GEOGRIDS IN CONCRETE

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GEOGRID REINFORCED CONCRETE

GEOGRID REINFORCED CONCRETE1

C.SAI CHANDRAB110831CEContents

GeogridsApplications in present scenarioFactors favouring geogrids to use with concreteTest setup and measurement instrumentationResults and graphs of testObservations and analysisConclusionsrecommendations

2GeogridA geosynthetic materialmade ofpolymermaterials such aspolyester polyethylene Polypropylenecharacterized by bands of narrow elements in grid-like patternlarge voids between those bands3

Functioning of geogrids(CLk)capture the aggregates - interlock the aggregates - create a mechanically stabilized earthworkredistributes the load over wider area and reduce the vertical stressProvides Lateral RestraintImproved Bearing Capacity Tension Membrane Effect(clk)

4Types of geogridsBased on shape:Uniaxial geogrids - Wall, slope applicationsBiaxial geogrids - roadsTriangular geogrids - trafficked surfaces

Based on method of manufacture:Punched and drawn geogridsCoated yarn geogridsLaser welded geogrids

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Fig.1 Uniaxial geogridFig.2 Biaxial geogridFig.3 Triangular geogrid6Geometry of geogridsApplications Geogrids in pavementsShifts the failure envelop from weaker subgrade to stronger base materialEnhances the bearing capacity of subgrade without any soil treatmentReduces the structural cross section for given service life

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Fig 4Fig 5Geogrids in steep slopesImproves the soil retention on slip plane surfaceIts tensile strength carries loading forces imposed of failure wedgeProvides the possibility of slopes of our desired steepness.

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Fig 6Fig 7

Geogrids in retaining wallsResist the force of unstable soil wedge on retaining wallsPermit to construct retaining walls of suitable heights by using geogrids of proportional length and size.

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Fig 89Geogrids in concrete Factors favoring geogrids to be used with concrete:Resistant to chemicalsInert to aqueous solutions of acids, alkalis and saltsNo nutritional values - not attacked by micro organismsCorrosion resistantGood tensile strengthTemperature resistant

10Flexural test on geogrid reinforced beamsSpecimen details:Cross section 150 x 150 mmSpan length 530 mmTriangular notchWidth=8mmDepth=4.5mmMade across the beams bottom surfaceA geogrid layer at 50mm above the bottom surface

11Numbers of specimens tested: 2112 Normal strength concrete blocks(35Mpa)3 with no reinforcement(serves as control)3 with uniaxial geogrid3 with biaxial geogrid3 with triangular geogrid9 high strength concrete blocks(45Mpa)3 with no reinforcement3 with biaxial geogrid3 with triangular geogrid

12Specimen fabricationPCC mix Portland cement natural sand(fine aggregates) medium sized limestone(NMAS 9.5mm) coarse limestone aggregates(NMAS19mm)Normal strength beamsMix ratio coarse:medium:fine:cement=1.7:1.2:2:1Water cement ratio=0.52High strength beamsMix ratio coarse:medium:fine:cement=1.5:0.8:1.7:1Water cement ratio=0.43

13Details of geogrids used

Table 1 uniaxial geogrid click14

Table 2 biaxial geogrid(CLICK)table 3 triaxial geogrid1516

fig 9 dimensions of geogridsTesting setup and measurement instrumentationFlexural testing is done according to ASTMMonotonic loading by hydraulic UTMDisplacement control at constant cross head rate of 0.002mm/secData acquisition system to collect dataClip-on gauge to measure crack mouth opening displacement(CMOD)(CLK)Transducers to measure the horizontal and vertical displacements at notch 17

Fig.10 longitudinal section showing loading position and reinforcement layout18

Fig.11 Testing and measurement instrument setup(CLICK)19Results and analysisload vs vertical displacement of normal strength beams

20Load vs. vertical deflection of high strength beam:

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22Continued.

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24Summary of test results25

Pcontrol=max load of unreinforced specimenPmax = load at first peak in reinforced specimenPp = post peak loadContinued.

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max = deflection at max loadcontrol= deflection at post peak loadContinued.

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CMOD = crack mouth opening displacementTable 4 brief summary of test resultsobservationsRepeatability is observed in the behavior of replicatesSmall variability is due to slight difference inFabricationTesting Consistent behavior of geogrid(CLK)Load of failure is maximum for replicate in which load propagation started at notchUnreinforced beams failed by brittle failure(clc)28Continued..In reinforced beams the first drop is due toInability of concrete in taking the load after crackingDebonding between the concrete and geogridNew rise is due to load taken by geogridSlope of new rise is less due to less elasticity is modulusFurther series of drops are due to tear in the one or more ribs at once(clk)

29ContinuedInclusion of geogrid layer increased the maximum load and deformation of initial peak(CLK)Increment in strength and deformation at initial peak of reinforced beams over unreinforced beams is 20% and 40% - uniaxial 12% and 25% - biaxial 28% and 48% - triaxialPost peak load capacity is more than first peak capacity in uniaxial geogrids(CLK)30Continued.More multiple peaks are observed in uniaxial geogrid reinforced beams(CLK)Uneven distribution of junctions in triaxial geogrids causes it to act as one whole reinforcementSingle peak is observed in triaxial reinforced beamsChange in post peak behavior of triaxial high strength beam indicates(clk)correlation between concrete strength and mechanical characteristics of reinforcement31Failure mechanism

32Fig.8 failure mechanismsFailure mechanisms observed in beamsFig a immediate brittle failure leading to specimen Separation in control specimensFig b crack initiation and propagation in uniaxial geogrid beamsFig c delayed failure due to geogrids holding the specimen intactFig d failure mode just before the total failure in uniaxial geogrid beamsFig e geogrid junction resisting load at crack

33ContinuedFig f rib failure; failure mode of geogridsFig g rib failure in biaxial geogridsFig h rib failure in triaxial geogrids

34Load verses CMOD Graphs

35observationsCMOD measures the resistance of the beam to growing a crackCMOD values are more related to concrete strength till the failure of bottom concrete occursThe type and property of the geogrid influence the CMOD value after the load transfer36Flexural strengthFlexural strength calculated as modulus of rupture R is calculated with formula where P=max total load in Kn l= span length b = specimen width d = specimen heightIncrement in flexural strength in normal and high strength beams is20% - uniaxial geogrids12% and 0% - biaxial geogrids28% and 6% - triaxial geogrids

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Fracture energyArea under load CMOD graphGeogrid reinforcements increased the fracture energyHighest increase is seen in uniaxial type due to more ductilityHigh strength specimens attained less energy compared to low strength specimens

38 ConclusionsAll types of geogrids provided Ductile post cracking behaviorHigh fracture energyHigh flexural strengthLarge deflectionPhysical and mechanical properties of geogrids have impact on peak and post peak behaviorPost peak behavior in descending order uniaxial>biaxial>triaxial geogrids

39continued.A correlation exists between concrete strength, tensile properties of geogrids.Provide considerable benefits when used as non structural reinforcement under light loading conditions

40Recommendations

Still more parameters likemethods to improve the interlocking use of multiple geogrid layers effects of junction location behavior under cyclic loading are to be investigated to reveal complete significance of geogrids in concreteStudies on reduction of ballast thickness of railtracks by using geogrids can be carried

4142THANK YOU

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