Description:F O R M 2

THE PATENTS ACT, 1970
(39 of 1970)

COMPLETE SPECIFICATION
(See section 10 and rule 13)

TITLE
COMPOSITE JACKETING MATERIAL FOR CONCRETE STRUCTURES AND METHOD OF APPLICATION THEREOF
INVENTORS:
KARINGAMANNA, Jayanarayanan, Indian Citizen
Department of Chemical Engineering and Materials Science
MADHAVAN, Mini K., Indian Citizen
JOSEPH, Lakshmi, Indian Citizen
Department of Civil Engineering,
Amrita School of Engineering, Coimbatore, Tamil Nadu, India 641 112

APPLICANT
AMRITA VISHWA VIDYAPEETHAM
Clappana P.O Amritapuri, Vallikavu, Kerala 690525, India

THE FOLLOWING SPECIFICATION PARTICULARLY DESCRIBES THE INVENTION AND THE MANNER IN WHICH IT IS TO BE PERFORMED:

COMPOSITE JACKETING MATERIAL FOR CONCRETE STRUCTURES AND METHOD OF APPLICATION THEREOF
CROSS-REFERENCES TO RELATED APPLICATION
[1] None.
FIELD OF INVENTION
[2] The present disclosure relates to a jacketing material for reinforcement of concrete structures, and in particular a composite jacketing material to be applied to concrete columns/structure for strengthening and retrofitting.
DESCRIPTION OF THE RELATED ART
[3] The repair and strengthening of damaged concrete structures are of immense importance in infrastructure development. The damaged and structurally inadequate buildings need to be rebuilt or strengthened to maintain safety requirements and structural integrity. However, due to the environmental impacts and high cost, demolition and rebuilding options of the existing structures may not be a viable option. Currently, fiber reinforced polymer (FRP) composites are used as a possible material for strengthening and retrofitting. The ease of installation, corrosion resistance, high strength to weight ratio and improved tensile strength are the most appealing attributes of FRPs which further qualifies those as materials of immense relevance in structural rehabilitation.
[4] For concrete retrofitting, natural fibers like coir, jute, sisal and flax etc. have also used since they have low density, low cost, moderate tensile and flexural properties with respect to the synthetic fiber counterparts. The natural fibers have an extraordinary capability in the retrofitting of concrete structures. Apart from FRP application fabric reinforcements are also widely used in fabric reinforced cementitious mortar which is a composite made up of a fiber mesh (or grid) bounded on a structural member by means of an inorganic matrix.In FRP composites, the thermoset polymer epoxy epoxy resin is a widely used matrix material. However, under exposure to severe environmental conditionsfor greater periods of time, epoxy tends to degrade and results in deterioration of various mechanical properties. Into the traditional fiber reinforced polymer composites when carbon nanotubes (CNTs) are incorporated it significantly improvestheir properties.However, at higher concentrations, Van der Waals forces between the individual nanotubes result in agglomeration and CNT bundling.
[5] Various publications have tried to address the problems encountered for strengthening and retrofitting of concrete structures. EPpublication0378232B1 discloses method for reinforcing concrete structure by attaching a long fibre sheet using an adhesive agent. EP publication 2398955B1 discloses a composite composition having carbon nanotube (CNT)-infused fibers dispersed in a matrix material. Kazemiet. alin “Effect of Modified Carbon Nanotubes Epoxy on the Mechanical Properties of Concrete Reinforced with FRP Sheets” discusses effects of adding the best percentage of nano-carbons to adhesive epoxy resin to the axial, shear and bending strengths in concrete samples. In “Performance of Concrete Confined with a Jute–Polyester Hybrid Fiber Reinforced Polymer Composite: A Novel Strengthening Technique”, Wahabet. al. usage of jute–polyester hybrid FRP composites for confining concrete columns. Irshidat et.al. discusses the viability of using carbon fiber reinforced epoxy composites modified with carbon nanotubes to strengthening reinforced concrete (RC) columns in “Strengthening RC Columns Using Carbon Fiber Reinforced Epoxy Composites Modified with Carbon Nanotubes”. In “Characterization and Evaluation of Mechanical Behavior of Epoxy-CNT-Bamboo Matrix Hybrid Composites” Thakur et.al. mentions a composite material made by using bamboo fiber reinforced in the epoxy epoxy resin with varying percentage of CNT. Mohan et.al studies MWCNT filled banana-jute-flax fiber reinforced composites in “Fabrication and Characterization of MWCNT Filled Hybrid Natural Fiber Composites”.
[6] Presently, there is a requirement of an efficient external confinement system in concrete structuresfor strengthening which is capable of increasing the loading bearing capacity, resisting external adverse effects such as harsh weather conditions, increased ductility and other mechanical properties which would prevent a catastrophic collapse of the structures in the event of disasters or due to wear and tear.
SUMMARY OF THE INVENTION
[7] The present subject matter relates to a composite jacketing material for concrete structures.
[8] In one embodiment of the present subject matter, a composite jacketing material as external confinement inconcrete for structural strengthening and retrofitting.The composition includes multi-walled carbon nanotubes (MWCNTs) functionalized with carboxylic acid (–COOH) as nanofiller, a two-part epoxy resinand hardener to form a resin mixture with the MWCNTs, wherein the weight percentage of MWCNTs in the epoxy resin mixture is 0.5% to 1.5% and sisal and basalt fibers as bidirectional woven plain fabric to form plurality of layers, wherein the fibers are infiltrated with the MWCNT incorporated epoxy resin mixture to form the composite. In some embodiments, the purity of the nanofilleris 97% or better.
[9] In various embodiments, the MWCNTs have an average length of 2–10 microns, outer diameter 5–20 nm or specific surface area of 250–270 m2/g, the sisal and basalt fibers are in the form of woven fabric of thickness 0.8mm to 1mm and density of basalt fibers is 2630 kg/m3 or the density of sisal fiber is 1580 kg/m3.
[10] In various embodiments, the sisal fibers are soaked in NaOH solution and dried at room temperature for 72hrs prior to forming the composite.
[11] In various embodiments, to form the resin mixture the MWCNTs are uniformly dispersed within the epoxy resinfor a period of 30 min using an ultrasonic probe sonicator and the epoxy resin mixture is cured at room temperature for 72hrs after infiltration on the fiber.
[12] In an embodiment, a method for application of a composite jacketing material as confinement inconcrete for structural strengthening and retrofitting. The method includes applying a layer of MWCNT incorporated epoxy resin mixture on clean surface of a concrete structures, wrapping a layer of fiber impregnated with the MWCNT incorporated epoxy resin mixture over the radial surface, removing the entrapped air using roller after placing a layer of fabric to provide proper epoxy resin impregnation between the layers, curing the fiber wrapped concrete structuresand wrapping successive layers of the fiber over the concrete structures to ensure proper bonding between the concrete and composite jacketing material. The method also includes the curing of the fibre wrapped concrete structures for 24hrs between successive layers. The method further includes wrapping havingoverlapping distance between successive layers of fiber either by 150mm or more, or at least by one-fourth of the circumference of the structure.
[13] This and other aspects are described herein.

BRIEF DESCRIPTION OF THE DRAWINGS
[14] The invention has other advantages and features, which will be more readily apparent from the following detailed description of the invention and the appended claims, when taken in conjunction with the accompanying drawings, in which:
[15] FIG. 1Aillustrates the multiscale composite jacketing material, according to an embodiment of the present subject matter.
[16] FIG. 1B illustrates the multiscale composite jacketing applied in multiple layers to a structure S, where d represents the overlap distance for the successive layers.
[17] FIG. 2illustrates the method for application of a multiscale composite jacketing material as confinement for concrete structures, according to an embodiment of the present subject matter.
[18] FIGS. 3A, 3B and 3Cillustrate the distribution of MWCNTs in epoxy with weight percentage of 0.5%, 1% and 1.5% respectively, according to an embodiment of the present subject matter.
[19] FIGS. 4A and 4B illustrate the tensile properties of epoxy with MWCNT composites, according to an embodiment of the present subject matter.
[20] FIG. 5illustrates theflexural strength of epoxy with MWCNT composites, according to an embodiment of the present subject matter.
[21] FIG. 6 illustrates the axial compressive behavior of FRP wrapping on concrete columns/structure, according to an embodiment of the present subject matter
[22] FIG. 7 illustrates stress-strain response of FRP wrapping on concrete columns/structure, according to an embodiment of the present subject matter.
[23] Referring to the figures, like numbers indicate like parts throughout the various views.
 
DETAILED DESCRIPTION OF THE EMBODIMENTS
[25] While the invention has been disclosed with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt to a particular situation or material to the teachings of the invention without departing from its scope.
[26] Throughout the specification and claims, the following terms take the meanings explicitly associated herein unless the context clearly dictates otherwise. The meaning of “a”, “an”, and “the” include plural references. The meaning of “in” includes “in” and “on.” Referring to the drawings, like numbers indicate like parts throughout the views. Additionally, a reference to the singular includes a reference to the plural unless otherwise stated or inconsistent with the disclosure herein.
[27] The present subject matter describesa composite jacketing material as external confinement for concrete structural strengthening and retrofitting. A method of applying the jacketing material is also disclosed. The jacketing includes a fabric made of sisal or basalt fibers, infiltrated by anepoxy resin having multi-walled carbon nanotubes (MWCNTs) as reinforcement. The composite jacketing material, when applied for confinement of concrete structures, considerably increases the load bearing ability of the structures. Significant improvement may be observed in strength, ductility index as well as resistance to externally applied loads.
[28] The multiscale composite jacketing material 100in various embodiments is composed of a fabric reinforcement105infiltrated bya two-part epoxy resin 102reinforced withmulti-walled carbon nanotubes (MWCNTs) 104 as nanofiller, as further illustrated with reference to FIG. 1A and 1B. FIG. 1A illustrates one ply of fabric infiltrated by the resin, showing the presence of carbon nanotubes or nanofiller within the resin. The MWCNTs104 may in some embodiments befunctionalized withcarboxylic acid (–COOH). In some embodiments, the nanofillerisof purity 97% or better. The weight percentage of MWCNTs 104in the epoxy resin102mixture in various embodiments is in the rangeof 0.5% to 1.5%. The fabric 105 in various embodiments may be made of sisal or basalt fibers106.In various embodiments, multiple layers of sisal and basalt fibers may be used, as illustrated with reference to FIG. 1B, with an overlap distance “d” between different layers of fabric 105. In some embodiments, alternate layers of the fabric 105 may have sisal and basalt fibers. In some embodiments, every two layers 105may be sisal, followed by two layers of basalt fabric. In various embodiments, the fabric may be a bidirectional plain woven fabric. In various embodiments, in each layer the fabric may be infiltrated with the MWCNT incorporated epoxy resin mixture and cured to form the composite.
[29] In various embodiments, the MWCNTs 104utilized to form the epoxy resin mixture may have an average length of 2–10 microns. In various embodiments, theMWCNTs may have outer diameter in the range 5–20 nm. In various embodiments, the MWCNTs may have specific surface area of 250–270 m2/g. In various embodiments, the resin may be two-part epoxy resin comprisingepoxy resin (Part A) and a hardener (Part B) which are blended in a proportion recommended by the manufacturer. The MWCNTs 104may be uniformly dispersed in the epoxy resin for a period of 30 minutes using an ultrasonic probe sonicator. In one embodiment, the optimum content of MWCNTs104as nanofillerin the epoxy resin102is 1wt %. The prepared epoxy resin mixture is cured at room temperature for a period of 72 hours prior to applicationon to the structure.
[30] The sisal orbasalt fiber fabrics 105having sisal or basalt fibers 106in various embodiments, may be in the form of plain woven fabric having thickness 0.8mm to 1mm. In some embodiments, the density of basalt fiber of 380 GSM is 2630 kg/m3 while density of sisal fiber with 300 GSM is 1580 kg/m3. In some embodiments, plain carbon fiber fabric of 200 GSM with density 1380 kg/m3 and thickness 0.45 mm may also be utilized for the preparation of composite jacketing material. The sisal fibers106 in some embodiments may be soaked in NaOH solution for 72 hoursand dried at room temperature prior to forming the composite. This step is configured to facilitate an improvement in surface roughness of the fibers, resulting in increased mechanical interlocking with the resin matrix.
[31] In various embodiments, the invention discloses a method 200for application of the composite jacketing material on concrete structures, with reference to FIG. 2. In a first step 202 of the method, the MWCNT incorporated epoxy resin mixture is applied on a cleaned surface of concrete structures. Then, a layer of fabric impregnated with the epoxy resin mixture is wrapped radially over the concrete structure as mentioned in step 204. In various embodiments of the method, the successive fabric layers may be of sisal fiber impregnated with epoxy mixture and basalt fiber impregnated with epoxy mixture, alternately. In some embodiments of the method step 204, every 2 layers of the jacketing may be of sisal and basalt, alternately. In the third step 206, another layer of epoxy resin mixture is applied over the fabric layerto provide better impregnation and continuity of the epoxy resinmatrix between successive layers of fabric. The entrapped air present after application of the epoxy resin mixture is removed using a roller on the concrete surface in step 206. The fabric wrapped concrete structure is then allowed to cure for 24 hours as provided in step 208. Successive layers of fabric are wrapped onto the concrete structure as provided in step 210with overlap therebetween. In various embodiments of the method, the overlapping distance between successive layers of fabric is 150mm or more. In alternative embodiments, the extent of overlap may be at least by one-fourth of the circumference of the structure.Proper bonding between the concrete structure and fabric layers is achieved due to the adhesive properties of the prepared epoxy resin mixture.
[32] The invention has multiple advantages as set forth here. The huge interfacial area and interaction provides mechanical interlocking between the MWCNT and epoxy resin chains and thereby results in an anchoring effect to resist deformation. For epoxy resin hybrid composites with two layers each of basalt and sisal fibers along with 1wt. % of MWCNT, provides improvement of about 168% in the tensile strength and an 89% enhancement in Young's modulus of the laminate. The improvement in tensile strength and modulus may be assigned to the enhanced load bearing capacity of epoxy incorporated with MWCNTs.
EXAMPLES
[33] EXAMPLE 1: Specimen Configurations Tested
[34] Cylinders of 300 mm height and 150 mm inside diameter was fixed as base concrete specimens. 60 cylindrical concrete specimens were cast and tested. Specimens were classified mainly as the control specimens (unconfined specimens), single fiber FRP confined specimens and specimens confined with a hybrid FRP. The test incorporated multiple hybrid configurations consisting of various inner and outer FRP confinements. The nomenclature used for the test specimens are provided in Table 1. The cast concrete column specimens were tested in axial compression using a 2000kN capacity compression testing machine. High strength steel plates of 10 mm thickness were kept over the top and bottom sides of the test specimens in order to ensure uniform application of load on the concrete core. During the process of testing 0.2 mm/ min constant displacement was applied on the specimens. Since a high axial displacement is expected, 1 mm/min constant loading rate was kept. Linear variable differential transducers (LVDTs) with a capacity of 50 mm were used as the instrumentation to record axial strains on the concrete specimens.
TABLE 1: Test specimen details
Group Specimen Core specimen
material CNT % Number of sisal
Layer (Inside) Number of basalt
Layer (Outside) Total fiber
layer No. of
specimens

A E Epoxy 0 0 0 3
EC0.5 Epoxy 0.5 0 0 3
EC1 Epoxy 1 0 0 3
EC1.5 Epoxy 1.5 0 0 3

B EC0S2B0 Epoxy 0 2 0 2 3
EC0S2B2 Epoxy 0 2 2 4 3
EC1S2B0 Epoxy 1 2 0 2 3
EC1S2B2 Epoxy 1 2 2 4 3

C CS Concrete 0 0 0 3
C-EC0S2 Concrete 0 2 0 2 3
C-EC0S2B1 Concrete 0 2 1 3 3
C-EC0S2B2 Concrete 0 2 2 4 3
C-EC0S2B3 Concrete 0 2 3 5 3

D C-EC0.5S2 Concrete 0.5 2 0 2 3
C-EC0.5S2B1 Concrete 0.5 2 1 3 3
C-EC0.5S2B2 Concrete 0.5 2 2 4 3
C-EC0.5S2B3 Concrete 0.5 2 3 5 3

E C-EC1S2 Concrete 1 2 0 2 3
C-EC1S2B1 Concrete 1 2 1 3 3
C-EC1S2B2 Concrete 1 2 2 4 3
C-EC1S2B3 Concrete 1 2 3 5 3

F C-EC1.5S2 Concrete 1.5 2 0 2 3
C-EC1.5S2B1 Concrete 1.5 2 1 3 3
C-EC1.5S2B2 Concrete 1.5 2 2 4 3
C-EC1.5S2B3 Concrete 1.5 2 3 5 3

[35] EXAMPLE 2: High-resolution transmission electron microscope (HRTEM) analysis of epoxy nanocomposites
[36] TEM is the most appropriate methodology adopted to analyze the alignment, morphology distribution and particle size of the nanofiller material in the base polymer.FIGs.3A, 3B and 3C demonstrate the TEM images corresponding to MWCNT epoxy resin mixture with MWCNT weight percentage of 0.5%, 1% and 1.5% respectively. In base polymer, the nanoscale dispersion of MWCNT was clearly visible from the TEM images. Presence of nano particle clusters was found in certain spaces even after ultrasonication. The formation of clusters of MWCNT diminishes the interfacial region which in turn may result in the reduction in chemical and physical bonding between epoxy resin and MWCNT. FIG. 3A depicts the dispersion of 0.5wt. % MWCNT in the epoxy resin mixture. The distribution of MWCNT is uniform with 1–10 μm average length and 5–10 nm average diameter. FIG. 3B portrays the epoxy resin mixture morphology corresponding to 1wt. % MWCNT and at this wt.% the MWCNT nanoparticles were found to be well distributed within the epoxy. The multifarious entanglement of epoxy resin with MWCNTs can prompt better exchange of applied load which further prevents crack propagation within composites. A combination of MWCNT dispersion and agglomeration was noticed in the TEM images corresponding to 1.5wt. % CNT. The agglomeration was pronounced at higher MWCNT content as evidenced from FIG. 3C leading to lower inter-particle distance and weak mechanical properties.
[37] EXAMPLE 3: Tensile properties of epoxy resin composites
[38] The tensile properties of epoxy specimens were assessed as per ASTM D3039 using INSTRON 502 Universal testing machine with a crosshead speed of 1 mm/min. The length, width and thickness of the epoxy specimens were 100mm, 10mm, and 3mm respectively. The results are presented in FIGs. 4A and 4B and Table 2 and it was observed that with the addition of MWCNT, there is significant enhancement in tensile properties. With 1wt. % of MWCNT addition, the epoxy resin mixture exhibited a 65% improvement in tensile strength and 41% improvement in Young's modulus with respect to neat epoxy. The huge interfacial area and interaction provides mechanical interlocking between the MWCNT and epoxy resin chains and thereby results in an anchoring effect. For epoxy resin hybrid composites with two layers each of basalt and sisal fibers along with 1wt. % of MWCNT, improvement of about 168% in the tensile strength and an 89% enhancement in Young's modulus was noticed. The improvement in tensile strength and modulus may be assigned to the enhanced load bearing capacity of epoxy incorporated with MWCNTs. The inter-particle distance between MWCNT diminishes at its higher percentages in epoxy and further it reduces the interfacial interaction between epoxy and MWCNT as well as the fibers. The pronounced agglomeration at 1.5wt. % leads to lower inter-particle distance and reduction in the mechanical properties.
TABLE 2: Tensile Properties of Epoxy Resin and Hybrid Composites
Sample Tensile strength (MPa) Young's modulus (GPa) Elongation (%)
E 37 ± 0.8 1.8 ± 0.02 7.3 ± 0.4
EC0.5 44 ± 0.8 1.98 ± 0.03 8.5 ± 0.2
EC1 61 ± 0.1 2.56 ± 0.02 10.2 ± 0.1
EC1.5 48 ± 0.7 2.20 ± 0.04 8.4 ± 0.1
EC0S2B0 69 ± 0.8 2.88 ± 0.03 10.2 ± 0.2
EC0S2B2 72 ± 1.8 2.96 ± 0.80 10.7 ± 0.8
EC1S2B0 83 ± 2.0 3.18 ± 0.80 11.5 ± 0.6
EC1S2B2 99 ± 2.1 3.44 ± 0.80 10.3 ± 0.9

[39] EXAMPLE 4: Fracture toughness of epoxy composites
[40] Single-edge notched bending (SENB) test was adopted to evaluate the fracture toughness of the epoxy composite specimens in a universal testing machine (UTM) with 1 mm/min constant crosshead displacement rate. The stress intensity produced due to the residual stresses is predicted using the linear-elastic fracture toughness of material (KIC) while the measure of energy dissipated during fracture per unit fracture surface area is predicted by plastic-elastic fracture toughness (GIC). From Table 3 it was observed that with the addition of hybrid fibers there is a prominent improvement in the fracture toughness values compared with neat epoxy resin. At the crack tip, the delamination growth is resisted by the presence of hybrid fibers. The incorporation of MWCNT enhances bridging effect at the crack tip and thus resists crack propagation considerably. For higher weight percentages of MWCNTs, fracture toughness value declines due to the agglomeration of the nanofiller within the epoxy matrix. The improvement in the strength and fracture toughness characteristics can be assigned to uniform dispersion of nanoparticles. Epoxy exhibited an increase in the failure load when filled with MWCNTs, the same was visible in the case of EC0.5 and EC1. These complex polymer chain networks undergo high strain and could reduce the crack propagation providing a large energy release rate. As seen in EC1.5, at higher MWCNT weight percentage, there was a decrease in values of fracture toughness which can be attributed to the aggregation of the nanofiller. It can be concluded that uniform dispersion of nanoparticles has a major contributionin deciding the performance of a reinforced polymer system.
TABLE 3: Fracture Toughness Properties of Epoxy and Hybrid Composites
Sample KIC (MPa.m1/2) GIC (kJ/m2)
E 1.7 ± 0.2 1.7 ± 0.2
EC0.5 3.0 ± 0.1 4.5 ± 0.3
EC1 4.0 ± 0.2 6.2 ± 0.4
EC1.5 3.4 ± 0.3 5.2 ± 0.1
EC0S2B0 3.4 ± 0.1 4.0 ± 0.1
EC0S2B2 4.5 ± 0.8 6.8 ± 0.6
EC1S2B0 3.8 ± 0.7 4.5 ± 0.6
EC1S2B2 5.6 ± 0.8 9.2 ± 0.8

[41] EXAMPLE 5: Flexural properties of epoxy resin composites
[42] The flexural tests were carried out as per ASTM D790 in a 3-point bending mode using UTM at 1.25 mm/min crosshead speed. The flexural modulus and strength of the various composites were assessed as shown in FIG. 5. For the neat epoxy resin, the flexural strength was found to be 100MPa whereas that of the composite with 1wt % MWCNT manifested 160 MPa. The presence of MWCNTs enables the epoxy chains to resist elevated bending loads due to the anchoring effect. The maximum increase in flexural strength was exhibited with 1wt. % addition of MWCNT. For epoxy hybrid composites with two layers of basalt and sisal fibers each, and 1wt. % of MWCNT, there was an increment of about 120% in the flexural strength. However, there was a decline in flexural properties beyond 1wt. % addition of MWCNT due to the reduction in the free volume space leading to the impeded mobility of epoxy chains.
[43] EXAMPLE 6: Dynamic mechanical analysis (DMA) of epoxy resin composites
[44] The DMA was carried out on epoxy composites rectangular samples of 2mm thickness using PerkinElmer DMA800 in three-point bending mode in the temperature range of 25–160 C at a heating rate of 5 C/min at a fixed frequency of 1 Hz as per ASTM D 5023. Elastic response of the material can be estimated from storage modulus and it is observed that the composite with 1wt. % loading of MWCNT exhibits exemplary storage modulus up to 70 C. The rigidity and thereby the binding capability of nano modified epoxy resin mixture can be considered to be superior as the storage modulus in the three-point bending mode can be taken as a relative measure of the flexural strength of the composite. Further, the dip in storage modulus from a plateau region to a steep slope region with a characteristic shoulder occurs at a higher temperature in the case of EC1. The sharp drop in storage modulus occurs at the glass transition temperature (Tg) of epoxy is due to the segmental mobility of polymer chains. The mobility of the polymer chains is hindered by the dispersion of nanofiller elevating the mechanical properties of the nano modified epoxy. The peak value in loss modulus curves is observable at the glass transition temperature, beyond which it drops. The higher loss modulus presented by EC1 is due to the superlative energy dissipation characteristics and better interfacial adhesion prevalent between the MWCNT and epoxy macromolecules. Furthermore, a shift in the glass transition towards the higher temperature was manifested with increase in MWCNT content in epoxy. The shortening and broadening of the tan delta peak of EC1 is a testimony of the immobilization of the long chain polymer molecules as they are anchored onto the MWCNTs. The broadening of the peak aids the energy absorption during dynamic loading. The Tg value obtained from the tan delta peak is highest for EC1, followed by EC0.5.
[45] EXAMPLE 7: Effect of epoxy resinmixture withMWCNTascomposite jacketingmaterialfor concrete
[46] The specimens in Group C, D, E and F were used to investigate the confinement effect due to the percentage variation of MWCNT on the ductility and load-carrying capacity of cylinders confined with different types of composite jacketing. Epoxy resin-MWCNT nano-composites containing 0.5, 1 and 1.5wt. % of MWCNT were prepared and applied in between the fiber layers as adhesive.
[47] Axial compressive behaviorof composite jacketingmaterialfor concrete
[48] In Table 4 the results of the axial compression test for specimens confined with different FRP's for different percentage variation of CNT are presented. f'co indicates the unconfined concrete strength and f'ccisthat of the FRP confined concrete. In the case of wrapped concrete the confinement effectiveness is represented by f'cc/f'co. The axial strain for unconfined and composite strengthened specimens were represented by εco and εcc respectively. From the test results a significant improvement in load carrying capacity by the jacketing of plain concrete cylinders with FRP was evident.
[49] The greatest improvement in axial load carrying capacity was observed for 1wt. % of MWCNT incorporated composite wrapped specimens followed by 1.5wt. % as presented in FIG. 6. The confinement effectiveness for 1.5,1,0.5 wt.% of MWCNT modified epoxy resin composite wrapped specimens and neat epoxy wrapped specimens are 1.71, 1.90, 1.62 and 1.45 respectively with respect to plain concrete for 5 layers of hybrid wrapping. The effect of confinement offered by the MWCNT incorporation was the major reason for improved axial load carrying capacity. There is also a pronounced improvement in the load carrying capacity of hybrid sisal and basalt fiber composite wrapped concrete cylinders. Individual sisal fiber confinement exhibited an increase in load carrying capacity significantly but when compared, hybrid composite jacketing performed better. This is due to the synergetic effect offered by the hybrid fibers to the structure's improved load bearing capacity.
TABLE 4: Compression Test Results of CNT Modified FRP Confined Specimens
No. Specimen Comp. Strength (MPa)
fccor fco Strength Increase Effectiveness of Confinement
fcc/fco Axial Comp. Strain
cc or co Modulus of Elasticity
(GPa)
1 CS 14.29 - - 0.36 9.40
2 C-EC0S2 16.89 18.18 1.18 1.06 10.10
3 C-EC0S2B1 18.84 31.82 1.32 1.23 10.20
4 C-EC0S2B2 20.79 45.45 1.45 1.41 10.40
5 C-EC0S2B3 23.39 63.64 1.64 1.45 10.60
6 C-EC0.5S2 18.19 27.27 1.27 1.32 10.20
7 C-EC0.5S2B1 21.44 50.00 1.50 1.53 10.60
8 C-EC0.5S2B2 25.33 77.27 1.77 1.54 10.90
9 C-EC0.5S2B3 27.93 95.45 1.95 1.62 11.20
10 C-EC1S2 20.79 45.45 1.45 1.50 10.30
11 C-EC1S2B1 25.33 77.27 1.77 1.56 10.80
12 C-EC1S2B2 27.28 90.91 1.91 1.64 11.10
13 C-EC1S2B3 30.53 113.64 2.14 1.90 11.60
14 C-EC1.5S2 18.84 31.82 1.32 1.45 10.20
15 C-EC1.5S2B1 20.79 45.45 1.45 1.41 10.30
16 C-EC1.5S2B2 25.98 81.82 1.82 1.48 10.90
17 C-EC1.5S2B3 28.58 100.00 2.00 1.71 11.40

[50] Stress-strain responseof composite jacketing material for concrete
[51] While the plain concrete specimens exhibited a single linear regime in the stress-strain curve, the composite confined specimens manifested different regimes. The initial region of the curve exhibited almost a similar behavior as that of unconfined specimens. In the first region, due to insignificant lateral deformation of core, the effect of FRP jacketing is not appreciable. A transition zone is developed where the micro-cracks are observed, when applied stress reaches the ultimate compressive strength. Eventually, the effect of confinement was activated in the next stage of the stress-strain curve on reaching the peak compressive strength. Beyond that, with reduced slope a linear trend was observed. Thus, the last two stages of the curve exhibited superior confinement effect due to the presence of MWCNT in the epoxy matrix. These two stages usually govern the ultimate properties of the concrete and the MWCNT incorporated composites. Control specimens exhibit failures at the end of the initial stage itself due to its brittle nature. On the contrary, MWCNT incorporated composite confined specimens after yielding shows ductile mode of failure. Further studies were carried out for different weight percentages of MWCNT incorporated composite jacketing and upon analysis of test results it was clear that 1% of MWCNT incorporated composite wrapped specimens exhibited superiorductile and yielding properties. An enhancement in axial compressive strength and strain was observed with increase in composite layers.
[52] Ductile behavior and energy absorptionof composite jacketing material for concrete
[53] An increase in efficiency of confinement leads to increased ductility which in turn elevates the energy absorption without catastrophic failure. The ductility index is used as the measure of the ductility which is defined as the ratio of fracture energy of composite confined concrete to plain concrete. The ductility and energy absorption values for different confined specimens are given in Table 5. It is evident that composite confinement increases the ductility characteristics to a greater extent. Due to monolithic compressive behavior, the specimen C-EC1S2B3 recordedan energy absorption value of 39.48 MPa, showing an increase of about 87% and ductility index value of 7.35 relative to the control specimen. It was noticed that MWCNT modified composite confinement exhibited an increase from 68% to 87% in their energy absorption values relative to control specimen and in non-CNT incorporated fiber confinement the increased energy absorption is due to the contribution from composite-fiber confinement wraps. Conclusions were made that apart from compressive strength improvement, composite-fiberwrapping improved the fracture energy as well as ductility of the confined concrete specimens.

TABLE 5: Energy Ductility Index of Different Layer of CNT Modified FRPConfined Specimens

No. Specimen Energy Absorbed (MPa) Energy Ductility Index
1 CS 5.37 1
2 C-EC0S2 11.86 2.07
3 C-EC0S2B1 16.05 2.83
4 C-EC0S2B2 21.60 3.85
5 C-EC0S2B3 26.15 4.75
6 C-EC0.5S2 16.41 2.98
7 C-EC0.5S2B1 23.57 4.32
8 C-EC0.5S2B2 29.10 5.35
9 C-EC0.5S2B3 34.52 6.36
10 C-EC1S2 22.02 4.03
11 C-EC1S2B1 27.85 5.11
12 C-EC1S2B2 33.50 6.17
13 C-EC1S2B3 39.48 7.29
14 C-EC1.5S2 19.14 3.50
15 C-EC1.5S2B1 22.66 3.96
16 C-EC1.5S2B2 28.21 5.17
17 C-EC1.5S2B3 37.95 7.01

[54] EXAMPLE 8: Effect of different types of fiberson composite jacketing material for concrete
[55] The specimens with different types of fiber confinement were adopted to analyze the influence of different fiber systems on the ductility and load-carrying capacity of confined specimens with composite-fiber jackets. The various specimens considered are sisal fiber reinforced polymer (SFRP) wrapped with two layers of FRP confinement, basalt fiber reinforced polymer (BFRP) wrapped specimen with two layers of FRP confinement, hybrid sisal-basalt fiber reinforced polymer (HSBFRP) wrapped specimen with four layers of FRP confinement with two layers sisal and basalt fiber layers each, carbon fiber reinforced polymer (CFRP) wrapped specimen with single layer of carbon fiber confinement.
[56] Axial compressive behaviorof composite jacketing material for concrete with fiber wrapping
[57] The results of axial compression tests conducted on various column specimens jacketed with different types of fiber systems are presented in Table 6. The highest load carrying capacity was exhibited by HSBFRP specimens followed by a single layer of CFRP wrapped specimens. The confining pressure effect offered by modified FRP around the unconfined specimens was found to be the reason for enhanced axial load carrying capacity. From the listed FRP types, both CFRP and HSBFRP composite jacketing exhibited better performance in terms of axial load carrying capacity. Even the individual BFRP and SFRP confinement exhibited satisfying property improvement. HSBFRP composite wrapping performed better when compared with individual basalt, sisal and carbon confinement. The strength enhancement is due to the synergetic impact of both the fibers in improving the load bearing capacity of the specimens. A significant improvement in ductile performance was evidenced in all specimens with FRP wraps.
TABLE 6: Compression Test Results of Different FRPSystems
No. Specimen FRP Compressive strength (MPa)
(f'cc or f'co) Strength enhancement
% Confinement effectiveness
f'cc/f'co Axial compressive
strain (εcc or εco) Modulus of Elasticity (GPa)
1 CS 14.29 - 0.36 9.40
2 C-EC1S2 SFRP 20.79 45.45 1.45 1.50 10.30
3 C-EC1B2 BSRP 24.04 68.18 1.68 1.56 10.80
4 C-EC1Ca1 CFRP 26.63 86.36 1.86 1.58 10.94
5 C-EC1S2B2 HSBFRP 27.28 90.91 1.91 1.64 11.10

[58] Stress- strain response of composite jacketing material for concrete with fiber wrapping
[59] The axial compressive stress versus axial strain observed for specimens jacketed with different fiber systems is shown in FIG. 7. The stress-strain curve exhibited different regimes in the case of confined specimens. When control specimens are considered, they tend to fail during the end of the initial stage due to the brittle nature of control specimens. FRP confined specimens exhibited ductile nature i.e., failure occurs after FRP yielding. The addition of natural fiber has exhibited sensible enhancement in the ductile nature of confined specimens. From Table 7 it was clear that when compared, the structural properties particularly ductile behavior was commendable when confined with HSBFRP. The stress-strain plot for HSBFRP confined specimens exhibited similar trends as that of individual sisal and basalt FRP confined specimens. It may be noted that during the first stage,HSBFRP confinement has less impact due to the insignificant deformations concentrating in the concrete core. Once the ultimate compressive strength is reached in case of unconfined columns, a transitional zone may be noted along with development of numerous micro-cracks. While in case of confined specimens at this stage the confinement effect offered by HSBFRP laminate will be completely activated. The second stage was found to be dominated by the combined properties offered by FRP and concrete. It was noticed that the inner fiber sheet possesses lower elongation properties and they tend to rupture first and the outer basalt layer survives for a long period in case of hybrid systems. This may be due to the dominance offered by basalt FRP as it could contain greater rupture strain. Similar studies were conducted by Rousakis on the performance of hybrid FRP systems. Major observations were made that during the failure process a significant drop in load carrying capacity was noticed after the inner sisal sheets werefractured and energy was released but similar energy was found to be absorbed by the fiber sheets and further enabledthe specimens to have a ductile failure. It was clear that HSBFRP and CFRP wrapped specimens survived more in the second and final stage exhibiting their better ductile and yielding properties. Thus, reducing the probability of catastrophic failure.

TABLE 7: Energy Ductility Index of Concrete Strengthened with Different FRPSystems
Sl. No. Specimen Energy absorbed (MPa) Energy ductility index
1 CS 5.37 1
2 C-EC1S2 22.02 4.10
3 C-EC1B2 27.85 5.18
4 C-EC1Ca1 31.23 5.81
5 C-EC1S2B2 33.50 6.24

[60] Ductile behavior and energy absorption of composite jacketing material for concrete with fiber wrapping
[61] The energy absorption and ductility index values corresponding to different FRP jacketed specimens are given in Table 7. A significant enhancement in fracture energy was observed in HSBFRP specimens compared to control specimens along with enhancement inductile behavior and energy absorption property. The control specimen exhibited a moderate energy absorption value and was evident that FRP confinement ramps up the ductility characteristics of the unconfined cylinders. The HSBFRP specimens exhibited a monolithic compressive behavior and recorded an energy absorption value of 33.50 MPa, with an increase of about 523% with respect to the unconfined ones, and ductility index value of 6.24 when compared. At the same time the CFRP specimen recorded an energy absorption value of 31.23 MPa, showing increases of about 481% and ductility index value of 5.81. This enhancement was found to be due to the FRP modifications. It was noticed that sisal FRP confinement exhibited an increase in their energy absorption when compared with that of control specimens by 310% and the impact of the same was visible in HSBFRP confined specimens too. Thus, conclusions may be made that HSBFRP composite wrapping could improve the fracture energy and ductility property of confined concrete columns and thereby exhibiting an excellent solution for systems lacking internal reinforcement
[62] A composite jacketing material with MWCNTs dispersed in epoxy resin has several advantages over prior art particularly for strengthening concrete structures. The load bearing ability in the axial direction of the structure could be remarkably improved by fiber wrapping as evidenced from the compression test results. Further, a pronounced improvement in ductility characteristics, fracture energy and axial strain could also be accomplished.The usage of 1wt. % MWCNT in epoxy resin facilitatesmaximum improvement in mechanical properties for nano and multiscale composites. With an enhancement of 60% for epoxy resin composites and 120% for epoxy fiber multi-scale composites containing 1wt. % of MWCNT for flexural properties.Additionally the usage of sisal and basalt fiber sheets for confinement of concrete structures allows increase in the straining capacity and compressive strength of MWCNTmodified epoxy resin composites.
[63] Further, in confined concrete the ductility index and fracture energy for concrete structures improves with hybrid confinement and they significantly varied with the quantity of fiber layers and MWCNT modified epoxy resin.The composite jacketing material also assists in resisting the externally applied loads after a significant period of ultimate loading and thereby avoiding catastrophic failure to an extent of the concrete structures. The composite jacketing material facilitates repair and retrofitting of concrete structures and may be used for structures in seismic prone zones where the structures require greater ductility and strength properties.
[64] Although the detailed description contains many specifics, these should not be construed as limiting the scope of the invention but merely as illustrating different examples and aspects of the invention. It should be appreciated that the scope of the invention includes other embodiments not discussed herein. Various other modifications, changes and variations which will be apparent to those skilled in the art may be made in the arrangement, operation and details of the system and method of the present invention disclosed herein without departing from the spirit and scope of the invention as described here, and as delineated in the claims appended hereto.
, Claims:WE CLAIM:
1. A composite jacketing material (100) as external confinement inconcrete for structural strengthening and retrofitting, the composition (100) comprising:
multi-walled carbon nanotubes (MWCNTs) (104) functionalized with carboxylic acid (–COOH) as nanofiller;
a two-part epoxy resin(102) to form a epoxy resin-hardener mixture with the MWCNTs, wherein the weight percentage of MWCNTs in the epoxy resin mixture is 0.5% to 1.5%; and
sisal or basalt fibres (106) as bidirectional woven plain fabric (105) to form a plurality of layers, wherein the fibresare infiltrated with the MWCNT incorporated epoxy resin mixture to form the composite.

2. The composite material as claimed in claim 1, wherein the purity of the nanofiller comprises 97% or better.

3. The composite (100) as claimed in claim 1, wherein the MWCNTs (104) have an average length of 2–10 microns, outer diameter 5–20 nm or specific surface area of 250–270 m2/g.

4. The composite (100) as claimed in claim 1, wherein the sisal or basalt fibres (106) are in the form of woven fabric (105) of thickness 0.8mm to 1mm.

5. The composite (100) as claimed in claim 1, wherein density of basalt fibresis 2630 kg/m3or the density of sisal fibre is 1580 kg/m3.

6. The composite (100) as claimed in claim 1, wherein the sisal fibres (106) are soaked in NaOH solution and dried at room temperature for 72hrs prior to forming the composite.

7. The composite (100) as claimed in claim 7, wherein the epoxy resin mixture is cured at room temperature for 72hrs after infiltration on the fibers.

8. A method (200) for application of a composite jacketing material as external confinement in concrete for structural strengthening and retrofitting, the method (200) comprising:
applying (202) a layer of MWCNT incorporated epoxy resin mixture on clean surface of a concrete structures, wherein the epoxy resin mixture is prepared with MWCNTs in two-part epoxy resin and hardener with weight percentage of MWCNTs in the epoxy resin mixture in the range 0.5% to 1.5%;
wrapping(204) a layer of fibre impregnated with the epoxy resin mixture over the radial surface, wherein the fibre includes sisal and basalt as bidirectional woven plain fabric;
removing(206) the entrapped air using roller after placing a layer of fibre to provide proper epoxy resinimpregnation between the layers;
curing(208) of the fibre wrapped concrete structures; and
wrapping(210) successive layers of the fibre over the concrete structures to ensure properbonding between the concrete and composite jacketing material.

9. The method (200) as claimed in claim 8, comprising curing the fibre wrapped concrete structures for 24hrs between successive layers.

10. The method (200) as claimed in claim 8, wherein the wrapping comprises overlappingsuccessive layers of fibre either by 150mm or more, or at least by one-fourth of the circumference of the structure.

11. The method (100) as claimed in claim 8, comprising prior to applying (202), forming the epoxy resin mixture by dispersing the MWCNTs (104) within the epoxy resin (102) for a period of 30 min using an ultrasonic probe sonicator.

Sd.- Dr V. SHANKAR
IN/PA-1733
For and on behalf of the Applicants