Performance assessment of surface modified natural fibre using NaOH in composite concrete

Abaca fiber degradation in concrete owing to its alkaline nature decreases the strength of concrete. This research focuses on overcoming the degradation by alkaline treatment with sodium hydroxide (NaOH) to improve fiber performance. This study was completed with the extraction process of fiber, mechanical properties, micro-structural analysis of composite fiber concrete for both M30 and M40 grades, and durability performance if the fiber content, aspect ratio of fiber and molarities of Sodium Hydroxide were optimized using splitting tensile strength of the concrete matrix and it was found that the optimum percentage of fiber content was 1% at 12% alkali treatment. The composite concrete has achieved an increase of 2700 to 3100 kg m−2 in split tensile strength with treated abaca fibers compared to untreated fiber concrete. In addition, treated abaca fiber concrete provides better performance in mechanical and durability studies. The binding nature of fiber concrete is better than that of conventional concrete, which is evidenced in microstructural analysis. This study ultimately concluded that the treated abaca fiber composite concrete is a better alternative to commercially available untreated abaca fibers and other natural fibers.


Introduction
Plain cement concrete is essential to a developing construction industry and a prime contender for improving structural performance.Most structural and non-structural parts are made of plain cement concrete.Globally, the concrete industry is a major source of CO2 emissions [1,2].A number of studies have tried to partially substitute conventional building materials with sustainable waste [3][4][5][6] in response to the growing awareness about climate change and sustainable construction, while maintaining the materials' mechanical qualities and sustainability [7,8].Every year, more landfill space is needed to dispose of hypo sludge, a sustainable waste product from the paper mill [9].One of the essential ingredients for making concrete matrices is cement, which is bad for the environment [10].As a result, a number of research have looked into partially substituting equivalent materials at various ratios for cement.These replacements were carried out using mineral admixtures, which greatly extend concrete's lifespan and reduce its negative effects on the environment [9,[11][12][13].
Despite having a remarkable high compressive strength, plain cement concrete is highly brittle and prone to cracking because of tensile stress, which is often carried by steel reinforcement bars [14].In the past, adding fibre as reinforcement to ordinary concrete has significantly improved its tensile qualities.Concrete can be strengthened mechanically by the addition of fibres, which also help to narrow cracks and stop them from spreading [15].Therefore, a wide-ranging study was conducted to upgrade the mechanical properties of concrete by the inclusion of fibers.
The fibres that come from plants, animals, or minerals are known as natural fibres.Natural fibres are categorised based on where they come from.Vegetable, or cellulose-base, fibres include jute, cotton, and flax, among other significant fibres.Wool, silk, and mohair are examples of fibrous materials generated from proteins or animals.Among the often used fibre kinds are steel, glass, synthetic fibres like carbon, acrylic, and polyethylene terephthalate, as well as natural fibres like coconut, sugarcane bagasse, jute, wood, palm, abaca, and basalt [16][17][18][19][20][21][22][23][24][25][26][27].By adding the fibres by volume fraction percentage, these fibres decrease structural and shrinkage cracks and enhance the physio-chemical properties of the concrete [28,29].Although some natural fibers are derived from animals, most of them come from plants.Special attention will be paid to ligno cellulosic or cellulose-based fibers, these words will be used interchangeably with 'natural fibers' throughout the book.They are divided into five categories, best fibers, such as banana, ramie, jute, hemp, flax and kenaf.Piassava, abaca, and pineapple are some of the leaf fiber [18][19][20][21][22][23][24].Fruit fibers include coconut, oil palm, and assai [25].Seed fibers include cotton, coir, and kapok [26].Finally, stalk fibers such as wood, bamboo, grass, barley straw, bagasse [27][28][29].The 1990s saw a rise in publications on natural fibres and natural fibre composites due to claims about their supposed environmental advantages, which include biodegradability, reduced dependency on nonrenewable energy sources, and lower emissions of pollutants.Natural fiber composites lifecycle assessment studies revealed that, in contrast to their glass fiber composite counterparts, their production has a lower environmental impact; they use more fiber for an equivalent performance, which reduces the amount of polluting base polymer; they are lightweight, which increases fuel efficiency and lowers emissions; and they degrade naturally based on their convenient lives, producing recuperate energy and carbon credits [30][31][32][33][34][35].All plants with fiber properties have a different nature for growing.The abaca plant grows in all kinds of climatic conditions, and the plants that grow in hot climates, yield high fiber production [36].Except in clay and lowtolerance oil conditions, the abaca plant can be cultivated in almost all soil conditions [24].The cultivation of abaca fiber is a simple and easy process with less care that is resilient to diseases [37].The harvest of the abaca plant is usually done after one to two years of cultivation.The abaca plant has a productivity life of up to 12 years, and it has a maximum of 180-240 leaves in a single plant.The cultivation of abaca fiber has given a solution to overcome poverty for people in poor countries [38][39][40].
The physical and chemical properties of the abaca fiber include a high lignin content of 13.6%, cellulose content of 66.43%, hemicellulose content of 24.7% and water content of 0.7% [41].The resulting abaca fiber in concrete has high tensile and compressive strengths, depending on the addition of fiber percentage.The commercial value of leaf fiber is low because it is coarser than the best plant fibers and the uses are limited.The fibers are obtained through a mechanical process in that the non-fibrous material in the player of the leaf is removed to obtain the fiber.They are then washed and dried, often in the sun, which also causes bleaching.The Philippines provides the majority of the world's abaca fibre for cordage and pulp for specialised paper.It provides 85% of the abaca fiber required globally [12][13][14][15][16][17].
Most of the researchers and developers have more interest in composite materials with natural fibers.Many researchers have focused on natural fibers because of their low cost and biodegradability [42].Retting is one of the oldest and most traditional methods of removing contamination from the plant, which is performed by an abio-gradation process, comprising microbial abaca leaves with fiber from the pitch.Generally, this process requires 2-3 weeks for one cycle of extraction [24].
There are several techniques for the separation of abaca fiber, but they are generally separated from the abaca leaf by pretreatment with chemicals called alkali treatment.Alkali treatment is one of the most useful methods for the surface modification of cellulosic fibers.The abaca fibers were immersed in an aqueous NaOH solution (5%) for 2 h under a vacuum to ensure good penetration of the alkali solutions to fiber bundles.One frequent technique to increase the computability between natural fibres and resin material is fibre surface modification, which involves chemically treating natural fibre with an alkali solution.
There are many methods and processes to dry fibers.This process is easy and economical because the waste timber is dried ground into fibers and then mixed with synthetic glue [37].The synthesis is also known as polymeric methylene diphenyl diisocyanate, which is used in very small quantities of approximately 3%-4% [38].

Abaca fiber extraction process
The primary focus of this project is to use abaca fiber in the concrete and to study its properties.The extracted fiber from the abaca plant was strong and had a high tensile strength [40].Abaca fiber is a natural fiber and it is very easy to cultivate.The fiber has many features like high strength with strong bonds, good durability, and also a water resistance nature.The physical appearance of abaca fibers was a little coarser, flexible and smooth.Abaca fiber can be used alone or blended with acrylic because it has a strong bonding capacity.Table 1 lists the characteristics of the abaca fibres that were examined.

Materials and methods
The ingredients used to prepare the concrete and their properties are discussed in this section.The ingredients used in this project were, Ordinary Portland Cement (OPC) as binding material, natural coarse aggregate, fine aggregate (M sand) of size less than 4.36 mm, abaca fiber, superplasticizer, and ordinary portable drinking water.

Workability and compaction of concrete
This fibre significantly reduces workability.The consolidation of fresh mix is negatively impacted by this circumstance.Not even extended external vibration can cause the concrete to compress.The volume of fibre will approach.The uneven distribution of fibres is another effect of low workability.Generally speaking, adding more water to the cement or using admixtures that reduce water content improves the workability and compaction standards of the mix.

Binder material
The OPC of 53-grade cement is used as an imperative material for both concrete grades.The 53-grade cement under the Ultra Tech brand OPC was recently produced in the industry and was acquired from a domestic market.All basic tests on cement were performed by confirming the IS4031:1988 [43].

Aggregate and natural fibers
In recent times, the availability of river sand has been very difficult in the local market, and all construction projects have started manufacturing sand as a fine aggregate in construction.The aggregate's bulk density was less than 1920 kg m −3 , and it passed through a sieve with a size of less than 4.36 mm.It was found that the specific gravity was 2.6.Likewise, coarse aggregate with a specific gravity of 2.75 was extracted from size ranges of 20 to 12.5 mm.Before being used in concrete, both fine and coarse aggregates were completely cleaned to get rid of any dirt, and then they were dried.
Because of their purported environmental advantages, including biodegradability, reduced dependency on non-renewable energy sources, and lower pollutant emissions, natural fibres and natural fibre composites experienced a spike in publications later in the 1990s.Natural fiber composite's life cycle assessment studies revealed that, in contrast to their glass fiber composite counterparts, their production has a lower environmental impact than they use.
The use of abaca fiber in cement concrete was the primary focus of this study.The extraction of abaca fibers from the abaca plant is shown in figure 1.The process involves pseudostem, tuxying, stripping, and extraction of fiber, and the fiber is used in concrete for research work.The tuxy waste shea this left unused.
Due to the above properties, abaca fiber has various advantages over other fibers.Abaca fiber can be recyclable, and it has low maintenance with high durability.Abaca fiber has high impact resistance properties, good sound, and does not easily absorb moisture, dust particles and water.

Natural fiber's interfacial bond behaviour in a cement matrix
One of the most crucial elements that enhanced the strength characteristics of concrete with abaca fibre is the coupling of faces during the transition zone between the cement matrix and fibre.A significant improvement was observed in the oven heated abaca fiber which is due to the presence of cellulose.The cellulose in the fibre increases the concrete's initial strength and serves as reinforcement to increase the concrete's longevity.The abaca fibre was maintained at 150 degrees Celsius for eight hours.After being heated up in the oven, abaca fibre was cut into a cross-section and photographed using a scanning electron microscope (SEM).This research showed that heating the cellulose during the alkalization process improves the extraction of lignin and hemicellulose matrix separation compared to not heating the cellulose during the alkalization process.The polymers lignin and hemicellulose have amorphous phases.The cellulose fiber's degree of crystallinity increased as a result of those components being removed.
The resulting cellulose's degree of crystallinity was assessed using XRD analysis; figure 2 displays the diffractogram [44].
Figure 2 shows that Sel B surface is smoother than Sel A, the lignin has been extracted from the matrix.Sel A and B had crystallinity degrees of 65 and 44%, respectively.
From figure 3, it can be seen that there are no changes in the microstructure of the surface and cross-section.Therefore, it can be concluded that the bonding between the cement mortar and abaca fiber is good, even if it is heated.
The abaca fiber is used in both M30 and M40 grade concrete.The quantity of abaca fiber is calculated in terms of percentages of the cement weight.To find the optimum percent level of abaca fiber content, more castings and testing were done with abaca fiber at 0.5, 0.75, 1, 1.25, and 1.5% with aspect ratios of 100, 200, 300 and 400.

Superplasticizer and water
The optimum degree of super-plasticizer for both the concrete is found by conducting or perforating the Marsh cone test.The time required to measure the material and to stream out of the conies recorded.The superplasticizer in this study is Glenium C380.It is a new form of water reducer that is not only suitable for prestressed concrete or high-strength concrete but also for special concretes.Improving the early and late strengths of concrete is one of the major advantages.It makes regular concrete more workable.Concrete is made and the curing procedure is carried out using the portable drinking water.

Mix proportion
The mix proportions for both M30 and M40 grade concrete have been designed according to IS 10262-2009 [45], and the ratios were found to be 1:2.49:3.23:0.42 and 1:2.15:2.96:0.39,respectively.Table 2 lists the material proportions for the concrete grade mentioned above based on the mix ratio.
The concrete's workability has been determined using the slump test and the compaction factor test.Table 3 lists the necessary requirements for concrete of grades M30 and M40.

Alkali treatment
Abaca fiber is obtained naturally from the abaca plant.The natural fiber will get decay at an earlier stage, to avoid that, the fiber is undergone alkali treatment (NaOH).In this process, the fiber is subjected to a concentrated aqueous solution which is a very strong base for swelling.The alkaline solution results in changes in the mechanical properties, material dimensions, morphology and structure of concrete [46].Alkali treatment is done with Sodium Hydroxide solutions at 2, 6, 8, 10, 12, 16 and 20% with fibers in different chambers.The fibers were treated with various percentages of NaOH concentrations for 48 h based under normal conditions, after which 1% acetic acid was added to remove the excess solution.The treated fibers were washed in clean water to remove the acid content.Finally, the treated fibers were left to dry for 2-3 days, till constant weight was achieved [47].

Specimen preparation and testing
To find the optimum molarities of the alkali treatment, the cylindrical specimen with a size of 150 × 300 mm, cubical specimen of standard size 150 mm × 150 mm and beam size of 3.2 mm × 12.7 mm × 125 mm were cast.The specimen was cast for both the concrete grades, to obtain the optimum fiber content.On the 28th day of the curing time, the test was conducted, and the outcomes were contrasted with standard concrete.

Compressive strength test
In order to determine the compressive strength, 150 × 150 × 150 mm cubes were cast.The concrete is appropriately tempered before being poured into the mould to avoid voids.The test specimens are placed in water to cure after the moulds are removed after a 24-hour period.These specimens should have a nice, level top surface.This is achieved by evenly covering the specimen's whole surface with cement paste.Following a curing period of either seven or 28 days, the specimens are subjected to compression testing apparatus.A load of 140 kg cm −2 per minute should be applied gradually until the specimens fail.The specimen area divided by the load at failure yields the compressive strength of concrete.The compressive strength test was performed on the abaca fiber concrete and conventional concrete after 7, 14 and 28 of curing.The test was done according to IS 516-1959 [48].

Split tensile test
To carry out this test, a cylindrical specimen with a 150 mm diameter and 300 mm height has been cast.To determine the concrete's splitting characteristics, this test was conducted using a Split Cylinder testing apparatus.Submerge the cast specimen in water at 27 degrees Celsius for a duration of 24 h.After that, the specimen needs to be removed from the mould and immersed in fresh water.Remove the specimen from the submerged water and clean the water before beginning the test.Next, record the specimen's dimensions and weight.Layer the plywood strip both on top and underneath the specimen.Next, the specimen needs to be put on the testing device.Next, gradually increase the stress at a rate of 1.2 to 2.4 MPa min −1 while referring to IS 5816 1999 as a guidance.The test was conducted according to IS 516-1959 [48].

Flexural strength test
The beam measures 750 × 150 × 150 mm in dimension.A universal testing apparatus equipped with a threepoint bend fixture is used to conduct this test.It is necessary to position the specimen on the loading sites.No loading points should come into contact with the specimen's hand-finished surface.It will be guaranteed that the specimen and loading points make appropriate contact by doing this.Load the specimen without causing any stress until it starts to fail steadily.Measure the cross-section of the tested item at both ends and the centre to find the average height and depth.In accordance with IS 516-1959 [48], the flexural beam strength test was finished for each of the four optimal mixes.

Impact test
The cylindrical specimen size is 150 mm × 300 mm.The Charpy impact test is used to determine material toughness.The ACI 544 drop weight test is a very simple test that requires striking 152 mm in diameter and 63.5 mm in height cylindrical specimens by hand.A 4.45 kilogramme mass repeatedly descends freely from a height of 457 mm until collapse.The specimen is set up on a steel disc and is supported by a centrally located 63.5 mm diameter steel ball and a specific positioning lug.The test specimen is supported by petroleum jelly or grease, and the load is distributed by the steel ball.The impact number which is the impact number required to induce cracking is recorded at the time the first crack appears.Testing is then carried out continuously until failure occurs, which is determined by the impact number at which the crack widens and contacts the side lugs.The impact strength test was conducted according to ACI 544.IR-96 [49].A disc specimen of 150 × 63.5 mm was produced in order to evaluate the concrete's resilience to impact.On the 28th day of the curing time, the test was done.

Optimization of abaca fiber content and aspect ratio
There are several techniques for the separation of abaca fiber, but generally, it is separated from the abaca leaf by retreating with chemicals called alkali treatment.This method is used with a 5% Sodium Hydroxide solution and with constant volume and length of fiber that is reinforced at the site.The optimization of fiber is one of the important parameters to be considered, where the quantity of fiber to be used in the concrete increases its performance.The casting sand testing was done with abaca fiber at 0.5, 0.75, 1, 1.25 and 1.5% with aspect ratios of 100, 200, 300 and 400.Abaca fibres undergo structural and chemical modifications as a result of alkali treatments; the extent of these modifications rises with alkali concentration.Because natural fibres contain hydroxyl groups, they can be chemically surface treated.The hydroxyl groups have two possible actions: they can either form hydrogen bonds with the cellulose molecules to activate these groups or they can introduce additional moieties that offer helpful interlocks within the system.Surface characteristics including adhesion, surface tension, wetting, and fibre porosity can all be improved by chemical treatment.The irregularities on the fibre surface have a major impact on the mechanical interlocking at the contact.By altering the components, the physical and chemical interactions at the interface can be altered, improving the interfacial characteristics (John et al 2008, John and Anandjiwala 2008).The abaca fibre test results at various aspect ratios and percentages are shown in figures 4 and 5.
Based on the results, it was detected that both the concrete grades and strength were found to increase for the abaca fiber at 0.5, 0.75 and 1% for 100 and 200 aspect ratios.The strength decreased with a further increase in the fiber percentage, i.e., for 1.25 and 1.5%.Similarly, the strength was decreasing for aspect ratios of 300 and 400.With these results, It is evident that an aspect ratio of 200 and a fibre content of 1% are suitable.

Optimization of molarity of alkali treatment
The 28-day split tensile strength test results for abaca fibre concrete (30M2 and 40M4) and conventional concrete (30M1 and 40M3) are shown in figure 6.According to the test results, the strength reduced by 16% and 20%, respectively, while the split tensile strength increased for 2, 6, 8, 10%, and 12% alkali molarities.This result pattern was found to be similar for both M30 and M40 grade concrete, with pictures that the abaca fiber treated with 12% alkali molarities has attained high strength and thus it is concluded as the optimum treatment percentage.From this, all the mechanical properties and based on their durability can be done for the optimum fiber content obtained from various aspect ratios with abaca percentage (200,1%) and alkali molarities (12%).

Effect of fibre content on slump
It has been observed that adding abaca fibres to fresh concrete significantly altered its stability, workability, and compatibility.A more cohesive mixture was produced by the abaca fibre concrete, which is a positive sign for stiffness and stability.The fibres' interweaving created a matrix that the concrete was encased in, increasing its cohesiveness.Workability-wise, mixtures with a reduced slump were produced by adding more fibre while maintaining a constant water-to-cement ratio and superplasticizer content.It was discovered during casting that the mixture's fibre content affected the concrete's compatibility.

Compressive strength test
Figure 7 illustrates the compression testing machines used to assess the cubes for exploitation, which has a 1500 kN capacity.
For M30 and M40 grade concrete, it was discovered that after 7, 14, and 28 days, the strengths of both conventional concrete and abaca fibre concrete increased.Compared to conventional concrete the strength of abaca fiber concrete was found to be higher in both grades of concrete.The 28thday test results of mix30M1 was 33.5 N mm −2 , and 30M2 was 37.3 N mm −2 which is 11.34% higher than 30M1 concrete.Similarly, the mix 40M3 has attained its compressive strength of 41.6 N mm −2 , whereas 40M4 has attained 45.4 N mm −2 which is 9.13% more than 40M3.Figure 8 illustrates the compressive strength of both conventional and abaca fibre concrete.The abaca fibre incorporated in the concrete is what allows the abaca fibre concrete to reach a higher strength than normal concrete, as demonstrated by the preceding data.The foregoing result demonstrates that the addition of fibre enhances not only the flexural and split tensile strengths but also the compressive strength.

Scanning electron microscopy (SEM) analysis
The SEM analysis of both conventional and abaca fiber concrete was done to evaluate the surface fractures, flaws and other contaminants.The SEM images of (a) 30M1, (b) 30M2, (c) 40M3 and (d)4 0M4 are shown in figure 9.The SEM image of 30M1 clearly shows the formation of a clustered effect in concrete.Compared with 30M2, the  pore content is high in 30M1, and at the same time the formation of C-S-H gelisalsolowin30M1.The HS which has high calcium content and abaca fiber stimulates the better formation of calcium precipitate in concrete.This is an important factor for the increase in the strength of 30M2.The below images clearly show the difference between concrete with and without fiber content.The cluster effect is high in 30M2 and 40M4, due to the presence of alkali-treated fiber.
The SEM analysis for 30M1, 30M2, 40M3 and 40M4 was done at different magnifications to obtain a clear and crystal view of the concrete mix.The SEM analysis of 30M1 and 40M3 shows a scatter effect with a lot of porous in it and does not have much C-S-H formation, whereas the image of 30M2 and 40M4 has high C-S-H gel formation, raising high calcium content in the presence of HS.The porous content based on the images 30M2 and 40M4 is less compared to 30M1 and 40M2.

Split tensile strength test
The testing of cylindrical specimens of both conventional and abaca fiber concrete is shown in figure 10.
As with the results of the compressive strength test, the split tensile strength test clearly shows that the abaca fibre concrete in both grades of concrete has higher strength.The 28th-day test result of 30M1 was 3.51 N mm −2 , whereas the strength of 30M2 achieved 3.98 N mm −2 , which is 13.4% higher than 30M1.Similarly, the28thday strength of 40M3 was 4.27 N mm −2 , whereas the strength of 40M4 was 4.61 N mm −2 , which is 7.96% higher than the 40M3 mix.This demonstrates how adding fibres to concrete raises its tensile strength.Figure 11 displays the split tensile test results for both varieties of concrete.

Flexural strength test
Similar to the compression and split tensile test, the flexural strength test results also clearly show that the highest strength lies in the abaca fiber concrete in both grades of concrete.The 28thday test result of 30M1 was 3.86 N mm −2 , whereas the strength of 30M2 has achieved 4.12 N mm −2 , which is 6.7% higher than 30M1.Similarly, the 28th-day strength of 40M3 was 4.57 N mm −2 , whereas the strength of 40M4 was 4.82 N mm −2 , which is 5.47% higher than the 40M3 mix.This indicates that the addition of fibres to concrete boosts its flexural strength.Figure 12 displays the results of the flexural tests for both types of concrete.

Impact strength test
On the 28th day of the curing time, the impact test was carried out.The test results for abaca fibre and ordinary concrete are displayed in table 4. The number of strikes needed to achieve the first and last cracks is indicated in the table, as is the number of blows that are turned into energy (Nm), which is also shown in table 4.
According to the findings, because abaca fibre is present in typical concrete, its resistance is higher than that of pure concrete.The alkali-treated fiber had higher rigidity compared to the untreated fibres.Figure 13 shows the specimen which achieved its final crack due to the impact load.

Non-destructive testing of concrete specimen (NDT)
The rebound hammer was used to conduct the NDT for the cube specimen.Before the specimen was tested under a compressive testing machine, the entire specimen was subjected to NDT.This test is conducted to compare the rebound hammer test values with destructive test results.The test was carried out for 7, 14 and 28 days based on the curing period and the results were recorded, however, only the 28th test results were projected in this study.Figure 14 shows the test results for the NDT and destructive test values.
The 28thday NDT value for 30M1 is 31.5 N mm −2 and the strength of 30M2 was 36 N mm −2 .Similarly, the NDT of 40M3 was 42.5 N mm −2 and 40M4 has achieved 48 N mm −2 .The destructive test results of 30M1, 30M2, 40M3 and 40M4 were 33.5, 37.3, 41.6 and 45.4 N mm −2 .While comparing the NDT and destructive  values, the results are almost the same for M30 grade concrete and conventional concrete of M40 grade, but there was an increment of 5.7%in strength in M40 grade abaca fiber concrete.

Durability properties -water absorption
The ability of concrete to withstand weathering and chemical attack while maintaining the intended engineering capabilities was ascertained by looking at its durability characteristics.The rapid chloride permeability test (RCPT) and Sorptivity tests were conducted for both concrete classes in this study to assess durability features,   such as water absorption.Water absorption was calculated using conventional operating procedures.During days 14, 28, 56, 90, and 180 of the strengthening period, the experiment was conducted.After casting, the specimens were water-cured.The curing water was changed at an interval of 2 days.After 30 days of curing the specimens were placed in the oven for 24 h, and then placed in water.Figure 15 shows the water absorption values for both the conventional and abaca fiber concrete.The water absorption for conventional concrete was high compared to abaca fiber concrete for both grades.The 180th-day water absorption of 30M1 and 40M3 was 3.11 and 2.97, whereas the values of 30M2 and 40M4 were 2.54 and 2.02.When comparing the two different results the abaca fibre concrete is ranked 18.32 and 31.9%lower than 30M1 and 40M3.The abaca fibre was shielded from additional water absorption by the alkali solution treatment.

RCPT
After 28 days of water curing, the RCPT test was performed on both concrete grades.The test has been conducted according to the standard AASHTO T 277 [50].The RCPT was conducted by placing the samples between a core and a cylinder.A constant voltage of roughly 60 V DC was maintained.A qualitative rating's concrete permeability is determined by the charge that flows through the sample.The Sorptivity method is carried out by infiltration of water into a pore of the cube by capillary action.The sample of 100 mm dimension was kept in the oven for 24 h for drying and then 24 h for cooling [51,52].After the cycle of drying and wetting was completed, the water content of 5-10 mm was present.The swelling of water volume which is plotted as 'q' penetrated per unit surface.The movement of water in capillary pores is assessed by the slope intermediate line as calculated.The test is performed to identify the pores present inside the concrete mix through chloride penetration.Table 5 shows the charge passed in coulombs for both conventional and abaca fiber concrete on the 28 th day.It is possible to assume from the test result that abaca fibre concrete has a lower proportion of chloride penetration.When compared to abaca fibre concrete, conventional concrete has a higher percentage of porous  material due to the significant chloride penetration.The fiber content seals the porous and acts as a barrier inside the concrete.

Sorptivity
By monitoring and increasing the specimen's mass and measuring the amount of water it absorbs over time throughout the exposed surface, a Sorptivity test has been conducted to determine the rate of water absorption on the concrete.The capillary water test was carried out for 1 h with intervals of a few minutes [53].The Sorptivity test results for both conventional and abaca fiber concrete are shown in below figure 16.
The result shows that the capillary rise in the conventional concrete is quite higher compared to abaca fiber concrete, and the resulting pattern is found to be similar in both concrete grades.The results prove that the treated abaca fiber does not absorb more water, and also acts as a barrier for the concrete from external effects.

Conclusion
According to this study, the traditional usage of abaca fibers strengthens concrete that has been evaluated using these various tests performed in this study.Concrete now performs better in terms of strength, resistance, and longevity thanks to fibre that has been alkali-treated.Being natural the fiber is extracted from abaca fiber at a low cost.The following points were proven in both the grades of concrete (M30 and M40) during this research work.
It has been revealed that abaca fibre concrete has greater strength than plain concrete through mechanical attributes like Compressive strength, Flexural Strength & Split tensile strength.The SEM image of the abaca fiber was found to have less porosity, high C-S-H formation and a cluster effect which is the main reason for the high strength in the concrete.When compared to normal concrete, abaca fibre concrete has a higher impact resistance because the fibres in the concrete create a strong resistance against impact loads.The abaca fiber seals are micro-porous which act as a barrier in the concrete, that do not allow the concrete to absorb much water, and hence proven that the abaca fiber concrete has less water permeability and chloride penetration.Overall, abaca fiber concrete can be strongly suggested for all types of structural works and marine structures.The slump reduces and the mixture gets more difficult to mix for both grades as the fibre content rises.The amount of fibre included in the mixture had a role in the concrete's increasing compatibility.
The amount of fibre added to the concrete had an inverse relationship with the density of the abaca fibre concrete.In comparison to the control mix (2340 kg m −3 ), the hardened concrete became a substantially lighter  composite (2060 kg m −3 ) as the fibre percentage improved (1.00%).At 1.00% fibre content, the density decreased by 12%.The concrete matrix's ductility was enhanced as a result of the higher modulus of elasticity.By spreading and absorbing some of the crack energy, the abaca fibres in the concrete mix served as a medium to slow down and eventually cease the spread of cracks.This strengthened the concrete matrix's localised ductility to some extent.Abaca fiber has various advantages over other fibers.Abaca fiber can be recyclable, and it has low maintenance with high durability.Abaca fiber has high impact resisting properties, good sound, and does not absorb moisture, dust particles and water easily.Overall, the abaca fiber concrete can be strongly suggested for all kinds of structural works and marine structures.

Figure 7 .
Figure 7. Casting and testing of conventional & abaca fiber concrete cubes.

Figure 14 .
Figure 14.Comparison of NDT and destructive test values.

Figure 15 .
Figure 15.Water absorption of conventional and abaca fibre concrete.

Figure 16 .
Figure 16.Sorptivity test values of conventional and abaca fibre concrete.

Table 1 .
Properties of abaca fiber.

Table 2 .
Material proportions of concrete.Fine aggregate in kg/m 3 Coarse aggregate in kg/m 3

Table 4 .
Impact resistance of convention and abaca fiber concrete.