm and diameter 150mm Breaking load and failure patterns noted

34Specimen Split tensile failure load (kN)Split tensile strength (N/mm2)% increaseConventional concrete1602.27_0.015% MWCNT2102.9730.840.030% MWCNT2353.345.370.045% MWCNT2653.77566.3Source: Madhavi et al., 2013Nanoparticles have tendency to agglomerate Thus efficient dispersion techniques must be employed

Addition of CNTs at 0.1% by weight of cement attained 54% and 14% higher compressive and flexural strengths than PCC

Split tensile strength increases (66.3%) and water absorption(17.76%) reduces with addition of 0.045% by weight of MWCNTs

Flow tests indicate that compressive strengths of composites increased with higher flow rates35ConclusionsMechanical properties of concrete is improved by addition of CNTs

Durability and corrosion resistance of concrete and reinforcing steel are also increased

However, for proper utilisation of these advantages, CNTs must be dispersed uniformly in the cement matrix

Preparation of CNT reinforced composites must be carried out with utmost care

36Interpretation By AuthorAlso techniques for mass production of CNTs at lower costs must be developed

Environmental effects of CNT synthesis and CNT reinforced composites must be studied

If properly utilized, CNTs have a great potential to revolutionize the traditional practices followed in the construction industry.

37Baoguo, H., Zhengxian, Y., Xianming, S. and Xun, Y. (2012). Transport properties of carbon-nanotube/cement composites. Journal of Materials Engineering and Performance, 22(1), ASM International, pp. 184-189.Bryan, M. T. (2010). Carbon nanotube and nanofiber reinforcement for improving the flexural strength and fracture toughness of Portland cement paste. Thesis, Texas A&M University, US.Florence, S., and Konstantin, S. (2010). Nanotechnology in concrete- a review. Construction and Building Materials, 24, Elsevier, pp. 2060-2071.Gammampila, R., Mendis, P., Ngo, T., Aye, L., Jayalath, A. S., and Rupasinghe, R. A. M. (2010). Application of nanomaterials in the sustainable built environment. Int. Conf. on Sustainable Built Environment, Department of Civil and Environmental Engineering, The University of Melbourne, Victoria, Australia, pp. 20-27.Giuseppe, F., Jean, M. T., and Simone, M. (2011). Carbon nanotubes cement composites. G. Ferro et alii, Frattura ed Integrit Strutturale, 18(2011), Gruppo Italiano Frattura, pp. 34-44.

38ReferencesJose, L. F., Jose, M. D. C., and Juan, A. G., (2014). Carbon nanotube-cement composites in the construction industry: 1952-2014. A state of the art review. Second Int. Conf. on Emerging Trends in Engineering and Technology, London, UK, pp. 137-144.Kurapati, S. (2014). Nanomaterials for concrete technology. International Journal of Civil, Structural, Environmental and Infrastructure Engineering Research and Development, 4(3), Trans Stellar, pp. 79-90.Madhavi, T. C., Pavithra, P., Sushmita, B. S., Vamsi, R. S. B., and Surajit, P. (2013). Effect of multiwalled carbon nanotubes on mechanical properties of concrete. International Journal of Scientific Research, 2(6), pp. 166-168.Nur, Y. and Vinoth, M. (2014). Carbon nano-tube and nano-fiber in cement mortar: effect of dosage rate and water cement ratio. International Journal of Material Science, 4(2), Science and Engineering Publishing Company, pp. 45-52.Pacheo, T. F., and Said, J. (2011). Nanotechnology: advantages and drawbacks in the field of construction and building materials. Construction and Building materials, Elsevier, pp. 582-590.

39Radu, O. (2011). Nanomaterials and nanotechnologies for civil engineering. Gheorghe Asachi Technical University of Iai, Civil Engineering and Building Service, pp. 109-117.Saptarishi, S., Bhuvaneshwari, B., and Nagesh, R. I. (2013). Can carbon nanotubes make wonders in civil/structural engineering? Progress in Nanotechnology and Nanomaterials, 2(4), CSIR-Structural Engineering Research Centre, Chennai, India, pp-117-129.Shama, P., Sohel, R., and Raul, F. (2013). A review on nanomaterial dispersion, microstructure, and mechanical properties of carbon nanotube and nanofiber reinforced cementitious composites. Journal of Nanomaterials, Hindawi Publishing Corporation, pp. 1-19.Surinder, M. (2006). Nanoforum report: Nanotechnology and construction. Nanoforum, pp-1-55.www.globalcement.com/news/itemlist/tag/cement%20production%20statistics accessed on 30/10/2014.www.nanoscience.com/products/carbon-nanotube-synthesis/technology-overview/ accessed on 24/10/2014.

40Thank You41