Environmental awareness motivates researchers worldwide to perform studies of natural fibre reinforced polymer composites, as they come with many advantages and are primarily sustainable. The present study aims at evaluating the mechanical characteristics of natural woven jute fibre reinforced polymer (FRP) composite subjected to three different pretreatments, alkali, benzyl chloride, and lastly heat treatment. It was concluded that heat treatment is one of the most suitable treatment methods for enhancing mechanical properties of jute FRP. Durability studies on Jute FRP pertaining to some common environmental conditions were also carried out such as effect of normal water and thermal aging on the tensile strength of jute FRP followed by fire flow test. The heat treated woven jute FRP composites were subsequently used for flexural strengthening of reinforced concrete beams in full and strip wrapping configurations. The study includes the effect of flexural strengthening provided by woven jute FRP, study of different failure modes, load deflection behavior, effect on the first crack load, and ultimate flexural strength of concrete beams strengthened using woven jute FRP subjected to bending loads. The study concludes that woven jute FRP is a suitable material which can be used for flexural upgradation of reinforced concrete beams.
A structure is designed for a specific life span, and depending on the nature of the structure, its purpose, and its usability, its design life varies. For a domestic building, this design life could be thirty to forty years, whereas for a public building, it could be fifty to sixty years. Deterioration in concrete structure is a major challenge faced by the infrastructure and bridge industries worldwide. The deterioration can be mainly due to environmental effects, which include corrosion of steel, gradual loss of strength with aging, repeated high intensity loading, variation in temperature, freeze-thaw cycles, contact with chemicals and saline water and exposure to ultraviolet radiations, and also deterioration due to exposure to an aggressive environment and accident events such as earthquakes. That is why reinforced concrete structures often have to face modifications and improvements of their performance during their service life. When possible, it is often better to repair or upgrade the structure by retrofitting which is prestrengthening a structure before its failure. The most common and advanced material used worldwide for structural strengthening is FRP (fibre reinforced polymer) composites, which are used for the strengthening purposes be it in flexure or shear or the ductility parameter or even confinement, and is successfully used all over the world the said purpose [
Natural fibres, often referred to as vegetable fibres, are extracted from plants and are classified into three categories, depending on the part of the plant they are extracted from, fruit fibres such as oil palm fibres, bast fibres such as jute fibres, and leaf fibres such as sisal fibres. Nowadays, there is a demand for these natural fibres to be used as reinforcement in polymer matrices. In recent years, there has been increasing interest in the replacement of fibreglass in reinforced plastic composites by natural fibres such as kenaf, oil palm, ramie, sisal, coir, and jute. Jute fibres are bast fibres, and are one of the strongest bast fibres, and it withstands rotting very easily. Jute is the most common agricultural fibre. The fibres of jute are nonabrasive, exhibit moderately higher mechanical properties, and are abundantly available exclusively in Bangladesh, India, Thailand, and also in some parts of Latin America. Researchers have shown that suitable pretreatments of jute yarn can lead to an improvement in its mechanical properties and that jute fibre composites have shown immense potential in terms of its mechanical characteristics [
The woven jute was collected from Extra Weave Private Ltd, Cherthala, Kerala, India. All other chemicals used for the fabrication of the natural woven jute FRP composite for its mechanical characterisations and structural strengthening, such as MBrace saturant, which consists of Part A epoxy resin and Part B hardener, were also collected and utilized. Strengthening of the RC beams with FRP composite wrapping using natural jute FRP composite was carried out with the help of chemicals such as concresive 2200 and MBrace primer in conjunction with the MBrace saturant (epoxy-rein-hardener system) were all obtained suitably for the said purpose.
The chemical treatment of fibre is aimed at improving the adhesion between the fibre surface and the polymer matrix by modifying the fibre surface and the fibre strength. It also reduces the water absorption capacity of the fibre and helps in improving the mechanical properties. Following are the different pretreatments carried out. The woven jute mats were cut into the size required for flexural strength test as per ISO 14125:1998 and tensile strength test as per ISO 527-4:1997(E), and then, the various pretreatments were carried out. Some samples were left untreated as controlled samples for comparison study purpose.
Alkaline treatment is one of the most commonly used chemical treatment procedures, for treating natural fibres when used as reinforcements in thermoplastics and thermosets. The important modification done by alkaline treatment is the disruption of hydrogen bonding in the network structure, thereby increasing surface roughness. This treatment removes a certain amount of lignin, wax, and oils covering the external surface of the fibre cell wall. Addition of aqueous sodium hydroxide (NaOH) to natural fibre promotes the ionization of the hydroxyl group to the alkoxide. Thus, alkaline processing directly influences the cellulosic fibril, the degree of polymerization, and the extraction of lignin and hemicellulosic compounds. It is reported that alkaline treatment has two effects on the fibre: it increases surface roughness resulting in better mechanical interlocking and it increases the amount of cellulose exposed on the fibre surface, thus increasing the number of possible reaction sites. Consequently, alkaline treatment has a lasting effect on the mechanical behaviour of natural fibre, especially on fibre strength and stiffness. Woven jute fibre mats in deemed sizes were immersed in 4% NaOH solution at room temperature. Then, they were removed from the NaOH solution and then washed several times with fresh water to remove any NaOH sticking to the surface, followed by neutralisation with dilute acetic acid. Finally, these woven jute fibre mats were washed again with distilled water, ensuring that a final pH-7 was maintained. The fibre mats were then dried at room temperature for 48 hours followed by oven drying at 50°C for 24 hours.
Benzoylation is an important transformation in organic synthesis. Benzyl chloride is most often used in fibre treatment. Benzyl chloride includes benzyl (C6H5C=O) which is attributed to the decreased hydrophilic nature of the treated fibre and improved interaction with the hydrophobic polymer matrix. Woven jute fibre mats in deemed sizes were immersed in 10% NaOH solution agitated with benzyl chloride. This mixture was kept for 15 minutes. After that, the fibre mats were removed from the mixture of NaOH and benzyl chloride and washed thoroughly with normal water. Then, these wet fibre mats were dried thoroughly using filter paper (white paper). Then, they were soaked in ethanol for 1 hour to remove any benzyl chloride sticking to their surfaces. Finally, the fibre mats were washed thoroughly with water and then dried in the oven at 40°C for 48 hours.
The mechanical treatment in the form of heat treatment was carried out in the following manner. Woven jute fibre mats in deemed sizes were placed into the oven at 50°C for 48 hours. After that, these samples were kept in an air tight chamber so that atmospheric moisture could not be absorbed by these samples. Basically, the raw fibres when exposed to atmosphere absorb moisture, and this moisture which gets accumulated in the fibres requires to be eliminated. This elimination of the moisture from the fibres can be attained by the process of heat treatment. Heat-treated composites of natural textile or fabrics have higher strength than untreated composites of natural jute fibre textiles.
A plastic bit mould with suitable dimensions was used for casting the woven jute composite sheets. The usual hand lay-up technique was used for preparation of the samples. A calculated amount of epoxy resin and hardener ratio of 10 : 4 by weight was thoroughly mixed with gentle stirring to minimize air entrapment. For quick and easy removal of composite sheets, a mould releasing agent was used, which was silicone grease. Electrical insulating paper was put underneath the plastic bit mould, and silicone grease was applied at the inner surface of the mould. After keeping the mould on the insulating sheet, a thin layer (
Two mechanical tests were performed for all the samples of woven jute fibre composites, the two tests were tensile strength test, and flexural strength test. All treated FRP composites were subjected to the above mentioned two tests. During the tensile test, an uniaxial load was applied through both the ends of the specimen, using suitable jaws as an attachment to the UTM. The tensile test was performed in the universal testing machine (UTM) which was HEICO digital universal testing machine, and results were obtained digitally with the digital data acquisition system, which aided us in calculating the tensile strength of composite samples. The tensile strength test for jute FRP composites was done in accordance to ISO 527-4:1997(E), as jute falls under the category of Type-2 materials. All the results were taken as an average value of 5 samples each. Figure
Tensile strength property of pretreated and untreated (controlled) woven jute FRP composites.
Mechanical property | Alkali treated jute fabric FRP | Benzoylated treated jute fabric FRP | Untreated jute fabric FRP | Thermally/heat treated jute fabric FRP |
---|---|---|---|---|
Tensile strength (MPa) | 83.836 | 101.534 | 148.603 | 189.479 |
Tensile modulus (MPa) | 15000 | 13500 | 16000 | 32500 |
Flexural strength (MPa) | 158.631 | 97.572 | 183.932 | 208.705 |
Flexural modulus (MPa) | 2750 | 2500 | 4250 | 4500 |
(a) Tensile testing; (b) tensile fracture samples of woven jute FRP.
(a) Flexural testing; (b) flexural fracture of woven jute FRP.
(a) Tensile behaviour of jute FRP composite, woven jute being subjected to different pretreatments; (b) flexural behaviour of jute FRP composite, woven jute being subjected to different pretreatments.
While most of us have general sense of what the term “durability” means, is not easily defined in the context of infrastructure materials, and numerous definitions have been proposed in the literature. In the current educational module durability, is defined on the basis of a definition offered by Karbhari et al. [
The mechanical properties of thermoset resin matrix composite materials are affected when exposed to wet environments. The absorbed water causes matrix plasticization and or interface degradation. The effect of water environment on moisture (H2O) absorption characteristics of woven jute epoxy composite material has been investigated by the measurement and analysis of percentage moisture content, thickness swelling, and effect of water on the tensile strength property of woven jute FRP composite. Firstly, the composites were weighed and their thicknesses were measured. Normal water was then collected and heated (till bubbles started appearing) to 100°C along with the composites for 30 min, then the composites were removed from the hot water and wiped with cotton and then weighed again and their thicknesses were measured. The relative mass change of the epoxy in the specimens under study was expressed as a percentage obtained using the expression: Moisture content = (weight of soaked specimen − weight of dry specimen)/weight of dry specimen. Thickness swelling index was also measured by measuring the thickness of the composites before and after boiling. Lastly, tensile strength tests were carried out on these composite samples. It was observed that the moisture content percent was 6.6% and thickness swelling was 8.9%, but the tensile strength increased from 189.48 MPa under dry conditions to 213.42 MPa under wet conditions. The hygrothermal effects on the woven jute FRP could be viewed as a result of two mechanisms. Firstly, at the macroscopic level, the expansion of the matrix due to absorption of water may cause tensile stresses in the fibres and compressive stresses in the matrix which is similar to differential thermal expansion. Secondly, at the molecular level, the diffusing molecules of water may strain or rupture the intermolecular bond in the matrix and at the interface.
Thermal aging behaviour of composites is of special interest because of their expanding use for structural applications where increased temperatures is a common environmental condition. There are significant chemical and structural changes in epoxy networks which take place during thermal aging. Delamination and microcracking are some of the most frequently observed damaging phenomena that may develop in polymer composites exposed to cryogenic temperatures (low temperature conditions). It is important to understand the aging mechanism of polymer composites for their use in thermal environments. The mechanical behaviour of composites depends on the ability of interface to transfer stress from the matrix to the reinforcement fibre. Two batches of samples were fabricated for this test. The first batch of samples was kept in temperature of +75°C (in oven) for 10 hours. And the second batch of samples was similarly exposed to ultra-low deep freezing conditions at −75°C temperature, in the freezer for 6 hours. These were followed by tensile strength testing for both the batches of the samples immediately. It was observed that the tensile strength of woven jute FRP composite increased from 189.48 MPa under unexposed conditions to 197.51 MPa under high temperature, that is, +75°C conditions, and came down to 168.11 MPa under low temperature, that is, −75°C conditions. The most common damage modes in thermal aging are matrix cracking, delamination growth, and fibre fracture. Cryogenic exposure introduces matrix cracking and/or interfacial debonding. During cryogenic conditioning the fibre/matrix adhesion is low. So the first form of damage in laminates is commonly matrix microcracks and interlaminar cracks at such low temperature conditions. This is one of the reasons for the decrease in the tensile strength of composites, when subjected to very low temperatures. Thermal conditioning at higher temperatures imparts better adhesion, and thus an improved tensile strength values are observed, since fibre cross linking is highly probable during thermal conditioning when the composites are exposed to higher temperatures, hence, it increases the tensile strength of the composites.
From the civil engineering point of view, we are looking towards implementing the FRP composite in old structures or deficient structures as a retrofitting or strengthening material. A fire flow study of any material is very important for the constructional performance, upon studying we can easily know that if any fire-related accident happens, how fast the fire can flow with respect to time considering the building material and how we can reduce the flow rate of fire and what will be the effect in the environment when those particular materials are burnt. This test was performed in accordance to ASTM D635 standard, and the burning rate was measured. It was observed that woven jute FRP composite had a burning rate of 8.1 mm/min.
Ordinary Portland cement of 53 grade, conforming to IS: 12269-1987, has been used. Locally available clean river sand have been used in this work. The maximum size of coarse aggregate considered was 12 mm. The coarse aggregate used for the casting of RCC beams passed through 12 mm IS sieve. As per Indian standard specifications, the mix proportion of the concrete was carried out, in accordance to IS 10262-2009, in order to achieve the desired compressive strength of 20 N/mm2. In accordance, the mix proportion by weight of cement: fine aggregate: coarse aggregate was found to be 1 : 2.07 : 1.87. The designed water cement ratio was 0.5. Three numbers of cubes were also cast using the stated mix proportion and water cement ratio, and the average compressive strength for 28 days was 22.309 N/mm2. Here, Fe 415 HYSD bars of 8 mm diameter, having characteristic strength of 415 N/mm2, were used. Three samples of bars were placed in the universal testing machine one after another and were tested for their yield strength. It was found that the bars had average yield strength of 415 N/mm2. The mentioned bars were both used for the longitudinal reinforcement as well as stirrups. The experimental program contained three beam groups. All the three groups of beams were utilized for the study of the effect of flexural strengthening. All the beams in groups A, B, and C had the same reinforcement detailing, although the beam length for design was 1.3 m, it was cast as 1.4 m, for providing 50 mm clearance from both the sides at the supports and had a cross section of 140 mm width and 200 mm depth. The RCC beam design was carried out as per IS-456: 2000. The entire reinforcement details, which were followed for all the three groups of beams, are shown in Figure
Reinforcement detailing of RCC beams (all sets, group A, B, and C).
The beams in group A were designed as controlled specimen (2 number of models, Con1 and Con2), where no FRP application was carried out. The beams in group B were designed to investigate the effect of full wrapping technique 90° (3-sided U wrap) for flexural strengthening provided by using woven jute FRP (2 number of models, JF1 and JF2). The beams in group C were designed to investigate the effect of strip wrapping technique 90° (3-sided U wrap) where 50% of the total area was used for strengthening, that is, 62 mm strips were placed at 124 mm C/C throughout the length of the beam and at a clear gap of 49 mm at the support ends, for flexural strengthening provided by using woven jute FRP (2 number of models, JF3 and JF4); a summary of the test beams are shown in Table
Summary of test beams.
Beam group | Wrapping configuration | Strengthening material | Beam designation | Type of strengthening | Strengthening scheme |
---|---|---|---|---|---|
Group A | Nil |
Nil | Control specimen Con1, Con2 | No strengthening | Nil |
| |||||
Group B | Full wrapping 90°, single layer |
Jute FRP | JF1, JF2 | Flexural strengthening throughout using jute FRP | U-Wrap, three-sided wrap |
| |||||
Group C | Strip wrapping 90°, single layer 62 mm strips at 124 mm C/C (at a clear gap of 62 mm) so as to achieve 50% of total area strengthening, with end clear gaps of 49 mm. |
Jute FRP | JF3, JF4 | Flexural strengthening throughout using jute FRP | U-Wrap, three-sided wrap |
Typical properties of MBrace Saturant.
Mechanical property | MBrace Saturant |
---|---|
Description | 2 parts; Part A: epoxy and Part B: hardener |
Density | 1.06 kg/Lt (Mixed density) |
Colour | Blue |
Bond strength | >2.5 N/mm2 (Failure in concrete) |
(a) Surface preparation of beams by grinding; (b) primer application on beam surface; (c) application of epoxy-hardener mix on the beam; (d) bonding of woven jute; (e) bonding of woven jute in strips; (f) final coating of epoxy-hardener mix on the bonded fabric.
A third point loading system was adopted for the beam tests. At the end of each load increment, deflection, ultimate load, type of failure, and so forth were carefully observed and recorded. The experimental set-up under the third point loading system is shown in Figure
(a) Two pint loading system on a 50 ton loading frame; (b) loading on fully wrapped beam with woven jute FRP.
The ultimate load carrying capacity, that is, the ultimate flexural strength of all the beams along with the nature of failure and deflections, are given in Table
Summary of test results.
Group designation | Beam designation | Failure of FRP | Deflection at midspan (mm) | Average deflection at midspan (mm) | Comments on deflection | Pultimate, (KN) | Pultimate, (KN) |
Strengthening effect (%) |
---|---|---|---|---|---|---|---|---|
Group A | Con1 |
— | 11.271 |
11.426 | — | 78 |
80 | — |
| ||||||||
Group B | JF1 |
Yes | 23.882 |
23.211 | Results in huge deflection, hence gives sufficient warning. | 126 |
130 | 62.5% |
| ||||||||
Group C | JF3 |
No | 17.021 |
17.863 | Deflections are lower than fully wrapped beams, since failure occurs at lower loads as compared to fully wrapped beams. | 97 |
100 | 25% |
(a) Control beams (group A, Con1) under load; (b) formation of flexure crack in the beam JF1, under load; (c) formation of flexure crack in the beam JF2, under load; (d) formation of flexure crack in the beam JF3, under load.
Load versus midspan deflection of (a) Control; (b) woven jute FRP strip wrapped beams; (c) woven jute FRP fully wrapped beams.
(a) Comparison of ultimate load carrying capacity of all beams; (b) comparison of first crack load of all beams.
The first set of beam, that is, group A and Con1 and Con2, failed in flexure which proved that the beams were strong in shear, and henceforth flexural failure took place before shear failure. Major vertical cracks developed in the midspan that is, in the pure flexure zone, these cracks firstly developed at the lower face, that is, at the bottom side of the beam, and extended from the bottom side towards the top face of the beam. Both the beams Con1 and Con2 failed in similar manner, and Figure
In the second set of beams in group B, in which the beams were strengthened by fully U wrapped woven jute FRP, JF1, and JF2, it was seen that both beams failed in flexure and their flexural strength was much higher than that of Group A beams. When load was applied on JF1 and JF2, firstly the matrix started cracking, then on further increment of load, the jute fibres in jute FRP started to crack, then again on further load increment the cracks in jute FRP started to widen, then the RCC beam showed vertical crack in the flexure zone, and then this crack started to slowly move from the bottom side of the beam to the top side. Both the failure modes depicted in JF1 and JF2 were very ductile in nature, and the beam carried huge deflection. There was no debonding of jute FRP at all from the beam face in any direction even at very high load, and hence cracks were visualized only on the woven jute FRO and not on the RCC beam. Only a single crack appeared in JF1 on the woven jute FRP, and this crack started to widen with the increase in the load, without the development of any other cracks. The widening of this crack showed and exposed the crack in the RCC beam, at the same location. In the other beam JF2, two cracks appeared on the woven jute FRP which started to widen with the increase in the load, without the development of any other cracks, and the widening of the two cracks exposed the cracks in the RCC beam at the same locations. All the cracks observed in both the beams JF1 and JF2 were at the beam flexure zone, and the ultimate flexural load was reached by further widening of these cracks, without the generation of any other alternate cracks. The average ultimate strength of group B beams JF1 and JF2 was 130 KN. Both the beams JF1 and JF2 failed in similar manner. Figure
The third set of beams in group C, in which the beams were strengthened by strips, that is, U wrapped woven jute FRP in strips, JF3 and JF4, and all strip wrapped strengthened beams were tested to find out their ultimate flexural strength. It was seen that the beams JF3 and JF4 showed higher ultimate load carrying capacity than that of group A beams, but lower than that of group B beams. In the group C beams, it was observed that cracks first developed in the RCC beams, that is, on the concrete surface only, and not on the woven jute FRP composite; this indicated that the presence of bonded woven jute FRP on RCC beams imparted additional strength to the beams, and thereby enhanced their flexural strength as compared to controlled beams. When load was applied on JF3 and JF4, then major vertical cracks developed in the mid span that is, in the pure flexure zone, and these cracks developed only in the beam area, and a single flexural crack did not develop on the FRP nor did the FRP undergo rupture or debonding, these cracks on the beam firstly developed at the lower face, that is, beam bottom face, and extended from the bottom side towards the top face of the beam. The strip wrapping technique of FRP strengthening increased the ultimate load carrying capacity up to a point which lied between the load carrying capacity increased by that of full wrapping technique and the unstrengthened, that is, controlled beams. The failure modes of beams JF3 is depicted in Figure
The following conclusions can be drawn from the study.
(1) The woven jute FRP composite which was mechanically subjected to heat has shown highest tensile strength of 189.479 N/mm2 and tensile modulus of 32500 N/mm2, which is the highest tensile strength value, obtained from all the pretreatment procedures used for pretreating the woven jute, and is also higher as compared to controlled samples of woven jute FRP, where no treatment was carried out.
(2) Similarly, the woven jute FRP composite which was mechanically subjected to heat has shown the highest flexural strength of 208.705 N/mm2 and flexural modulus of 4500 N/mm2, which is the highest flexural strength value, obtained from all the pretreatment procedures used for pretreating the woven jute, and is also higher as compared to controlled samples of woven jute FRP, where no treatment was carried out.
(3) It was observed that the composites of woven jute FRP, which was untreated or control specimen along with the heat treated woven jute FRP composite, displayed highest tensile and flexural strength, that is, superior mechanical properties, as compared to both the chemically treated, that is, alkali treated or benzylated woven jute FRP composite samples. The reason for this lies in the fact that, we are hereby using woven yarns of jute (not loose jute fibres), chemical treatment results in, partial unwinding of yarns (as hemicellulose dissolves off) and hence the alignment of the fibres gets antagonized. This results in, lowering of strength of woven or textile composites, when subjected to chemical treatment. Another reason is that as woven jute is composed of thick strands and knots of the fibres, the alkali and benzyl chloride agents do not penetrate the fabric or textile uniformly, and therefore the interfacial properties between the woven jute and the matrix does get improved enough. The lower strength properties of the composites containing alkali treated as well as benzylated woven jute fibres because of the result of nonuniform penetration of chemicals within the thick strands of the fabric or textile. It can be seen that the highest values are exhibited by thermally treated composites. This could be attributed to the fact that upon continuous heat treatment, the crystallinity of cellulose increases due to the rearrangement of molecular structure at elevated temperatures. The thermal treatment also resulted in moisture loss of the woven jute, thereby enhancing the extent of bonding between woven jute and the matrix.
(4) It can also be concluded that the heat treatment process which aids in the demoisturisation of fibres is a better treatment method as compared to any other chemical treatment method for improving mechanical properties of natural fibre woven or textile composites. Thermally treated composites exhibited superior mechanical properties, both in terms of tensile strength and flexural strength because of increased crystallinity.
(5) From the durability study based on the effect of normal water on woven jute FRP, it could be concluded that woven jute FRP composites behaved similarly to artificial FRP composites of glass and carbon, that is, ultimate tensile strength of wet samples were higher than that for dry samples. This could be attributed to the fact that high amounts of water causes swelling of the fibres, which fills the gaps between the fibre and the polymer-matrix and eventually leads to an increase in the mechanical properties of the fibre composites, but the percentage of moisture absorption and thickness swelling of woven jute FRP composites were slightly on the higher side as compared to artificial FRP composites.
(6) From the durability study based on the effect of thermal aging on woven jute FRP, it could be concluded that woven jute FRP composites behaved similarly to artificial FRP composites of glass and carbon, that is, ultimate tensile strength under cryogenic exposure was lower, and ultimate tensile strength under higher temperature conditioning was higher.
(7) The work being done in this study is important to the composites industry because it is a beginning of systematic research into how the fibre type and also the content affect the overall fire performance of the composites. The burning rate of jute FRP was substantially lower than the burning rate of other artificial FRP composites.
(8) The application of woven jute FRP sheets showed a better performance in increasing the ultimate flexural strength capacity of RC beams as compared to the controlled RC beams. Maximum ultimate load of 126 KN and 134 KN was carried, respectively, by the beams JF1 and JF2, when full U wrapping technique was used, whereas the controlled RCC beams failed at an average ultimate load of 80 KN. Thus, we can conclude that flexural strengthening of RCC beams can be achieved by the use of woven jute FRP composites.
(9) In the beams, JF1 and JF2, the strengthening effect was very noteworthy with one layer itself, providing an increase in the flexural strength by 62.5%, and woven jute FRP bonding also promoted ductile failure without any concrete crushing or FRP rupture or any debonding of FRP, even at very high loads. Hence with increasing the number of layers of jute FRP, a more significant strength improvement could be attained in the flexural strength.
(10) Increase in the ultimate flexural strength of beams by 25%, with woven jute FRP in strips, was observed for beams belonging to group C, where the strip wrapping technique was followed. The presence of strips delayed the first crack formation at locations where FRP was bonded to the beams. By the use of natural jute FRP in the strengthened beams, the initial cracks were formed at higher loads than their respective control beams. This showed that the use of natural woven FRP is very effective in the case of flexural strengthening of structures.
(11) The ultimate strength of beams could be increased by the use of natural woven jute FRP, being bonded to the beam in full length or being bonded in strips. The ultimate flexural loads of beams strengthened with U full wrapping were greater than the beams strengthened by bonding using strip wrapping. Increase in strength depends on the width of the strip that was bonded to the beam.
(12) The load deflection behavior was better for beams strengthened with woven jute FRP compared to the controlled beams. Woven jute FRP strengthened beams in full length depicted typical ductile failure and carried large deflections before undergoing failure and totally avoided any mode of catastrophic failure of beams.
(13) Natural woven fibres of jute FRP have great potential in increasing the load carrying capacity of RCC beams, and also enhanced the material efficiency. Hence, the woven jute FRP can be regarded as a suitable strengthening material for flexural strengthening of concrete structures particularly, and as a good alternative methodology among the fabric reinforcement in FRP considering economic and environmental aspects of FRP products.
The authors acknowledge the support extended to the work by various undergraduate and postgraduate students working under the guidance of the authors and also laboratory supporting staff members and the laboratory assistants.