BEHAVIOR OF CEMENT MORTAR WITH THE ADDITION OF COCONUT FIBERS

Purpose: Analyze the physical and mechanical parameters of cement mortar with the addition of coconut fibers (FC). Theoretical framework: In recent years, there has been a comprehensive approach towards incorporating natural fibers as reinforcing elements in cementitious composites. This approach is motivated by the availability of these fibers, the reduced costs involved and the positive effects in mitigating the environmental impacts caused by the use of polymeric fibers from non-renewable sources. However, increasing the proportions of these elements in mortars, for example, does not always result in improvements to the integrity of the material produced. Method: The initial phase was directed to the literature review focused on studies that explored the behavior of cement mortars with vegetable fibers. Next, the process of mechanical extraction and treatment of coconut fibers was carried out, aiming for the subsequent characterization of the materials. A dosage study was carried out using a 1:3 mixture (cement:sand) using percentages of 3%, 5% and 7% of coconut fibers, based on the total volume of the composite. Based on the preliminary study, the mix with 5% addition of coconut fibers was selected due to its superior performance. To evaluate the material with the defined percentage of FC, tests were carried out covering physical indices and mechanical resistance in the fresh and hardened state. Parameters such as consistency index, compressive strength, tensile strength, water absorption, void index and specific mass were analyzed. Results and conclusion: The results indicate that the addition of 5% by volume has a positive impact on increasing the tensile strength of mortars from 1.83 MPa (without fibers) to 2.36 MPa (with fibers). However, this addition does not have a favorable influence on other mechanical properties, such as compressive strength, although it does not cause significant harm to its applicability. Research implications: Composites with vegetable fibers offer the possibility of combining traditional construction techniques with unconventional elements, using the reuse of waste. Originality/value: The contribution to the evaluation of the behavior and adaptation of this material, in order to make it economically viable and durable.


INTRODUCTION
In the last two decades, the production of works that investigate new construction solutions using natural fibers in composites has grown throughout the world (BARBOZA et al ., 2020).This is due to the availability of these fibers, the low cost involved and the benefits in reducing environmental impacts (LIMA et al ., 2014), with the environmental issue being one of society's important issues, aiming at sustainability guidelines (GONZAGA; SILVA; ANDRADE, 2021).Composites, in turn, are formed by the combination of two or more materials, which, after mixing, can be macroscopically identified among themselves and exhibit combined properties (SALES, 2015).
With the addition of vegetable fibers as reinforcement in cement matrices, it is possible to observe a reduction in cracking, accompanied by an increase in the energy absorption capacity under dynamic efforts (SALES, 2015).These composites offer a significant advantage in terms of post-rupture behavior, resulting in improvements in tensile strength and toughness (SAVASTANO JR; AGOPYAN; OLIVEIRA, 1997).3 There are several organic fibers suitable for use.Savastano (2000), Passos (2005) and Toledo Filho et al . (1997) highlight coconut fiber ( Cocos nucifera ).According to the Brazilian Institute of Geography and Statistics (IBGE), the production of Cocos nucifera in Brazil in 2021 was 1,638,573 thousand fruits.Typically, coconut shells are discarded in landfills, beaches, vacant lots and roadsides (SILVEIRA, 2008).It is worth noting that the shell of the coconut fruit takes more than 8 years to decompose, which results in conditions conducive to the proliferation of diseases (PASSOS, 2005).
In this context, the civil construction sector, one of the sectors that generates the most impacts on the environment (LEITE et al., 2023), presents itself as a favorable alternative for the reuse of this waste through the application of coconut fibers in cementitious composites ( CARNEIRO, 2010).Toledo Filho et al . (1997) report that these materials offer the possibility of combining traditional construction techniques with unconventional elements.Therefore, it is important to carry out scientific research that contributes to the evaluation and adaptation of these materials, in order to make them economically viable and durable.
The objective of this study is to evaluate the physical and mechanical behavior of cement mortars reinforced with coconut fibers.Specifically, the effects when subjected to compression and traction stresses.

Vegetable Fibers
Plant fibers are composed of individual cells made up of microfibrils rich in cellulose (SAVASTANO, 2000).They can be obtained from fruits, leaves, stems and seeds, as mentioned by Wiedman (2002).The fundamental composition of these fibers includes cellulose, hemicellulose, lignin, pectin and minerals, and the importance of the presence of lignin stands out, as it provides resistance to compression to cellular tissue and fibers, in addition to providing resistance against rotting (STEPS 2005).
Extractives contained in plant fibers, such as resins, polyphenols, oils, greases and sugars, can be released when in contact with aqueous solutions.This can delay the cement setting process and affect the strength of the resulting composite (SAVASTANO JR; AGOPYAN; OLIVEIRA, 1997).Furthermore, when fibers are incorporated into cementitious matrices, calcium hydroxide generated during the hydration of Portland cement can cause deterioration in fiber components such as cellulose, hemicellulose and lignin.These problems can be minimized or avoided through treatments applied to the fibers (CARNEIRO, 2010).

Cocos nucifera
As illustrated in Figure 1, the coconut fruit is composed of different parts, which include the epicarp, mesocarp, endocarp and solid albumen (CARNEIRO, 2010).The average unit weight varies from 700 g to 2000 g (ARAGÃO et al ., 2002).FC are obtained from the fruit mesocarp, with an average yield of 30% fiber and 70% powder per unit (NUNES, 2021).According to Aragão et al . (2002) apud Silveira (2008), CF are classified as long fibers.Its physical and mechanical characteristics exhibit great variability, with a coefficient of variation greater than 40% (SAVASTANO JR., 2000).This discrepancy can be attributed to the difference in production area, age of the coconut tree and dimensions of the fibers (TOMCZAK; SYDENSTRICKER; SATYANARAYANA, 2007).
The extraction of CF, according to Wiedman (2002), can be carried out through chemical, biological and mechanical processes.Chemical processes involve the use of products in the maceration stage, aiming to facilitate the release of fibers.Biological processes occur through the natural decomposition of the fruit in water tanks, which may or may not include the addition of bacteria cultures and enzymes to accelerate the obtaining of fibers.Mechanical processes can be carried out using shredders, crushers or manual extraction.
An alternative treatment proposed by Asasutjarit et al . (2007) suggests that fibers be boiled for 2 hours, washed in running water and dried in the sun for two days, in order to reduce sugars, starch, fat and other unwanted components.This study reports that the fibers subjected to this process became more rigid and resistant.Silva et al . (2017) describes a treatment that involves the combination of natural latex and silica fume.According to the authors, fibers treated in this way maintain their integrity and have good adhesion to the cement matrix, which produces a composite with adequate performance and durability.On the other hand, untreated fibers tend to become brittle and create high porosity in the transition zone between the fiber and the matrix.
Table 1 shows a comparison of the mechanical properties of some natural and synthetic fibers applied in composites.According to Carneiro (2010), FC demonstrates one of the highest values of elongation at break, similar to that of synthetic polypropylene fiber.JR., 2000).Source: Adapted from Toledo Filho et al ., (1997);Savastano Jr. andAgopyan , (1997) apud Savastano Jr., (2000).
Although they present higher elongation values at break, coconut fibers have lower tensile strength moduli and elasticity moduli compared to other fibers.However, this does not prevent its application, as highlighted by Savastano (2000).

Cementitious Composites with Fibers
In the study conducted by Ali et al . (2012), several attributes of concrete reinforced with coconut fiber were examined after 28 days of curing, such as consistency, modulus of rupture, compressive strength and flexural strength.Different proportions of fiber in relation to the cement mass were explored, namely 1%, 2%, 3% and 5%, covering different fiber lengths: 25 mm, 50 mm and 75 mm.The results indicated that the most advantageous combination of properties was obtained when using coconut fiber with a length of around 50 mm and a proportion of 5% in relation to the cement mass.Silva et al . (2014) evaluated mortars with a ratio of 1:2.3 ( cement:sand ), maintaining the water/cement ratio at 0.55 and adding 0.3% coconut fibers in relation to the cement mass.FC were tested in lengths of 12.5 mm; 25.0mm; 37.5mm; 50.0mm; 62.5mm and 75.0mm.A decrease in compressive strength of up to 12% was observed when compared to the fiber-free mixture, with the length that showed the best performance being 25 mm.The researchers also found an increase in the ductility of the composite after cracks occurred, in contrast to the reference mortar.
In order to establish a comparison between the natural fiber used and a synthetic fiber widely recognized on the market, Barboza et al . (2023) introduced 0.5% polypropylene macro fibers into a cement mortar.After a period of 7 days of curing, the results obtained were 30.10 MPa for compressive strength and 2.05 MPa for diametrical compression tensile strength.
In a previous study, Colombo et al . (2019) introduced thin polypropylene filaments at a proportion of 500g/m³.The researchers observed a decrease in resistance to both compression and traction in flexion, when compared to mortar without fibers.
In turn, Centofante and Dagostini (2014) incorporated 250g of polypropylene fibers for each bag of cement.This resulted in an 18.2% increase in flexural tensile strength, while compressive strength decreased by 16.7%.However, even with the reduction in compressive strength, the fibers contributed to the reduction of cracks in the mortar.

METHODOLOGY
The methodological stages of this work are presented in Figure 2, with the main sources for consulting academic publications on this topic being the journal manager Web of Science

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(WOS), ScienceDirect (Elsevier), in addition to the Scielo digital library .The literature review was directed to works that evaluated the behavior of mortars with the addition of vegetable fibers.

CF Extraction and Treatment
Cocos nucifera were collected from commercial waste in the city of Dourados -MS, Brazil .Fiber extraction followed the method described by Neto et al . (2019).The process began with dividing the fruit into four parts and extracting and discarding the solid albumen.Then the parts were exposed to the sun for two days so they could dry completely.After drying, the portions were crushed in the TRE25 mechanical crusher and the fibers were manually separated for subsequent treatment (Figure 3).The fibers were cut manually in order to reach the desired size, according to Ali et al . (2012), ideal between 25 and 50mm.For the surface treatment of coconut fibers, with the aim of improving adhesion between the fiber/cementary matrix, the procedure proposed by Asasutjarit was carried out.et al .( 2007).The fibers were immersed in water and boiled for 2 hours, then washed in running water until the color of the water became clear and, finally, dried in the sun for two days.This method was chosen because there is no complexity in execution and because it does not require materials that are difficult to obtain.
The purpose of the treatment used is to remove existing extractives, as mentioned by Carneiro (2010).However, it is important to emphasize that the objective of this work was not to analyze the treatment of fibers and its consequences.For this reason, it was decided to apply the same treatment to all mortar mixes, in order to avoid interfering with the results.Figure 4 displays the fibers in three stages: untreated, during treatment and after treatment.

Characterization of the Materials Used
This stage consisted of investigating the characteristics of the materials used.All tests in this work were carried out at the Civil Engineering Laboratory (LEC) at the Federal University of Grande Dourados (UFGD).
After extracting and treating the coconut fibers, due to the variation in length and diameter of the fibers, the shape index was calculated, with adaptations to NBR 7809 (ABNT, 2019).For this, a random sample containing 50 treated and cut fibers was selected, and length and diameter measurements were taken with the aid of a digital caliper.
Additionally, the specific mass and water absorption test of coconut fibers was conducted, with adaptations of NBR 16916 (ABNT, 2021) for fine aggregate.It is important to highlight that, currently, there are no specific standards for the characterization of fibers.
The fine aggregate was characterized through particle size composition, unit mass, void index, specific mass and water absorption tests, in accordance with their respective standards NBR 17054 (ABNT, 2022), NBR 16972 (ABNT, 2021) and NBR 16916 (ABNT, 2021).Drinking water was supplied by the local public network.The Portland cement used was CP V-ARI, chosen due to its higher hydration speed and lower content of mineral additions (SILVA et al ., 2017).

Study of Traits
For the study of traces, following the NBR 7215 standard (ABNT, 2019), the reference dosage of 1:3 ( cement:sand ) was adopted.The water/cement ratio was set between 0.5 and 0.6 to ensure good workability of the mixture.Different percentages of coconut fiber addition were tested, being 3%, 5% and 7% in relation to the volume of the composite.The traits used in this study are presented in Table 2. Where: REF: fiber-free reference mortar; 3FC: mortar with 3% coconut fibers; 5FC: mortar with 5% coconut fibers; 7FC: mortar with 7% coconut fibers.
The mortars were prepared in an automatic mortar machine , following the guidelines of NBR 7215 (ABNT, 2019).The process consisted of the following steps: first, the addition of water, followed by the addition of previously mixed cement and sand.For mortars with fibers, as described by Capelin et al . (2020), a process analogous to the reference was carried out, where the fibers were added gradually as soon as the mortar was turned on, ensuring a uniform distribution.
In order to determine the appropriate mixture, tests were carried out on the consistency index of the mortar in a fresh state, adapted from Annex A of NBR 7215 (ABNT, 2019), compressive strength and tensile strength by diametrical compression, following the corresponding standards, NBR 7215 (ABNT, 2019) and NBR 7222 (ABNT, 2011).The tests on the 50x100mm specimens were carried out with only 7 days of curing in a humid chamber.This is due to the use of Portland CP V-ARI cement which, as established in NBR 16697 (ABNT, 2018), meets the high resistance criterion after 7 days of curing.
The different percentages of fibers were explored with the aim of finding the ideal trait that would provide adequate workability and better resistance performance.The material

Obtaining Physical and Mechanical Indices
After defining the appropriate mix of 1:3 ( cement:sand ) with the addition of 5% FC by volume, the mortar was prepared following NBR 7215 (ABNT, 2019).Then, the consistency index was carried out in accordance with Annex A of this same standard.The determination of water absorption, void index and specific mass of the mixture was carried out in accordance with NBR 9778 (ABNT, 2005).
As shown in Figure 2, the tests for the chosen trait were carried out at different curing ages in a humid chamber: 3, 7 and 28 days.As a result, a total of 18 fiber specimens were molded, equivalent to the quantity for the reference ones, all with dimensions 50×100mm.

Coconut Fibers (CF)
In accordance with what was mentioned in section 2.2, data regarding the length and diameter of the fibers were acquired from a sample containing 50 units.Figure 6 provides a view of the ranges of shape indices (length/diameter ratio) along with their respective frequencies observed in the sample.Typical shape index values for fibers with lengths of 6.4 to 76 mm range from 30 to 150 (BASTOS, 1999).As evidenced in the graph, 70% of the fibers are concentrated within this range.As for the mean diameter of the CF, it was 0.27 mm with a standard deviation of 0.071 mm.
In accordance with what was mentioned in section 3.2, the analysis of the specific mass of coconut fibers resulted in 1.142 g/cm³ when measured in a dry state, and 1.314 g/cm³ with the aggregate saturated on a dry surface.As for water absorption, a rate of 15.02% by mass was recorded.The data conformed to the range of values described in the standard.

Fine aggregate
Through the characterization of the fine aggregate, according to the method described in item 3.2, the following values were obtained: unit mass of 1.551 g/cm³, void index of 43.57%, specific mass of 2.748 g/cm³ and water absorption of 0.32%, by mass.
The results of the particle size composition test of the fine aggregate are shown in Appendix A. According to the definitions of NBR 17054 (ABNT, 2022), the fine aggregate analyzed has a maximum characteristic dimension of 1.2 mm and its fineness modulus presents a value of 1.80.
The granulometric curve is shown in Figure 7, according to the lower and upper limits presented in NBR 7211 (ABNT, 2022).

Study of Traits
The mortars were prepared as described in item 2.3.It was noted that with the incorporation of fibers, the mixture required a greater amount of water to reach the appropriate consistency.As a consequence of this adjustment, the water/cement ratios varied depending on the composition of the mixture.The corresponding values of these w/c ratios are as follows: 0.54 (REF); 0.54 (3FC); 0.55 (5FC); 0.56 (7FC).
In total, there were 3 specimens for each FC percentage, tested only after 7 days of curing.Figure 8 shows the consistency index of the different traces produced.As reported by several authors, such as Savastano (2000) and Capelin (2020), it is noted that when increasing the proportion of vegetable fibers in the mortar, even with a greater addition of water, there is a tendency to decrease the consistency index.This effect is the result of the fibers' ability to absorb part of the water, consequently reducing the workability of the material.
Despite the decrease in this index, based on what is stipulated by Annex A of NBR 7215 (ABNT, 2019), the inclusions of 3% and 5% FC present a value considered adequate, falling within the normal range of at least 165±5mm.12 Regarding the mechanical indices of the mortars in the trace study, the test specimens were manufactured and subjected to tests as described in item 2.3.The results obtained for the compressive strength of the mortars after 7 days of curing are shown in Figure 9.The addition of FC resulted in a reduction in compressive strength values, in relation to the reference mortar, between 12.3% and 18.17%.Among the traits with incorporated fibers, the 5FC mixture obtained the best results.
The results of the diametral compression tensile test are shown in Figure 10.It was found that all mortars with additions showed superior performance compared to the reference mortar, with an increase of up to 34.68% when 5% FC was added.Among the traits analyzed, the 5FC mixture achieved better results due to the lower loss of resistance.
Based on the values demonstrated, the trait that presented the best performance and was considered the most suitable in this study was with 5% addition of coconut fibers (5FC).This is due to both the lower loss of compressive strength and the higher value of tensile strength due to diametral compression.Furthermore, it is important to mention that the consistency index for this mortar met the values established by Annex A of NBR 7215 (ABNT, 2019).

Assessment of Mortars with 5% FC
After selecting the 5FC mixture and taking new molds of the specimens, tests were carried out at 3, 7 and 28 days, and the results obtained are presented in this topic.The mortar in its fresh state recorded a consistency index of 166.32 mm, 7.3% lower than the reference mortar, calculated by the arithmetic mean of two orthogonal diameters.
Continuing with the physical indices of the analyzed dosage, Table 4 presents the values corresponding to the specific mass, water absorption and void index of the mortar hardened after 28 days of curing.These values were obtained for both the reference mortar and the mortar with added fibers, as detailed in item 2.4.The 5FC hardened mortar showed higher water absorption due to the ability of coconut fibers to absorb it.Regarding the void index and specific masses of both compositions, with and without the presence of fibers, a minimal variation was observed.This demonstrates that fiber inclusions in reduced percentages did not have a significant impact on these properties.
The mechanical indices of the mortars were obtained according to item 2.4.The data is presented in Figure 11.As can be seen, the 5FC mix showed a reduction in its resistance values compared to the reference mortar, as well as in the mix study.According to Savastano (2000), increasing the water/cement ratio in mortar with coconut fibers can influence the decrease in compressive strength.Furthermore, according to Toledo Filho et al . (1997), the lower workability of the mortar can lead to inefficient compaction of the material in its fresh state, resulting in a greater number of defects and, consequently, loss of strength.
Authors such as Barboza et al . (2023), Colombo et al . (2019), Centofante and Dagostini (2014), reported a reduction in compressive strength when synthetic polypropylene fibers were added to cement mortar.These observations indicate that the values obtained with coconut fibers are within an acceptable range when compared with other synthetic fibers.14 Likewise, Figure 12 shows the results of tensile strength by diametrical compression, for both mortars at the three curing ages.The mortar with the addition of fibers achieved a performance of 28.9% above the reference values after 28 days, a figure already expected after carrying out the trace study.This behavior can be attributed to the formation of connections between the cracked parts during tensile stress, which results in an increase in the ductility of the material (CAPELIN, 2018).
Figure 12: Tensile strength by diametral compression of the reference mortars and with 5% addition of FC after 3, 7 and 28 days of curing .Source: Authors (2023).Silva et al . (2014) highlight that the coconut fibers kept the faces of the mortar cracks together, preventing sudden rupture of the material and ensuring the continuity of the composite and describe that this behavior highlights the greater deformation capacity provided by the fibers in the mortar.Figure 13 shows the specimens after rupture, indicating that mortars with fibers reduce fragmentation and guarantee greater material integrity.Additionally, Carneiro (2010) reports that, even after the occurrence of cracks in the matrix, coconut fibers demonstrated a remarkable ability to absorb energy, contrary to the immediate collapse observed in other composites and in the unreinforced matrix.This greater load absorption capacity is also corroborated by Toledo Filho et al . (1997).In this study, the fiber-reinforced specimens did not fracture into multiple fragments after reaching the breaking point, unlike the reference mortar, devoid of coconut fibers.
It is important to highlight that there is no specific legislation for the use of mortars with added fibers, but the reduction in compressive strength does not necessarily represent an impediment to their use, as cited by Savastano ( 2000

CONCLUSION
As coconut fibers are incorporated in greater quantities, the consistency index of fresh mortars decreases.This decline can be justified by the ability of coconut fibers to absorb water.
In the context of the physical characteristics of the mortar, after curing, the presence of fibers results in higher water absorption.However, both the specific mass and the void ratio of the mortar, whether with or without the addition of fibers, do not exhibit significant variation.This may be associated with the relatively low proportion of incorporated fibers.
Among the different proportions of fibers investigated in the trace study, the inclusion of 5% stood out compared to the other combinations.This percentage achieved the best performance among mixtures with FC, considering that they all had lower compressive strength than the reference mortar.
The incorporation of coconut fibers has a negative influence on compressive strength, however, it does not preclude its use.Another relationship identified was the increase in tensile strength due to diametral compression in all proportions and combinations analyzed.This increase was up to 28.9% (from 1.83 MPa to 2.36 MPa) after 28 days of curing , when 5% of coconut fibers were incorporated in relation to the total volume of the composite.Authors report that this is due to the connection between the cracked parts during the tensile effort, in addition to the fact that the fibers provide the composite with greater energy absorption capacity.
In this context, the incorporation of coconut fibers in cement mortar offers the opportunity to integrate waste into composites, improve some of their properties and encourage the development of new materials for civil construction.With a view to subsequent investigations, the following research questions are suggested: • Analysis of the durability of the fibers in this composite; • Assessment of material deformation; • Study of new treatment approaches to preserve coconut fibers from the alkaline environment and minimize gaps between the cement matrix and the fibers; ___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.17.n.10 | p.1-19 | e04322 | 2023.

Figure 1 :
Figure 1: Cross section of parts of Cocos nucifera Source: Adapted from Van Dam et al. (2004).

Figure 2 :
Figure 2: Flowchart of the methodological steps of this work.Source: Authors (2023).
___________________________________________________________________________ Rev. Gest.Soc.Ambient.| Miami | v.17.n.10 | p.1-19 | e04322 | 2023.9 adapted to carry out the consistency tests and the equipment used to break the test specimens, a Solocap digital electric press , are shown in Figure 5.

Figure 10 :
Figure 10: Tensile strength of mortars for the study of traces Source: Authors (2023).

Figure 11 :
Figure 11: Compressive strength of reference mortars and with 5% addition of FC after 3, 7 and 28 days of curing Source: Authors (2023).

Table 1 :
Mechanical properties of fibers used in cementitious composites .

Table 2 :
Study of traces with different coconut fiber contents.

Table 3 :
Specific mass, water absorption and void index