Ballistic impact and mechanical strength of cement-composite mortars: The role of lignosulfonate-treated sisal and piassava fibers

ABSTRACT

Natural lignocellulosic (NLF) have emerged as sustainable reinforcements for mortars and concrete, however, fiber-matrix incompatibility remains a major challenge. This study investigates the use of sodium lignosulfonate (NaLS) to treat piassava (Attalea funifera) and sisal (Agave sisalana) fibers, aiming to improve their properties in cementitious composites. Fly ash (FA) and metakaolin (MK) were incorporated as supplementary cementitious materials (SCM) to lower matrix alkalinity and prevent degradation. For the first time, the impact of NaLS on the mechanical and ballistic performance of mortars with MK and FA as SCM was evaluated. Results showed that NaLS treatment improved fiber-matrix bonding, reduced porosity at the interfacial transition zone (ITZ), and mitigated fiber mineralization, particularly in sisal composites. NaLS-treated sisal fibers significantly enhanced ballistic energy absorption (+9.3%) compared to the unreinforced matrix, with no significant modifications in compressive and split tensile strength. In contrast, NaLS-treated piassava composites exhibited decreased tensile and compressive strengths, due to higher degree of fiber mineralization, with negligible change in ballistic performance. Microstructural analysis confirmed that the treated fibers promoted a denser ITZ and better interface quality, highlighting the critical role of fiber treatment in optimizing NLF-reinforced cementitious composites.

Keywords:
Cement mortar; Natural lignocellulosic fiber; Sodium lignosulfonate; Surface treatment; Ballistic test

1. INTRODUCTION

Sustainability is a pressing global priority, underscored by climatic events that indicate significant environmental changes [¹, ²], predominantly driven by the emission of greenhouse gases such as CO₂ into the atmosphere. The construction industry stands out as a major contributor to these emissions and a significant consumer of non-renewable resources, thereby exacerbating climate change. To mitigate its environmental impact, a key strategy involves reducing the reliance on synthetic materials in building composition and transition toward sustainable, natural alternatives, which often provide ecological benefits [³]. Among these alternatives, natural lignocellulosic fibers (NLF) and their composites emerge as promising materials for several construction applications [⁴, ⁵, ⁶, ⁷, ⁸, ⁹, ¹⁰, ¹¹]. These materials deliver critical environmental advantages, including biodegradability, renewability and reduced carbon footprint, as they sequester CO₂ during plant growth and enable energy recovery through end-of-life incineration [¹², ¹³, ¹⁴, ¹⁵, ¹⁶].

The reinforcement of cementitious materials with NLF has been extensively studied and validated [³, ¹⁷, ¹⁸, ¹⁹, ²⁰, ²¹, ²², ²³]. Among these, sisal (Agave sisalana) and piassava (Attalea funifera) stand out as promising options for the construction industry, due to their wide availability and suitability for large-scale applications. For instance, FONSECA et al. [²¹] demonstrated that incorporating piassava fibers enhances tensile strength and crack dispersion in mortars. RAMAKRISHNA and SUNDARARAJAN [¹⁹] identified optimal sisal fiber content for tensile strength in mortar plates, while SANTANA et al. [²²] determined the optimal piassava fiber content for reinforcing lightweight mortars. Similarly, ROCHA et al. [¹⁷] reviewed natural versus synthetic fibers in cement composites, including sisal and piassava, concluding that although natural fiber composites generally have lower tensile and flexural strengths, surface treatments can enhance the fiber-matrix interface, improving overall mechanical performance.

More recently, SUBRAMANIAM et al. [²⁴] evaluated Na₂CO₃-treated sisal fiber-reinforced concretes with partial substitution of cement with powdered glass. They found that the optimized condition for cement replacement with glass powder was 15%, and 1.5% of sisal fibers. YIMER and GEBRE [²⁵] evaluated NaOH-treated sisal fiber-reinforced concretes. They found that the addition of treated sisal considerably increases concrete’s flexural strength and toughness, but did not significantly change the compressive strength (~28 MPa).

It is known that NLF are rich in cellulose, hemicellulose, and lignin, making them hydrophilic due to hydroxyl groups in their structure. This hydrophilicity weakens the fiber-matrix bond in cementitious materials [¹⁷, ²¹, ²⁶]. A weak bond prevents effective stress transfer, impacting the composite’s mechanical properties. Factors like swelling, oil, and wax impurities further reduce cohesion, forming voids at the interface [²⁷]. To counteract these issues, chemical and physical fiber treatments reduce hydrophilicity and enhance fiber-matrix interactions [²⁸, ²⁹, ³⁰, ³¹, ³², ³³].

A promising treatment method that has been considered is the immersion of fibers in solutions of lignosulfonates (LS) [³⁴, ³⁵, ³⁶, ³⁷, ³⁸, ³⁹], which are biomass-derived by-products from the papermaking industry. Recently, sodium lignosulfonate (NaLS) has shown favorable outcomes as a surface modifier for sisal and piassava fibers [³⁸, ³⁹]. AGRIZE et al. [³⁸] found that ultrasonic bath treatment with NaLS effectively cleaned piassava fiber surfaces while preserving their cellulosic structure, increasing tensile strength from 386 ± 140 MPa to 524 ± 126 MPa. GUALBERTO et al. [³⁹] used NaLS to treat sisal fibers for cement plates, reducing fiber permeability and degradation, particularly at a 4% lignosulfonate-to-sisal mass ratio. OLIVEIRA et al. [³⁷] observed enhanced impact resistance in sisal fiber-reinforced (phenolic matrix) composites after NaLS treatment using an ultrasonic bath.

In addition to treated NLF, the use of supplementary cementitious materials (SCM) like metakaolin (MK) and fly ash (FA) reduces the carbon footprint and improves the compatibility of natural fibers in cementitious composites. SCMs create a less alkaline environment, reducing fiber degradation and enhancing fiber-matrix bonding [⁴⁰, ⁴¹, ⁴², ⁴³]. MELO FILHO et al. [⁴²], FERREIRA et al. [²⁶, ⁴³] and FODE et al. [²⁷] utilized MK and FA in sisal fiber-reinforced mortars, resulting in improved workability, strength, and durability, by eliminating free calcium hydroxide (CH). NAWAB et al. [⁴⁴] investigated coir fiber-reinforced cement composites replacing 20% of the binder with silica-fume and MK. The formulation with best results was 10% silica fume, 10% metakaolin, and 6% coconut fibers, which showcased superior mechanical and physical properties.

One specialized application of building materials is structural shielding, traditionally used in military and high-security buildings, such as nuclear power plants and embassies. However, the need for ballistic protection extends to urban areas affected by armed violence and terrorism [⁴⁵]. In Brazil, firearm-related homicides predominantly occur in urban outskirts. A study in Rio de Janeiro’s Complexo da Maré revealed that 86.7% of residents feared firearm violence [⁴⁶, ⁴⁷]. This highlights the importance of researching the dynamic-ballistic behavior of construction materials to enhance safety, cost-efficiency, durability, and sustainability. Recently, NLFs have been considered for ballistic protection due to their potential to replace synthetic fibers. For example, GARCIA FILHO et al. [⁴⁵] examined the ballistic impact performance of a 7.62 mm projectile on a polymer composite reinforced with piassava fibers and found enhanced energy absorption, comparable to the performance of Kevlar. NAYAK et al. [⁴⁸] conducted a literature review on the use of natural fibers as reinforcement in composites for ballistic armor. The analysis revealed that natural fibers achieved performance like Kevlar in terms of energy absorption. The study concluded that natural fibers show promising results and should be actively considered as potential substitutes for synthetic fibers for some armor applications.

Although several works have been dedicated to investigating the modifications in the fiber-cement interface due to physical and chemical treatments [²⁷, ⁴⁹, ⁵⁰, ⁵¹, ⁵², ⁵³, ⁵⁴] and the mechanical properties of the respective composites [³¹, ³⁴, ³⁷, ³⁸, ³⁹, ⁵⁵, ⁵⁶, ⁵⁷, ⁵⁸], few works evaluated NaLS as the treatment substance [³⁴, ³⁵, ³⁶, ³⁷, , ³⁸, ³⁹], and no work focused on evaluating the effect of the NaLS treatment to the fiber-cement interface and mechanical properties of mortars prepared with MK and FA as SCM, especially focusing on compressive, tensile and ballistic strengths.

Therefore, this study analyzed the mechanical strength and ballistic absorption properties of a pozzolanic mortar with partial replacement of Portland cement by FA and MK, reinforced with natural lignocellulosic fibers (NLF) from piassava (Attalea funifera) and sisal (Agave sisalana). The fibers were previously treated with bath immersion in a solution of sodium lignosulfonate. Mechanical properties were assessed through axial compressive strength tests, split tensile strength tests (Brazilian test) and ballistic impact absorption tests.

2. MATERIALS AND METHODS

Composite mortars were produced using a 1:0.5:0.4 ratio (binder:sand:water/binder), by weight [⁴³]. The binder consisted of 33% Portland cement, 27% metakaolin and 40% fly ash. This formulation was intended to be CH-free, by incorporating the metakaolin and fly ash as partial cement replacement in the bulk, in order to produce a conducive environment for natural fibers and avoid the mineralization phenomenon [⁴³]. Natural sisal (Agave sisalana) and piassava fibers (Attalea funifera) were applied as reinforcements, either untreated or surface-treated with sodium lignosulfonate (NaLS). Mortars without reinforcement were also produced for comparison.

The sisal fibers were incorporated into the mix at a content of 2% relative to the cement mass, with a fiber length of 40 mm. The piassava fibers were added at a rate of 5% of the total mix volume, with a length of 20 mm [³⁷, ³⁹].

2.1. Materials

In this study, CP-V ARI type Portland cement was used, which was donated by LafargeHolcim company, located in Cantagalo, Rio de Janeiro, Brazil. The cement complies with the specifications set by the Brazilian Standard NBR 16697 [⁵⁹].

Metakaolin and fly ash, used as SCM, were provided by Metacaulim do Brasil and Pozo Fly, respectively. The specific gravities were measured at 2.67 ± 0.01 g/cm³ for the metakaolin and 2.90 ± 0.11 g/cm³ for the fly ash.

The superplasticizer MasterGlenium® 51 was incorporated into the mix at a dosage of 0.8 kg/m³ to enhance the fluidity of the mortars. This product, manufactured by BASF, conforms to Brazilian Standard NBR 11768-1 [⁶⁰] and ASTM standard C494 (Type A and F) [⁶¹]. MasterGlenium® 51 is composed of polycarboxylic ether compounds with a solid content ranging from 28.5 to 31.5%, a pH from 5 to 7, and a density between 1.067 and 1.107 g/cm³. Rheomac® UW 410, a high molecular weight cellulose polymer produced by BASF, was used as a viscosity modifier.

Natural sand was obtained from local sources, homogenized, and characterized for particle size distribution according to the NBR NM 248 standard [⁶²]. Sand passing through a 600 μm sieve was selected to ensure fine granularity, enhancing fluidity and reducing segregation. The specific gravity of the sand was determined to be 2.56 ± 0.11 g/cm³, as per ABNT NBR 16916 [⁶³].

Deionized water was used in the preparation of the mortar, with the natural water initially provided by Aguas de Niterói, the utilities company in Niterói, Rio de Janeiro, Brazil. The deionization process was carried out in the laboratory.

Sisal fibers, obtained from a local supplier in Niterói, Rio de Janeiro, Brazil, were utilized in the experiments. These fibers were cut to a length of 25 mm, deemed ideal based on pullout test results reported by FERREIRA et al. [⁴³]. The specific gravity of the sisal fibers was measured at 1.41 g/cm³.

Piassava fibers were also used as reinforcement, provided in a raw state and cut to a length of 20 mm, based on results presented by SANTANA et al. [²²]. The fibers were donated by Vassouras Rossi, a company located in Petrópolis, Rio de Janeiro, Brazil. The specific gravity of the piassava fibers was measured at 1.12 g/cm³. The general appearance of the sisal and piassava fibers is shown in Figures 1a and 1b, respectively.

Figure 1
General appearance of the sisal and piassava fibers.

For the surface treatment of lignocellulosic fibers, sodium lignosulfonate type 1259 Ultrazine NA (CAS No. 8061-51-6) was used. This water-soluble brown powder was provided by Borregaard Lignotech Brasil. It is derived from highly refined and modified spruce wood and sulfite liquor, according to the manufacturer’s specifications (Table 1).

Table 1
Basic specifications of ultrazine NA sodium lignosulfonate.

LIGNOSULFONATE SPECIFICATIONS
pH (10% solution)	8.7 ± 0.8
Insolubles (w/w)%	Max. 0.1
Sodium (%)	7
Calcium (%)	Max. 0.1
Chloride (%)	Max. 0.10
Alkali (%)	Max. 12
Reducing sugars (%)	1

2.2. Methods

The treatment of sisal fibers was based on the procedure described by GUALBERTO et al. [³⁹] and OLIVEIRA et al. [³⁷], which yielded favorable outcomes for concretes using with Portland cement as binder. The fibers were placed in a beaker and submerged in a 4%-sodium lignosulfonate solution (relative to the mass of sisal used to prepare the specimens). The fibers were then immersed in the solution for 10 minutes, removed, filtered through a sieve, and placed in an oven at 102 ± 2 °C to dry until a constant mass was achieved.

The piassava fibers underwent the treatment applied by AGRIZE et al. [³⁸], who reported favorable outcomes. The fibers were separated, weighed for the preparation of test specimens, and treated with a 5% sodium lignosulfonate, relative to the amount of water. Subsequently, the fibers were submerged in deionized water for 1 hour and then dried in an oven at 104 ± 2 °C until a constant mass was achieved. Initially, enough water was added in the beaker to submerge the fibers, followed by the addition of the fibers. Sodium lignosulfonate was then dissolved in the water with fibers, and the mixture was manually stirred using a glass rod. The beaker was then placed in an ultrasonic bath for 20 minutes, followed by a 10-minute pause, and then the ultrasonic bath was turned on again for another 20 minutes, totaling 60 minutes with the ultrasonic bath on, adhering to the manufacturer’s usage restrictions. The ultrasonic bath used was manufactured by Planatc, model CBU-100, operating at a frequency of 40 kHz, with a capacity of 1 liter. The water level in the bath was adjusted to match the water level in the beaker. A heating element was inserted into the water in the bath to reach a water temperature of 55°C, and a thermometer was placed in the water of the beaker. Finally, the fibers were dried to a constant mass.

The analysis of the microstructure and fiber-matrix interface was conducted using scanning electron microscopy (SEM), in a model JSM 7100F JEOL equipment.

Cylindrical specimens measuring 50 × 100 mm (diameter x height) were prepared, using the unreinforced (C) mortar as the reference and reinforced with various types: untreated sisal fiber (S), untreated piassava fiber (P), treated sisal fiber (ST), and treated piassava fiber (PT). Additionally, plates with dimensions of 195 × 195 × 20 mm were fabricated following the same references and procedures as the cylindrical specimens, and these plates were subjected to ballistic impact testing. To reduce water absorption, the fibers were saturated for 24 hours prior to mixing, and the absorbed water subtracted from the mortar mix ratio [²⁰].

The mortar’s consistency was evaluated using a consistency index test following ABNT NBR 13276 [⁶⁴]. Based on three measurements, an average consistency index of 417 mm was obtained, classifying the mortar as fluid, making it suitable for wall coverings, structural repairs and rehabilitation.

The compressive strength test was conducted using a servo-hydraulic press with a capacity of 700 bar, manufactured by Intermetric Instruments. This test followed the guidelines of the ABNT NBR 7215 Standard [⁶⁵]. All specimens had their top and base squared using an Engetotus manual grinder.

The split tensile strength test, also known as the Brazilian test, was employed to determine the tensile strength of cylindrical test specimens under compression. This test involves applying a load perpendicular to the longitudinal axis of the specimen, causing failure due to internal tension (Figure 2). The Brazilian test was carried out in accordance with the ABNT NBR 7222 standard [⁶⁶], using the same servo-hydraulic press as that used for the compressive strength test, and the specimens were squared using the same procedure.

Figure 2
Stresses in the Brazilian test.

For the ballistic tests, an Airforce Texan air rifle was used, firing a .45 caliber lead pellet with an approximate mass of 14.4g. To measure the energy absorption, two ProChrono Pal ballistic chronographs, with an accuracy of 0.31 m/s, were employed to record both the impact velocity and residual velocity. The air rifle was positioned 5 m away from the target, which consisted of a plate secured in a bench vise and aligned perpendicularly to the rifle. One ballistic chronograph was positioned 10 cm before the target, and the other was placed 10 cm behind the target (Figure 3). Six plates were produced per group, and each plate subjected to a maximum of five shots, or until it shattered. A total of 16 test rounds were conducted per group.

Figure 3
Ballistic impact test setup.

The energy absorbed by the mortar plate from the projectile (E_abs) was calculated by the difference in kinetic energy before and after impact, using the initial velocity (v_i) of the projectile and the residual velocity (v_r) (after impact). The employed equation was:

(1) $$E_{abs}=m\frac{v_i^2-v_r^2}{2}$$

where: m represents the mass of the projectile.

The data obtained from the mechanical and ballistics tests were analyzed using Analysis of Variance (ANOVA), a fundamental statistical tool used to determine whether multiple means originate from the same population. The ANOVA examines the entire set of means simultaneously. A significant result from an ANOVA indicates that at least two groups differ, but it does not specify which groups [⁶⁷]. In this study, One-way ANOVA was performed on the mechanical and ballistics tests. The ANOVA calculations include degrees of freedom (DF), sum of squares (SS), mean squares (MS), Snedecor’s F, which is compared to its critical value (F_c), as well as the p-value, which is compared to the chosen level of significance (α) [⁶⁷, ⁶⁸, ⁶⁹]. The significance level α = 0.05 was established prior to the analysis.

The ANOVA is often followed by an additional analysis to identify the specific patterns of differences among the results. This usually involves evaluating all pairs of means to determine which ones show significant differences. One of the most commonly used methods for this purpose is the Tukey’s Test [⁶⁸], which calculates the Least Significant Difference (LSD) [⁶⁷, ⁶⁹], as follows:

(2) $$LSD=q\sqrt{\frac{EMS}{r}}$$

where: q is a constant tabulated for α = 0.05; EMS is the error mean square from the ANOVA; r is the number of observations.

A post-hoc power analysis was performed to evaluate the power of the study based on observed results. The calculations of the power (probability of the 1-β error) were done using the software G*Power 3.1.9.7 [⁷⁰], by inputting the effect sizes (f), level of significance (α = 0.05%), number of groups (5) and sample sizes for each test (compressive, tensile or ballistic). The effect size was calculated using Equation 3 [⁷¹].

(3) $$f=\sqrt{\frac{{\eta }^2}{1-{\eta }^2}}$$

where: η = SS_between / S_Stotal; SS_between = Σn_i (x_i – x_m)² is the between-group sum of squares; SS_total = SS_between + SS_within; SS_within = Σ(n_i–1)s_i² is the within-group sum of squares; n_i is the sample size per group; x_i is the mean of the group i; x_m is overall mean across all groups; s_i is the standard deviation of the group i.

3. RESULTS AND DISCUSSION

3.1. Compressive strength

Table 2 and Figure 4 present the results of the compressive strength tests. Individual test values are provided alongside with the calculated average (x̅), percentage gain (%gain) relative to the unreinforced specimen (C), standard deviation (σ), and coefficient of variation (C.V.). Figure 4 offers a graphical comparison of the compressive strength among the tested groups. The results indicate that neither the addition of fibers nor the treatment with NaLS led to improvements in compressive strength. This aligns with existing literature, which reports that natural fiber-reinforced concretes and mortars typically exhibit reduced compressive strength compared to the unreinforced matrix [¹⁷], as the fibers may behave as structural defects [²³, ²⁹]. Nevertheless, the mortars reinforced with sisal fibers (S) and NaLS-treated sisal fibers (ST) demonstrated notable performance. Their compressive strength did not differ significantly from that of the unreinforced group (C) at a 95% confidence level. Besides, despite strength variations, only the C specimens experienced complete fracture during testing, as shown in Figure 5. In contrast, all fiber-reinforced groups (S, ST, P and PT) demonstrated enhanced resistance to cracking compared to the unreinforced group (C), with the NaLS-treated fibers (ST and PT) showing the most significant improvement, presenting no visible cracks.

Table 2
Compressive strength test data.

COMPRESSIVE STRENGTH (MPa) BY GROUP
SAMPLE	C	S	P	ST	PT
1	29.18	28.21	21.90	24.24	21.35
2	29.34	28.67	22.84	28.27	22.62
3	30.15	28.52	27.5	26.74	21.27
4	29.18	28.78	27.41	25.72	20.73
5	29.39	28.67	24.90	27.88	23.25
6	28.68	29.34	28.88	26.45	25.36
$\overline{x}$ (MPa)	29.32	28.70	25.41	26.55	22.43
%gain	0	–2.1	–13.3	–9.4	–23.4
σ (MPa)	0.48	0.37	2.93	1.47	1.72
C.V. (%)	1.63	1.28	11.53	5.53	7.65

Figure 4
Compressive strength averages for the several groups.

Figure 5
Broken specimens from the compressive strength tests.

The ANOVA results, presented in Table 3, indicate a significant difference between the evaluated groups, as evidenced by Snedecor’s F value exceeding the corresponding critical value Fc, and a p-value < α. The differences between groups are further clarified by Tukey’s Test, shown in Table 4. Notably, the piassava groups (P and PT) did not effectively reinforce the cementitious material, resulting in lower compressive strength. The sisal composites (S and ST), however, did not significantly influence the compressive strength, compared to the unreinforced group (C). The calculated effect size (f) and power were 1.64 and 1.00, respectively, which suggests substantial differences in mean strengths across groups relative to within-group variability. In other words, there was sufficient power to detect the observed effects.

Table 3
ANOVA applied to the compressive test results.

SOURCE OF VARIATION	DF	SS	MS	F	FC	P-VALUE
Between groups	4	183.24	45.80	16.31	2.76	1.08 × 10–6
Within groups	25	70.21	2.80
Total	29	253.45

Table 4
Tukey’s test applied to the compressive test results.

MEAN DIFFERENCE (MPa)
MATERIAL	C	S	P	ST	PT
C	0	0.62	3.91	2.77	6.89
S	0.62	0	3.29	2.15	6.27
P	3.91	3.29	0	0.98	2.98
ST	2.77	2.15	1.14	0	4.12
PT	6.89	6.27	2.98	4.12	0
Tukey’s LSD					2.84

3.2. Split tensile strength test (Brazilian test)

The results of the split tensile strength tests are presented in Table 5, Figure 6 and Figure 7, using the same parameters as in the compressive strength tests: individual test values, $\overline{x}$, %gain, σ and C.V. The initial effect size (f) and statistical power were calculated as 0.66 and 0.76, respectively, indicating an underpowered analysis according to Cohen’s benchmark (0.8). This limitation was primarily attributed to the P group, which exhibited the highest standard deviation—likely due to segregation in sample 3 (2.26 MPa). To preserve the validity of comparisons among the remaining groups, the P group was excluded from the ANOVA. Upon recalculation, the effect size and power increased to 0.76 and 0.83, respectively, indicating sufficient power to detect the observed effects. The ANOVA results (Table 6) revealed a statistically significant difference among the evaluated groups. According to the Tukey’s test (Table 7), the ST group exhibited significantly higher tensile strength than PT. No other statistically significant differences were observed, and no conclusions were drawn about the P group due to its exclusion.

Table 5
Split tensile strength test data.

SPLIT TENSILE STRENGTH (MPa) BY GROUP
SAMPLE	C	S	P	ST	PT
1	4.60	4.91	4.53	5.68	4.31
2	5.72	3.91	4.21	4.39	3.30
3	3.42	4.06	2.26	4.94	3.19
4	3.71	3.03	4.55	4.94	3.80
5	4.91	4.42	3.98	5.09	4.36
6	4.58	4.36	4.55	4.86	4.01
$\overline{x}$ (MPa)	4.49	4.1	4.01	4.98	3.83
%gain	0	–8.2	–2.3	+10.9	–14.7
σ (MPa)	0.83	0.64	0.89	0.42	0.50
C.V. (%)	18.50%	15.43%	22.16%	8.35%	12.94%

Figure 6
Split tensile strength averages for several groups.

Figure 7
Broken specimens from the split tensile strength tests.

Table 6
ANOVA applied to the split tensile test results, excluding P group.

SOURCE OF VARIATION	DF	SS	MS	F	FC	P-VALUE
Between groups	3	4.49	1.50	3.95	3.10	2.30 × 10–2
Within groups	20	7.57	0.38
Total	23	12.06

Table 7
Tukey’s test applied to the tensile test results, excluding P group.

MEAN DIFFERENCE (MPa)
MATERIAL	C	S	P	ST	PT
C	0	0.38	–	0.49	0.66
S	0.38	0	–	0.87	0.29
P	–	–	–	–	–
ST	0.49	0.87	–	0	1.15
PT	0.66	0.29	–	1.15	0
Tukey’s LSD					0.89

As observed in the fractured specimens (Figure 7), similar to the compressive tests (Figure 5), only the C specimens experienced complete fracture during testing. All fiber-reinforced groups (S, ST, P and PT) demonstrated improved resistance to cracking compared to the unreinforced group (C).

3.3. Ballistic impact tests

Table 8 and Figure 8 present the results of the ballistic energy absorption tests. The data indicate that the ST group exhibits a higher ballistic energy absorption, with an increase of +9.34% compared to the unreinforced specimens (C). The ANOVA results, shown in Table 9, confirm the significance of these findings, as F > Fc and the p-value is less than α. Additionally, Tukey’s Test, detailed in Table 10, reveals that the ST group is statistically superior to C, P and PT groups in terms of energy absorption. The calculated effect size (f) and power were 0.45 and 0.90, respectively, which indicates robust sensitivity.

Table 8
Ballistic energy absorption test data.

	BALLISTIC ENERGY ABSORPTION (J) BY GROUP
SAMPLE	C	S	P	ST	PT
1	254.03	267.04	230.3	317.55	249.58
2	248.07	268.75	276.11	326.42	274.96
3	236.39	262.68	272.81	346.94	285.07
4	261.76	272.79	212.97	324.85	299.74
5	290.68	225.32	244.16	315.05	295.89
6	263.27	281.62	271.03	326.52	274.12
7	279.14	285.67	258.94	308.19	299.11
8	297.19	275.44	248.38	310.74	287.80
9	279.00	300.49	302.44	293.00	270.79
10	377.85	332.8	300.68	293.62	309.25
11	294.18	288.96	306.87	295.04	273.47
12	314.27	317.44	302.87	321.36	301.06
13	314.37	312.41	318.53	293.11	279.76
14	252.73	311.60	313.96	307.21	291.55
15	297.76	302.58	305.17	287.78	281.81
16	298.47	298.84	297.35	318.04	273.94
$\overline{x}$ (MPa)	284.95	287.78	278.91	311.59	284.24
%gain	0	+0.99	–2.11	+9.34	–0.24
σ (MPa)	34.41	26.24	32.22	16.20	15.04
C.V. (%)	12.08	9.12	11.55	5.20	5.29

Figure 8
Ballistic energy absorption averages for several groups.

Table 9
ANOVA applied to the ballistic energy absorption results,

SOURCE OF VARIATION	DF	SS	MS	F	FC	P-VALUE
Between groups	4	10421.92	2605.48	3.83	2.49	6.89 × 10–3
Within groups	75	50981.60	679.75
Total	79	61403.53

Table 10
Tukey’s test applied to the ballistic energy absorption results.

	MEAN DIFFERENCE (J)
MATERIAL	C	S	P	ST	PT
C	0	2.83	6.04	26.64	0.7
S	2.83	0	8.87	23.81	3.53
P	6.04	8.87	0	32.68	5.33
ST	26.64	23.81	32.68	0	27.34
PT	0.7	3.53	5.33	27.34	0
Tukey’s LSD					25.76

Figures 9, 10 and 11 illustrate the general condition of the plates subjected to ballistics tests. The C and P groups experienced cracks radiating from the impact point after the first shot and began to shatter severely after the third shot. In contrast, the sisal composites (S) and the treated groups (ST and PT) resisted to shattering until final shot, demonstrating better structural integrity state after the tests.

Figure 9
General condition of the plates subjected to ballistics tests: S, C and P groups.

Figure 10
General condition of the plates subjected to ballistics tests: PT group.

Figure 11
General condition of the plates subjected to ballistics tests: ST group.

3.3. Microstructure and discussion of mechanisms

Scanning electron microscopy (SEM) analyses were conducted to examine the bonding and interaction between the fibers and the cementitious matrix. Figures 12 to 19 present detailed images of the fractured surfaces of the specimens subjected to ballistic testing.

Figure 12
SEM micrographs for the C specimens subjected to ballistic impact: (a) 1.000×; and (b) 5.000×.

Figure 13
X-ray maps in C specimen: (a) Layered image; (b) Ca Kα map; (c) O Kα map; (d) Si Kα map; (e) Al Kα map.

Figure 14
SEM micrographs for the P specimens subjected to ballistic impact: (a) Fiber surface, 1.000×; (b) fiber surface, 5.000×; (c) interface and ITZ, 500×.

Figure 15
SEM micrographs for the PT specimens subjected to ballistic impact: (a) fiber surface, 1.000×; (b) interface and ITZ, 1.000×.

Figure 16
SEM micrographs for EDS analysis of the fiber surfaces: (a) P and (b) PT specimens.

Figure 17
SEM micrographs for the S specimens subjected to ballistic impact: (a) Interface, 500×; (b) fiber surface, 1.000×; (c) fiber surface, 5.000×; (d) fiber imprint in the matrix, 500×.

Figure 18
SEM micrographs for the ST specimens subjected to ballistic impact: (a) Fiber surface, 500×; (b) Interface, 500×; (c) interface, 1.000×; (d) interface and ITZ, 500×.

Figure 19
SEM micrographs for EDS analysis of: (a) S and (b) ST specimens.

The fracture of the C specimen, shown in Figure 12, displays the typical brittle microstructure of the ordinary cement mortars, characterized by small fibrous calcium silicate hydrate (C-S-H) formations. According to MEHTA and MONTEIRO [⁷²], the microstructure of the hydrated cement paste generally comprises approximately 60% C-S-H by volume, 20–25% calcium hydroxide (CH) crystals, and 20-25% ettringite needles. The addition of SCM/pozzolans tends to consume CH and ettringite [⁷³], resulting in a microstructure dominated by C-S-H, with possible presence of residual pozzolans and other minor crystalline and amorphous phases. Figure 14 presents the EDS analysis in the C specimen, including the layered SEM image (Figure 13a) and corresponding X-ray maps for calcium (Ca), oxygen (O), silicon (Si), and aluminum (Al) (Figures 13b to 13e). These maps show that Ca, Si and Al are not homogeneously distributed within the microstructure. The maps also confirm the presence of unreacted pozzolan particles embedded in the matrix, including characteristic FA spheres and MK particles, as evidenced by Si and Al segregation in Figures 13d and 13e.

Table 11 summarizes the average elemental composition of the analyzed area in Figure 13, along with two specific locations marked as “Spectrum 1” and “Spectrum 2”. The selected points exhibit lower a lower Ca/Si ratio compared to the overall area, supporting the identification of these features as unreacted FA. The Ca-rich regions, as the bright areas in Figure 13c, are attributed to the C-S-H.

Table 11
Chemical composition of the selected regions of C specimen in Figure 13.

	ELEMENT (%)
REGION	O	Ca	Si	Al	C	OTHERS
Area	48.3	18.6	8.2	4.7	12.6	7.6
Point: Spectrum 1	49.2	0.9	27.1	17.8	–	4.5
Point: Spectrum 2	57.6	2.0	30.6	9.2	–	0.6

Figure 14 presents the fracture surface of the P specimen, characterized by a rough, granular, and porous texture, with abundant hydrated products and unreacted FA particles visible in Figures 14a and 14b. Notably, the original fiber surface and its natural morphological features, such as surface protrusions reported by AGRIZE et al. [³⁸], are no longer distinguishable. The interfacial transition zone (ITZ), labeled as “matrix” in Figure 14c, appears more porous than other regions of the specimen and shows increased porosity compared to the unreinforced (C) specimen (Figure 12).

Figure 15 shows the fracture surface of the PT specimen, which appears smoother and less granular than both C and P specimens, exhibiting a more amorphous texture. Although FA spheres are still present at both surface and subsurface levels, the ITZ displays finer, though still abundant, porosity.

A notable feature in both P and PT specimens (Figures 14 and 15) is fiber debonding from the matrix, as evidenced by the large gaps between the fiber and the surrounding matrix, particularly visible in Figures 14c and 15b. This observation suggests poor fiber-matrix interfacial bonding and contributes to low mechanical performance of these composites.

Energy-dispersive spectroscopy (EDS) spectra were collected at selected points in the P (Figure 16a) and PT (Figure 16b) specimens, as indicated in Figure 16. The composition of two points with prominent carbon Kα peaks are shown in Table 12. Notably, the carbon content at these locations is only marginally higher than that observed in the overall area of the C specimen (Table 11). These low carbon percentages suggest that the hydration product layer covering the fibers is sufficiently thick to attenuate the characteristic C Kα X-rays, preventing them from reaching the detector. In other words, the observed morphological characteristics, combined with the low detected carbon content, indicate fiber mineralization within the P and PT specimens. According to MELO FILHO et al. [⁴²] and WEI and MEYER [⁷³], fiber mineralization results from the migration and deposition of hydration products, mainly CH, within the fiber structure, leading to increased brittleness in natural fibers. The concurrent presence of high ITZ porosity and extensive fiber mineralization likely explains the reduced compressive, tensile, and ballistic strengths observed in the piassava composites. Furthermore, the even lower carbon content and denser hydration layer on the fiber surface in the PT specimen suggest a higher degree of mineralization, which correlates with its comparatively lower mechanical performance.

Table 12
Chemical composition of the selected regions of P and PT specimens in Figure 16.

		ELEMENT (%)
SPECIMEN	REGION	O	Ca	Si	Al	C	OTHERS
P	Point: Spectrum 9	55.69	22.72	–	–	21.59	–
PT	Point: Spectrum 9	48.75	9.78	23.85	0.38	17.24	–

Figure 17 presents the fracture surface of the S specimen. Similar to the P specimen, the ITZ morphology appears rough and granular (Figure 17a), with a fine porosity visible in Figure 17d. Although hydration products cover the fiber surface, portions of the original fiber morphology remain exposed, as seen in Figure 17b and 17c. Evidence of fiber debonding from the matrix is also apparent, as indicated in the gap between the fiber and matrix in Figure 17a and the fiber imprint visible in Figure 17d.

Figure 18 shows the fracture surface of the ST specimen. The fiber surface is partially covered with granular hydration products and FA particles; however, most of the original fiber surface remains visible, with natural surface features clearly identifiable (Figure 18a). The ITZ microstructure in this specimen appears smoother, with finer and less abundant porosity compared to S and P specimens. Furthermore, the fiber-matrix interface is compact, with no visible voids or signs of fiber debonding.

To evaluate the extent of fiber mineralization, EDS spectra were collected at selected points in the S (Figure 19a) and ST (Figure 19b) specimens, as shown in Figure 19. The elemental compositions of two points with prominent carbon Kα peaks are shown in Table 13. Notably, the carbon content at these locations was significantly higher than that observed in the overall area of the C specimen (Table 11) and in the P and PT specimens (Table 12). These higher carbon levels suggest a better preservation of the original fiber chemical composition in both S and ST specimens, indicating a lower degree of mineralization.

Table 13
Chemical composition of the selected regions of S and ST specimens in Figure 19.

		ELEMENT (%)
SPECIMEN	REGION	O	Ca	Si	Al	C	OTHERS
S	Point: Spectrum 19	31.86	6.94	4.43	2.92	52.84	1.01
ST	Point: Spectrum 12	26.41	15.62	2.51	1.37	54.09	–

The observed differences in the degree of fiber mineralization may be attributed to variations in the maximum water absorption capacity of piassava and sisal fibers, combined with the chemical processes occurring during the early stages of cement curing. According to GUALBERTO et al. [³⁹], untreated sisal fibers exhibit a maximum water absorption of approximately 4%, which increases slightly to 4.7% following treatment with a 4% NaLS solution. In contrast, AGRIZE et al. [³⁸] reported that piassava fibers, both untreated and NaLS-treated, exhibit a much higher moisture absorption capacity, around 16% after 24 hours. It is important to note that in the present study, all fibers were pre-soaked before mortar mixing to ensure full saturation.

ZENG and LI [⁷⁴], reported that pozzolanic reactions typically commence later than the initial cement hydration, starting approximately 10 hours after water addition. During this early curing period, ionic exchanges can occur at the fiber-solution interface, allowing the diffusion of Ca²⁺ and OH⁻ ions into the fiber interior. Given the higher water content in piassava fibers, this diffusion process would likely be more pronounced, promoting greater mineralization. This mechanism also explains the increased ITZ porosity observed in the P and PT specimens.

Furthermore, as highlighted by ZENG and LI [⁷⁴], the pozzolanic reaction consumes CH and refines the pore structure by filling existing voids with additional hydration products, thereby enhancing the density and strength of the cementitious matrix. However, when Ca²⁺ and OH⁻ ions migrate into the fiber interior during early hydration, this reduces their availability in the ITZ, limiting the beneficial effects of the pozzolanic reaction in that region.

WEI and MEYER [⁷³] further emphasized that the strength of NLF-reinforced cement composites is more strongly influenced by the matrix characteristics—particularly ITZ density and pore structure—than by fiber type, size, or content. Therefore, a denser ITZ, with fewer voids, is critical for improving both the ballistic and tensile performance of the composites.

4. CONCLUSIONS

This study investigated the effects of sodium lignosulfonate (NaLS) treatment on piassava (Attalea funifera) and sisal (Agave sisalana) fibers in mortars containing fly ash (FA) and metakaolin (MK) as supplementary cementitious materials (SCMs). Based on the mechanical, ballistic and microstructural analyses, the following conclusions were drawn:

• NaLS treatment had no significant effect on the compressive strength of the sisal fiber-reinforced composites but resulted in reduced strength in piassava composites, attributed to a higher degree of fiber mineralization. Nonetheless, all fiber-reinforced mortars demonstrated improved post-cracking resistance compared to the unreinforced matrix.

• The NaLS treatment did not significantly influence the split tensile strength of the sisal composites or unreinforced mortar. In contrast, NaLS-treated piassava composites exhibited reduced tensile strength compared to the other groups, although statistical comparison with untreated piassava composites was not possible due to data variability.

• NaLS treatment significantly enhanced the ballistic absorption of sisal fiber-reinforced mortars, reaching 312 ±16 J – a +9.3% increase compared to the unreinforced group (285 ± 34 J). Furthermore, both treated and untreated sisal composites, as well as NaLS-treated piassava composites, exhibited better structural integrity after testing.

• SEM and EDS analyses confirmed that NaLS treatment improved fiber-matrix bonding, reduced the interfacial transition zone (ITZ) porosity, and decreased fiber mineralization in sisal composites. In piassava composites, NaLS was less efficient to prevent mineralization and fiber-matrix debonding but did contribute to ITZ porosity refinement. These differences were mainly attributed to variations in fiber water absorption and reactions during early-age curing.

5. ACKNOWLEDGEMENTS

The authors of the present work would like to thank: FAPERJ for funding the project in the APQ1 Program, process nº E-26/211.544/2021, and JCNE Program, process nº E-26/204.458/2024; Borregaard Lignotec Brasil, for the donation of the sodium lignosulfonate; Vassouras Rossi Ltda., for the donation of the piassava fibers; LAMAR/CAIPE/UFF for the MEV/EDS analyzes.

DATA AVAILABILITY

Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.

6. BIBLIOGRAPHY

• ^[1] CHIU, C.-L., HSIAO, I.-F., CHANG, L., “Overviewing global surface temperature changes regarding CO₂ emission, population density, and energy consumption in the industry: policy suggestions”, Sustainability, v. 15, n. 8, pp. 7013, Apr. 2023. doi: http://doi.org/10.3390/su15087013.
  » https://doi.org/10.3390/su15087013
• ^[2] FRIEDLINGSTEIN, P., O’Sullivan, M., JONES, M.W., et al, “Global carbon budget 2023”, Earth System Science Data, v. 15, n. 12, pp. 5301–5369, Dec. 2023. doi: http://doi.org/10.5194/essd-15-5301-2023.
  » https://doi.org/10.5194/essd-15-5301-2023
• ^[3] AZEVEDO, A.R.G.D., KLYUEV, S., MARVILA, M.T., et al, “Investigation of the potential use of Curauá fiber for reinforcing mortars”, Fibers, v. 8, n. 11, pp. 69, Nov. 2020. doi: http://doi.org/10.3390/fib8110069.
  » https://doi.org/10.3390/fib8110069
• ^[4] RAJA, S., RAJESH, R., INDRAN, S., et al, “Characterization of industrial discarded novel Cymbopogon flexuosus stem fiber: a potential replacement for synthetic fiber”, Journal of Industrial Textiles, v. 51, n. 1, pp. 1207S–1234S, Jun. 2022. doi: http://doi.org/10.1177/15280837211007507.
  » https://doi.org/10.1177/15280837211007507
• ^[5] DOLZA, C., FAGES, E., GONGA, E., et al, “Development and characterization of environmentally friendly wood plastic composites from biobased polyethylene and short natural fibers processed by injection moulding”, Polymers, v. 13, n. 11, pp. 1692, May. 2021. doi: http://doi.org/10.3390/polym13111692. PubMed PMID: 34067283.
  » https://doi.org/10.3390/polym13111692
• ^[6] CHIHAOUI, B., SERRA-PARAREDA, F., TARRÉS, Q., et al, “Effect of the fiber treatment on the stiffness of date palm fiber reinforced PP composites: macro and micromechanical evaluation of the young’s modulus”, Polymers, v. 12, n. 8, pp. 1693, Jul. 2020. doi: http://doi.org/10.3390/polym12081693. PubMed PMID: 32751192.
  » https://doi.org/10.3390/polym12081693
• ^[7] DONG, Z., LI, N., DONG, A., et al, “Enhancement of interface between lignocellulosic fibers and polypropylene matrix via the structure alteration of lignin at elevated temperatures”, Materials, v. 13, n. 23, pp. 5428, Nov. 2020. doi: http://doi.org/10.3390/ma13235428. PubMed PMID: 33260626.
  » https://doi.org/10.3390/ma13235428
• ^[8] TEIXEIRA, F.P., LIMA, V.N., MOUTINHO, D.J.C., et al, “Mechanical properties and fractography of cement-based composites reinforced by natural piassava and jute fibers”, Cerâmica, v. 68, n. 385, pp. 60–66, Mar. 2022. doi: http://doi.org/10.1590/0366-69132022683853174.
  » https://doi.org/10.1590/0366-69132022683853174
• ^[9] NIMANPURE, S., HASHMI, S.A.R., KUMAR, R., et al, “Mechanical, electrical, and thermal analysis of sisal fibril/kenaf fiber hybrid polyester composites”, Polymer Composites, v. 40, n. 2, pp. 664–676, Feb. 2019. doi: http://doi.org/10.1002/pc.24706.
  » https://doi.org/10.1002/pc.24706
• ^[10] KANDEMIR, A., LONGANA, M.L., PANZERA, T.H., et al, “Natural fibres as a sustainable reinforcement constituent in aligned discontinuous polymer composites produced by the HiPerDiF method”, Materials, v. 14, n. 8, pp. 1885, Apr. 2021. doi: http://doi.org/10.3390/ma14081885. PubMed PMID: 33920098.
  » https://doi.org/10.3390/ma14081885
• ^[11] MONTEIRO, S.N., LOPES, F.P.D., BARBOSA, A.P., et al, “Natural lignocellulosic fibers as engineering materials: an overview”, Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, v. 42, n. 10, pp. 2963–2974, Oct. 2011. doi: http://doi.org/10.1007/s11661-011-0789-6.
  » https://doi.org/10.1007/s11661-011-0789-6
• ^[12] MOHANTY, A.K., VIVEKANANDHAN, S., PIN, J.-M., et al, “Composites from renewable and sustainable resources: challenges and innovations”, Science, v. 362, n. 6414, pp. 536–542, Nov. 2018. doi: http://doi.org/10.1126/science.aat9072. PubMed PMID: 30385569.
  » https://doi.org/10.1126/science.aat9072
• ^[13] ALVES, C., FERRÃO, P.M.C., SILVA, A.J., et al, “Ecodesign of automotive components making use of natural jute fiber composites”, Journal of Cleaner Production, v. 18, n. 4, pp. 313–327, Mar. 2010. doi: http://doi.org/10.1016/j.jclepro.2009.10.022.
  » https://doi.org/10.1016/j.jclepro.2009.10.022
• ^[14] RAJAK, D., PAGAR, D., MENEZES, P., et al, “Fiber-reinforced polymer composites: manufacturing, properties, and applications”, Polymers, v. 11, n. 10, pp. 1667, Oct. 2019. doi: http://doi.org/10.3390/polym11101667. PubMed PMID: 31614875.
  » https://doi.org/10.3390/polym11101667
• ^[15] SARKER, F., KARIM, N., AFROJ, S., et al, “High-Performance graphene-based natural fiber composites”, ACS Applied Materials & Interfaces, v. 10, n. 40, pp. 34502–34512, Oct. 2018. doi: http://doi.org/10.1021/acsami.8b13018. PubMed PMID: 30222307.
  » https://doi.org/10.1021/acsami.8b13018
• ^[16] KARIM, N., SARKER, F., AFROJ, S., et al, “Sustainable and multifunctional composites of graphene‐based natural jute fibers”, Advanced Sustainable Systems, v. 5, n. 3, pp. 2000228, Mar. 2021. doi: http://doi.org/10.1002/adsu.202000228.
  » https://doi.org/10.1002/adsu.202000228
• ^[17] ROCHA, D.L., TAMBARA JÚNIOR, L., MARVILA, M., et al, “A review of the use of natural fibers in cement composites: concepts, applications and brazilian history”, Polymers, v. 14, n. 10, pp. 2043, May. 2022. doi: http://doi.org/10.3390/polym14102043. PubMed PMID: 35631925.
  » https://doi.org/10.3390/polym14102043
• ^[18] PICANÇO, M.D.S., GHAVAMI, K., “Comportamento à compressão de argamassas reforçadas com fibras vegetais da Amazônia”, Revista Escola de Minas, v. 61, n. 1, pp. 13–18, Mar. 2008. doi: http://doi.org/10.1590/S0370-44672008000100003.
  » https://doi.org/10.1590/S0370-44672008000100003
• ^[19] RAMAKRISHNA, G., SUNDARARAJAN, T., “Impact strength of a few natural fibre reinforced cement mortar slabs: a comparative study”, Cement and Concrete Composites, v. 27, n. 5, pp. 547–553, May. 2005. doi: http://doi.org/10.1016/j.cemconcomp.2004.09.006.
  » https://doi.org/10.1016/j.cemconcomp.2004.09.006
• ^[20] FONSECA, R.P.D., ROCHA, J.C., CHERIAF, M., “Influence of different types of treatments on amazonian vegetable fibers on the performance of mortars based on portland cement, metakaolin and fly ash”, Materials Research, v. 24, e20210320, 2021. doi: http://doi.org/10.1590/1980-5373-mr-2021-0320.
  » https://doi.org/10.1590/1980-5373-mr-2021-0320
• ^[21] FONSECA, R.P., ROCHA, J.C., CHERIAF, M., “Mechanical properties of mortars reinforced with amazon rainforest natural fibers”, Materials, v. 14, n. 1, pp. 155, Dec. 2020. doi: http://doi.org/10.3390/ma14010155. PubMed PMID: 33396353.
  » https://doi.org/10.3390/ma14010155
• ^[22] SANTANA, M.R.O., DOMINGUEZ, D.S., IGLESIAS, S.M., et al, “Modelos de regressão aplicados na caracterização de argamassas leves contendo agregados não convencionais de EVA e fibras de piaçava”, Matéria, v. 23, n. 3, e12168, Oct. 2018. doi: http://doi.org/10.1590/s1517-707620180003.0502.
  » https://doi.org/10.1590/s1517-707620180003.0502
• ^[23] BOUMAAZA, M., BELAADI, A., BOURCHAK, M., “Systematic review on reinforcing mortars with natural fibers: challenges of environment-friendly option”, Journal of Natural Fibers, v. 19, n. 16, pp. 14262–14286, Nov. 2022. doi: http://doi.org/10.1080/15440478.2022.2060408.
  » https://doi.org/10.1080/15440478.2022.2060408
• ^[24] SUBRAMANIAM, A., SHANAVAS, S., SHANMUGAM, K., et al, “Influence of glass powder in strength and durability performance of sisal fiber reinforced concrete”, Matéria, v. 29, n. 4, e20240674, 2024. doi: http://doi.org/10.1590/1517-7076-rmat-2024-0674.
  » https://doi.org/10.1590/1517-7076-rmat-2024-0674
• ^[25] YIMER, T., GEBRE, A., “Effect of fiber treatments on the mechanical properties of sisal fiber-reinforced concrete composites”, Advances in Civil Engineering, v. 2023, pp. 1–15, Apr. 2023. doi: http://doi.org/10.1155/2023/2293857.
  » https://doi.org/10.1155/2023/2293857
• ^[26] FERREIRA, S.R., SILVA, F.D.A., LIMA, P.R.L., et al, “Effect of hornification on the structure, tensile behavior and fiber matrix bond of sisal, jute and curauá fiber cement based composite systems”, Construction & Building Materials, v. 139, pp. 551–561, May. 2017. doi: http://doi.org/10.1016/j.conbuildmat.2016.10.004.
  » https://doi.org/10.1016/j.conbuildmat.2016.10.004
• ^[27] FODE, T.A., JANDE, Y.A.C., KIVEVELE, T., et al, “A review on degradation improvement of sisal fiber by alkali and pozzolana for cement composite materials”, Journal of Natural Fibers, v. 21, n. 1, pp. 2335327, Dec. 2024. doi: http://doi.org/10.1080/15440478.2024.2335327.
  » https://doi.org/10.1080/15440478.2024.2335327
• ^[28] LI, X., TABIL, L.G., PANIGRAHI, S., “Chemical treatments of natural fiber for use in natural fiber-reinforced composites: a review”, Journal of Polymers and the Environment, v. 15, n. 1, pp. 25–33, Feb. 2007. doi: http://doi.org/10.1007/s10924-006-0042-3.
  » https://doi.org/10.1007/s10924-006-0042-3
• ^[29] KHALID, M.Y., IMRAN, R., ARIF, Z.U., et al, “Developments in chemical treatments, manufacturing techniques and potential applications of natural-fibers-based biodegradable composites”, Coatings, v. 11, n. 3, pp. 293, Mar. 2021. doi: http://doi.org/10.3390/coatings11030293.
  » https://doi.org/10.3390/coatings11030293
• ^[30] XU, F., SHANG, J., ABDUREXIT, A., et al, “Effect of chemical treatment of cotton stalk fibers on the mechanical and thermal properties of PLA/PP blended composites”, Polymers, v. 16, n. 12, pp. 1641, Jun. 2024. doi: http://doi.org/10.3390/polym16121641. PubMed PMID: 38931991.
  » https://doi.org/10.3390/polym16121641
• ^[31] BACCOUCH, W., GHITH, A., YALCIN-ENIS, I., et al, “Enhancement of fiber-matrix interface of recycled cotton fibers reinforced epoxy composite for improved mechanical properties”, Materials Research Express, v. 7, n. 1, pp. 015340, Jan. 2020. doi: http://doi.org/10.1088/2053-1591/ab6c04.
  » https://doi.org/10.1088/2053-1591/ab6c04
• ^[32] KALIA, S., KAITH, B.S., KAUR, I., “Pretreatments of natural fibers and their application as reinforcing material in polymer composites: a review”, Polymer Engineering and Science, v. 49, n. 7, pp. 1253–1272, Jul. 2009. doi: http://doi.org/10.1002/pen.21328.
  » https://doi.org/10.1002/pen.21328
• ^[33] SUPRIYA, J.P., SHETTY, S., SHETTY, R., et al, “Quantitative and deep learning based fourier transform infrared radiation and tensile characteristics study on chemically treated hibiscus rosa-sinensis plant fibers”, Materials Research Express, v. 11, n. 7, pp. 075102, Jul. 2024. doi: http://doi.org/10.1088/2053-1591/ad61c0.
  » https://doi.org/10.1088/2053-1591/ad61c0
• ^[34] RUWOLDT, J., “A critical review of the physicochemical properties of lignosulfonates: chemical structure and behavior in aqueous solution, at surfaces and interfaces”, Surfaces, v. 3, n. 4, pp. 622–648, Nov. 2020. doi: http://doi.org/10.3390/surfaces3040042.
  » https://doi.org/10.3390/surfaces3040042
• ^[35] FURSZYFER DEL RIO, D.D., SOVACOOL, B.K., GRIFFITHS, S., et al, “Decarbonizing the pulp and paper industry: A critical and systematic review of sociotechnical developments and policy options”, Renewable & Sustainable Energy Reviews, v. 167, pp. 112706, Oct. 2022. doi: http://doi.org/10.1016/j.rser.2022.112706.
  » https://doi.org/10.1016/j.rser.2022.112706
• ^[36] XU, Y., ADEKUNLE, K., RAMAMOORTHY, S.K., et al, “Methacrylated lignosulfonate as compatibilizer for flax fiber reinforced biocomposites with soybean-derived polyester matrix”, Composites Communications, v. 22, pp. 100536, Dec. 2020. doi: http://doi.org/10.1016/j.coco.2020.100536.
  » https://doi.org/10.1016/j.coco.2020.100536
• ^[37] OLIVEIRA, F., SILVA, C.G., RAMOS, L.A., et al, “Phenolic and lignosulfonate-based matrices reinforced with untreated and lignosulfonate-treated sisal fibers”, Industrial Crops and Products, v. 96, pp. 30–41, Feb. 2017. doi: http://doi.org/10.1016/j.indcrop.2016.11.027.
  » https://doi.org/10.1016/j.indcrop.2016.11.027
• ^[38] AGRIZE, P.L., SILVA, B.D.L., VEIGA, B.C., et al, “Structure and mechanical behavior of lignosulfonate-treated piassava (Attalea funifera) fibers”, Matéria, v. 28, n. 2, e20230041, 2023. doi: http://doi.org/10.1590/1517-7076-rmat-2023-0041.
  » https://doi.org/10.1590/1517-7076-rmat-2023-0041
• ^[39] GUALBERTO, S.L., MOTTA, L.A.C., PASQUINI, D., “Treatment of sisal fibers with lignosulphonate to improve the properties of fiber cement composites”, Revista Virtual de Química, v. 13, n. 6, pp. 1257–1267, 2021. doi: http://doi.org/10.21577/1984-6835.20210077.
  » https://doi.org/10.21577/1984-6835.20210077
• ^[40] NIE, Y., SHI, J., HE, Z., et al, “Evaluation of high-volume fly ash (HVFA) concrete modified by metakaolin: Technical, economic and environmental analysis”, Powder Technology, v. 397, pp. 117121, Jan. 2022. doi: http://doi.org/10.1016/j.powtec.2022.117121.
  » https://doi.org/10.1016/j.powtec.2022.117121
• ^[41] WANG, D., XIAO, J., DUAN, Z., “Strategies to accelerate CO₂ sequestration of cement-based materials and their application prospects”, Construction & Building Materials, v. 314, pp. 125646, Jan. 2022. doi: http://doi.org/10.1016/j.conbuildmat.2021.125646.
  » https://doi.org/10.1016/j.conbuildmat.2021.125646
• ^[42] MELO FILHO, J.D.A., SILVA, F.D.A., TOLEDO FILHO, R.D., “Degradation kinetics and aging mechanisms on sisal fiber cement composite systems”, Cement and Concrete Composites, v. 40, pp. 30–39, Jul. 2013. doi: http://doi.org/10.1016/j.cemconcomp.2013.04.003.
  » https://doi.org/10.1016/j.cemconcomp.2013.04.003
• ^[43] FERREIRA, S.R., SILVA, F.D.A., LIMA, P.R.L., et al, “Effect of fiber treatments on the sisal fiber properties and fiber-matrix bond in cement based systems”, Construction & Building Materials, v. 101, pp. 730–740, Dec. 2015. doi: http://doi.org/10.1016/j.conbuildmat.2015.10.120.
  » https://doi.org/10.1016/j.conbuildmat.2015.10.120
• ^[44] NAWAB, M.S., ALI, T., QURESHI, M.Z., et al, “A study on improving the performance of cement-based mortar with silica fume, metakaolin, and coconut fibers”, Case Studies in Construction Materials, v. 19, pp. e02480, Dec. 2023. doi: http://doi.org/10.1016/j.cscm.2023.e02480.
  » https://doi.org/10.1016/j.cscm.2023.e02480
• ^[45] GARCIA FILHO, F.C., LUZ, F.S., OLIVEIRA, M.S., et al, “Influence of rigid Brazilian natural fiber arrangements in polymer composites: energy absorption and ballistic efficiency”, journal of composites science, v. 5, n. 8, pp. 201, aug. 2021. doi: http://doi.org/10.3390/jcs5080201.
  » https://doi.org/10.3390/jcs5080201
• ^[46] INSTITUTO DE PESQUISA ECONÔMICA APLICADA, Atlas da Violencia v.2.8 – Mapa, Brasília, IPEA, 2025, https://www.ipea.gov.br/atlasviolencia/dados-series/35, accessed in February, 2025.
  » https://www.ipea.gov.br/atlasviolencia/dados-series/35
• ^[47] IACHAN, L., MOREAU, F., HERITAGE, P., et al, “How does urban violence impact choices of cultural participation? The case of the Maré favela complex in Rio de Janeiro”, Journal of Cultural Economics, v. 47, n. 4, pp. 609–641, Dec. 2022. doi: http://doi.org/10.1007/s10824-022-09465-4. PubMed PMID: 38625298.
  » https://doi.org/10.1007/s10824-022-09465-4
• ^[48] NAYAK, S.Y., SULTAN, M.T.H., SHENOY, S.B., et al, “Potential of natural fibers in composites for ballistic applications: a review”, Journal of Natural Fibers, v. 19, n. 5, pp. 1648–1658, May. 2022. doi: http://doi.org/10.1080/15440478.2020.1787919.
  » https://doi.org/10.1080/15440478.2020.1787919
• ^[49] CAMARGO, M., TAYE, E.A., ROETHER, J., et al, “A review on natural fiber-reinforced geopolymer and cement-based composites”, Materials, v. 13, n. 20, pp. 4603, Oct. 2020. doi: http://doi.org/10.3390/ma13204603. PubMed PMID: 33081091.
  » https://doi.org/10.3390/ma13204603
• ^[50] AKINYEMI, A.B., OMONIYI, E.T., ONUZULIKE, G., “Effect of microwave assisted alkali pretreatment and other pretreatment methods on some properties of bamboo fibre reinforced cement composites”, Construction & Building Materials, v. 245, pp. 118405, Jun. 2020. doi: http://doi.org/10.1016/j.conbuildmat.2020.118405.
  » https://doi.org/10.1016/j.conbuildmat.2020.118405
• ^[51] DI MAIDA, P., SCIANCALEPORE, C., RADI, E., et al, “Effects of nano-silica treatment on the flexural post cracking behaviour of polypropylene macro-synthetic fibre reinforced concrete”, Mechanics Research Communications, v. 88, pp. 12–18, Mar. 2018. doi: http://doi.org/10.1016/j.mechrescom.2018.01.004.
  » https://doi.org/10.1016/j.mechrescom.2018.01.004
• ^[52] ZHANG, W., ZOU, X., WEI, F., et al, “Grafting SiO₂ nanoparticles on polyvinyl alcohol fibers to enhance the interfacial bonding strength with cement”, Composites. Part B, Engineering, v. 162, pp. 500–507, Apr. 2019. doi: http://doi.org/10.1016/j.compositesb.2019.01.034.
  » https://doi.org/10.1016/j.compositesb.2019.01.034
• ^[53] TEIXEIRA, R.S., TONOLI, G.H.D., SANTOS, S.F., et al, “Nanoindentation study of the interfacial zone between cellulose fiber and cement matrix in extruded composites”, Cement and Concrete Composites, v. 85, pp. 1–8, Jan. 2018. doi: http://doi.org/10.1016/j.cemconcomp.2017.09.018.
  » https://doi.org/10.1016/j.cemconcomp.2017.09.018
• ^[54] LI, Y., LI, W., DENG, D., et al, “Reinforcement effects of polyvinyl alcohol and polypropylene fibers on flexural behaviors of sulfoaluminate cement matrices”, Cement and Concrete Composites, v. 88, pp. 139–149, Apr. 2018. doi: http://doi.org/10.1016/j.cemconcomp.2018.02.004.
  » https://doi.org/10.1016/j.cemconcomp.2018.02.004
• ^[55] TEIXEIRA, F.P., LIMA, V.N., MOUTINHO, D.J.C., et al, “Mechanical properties and fractography of cement-based composites reinforced by natural piassava and jute fibers”, Cerâmica, v. 68, n. 385, pp. 60–66, Mar. 2022. doi: http://doi.org/10.1590/0366-69132022683853174.
  » https://doi.org/10.1590/0366-69132022683853174
• ^[56] SALIH, A.A., ZULKIFLI, R., AZHARI, C.H., “Tensile properties and microstructure of single-cellulosic bamboo fiber strips after alkali treatment”, Fibers, v. 8, n. 5, pp. 26, Apr. 2020. doi: http://doi.org/10.3390/fib8050026.
  » https://doi.org/10.3390/fib8050026
• ^[57] CHIHAOUI, B., SERRA-PARAREDA, F., TARRÉS, Q., et al, “Effect of the fiber treatment on the stiffness of date palm fiber reinforced pp composites: macro and micromechanical evaluation of the Young’s modulus”, Polymers, v. 12, n. 8, pp. 1693, Jul. 2020. doi: http://doi.org/10.3390/polym12081693. PubMed PMID: 32751192.
  » https://doi.org/10.3390/polym12081693
• ^[58] NIMANPURE, S., HASHMI, S.A.R., KUMAR, R., et al, “Mechanical, electrical, and thermal analysis of sisal fibril/kenaf fiber hybrid polyester composites”, Polymer Composites, v. 40, n. 2, pp. 664–676, Feb. 2019. doi: http://doi.org/10.1002/pc.24706.
  » https://doi.org/10.1002/pc.24706
• ^[59] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 16697 Portland cement: requirements, Rio de Janeiro, ABNT, 2018.
• ^[60] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 11768-1 chemical admixtures for Portland cement concrete part 1 – requirements, Rio de Janeiro, ABNT, 2019.
• ^[61] AMERICAN SOCIETY FOR TESTING AND MATERIALS, ASTM C494/C494M-05 standard specification for chemical admixtures for concrete, West Conshohocken, ASTM, 2017.
• ^[62] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR NM 248 Aggregates – sieve analysis of fine and coarse aggregates, Rio de Janeiro, ABNT, 2003.
• ^[63] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 16916 Fine aggregates – determination of density and water absorption, Rio de Janeiro, ABNT, 2021.
• ^[64] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 13276 Mortars applied on walls and ceilings – Determination of the consistence index, ABNT, 2016.
• ^[65] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 7215 Portland cement – Determination of compressive strength of cylindrical test specimens, ABNT, 2019.
• ^[66] ASSOCIAÇÃO BRASILEIRA DE NORMAS TÉCNICAS, ABNT NBR 7222 Concrete and mortar – determination of the tension strength by diametrical compression of cylindrical test specimens, ABNT, 2011.
• ^[67] HENSON, R.N., “Analysis of variance (ANOVA)”, In: Toga, A.W. (ed), Brain mapping: an encyclopedic reference, London, Academic Press, pp. 477-481, 2015. doi: http://doi.org/10.1016/B978-0-12-397025-1.00319-5.
  » https://doi.org/10.1016/B978-0-12-397025-1.00319-5
• ^[68] ABDI, H., WILLIAMS, L.J., “Newman-Keuls test and Tukey test”, In: Salkind, N. (ed), Encyclopedia of Research Design, Thousand Oaks, SAGE Publications, 2010.
• ^[69] BRAGA, F.D.O., BOLZAN, L.T., RAMOS, F.J.H.T.V., et al, “Ballistic efficiency of multilayered armor systems with sisal fiber polyester composites”, Materials Research, v. 20, pp. 767–774, Jan. 2018. doi: http://doi.org/10.1590/1980-5373-mr-2017-1002.
  » https://doi.org/10.1590/1980-5373-mr-2017-1002
• ^[70] FAUL, F., ERDFELDER, E., BUCHNER, A., et al, “Statistical power analyses using G*Power 3.1: Tests for correlation and regression analyses”, Behavior Research Methods, v. 41, n. 4, pp. 1149–1160, Nov. 2009. doi: http://doi.org/10.3758/BRM.41.4.1149. PubMed PMID: 19897823.
  » https://doi.org/10.3758/BRM.41.4.1149
• ^[71] COHEN, J., Statistical power analysis for the behavioral sciences, 2 ed., Hillsdale, Erlbaum Associates, 1988.
• ^[72] MEHTA, P.K., MONTEIRO, P.J.M., Concrete: microstructure, properties, and materials, 3 ed., New York, McGraw-Hill, 2006.
• ^[73] WEI, J., MEYER, C., “Degradation mechanisms of natural fiber in the matrix of cement composites”, Cement and Concrete Research, v. 73, pp. 1–16, Jul. 2015. doi: http://doi.org/10.1016/j.cemconres.2015.02.019.
  » https://doi.org/10.1016/j.cemconres.2015.02.019
• ^[74] ZENG, Q., LI, K., “Reaction and microstructure of cement–fly-ash system”, Materials and Structures, v. 48, n. 6, pp. 1703–1716, Jun. 2015. doi: http://doi.org/10.1617/s11527-014-0266-y.
  » https://doi.org/10.1617/s11527-014-0266-y

Publication Dates

• Publication in this collection
  25 Aug 2025
• Date of issue
  2025

History

• Received
  17 Apr 2025
• Accepted
  10 July 2025