Fabrication and Characterization of Cement-Based Hybrid Concrete Containing Coir Fiber for Advancing Concrete Construction

Abstract

Nowadays, the incorporation of natural fiber, such as coir fiber, to high-strength concrete has sparked a lot of attention in the construction materials industry. This is because coir fibers are significantly cheaper and more widely accessible than synthetic fibers. Natural fibers such as bamboo, flax, hemp, and coir have distinct microstructures and chemical compositions from cement-based materials. The physical and mechanical properties of natural fiber, such as coir fiber, are significantly correlated with fiber concentration and cellulose component. However, coir fiber has high stretching to failure, while bamboo, flax, and hemp fibers are very resistant to stress and increase stiffness. Based on these distinctive fiber qualities, it is anticipated that coir fiber would facilitate the development of cement-based materials for advanced concrete building applications. In this paper, coir fiber-reinforced cement-based concretes were evaluated in terms of workability, compressive strength, flexural strength, splitting tensile strength, modulus of elasticity, and permeability. The relationship between strength and fiber content was analyzed to understand the impact of coir fiber on the properties of coir fiber-reinforced cement-based concrete. Based on the results obtained, it is determined that 2% coir fiber modification offers the highest compressive strength, splitting tensile strength, and flexural strength. Moreover, the modulus of elasticity is increased, and the permeability is plummeted by the volume fractions of coir fiber 1%, 2%, and 3% because the blending of coir fiber has a bridging and dispersing mechanism of the force-carrying capacity in concrete. In conclusion, coir fiber might be a viable choice for improving the strength and durability of concrete. Therefore, the sparing use of coir fiber presented in this research can be implemented for the manufacturing of concrete in the future.

1. Introduction

Concrete is the most extensively used construction material all over the world, and its use in numerous industries has increased since its development in the Roman era. This trend can be explained principally by its advantages in terms of strength, stability, and efficiency over other types of construction materials [1,2,3,4]. However, its application is severely limited due to its low tensile strength, low resistance to fracture, and low inclination to mechanical distortion. Fiber-reinforced concrete is commonly measured as an option to compensate for concrete’s brittleness [5]. Since Biblical times [6], fiber has been employed to strengthen fragile matrices. Synthetic fibers, glass fibers, steel fibers, polyvinyl alcohol fibers [7,8], and natural fibers are some of the fibers that have been utilized in concrete to improve tensile strength. Steel fiber is the most often used among them [6,9]. On the other hand, corrosion is a problem with steel fibers, which limits their use [10]. Synthetic fibers are often regarded as the greatest solution to this problem, according to most experts, though the manufacturing of synthetic fiber is both costly and energy intensive. In these circumstances, natural fibers are usually regarded as a viable fiber option for the manufacture of fiber-reinforced concrete. Individual natural fibers are randomly dispersed throughout the matrix, and tiny diameters are discontinuous in concrete. Natural fiber has environmental, economic, energy, and resource conservation benefits [11].

Additionally, natural fibers are traditionally categorized into three categories based on their source: animals, minerals, and plants [12]. Among them, plant fibers are favored. Plant fiber is the most desired fiber because cellulose is a crucial component in plant fiber, whereas animal fiber is primarily rich in terms of protein and mineral fiber is associated with health. Apart from the report written by Pickering et al. [12], plant fiber is stronger and stiffer than fiber produced from animals. It has been remarked that the possibilities of plant fibers used in mixtures of concrete can significantly improve the properties and performance of concrete [11]. Moreover, due to their strong tensile characteristics and unique microstructure, cellulose-based plant fibers can be used in concrete as a reinforcement material because of their small densities [13,14]. The option of combining several fibers in concrete, such as nylon fiber, jute fiber, human hair fiber, coir fiber, sisal, and hemp fiber [15], was investigated to progress concrete’s characteristic strength. Natural fibers were reported to enhance mechanical characteristics, such as compressive strength, tensile strength, cracking and damage tolerance, and the ability of concrete to deform [15,16,17,18]. Natural fiber also has the advantage of requiring less energy to convert into fiber [19]. Because of their advantageous features, synthetic fibers are frequently employed to increase concrete tensile strength. However, these synthetic fibers, e.g., acrylic and steel, are costly. Therefore, synthetic fibers raise the project’s overall cost. Moreover, natural fibers are a less expensive, environmentally friendly, and long-term option for increasing concrete’s tensile strength [15]. In this research work, coir (or coconut) fiber is utilized in concrete to develop the properties of concrete. Coir fiber is a by-product of the coconut oil manufacturing process. It is extensively used across the world’s tropical climates, notably in Africa, Asia, and America. In 2020, the worldwide coco coir market was estimated to be worth roughly USD 304.8 million. The market is predicted to develop at an 8.1% CAGR from 2022 to 2027, reaching a value of roughly USD 485.9 million by 2026 [20]. Coir fiber is rarely used in construction and is mainly dumped as agricultural waste [21]. Given the demand for cheap housing systems for urban and rural populations in developing countries, numerous programs have been proposed to decrease the cost of conventional building ingredients. One of the most innovative proposals is to find, develop, and use a substitute, non-traditional local building constituents, such as agricultural waste and residues, as reinforcing for traditional building materials [22]. One such alternative method is the mass production of coir fiber, which can be applied as a reinforcing material in concrete. The plant produces a lot of coir fiber waste. At present, industrial incineration waste management practices are being carried out in an uncontrolled manner, consequently contributing significantly to air pollution. Therefore, it becomes expensive to dispose of these residues in an environmentally friendly manner. In this case, efforts are being made to progress the usage of these by-products by developing value-added products. One way to get rid of this waste is to use coir fiber in building materials as reinforcement components. In the early 1900s, fibers were utilized in concrete to enhance ductility and flexural strength [23]. Fibers in concrete can increase toughness, decrease crack propagation, and improve tensile and flexural strength [24,25,26,27]. Moreover, plastic shrinkage and drying shrinkage cracking can be controlled by the fiber [28,29]. Therefore, limited research studies have been conducted on coir (or coconut) fiber by the volume fraction in concrete.

Hence, this research investigation is to measure the workability, compressive strength, splitting strength, flexural strength, modulus of elasticity, and permeability of concrete that contains varying amounts of coir fiber as a reinforcement ingredient. Furthermore, this study suggests the math models equation for the properties of concrete reinforced with various content of coir fiber by the volume fraction of concrete.

2. Materials and Methods

2.1. Materials

Coir fiber (CF) was obtained from the Sukkur region, Sindh, Pakistan, where it was readily available and was used as a volume fraction in concrete. Coir fiber is accessible in several lengths, fluctuating from 10 to 30 mm and 0.2 mm in diameter. In this research work, Portland cement (PC) was used as a binding component. The PC was purchased in a local market in Hyderabad, Pakistan.

Table 1. Chemical composition of PC.

Type of Binder	Compound (%)
	CaO	SiO2	MnO	Al2O3	P2O5	MgO	Fe2O3	K2O	SO3	Na2O
Portland Cement (PC)	60.22	20.78	0.18	5.11	0.30	3.82	3.17	0.72	2.86	0.18

shows the oxides composition of PC, and

Table 2. Chemical composition of coir fiber [34,35].

Type of Fiber	Chemical Composition (%)
	Cellulose	Lignin	Water Soluble	Hemi-Cellulose	Pectin’s Related Compound	Ash
Coir fiber	43.44	45.84	5.25	0.25	3.33	2.22

displays the chemical properties of CF. Moreover,

Table 3. Physical properties of aggregates.

Physical Properties	Fine Aggregate	Coarse Aggregate
Water absorption (%)	1.30	0.75
Specific gravity (g/cm3)	2.61	2.65
Fineness modulus (no unit)	2.15	6.75
Bulk density (kg/m3)	1845	1630

indicates the physical properties of the aggregates. The fine aggregates (FA) were river sand that passed through a #4 sieve, while the coarse aggregates (CA) were crushed stones with a size of 20 mm. The bulk density and sieve analysis of aggregates was estimated using ASTM C29/C29M-97 [30] and ASTM C136/C136M-19 [31] consistently. The grading curves for CA and FA are demonstrated in Figure 1. Furthermore, ASTM C128-01 [32] and ASTM C127-15 [33] were applied to determine the specific gravity and water absorption of FA and CA congruently. In addition, for the research investigation, tap water was utilized to help in the mixing and curing processes.

2.2. Mix Proportions of Conrete

On fresh and hardened concrete, the investigative process was performed on mixtures containing 0 %, 1%, 2%, 3%, and 4% coir fiber introduced by volume fraction. However, five concrete mixes were constructed with cement or cement + coir fiber/fine aggregate/coarse aggregate ratio of 1:1.5:3, and the water-to-cement ratio was kept constant at 0.50. One of which was built entirely of PC and the other four with the reinforcement of 1%, 2%, 3%, and 4% coir fiber by volume fraction of concrete, as shown in

Table 4. Mixture proportions of concrete (kg/m³).

Mix ID	PC	Coir Fiber	Fine Aggregate	Coarse Aggregate	Water	Water/Binder Ratio
C	373	0	560	1120	187	0.50
CF1	373	3.73	560	1120	187	0.50
CF2	373	7.46	560	1120	187	0.50
CF3	373	11.19	560	1120	187	0.50
CF4	373	14.92	560	1120	187	0.50

.

2.3. Testing Methods

2.3.1. Slump Test

This test was performed on five mixes containing coir fiber accumulation in varying amounts by volume fraction in concrete by witnessing the ASTM C143/C143M-20 [36].

2.3.2. Mechanical Testing

The cubical samples (100 × 100 × 100 mm) were prepared using various proportions of CF, and the compressive strength of the concrete was tested by following ASTM C39/C39M-21 [37], while the cylinder samples (200 × 100 mm) were made of concrete reinforced with different contents of CF for determining the split tensile strength by obeying the ASTM C 496/C496M-17 [38] code procedure. Moreover, prisms (500 × 100 × 100 mm) were cast with varying quantities of CF and tested for central point flexural strength according to ASTM C293/C293M-16 [39]. Furthermore, ASTM C469/C469M-22 [40] was used to determine the modulus of elasticity of the cylindrical samples (300 × 150 mm) that were concrete mixtures blended with several quantities of CF by volume percent, while the permeability was measured on the cubic samples (100 × 100 × 100 mm) of concrete reinforced with varying content of CF by volume fraction of concrete by following BS EN 12390-8:2019 [41]. In addition, three concrete samples were cast and tested for each content of CF after 28 days of curing. Figure 2 shows the experimental setup for testing the samples.

3. Results and Discussions

3.1. Slump Test

The workability was evaluated through the slump test on a fresh mix of concrete reinforced with coir fiber at inclusion levels of 0%, 1%, 2%, 3%, and 4%. Figure 3 illustrates the slump of coir fiber-reinforced cement-based hybrid concrete recorded in the experiment. It is evident from the outcomes that the workability declined with the inclusion of coir fiber in the concrete. At the extreme limit of coir fiber-reinforcement, i.e., 4% in this work, the workability of concrete decreased by more than 50% of that of the control mix. Fibers improve the water requirement of concrete by absorbing a greater quantity of water, leading to less workable and flowable concrete [42,43,44,45]; this is well documented in the current literature. The decline in workability due to higher water absorption of coir fiber is also reported by Ali et al. [46] and Bheel et al. [47]. Usually, the researcher has presented that since the accumulation of coir fiber reduced the workability of the cement-based material, adding more mixing water to the mortar than that of the mortar without coir fiber was necessary for such research. This effect could be related to the structure of the coir fiber having high-water absorption [48].

To evaluate the workability of the mortar containing coir fiber, the researchers used the flow table test, and though the consistency of the mortar was kept constant at 140 ± 5 mm, the quantity of mixing water required for each mortar was different. It was noted that the accumulation of coir fiber increased the amount of water necessary to reach the appropriate workability. The water-to-binder ratio increased with increases in the fiber’s length and volume fraction. It was also stated that longer fibers influenced workability negatively compared to shorter fibers [49]. Sathiparan et al. determined that, with higher content of the coir fiber in cement and lime-based material, the quantity of water required also increased. Despite the use of a different binder, the addition of coir fiber decreased the apparent density of the mortar. This shows that the incorporation of fiber in the cement-based mortar produces a light-weight material, which also indicates the reduced workability of the cement-based material. These findings suggest that a high quantity of fibers requires higher mixing water content to reach the desirable workability [50].

3.2. Compressive Strength

Figure 4 and

Table 5. Compressive strength of concrete.

Mix ID	Compressive Force (KN)	Compressive Strength (MPa)	Average Compressive Strength (MPa)
C	288.0	28.80	29
	290.0	29.00
	292.0	29.20
CF1	306.8	30.68	30.20
	300.0	30.00
	299.2	29.92
CF2	318.8	31.88	32
	323.6	32.36
	317.6	31.76
CF3	297.8	29.78	29.80
	296.2	29.62
	300.0	30.00
CF4	270.0	27.00	26.50
	261.8	26.18
	263.2	26.32

demonstrate the influence of coir fiber reinforcement on the compressive strength of concrete. It has been remarked that the compressive strength of concrete is improved with the inclusion of coir fiber up to a reinforcement level of 2%, but with more, the strength declined. This is consistent with the fact that the inclusion of fibers tends to make the aggregates enter the pores to ensure adequate bonding, but increases in fiber content result in bulkiness, which distorts the bonding to yield less strength. Moreover, the formation of a weaker transition zone around the fibers tends to make the entire concrete specimen weaker. Not only this, but the impurities present on the fiber’s surface and the thickness of fibers can also hinder the improvement in the bonding of concrete ingredients. Hence, it is easy to deduce that, although fibers improve the strength of concrete, there always occurs an optimum fiber inclusion level [51]. In this case, the optimum fiber reinforcement level was deemed to be 2%.

Considering the compressive strength of concrete containing coir fibers, the work presents a contradictory outcome to that of the works published previously. For instance, Hwang et al. [49] described that the accumulation of coir fiber retards the compressive strength of cement-based material with high fiber content. The authors suggested that the retarding in strength is about the gathering of fiber in the cement paste. It was observed that growth in the volume of space in the material occurred instead, which points to a more porous microstructure. Contrary to Hwang et al.’s work, other researchers’ findings are in the same line as the strength results of this paper [49]. This effect is referred to as the scattering of stress by the coin fiber stack [52]. In what concerns the cement-lime mortar along with coir fiber, Sathiparan et al. [50] described that the compressive strength of the mortar increased in material containing coir fiber up to 0.5%, whilst a large amount of coir fiber retards the compressive strength of the mixture compared to the mortar containing no coir fiber. Figure 5 shows the relationship between coir fiber content and compressive strength, the estimation equation of the compressive strength at 28 days, and the r square value for concrete containing coir fiber.

Figure 5 also includes an equation formula with an r² equal to 1, and the r square is a strong indicator of the presence of a relationship between the characteristics. It states that the increase in compressive strength depends on the content of coir fiber (Figure 5). In light of the results, it is obvious that the first three contents of coir fiber have an increasing effect on the compressive strength of the coir fiber-modified concrete. This could be closely related to the mechanism of bridging the fiber (Figure 4 and Figure 5).

3.3. Splitting Tensile Strength

Figure 6 and

Table 6. Splitting tensile strength of concrete.

Mix ID	Applied Force (KN)	Splitting Tensile Strength (MPa)	Average Splitting Tensile Strength (MPa)
C	97.654	3.11	3.10
	96.398	3.07
	97.968	3.12
CF1	102.050	3.25	3.30
	104.248	3.32
	104.562	3.33
CF2	107.388	3.42	3.45
	109.272	3.48
	108.330	3.45
CF3	101.736	3.24	3.25
	101.736	3.24
	102.678	3.27
CF4	93.572	2.98	3.00
	94.200	3.00
	94.828	3.02

demonstrate the impact of coir fiber accumulation in concrete on the tensile capacity of concrete, tested at 28 days. It was noted that identical to the trend observed for compressive strength, the tensile strength of coir fiber-reinforced concrete increased first with the accumulation of fibers and later decreased after the 2% reinforcement level. The strength gain in concrete is attributed to the general fact that implies that fiber reinforcement enhances the tensile capacity of concretes while the sudden decrease in strength can be due to the formation of a weaker inter-transition zone around fibers and physical properties of coir fibers, such as length and thickness [51].

Filho et al. investigated the free, restricted, and drying shrinkage of cement mortar supplemented with coir fibers. According to the author, the inclusion of vegetable-based fiber slowed the initial crack opening and fracture propagation caused by tensile tension [53]. This impact is mostly related to the technique of fiber bridging around the fracture. Due to the fiber’s ability to disperse stress, Hwang et al. [49] and Sathiparan et al. [50] indicate that the incorporation of coir fiber prevents crack opening and development. Contrarily to the mortar containing no fiber, which presents brittle fracture, the fiber-reinforced mortar shows ductility and fracture gradually. The same trend that was mentioned in the above paragraph was shown in the mortar containing coir fiber in this work, as will be understood from Figure 6. However, Figure 7 gives a fourth-degree relationship between the content of coir fiber and the splitting tensile strength of the coir fiber-modified concrete.

Figure 7 also includes an equation formula with an r² equal to 1, and the r square is a strong indicator of the presence of a relationship between the characteristics. It states that the increase in splitting tensile strength depends on the content of coir fiber (Figure 7). In light of the results, it is obvious that the first three contents of coir fiber have a ductile effect by increasing the splitting tensile strength of the coir fiber-modified concrete. This could be closely related to the mechanism of the bridging of the fiber (Figure 6 and Figure 7).

3.4. Flexural Strength

The findings of the flexural strength of the specimens are illustrated in Figure 8 and

Table 7. Flexural strength of concrete.

Mix ID	Applied Force (KN)	Flexural Strength (MPa)	Average Flexural Strength (MPa)
C	5.973	4.48	4.52
	6.067	4.55
	6.040	4.53
CF1	6.427	4.82	4.80
	6.347	4.76
	6.427	4.82
CF2	6.720	5.04	5.00
	6.667	5.0
	6.613	4.96
CF3	6.227	4.67	4.70
	6.293	4.72
	6.280	4.71
CF4	5.866	4.40	4.42
	5.893	4.42
	5.920	4.44

, while

Table 8. Descriptive statistical analysis of concrete subjected to compressive, splitting tensile, and flexural strength.

Properties	Concrete Mix	Mean (MPa)	Standard Deviation, S.D.	Variance, σ
Compressive Strength	C	29.00	0.20	0.0400
	CF1	30.20	0.42	0.1700
	CF2	32.00	0.32	0.1000
	CF3	29.80	0.19	0.0360
	CF4	26.50	0.44	0.1920
Splitting Tensile Strength	C	3.10	0.026	0.0007
	CF1	3.30	0.044	0.0020
	CF2	3.45	0.030	0.0010
	CF3	3.25	0.017	0.0030
	CF4	3.00	0.020	0.0004
Flexural Strength	C	4.52	0.036	0.0013
	CF1	4.80	0.035	0.0012
	CF2	5.00	0.040	0.0016
	CF3	4.70	0.026	0.0007
	CF4	4.42	0.020	0.0004

presents a descriptive statistical analysis of the compressive, splitting tensile, and flexural strength results. Previous efforts have indicated that coir fiber has a development effect on the toughness of cement-based material [49,50]. According to Sathiparan et al., the evidence of flexural toughness in the fiber-reinforced cement mortar is much greater than that of the mortar containing no fiber, resulting in increased energy absorption during the post-peak of flexural force. The authors reported that their toughness findings are on the overall area of the MOE curves determined with the flexural strength test. As a result, the researchers verified that the addition of coir fiber enhanced the ductility and flexural strength of the mortar with coir fiber, i.e., the fiber-reinforced mortar had a more ductile rupture than the mortar with no fiber. They also demonstrated development in terms of excess strength, ductile capacity, and toughness percent when coir fiber was added to cement-based mortar [50]. Hwang et al. found that increasing the quantity of coir fiber increases the hardness of mortar significantly. This development could be referred to as the mechanism of the bridging effect of the fiber, which transfers the stress in the matrix across the opening crack and resists a surplus load after reaching the maximum load [49]. In this work, the effect of coir fiber on flexural strength with different fiber percentages was evaluated. At contents of 1%, 2%, and 3% coir fiber, flexural strength increases with the increased percentage of fiber. Nevertheless, the flexural strength with content of coir fiber- 4% was retarded. The maximum flexural strength was achieved at a 2% content of coir fiber, which was 5 MPa (Figure 8).

Flexural strength is also a measure of the capacity of splitting tensile strength in concrete. It is obvious that the results are identical to the tensile strength test results in improving flexural strength up to 2%. The addition of fiber results in an increase in strength [44], whilst the sudden decrease in strength can be due to the formation of a weaker inter-transition zone around fibers and the physical properties of coir fibers, such as length, diameter, and thickness. Moreover, the pollution available on the outer surface of the fiber stack can also result in the retardation of strength, as mentioned by Ranjitham et al. [51]. However, Figure 9 gives a fourth-degree relationship between the content of coir fiber and the flexural strength of the coir fiber-modified concrete, tested at 28 days.

Figure 9 also includes an equation formula with an r² equal to 1; the r square is a strong indicator of the presence of a relationship between the characteristics. It states that the increase in flexural strength depends on the content of coir fiber (Figure 9). In light of the results, it is obvious that the first three contents of coir fiber have a ductile effect as an increaser for the flexural strength of the coir fiber-modified concrete. This could be closely related to the mechanism of bridging the fiber (Figure 8 and Figure 9).

3.5. Modulus of Elasticity (MOE)

The MOE of concrete is an indicator of its stiffness and resistance to possible deformation; that means the higher the elastic modulus of the concrete is, the more resistant it will be to deformation. Figure 10 demonstrates the effect of coir fiber reinforcement on the MOE of concrete, while

Table 9. Descriptive statistical analysis of concrete subjected to MOE.

Properties	Concrete Mix	Mean (GPa)	Standard Deviation, S.D.	Variance, σ
Modulus of Elasticity	C	27.00	0.016	0.0112
	CF1	28.45	0.050	0.0025
	CF2	29.06	0.053	0.0028
	CF3	29.88	0.087	0.0076
	CF4	30.25	0.062	0.0039

presents the descriptive statistical analysis of MOE results. Different authors also analyzed the MOE of cement-based material containing vegetable fiber and confirmed a similar trend in the results obtained [54,55]. The findings indicate that the MOE of concrete improved with the increase in coir fiber reinforcement. The increase in the MOE of concrete is because fiber’s contribution adds to the stiffness of concrete and delays the anticipated propagation of minor and major cracks [42]. Moreover, the fiber also tends to change the brittle failure to a plastic nature failure [51].

Hwang et al. stated that the area under the MOE of the cement-based material containing coir fiber was higher than that of the cement-based material containing no coir fiber, which shows an increase in toughness evident in the material modified [49]. Xie et al. and Beninese et al. discovered a similar pattern where the inclusion of rice, bamboo, and date mesh palm fibers developed the post-peak of MOE by preventing rapid fractures. This fracture characteristic was referred to as the mechanism of bridging of fiber for force, which enables more ductility [54,55]. In another work carried out by Pereira et al., it was determined that longer sisal shows a greater toughness of fracture than the one which is shorter [56]. From the results of the work, it was recognized that the blending of coir fiber provides a more ductile characteristic and lower susceptibility to cracking for concrete. Considering the toughness of fracture, it was understood that the modified concretes showed an increase in relation to the increase in the content of coir fiber. To infer, the toughness of concrete demonstrated a remarkable increase because coir fiber was added to the concrete. Additionally, the coir fiber-reinforced concrete had a higher ductile feature based on the content values examined. Therefore, the concrete with the blending of coir fiber was unveiled to be less susceptible to cracking. Moreover, a greater volume fraction of coir fiber provided a better load-carrying capacity for concrete along with coir fiber up to 3% after reaching the maximum peak force.

3.6. Permeability

The results of the permeability of concrete along with 1%, 2%, 3%, and 4% coir fibers are presented in Figure 11, while

Table 10. Descriptive statistical analysis of concrete subjected to permeability.

Properties	Concrete Mix	Mean (mm)	Standard Deviation, S.D.	Variance, σ
Permeability	C	23.00	0.45	0.2100
	CF1	21.00	0.40	0.1600
	CF2	18.75	0.25	0.0625
	CF3	17.10	0.10	0.0099
	CF4	14.00	0.05	0.0025

presents the descriptive statistical analysis of the permeability results. This test measures the connectivity of pores inside the concrete, and it is strongly related to the MOE, hardness, and mechanical strengths mentioned above. The permeability of coir fiber-reinforced concrete was tested in terms of water penetration depth of concrete specimens subjected to water under pressure. The specimens were split, and afterward, the water penetration depth was noted in line with the guidelines of the BS EN 12390-8 standard [41] to assess the permeability of the concrete. From the results, it can be noticed that the permeability of coir fiber-reinforced concrete was recorded as 21, 18.75, 17.10, and 14 mm at 1%, 2%, 3%, and 4% coir fiber-reinforcement content, respectively. The inclusion of coir fibers in concrete increases the stiffness of concrete, which prevents the penetration of moisture, consequently enabling the specimens to withstand the cracking forces.

In various works, other authors have also presented that the addition of coir fiber did not increase the workability of the cement-based material; therefore, it was essential to put more water compared to that of the cement-based material containing no coir fiber. This effect is related to the demand for high-water absorption and the absorptive nature of the coir fiber [46]. Moreover, cement-based material containing a greater volume fraction of fiber showed a greater porosity. Previous works are also in agreement with those results found in this work [56]. To conclude, the blending of coir fiber decreases the permeability of the concrete. It can be correlated that the concrete with a lower permeability obtained a greater modulus of elasticity and mechanical strengths.

4. Conclusions

Coir fiber was used as a reinforcing element in concrete in this experiment to assess the fresh and mechanical characteristics of the concrete. The experimental findings reveal the following crucial points:

• The workability of fresh concrete is measured by 51, 45, 36, and 27 mm with the application of 1%, 2%, 3%, and 4% of coir fiber by volume fraction, which is smaller than concrete blended with 0% coir fiber. It was noticed that the blending of coir fiber resulted in a reduction in the workability of concrete.
• The optimum compressive strength and split tensile strength was measured as 32 and 3.45 MPa at 2% coir fiber, and the minimum strength was 26.5 and 3 MPa at 4% coir fiber at 28 days. It has been detected that the compressive strength and tensile strength are boosted with the application of coir fiber up to 2% by volume fraction in concrete. With the further addition of coir fiber, the strength reduces.
• The highest flexural strength was recorded as 5 MPa with 2% coir fiber, and the lowest flexural strength was measured as 4.4 MPa at 4% coir fiber as reinforcement ingredient in concrete at 28 days. It has been perceived that flexural strength is enhanced with the application of coir fiber up to 2% by volume fraction in concrete.
• The MOE is enhanced with the application of coir fiber in concrete, and the permeability of concrete plummets because of the use of coir fiber in concrete.