Sustainable Engineered Cementitious Composite using Natural Sisal and Coir Fibers

Engineered Cementitious Concrete (ECC) or bendable concrete is a high-performance concrete (HPC) with high ductility characteristic. Generally, it has been used to strengthen or retrofit existing structures to increase structural resilience against extreme loadings such as earthquakes or blasts. The constituent materials of ECC are fine aggregates, cement, supplementary cementitious composite (silica fume, fly ash, etc.), superplasticizer, water, and the use of fibers up to 2% volume fraction. With the use of fibers and the elimination of coarse aggregate, ECC has deflection-hardening in bending and exhibits fiber-bridging by multiple cracking. However, the development of ECC has so far been limited to using only synthetic and inorganic fibers, which are scarce yet expensive in Indonesia. As Indonesia boasts the second highest level of biodiversity in the world as the source of natural fibers, in this research, the natural fibers are used to replace synthetic and inorganic fibers in making ECC more sustainable, low cost yet locally available. Not only did the natural fibers are locally available at affordable prices, but the fibers also have distinctive characteristics of sustainable materials with high tensile strength and significant elongation. From the experiments, one may be concluded that natural fibers of sisal and coir can improve the ECC flexural strength up to 39.5% of the non-fiber mix. This highlights its ability to replace synthetic and inorganic fibers in ECC mixture.


Introduction
ECC or bendable concrete is a fiber reinforced cementitious material consisting of a cement composite with a random distribution of short fibers with a volume fraction of about 2% with extremely high ductility and toughness.ECC has much higher flexural and tensile strength characteristics than normal concrete, thus reducing structural damage due to extreme tensile and bending events, for example, blast [1] and impact [2].Engineered Cementitious Composite (ECC) or Bendable Concrete is a Fiber Reinforced Concrete (FRC) development, as ECC contains fiber in its mixture too.However, under tensile loads, FRC produces tension-softening properties after the concrete shows initial cracking, so that the load-bearing capacity of the concrete then decreases.ECC is the result of several constituent materials that can make concrete become ductile.ECC or bendable concrete, is designed with the aim of overcoming the weaknesses of ordinary concrete, low tensile deformation capacity.ECC's stress-1245 (2023) 012007 IOP Publishing doi:10.1088/1755-1315/1245/1/012007 2 strain typically has a similar trend to metallic materials subjected to tensile strain-hardening properties.This thing due to ECC can create multiple cracking after the initial crack is exceeded [3].
Fiber is a small filament of natural or synthetic materials with a minimum aspect ratio of 100 times and has flexible and strong properties.Fibers can be classified as synthetic, semisynthetic, and natural fibers [4].Synthetic fibers are man-made fibers through chemical synthesis, generally made of polymer or steel, which have a uniform and high mechanical property.However, they are high-priced, scarce especially in remote areas, yet not environmental-friendly.Natural fibers, on the other hand, can easily be found in the remote areas of Indonesia, and have long been used to meet human needs to support a broad type of industries.Nowadays, natural fibers are used in textiles, paper, crafts, accessories, decoration, and bio-composite materials.Natural fibers include cotton, silk, palm, sisal, coir, and empty fruit bunch of palm oil.
Currently, ECC is being developed as a reinforced or retrofit material made of cement paste and synthetic fibers such as polymer and steel fibers.In Indonesia, synthetic fibers, especially polymer fibers, are not manufactured locally.The procurement of synthetic fiber must be done through import, and this causes the cost of ECC production in Indonesia very expensive.Providentially, Indonesia boasts the second highest level of biodiversity worldwide as the source of natural fibers.A Map of the distribution of natural fiber sources in Indonesia is shown in Figure 1.Not only did the natural fibers are locally available with affordable prices, but the fibers also have distinctive characteristics of sustainable materials with high tensile strength and significant elongation.This paper comprises preliminary results of the experimental characterization of mechanical properties of ECC and effect of length and volume fraction of fiber in ECC with natural fibers, namely sisal and coir fiber.

Research Significance
In the development of ECC, commonly only polymer and/or steel fibers are utilized.In this study, a new set of ECC is developed considering environmental sustainability and domestic availability.Specifically, synthetic fiber is herein substituted by natural fibers namely sisal and coir fiber.These sisal and coir fiber ECCs are expected to promote infrastructure resilience and sustainability through simultaneous enhancements of natural fiber.

Material
The mixtures carried out in this study consist of Ordinary Portland Cement (OPC), Silica Fume, Class F fly ash as cementitious material, quartz sand as fine aggregates, sisal and coir fibers, water, and polycarboxylate-based High Range Water Reducing (HRWR) admixture as shown in Figure 2. The cement Type 1 OPC which conforms to ASTM C150 standard [5] is used.The chemical composition of OPC, fly ash, and silica fume are evaluated through XRF analysis and presented in Table 1.All the materials are available locally in Indonesia.Sisal and coir fibers were obtained from Blitar, East Java, and Banyumas, Central Java, respectively.

Natural Fiber Tensile Strength and Elongation Test
Testing of the tensile characteristics of natural fibers is carried out in accordance with SNI 08-1112-1989 [6].The tensile test was carried out per bundle basis as the dimensions of each single sample vary greatly with the testing setup as shown in Figure 3.

Slump Test
Characteristics of fresh ECC with sisal and coir fibers were evaluated to comprehend its workability.Slump tests conforming to ASTM C143 [7] are measured periodically at 0, 30, 60, 90 and 120 min to obtain the slump loss.

Mixing Procedures
The mixing was carried out conventionally by using a Hobart mixer as shown in Figure 4. Initially, the dry ingredients of quartz sand, fly ash, silica fume, and OPC, in accordance with the mixture proportion of ECC, were added to the mixing bowl and mixed until homogeneous.Table 2 shows the mixture proportion of the ECC with sisal and coir fibers.Fibers were added gradually while stirring the dry mixture.Water and superplasticizer were then poured into the mixture.After the mix was consistent and homogenous, it was then carefully poured into the specified molds.

Curing of Specimens
Upon casting the specimens, they were left in their specified molds.After hardened, the specimens were then placed in a water pond for the required number of days in room temperature water as shown in Figure 5.

Compressive Strength Test
Casted specimens were tested for 3, 14, and 28 days for their compressive strength.In doing the compressive strength test, ASTM C39 was adhered [8], determining the specimen's maximum compressive load before failure.Figure 6 shows the setup of the compressive strength test with a cylinder specimen.

Flexural Test
The next key parameter to be studied to reach the objectives of this study is to determine the flexural strength of the ECC mixes.Unlike the compressive strength test, the flexural test will be carried out for the 28-day strength of each mix.For the flexural strength test, a beam mold of 500 mm x 100 mm x 100 mm is used.The beam of length L rests on two roller supports is subjected to a four-point bending test using two concentrated load P in accordance to ASTM C78 as shown in Figure 7 to determine the flexural strength of the ECC [9]. .This may be due to the nature of the natural fibers.Its strength is strongly influenced by the growth conditions of fiber-producing plants.In Indonesia, natural fibers are generally harvested from fiber-producing plants that were grown with minimal treatment.This may affect the quality of the natural fibers e.g., lower tensile strength.Sisal fiber has the highest tensile strength based on both literature (510-710 MPa) [15] and observation (335.35MPa).Unlike its tensile strength values, the elongation of natural fibers (Figure 9) that obtained from observations is higher than the elongation based on the literature.The highest elongation of natural fibers is achieved by coir fiber which is 30 % based on literature [10] and 51,84% by observation.

Fresh Concrete Behavior
Characteristics of the fresh mixture of ECC with natural fiber are evaluated with respect to its slump and slump loss.Figure 10 shows the slump values of various ECC proportions.Theoretically, the workability of concrete is only affected by the absorption of water by the aggregate, evaporation, and hydration of the cement.As the ECC mixture contains fibers, the number of fibers, i.e. fiber volume fraction will also affect the workability.Based on the experimental observation, the higher volume fraction of fiber in the concrete, the lower the slump value is.The volume fraction of fiber in the ECC strongly affects its slump value.This is mainly due to the increase in friction between the ECC constituent material and the fiber, which is proportional to the amount of the mixed fiber.
Similarly, slump loss of ECC for both types of natural fibers show a comparable trend over the reviewed time duration.Within two hours of duration, a decrease in the slump of 52.4% for non-fiber mixtures, 60.1% for 1% sisal fiber ECC, and 80.3% for 2% sisal fiber ECC were observed.This shows that the decrease in the slump is considerably affected by the volume fraction of fiber in the ECC mixture.

Concrete Compressive Strength
The cylinder specimens were tested to obtain the compressive strength of ECC with sisal and coir fibers as shown in Figure 11(a) and (b) respectively at 14 and 28 days.At 14 days, the compressive strength of ECC non fiber (ECC-NF-S) concrete showed a higher value (41.1 MPa) compared to ECC using a volume fraction of 1% and 2% sisal fiber relatively.
Conversely, the compressive strength of the ECC non fiber (ECC-NF-C) mixture showed a lower value (15.77 MPa).This low strength may be due to the high volume of fly ash as pozzolan used in the ECC coir fiber mixture.For both ECC with sisal and coir fibers, ECC with a volume fraction of 1% has a higher compressive strength value than 2% fiber.The strength variation, however, is rather insignificant for ECC with sisal fiber, in comparison to ECC with coir fiber.Meanwhile, the variation of fiber length is observed to have no effect on the compressive strength of ECC at 14 days.
Until it is fully hydrated, ECC continued to experience an increase in compressive strength.From the experiment, it is observed that the compressive strength of ECC with sisal fiber has a rather similar value with less fluctuation.The non-fiber ECC mixture has a compressive strength of 46.15 MPa, while ECC with sisal fiber has a value between 40.73 to 45.40 MPa.For ECC with a coir fiber mixture, a significant difference in compressive strength is observed as the volume fraction is varied.The non-coir fiber ECC mixture shows an extreme ascent up to 37.27 MPa, while ECC using coir fiber achieves compressive strength from 26 to 36.67 MPa.This may again be due to the high volume of fly ash as pozzolan used in the ECC coir fiber mixture.It may then be concluded that the compressive strength of ECC was not significantly affected by variations in the length and volume fraction of fibers used in the mixture.

Flexural Strength
Figure 12 shows the comparison of ECC flexural strength between natural fiber and synthetic fiber obtained from literatures [16][17] [18] with respect to fiber volume fraction.It is evident that the addition of natural fibers in the ECC mixture increases the maximum flexural strength of the materials in comparison to the non-fiber sample.In this study, however, this increase is not accompanied by the presence of a deflection hardening zone.The flexural strength of non-fiber ECC mixture is 2,671 MPa.The use of natural fiber in the ECC mixture results in an increase with respect to the flexural strength of around 28.5% to 39.5% for ECC with sisal fiber and 12.3% to 24.7% for ECC with coir fiber in comparison to the flexural strength of non-fiber ECC.The highest flexural strength of ECC with natural fiber was 3.727 MPa i.e., ECC of 2% volume fraction with 12 mm length of sisal fiber and 3.33 MPa for ECC of 1% volume fraction of mix-length (12 and 30 mm length) of coir fiber.The flexural behavior before and after cracking is also reviewed.The load-deflection curves of three mixtures of different fiber contents are illustrated in Figure 13.The flexural stiffness in the elastic state (first slope) is rather similar for the three curves, while the flexural stiffness after the yielding point varies.
150  is toughness, obtained through integration of the load deflection curve, i.e. total area under the curve up to a net deflection of 1 150 ⁄ of the span length. 1 is first-peak strength, whereas b and d are the width and the depth of flexural specimen, respectively.The flexural toughness of ECC with sisal fiber is 10.58 Joule, nearly two times higher than that of the ECC with coir fiber i.e. 5.41 Joule.Equivalent flexural strength ratio,  .150  , of ECC with sisal fiber is 50.4%, about 1.83 times higher than that of the ECC with coir fiber which is 27.4%.Given Indonesia's archipelagic nature and its susceptibility to geohazards such as earthquakes and landslides, the higher flexural strength and flexural toughness of Engineered Cementitious Composites (ECC) reinforced with natural sisal fibers offer promising prospect.This locally available and costeffective solution holds great potential as a geohazard retrofit material, thereby contributing to sustainability initiatives aimed at strengthening the housing and infrastructures.The use of ECC with natural sisal fibers as geohazard retrofit material could serve as a ground-breaking suggestion for promoting resilient housing and infrastructure practices.

Conclusion
This paper evaluates the mechanical properties of ECC with the use of natural fibers of sisal and coir fibers.Sisal fiber is found to be among the natural fibers with the highest tensile strength, 335 MPa tensile strength.Coir fiber, on the other hand, is among the natural fibers with the highest elongation viz., 51.84% elongation.The volume fraction of natural fibers in the ECC mixture significantly affected its workability, i.e. slump and slump loss.The more volume fraction of ECC, the lower slump, and the higher slump loss is gained.ECC with the use of sisal fiber produces a compressive strength between 40.73 to 45.40 MPa.It was observed that the compressive strength of ECC concrete was not significantly affected by variations in length and volume fraction of fiber.The use of natural fibers increases the flexural strength of ECC around 28.5% to 39.5% and 12.3% to 24.7% for sisal and coir fibers.It has also been analysed that ECC with sisal fiber exhibits higher flexural toughness nearly two times than the ECC with coir fiber.This feature highlights its potential as a retrofit material for geohazard mitigation in housing and infrastructure applications.

Figure 13 .
Figure 13.Load-deflection curves of ECC with natural fibers Conforming to ASTM C1609, equivalent flexural strength ratio,  .150  which correlates to flexural toughness with the formula shown in Equation (1) is also evaluated for each variation of ECC mixtures.

Table 2 .
Mix proportion of ECC using sisal and coir fibers