an experimental study on reinforced concrete beams

AN EXPERIMENTAL STUDY ONREPAIR TECHNIQUES OF

REINFORCED CONCRETE BEAMSIN COMPARISON WITHCONVENTIONAL BEAMS

K.N.Lakshmaiah1, P. Lingachari2,K.V.Madhav3,

1Asst.professor,Narasaraopeta Engineering College,

[email protected]

2,3Asst.professorD.M.S.S.V.H College of Engineering

& [email protected]

[email protected]

June 22, 2018

Abstract

In present scenario in the world, the beams areimportant structural elements for withstanding loads, sofinding the efficient repair and strengthening methods arenecessary inters of maintaining the safety of the structures.Beam of any structural member which cross section ismuch smaller compare to its length and undergoes lateralload, is known as beam. In other words a horizontal orinclined structural members spanning a distance between

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International Journal of Pure and Applied MathematicsVolume 120 No. 6 2018, 4383-4404ISSN: 1314-3395 (on-line version)url: http://www.acadpubl.eu/hub/Special Issue http://www.acadpubl.eu/hub/

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one or more supports, and carrying vertical loads across(transverse to) its longitudinal axis as a girder, joist,purlin or rafter. Repair and strengthening of damaged orvulnerable reinforced concrete structures is important inorder to guarantee the safety of residents or users. Thepresent study investigates about the various repair,retrofit, and strengthening techniques for reinforcedconcrete beams, the compassion and summary of eachrepair and strengthening method. The present study dealsabout the experimental test of repair and strengtheningtechniques for reinforced concrete beams. A reduction of20 % and 25% of load at first crack was observed in fibrereinforced plastic retrofitting concrete beams compared toReinforced cement concrete beams for two point loadingconditions respectively.

1 INTRODUCTION

Ordinary Portland Cement (OPC) is one of the main ingredientsused for the production of concrete and has no alternative in civilconstruction industry. But, production of cement involves emissionof large amount of carbon dioxide gas into the atmosphere whichresults to global warming. So it is advisable to search for anothermaterial or partly replace it by other material that should lead tolowest environmental impact.

Plain concrete possess a very low tensile strength, limitedductility and little resistance to cracking. Internal micro cracksare present in the concrete and its poor tensile strength is due tothe propagation of such micro cracks.

In plain concrete, structural cracks (micro-cracks) develop evenbefore loading, due to drying shrinkage or other causes of volumechange. The width of these initial cracks is few microns, but theirother dimensions may be of higher magnitude.

When loaded, the micro cracks propagate and open up, andadditional cracks form in places of minor defects. The developmentof such micro cracks is the main cause of inelastic deformationsin concrete. The addition of small closely spaced and uniformlydispersed fibers to concrete would act as crack arrester and wouldsubstantially improve its static and dynamic properties. This type

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of concrete is known as fiber Reinforced Concrete.

2 RESEARCH SIGNIFICANCE

In this investigation steel fibers are used as a source material. Thepresent study is intended to study the mechanical properties ofviz. compressive strength, split tensile strength, flexural strengthof concrete mixes made with normal and FRP, Silica fume, differentproportion to Study the flexural strength and cracking behaviourof concrete beams made with normal and admixture.

3 EXPERIMENTAL

INVESTIGATION

The present work is aimed to determine and compare the flexuralbehaviour of normal reinforced concrete beams. As the beamelement is composite material, the total work is carried out in twophases.

In the first phase of work the mechanical properties of concretemade with different ratios are studied. In the second phase ofwork beam elements were casted by using mechanical propertiesof Concrete which are obtained in the first phase of work. Themixing and casting procedures, testing methods, are presented inthe following respective sections. In the third phase of work, thebeams are repaired by different techniques such as epoxy resininjection, Fibre reinforced plastic overlay, silica fume concreteoverlay.

3.1 Phase-I of Investigation (Study onMechanical Properties of CC)

This part of investigation presents the mix design of concrete andthe experimental investigations carried out on the test specimensto study the mechanical properties viz. compressive strength,flexural strength and split tensile strength of specimens made withconventional concrete.

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a) Mix Design M20 grade Normal ConcreteThe formulation of the Concrete mixtures was done by trial and

error basis. The following were the key factors considered in themix design.

• In the design of concrete mix, total aggregates (fine andcoarse) taken as 77% of entire concrete mix by mass. Thisvalue is similar to that used in OPC concrete in which it willbe in the range of 75 to 80% of the entire concrete mix bymass.

• Fine aggregate was taken as 30% of the total aggregates. .

• By assuming the ratios of water and cement as 0.5and as perthe IS 10262 maximum water content should be 186 lit wasfound out.

• To obtain the normal mix of concrete, the ratio of cement,fine aggregate and coarse aggregates was fixed as 1:1.84:3.17.

b) Preparation of ConcreteThe preparation of concrete mix involves preparation of

materials, mixing, casting and curing.

c) Tests on Specimens Concrete

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The cubes, cylinders and prisms were tested for compressivestrength, split tensile strength and flexural strength as per Indianstandard code.

3.2 Phase-II of Investigation (Study onFlexural behavior Of CRC (conventionalreinforced concrete) Beams)

This part of investigation presents experimental procedurescarried out on the beam specimens to study the flexuralbehaviour.

a) Geometry and Reinforcement Details of BeamsAll the beams were cast in wooden moulds to maintain the

dimension of the beam specimen as 125 mm wide, 200 mm deep,and 1500mm long.

Figure 1: Geometry of Beam Specimen (All Dimensions Are Inmm)

The reinforcement details for each beam are tabulated below.Typical beam reinforcement details are illustrated. Simplysupported CRCB beams and were subjected to pure flexuralfailure by subjecting them to two point loading test.

b) Experimental Test Setup for Flexure Test of BeamsThe beams CRCB I and CRCB - II and CRCB III and

CRCB-IV were tested for double point loading. The test setupsare illustrated and shown below.

Test Setup for Two Point Loading

The test setup for two point loading was shown in figures. Thetest specimens are mounted in a UTM of 400 kN capacity. The

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Figure 2: Reinforcement details for the beam

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Figure 3: Test Setup for Two Point Loading

beams were simply supported and the supports of the beams arerested on stiffened steel girder of length 2500 mm. The effectivespan of the beam was 1350 mm.For two point static loading, theload was applied on two points each 225 mm away from the centerof the beam towards the support. Dial gauges of 0.01 mm leastcount were used to for measuring deflections under the load pointsand at mid span for measuring deflection. The dial gauge readingswere recorded at different loads. The behaviour of the beams wasobserved carefully and the first crack load and ultimate loads areobtained by visual examination. The crack patterns and failuremode of the beams was also recoded.

4 RESULTS AND DISCUSSIONS

4.1 a) Compressive Strength of conventionalConcrete Thecompressive strength of conventional Concrete is carried outbyUTM (universal testing machine) with the maximumcapacity of400 kN. All the dimension of the beam specimen as 125 mm wide,200 mm deep, and 1500mm long. The test specimens are mountedin a UTM and tested for the compressive strength of beam

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specimens . Here we observed that the average compressivestrength of conventional Concrete is gradually increases withrespective of 7days & 28days.

Figure 4: Compressive strength of conventional concrete

4.1 b) Compressive Strength ofFibre Reinforced Plasticconcrete

Fibre Reinforced Plastic concrete is made with the replacing of2%, 4%, 6%, and 8% of silica to the concrete respectively. Thespecimens were tested under UTM with 7days and 28days cured

From the above Fig.5 shows that the Compressive strength ofFibre Reinforced Plastic concrete is deceased gradually increasingof plastic in to the mixture of concrete as 2%, 4%, 6%, and 8%respectively. And here we observe that there no use of adding ofplastic in to the concrete about the Compressive strength becausehere the Compressive strength isdecreasing. So the fiberreinforced Plastic concrete having low Compressive strength andsomewhat better to increases the compressive strength ascompared to the conventional concrete

4.1 c) Compressive Strength of Silica FumeSilica Fume concrete is made with the replacing of 5%, 10%,

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Figure 5: Compressive strength of fiber reinforced Plastic

15%, and 20% of silica to the concrete respectively. The specimenswere tested under UTM with 7days and 28days cured.

Figure 6: Compressive strength of silica fume

4.2 Here we observed that the compressive strength is increasedfirst and then decreased up to last observation of 20% of silicafume. The maximum Compressive strength occurred at 10% ofSilica Fume. The replacement of 10% of silica fume is preferable into the concrete to decrease the amount of usage of fine aggregate

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and then automatically the cost should be decreased.a) Flexural Strength of conventional Concrete

The results of flexural strength of conventional Concrete wereobtained from the mounting of beams in UTM (universal testingmachine). And taken the average values of flexural strength forthree beams. Draw a graph forgiven results as shown below.

Figure 7: Flexural strength ofconventional concrete

The fig 7 shows that the flexural strength of conventionalconcrete, here we observed that the flexural strength ofconventional concrete is gradually increased as discussed abovealready in 4.1 a. Theflexural strength also increased as pernumber of curing days respectively. 4.2 b) Flexural Strengthof fiber Reinforced Plastic Fibre Reinforced Plastic concrete ismade with the replacing of 2%, 4%, 6%, and 8% of silica to theconcrete respectively. The specimens were tested under UTMwith 7days and 28days cured.

From the above Fig.8 shows that the Flexural strength ofFibre Reinforced Plastic concrete is deceased gradually increasingof plastic in to the mixture of concrete as 2%, 4%, 6%, and 8%respectively. And here we observe that there no use of adding ofplastic in to the concrete about the Flexural strength becausehere the Flexural strength is decreasing. So the fiber reinforcedPlastic concrete having low Flexural strength and somewhat

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Figure 8: Flexural strength of fiber Reinforced Plastic

better to increases the Flexural strength as compared to theconventional concrete

4.2 c)Flexural Strength of silica fumeSilica Fume concrete is made with the replacing of 5%, 10%,

15%, and 20% of silica to the concrete respectively. The specimenswere tested under UTM with 7days and 28days cured

Here we observed that the compressive strength is increasedfirst at 10% replacement of silica fume and then decreased up tolast observation of 20% of silica fume. The maximum Compressivestrength occurred at 10% of Silica Fume. The replacement of 10%of silica fume is preferable in to the concrete to decrease theamount of usage of fine aggregate and then automatically the costshould be decreased.

4.3 a) Split Tensile Strength of conventional ConcreteThe values of results for Split Tensile Strength of conventional

Concrete were obtained from the mounting of beams in UTM(universal testing machine). And taken the average values of SplitTensile Strength for three beams. Draw a graph forgiven resultsas shown below.

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Figure 9: Flexural strength of silica fume

Figure 10: Split tensile strength ofnormal concrete

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The above fig shows that the split tensile strength ofconventional concrete which were gradually increased as per theircuring with 7days and 28days. And we took the average splittensile strength of three specimens of beam.

4.3 b) Split Tensile Strength of Fiber Reinforced PlasticThe split tensile strength of fiber Reinforced Plastic is shown

below the graph with partial replacement of 2%,4%,6% and 8% offine aggregate.

Figure 11: Split tensile strength of fiber Reinforced Plastic

4.3 From the graph we observed that the increased percentageof fiber reinforced plastic decreases the split tensile strength whichwere slightly differ each from 7days and 28days of curing.

c) Split Tensile Strength of silica fume concrete:The split tensile strength of silica fume concreteis shown below

the graph with partial replacement of 5%,10%,15% and 20% of fineaggregate.

Here we observed that the split tensile strength is increasedfirst at 10% replacement of silica fume and then decreased up tolast observation of 20% of silica fume. The maximum split tensilestrength occurred at 10% of Silica Fume. The replacement of 10%of silica fume is preferable in to the concrete to decrease the

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Figure 12: Split tensile strength of silica fume

amount of usage of fine aggregate and then automatically the costshould be decreased.

4.4 a) Comparison of Load Vs Deflection BetweenCRCB-I before retrofitting and after retrofitting:

From the above graph the deflections of CRCB-I were studiedat before retrofitting and after retrofitting, here we observed thatthe deviations in deflections were almost same at 40kN after the itchanges more up to 1.7mm of deflection at 94kN load. And thecomparison of CRCB-5 having less deflects as compared to the ofCRCB-1 beam. So after retrofitting the beam has less amount ofdeflection as compared to the before retrofitting of beam. Itmeans it carries more amount load with lowered deflection

4.4 b) Comparison of Load Vs Deflection betweenCRCB-II before retrofitting and after retrofitting:

From the Fig14, the deflections of CRCB-II were studied atbefore retrofitting and after retrofitting, here we observed that thedeviations in deflections were almost same at 30kN. And thecomparison of CRCB-2 having less deflects as compared to the ofCRCB-6 beam. So after retrofitting the beam has less amount ofdeflection as compared to the before retrofitting of beam. Itmeans that it carries more amount load with lowered deflection.

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Figure 13: Comparison of Load Vs Deflection Between CRCB-Ibefore retrofitting and after retrofitting

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Figure 14: Comparison of Load Vs Deflection between CRCB-IIbefore retrofitting and after retrofitting

The same deflection of 3.4mm at the load of 118kN for bothCRCB-6 & CRCB-2. The retrofitted beam carries the better loadas compared to the beam which before retrofitting.

4.4 c) Comparison of Load Vs Deflection betweenCRCB-III before retrofitting and after retrofitting:

From the Fig15, the deflections of CRCB-III were studied atbefore retrofitting and after retrofitting, here we observed that thedeviations in deflections were almost same at 30kN. And thecomparison of CRCB-3 having less deflects as compared to the ofCRCB-7 beam. So after retrofitting ofthe beam has less amountof deflection as compared to the before retrofitting of beam. Itmeans that it carries more amount load with lowered deflection

4.4 d) Comparison of Load Vs Deflection betweenCRCB-IV before retrofitting and after retrofitting:

From the Fig16, the deflections of CRCB-III were studied atbefore retrofitting and after retrofitting, here we observed that thedeviations in deflections were almost same at 50kN. And the

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Figure 15: Comparison of Load Vs Deflection between CRCB-IIIbefore retrofitting and after retrofitting

Figure 16: Comparison of Load Vs Deflection between CRCB-IVbefore retrofitting and after retrofitting

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comparison of CRCB-4 having less deflects as compared to the ofCRCB-8 beam. So after retrofitting of the beam has less amountof deflection as compared to the before retrofitting of beam. Itmeans that it carries more amount load with lowered deflection.

4.5 Observation of Crack DevelopmentCracks were not observed initially at the beginning of the test.

When the load was increased linearly as expected, flexure cracksinitiated in the bending zone. As the load increased, existing crackspropagated and new cracks developed along the span. In the shearspan regions, the flexural cracks gave way to inclined cracks withincreasing load. The width and the spacing of cracks varied alongthe span. At ultimate stage, most of the cracks traversed up to thetop of the beams. The failure mode of both CRCB and Retrofittingof beams was similar.The crack patterns of fiber reinforced plastic,silica fume, epoxy injection of beams and conventional concretebeams are shown in following figures.

5 CONCLUSIONS

The following main conclusions were drawn from the experimentalresults obtained from this study:

1. In case of fibre reinforced plastic retrofitting concrete beamthe first crack load was 33.33% in two point loading condition,where in case of reinforced cement concrete beams the firstcrack load was 25% in two point loading condition.

2. The first cracking load of fibre reinforced plastic retrofittingconcrete beams shows slightly lesser value when comparedto cement concrete beams for two point loading conditions.A reduction of 20% and 25% of load at first crack wasobserved in fibre reinforced plastic retrofitting concretebeams compared to Reinforced cement concrete beams fortwo point loading conditions respectively.

3. The ultimate load was 13.33% more infibre reinforced plasticretrofitting concrete beams than the normal reinforced cementconcrete beams in case of two point loading condition.

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4. The load deflection characteristics at mid span of the fibrereinforced plastic retrofitting beam and RCC beams werefound to be almost similar. Also, thefibre reinforced plasticretrofitting beamshowed slightly more deflections at thesame load than the RCC beams.

5. In case of silica fume retrofitting concrete beam the firstcrack load was 32.5% in two point loading condition, wherein case of reinforced cement concrete beam the first crackload was25% in two point loading condition.

6. The first cracking load of silica fume retrofitting concretebeam shows slightly lesser value when compared to cementconcrete beams for two point loading conditions.A reductionof 20% and 25% of load at first crack was observed in silicafume retrofitting concrete beams compared to reinforcedcement concrete beams for two point loading conditionsrespectively.

7. In case of silica fume retrofitting concrete beam the ultimateload was6.25% more in two point loading condition, where asin case of reinforced cement concrete beam the ultimate loadwas 7.14% more in two point loading condition.

8. The ultimate load was13.33% more in silica fume retrofittingconcrete beams than the reinforced cement concrete beams incase of two point loading condition.

9. The crack loading of epoxy resin retrofitting beam showsslightly lesser value when compared to cement concretebeam for two point loading conditions.A reduction of 20% to25% of load at first crack was observed in epoxy resin liquidretrofitting concrete beam compared to reinforced cementconcrete beam for two point loading conditions respectively.

10. The ultimate load was 13.33% more in epoxy resin liquidretrofitting concrete beam than the reinforced cementconcrete beam in case of two point loading condition.

11. The ultimate load carrying capacity of epoxy resin liquidretrofitting concrete beam is slightly higher when compared

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to reinforced cement concrete beam for two point loadcondition.

12. From the experimental study it can be concluded thatfibrereinforced plastic, silica fume, epoxy resin liquid,concrete possesses enhanced properties than conventionalconcrete and its behaviour is similar to conventionalconcrete.

References

[1] Saadamanesh (1989) studied the Mechanical Properties ofFiber reinforced plastic Concrete. In his study, steel fibersreinforced plastic was used in various proportions (0.5%, 1.0%and 1.5%) and the test items were casted & tested.

[2] Ziraba et al (1994) investigated the Mix Design ofFiber Reinforced plastic (FRP). The study focuses on thecompressive strength performance of the blended concretecontaining different percentage of Fibre reinforced plastic asa partial replacement of OPC

[3] Meier (1995) this can be accomplished by optimizing theFibre reinforced plastic

[4] Vichit-vadakan(1997) the failure mechanisms and currentanalytical techniques in the retrofit of concrete structuresthrough studies on concrete beams externally reinforced withFibre reinforced plastic.

[5] Perumal & sundarajan (2004) observes the effect of partialreplacement of cement with silica fume on the strength anddurability properties of high grade concrete.

[6] Ghutke & bhandari (2014):examine the Influence of silicafume on concrete.Results showed that the silica fume is a goodreplacement of cement.

[7] Hanumesh, varun & harish (2015) observes theMechanical Properties of Concrete Incorporating Silica Fumeas Partial Replacement of Cement.The main aim of this work

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is to study the mechanical properties of M20 grade controlconcrete and silica fume concrete with different percentages(5, 10, 15and 20%) of silica fume as a partial replacementofcement. The result showed that The compressive strengthof concrete is increased by the use ofsilica fume up to 10%replacement of cement.

[8] Kumar & Dhaka(2016)The main parameter investigated inthis study M-35 concrete mix with partial replacement by silicafume with varying 0, 5, 9, 12 and 15% by weight of cement Thepaper presents a detailed experimental study on compressivestrength, flexural strength and split tensile strength for 7 daysand 28 days respectively.

[9] Shash et al (2005):The most common cause that leads todeterioration of concrete structures is cracking. He investigatedthe causes of cracks on concrete beams in the universitycampus.

[10] Sutherland: It is presented a report containing a largeresearch program about the applications of glass fibres in aresin matrix to build a wind turbine blades that was undertaken in the early 1990s in united states

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an experimental study on reinforced concrete beams

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