Sustainable Retrofitting Solutions: Evaluating the Performance of Jute Fiber Nets and Composite Mortar in Natural Fiber Textile Reinforced Mortars

: Sustainable building materials for integrated (structural and thermal) retrofitting are the need of the hour to retrofit/upgrade the seismic vulnerable and ill-insulated existing building stocks. At the same time, the use of natural fibers and their recyclability could help construct safer and more sustainable buildings. This paper presents three aspects of jute fiber products: (1) the evaluation of the mechanical performance of the jute nets (2.5 cm × 2.5 cm and 2.5 cm and 1.25 cm mesh configurations) through tensile strength tests (with the aim for these to be used in upgrading masonry wall with natural fiber textile reinforced mortars (NFTRM) systems); (2) the hundred percentage recyclability of left-over jute fibers (collected during the net fabrication and failed nets post-tensile strength tests) for the composite mortar preparation; (3) and the evaluation of insulation capacity of the recycled jute net fiber composite mortar (RJNFCM) through thermal conductivity (TC) measurements, when a maximum amount of 12.5% of recycled jute fiber could be added in the mortar mixture at laboratory conditions and with available instruments Notably, when more than the said amount was used, the fiber–mortar bonding was found to be not optimal for the composite mortar preparation. These studies have been carried out considering these products’ applicability for integrated retrofitting purposes. It has been found that the denser mesh configuration (2.5 cm × 1.25 cm) is 35.80% stiffer than the other net configurations (2.5 cm × 2.5 cm). Also, the mesh configuration (2.5 cm × 1.25 cm) shows about 60% more capability to absorb strain energy. TC tests have demonstrated the moderate insulation capacity of these composite mortar samples, and the TC values obtained from the tests range from 0.110 (W/mK) to 0.121 (W/mK).


Introduction
Creating thermally efficient and structurally safe building stocks stands as a key objective within the contemporary construction and building (C&B) sector.This commitment arises from the industry's pursuit of constructing safer, more sustainable, environmentally friendly, and nearly self-sufficient buildings.
Moreover, a building in its complete service life generates vast amounts of waste, some of which is recyclable, and others are not, and therefore, are responsible for creating environmental problems.In the European Union (EU), construction and demolition (C&D) accounts for about 180 tons of waste per year [1].The C&D wastes of the C&B sector are mainly dumped in landfills, thus directly damaging the environment and ecosystem and detrimental to human health [2].The EU, with Directive 2008/98/EC [3], discourages the disposal of 100% of demolition wastes and, to reinforce its Sustainable Development Strategy, in the last decade gradually developed the Integrated Product Policy [4,5] to reduce the environmental impacts of products throughout their life-cycle.Considering environmental and ecological sustainability, different research groups have studied the recyclability of C&D wastes [6][7][8][9][10][11][12] for various C&B applications.Similarly in the literature, the use of argo-wastes also can be found in [6,[13][14][15][16][17][18].
In the EU, buildings stocks constructed before the 1990's are not energy efficient [19], and mostly these buildings are constructed without having properly followed the seismic standard [20].At the same time, these buildings are known to be some of the highest producers of CO 2 and other greenhouse gases, and these figures are about 39% globally and 36% in the EU [21].On the other hand, the C&B sector, directly and indirectly, consumes nearly 36% globally and 40% in the EU, of the total produced energy [22].
Notably, both ancient and modern building stocks are vulnerable to natural and manmade created/caused disasters [23].According to [24], in the Asian continent, the northern Indian traditional Himalayan buildings, particularly the rammed earth and dry-stone buildings, are predominantly vulnerable and susceptible to seismic activity.
Recently, various laws and regulations, obligatorily or voluntarily, obliged the public and private entities to structurally or/and thermally retrofit/upgrade existing buildings according to the latest standards, like Eurocode 8 [25] and near-zero energy building (nZEB) [26].Whereas, Ref. [27] has proposed higher energy-performance buildings by 2030 (2027 for the public sector) with new zero-emission buildings (ZEB) requirements.
Therefore, a wide range of newer building materials and composite materials have been studied by many research groups, with the aim to use these materials for structural, thermal, integrated retrofitting or upgrading purposes, and obviously during new building construction.
Due to superior mechanical properties, man-made fibers, like carbon, basalt, steel, glass, etc., have been used predominantly in raw or in textile form, for structural retrofitting or upgrading [20] of building stocks and various structures.
It is well established that natural fibers are cheaply and abundantly available [28], and are also known to have good thermo-mechanical properties [29].At the same time, they have 78-79.4%lesser carbon footprint [30]; therefore, these fibers can be used for making greener and sustainable building materials.
Whereas due to good insulation capacity, natural fibers like wool, hemp, jute, sisal, etc., are particularly usable for thermal upgrading [20].
Fiber reinforced polymer (FRP) is predominantly used for civil reinforcement applications [48] due to its strength.Particularly carbon FRP [49], glass FRP [50], and basalt FRP [51,52] are mainly used for civil applications, while scholars and researchers are also working on the natural FRP [53,54] or hybrid FRP [55], extensively.
The use and application of a natural fiber (NF) for TRM systems is also gaining momentum, but still its use at commercial level is very limited and its applicability can be found at the research level only.Some important works, and the use of NFTRM, can be found in [64][65][66][67] for jute fiber TRM, hemp fiber TRM, flex fiber TRM systems and banana TRM, respectively.Among all natural fibers, jute fiber ranks second in terms of the amount/quantity being produced [68].Notably, jute fiber-made building materials and composite mortars have been developed, and their mechanical and thermal behaviors have been studied and reported in [31,[69][70][71][72][73][74], respectively.
Authors already have proposed in their previous works [75,76], various compositions of jute fiber composite mortars with different proportions of raw fiber (depending on dry mortar mass) mortar and water combinations, while their physical behaviors and thermo-structural performances are reported and were evaluated.
Also, authors have recycled and used jute fiber waste, derived from various sources, to prepare jute fiber composite mortars [77,78] and other fibers (loofa, sheep wool, hemp shives, thistle fibers) for composite building materials [31,77,78] with the aim that these materials could be used for thermal retrofitting or upgrading.
This paper validates the capability of jute fiber nets that are to be used for NFTRM retrofitting or upgrading masonry walls and analyzes the performance of the recycled jute net fiber mortar that might be used for thermal retrofitting.Therefore, to encourage the United Nationals Sustainable Goals (UNSG) and by following the directive of the EU "EU 2008/98/EC", this research was conducted to encourage the recycling of C&B sector residual wastes.By doing so, 100% of the residual scape thread and net fibers, leftover during the net fabrication process and post-flexural tests were recycled to prepare the jute net fiber composite mortar, with the aim of this composite mortar to be used for the thermal retrofitting purpose.Therefore, the novelty of this research work is threefold: (1) the applicability of natural fiber (jute) for integrated upgrading/retrofitting of masonry walls/structures, (2) the assessment and validation of strength (jute fiber net) and insulation properties of the jute fiber composite mortar, and (3) the possible recyclability of the residual natural fiber (jute) from a previous process (net fabrication), therefore encouraging a sustainable production process.
The structure of this paper can be highlighted as it starts with a brief introduction, thereafter the materials and methods used are explained.Section 3 is subdivided into two parts; in Section 3.1 the observations of the jute net tensile strength tests are reported, while in Section 3.2 the thermal conductivity test results are reported and at the end, in Section 4, the conclusive remarks are stated.

Materials and Methods
For this experimental campaign, the main raw material for net preparation (i.e., jute threads) was collected from the state of West Bengal, India.This three-yarn jute thread type was fabricated in a local jute mill.
While the mortar used for the composite-mortar preparation is a lime-based mortar and has a dry density equal to 750 kg/m 3 .It is a thermo-dehumidifying plaster and it certified as R and T/CSII (EN 998-1 [79]).

Jute Fiber Net Preparation
Figure 1 presents the class 1 mm (1.19 mm with Co.V. of 7.27) [78] jute fiber thread, which has been selected for the jute net fabrications and has tensile strength (f t ) and strain energy (U) measured equal to 122.45 MPa (with Co.V. of 26.16%) and 1.03 kN.mm (with Co.V. of 34.59%), respectively [78].
Two types of jute nets were manually prepared with two distinct inner mesh configurations: (1) 2.5 cm × 2.5 cm and (2) 2.5 cm × 1.25 cm, respectively, in the Strength Laboratory at the University of Salerno, Italy (Figure 2).Notably these configurations have been considered for better mortar penetration during the net application on the wall surface.
The length of each tested sample with net mesh types 2.5 cm × 2.5 cm and 2.5 cm × 1.25 cm, were 0.5 m long.About 18 cm of net (Figure 3) was exposed to the applied loads.The net samples are placed inside two clamps, as shown in Figure 4, and the top and the bottom fixtures were tied with a torque wrench with an adjustable preset torque value of 50 N/m (Figure 4), this was performed to bind the edges of the net uniformly with quasi-equal force.Two types of jute nets were manually prepared with two distinct inner mesh configurations: (1) 2.5 cm × 2.5 cm and (2) 2.5 cm × 1.25 cm, respectively, in the Strength Laboratory at the University of Salerno, Italy (Figure 2).Notably these configurations have been considered for better mortar penetration during the net application on the wall surface.The length of each tested sample with net mesh types 2.5 cm × 2.5 cm and 2.5 cm × 1.25 cm, were 0.5 m long.About 18 cm of net (Figure 3) was exposed to the applied loads.The net samples are placed inside two clamps, as shown in Figure 4, and the top and the bottom fixtures were tied with a torque wrench with an adjustable pre-set torque value of 50 N/m (Figure 4), this was performed to bind the edges of the net uniformly with quasiequal force.Two types of jute nets were manually prepared with two distinct inner mesh configurations: (1) 2.5 cm × 2.5 cm and (2) 2.5 cm × 1.25 cm, respectively, in the Strength Laboratory at the University of Salerno, Italy (Figure 2).Notably these configurations have been considered for better mortar penetration during the net application on the wall surface.The length of each tested sample with net mesh types 2.5 cm × 2.5 cm and 2.5 cm × 1.25 cm, were 0.5 m long.About 18 cm of net (Figure 3) was exposed to the applied loads.The net samples are placed inside two clamps, as shown in Figure 4, and the top and the bottom fixtures were tied with a torque wrench with an adjustable pre-set torque value of 50 N/m (Figure 4), this was performed to bind the edges of the net uniformly with quasiequal force.

Jute Fiber Nets Tensile Strength Tests
The fix-clamp fixtures holding the net sample(s) were fixed to the testing machine (Figure 5) and thereafter the mechanical behavior of these net samples was evaluated through the tensile strength tests.For this test, a Schenck universal machine (Figure 6), was used, and it has a maximum load capacity and maximum workable length of 630 kN and 20 cm, respectively.The tensile tests were conducted at a rate of 2 mm/min.

Jute Fiber Nets Tensile Strength Tests
The fix-clamp fixtures holding the net sample(s) were fixed to the testing machine (Figure 5) and thereafter the mechanical behavior of these net samples was evaluated through the tensile strength tests.For this test, a Schenck universal machine (Figure 6), was used, and it has a maximum load capacity and maximum workable length of 630 kN and 20 cm, respectively.The tensile tests were conducted at a rate of 2 mm/min.

Recycled Jute Fiber Net Composite Mortar (RJFNCM) Preparation
Notably during the net fabrication and after the jute-net tensile strength tests, a significant amount of jute net and thread fibers were left over, and these scrap fibers were recycled along with the tensile test failed net fibers (Figure 7), to prepare the recycled jute net fiber composite mortar (RJNFCM).
The composite mortar's grout was prepared following EN1015-2 [80], while no workability test has been performed as these samples have only been used for the thermal conductivity test.The quantity of water added during the grout preparation was based on the

Recycled Jute Fiber Net Composite Mortar (RJFNCM) Preparation
Notably during the net fabrication and after the jute-net tensile strength tests, a significant amount of jute net and thread fibers were left over, and these scrap fibers were recycled along with the tensile test failed net fibers (Figure 7), to prepare the recycled jute net fiber composite mortar (RJNFCM).author's previous calculation, and experience of working with raw-jute fiber, threads, and composite mortars, while the information about this research work and respective observations can be found in [20,78].
During the mixture preparation, the pre-present aggregates were separated from the mortar, and thereafter 12.5% recycled jute net fibers (Table 1) were added based on the measured mortar mass (without any aggregates).During mixing, about 49.8% of water (Table 1) with respect to the total mixture (mortar + fiber) mass was added slowly to prepare the grout.The mixing process was performed for approximately 7 min.Thereafter, two molds of the dimensions 160 mm × 140 mm × 40 mm were used to prepare two samples to be used for thermal conductivity tests.The samples were left inside molds and in plastic bags for the first 2 days, then they were taken out from the molds and re-placed inside another plastic bag for another 3 days.After, they were left in a quasi-constant environmental condition (22 °C and 65% RH) in a room until the 28th aging day.This first drying process is the part to which the utmost attention must be paid, avoiding the formation of surface depressions or specimen distortions, which would compromise their subsequent thermal characterization tests.After this period, the samples were oven dried (at 50 °C) to remove the remaining moisture, which would influence measurements and thermal conductivity values.

Total Recycled Jute Net Fiber Used
Total Water Used for the Mixture 12.5% of the dry mortar mass 49.8% of the total mixture (mortar + fiber) mass  The composite mortar's grout was prepared following EN1015-2 [80], while no workability test has been performed as these samples have only been used for the thermal conductivity test.The quantity of water added during the grout preparation was based on the author's previous calculation, and experience of working with raw-jute fiber, threads, and composite mortars, while the information about this research work and respective observations can be found in [20,78].
During the mixture preparation, the pre-present aggregates were separated from the mortar, and thereafter 12.5% recycled jute net fibers (Table 1) were added based on the measured mortar mass (without any aggregates).During mixing, about 49.8% of water (Table 1) with respect to the total mixture (mortar + fiber) mass was added slowly to prepare the grout.The mixing process was performed for approximately 7 min.Thereafter, two molds of the dimensions 160 mm × 140 mm × 40 mm were used to prepare two samples to be used for thermal conductivity tests.The samples were left inside molds and in plastic bags for the first 2 days, then they were taken out from the molds and re-placed inside another plastic bag for another 3 days.After, they were left in a quasi-constant environmental condition (22 • C and 65% RH) in a room until the 28th aging day.This first drying process is the part to which the utmost attention must be paid, avoiding the formation of surface depressions or specimen distortions, which would compromise their subsequent thermal characterization tests.After this period, the samples were oven dried (at 50 • C) to remove the remaining moisture, which would influence measurements and thermal conductivity values.

Jute Net Fiber Composite Mortar Thermal Conductivity Test
The thermal conductivity values of these samples have been determined at the Applied Thermodynamic and Energetic Laboratory at the University of Cagliari using a TAURUS TCA 300 (Figure 8) device.It is a heat flow meter instrument, that conducts measurements according to ISO 8301 (1991) [81] and EN 1946EN -3 (1999) ) [82].

Jute Net Fiber Composite Mortar Thermal Conductivity Test
The thermal conductivity values of these samples have been determined at the Applied Thermodynamic and Energetic Laboratory at the University of Cagliari using a TAURUS TCA 300 (Figure 8) device.It is a heat flow meter instrument, that conducts measurements according to ISO 8301 (1991) [81] and EN 1946EN -3 (1999) ) [82].The measuring chamber of the TAURUS TCA 300 has two measuring plates, an upper cold plate and a lower hot plate.Notably, the function of these plates can be reversed and can be set accordingly, as required.The original plates have a 300 mm × 300 mm total surface area, while the main measuring zone is located exactly at the center of these plates and the active zones have a 100 mm × 100 mm surface area (Figure 8).Measuring like sample specifications and instrument parameters (Table 2) were set using an instrument- The measuring chamber of the TAURUS TCA 300 has two measuring plates, an upper cold plate and a lower hot plate.Notably, the function of these plates can be reversed and can be set accordingly, as required.The original plates have a 300 mm × 300 mm total surface area, while the main measuring zone is located exactly at the center of these plates and the active zones have a 100 mm × 100 mm surface area (Figure 8).Measuring like sample specifications and instrument parameters (Table 2) were set using an instrumentintegrated computer.

Measuring Intervals min
Intermediate sampling time 1 Total measuring time 300 According to EN 12939 [83], the tests were carried out at sample mean temperatures equal to 10 • C, 20 • C, and 30 • C (Figure 9), always maintaining a difference of 20 • C between the two plates.Consequently, the TC values were calculated based on Equation (1), using the measured heat fluxes values: where Q = heat flux in W/m 2 ; s = sample thickness (m); t H = temperature of the hot plate In Figure 9, the uncertainty bands relating to conductivity values at the three different temperatures are already graphically expressed.While considering the calibration uncertainty of the TAURUS, the repeatability of the measurements obtained and the linear regression error, it is possible to estimate an average standard deviation (SD) equal to 0.004 W/mK.

Results
In this section, the mechanical strength of the jute nets (fabricated by using 1 mm diameter jute threads) and the thermal conductivity value of the recycled jute net fiber composite mortar are reported.
During this experimental campaign, the mechanical strength of the two types of jute Figure 9 presents a typical result sheet with all measured (heat flow in W/m 2 , temperatures of cold and warm side in • C) and calculated (temperature difference in K and thermal conductivity in W/mK) quantities, with respect to the set sample mean temperatures (10 • C, 20 • C, and 30 • C).
In Figure 9, the uncertainty bands relating to conductivity values at the three different temperatures are already graphically expressed.While considering the calibration uncertainty of the TAURUS, the repeatability of the measurements obtained and the linear regression error, it is possible to estimate an average standard deviation (SD) equal to 0.004 W/mK.

Results
In this section, the mechanical strength of the jute nets (fabricated by using 1 mm diameter jute threads) and the thermal conductivity value of the recycled jute net fiber composite mortar are reported.
During this experimental campaign, the mechanical strength of the two types of jute nets, with 2.5 cm × 2.5 cm and 2.5 cm × 1.25 cm mesh configurations, were evaluated through tensile strength tests.
Subsequently, the fiber scraps during the net fabrication and the post-tensile test failed net fibers were collected and recycled to prepare the jute net fiber composite mortar and later the thermal conductivity value of these samples was estimated.

Jute Net Tensile Strength Tests
A total of seven samples of each type of jute thread net (2.5 cm × 2.5 cm and 2.5 cm × 1.25 cm mesh configurations) were used for the displacement-controlled tensile strength tests.The tensile strength and the axial displacement were recorded during the tests.Notably, from each net type, two non-satisfactory results were discarded and were not considered due to faulty measurements.
The results presented in this section clearly highlight that the denser mesh configuration (2.5 cm × 1.25 cm) was found to be significantly more rigid, with an average stiffness increase of 35.80%, compared to the 2.5 cm × 2.5 cm mesh samples (see Figures 10-12).Furthermore, the load-bearing capacity of the denser mesh was observed to be over 50% greater, accompanied by a 14.35% increase in maximum elongation.This mesh also demonstrated superior strain energy transfer, exceeding its counterpart by more than 60%, as evidenced in Table 3.
Further, Table 3 presents a detailed comparison of the mechanical properties, including maximum load, displacement, strain energy, and stiffness, along with the coefficient of variation for each parameter, offering insights into the reliability and variability of the measurements.The different performances of the two mesh configurations can be easily explained, considering that the denser mesh presents more threads for unit area than the other configuration.
Figures 10 and 11 illustrate the force-displacement behavior for each type of mesh configuration.The primary mechanical observations from these tests are further documented in Tables 4 and 5.These tables present specific data points, such as the first collapse load, maximum load, and the corresponding displacement at maximum load for individual samples, providing a granular view of the performance characteristics.Interestingly, none of the net samples experienced complete rupture during testing.Instead, multiple collapses were observed, attributed to failures at knot points or within the thread fiber between knots.This behavior resulted in various spikes in the force-displacement graphs, (Figures 10 and 11), indicating the localized nature of the failures.On the positive side, the denser mesh configuration shows promise for enhanced load-bearing capacity and stiffness, which are desirable traits for applications in construction.However, the occurrence of the multiple collapses suggests that while the material is strong, the nets' reliability is related to the manufacturing processes or material behavior at micro-scales, such as at knots.   Figure 12 presents a comparison of the stiffnesses between the jute net mesh configurations 2.5 cm × 1.25 cm and 2.5 cm × 2.5 cm.It is clearly noticeable that the first configuration is stiffer than the latter configuration.The maximum and minimum stiffness for the 2.5 cm × 1.25 cm mesh configuration was found to be 11.75 N/mm and 8.41 N/mm, respectively.While 9.83 N/mm and 5.48 N/mm are the maximum and minimum stiffness for the 2.5 cm × 2.5 cm mesh configuration.

Recycled Jute Net Fiber Composite Mortar (RJNFCM) Thermal Conductivity Tests
The TC values of the jute fiber (12.5% of fiber, with respect to the dry mortar mass) composite mortar samples were evaluated.The samples were prepared based on the authors previous experience, which can be found in [20,75].
Table 6 presents the TC values measured at 10 °C, 20 °C and 30 °C, respectively, and it has been found that the composite sample RJNF(12.5%)CM with 12.5% (with respect to the dry mortar mass) recycled jute fiber is 48.36%, 47.61%, and 46.22%, respectively lower (in average) than the sample [75] with the 6.5% of recycled jute fiber (added with respect to the dry mortar mass) composite mortar (Figure 12).
Figure 13 presents a comparison between the obtained TC values of the RJNFCM (under observation) and similar types of samples (with different fiber lengths and fiber percentages (with respect to the dry mortar mass) combinations) reported in [20,75], while the sample preparation and drying conditions are same.Notably the comparison has been also carried out with the samples made with 6.5% recycled fibers [75].In this regard, it is the authors' opinion that the previous processing of jute fibers does not influence the thermal conductivity of the samples to a significant extent.
Notably, the samples considered here are oven dried before conducting the TC measurements.However, as highlighted by the authors in [78], during the composite mortar mixing, fiber balls are formed when the jute fibers came in contact with water.Therefore, jute fibers not only have the ability to absorb water individually but also can trap some extra water collectively in the fiber balls cavity.As the fiber used in this case were three yarn jute threads, therefore in the yarn cavity, too, there could be the possibility of trapping a small amount of water.Interestingly, none of the net samples experienced complete rupture during testing.Instead, multiple collapses were observed, attributed to failures at knot points or within the thread fiber between knots.This behavior resulted in various spikes in the forcedisplacement graphs, (Figures 10 and 11), indicating the localized nature of the failures.On the positive side, the denser mesh configuration shows promise for enhanced load-bearing capacity and stiffness, which are desirable traits for applications in construction.However, the occurrence of the multiple collapses suggests that while the material is strong, the nets' reliability is related to the manufacturing processes or material behavior at micro-scales, such as at knots.
Figure 12 presents a comparison of the stiffnesses between the jute net mesh configurations 2.5 cm × 1.25 cm and 2.5 cm × 2.5 cm.It is clearly noticeable that the first configuration is stiffer than the latter configuration.The maximum and minimum stiffness for the 2.5 cm × 1.25 cm mesh configuration was found to be 11.75 N/mm and 8.41 N/mm, respectively.While 9.83 N/mm and 5.48 N/mm are the maximum and minimum stiffness for the 2.5 cm × 2.5 cm mesh configuration.

Recycled Jute Net Fiber Composite Mortar (RJNFCM) Thermal Conductivity Tests
The TC values of the jute fiber (12.5% of fiber, with respect to the dry mortar mass) composite mortar samples were evaluated.The samples were prepared based on the authors previous experience, which can be found in [20,75].
Table 6 presents the TC values measured at 10 • C, 20 • C and 30 • C, respectively, and it has been found that the composite sample RJNF(12.5%)CM with 12.5% (with respect to the dry mortar mass) recycled jute fiber is 48.36%, 47.61%, and 46.22%, respectively lower (in average) than the sample [75] with the 6.5% of recycled jute fiber (added with respect to the dry mortar mass) composite mortar (Figure 12).The TC values of RJNF(12.5%)CMsample were compared to the sample combinations with different fiber percentages (0.5%, 1.0%, 1.5%, and 2.0%) and fiber lengths (30 mm, 10 mm, and 5 mm), as highlighted in [75].The TC values of the RJNF(12.5%)CM are lower in the range between 74% and 80% approximately, with respect to the samples mentioned [75].
Figure 13 presents a comparison between the obtained TC values of the RJNFCM (under observation) and similar types of samples (with different fiber lengths and fiber percentages (with respect to the dry mortar mass) combinations) reported in [20,75], while the sample preparation and drying conditions are same.Notably the comparison has been also carried out with the samples made with 6.5% recycled fibers [75].In this regard, it is the authors' opinion that the previous processing of jute fibers does not influence the thermal conductivity of the samples to a significant extent.
Notably, the samples considered here are oven dried before conducting the TC measurements.However, as highlighted by the authors in [78], during the composite mortar mixing, fiber balls are formed when the jute fibers came in contact with water.Therefore, jute fibers not only have the ability to absorb water individually but also can trap some extra water collectively in the fiber balls cavity.As the fiber used in this case were three yarn jute threads, therefore in the yarn cavity, too, there could be the possibility of trapping a small amount of water.
Here, it is worth highlighting that with the available instruments and at the given laboratory condition, it was only possible to prepare the composite mortar with a maximum of 12.5% of recycled jute fiber.Notably, more than the said amount of the fiber-mortar bonding was not optimum for the composite mortar preparation.
When the RJNF(12.5%)CMsamples dried and the trap water was removed, there must be some empty cavities formed inside of the said samples.So, a higher fiber density in the sample means more numbers of empty cavities, consequently improving the insulation capacity of the sample.Therefore, it can be said that RJNF(12.5%)CM is a better insulator than the other compared samples in Figure 13.
where, Co.V. is the coefficient of variation.

Conclusions
This study investigates the mechanical and thermal properties of jute fiber products and the recyclability of residual waste thread and net fibers, which are leftover during the net fabrication process and post-flexural tests.
Tensile strength tests have been conducted to evaluate the feasibility of the jute fiber nets to be used for net fiber textile retrofitting mortar (NFTRM) of the masonry walls or structures.For this campaign, two types of jute nets with 2.5 cm × 2.5 cm and 2.5 cm × 1.25 cm were tested.
Both types of jute nets were manually fabricated using jute fiber threads in the Strength laboratory of the University of Salerno, Italy.During the net fabrication process, scrap thread fibers and net fibers were collected.Additionally net fibers leftovers after the tensile strength tests were also collected and all these collected fibers were recycled to prepare RJNFCM.About 12% of recycled jute fiber (with respect to the dry mortar mass) was used for RJFCM preparation.
The tensile strength tests have demonstrated that the net sample 2.5 cm × 1.25 cm is 35.80% stiffer than the other net configurations (2.5 cm × 2.5 cm).While the previous one also has the capability to dissipate about 60% more applied load in terms of strain energy.
Whereas the TC tests have shown the TC values of the RJNFCM range from 0.110 (W/mK) to 0.121 (W/mK), and these composite samples have shown better insulation capacity in comparison to the author's previous works [20].
Following this experimental campaign, authors have used these jute fiber products (jute fiber nets and jute fiber composite mortars) for integrated upgrading of the masonry walls, and both structural behavior and thermal performance of these walls are evaluated.
Therefore, this work shows how it is possible to use these natural fiber products for integrated retrofitting or upgrading of the masonry wall or structures, to have sustainable, eco-friendly, greener, healthier, safer, and energy-efficient buildings.
More research is needed to optimize the thickness of TRM in order to obtain a given structural or thermal performance.In addition, the production process of jute nets should be improved to be scaled for industrial production.Further research is also scheduled to analyze the aging time of the jute net (prepared with jute threads (Figure 1), which are about one year older) used for the TRM system.
Finally, it is important to highlight that incorporating life cycle assessment (LCA) strategies is essential to comprehensively understand the environmental implications of jute fiber products and fiber-reinforced mortars in the construction industry, see for example [84].LCA can produce a detailed analysis of the carbon footprint at every stage of a product's life; from the cultivation of jute, which typically requires lower inputs of fertilizers and pesticides compared to other crops, thereby reducing the initial environmental impact, through the processing and manufacturing phases, where energy consumption and waste generation can be significant.For jute fiber-reinforced mortars, an LCA would consider not only the direct emissions and energy use during production, but also the potential savings in the use phase, due to improved energy efficiency from the material's insulating properties.Furthermore, the end-of-life recyclability of jute enhances its sustainability profile, potentially reducing landfill waste and allowing for the material's reuse or repurposing, thus contributing to a circular economy [85].By applying LCA to jute products, the construction industry can better align with the EU's sustainability directives, moving towards greener building practices that minimize the carbon footprint and foster long-term ecological balance.

Figure 4 .
Figure 4. (a) Complete view and (b) the set parameter of the adjustable torque-wrench.

Figure 5 .
Figure 5. Net samples with mesh configurations.(a) 2.5 cm × 2.5 cm and (b) 2.5 cm × 1.25 cm were placed in the machine for the tensile strength test.

Figure 5 .
Figure 5. Net samples with mesh configurations.(a) 2.5 cm × 2.5 cm and (b) 2.5 cm × 1.25 cm were placed in the machine for the tensile strength test.

Figure 5 .
Figure 5. Net samples with mesh configurations.(a) 2.5 cm × 2.5 cm and (b) 2.5 cm × 1.25 cm were placed in the machine for the tensile strength test.

Figure 6 .
Figure 6.Schenck universal machine used for tensile strength tests.

Figure 6 .
Figure 6.Schenck universal machine used for tensile strength tests.

Figure 7 .
Figure 7. Leftovers from the jute net fabrication and post-tensile test used for composite mortar preparation.

Figure 7 .
Figure 7. Leftovers from the jute net fabrication and post-tensile test used for composite mortar preparation.
( • C); t C = temperature of the cold plate ( • C); and A = the active zone surface area (m 2 ).Sustainability 2024, 16, x FOR PEER REVIEW 9 of 19

Figure 9 .
Figure 9. Thermal conductivity values of measured sample.

Figure 9 .
Figure 9. Thermal conductivity values of measured sample.

Table 1 .
Amount of fiber and water used.

Table 1 .
Amount of fiber and water used.

Recycled Jute Net Fiber Used Total Water Used for the Mixture
12.5% of the dry mortar mass 49.8% of the total mixture (mortar + fiber) mass

Table 3 .
Mechanical properties of jute fiber nets.
where, Co.V. is the coefficient of variation.

Table 4 .
Mechanical properties of the jute fiber net type N_2.5.

Table 5 .
Mechanical properties of the jute fiber net type N_1.25.

Table 6 .
Thermal conductivity of the RJNFCM.