Using Jute Fiber to Improve Fresh and Hardened Properties of Concrete

ABSTRACT

The brittle nature of concrete sometimes makes it challenging for many critical applications. Research has indicated that including discrete short-length, closely spaced fibers in concrete could improve its ductility and act as a crack arrester. As Bangladesh is the prime producer of natural fiber jute, this research aimed to improve the concrete property with this biomaterial. Laboratory work evaluated the mechanical property and shrinkage cracking resistance of jute fiber reinforced concrete with different fiber fractions (viz. 0.1%, 0.2%, 0.3%, and 0.4% by concrete volume) and lengths. The fibers were designated J20 and J25 for 20 and 25-mm lengths, respectively. A portion of the fiber was treated with alkali before using in concrete to improve its property. Jute Fiber Reinforced Concrete (JFRC) was analyzed qualitatively, semi-quantitatively, and quantitatively for compressive, splitting tensile strength, and plastic shrinkage cracking. It was found that the compressive and splitting tensile strengths can be improved by 7% and 25%, respectively. Furthermore, the bio-fiber had a significant influence on shrinkage crack control. In a controlled environment, up to 61% crack area and 62% maximum crack width reduction were achieved. Overall, jute fiber was found to be a sustainable biomaterial for concrete construction in an arid region.

摘要

混凝土的脆性有时使其对许多关键应用具有挑战性. 研究表明，在混凝土中加入离散的短长度、紧密间隔的纤维可以提高其延性，并起到防裂剂的作用. 由于孟加拉国是天然纤维黄麻的主要生产国，本研究旨在用这种生物材料改善混凝土性能. 实验室工作评估了不同纤维含量（即混凝土体积的0.1%、0.2%、0.3%和0.4%）和长度的黄麻纤维增强混凝土的力学性能和抗收缩开裂性能. 纤维分别被指定为长度为20毫米和25毫米的J20和J25. 在用于混凝土之前，对部分纤维进行了碱处理，以改善其性能. 对黄麻纤维混凝土（JFRC）的抗压强度、劈拉强度和塑性收缩开裂进行了定性、半定量和定量分析. 研究发现，抗压强度和劈拉强度分别可以提高7%和25%. 此外，生物纤维对收缩裂缝的控制有显著影响. 在受控的环境中，实现了高达61%的裂纹面积和62%的最大裂纹宽度缩减. 总的来说，黄麻纤维被发现是干旱地区混凝土建筑的可持续生物材料.

KEYWORDS:

• Jute fiber (JF)
• Fibre-reinforced concrete (FRC)
• compressive
• splitting tensile strength
• Shrinkage cracking
• fiber length

关键词:

• 黄麻纤维
• 纤维增强混凝土
• 压缩，
• 劈裂抗拉强度
• 收缩开裂
• 纤维长度

Introduction

Concrete is the most widely utilized construction material due to its durability, versatility, compressive strength and cost-effectiveness (Neville 2011; Yang, Qiang, and Bao 2011). Plain concrete is a heterogeneous composite material generally composed of cement, sand, coarse aggregate, and water in the proportions specified by the requirements. Compared to compression mode, it usually cannot tolerate significant tensile force. Studies worked around this major flaw to develop new materials for improving the ductility of concrete (Yan and Chouw 2013). The addition of discrete fibers to concrete increase tensile and impact, controls crack, wear and tear, fatigue and improves ductility (Mohammadi, Singh, and Kaushik 2008; Yazici, Inan, and Tabak 2007). Because of its remarkable flexibility and durability, Fiber Reinforced Concrete (FRC) is widely used in the military establishment and marine areas, for example, in armored structures, blast-resilient structures, offshore platforms, and the development of undersea oil engineering (Mezzal, Al-Azzawi, and Najim 2021). It is also used to improve pavement concrete (Affan and Ali 2022). According to ACI, FRC is a type of concrete that contains randomly oriented fibers scattered throughout the mixture (ACI 2018). Natural reinforcement, such as straw in mud bricks, was used for over millennia (Rosenberg et al. 2020). In the early 1960s (Romualdi and Mandel 1964), FRC was brought to the notice of academic and industry scientists worldwide (Zollo 1997). Lightweight aggregate such as scoria was added with fibers in concrete to improve the performance against fire (Aslani et al. 2019). Bheel et al. (2021) compared the performance of nylon and jute fibers in concrete. Fibers were also used in high strength concrete production (Parra et al. 2012; Zhang et al. 2020).

The fiber materials could be steel, glass, synthetic, carbon, or natural. Steel fiber, in particular, has a high elastic modulus and stiffness, making it efficient for increasing concrete compressive strength and toughness (Guler and Yavuz 2019). However, this fiber is prone to corrosion (Sun et al. 2021). In addition, it enhances concrete self-weight and could induce a balling effect during mixing, reducing workability. Furthermore, alkaline circumstances may cause glass fiber to be sensitive. Carbon fibers are chemically inactive and stiffer, but it is relatively expensive and exhibits anisotropy. Synthetic fibers, especially polymeric fibers, commonly give reduced elastic modulus, melting at low temperatures, and weak interfacial interaction with the inorganic matrix (Jiang et al. 2014). However, synthetic fibers may add advantages, including low cost due to abundance, biodegradability, processing flexibility and hence lower machine wear, minimal health concerns, low density, control of the fiber aspect ratio, and considerable tensile and flexural modulus (Gifta et al. 2021).

As with other types, natural fibers could improve similar mechanical and other properties of concrete (Aluko et al. 2020; Islam, Rizwan Hussain, and Abu Zakir Morshed 2012). Natural FRC may also have architectural and ornamental features. For example, sisal fibers are used in African regions to produce reinforced concrete tiles, roofing corrugated sheets, pipes, gas and water tanks, and silos (Elsaid et al. 2011). Bio-fibers such as coir and kenaf were compared with polypropylene fibers in high-performance concrete to improve their durability properties (Sivakumaresa, Narayanan, and Merina Rymond 2021). In addition, studies incorporated fibers to reduce the effect of shrinkage (Banthia, Yan, and Mindess 1996; Islam and Das Gupta 2016).

Adamjee Jute Mill of Bangladesh was the largest jute corporation in the world. In addition, China, India, and Thailand grow a small amount of the material. The bark of the plant is the source of fibers. The plant could be up to 2.5 m tall, with a stem diameter of around 25 mm at the base. First, the matured plants are wrapped into bundles and submerged underwater. The organic bark decomposed entirely during this period, and fibers became exposed. Then, the fibers are extracted from the plant stem, washed, and sun-dried (Mansur and Aziz 1982). This fiber was used to create composites in association with polypropylene fibers (Chandekar et al. 2021). Other studies found that jute could be effectively utilized for safety helmet manufacturing associated with waste polyester composites (Subbiah, Chandrasekaran, and Veerasimman 2021).

Jute fibers could be a cost-effective and sustainable construction material because they are biological engineering materials (Islam and Ju Ahmed 2018; Kim et al. 2012; Zakaria et al. 2016). In contrast, jute fiber weighs approximately one-seventh of steel fibers, and their tensile range is between 250–300 MPa (Kundu et al. 2012). Ramaswamy, Ahuja, and Krishnamoorthy (1983) found considerably high tensile strength of the natural air-dried jute fiber. Due to immersion in an alkaline medium (pH value 11) for four weeks, a 5–32% loss could have occurred. However, Zhou et al. (2013) reported a marginal loss while the fibers were embedded in cement concrete. Later Zakaria et al. (2020) reported improved compressive, tensile and flexural using jute and yarn fibers in concrete.

In most previous works, the concrete was not designed as contemporary. Moreover, limited work has been carried out on the effect of drying shrinkage, i.e., cracking in concrete, especially with natural fibers. In hot arid regions, drying shrinkage and associated cracks are a significant concern to field engineers. Therefore, this study aimed to evaluate the critical engineering properties of jute fiber reinforced concrete considering its design with modern superplasticisers. Moreover, the shrinkage crack resistance of jute fiber-reinforced concrete using the image analysis technique was assessed to use this biomaterial effectively in concrete construction.

Materials

A CEM I category cement with class 52.5N was used in experimental works. The fine and coarse aggregate requirements followed ASTM C33 (ASTM 2018). Table 1 shows characteristics of fine and coarse aggregates. These aggregates were collected from the northeastern region of Bangladesh. Modified polycarboxylic ether-based retarding superplasticisers were used for the experimental investigation. It allows a significant reduction in mixing water while maintaining set retardation control.

Table 1. Physical properties of aggregates.

Properties	Fine	Coarse	Test Standard
Specific gravity (SSD Basis)	2.55	2.65	ASTM C128/C127
Absorption capacity (%)	0.82	0.67	ASTM C128/C127
Dry rodded unit weight (kg/m^3)	1610	1590	ASTM C29
Fineness modulus (FM)	2.43	—	ASTM C136
Moisture content (%)	0.23	0.50	ASTM C125

“Tossa” Jute was used in this investigation. The processed sample was obtained from a local jute mill and was cut into 20 mm (J20) and 25 mm (J25) lengths. Fiber contents of 0.1%, 0.2%, 0.3%, and 0.4% by cement mass were considered to investigate the mechanical properties and shrinkage characteristics of FRC. Initially, the jute fibers were separated and soaked for 30 minutes in tap water to soften the fibers and eliminate coir dust. The washing and soaking were continued three times. After that, the fibers were straightened out and combed by hand with a steel comb. Most of the moisture was removed from the long-wet fibers by placing them in the open air.

Parallel to this, another portion of jute fibers was soaked in 10% (w/v) NaOH solution at ambient temperature for alkali treatment/interaction. The polar chemical nature and structure of the natural fiber interact with the polar nature of cement concrete. This concept justifies the reinforcing action of cement concrete. Characteristics of jute fiber are given in Table 2 (Alam 2022).

Table 2. Physical characteristics of jute fibers.

Fiber length	25 mm and 20 mm
Fiber diameter	0.02 mm/18 um, length 1–30 cm
Specific gravity	1.5
Bulk density (kg/m^3)	1.3–1.46 g/cm^3
Ultimate tensile strength (N/mm^2)	393–800 MPa
Modulus of elasticity (kN/mm^2)	10–30 GPa
Aspect ratio (l/d)	1250 and 1000
Elongation at fracture (%)	1.5%-1.8%

Mix Design and Concrete Preparation

The concrete mix was designed following the American Concrete Institute (ACI 211.1–91). In this investigation, the target 28-day compressive strength of concrete was 28 MPa with an 8.5 MPa safety margin and a slump value of 100–125 mm. The detailed mix proportions of this study are given in Table 3.

Table 3. Mix proportion of concretes (kg/m³) used in this experiment.

Mix ID	Water	Cement	Coarse Aggregate	Fine Aggregate	Admixture	Fiber
Control	180	405	1000	755	2.02	-
F1	180	405	1000	755	2.42	0.40
F2	180	405	1000	755	2.82	0.81
F3	180	405	1000	755	3.23	1.21
F4	180	405	1000	755	3.63	1.62

F0= Control Concrete (0% fiber), F1 = 0.1% fiber concrete, F2 = 0.2% fiber concrete, F3 = 0.3% fiber concrete, F4 = 0.4% fiber concrete.

Four volume fractions of fiber viz. 0.1%, 0.2%, 0.3% and 0.4%, were used. A part of the fibers was also used after treatment with NaOH solution. Fiber lengths of 25 and 20 mm are considered to investigate the properties of JFRC and shrinkage performance. The shrinkage test was conducted on concrete slab specimens (ASTM 2017). After preparation, the slabs were kept at 40 ± 2ºC and around 60% relative humidity. The shrinkage cracks formed on the slab surface within a controlled experimental condition were analyzed using image processing. A thin polyethene layer was placed inside the slab mold measuring 500 × 250 × 75 mm to reduce the base friction between the concrete and the wooden board. After casting, the concrete slabs were immediately stored in a controlled environmental chamber. This chamber is equipped with high-speed electric fans on the walls to speed up concrete drying while managing temperature and humidity.

Crack observation and measurement

The crack observation and analysis followed the process described by Islam and Das Gupta (2016) After casting, the slabs were kept in the controlled environmental chamber and visually examined every ½ hour for cracking. Images of cracks were captured using a high-quality digital camera simultaneously.

Mechanical strength evaluation

Compressive strength

The compressive strength test followed ASTM C39 (ASTM 2020). Compression testing equipment was used to test 153 cylindrical concrete specimens (Ø150 × 300 mm), where loads were applied at a uniform and constant rate (0.15–0.35 MPa/s). The diameter of the test specimens was measured before applying compressive loads. The compressive strength of concrete samples was measured at 7, 14, and 28 days of curing. The curing was done continuously underwater until the strength tests since it was demolded one day after casting.

Splitting tensile strength

As with the compression test, 153 cubical specimens (150 mm) were cast and tested for splitting tensile strength. The fiber volumes, lengths and treatment conditions were kept the same for this test. The curing ages before the test were 7, 14, and 28 days. The specimens were cured underwater until the test was conducted.

The splitting Tensile strength test result indirectly indicates the tensile properties and shear resistance of concrete. The test was conducted in compliance with EN 12,390–6 (EN 2009), placing a cubical concrete specimen (150 mm) in the compression machine. A diametral compressive force was applied to a cubical sample throughout this process. The bearing strips were positioned inside the upper and lower bearing blocks of the machine and the specimen. The load was then applied at a constant rate (0.04 MPa/s to 0.06 MPa/s) until failure occurred. This loading induces tensile stresses on the loading plane. As a result, tensile failure takes place rather than compressive failure. The splitting tensile strength was calculated by dividing the maximum recorded load by appropriate geometrical factors (EN 2009).

Result and discussion

Workability

Workability was evaluated through a slump test after mixing each concrete batch. The slump value of the control and FRCs are given in Figure 1. The mix design shown in Table 3 indicated that it was intended to maintain a similar slump level by varying superplasticiser dosage; however, the slump value changed slightly due to fiber length and content. The slump values were found within the target range of 100–125 mm for all mix cases. Therefore, it was considered that all the concrete samples had a similar level of workability and should give an equal compaction level with the same effort.

Figure 1. Variation of workability with fiber content.

Compressive strength

J25 Fiber

Figure 2 shows compressive test results for the concretes with 0–0.4% volume fraction of J25 fibers at various ages (7, 14, and 28 days). The compressive strength at early ages (7 and 14 days) were reduced with fiber addition. However, the situation was improved at the standard curing age of 28 days. Depending on the treatment of fibers using NaOH, the strength at 28 days of the curing period increased or decreased slightly. The maximum increase of compressive strength at 28 days curing period is 7% at 0.1% untreated fiber content than control concrete. The overall strength of fiber concrete was slightly higher than control concrete with untreated fibers. Elsaid et al. (2011) also found similar results using kenaf bio-fibers. Jute and yarn fibers were also reported to increase the compressive strength of concrete (Zakaria et al. 2020)

Figure 2. Compressive strength of concrete with J25 fiber.

The strength with treated fibers was higher than the control concrete with 0.1% fibers at 14 and 28 days of curing. However, with a higher fiber amount (0.2, 0.3 and 0.4%), the strength at 28 days was reduced (3–8%) compared to the control concrete. With increased fiber content added, the compaction might have interfered, thereby decreasing the strength at an early age. In addition, the increased fibers content leads to more interfacial surface bonding. These bonds might weaken early but become stronger with continued hydration reaction and pore blocking. On the other hand, untreated fibers had a rough surface compared to the NaOH-treated samples. This might help interlock the concrete matrix better than the treated smooth surface fibers. Islam and Das Gupta (2016) reported a slight reduction in compressive strength with polypropylene fiber (>0.1%) in concrete. However, the fiber was cleaner and had a smooth surface compared with the treated jute fiber.

J20 Fiber

Figure 3 shows the compressive strength test results obtained for 0–0.4% volume fraction of untreated/treated J20 fibers at various ages (7 days, 14 days, and 28 days). Compared to the J25 fiber concrete, compressive strengths were reduced from control concrete to 11% at 7 days and 5.5% at 14 days for untreated 0.4% fiber content. This was 17% and 7% higher than the treated fibers. At 28 days, the compressive strength was similar to slightly higher for each age with up to 0.2% untreated rough fibers. A similar trend was noted for treated fibers at 28 days, but the compressive strength was found to be slightly less compared to the control concrete.

Figure 3. Compressive strength of concrete with J20 fiber.

Compressive strength as a function of fiber length and treatment condition

It was observed that the fiber length influences the compressive strength of JFRC. In general, the J25 fiber gave increased compressive strength than the J20 fibers at 28 days. After treatment with NaOH the strength of the J25 fiber length is also higher compared to J20 fiber concrete. The 28-day compressive strength of untreated fiber concrete was higher (4% −7%) than the control concrete with 0.1–0.3% fiber content. Better interfacial bonds with untreated rough fibers contributed to this. This result agrees with Islam and Das Gupta (2016) and Sivakumar and Santhanam (2007). The compressive strength of fibrous concrete is also affected by chemical treatment. The strength of concrete with J25 treated fiber at 28 days increased slightly (3–6%) for fiber content of 0.1% and 0.2% compared to control concrete. As with no treatment case, the highest strength was obtained with the fiber content of 0.1%, and the compressive strength at 28 days decreased (3–8%) with high fiber content (0.3% and 0.4%) compared to the control concrete.

The compressive strength results with J20 fiber at 28 days show an increase of 14% and 2% for fiber content 0.1% and 0.2% compared to no fiber concrete. The highest strength is obtained at 0.1% fiber. Compressive strength at 28 days is similar to J25 fiber at 0.3% and 0.4% content. 28-day compressive strength decreased (1–7%) with NaOH-treated J20 fiber compared to no fiber, with a maximum of 7% reduction with 0.4% volume of fibers in the concrete. In addition, compressive strength decreases as fiber content increases. This is mainly to the high fiber content in the mixture, increased porosity, and air voids, which resulted from insufficient compaction.

Splitting tensile strength

J25 Fiber

The splitting tensile strength of concrete with untreated J25 fiber at 7, 14, and 28 days is shown in Figure 4. The splitting tensile strength of fiber concrete was found to be higher in each case than that of control concrete. At 7 days of curing, the maximum increase in splitting tensile strength over control concrete was one-fourth. A gradual increase (9–23%) compared to control concrete was noted for 0.1%-0.3% fiber content. Similar outcomes were found with bio-material coconut fiber (Ali et al. 2012; Ali, Xiaoyang, and Chouw 2013). Adding coconut fibers increased the splitting tensile strength by 11% compared to the control concrete. The splitting tensile strength increased with fiber content over a 28-day curing period. The 0.4% fiber provides the highest (19%) strength increase at 28 days compared to control concrete.

Figure 4. Split tensile strength of untreated J25 fiber concrete.

Figure 5 shows the splitting tensile strength of concrete with NaOH-treated J25 jute fiber at 7, 14, and 28 days. In contrast to the untreated fibers, the maximum increase of splitting tensile strength at 7 days curing period was 24.5% at 0.2% FRC. In each case splitting tensile strength of fiber concrete was higher than control concrete. A gradual increase in splitting tensile strength was noted during the 28-day curing period. The 0.4% fiber content gave the highest (16.0%) strength increment compared to control concrete.

Figure 5. Split tensile strength of treated J25 fiber concrete.

J20 fiber

Figures 6 and 7 show the splitting tensile strength of jute fiber concrete with untreated and treated J20 JFRC, respectively, at 7, 14, and 28 days. In general, the strengths of FRCs were higher than the control concrete. However, no definite trend was noted compared to J25 fibers. Splitting tensile strength was reduced with increased fiber content for 7 and 28 days, but a gradual increase was reported at 14 days for untreated fibers. At an early age, a gradual decrease in strength was noted with fiber volume but increased at 28 days for treated fibers. At an early age, the reaction of binding materials was insignificant; therefore, the strength was not found as expected. This indicates less bonding between the fiber and bonding matrix; therefore, scattering of data was noted. With the increase in curing age, the improved adhesion between the fibers and the binding agent gave its expected behavior (Shaikh 2020).

Figure 6. Split tensile strength of untreated J20 fiber concrete.

Figure 7. Split tensile strength of treated J20 fiber concrete.

Splitting tensile strength, fiber length and treatment conditions

Figure 8 shows the 0–0.4% volume fraction splitting tensile strength test results for comparing untreated and NaOH treated J25 and J20 fibers at 28 days. The length of the fibers and the chemical treatment of the concrete influence the splitting tensile strength of fibrous concrete. For example, at 28 days, the tensile strength of the concrete with untreated J25 fiber increased (3–19%) compared to the control concrete, and the highest tensile strength was obtained with 0.4% fiber content. The strong homogeneity and high compaction between the fibers and the concrete matrix may explain the increase in splitting tensile strength. This result generally agrees with Islam and Das Gupta (2016). While the J25 fiber was treated with NaOH, the splitting tensile strength at 28 days decreased slightly for F4; however, the opposite was noted for low fiber content concretes.

Figure 8. Effects of fiber length and treatment on concrete split tensile strength.

In contrast, for J20 fibers higher tensile strength was found for untreated low fiber content (0.1% and 0.2%) but the situation altered with increased fiber contents (0.3% and 0.4%). Zhou et al. (2013) found comparable results with jute fibers. The splitting tensile strength increase with adding fibers up to ¹/₆ of the corresponding compression value. After NaOH treatment, the strength of J25 fiber concrete was also higher than J20 fiber concrete. The fiber length was a key factor influencing the splitting tensile strength of JFRC. Zakaria et al. (2020) reported increased field-mixed concrete’s tensile strength with jute fibers. Error bars are plotted in Figures 4–7 in terms of standard deviation. The experimental splitting tensile strength data was found to be slightly scattered. These irregularities may be due to interference in the compaction process. The presence of bad coir dust in the fibers may also cause the creation of air voids.

Shrinkage crack resistance

Shrinkage crack measurement includes length, breadth (average and maximum), and the total area estimation. First, images of the shrinkage crack were acquired using a digital camera. Next, a ruler calibrated the captured images of various concrete specimens for actual size. Next, the recorded images were processed and altered using image analysis software (Rasband 2018) to provide a distinct crack profile through binarisation, thresholding, cleaning, and filtering operations. Finally, the length of the crack was measured by tracing the crack with a “curve tracing tool” in the image analysis software (Kejin, Shah, and Phuaksuk 2001). Figure 9 shows the key steps of image analysis.

Figure 9. Image analysis.

Shrinkage crack area

Jute fiber was efficient in reducing shrinkage cracks in fresh concrete. The crack width was visibly reduced by adding 0.1–0.4% fibers to plain concrete. Figure 10 shows the surface crack area as a function of fiber length, amount and treatment condition. With the addition of fibers, the overall crack area was reduced due to the crack bridging by fibers (Shafei et al. 2021). The dashed line in Figure 10 shows the crack area of the control concrete without jute fiber. It was noted that the extent of cracks decreased significantly with the increase in fiber amount in concrete.

Figure 10. Effect of fiber content on the total crack area.

As with compressive and splitting tensile strength test results, untreated fibers were more effective than NaOH-treated fibers in reducing shrinkage cracks. With each amount (%) of fibers similar performance was noted in both sizes (lengths) fibers. However, being smaller in length, with the same volume fraction, the J20 fibers are expected to discrete more than the J25 fibers. This may cause its better performance against shrinkage crack resistance. Using 0.4% fibers (by volume), plastic shrinkage cracking was reduced by 62% for J20 fiber compared to the control concrete. Islam and Das Gupta (2016) reported almost eliminating shrinkage cracks using polypropylene fibers in concrete.

Shrinkage crack width

The maximum crack width due to shrinkage in fresh concrete was recorded in the control sample without fibers. With fiber addition, the crack widths were also reduced. The use of fiber reduced crack width and the overall crack area significantly. The increase in fiber content reduced their spacing and also the tendency for crack initiation (Mingfeng et al. 2021). Figure 11 shows maximum crack widths resulting from plastic shrinkage. The crack width is reduced by 17% to 62% for J20 fiber (without NaOH treated) conditions (Islam and Das Gupta 2016).

Figure 11. Effect of fiber content on maximum crack width.

The maximum crack width (1 mm) was recorded in control concrete without fibers. However, the crack widths were reduced with the addition of fibers. As with the crack area, the crack control characteristics of the J20 fiber were better than those of the J25 fiber. With the addition of more fibers, the maximum crack width was also reduced. The use of jute fiber to reduce crack width resulted in a considerable reduction in the overall crack area. This was 1–30% for J20 fiber (NaOH treated) condition. The crack width was reduced by 10–49% for J25 fiber while this was reduced by 4–32% for J25 fiber (NaOH treated) condition. Therefore, it is concluded that J20 fibers performed better shrinkage crack reduction than J25 fibers. The NaOH treatment was not helpful for crack bridging as it was found for raw jute fibers without any treatment. This may be due to better bonding of raw fibers with concrete as noted earlier for strength characteristics. Polypropylene fiber addition significantly reduced plastic shrinkage cracks (50–99%) compared to plain concrete without fibers (Islam and Gupta, 2016).

According to the recommendation of ACI (ACI PRC 2001), plastic shrinkage cracks should not exceed 3 mm in width. In the study, all concrete samples conformed to the recommended value. The addition of fibers reduced the crack width. Fibers can act as a crack-bridging mechanism and contribute against shrinkage cracking (Shafei et al. 2021; Sivakumar and Santhanam 2007).

Practical implications

Jute is abundantly grown in south Asian countries, especially in Bangladesh. The natural fiber has many applications in the built environment. Due to the brittle nature of concrete, scientists studied the application of different types of fibers in concrete to improve its ductility. In addition, drying shrinkage is a key concern for concrete professionals in arid regions. In a hot and low humid zone, the mixing water provided in fresh concrete can rapidly evaporate. This may cause severe cracking in freshly laid concrete. In addition, with the improvement in superplasticisers, contemporary concrete technology uses low water content to improve ultimate strength, which further creates the risk of drying shrinkage cracks. The extensive experimental work carried out in this study indicates 0.1–0.2% natural fiber (jute) can enhance both tensile properties and drying shrinkage crack resistance of cement concrete.

Conclusion

This study aimed to assess the performance of locally available bio-fibers in cement concrete. Based on the extensive qualitative, semi-quantitative, and quantitative experimental analysis of the fresh, mechanical properties and shrinkage crack resistance of JFRC, the following conclusions are drawn:

• All the concrete mixes achieved a target slump range of 100-125 mm. In this regard, the superplasticiser level was varied slightly to maintain the same level of consistency. The admixture demand increased with fiber volume in the concrete mix.

• Depending on fiber length, content, and surface property, jute fibers can slightly increase the compressive strength up to 7% at low fiber content (0.1-0.2%). Higher fiber content interferes with the compaction process, negatively influencing strength.

• In most cases, splitting tensile strength increases with fiber content. For J25 fibers, the highest strength was achieved (increased 25%) with 0.4% fiber. As a result, jute fiber effectively reduced the total shrinkage crack area and limited its widths. The addition of J20 fibers reduced 18-61% shrinkage crack area while the crack width was reduced by 62%. The J25 fiber was also effective in reducing crack area and width; however, the effectiveness was slightly lower than the J20 fiber.

• NaOH treatment was applied to the fibers to improve durability and clean the coir dust attached to their surface. However, the treated clean fibers reduced strength slightly and were less effective in reducing crack area and maximum width. This also indicates that the fibers will have slight degradation in the highly alkaline cementitious system.

Overall, the results indicate the promising use of natural fibers for concreting in arid regions where drying shrinkage crack formation due to rapid evaporation of mixing water is an issue. It is also expected to increase the tensile properties of concrete required for particular engineering applications.

Highlights

• The performance of natural fiber (jute) was evaluated in cementitious media.

• The effect of fiber length was evaluated in terms of concrete properties improvement.

• The fiber content was varied from 0.1-0.4% by the volume of concrete to evaluate the effect.

• The biomaterial (jute) was found to improve concrete’s tensile strength and shrinkage crack.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.