1. Department of Civil Engineering, International University of Business Agriculture and Technology, Dhaka, Bangladesh; haxsib@gmail.com
2. Department of Civil Engineering, International University of Business Agriculture and Technology, Dhaka, Bangladesh; mahabuburiubat@gmail.com
3. Department of Civil Engineering, International University of Business Agriculture and Technology, Dhaka, Bangladesh; nakibrayhan2020@gmail.com
4. Department of Civil Engineering, International University of Business Agriculture and Technology, Dhaka, Bangladesh; engrhridayahmed@gmail.com

 

*             Correspondence: shaaxxx.haxsib@gmail.com

Keywords: natural fibre reinforced concrete, serviceability of NFRC, splitting tensile strength

1. INTRODUCTION

After water, concrete is the material that is used the most globally [1]. Each year, 30 billion tons of concrete are consumed globally and it is the most used construction material in the world. Ton for ton, it is used twice as much globally than steel, wood, plastics, and aluminum combined. By 2025, it is anticipated that the ready-mix concrete market, the largest section of the global concrete market, will generate more than $600 billion in annual sales [2]. Since around 200 years ago, concrete has been employed in the construction industry as a building material. Because of the widespread use of concrete and the necessity of making it more sustainable and durable, the desire to boost its mechanical qualities has been ongoing [3]. Fine and coarse aggregate are combined to form concrete, a composite material, which is then joined by a fluid cement (cement paste) that eventually solidifies over time with curing. When cement, water, and aggregate are mixed together, fluid slurry is created that is simple to pour and shape. When concrete dries, it takes on the consistency as stone, making it ideal for building bridges, factories, airports, rail roads, waterways, mass transit systems, and other structures [4]. By nature, concrete has a tendency to be brittle and is weak in tension but reasonably strong in compression. By using conventional reinforcements and, to some extent, by adding a tiny amount of randomly distributed fibers to the concrete mix, the weakness in tension can be somewhat mitigated [5]. The strength, elastic modulus, ductility, controlling of crack initiation and spread, and serviceability of the structures can all be significantly improved by adding fiber to the concrete mixtures [6]. It can change how the fiber matrix composite behaves when it cracks, increasing its toughness. Numerous researches were conducted using different types of fibers (steel, glass, polypropylene, polymer, natural fiber, nano-fibre, etc.) for the fabrication of structural fiber reinforced concrete [7]. A concrete mixture called Natural Fibre Reinforced Concrete (NFRC) includes water, cement, aggregate, and discontinuous fibers of varying lengths and forms. Because of their excellent strength and stiffness, natural fiber composites are thought to have potential utility as reinforcing materials in concrete [8]. The experimental study intends to modify concrete in terms of their strength properties using waste areca nut fibres that are readily available locally. Disposing of waste materials and reusing them has been one of the world’s most pressing issues [9]. One such waste is the areca nut shell, also known as betel nut shell and many other local names. It can be termed as an agricultural waste material. Chewing areca nuts is a common practice among a sizeable fraction of the world’s population and is widespread throughout the Indian subcontinent, much of south Asia, and Melanesia [10]. From Bangladesh alone, 89.13 thousand USD worth of areca nut was exported in the year of 2021. The total production of areca nut in Bangladesh was 328.61 thousand metric tons in the 2020 [11]. The areca fibre is extracted from the areca nut shells. These waste shells of this huge quantity of areca nut produced are massive in volume [12]. These materials are eco-friendly and offer good performance at a reasonable price. They are strong materials that are low in weight, naturally recyclable, non-toxic and non-hazardous, widely available, adaptable in use, and inexpensive [13].

2. LITERATURE REVIEW

Today, concrete is a flexible, cost-effective construction medium with inherent limitations. However, brittleness, weak tensile strength, poor impact resistance, fatigue, low ductility, and low durability limit concrete’s structural application [14]. Concrete cracks in both its plastic (early-age) and hardened (long-term) states due to its brittleness and lack of flexural strength. Fibre material strengthens brittle matrices and improves mechanical characteristics. Concrete is famous for being brittle and robust in compression but weak in tension [15]. Fibres boost concrete tensile strength by preventing cracks. They also increase toughness by dispersing energy, shear and compressive strength are other fibre-influenced properties. The strength and hardness of fibre reinforced concrete depend on many aspects, including fibre, matrix, fibre-matrix interface, size, geometry, and fibre volume/weight proportion [16]. Recent concrete research has focused on fibre-reinforced concrete. Fibre as secondary reinforcement in concrete prevents shrinkage, cracks, impact/abrasion, and considerably increases building quality, making it more sustainable than ordinary concrete [17]. A study tested concrete strengths with 30% natural areca fibre and waste tile powder additions, not substituting any concrete mix element [18]. The use of areca fibre and tile powder has increased concrete’s compressive, splitting tensile, and flexural strengths and provided a waste tile disposal option. NFRC is a cost-effective, biodegradable, and decomposable reinforcement material for composites [19]. The maximum tensile and flexural strength was 76.25 MPa and 136.36 MPa, which is close to experimental values with fibre 0.5%, 1%, 2%, and 3% substituting cement. Other than flexural and tensile strength, compressive strength and workability decreased [20]. Concrete with steel reinforcement is good for tensile strength but not comprehensive strength when compressed [21]. It is also expensive. Using areca palm fibres treated with 5% NaOH solution and fibre mixing ratios of 0.1%, 0.3%, 0.5%, 0.7%, and 0.9% by cement weight increased modulus of elasticity and compressive strength by 0.7%. Strongness reduced over this ratio [22]. Maritime structures, vehicles, aerospace, and civil engineering materials use natural fibre reinforced composites. It has found that fiber-reinforced concrete composites had better fiber-resin bonding and lower water absorption [23]. The dynamic behaviour of natural areca nut husk fine fibre mat in NaOH 6% treated reinforced epoxy resin with a hardener composite panel. A dynamic mechanical analyser set the loading frequency from 1-10 Hz for hand layup at 28–120 °C. An increase in storage modulus led to a 2.6 GPa temperature increase at 28˚C. An rise in temperature leads to a decrease in loss modulus (117 MPa at 28˚C). The glass transition temperature of the areca nut husk fibre composite is 67˚C (1-10 Hz). Decreased damping factor led to high glass transition temperature (67˚C at 1-10 Hz), which increased up to the highest storage modulus value (1.0 of the tan curve peak shift) before decreasing and vice versa [24]. It combined untreated natural henequen fibre with plain foamed concrete and 700kg/m3 fibre reinforced foam concrete. At volume fractions of 0.5%, 1%, and 1.5%, untreated or alkaline-treated natural fibre henequen strengthened the concrete with polypropylene fibre reinforcement [25]. After peak strength, compressive loading did not reduce compressive strength. Henequen fibres made energy absorption fibre reinforced foamed concrete tougher and ductile than plain foam concrete. It sought to reduce carbon footprint in eco-friendly insulating materials [26]. This work uses abaca and hemp to improve foamed geopolymers’ flexural, compressive, and thermal conductivity by 40%. Studies demonstrated that single-application material is limited, polymer-modified concrete with strong deformation and fibre reinforcing concrete displays remarkable crack resistance. To create a high-recital pavement material, a composite material design increased the reinforcement effect [27]. Use of Chinese cement concrete test regulations to study workability, compression, flexural resistance, and basic mechanical characteristics of high content hybrid fibre polymer modified concrete showed that sulphate resistance increases environmental durability [28]. Fiber-reinforced polymer concrete has good rigidity, reliability, and a modulus of elasticity of 35.93 MPa. Compressive strength was 52.82 MPa, 31.2% higher than C40 concrete. The hybrid concrete’s bending strength was 11.51 MPa, 191.4% more than normal concrete’s 3.95 MPa, proving that this research was effective [29]. The specimen outperforms fiber-reinforced concrete by 81.31% in corrosion resistance. Compared to plain concrete in cross-sectional scanning electron microscope SEM images, hybrid fiber-polymer concrete had a dense cementing layer and fewer micro holes and micro-cracks. Hybrid fiber-reinforced concrete has superior strength and environmental erosion resistance and can be used as a pavement material with superior mechanical properties [30]. Workability and compressive strength loss existed alongside flexural and tensile strength. More than 0.7% areca palm fibre in concrete reduced modulus of elasticity and compressive strength [31]. Fiber-reinforced concrete is less workable., after 28 days, the tensile strength was notably higher at a hardened condition than at an early stage, when it was comparable to standard concrete. Glass fibres boosted concrete density and later decreased coconut shell concrete density [32]. Despite using Ordinary Portland Cement, the early strength increase was purposeful. Bending strength increased for natural fiber-based concrete up to 1.5% fibre loading, then decreased due to cracks at the fibre concrete interface [33]. Areca fibre and arena nut husk fibre were added to strengthen fibre reinforced concrete (FRC) with other powders or fibres, however areca fibre alone was not employed in concrete to detect the change in mechanical properties in prior studies [34]. Concrete with only untreated areca fibre needs more research. Industrial wastes improve concrete’s permeability, durability, workability, and serviceability, but sustainability suffers [35].

3. MATERIALS AND METHODS

The IUBAT (International University of Business Agriculture and Technology) civil engineering lab at Uttara, Dhaka, was the site of all the experiments. The digital display hydraulic compression testing machine at the civil engineering materials lab has been used for the compressive strength and split tensile strength tests of hardened concrete. The STHX-1A drying oven at the civil engineering transportation lab has been used for the water absorption test of hardened concrete.

Figure 01: Flow Chart of work

Concrete consists of binding material, coarse aggregate and fine aggregate which adheres together with the binding material in order to attain stone like rigidity. The cement used in this study for the preparation of specimens is Ordinary Portland Cement (OPC) complying with the American Standard ASTM C 150 Type-I mark, the Bangladesh Standard BDS EN 197-1:2003 CEM-I 52.5 N, and the European Standard EN 197 type CEM-I. In the following table 01, OPC cement’s chemical characteristics are listed:

Table 01: Ingredients of Ordinary Portland Cement (OPC)

Components	Amount (In percentage)
Portland Clinker	95-100%
Gypsum	0-5%

Stone chips used as coarse aggregate for this study were collected from local construction site. ¾” downgraded chips were used as coarse aggregate for this study. Stone chips were soaked in water for about 1 hour and then sundried for 24 hours before the casting of concrete. The following table 02 shows the sieve analysis and the F.M. calculations using 2500 gm coarse aggregate sample:

Table 02: Sieve Analysis of Coarse Aggregate (crushed stone chips)

ASTM Sieve No.	Sieve Size (mm)	Mass Retained (gm)	%Retained Mass (%)	Cumulative % Retained (%)	%Finer (%)	Fineness Modulus (F.M.)
1”	25	139	5.56	5.56	94.44
¾”	19	854	34.16	39.72	60.28
½”	12.50	972	38.88	78.60	21.40
3/8”	10	404	16.16	94.76	5.24
#4	4.75	131	5.24	100	0
#8	2.36	0	0	100	0
#16	1.18	0	0	100	0
#30	0.60	0	0	100	0
#50	0.30	0	0	100	0
#100	0.15	0	0	100	0
Pan		0	0	–	–
Total		2500	100	= 807.08

Figure 02: Particle size gradation of Coarse Aggregate

Waste areca nut shell was collected from local tea stalls on a regular basis. The waste shell was washed thoroughly to wash away the dusts on their body and then soaked in water for 24 hours to reduce the amount on fine fibers. The more rigid and stiff coarse fibers were used in this study for adding into the NFRC (natural fiber reinforced concrete) mixes. The normal aspect ratio (L/D) for fibers ranges between 30 and 150. Six numbers of fiber were taken for their measurements and the average length (L) were found to be 50 mm. As the thickness of the fiber was not consistent, same number of fiber was taken for the measurement of their thickness and the thickness (T) was found to be 0.75mm on average. This makes the aspect ratio (L/T) of the fiber 66.7.

Figure 03: Areca Fibre (a) sample, (b) length, (c) Diameter

Concrete works as an artificial stone like block with the coarse aggregate and fine aggregate being adhered by the binding material. 3/4” downgraded crushed stone chips were used as coarse aggregate, locally available sylhet sand (Fineness Modulus= 2.91) was used as fine aggregate and Ordinary Portland Cement (OPC, CEM-1) was used as the binding material with a mix ratio of 1:1.5:3 by their volume. Waste areca fiber with an aspect ratio of 66.7 was used as the performance enhancing additive for this study. Following is the ASTM gradation specification for Fine aggregate according to ASTM C 33 code:

Table 03: ASTM C 33-18 gradation specifications for fine aggregate for Portland Cement Concrete

ASTM Sieve Designation	Percent passing
4.75 mm (No. 4)	95-100
2.36 mm (No. 8)	80-100
1.18 mm (No. 16)	50-85
0.60 mm (No. 30)	25-60
0.30 mm (No. 50)	10-30
0.15 mm (No. 100)	0-10

From the trial batches of M20 and M30 grade, it was deduced that the M20 grade concrete gained more accurate compressive strength than the M30 grade concrete. As per the result of this compressive strength tests, the M20 grade concrete was selected as the test specimen concrete and the mix ratio was fixed to 1:1.5:3 (Cement: Sand: Stone) for the rest of this study. 05 batches of concrete specimens were casted for this study. Plain concrete was casted with no addition of fiber tagged as NFRC0% mix batch. Other 4 batches were casted replacing cement with 1%, 2%, 3%, and 4% areca fiber by the weight and tagged as NFRC1%, NFRC2%, NFRC3% and NFRC4% mix batch, respectively. The rest materials and water/cement ratio of 0.55 were held constant throughout all the mix batches. 21 cylinders were casted for each mix batch. In total, 105 cylinders were casted for 0%, 1%, 2%, 3% and 4% fiber mix batches. Estimation of Casting Materials are following:

Volumetric ratio selected (C: FA: CA) = 1:1.5:3

Table 04: Estimation of Materials for All the Mix Batches

Mix Batch	Cement (kg)	Areca Fiber (kg)	Fine Aggregate (kg)	Coarse Aggregate (kg)	Water (liter)	W/C Ratio
NFRC0%	13.36	0	22.3	46.8	7.4	0.55
NFRC1%	13.23	0.134	22.3	46.8	7.3	0.55
NFRC2%	13.09	0.267	22.3	46.8	7.2	0.55
NFRC3%	12.96	0.402	22.3	46.8	7.1	0.55
NFRC4%	12.82	0.536	22.3	46.8	7.0	0.55

In total, 04 types of tests were conducted for fresh and hardened concrete specimens. For fresh concrete mixture, workability test was done. Slump test is the widely accepted test that is done for determining the workability or fluidity of fresh concrete. It provides an idea about the change of workability parameters with the introduction of natural fibers in different dosages compared to the plain concrete with no fiber concentration. For hardened concrete, 3 tests were done. They are compressive strength test, split tensile strength test and lastly, the water absorption test. For this study, compressive strengths of NFRC0%, NFRC1%, NFRC2%, NFRC3%, and NFRC4% were measured after the curing age of 7 days, 14 days, and 28 days. Compressive strength was measured in the digital display hydraulic compression testing machine showing the compressive load taken in Kilo newton (KN) unit. Compressive strength tests were done as per the ASTM C39/ C39M code. Splitting tensile tests for this study was conducted according to the ASTM C496/ C496M code. For this study, water absorption test was done for all the 5 variations of cylindrical specimens at the curing age of 28 days.

4. RESULT & DISCUSSION

This study focuses on both the advantageous and disadvantageous effects of using areca fibre as a mixing material in concrete structures. In order to measure these effects in total 4 tests were conducted in the laboratory such as slump test, compressive strength test, splitting tensile strength and lastly, the total water absorption test. All of these tests were done for conventional concrete with no fibre added, NFRC1% with 1% areca fibre added, NFRC2% with 2% areca fibre added, NFRC3% with 3% areca fibre added and finally, NFRC4% with 4% fibre added. The percentage of fibre addition was done by the weight of cement.

4.1 Slump Test Results for Fresh Concrete Mixes

Slump tests were conducted for both the fresh concrete with no fibre added and fresh concrete with varying dosage of fibre added according to the ASTM C143/ C 143M code standards [16].

Figure 04:  Slump Test results for 5 mix batches

4.1.1 Relationship between Slump Value and Density of Concrete Mixes

The slump values were measured from the slump test of fresh concrete for all the 5 mix batches. The density of concrete mix batches were calculated by dividing their measured mass by the volume of cylindrical specimens.

Figure 05: Relationship between slump value and density

4.1.2 Relationship between Slump Value and Yield Stress

The qualities of the mixture’s plastic viscosity and yield stress have a significant impact on the slump of the concrete. Hu, de Larrard [12] created an expression for yield stress in terms of slump and concrete density using a finite element model of a slump test. This expression is shown in Equation 1. Concretes with slumps varying from 0 to 25 cm were subjected to the finite element analyses.

Figure 06: Relationship between slump value and yield stress

4.2 Compressive Strength Test Results for Concrete Mixes

Compressive strength test was done for 3 samples of each fibre concentration at the curing ages of 7 days, 14 days and 28 days. For each fibre concentration 9 cylindrical specimens were prepared and in total 45 test specimens were prepared. The test specimens were taken out of the curing tank before 24 hours of the testing. From the test results of 3 samples, mean compressive strengths from each fibre concentration were determined as well as their standard deviation, coefficient of variance, standard error, and the lower and upper 95% confidence level of the compressive strengths.

Figure 07:  Compressive Strength test results

The compressive strength test results vary from 11.99 MPa to 21.69 MPa. Plain concrete with no fibre concentration revealed compressive strength of 20.04 MPa at the curing age of 28 days. Natural fibre reinforced concrete with fibre concentration of 1% showed the maximum compressive strength of 21.69 at the curing age of 28 days, while other fibre concentrations showed a decreasing compressive strength with increment in fibre concentration. Concrete with no fibre concentration attained compressive strength of 13.51 MPa after 7 days of curing and 13.69 MPa was the compressive strength for NFRC having 1% fibre concentration. After 14 days of curing the test results showed the similar results of NFRC with 1% having the maximum compressive strength and decreasing trend of compressive strengths with more fibre concentrations.

4.2.1 Variation in Compressive Strengths

The following figure 08 shows the percentage changes in compressive strengths for all the mix batches at 7 days, 14 days and 28 days of curing age with respect to the NFRC0% mix batch:

Figure 08: Compressive strength changes in percentage

The percentage changes in compressive strength vary from 0.46% to 13.97%. The maximum increment of compressive strength was 8.23% for NFRC having 1% fibre concentration compared to the plain concrete with no fibre concentration after curing of 28 days. The maximum decrement of compressive strength after 28 days of curing was shown by the NFRC having 4% was 13.97% decrement compared to the plain concrete having no fibre concentration. Only the NFRC having 1% fibre concentration gained more compressive strength of 1.33% after 7 days of curing compared to the plain concrete. NFRC with 1% and 2% fibre concentration showed respectively 1.56% and 0.46% compressive strength increment after 14 days of curing.

4.2.2 Observed Crack Pattern after Compressive Strength Test

The following figures show the observed crack patterns after compressive strength test was done in the laboratory:

Figure 09: Observed crack pattern in (a) NFRC0%, (b) NFRC1%, (c) NFRC2%, (d) NFRC3%, and (e) NFRC4%

4.3 Split Tensile Strength Test Results for Concrete Mixes

The sample numbers and total cylindrical specimen numbers for splitting tensile strength tests were the same as the test of compressive strength tests. Mean compressive strength, standard deviation, coefficient of variance, standard error, and the upper and lower 95% confidence interval for all the 45 specimens prepared for the splitting tensile test are calculated and shown in the

Figure 10: Splitting Tensile Strength Results

The splitting tensile strength for all the test specimens ranges from 1.77 MPa to 3.71MPa. The maximum splitting tensile strength of 3.71 MPa was achieved by the incorporation of 2% fibre in natural fibre reinforced concrete after the curing of 28 days. The lowest splitting tensile strength of 1.77 MPa was achieved by plain concrete having no fibre concentration at the curing age of 7 days. Splitting tensile strength for plain concrete was 3.12 MPa after the curing of 28 days.

4.3.1 Variation in Compressive Strengths

The following figure 10 shows the percentage changes in splitting tensile strengths for all the mix batches at 7 days, 14 days and 28 days of curing age:

Figure 11: Splitting Tensile Strength changes in percentage

The variation of splitting tensile strengths ranges from 3.39% to 24.29%. The maximum increment of splitting tensile strength was 24.29% after the incorporation of 2% areca fibre at the curing age of 7 days. The lowest increment of 3.39% was shown for the fibre concentration of 1% after 7 days of curing. The maximum splitting tensile strength increment of 18.91% was shown with the incorporation of 2% areca fibre after 28 days of curing, while increasing fibre concentration have shown decrement in splitting tensile strengths.

4.3.2 Observed Crack Pattern after Splitting Tensile Strength Test

Observed crack patterns after splitting tensile tests are shown in the following figures:

Figure 12: Observed crack pattern in (a) NFRC0%, (b) NFRC1%, (c) NFRC2%, (d) NFRC3%, and (e) NFRC4%

4.4 Relationship between Compressive Strength and Splitting Tensile Strength

Without performing any laboratory experiments, the splitting tensile strength can be calculated from the compressive strength value. To calculate the mechanical properties from compressive strength, there are many standards. ACI 318, ACI 363R, CEB-FIP, and AS 3600 [32-35], respectively, suggest using equations (2), (3), (4), and (5) to determine the splitting tensile strength from the compressive strength.

Figure illustrates the relationship between the splitting tensile strength and compressive strength of the HFRC test results and analytical computation using various fibre densities for 7, 14, and 28 days.

Figure 13: Relationship between compressive and splitting tensile strength as per experimental data and code standards

4.5 Total Water Absorption Test Results

Total amount of water content absorbed give us an insight about the void inside the hardened concrete. The water absorption ability of concrete materials can greatly affect the water absorption ability of the concrete itself. In this study, areca nut fibre, a natural material was used inside the concrete as a reinforcing agent.

Figure 14: Percentage of total was absorbed in concrete mix batches

The total water content absorption percentage ranges from 1.90% to 8.27 percentages. The highest value of 8.27 was attained with the NFRC4% mix batch having fibre concentration of 4% by the weight of cement.

4.5.1 Relationship between Total Water Absorbed and Density of Concrete

Density of concrete has a strong relation with the water absorbing capability of the hardened concrete. The water absorbing ability decreases with increasing density as there is lesser void within the concrete matrix.

Figure 15: Relationship between density and total water absorption

The density of concrete mixes ranges from 2143.971 kg/m³ to 2423.805 kg/m³. The density of concrete gradually decreased with the increment in total water absorption percentage. A linear relationship exists between these two variables that can be shown with a straight line.

4.6 Cost Analysis

In order to determine the cost of the individual mix due to production and transportation costs, this study also conducted an economic analysis, as shown in Table 05 and graphically represented in figure. The cost is assessed in BDT (1 USD = 104.48 taka). The production and transportation unit cost for concrete materials were collected from previous research having conjunction with the latest date and context of Bangladesh standards.

Table 05: Cost of Concrete mixes

Concrete Mix	Individual Material Cost (tk)				Total Cost (tk)	Cost Per Unit (tk/m3)
	Cement	Coarse Aggregate	Fine Aggregate	Water
NFRC0%	124.78	246.17	53.3	0.65	424.90	8331.37
NFRC1%	123.57	246.17	53.3	0.64	423.68	8307.45
NFRC2%	122.26	246.17	53.3	0.63	422.36	8281.57
NFRC3%	121.05	246.17	53.3	0.62	421.14	8257.65
NFRC4%	119.74	246.17	53.3	0.62	419.83	8231.96

Figure 16: Total Cost of Concrete Mix Batches

The total cost for making concrete mix batches in this study ranges from 8231.96 taka to 8331.37 taka. It can be seen that the total cost per m³ of natural fibre reinforced concrete is lesser than the conventional concrete. The increment in fibre concentration further decreases the total cost.

4.7 Sustainability Assessment

The material embodied energy, eCO₂ emission during production and transportation for cement and coarse aggregate were collected from (Hammond et al, 2011). Also, the eCO₂ emission during production and transportation for fine aggregate and water were collected from (Datta et al, 2022) and (Bostanci, 2020), respectively which are shown below.

Table 06: Energy, eCO2 emission during production and transportation for cement

Mix Batch	eCO2 emission (kg CO2/ kg concrete)			Percentage of CO2 emission
	Production	Transportation	Total	Production (%)	Transportation (%)
NFRC0%	255.77	94.73	350.51	72.97	27.03
NFRC1%	253.35	94.68	348.03	72.80	27.20
NFRC2%	250.74	94.62	345.36	72.60	27.40
NFRC3%	248.32	94.57	342.88	72.42	27.58
NFRC4%	245.70	94.51	340.21	72.22	27.78

Figure 17: Total eCO2 Emission of Concrete Mix Batches

 The eCO₂ emission for concrete mix batches ranges from 340.21 to 350.51 kg CO₂/ kg concrete. The maximum amount of 350.51 kg CO₂ was emitted by the conventional concrete mix while, the NFRC4% concrete mix emitted the minimum amount of CO₂. The replacement of cement by inclusion of natural areca fibre reduced the amount of CO₂ of concrete mixes.

5. CONCLUSION

The urge of reinforcing concrete with natural fibre is an ongoing process. As well the recycling of natural waste materials is a big concern throughout the globe. The mechanical characteristics of NFRC0% and NFRC specimens with various fibre concentrations in the concrete mixes were investigated experimentally. The workability of concrete decreases with the usage of natural areca fibre. The increasing concentration of areca fibre gradually decease the workability of concrete. It is found that, by using 2% areca fibre, concrete mixes can be produced with medium workability. The compressive strength test results have shown that by using areca fibre, compressive strength of concrete can be slightly increased. With the areca fibre concentration of 1% (NFRC1%), the maximum compressive strength of 21.69 MPa was achieved after 28 days of curing. Furthermore, increasing fibre concentration showed a gradual decrease of compressive strength. With the more concentration of fibre, more fibre balling effects occur thus, increasing the voids in the concrete. This is why the more fibre usage showed a gradual decline in their compressive strength. Based on the splitting tensile strength, it has been found that reinforcing concrete with natural waste areca fibre can substantially increase the splitting tensile strength. The highest splitting tensile strength of 3.71 MPa was achieved with the 2% fibre concentration (NFRC2%) after the curing of 28 days. This increment was 18.91% with reference to the control mix (NFRC0%). Further increment in fibre concentration also showed increasing trend of splitting tensile strength with respect to the control mix but the highest value was obtained with fibre concentration of 2% (by weight of cement). The interlocking of cement and areca fibre can be attributed for the increment in splitting tensile strength. The crack patterns after the compressive and splitting tensile failure revealed that the control mix (NFRC0%) showed no performance after the failure in load bearing. While, the fibre reinforced concrete mixes (NFRC1%, 2%, 3%, 4%) showed some post cracking performances. The more concentration of areca fibre increased the post cracking response of NFRC mixes. The NFRC mixes showed less crack width, more propagation in the cracks and also they did not crack in a defined single plane of axis. On top of that, they showed ductile behaviour to some extent in the higher concentration of fibre mixes. This altercation in post cracking behaviour can be attributed to the fibre bridging and fibre matrix of the NFRC mixed. The splitting tensile strengths were calculated with the formulas recommended by various code standards to compare with the experimental data. The experimental data were closest to the ACI 318R and furthest from the AS 3600 code standards. The total water absorption test results revealed that the percentage of water content increases with increasing fibre concentration. The highest water content of 8.27% was absorbed with the fibre concentration of 4%. The natural fibre can absorb water more than the conventional concrete materials. So, this increased water absorption can be attributed to the usage of natural fibre in concrete mixes. Due to the great improvement in splitting tensile strength and reasonably good improvement in crack controlling qualities relative to the succeeding NFRC mixes, the best fibre combination proposed in this study is the 2% of natural areca nut waste fibre mix, even though it performed worse than the control mix in compressive strength test.From the assessments of cost and eCO₂ emission, it has been found that the cost of producing Areca fibre reinforced concrete is lesser than the conventional concrete as well as the amount of eCO₂ emitted gradually decreases with replacing more cement with areca fibre, bringing sustainability criteria to the NFRC mix batches. The future scopes that can be done using this study are given below:

• This study was done with fibre length of 50 mm on average. Fibre with lesser lengths can be also used in future studies.
• Different methods of areca fibre extraction can be followed in the future studies regarding incorporation of areca fibre in concrete.
• Flexural strength of concrete prisms can be done in future studies.
• Tests of the properties of areca fibre can be done by researchers in the future studies.
• Scanning Electron Microscope (SEM) can be done to observe the fibre matrix of areca fibre reinforced concrete in future studies.

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