Experimental and Analytical Investigations on Flexural Behaviour of Retrofitted Reinforced Concrete

www.ijm-me.org

International Journal of Material and Mechanical Engineering (IJMME) Volume 3 Issue 3, August 2014 DOI: 10.14355/ijmme.2014.0303.02

Experimental and Analytical Investigations on Flexural Behaviour of Retrofitted Reinforced Concrete Beams with Geopolymer Concrete Composites C.K. Madheswaran1, Pinky merlin Philip2 CS IR-Structural Engineering Research Centre, Chennai, India

1

Saingits College of Engineering, Pathamuttom, Kerala., India

2

ckm@serc.res.in Abstract Existing multi-storey buildings in earthquake prone regions of India are vulnerable to severe damage under earthquakes.

So there is an urgent need for retrofitting of deficient and damaged buildings. Portland cement (PC) production is under critical review due to high amount of carbon dioxide gas released to the atmosphere and Portland cement is also one among the most energy-intensive construction material.

The current contribution of greenhouse gas emission from Portland cement production is about 1.5 billion tons annually or about 7% of the total greenhouse gas emissions to the earth’s atmosphere. So retrofitting of existing deficient building using eco-friendly material which could promise higher structural performance than the original building is essential.Geopolymer concrete (GPC) is a non-Portland cement binder based on alkaline activation of industrial wastes such as fly ash and GGBS. The application Geopolymer concrete in retrofitting can reduce the production of cement and can create an ecofriendly construction atmosphere to an extent. So the feasibility of geopolymer concrete in retrofitting of damaged structures is required to be studied. This paper presents the details of the mix designs of GPC mixes, preparation of retrofitted test specimen, testing and evaluation with respect to cracking, ultimate load, deflection and failure modes. Non-linear finite element analysis of beams by 3D modeling of concrete (solid 65 element) and discrete modeling of reinforcement (Link 8 element) was carried out using ANSYS software. The load deflection characteristics, failure modes and crack patterns are obtained from the experimental and analytical studies.

The results of the study indicate that the performance of retrofitted beam with GPC and control beam shows good agreement in ultimate load, failure modes and crack patterns.

Keywords Geopolymer Concrete (GPC); Finite Element Modelling; Flyash; Ground Granulated Blast Furnace Slag (GGBS); Retrofitting

62

Introduction Concrete is a versatile material having number of desirable properties, so widely preferred in construction industry. But a having major disadvantage that under severe vibrations such as earthquakes it gets cracked and concrete has poor modification and repair quality. Therefore some repair or strengthening must be performed so that damaged element must stand for further useful life.Many civil structures are no longer considered safe due to increased load specifications in the design codes. Such structures must be strengthened in order to maintain their serviceability.

The various strengthening techniques that are currently available includes steel plate bonding, polymer injection followed by concrete jacketing, use of advanced composite materials like Glass Fibre Reinforced Polymer(GFRP), Carbon Fibre Reinforced Polymer(CFRP), mats and Ferrocement (Amarnath,C., et al.,(2008) etc.

But all the above mentioned techniques are very sensitive to increase in temperature. The task of retrofitting of existing structure must ensure that the strength and stiffness of overall structure is resorted to original design requirements for long life and also the material used for retrofitting should produce less greenhouse gases, because the cement is proving to be ecologically hazardous material due to its inherent high internal energy content besides occurrence of emission of large quantities of carbon dioxide during its production.

The production of cement means the production of pollution because of the emission of COâ‚‚ during its production. To produce an environmental friendly

International Journal of Material and Mechanical Engineering (IJMME) Volume 3 Issue3, August 2014

concrete, it is necessary to replace the cement with ecofriendly material. In this respect, the new technology Geopolymer concrete (GPC) is a promising technique which uses industrial waste such as fly ash (FA) and ground granulated blast furnace slag (GGBS).

A huge amount of fly ash (FA) is generated in thermal power plants, causing several disposal-related problems; the total utilization of FA is only about 50% of produced. Disposal of fly ash is a growing problem as only 15% of fly ash is currently used for high value addition applications like concrete and building blocks, the remaining being used for landfills. Geopolymer technology can be appropriate process technology utilize all classes and grades of FA and therefore there is a great potential for reducing stockpiles of waste FA materials. GGBS is a by-product from the blastfurnaces used to make iron. GGBS is also used as a binder component in Geopolymer concrete.It has been reported that geopolymer material does not suffer from alkali-aggregate reaction even in the presence of high alkalinity and possesses excellent fire resistant.Geopolymer is used as the binder, instead of cementitious material, to produce concrete. The manufacture of geopolymer concrete is carried out using the usual concrete technology methods.

Research Significance One of the most important applications of geopolymeris in construction industry. However, the suitability of GPC to various structural components is yet to be established by large number of experimental studies. Various experimental works have been done to find out the suitability of geopolymer concrete to replace the Portland cement concrete (PCC) and based on these results the geopolymer concrete application can create an environmental friendly construction industry.

Since the majority of existing buildings are deficient for resisting earthquakes, so nowadays retrofitting of the building has become a major issue.The recent earthquakes in India occurred during 2001 in Gujarat, damaged many buildings that were seismically deficient. This calls for techniques those are environmental friendly, technically sound and economically feasible to upgrade deficient structures.

Various retrofitting techniques available are steel plate bonding, polymer injection followed by concrete jacketing, use of advanced composite materials like Glass Fibre Reinforced Polymer (GFRP), Carbon Fibre Reinforced Polymer (CFRP), and Ferrocement etc. But since these above mentioned methods are just

www.ijm-me.org

strengthening the existing structure without removing the damaged portion many disadvantages exists, like their behaviour changes as temperature varies, and also the materials tensile strength and stiffness not match with the concrete properties. So inorder to overcome these drawbacks, a new attempt was made i.e. retrofitting of damaged portion using geopolymer concrete. In this study the retrofitting is done after the removal of damaged concrete and is rebuilt with geopolymer concrete.

The experimental and analytical studies on control beams and retrofitted beams having two different dimensions one with 100 x150 x1500mm having 3.35% reinforcement and another with 100 x200 x1500mm with 1.28% reinforcement were carried out. Also the GPC was made with different concentration of sodium hydroxide solution i.e... GPC made from 3M and 5M alkaline solution. The behaviour of reinforced GPC (RGPC) beams 100 x150 x1500mm retrofitted with 3M (RGPC3M) and 5M (RGPC5M) GPC was also carried out.

Experimental Work Materials Ordinary Portland cement conforming to IS 12269, fine aggregates, coarse aggregates and portable water were used for the control specimen RC specimens. While for GPC beams and for retrofitting Ground Granulated Blast Furnace Slag (GGBS) as per IS 3812, Fly Ash (FA) conforming to IS 12089, fine aggregates (river sand) and coarse aggregates (crushed granite stones-12mm size) as per IS 2386 were used. Catalytic liquid system (CLS) is an alkaline activator solution (AAS) for GPC. It is a combination of solutions of alkali silicates and hydroxides, besides distilled water. The role of AAS is to activate the geopolymeric source materials (containing Si and Al) such as fly ash and GGBS. Specimen Details

(a)

63

www.ijm-me.org

International Journal of Material and Mechanical Engineering (IJMME) Volume 3 Issue 3, August 2014

(3.35%) two beams are reinforced PPC (RPPC) beam retrofitted with GPC one with 5M and the other one with 3M; other 2 beams are reinforced GPC (RGPC) beam retrofitted with geopolymer concrete one with 5M and other with 3M (b) FIG: 1 REINFORCEMENT AND DIMENSION DETAILS OF (A) 100 X200 X 1500MMRPPC BEAM (WITH 1.28% REINFORCEMENT) (B)100X 150 X 1500MMRPPC AND RGPC BEAM (WITH 3.35% REINFORCEMENT)

The beam specimens include 4 numbers of 100mm wide and 200mm deep beams and 3 numbers of 100mm wide and 150mm deep beams. They are 1500mm in length and simply supported over an effective span of 1350mm with M30 grade concrete.

The beams of 100x 200mm cross section is having 1.28% reinforcement with 2#8mmϕ compression reinforcement and 2#10mmϕ tension reinforcement, the compression reinforcement is provided only at the end portion of beams, not at the mid-span. Also 8mmϕ stirrups are provided at 125mm c/c. The clear cover of the beam was 20mm as shown in Fig 1(a). Of the 4 RPPC beams 2 beams are retrofitted with 5M GPC and other 2 beams are retrofitted with 3M GPC. The beams with 100 x 150mm cross section were designed as doubly reinforced sections with total reinforcement 3.35 %. All the beams are reinforced with two numbers of 16mm diameter rods at the bottom and two numbers of 8mm diameter rods at top of the beam. Apart from it, 8mm diameter stirrups are provided at 100mm c/c spacing. The clear cover of the beam is 25mm as shown in Fig 2(b). Of the 4 specimens

Preparation of Specimens Concrete is removed from the damaged portion of the beam. The damaged portions of concrete were cut and loose materials were removed and blower was used to clean the surface. The removed portion of the damaged beam is about 300mm at the mid-span for all specimens. Prior to casting, the inner walls of mould were coated with lubricating oil to prevent adhesion with the hardening concrete. GPC was mixed in a pan mixer machine of 60kg capacity for about three minutes. At the end of this mixing, the alkaline activator solution (AAS) was added to the dry materials. Then mixing was continued for another four minutes till a uniform consistency was achieved.

Immediately after mixing, the fresh concrete was casted in three layers of equal thickness and each layer was thoroughly compacted. Specimens were demoulded after 24 hrs. The retrofitted beams were cured with subsequently air cured under ambient conditions in the laboratory for a period up to 28 days after casting. The Fig 2 shows the steps involved for the preparation of retrofitted specimen

TABLE.1 SPECIMEN DETAILS

Specimen ID RC5M-1 RC5M-2 RC5M-3 RC3M-1 RC3M-2 RC3M-3 GPC5M GPC3M RPPC1-C RPPC2-C RGPC-C

64

Type

Details 3.35% reinforcement, PPC beam retrofitted RPPC3 with 5M GPC 1.28% reinforcement, PPC beam retrofitted RPPC1 with 5M GPC 1.28% reinforcement, PPC beam retrofitted RPPC1 with 5M GPC 1.28% reinforcement, PPC beam retrofitted RPPC2 with 3M GPC 1.28% reinforcement, PPC beam retrofitted RPPC2 with 3M GPC 3.35% reinforcement, PPC beam retrofitted RPPC4 with 3M GPC 3.35% reinforcement, GPC beam retrofitted RGPC1 with 5M GPC 3.35% reinforcement, GPC beam retrofitted RGPC2 with 3M GPC RPPC1-C 3.35% reinforcement, PPC control beam RPPC2-C 1.28% reinforcement, PPC control beam RGPC-C 3.35% reinforcement, GPC control beam

(a)

(b) FIG: 2 RETROFITTING PROCEDURE (A) DAMAGED CONCRETE IS REMOVED AND MOULDS ARE PLACED (B) DAMAGED PORTION IS RETROFITTED WITH GPC.

International Journal of Material and Mechanical Engineering (IJMME) Volume 3 Issue3, August 2014

A photograph of test setup is shown in Fig 3. The beam specimen was mounted in a UTM of 100 tons capacity. The beam specimen was simply supported on reaction blocks mounted on a sturdy box section of length 1700mm placed on the bottom plate of the UTM. The beam was simply supported over a span of 1350mm, which is considered as the effective span.

The load was applied on two points each 225mm symmetrically away from centre of the beam towards the support through a load spreader. Two dial gauges of 0.01mm least count were used for measuring deflections under the loading points. Another dial gauge of same least count was used at mid span for measuring the respective deflection.

All the specimens were white washed in order to facilitate marking of cracks. The load was applied in increments of 2.5KN until the first crack was obtained.

Later, the load was applied in increments in 5KN. The deflection at mid span and under the load points were measured using dial gauges. The behaviour of the beam was observed carefully. All the measurements including deflections, strain values and crack widths were recorded at regular intervals of load until the beam failed. The failure mode of the beams was also recorded.

retrofitted RPPC beams. Thus from the comparison the retrofitted beam attains 80% strength of the control beam for RPPC beams. Comparison of load deflection characteristics of retrofitted RGPC and controlRGPC is shown in Fig 5. The load-deflection behavior of retrofitted RGPC beams are similar to control RGPC beams. It was observed that retrofitted RGPC beams perform better than retrofitted RPPC beams. Based on the analysis of results, Geopolymer concrete can be used for strengthening of reinforced concrete structures and structural components.Table 1 shows the ultimate load and ultimate deflection of RPPC beams with two different % of reinforcement, before and after retrofitting with GPC. It also lists the ultimate load and deflection of RGPC control and retrofitted beam with RGPC.

120 100 80

Load (Kn)

Test Procedure

www.ijm-me.org

60

RPPC retrofitted beam( 100 x 150 x1500mm)

40

RPPC control beam (100 x 150x1500mm)

20 0 0

5

10 15 Deflection mm

20

FIG: 4 COMPARISON OF MID-SPAN LOAD DEFORMATION CHARACTERISTICS OF RPPC CONTROL AND RETROFITTED BEAM (100 X 150 X1500MM HAVING 3.35% REINFORCEMENT)

FIG: 3 TEST SETUP

Load Deformation Characteristics The retrofitted beam specimens were tested under two point loading until failure. As the load increased, beam started to deflect and flexural cracks developed along the span of the beams .All the beams failed in the same pattern due to yielding of the tensile steel (primary tension failure) followed by crushing of concrete at the compression face (secondary compression failure). Fig 4 shows the comparison of load deflection characteristics of control RPPC and

FIG: 5 COMPARISON OF MID-SPAN LOAD DEFLECTION CHARACTERISTICS OF RGPC CONTROL AND RETROFITTED BEAM (100X150X1500MMHAVING 3.35% REINFORCEMENT)

65

www.ijm-me.org

International Journal of Material and Mechanical Engineering (IJMME) Volume 3 Issue 3, August 2014

FIG: 6 COMPARISON OF MID-SPAN LOAD DEFLECTION CHARACTERISTICS OF RPPC BEAM RETROFITTED WITH 3M AND 5M GPC

FIG: 7 ANSYS MODELING OF CONTROL BEAM (100 X 150 X 1500MM)

TABLE: 1 COMPARISON OF RETROFITTED AND CONTROL RPPC AND RGPC BEAMS

Specimen ID

% reinforcement

RC5M-1 RC3M-3 RPPC1-C RC5M-2 RC3M-1 RPPC2-C GPC5M-1 GPC3M-1 RGPC-C

3.35% 3.35% 3.35% 1.28% 1.28% 1.28% 3.35% 3.35% 3.35%

Ultimate loadKN 87.1 80 104.9 65.55 60.15 80 104.84 78.05 104.39

Ultimate deflection) mm 16.65 13.54 8.53 14.66 18 10.82 12.59 12 11.6

Finite Element Modelling For analytical study on flexural behaviour of reinforced beams, finite element method was adopted by using ANSYS. Solid 65 elements were used to model PPC concrete as well as GPC. The input parameters like modulus of elasticity and Poisson’s ratio for PPC and GPC are different. The rebar capability of this model was not considered. All reinforcements were modeled using Link 8- 3D spar element. Flexural behaviour of control beam and retrofitted beam was studied using ANSYS. The Fig 7 shows ANSYS modelling of control beam. Similarly the Fig 8 shows ANSYS modeling ofRPPC beam retrofitted with geopolymer concrete.

FIG: 8 ANSYS MODELING OF RETROFITTED BEAM (100 X150 X1500MM)

Retrofitted RPPC (100 x150x 1500mm) beam

Comparison Experimental and Analytical Results Load-Deformation Characteristics The analytical and experimental results showed good agreement. The load deformation characteristics of RPPC beam retrofitted with geopolymer concrete in experiment and Ansys is compared as shown in Fig 9.

66

FIG: 9 COMPARISON OF LOAD-DEFORMATION CHARACTERISTICS OF RETROFITTED RPPC(100 X150 X1500MM) BEAM EXPERIMENTALLY AND ANALYTICALLY.

International Journal of Material and Mechanical Engineering (IJMME) Volume 3 Issue3, August 2014

www.ijm-me.org

Crack Pattern and Failure Modes

deflection at the same load than the RPPC beams.

The flexural cracks initiated in the pure bending zone as expected. As the load increased existing cracks propagated and the new cracks are developed along the span. The flexural cracks gave way to inclined cracks due to the effect of shear force. The spacing of cracks varied along the span. The total number of the flexural cracks developed was almost same for all the beams, with small variation of 2%to 3%. In case of retrofitted beams initially only flexural cracks develops then to shear cracks, due to good bond no cracks developed at the interface of GPC and PPC.

The ultimate strength of GPC retrofitted RPPC beam of 100 x 150 x1500mm is nearly 80% of the ultimate strength of control beam.

A few cracks appeared in the flexural zones of the concrete at initial loads. Subsequently the cracks widened as the load increased. The cracks at the midspan opened widely near failure. At failure loads, the beams deflected significantly. The failure pattern of the beam specimens was found to be similar. The beams failed initially by yielding of the tensile steel followed by the crushing of concrete in the compression face. Since the retrofitted beams initially subjected to ultimate load, the flexure cracks appears early for retrofitted beams compared to control beams.

The comparison of analytical and experimental crack patterns of retrofitted RPPC beam is shown from Fig 10.

The flexural capacity of retrofitted beams increase with increase in tensile reinforcement.

The crack patterns of the retrofitted beams and control beams are similar. The crack first occurs at the tensile side i.e. flexural crack. Then flexural crack give way to inclined shear crack.

The 3D Ansys modeling is able to properly stimulate the nonlinear behaviour of retrofitted RPPC beam with GPC and control RPPC beam with reinforcements. The load deflection behaviour of retrofitted and control RPPC in Ansys shows good agreement with experimental results.

The failure mode and crack patterns of control and retrofitted RPPC beams predicted by ANSYS are in good agreement with experimental results.

The ultimate deflection value for retrofitted beams are higher compared to control specimen; this is because the retrofitted specimen has yielded reinforcement.

Based on the analysis of results, Geopolymer concrete can be used for strengthening of damaged RC structure.

ACKNOWLEDGMENT

(a)

This paper is being published with the permission of the Director, CSIR-SERC, Chennai. The cooperation and guidance received from the technical staff of Advanced Seismic Testing and Research Laboratory and Advanced Material Laboratory of CSIR-SERC are gratefully acknowledged.

REFERENCES

Amarnath, C., Menon D., and Sengupta, A.K.,”Handbook on (b) FIG: 10 COMPARISON OF CRACK PATTERNS OF RETROFITTED BEAM IN (A) ANSYS (B) EXPERIMENT

Conclusion Based on the experimental and analytical investigation following conclusions are made: The load deflection characteristics at the mid span of the RPPC beams and RGPC beams were found almost similar. Also, the RGPC beams showed slightly more

Seismic Retrofit of Buildings” (2008), Narosa Publishing House Pvt.Ltd, New Delhi.

Bansal, P.P., Kumar, M, and Kaushik,S.K.,”Effect of type of wire mesh on strength of beams retrofitted using Ferrocement Laminates”, National Building Materials and Construction, July 2008, pp.272-278.

Costantino Menna et al,” Use of geopolymers for composite external reinforcement of RC members”, Composites: part B 45 (2013)1667-1676

67

www.ijm-me.org

International Journal of Material and Mechanical Engineering (IJMME) Volume 3 Issue 3, August 2014

F. Pacheco-Torgal, Z. Abdollahnejad, S. Miraldo, S. Baklouti,

retrofitted reinforced concrete shear beams using carbon

Y. Ding, “An overview on the potential of geopolymers

fiber composites”, Electronic Journal of Structural

for concrete infrastructure rehabilitation”, Construction

Engineering, 4(2004).

Rangan. B. V, Hardjito, D, 2005, Development and properties

and Building Materials 36 (2012)1053-1058.

H.R.Ronagh, A.Eslami, “flexural retrofitting of RC buildings

of low calcium fly ash based geopolymer concrete.

using GFRP/CFRP- A comparative study”, Composites:

Research report GC-1, Faculty of Engineering, Curtin

part-B, 46 (2013) 188-196.

University of Technology, Perth, Australia

IS456 (2000), Indian code of practice for plain and reinforced concrete, Bureau of Indian standards, New Delhi.

Madheswaran C K, Ambily P S, Rajamane N P and Arun G,” Studies on Flexural behavior of reinforced geopolymer concrete

beams

with

lightweight

aggregates”,

investigation and analytical modeling of reinforced Geopolymer concrete beam, international journal of civil and structural engineering, vol 2, 2012.

Warner, R.F, B.V.Rangan, A.S Hall, K.A. Faulkes (1998),

International Journal of Civil and Structural Engineering,

Concrete

vol:4, No:3(2014), ISSN 0976-4399

Longman Australia Ltd.

R.santhakumar, E.Chandrasekaran, R.Dhanaraj,”Analysis of

68

Uma K, Anuradha R, Venkatasubramani R, experimental

Structures,

Melbourne,

Addison

Wesley