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Article

Tensile Behavior of a Fiber-Reinforced Stabilized Soil—Cyclic Loading Frequency Study

by
António A. S. Correia
1,*,
Daniel S. Goulart
2 and
Paulo J. Venda Oliveira
3
1
Department of Civil Engineering, CERES, University of Coimbra, R. Luís Reis Santos, 3030-788 Coimbra, Portugal
2
Department of Civil Engineering, University of Coimbra, R. Luís Reis Santos, 3030-788 Coimbra, Portugal
3
Department of Civil Engineering, ISISE, University of Coimbra, R. Luís Reis Santos, 3030-788 Coimbra, Portugal
*
Author to whom correspondence should be addressed.
Appl. Sci. 2025, 15(16), 8825; https://doi.org/10.3390/app15168825
Submission received: 26 June 2025 / Revised: 8 August 2025 / Accepted: 9 August 2025 / Published: 10 August 2025
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Abstract

The present work aims to study the effect of cyclic loading on the tensile behavior of a chemically stabilized sandy soil, whether or not reinforced with polypropylene or sisal fibers. To this end, a series of splitting tensile strength tests were carried out by varying the frequency of the cyclic loading. During cyclic loading a substantial decrease in accumulated plastic axial displacement was observed with rising frequency when fibers were incorporated. On average, the reduction was 28% for polypropylene fibers and 14% for sisal fibers. For the polypropylene fibers, this effect is more pronounced because of a greater number of randomly distributed fibers, creating a strong and dense interlocking network. Regarding the load-displacement characteristics, fiber inclusion leads to a more ductile tensile response, which is identified by a secondary peak strength and residual strength. The cyclic loading frequency does not show a distinct trend concerning the post-cyclic tensile strength behavior; this behavior is dependent on the mechanical properties of materials (cemented matrix and fibers). Nevertheless, the cyclic stage resulted in an increased post-cyclic tensile strength for sisal fibers (ranging from 23% to 51%), although no clear trend was observed with respect to frequency variation. In contrast, for polypropylene fibers, the cyclic stage resulted in a more ductile tensile mechanical response, with post-cyclic tensile strength increasing from 1% to 16% as the frequency decreased.

1. Introduction

The effect of adding fibers to soils is a subject that has been investigated by many authors, whether subjected to static [1,2,3,4,5,6,7,8,9,10,11,12] or dynamic loadings [13,14,15]. At the same time, many researchers have studied the effect that the addition of fibers (synthetic or natural) has on the behavior of stabilized soils. In general, randomly distributed fibers act as a reinforcement of the stabilized soil and improve its geomechanical behavior. They mainly increase the unconfined compressive strength [16,17,18,19,20], shear strength [21], undrained shear strength [18], flexural strength [22], and tensile strength [20,23,24,25,26,27], as well as increasing the ductility and decreasing the loss of the post-peak strength, which bestows a more ductile behavior to the composite material [20,23,24,28,29]. Some researchers have pointed out that the assessment of strength is dependent on the soil and fiber type [22,24], length of fiber [24,30], binder content [19,30], fiber content [23,31], temperature [32], and failure mechanism imposed [23,24].
Despite the results reported above for static loading and the knowledge acquired, there is still a lack of knowledge about the behavior of stabilized soils reinforced with fibers when subjected to dynamic loadings that may be triggered, for example, by traffic loads, industrial and urban vibrations, earthquakes, wind loads, and sea waves, amongst others [33,34]. The number of studies examining the dynamic loading of these materials is indeed limited. Furthermore, such research has been carried out nearly exclusively on unreinforced materials under compressive loadings. It has been reported that the application of a dynamic loading to an unreinforced stabilized soil leads to a gradual failure of the cemented matrix. This process causes a rise in plastic deformations [35,36,37] and a reduction in both stiffness and yield stress [38,39]. In the case of stabilized soils reinforced with fibers, the results reported are sometimes not in accordance with each other [33,34,35,40,41,42,43,44]. During cyclic tests some authors have reported that plastic deformations increase with the number of load cycles, with the most significant increase happening for the first cycles [33,34,40,42], while other authors have reported that the sharp increase is linked with a high number of cycles [35]. Based on cyclic tests, Festugato et al. [41], Khattak et al. [43] and Venda Oliveira et al. [34] observed that the inclusion of polypropylene fibers in stabilized soils has a beneficial impact on the shear, compression, and tensile strength, while Ahmed and Naggar [45] reported a degradation of the compression strength with the increase in the number of load cycles for the case of a stabilized soil reinforced with tire fibers. Khattak et al. [43] have studied the impact of the cyclic loading on the tensile behavior of four cohesive soils, stabilized with Portland cement and reinforced with polypropylene or processed cellulose fibers, by conducting a series of splitting tensile cyclic tests. The authors reported that the behavior of the composite material is dependent on the fiber content, soil type, and curing time; the resilient modulus may increase or decrease depending on the soil type; and the plastic deformation decreases due to the addition of fibers, indicating a higher resistance to tensile cracking.
Regarding the impact of cyclic loading frequency, the findings reported in the literature are not entirely consistent. Some studies conducted on unstabilized and unreinforced marine clay indicate that frequency has little to no significant effect [46]. In contrast, research involving clays and sands suggests that at high frequencies, the effect is negligible, but at lower frequencies, it can be detrimental, leading to increased permanent plastic deformation [47,48,49,50,51]. Limited data on stabilized soils indicate a negative impact of increasing frequency, as it accelerates material degradation and results in higher plastic deformations during cyclic loading [38,52]. Conversely, the fiber reinforcement of a stabilized sand shows that the effect depends on the applied frequency; that is, frequencies below 1.0 Hz tend to reduce compression strength, while higher frequencies induce an opposite effect [40].
Despite the research to date, the impact of the cyclic loading frequency on the tensile behavior of a stabilized sand reinforced with fibers has not been properly studied. In addition, the fiber type (synthetic versus natural) is an important parameter on the ‘sustainable’ tensile behavior, which has been less discussed. Thus, the aim of the present work is to improve the existing knowledge about the tensile behavior of fiber-reinforced stabilized soils under dynamic actions, such as those resulting from traffic loads, industrial and urban vibrations, earthquakes, wind loads, and sea waves, amongst others, therefore promoting the future application of such composite materials.
The focus of this research is to analyze the effect of the cyclic loading frequency on the tensile and post-cyclic behavior of a stabilized sandy soil, unreinforced and reinforced with polypropylene or sisal fibers. The plastic deformations developed during the cyclic stage and the load-displacement curves will be used to assess the effect of the frequency of the cyclic loading and the type of fiber used as reinforcement. These effects are the focus and main novelty of this work. To achieve such goals, the following experimental testing program was designed: (i) monotonic splitting tensile strength (STS) tests performed with samples not subjected to cyclic loading; (ii) cyclic (Cyc) STS tests; and (iii) post-cyclic STS tests (STSpc). Table 1 summarizes the experimental testing plan.

2. Materials

2.1. Characteristics of the Soil

The soil selected for the study is a natural, non-plastic, and inorganic sandy soil composed of sand (97.8%), silt (1.8%), and clay (0.4%), with a specific gravity of the soil particles of 2.66, exhibiting a grain size curve (Figure 1) characterized by a median diameter of 0.179 mm, a coefficient of uniformity of 2.27, and a coefficient of curvature of 0.95. It is classified by the Unified Soil Classification System [53] as a poorly graded sand (SP). The standard Proctor test resulted in a maximum dry unit weight of 16.3 kN/m3 and an optimum moisture content of 14.2%.

2.2. Characteristics of the Binder and the Fibers

The binder employed in this study is Portland cement Type I 42.5 R [54], whose chemical composition is detailed in Table 2. According to the manufacturer, it has a specific gravity of 3.18 and a specific surface of 326.3 m2/kg. Due to its high CaO to SiO2 ratio [55], this binder possesses hydraulic properties, enabling it to react spontaneously upon contact with water.
Figure 2 shows the two different types of fibers used in this investigation, a synthetic and flexible fiber (polypropylene, PP) and a natural and more rigid fiber (sisal, S), whose main characteristics are presented in Table 2. These two types of fibers were chosen due to their widespread use in the scientific community. Polypropylene fibers, in particular, are known to significantly enhance the ductility of stabilized soils, more so than steel or natural fibers (e.g., sisal), while also providing superior tensile strength. On the other hand, sisal (natural) fibers offer sustainable performance, which supports their inclusion in this study. Although both fibers have the same length (12 mm), they exhibit different aspect ratios (L/D), roughness, and mechanical characteristics. Polypropylene fibers present a higher aspect ratio, lower roughness, tensile strength, and elasticity modulus than the sisal fibers. However, polypropylene fibers are considered non-biodegradable, while sisal fibers are biodegradable [57,58]. This particular characteristic may impose limitations on the use of sisal fibers in some geotechnical works, mainly in permanent works. Indeed, the primary concern regarding the use of natural fibers, compared to synthetic fibers, is their durability, as natural fibers are biodegradable [57,58]. Consequently, durability may limit the application of sisal fibers in certain geotechnical works, especially in permanent structures. Indeed, when sisal fibers are exposed to environmental agents such as ultraviolet rays, temperature fluctuations, and humidity, they can lose up to 90% of their initial tensile strength [61]. Additionally, a reduction of 30–40% in tensile strength has been observed after exposure to freshwater, due to microbiological activity [62]. Moreover, sisal fibers completely lose their flexibility and strength after immersion in a calcium hydroxide solution at pH 12 for 300 days. When incorporated into a cement matrix, the fibers exhibit a significant decrease in ductility after cycles of wetting and drying, as well as after six months of exposure to the open air weathering [63]. Despite these limitations, it is important to note that sisal fibers continue to serve as effective reinforcement within sandy matrices, contributing to improved mechanical performance compared to unreinforced materials [61]. To delay the degradation process and enhance durability, sisal fibers can be coated with a protective layer of graphene oxide [64] and used to reinforce cementitious materials [65]. Additionally, chemical treatments such as alkali treatment and acetylation can further increase their durability in cement composites [66].

3. Sample Preparation and Testing

The preparation of the stabilized soil samples, with or without polypropylene or sisal fiber reinforcement, followed the laboratory protocol outlined in Eurosoilstab [67], incorporating modifications suggested by Correia [68], Goulart [56], Correia et al. [23], and Venda Oliveira et al. [24]. The modifications introduced to the Eurosoilstab [67] protocol include the use of the standard Proctor test to define the optimum compaction characteristics and the inclusion of a fiber dispersion procedure to ensure uniform fiber distribution within the mixture. This procedure can be summarized as follows:
  • The sandy soil was first homogenized to reduce inherent variability and ensure reproducibility across tests. A dry soil mass corresponding to the maximum dry unit weight of 16.3 kN/m3, as determined by the standard Proctor test, was used.
  • The binder was added in a content of 10.5% (dry binder mass relative to dry soil mass), and mixed with the soil at the optimum moisture content of 14.2%, also established through the standard Proctor test, to create a slurry. For reinforced samples, polypropylene or sisal fibers were incorporated in a content of 0.6% (dry fiber mass relative to dry soil mass).
  • The resulting slurry (with or without fibers) was thoroughly blended in a mechanical mixer operating at a rotational speed of 142 rpm for 4 min, producing a homogeneous paste. The fibers were gradually added in small increments during the first minute of the mixing to avoid fiber clumping or uneven dispersion of the fibers within the composite matrix.
  • This paste was then placed into cylindrical PVC molds (70 mm in diameter, D, and 140 mm in length, L) in three successive layers (Figure 3a). Each layer was compacted using the same energy defined in the standard Proctor test, and its top surface was lightly scarified to improve adhesion/bonding with the subsequent layer.
  • After molding, the specimens were demolded (Figure 3b) and cured under controlled conditions (temperature of 20 ± 2 °C, relative humidity of 95 ± 5%) to minimize suction effects.
  • Following a 28-day curing period, the specimens were mounted on a loading frame, capable of both static and cyclic loading tests (Figure 3c). Instrumentation, including the load cell and linear displacement transducer, was properly configured, and data were continuously recorded using an automated acquisition system.
All the stabilized samples, reinforced or not with polypropylene or sisal fibers, have very similar initial porosities (without fibers n = 32.81%; reinforced with polypropylene fibers n = 32.09%; reinforced with sisal fibers n = 32.47%; based on [26]), due to the low fiber content (0.6%). Therefore, it is expected that any suction effect may be of the same order. Suction measurements were made on samples at the end of the curing period using a high-capacity tensiometer (Durham Geo-Technologies, UK), with recorded values ranging from 18.8 to 63.7 kPa. The measured suction values were low; thus, the suction in the samples is likely to be insignificant relative to the strengths being measured, in agreement with the findings of Consoli et al. [69].
Static (monotonic) STS tests were initially performed to evaluate the tensile mechanical properties of the composite material, including the load-displacement (F-δ) response, the tensile strength (fct = 2.F/(π.L.D)), and the corresponding displacement at failure (δf) ([70,71,72,73,74,75]). In the cyclic stage, samples were loaded to a tensile stress level equal to 50% (fcyclic/fct), corresponding to a safety factor of 2.0, using a sinusoidal excitation with frequencies of 0.25, 1.0, 2.0, and 4.0 Hz (simulating the passage of a car or train [50,51,76]; these values are within the range recommended by EN-13286-7 [77]), for a total of 5000 cycles [77]). The load amplitude (fmax-fmin) was set at ±7.5% of fct, which reflects a safety factor between 1.7 and 2.3 (fct/[(0.50 ± 0.075)× fct]). To evaluate how cyclic loading influences the tensile response of the composite material, a static (monotonic) STS test was performed following the cyclic stage, and its results were compared to the initial static (monotonic) STS test. All STS tests were carried out using a strain rate of 1.0 %/min, compatible with a stress increase not higher than 0.04 to 0.2 MPa/s in line with the standards EN 12390-6 [72] and EN 13286-42 [70]. Each test configuration was carried out in duplicate to ensure results consistency and reliability. The conformity criterion adopted required that the results fall within the range of ±10% of the average value of the two tests, which is a more demanding requirement than the ±15% tolerance specified in the standard EN-206-1 [78].

4. Analysis of the Results

As will be presented throughout this section, the samples tested for each condition present some dispersion of results. However, this dispersion is not significant, being justified by the experimental nature of the present study, involving the random dispersion of fibers that may lead to some local heterogeneities. Similar dispersions have been reported by other authors when testing similar materials [23,24,34,43,79,80,81].

4.1. Cyclic Stage

Figure 4 illustrates how different loading frequencies (0.25, 1.0, 2.0, and 4.0 Hz) influence the accumulated plastic axial displacement (δperm = Δδcyc-perm/D0) over the number of loading cycles for the three tested materials: stabilized soil without fiber reinforcement, with polypropylene fibers, and with sisal fibers. The trend in δperm exhibits a consistent pattern across all three materials and frequencies, characterized by an initial rapid growth during the first 250 cycles, followed by a smooth increase as loading cycles progress, resembling a hyperbolic evolution curve. Results further indicate that, independently of the frequency imposed, fiber-reinforced stabilized samples demonstrate a noticeable decrease in accumulated plastic axial displacement as the number of loading cycles increases, particularly for those incorporating polypropylene fibers. On average, the reduction was 28% for polypropylene fibers and 14% for sisal fibers. Such behavior can be attributed to the progressive mobilization of the tensile strength of fibers during cyclic loading. Indeed, as the plastic axial displacement develops, the effective mobilization of fibers becomes more effective, which justifies the reduction in the plastic displacement. This behavior is more pronounced with polypropylene fibers, probably due to a higher number of fibers inside the stabilized matrix, allowing a better redistribution of stresses under cyclic loading, minimizing the breakage of some cementation bonds and the deterioration of the cemented matrix.
As shown in Figure 4 and Figure 5, regardless of the material type and despite some natural experimental variability in data, a general trend can be seen characterized by a reduction in the accumulated plastic axial displacement as the frequency increases, suggesting that higher frequency levels result in less structural deterioration. As the loading frequency rises, the elastic displacement tends to increase, which can be attributed to smaller displacement mobility and a greater capacity of reversibility in deformation as a result of the less frequent occurrence of shear/breakage of the cementation bonds; this outcome is consistent with findings reported for other materials [47,48,82,83].

4.2. Load-Displacement Curves

Figure 6 shows the evolution of the load-displacement curves from the splitting tensile strength tests performed under static/monotonic loading conditions before the cyclic stage. As may be observed, the addition of the fibers to the stabilized material changes the behavior from brittle (unreinforced material) to ductile (reinforced with PP or sisal fibers), characterized by a second peak strength and a post-peak or residual strength, with a more pronounced effect for the PP fibers. At the beginning of the test the load-displacement curve is linear up to the first peak strength, which is directly related to an abrupt breakage of the cementation bonds, and as all materials have the same cementation level (induced by a constant binder content of 10.5%), they exhibit almost the same tensile strength value. This first peak strength is followed by a sudden and total loss of tensile strength in the case of the unreinforced soil (associated with a vertical crack induced by the failure mechanism), while, when in the presence of fibers, a partial loss of tensile strength is observed, followed by a second peak strength directly associated with the mobilization of the tensile strength of the fibers crossing the vertical crack. Indeed, as the displacement evolves during the STS test, there is a progressive fiber contribution to the development of the tensile strength until failure of the fibers, which may be linked to an insufficient length of anchorage and/or rupture of fibers by tensile stress (insufficient tensile strength). For high displacement levels the reinforced stabilized materials exhibit a non-negligible tensile strength (residual strength) due to the presence of the fibers. The behavior observed is in agreement with the findings of [23,79,84], who have reported that a second peak strength may occur for stabilized soils reinforced with synthetic or natural fibers due to a stress transference to the fibers that cross the vertical failure plane imposed by the STS test. This improvement in tensile strength is dependent on the mechanical characteristics of the fibers (tensile strength and roughness) and the number of fibers crossing the vertical failure plane: a greater number of fibers leads to a higher probability of some fibers crossing the failure plane, which has a major impact on the development of second-peak tensile strength. It is known that polypropylene fibers are present in a higher number than the sisal fibers (PP fibers have a lower density and higher aspect ratio, Table 2); therefore, for the same fiber content, it implies a higher number of PP fibers per cubic meter of soil. This induces a lower stress level in the PP fibers and, consequently, reduces the probability of fiber failure due to excessive tensile stress or loss of anchorage, thus exhibiting a better mechanical behavior than the sisal fibers (Figure 6).
Figure 7 illustrates how the cyclic loading (at different frequencies) influences the load-displacement curves obtained from the STS tests. Results are presented for the unreinforced stabilized soil (Figure 7a), as well as for the stabilized soil reinforced with polypropylene (Figure 7b) and sisal fibers (Figure 7c). The findings indicate that, regardless of the application of cyclic loading, the inclusion of either fiber type (PP or sisal) reduces the brittleness of the fiber-reinforced stabilized materials (Figure 7b,c) in comparison to the unreinforced samples (Figure 7a), which is consistent with the behavior previously observed (Figure 6). Moreover, following the application of the cyclic loading, the incorporated fibers helped to minimize the loss of tensile strength beyond the initial peak strength (failure), leading to the development of a secondary peak and a non-negligible residual strength as previously discussed. The influence of cyclic loading on the post-cyclic load-displacement behavior appears less significant for samples containing polypropylene fibers. This might be attributed to the fact that polypropylene fibers induce the formation of a denser spatial fiber network, which effectively absorbs and redistributes the imposed cyclic loading within the material matrix, thereby reducing the degree of material deterioration. In these conditions, the tensile behavior following the cyclic stage remains closely aligned with that observed under static (monotonic) loading. In contrast, for the samples reinforced with sisal fibers, the application of cyclic loading induces a more pronounced impact on the tensile behavior (Figure 7c), showing a marked increase in tensile strength in comparison to the static (monotonic) STS tests (Figure 6). This behavior might be explained by the higher tensile strength, stiffness, and surface texture/roughness of the sisal fibers, which enhance a more effective mechanical anchorage of the fibers within the matrix and allow for a more efficient mobilization of tensile strength for a specific deformation level. The level of plastic displacements induced during the cyclic loading stage appears sufficient to trigger the formation of some well-defined cracks, enabling early mobilization of the sisal fibers’ tensile strength from the beginning of the post-cyclic STS test, thereby contributing to a greater tensile strength. Indeed, it was observed that the post-cyclic tensile strength of sisal fibers increased by 23% to 51%, compared to an increase of 1% to 16% for PP fibers.
Figure 7 also shows that, independently of the material type, the tensile strength does not show any clear tendency as the cyclic loading frequency changes; this may also be observed in Figure 8, despite some scattering of the results, with the relative deviation from the average values remaining below 7.4% (Table 3). This behavior seems to be in contradiction with that observed for the plastic axial displacement (Figure 4 and Figure 5), but now the stress levels imposed are higher, which leads to the failure of the material (cemented matrix and/or fibers), which is dependent on the mechanical characteristics of the cementation bonds and of the fibers. Thus, for the frequencies studied here, the frequency level does not seem to have an impact on the final tensile strength behavior, which depends on the characteristics of the material. Figure 8 also shows that the effect of the cyclic loading (STSpc), compared to monotonic tests (STS), tends to cause a slight strengthening of the soil for the sisal fibers. This effect is more pronounced at lower frequencies.
The effect of the cyclic loading on the brittleness or ductility of the composite material can be quantitatively expressed by the brittleness index (IB), which is defined as a ratio between the maximum tensile strength (fct, associated with the axial displacement at failure δf) and the tensile strength mobilized for a displacement equal to a multiple of the displacement at failure (normally δ/δf = 2 or 3, [24,34]). However, the direct application of this index for the stabilized reinforced materials studied here leads to a brittleness index that is lower for the case of the sisal fibers (meaning a higher ductility), which is not in accordance with the results observed (Figure 6 and Figure 7). This is because of some particularities of the tensile behavior of the reinforced materials, namely, the two tensile strength peaks and the different mechanical characteristics of the fibers that induce a higher second peak in the case of PP fibers (corresponding to the maximum tensile strength). Thus, for the materials containing fibers, it is advisable to express the brittleness index (IB) as a ratio between the tensile strength measured for the two peaks, in a similar way as suggested by Yao et al. [84]:
I B = 1 − f c t − l o w e s t   p e a k f c t − h i g h e s t   p e a k
A brittleness index (IB) of zero indicates an ideal ductile behavior, meaning that the composite material retains its tensile strength after failure. In contrast, an IB value of one indicates a material with an ideal brittle behavior, where the material loses all tensile strength immediately after the peak failure. Figure 9 presents the IB values obtained for the three tested materials: stabilized soil without reinforcement and stabilized soil reinforced with the addition of polypropylene or sisal fibers. Although some dispersion/variability of the results is observed, which is more pronounced for the samples tested under static (monotonic) conditions (without a cyclic stage), the general trend of the IB aligns well with the previous observations about the tensile behavior; in particular, the stabilized samples reinforced with polypropylene fibers show a consistently lower IB (<15%), reflecting a more ductile behavior compared to those reinforced with sisal fibers. Furthermore, regardless of the applied frequency, cyclic loading tends to reduce the IB, with the most significant effect occurring at the lowest frequency tested (0.25 Hz). In fact, lower frequency levels are associated with higher plastic axial displacements (as shown in Figure 4), meaning that the breakage of cementation bonds may produce a well-defined vertical crack (consistent with the failure mechanism of the STS test). This behavior appears to induce a slight increase in the axial displacement beyond the peak failure in the stabilized unreinforced sample, thereby explaining the reduction in the IB after the cyclic stage. In stabilized fiber-reinforced samples, the presence of fibers crossing the vertical failure surface promotes a transference of stresses to the fibers, enabling an extra load capacity. This mechanism induces a secondary peak tensile strength, corresponding to an enhancement in ductility of the composite material, which is reflected in a lower IB value.
Figure 9 also demonstrates that cyclic loading (STSpc), in comparison to monotonic tests (STS), tends to cause a slight decrease in IB. This effect is more pronounced for unreinforced and unstabilized soils and when polypropylene fibers are used.

4.3. Tensile Mechanical Behavior

Incorporating fibers into the stabilized matrix confers a more ductile tensile behavior to the composite material, which is typically characterized by a double-peak tensile strength along with a non-negligible residual strength (refer to Figure 6). Following a sudden and abrupt breakage of cementation bonds, which occurs for small axial displacements, a vertical crack/failure surface develops, concentrating the axial deformations along this surface. The fibers crossing this failure plane will be progressively mobilized, allowing an extra loading capacity of the composite material, responsible for the second peak tensile strength and residual tensile strength. This extra loading capacity is dependent on the stresses applied on the fibers, which, in turn, depends on the mechanical properties of the fibers (linked to the breakage of the fibers by tensile or by insufficient anchorage length) and the number of fibers that cross the failure plane. With an increase in the number of fibers, there is a decrease in the stresses applied on the fibers, allowing a more pronounced ductile tensile behavior for higher displacement levels.
The effect of the cyclic loading on the tensile mechanical behavior of a stabilized material reinforced with fibers (see Figure 7) seems to be correlated with the plastic axial displacement developed during the cyclic stage (see Figure 4). As the frequency of the cyclic loading increases, there is a lower deterioration of the cemented matrix, which is explained by the fact that higher frequencies are associated with a larger portion of elastic deformation due to the limited displacement mobility and a higher degree of reversibility in deformation. Nevertheless, as plastic displacements evolve, there is a progressive transference of stresses to the fibers that contributes to a lower deterioration of the cemented matrix (in other words, a reduction in the plastic axial displacement). This effect is more evident for the materials with a higher number of fibers inside the composite matrix, which allows a more effective redistribution of the stresses.

5. Conclusions

The outcomes of the splitting tensile strength (STS) tests, carried out under both static (monotonic) and cyclic loading conditions (tensile stress amplitude (fmax-fmin) of ±7.5% around the level of 50% (fcyclic/fct), with frequencies of 0.25, 1.0, 2.0, and 4.0 Hz over 5000 cycles), on stabilized sandy soils without fiber reinforcement and reinforced with polypropylene or sisal fibers, support the following conclusions:
  • Incorporating fibers into the stabilized sandy soil confers a ductile tensile behavior, which is characterized by a double-peak tensile strength and a noticeable residual tensile strength. This behavior results from a progressive mobilization of fibers crossing the vertical failure surface imposed by the splitting tensile strength tests.
  • A higher number of fibers inside the stabilized matrix (associated with PP fibers) results in a higher probability of the fibers crossing the vertical failure plane. This induces a decrease in the stresses applied to the fibers and a better stress redistribution inside the composite matrix, which allows a more pronounced ductile tensile behavior.
  • During the cyclic stage, the incorporation of fibers and the increase in loading frequency led to a reduction in accumulated plastic axial displacement. On average, the accumulated plastic axial displacement decreased by 28% for polypropylene fibers and 14% for sisal fibers. The frequency dependent behavior is explained by the fact that, for higher frequency levels (4.0 Hz), there is a larger portion of elastic deformation due to the limited displacement mobility and a higher degree of reversibility in deformation due to a decrease in the shear/breakage of cementation bonds (i.e., lower deterioration of the cemented matrix).
  • In terms of maximum tensile strength, the cyclic loading makes sisal fibers a more effective reinforcement than PP fibers due to the greater mechanical characteristics of sisal fibers (higher tensile strength, stiffness, and roughness). The plastic axial displacements induced during the cyclic stage are sufficient to define small vertical cracks. This makes it possible to mobilize the tensile strength of sisal fibers (high stiffness and roughness) from the beginning of the post-cyclic STS test, thus leading to a greater tensile strength. Indeed, it was observed that the post-cyclic tensile strength of sisal fibers increased by 23% to 51%, compared to an increase of 1% to 16% for PP fibers.
  • The frequency level of the cyclic loading does not have a clear tendency regarding the post-cyclic tensile strength behavior, which seems to be related to the materials’ mechanical properties (cemented matrix and fibers).
Finally, it should be emphasized that the above conclusions are valid only for these specific materials (soil, binder, and fibers) and frequencies. Any extrapolation to other soils, fibers, or different testing conditions should be made with caution. Future studies are recommended to investigate the influence of different soil and fiber types, as well as varying binder and fiber contents, in order to assess the broader applicability and generalizability of the findings presented in this work. In addition, future research should include statistical validation of observed trends and examine the long-term durability and potential environmental degradation of fibers, with particular attention to natural fibers.

Author Contributions

A.A.S.C.: Conceptualization, Methodology, Validation, Resources, Writing—Original Draft, Supervision, D.S.G.: Investigation, Validation, Writing—Review and Editing, P.J.V.O.: Conceptualization, Methodology, Validation, Resources, Writing—Review and Editing, Supervision, Project administration. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by Fundação para a Ciência e Tecnologia, through the R&D Units ISISE (UIDB/04029/2020), CERES (10.54499/UIDB/00102/2020, 10.54499/UIDP/00102/2020), and ARISE (LA/P/0112/2020).

Data Availability Statement

Some or all data, models, or code generated or used during the study are available from the corresponding author upon reasonable request.

Acknowledgments

The authors would like to express their thanks to CIMPOR, Biu International and Cotesi for supplying the binders and the fibers, and to the institutions that financially supported the research: FCT (POCI-01-0145-FEDER-028382) and the R&D Units ISISE (UIDB/04029/2020), CERES (10.54499/UIDB/00102/2020, 10.54499/UIDP/00102/2020), and ARISE (LA/P/0112/2020).

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
Cyccyclic stage
D0sample’s initial diameter
Fload (N)
fctmaximum tensile strength (Pa)
IBbrittleness index
PPpolypropylene fiber
STSsplitting tensile strength test
STSpcpost-cyclic splitting tensile strength test
Δδcyc-permvariation in the axial or vertical displacement of the sample during the cyclic stage
δfdisplacement at failure (%)
δpermcumulative plastic displacement or permanent displacement (%)

References

  1. Liu, J.; Bu, F.; Bai, Y.; Chen, Z.; Kanungo, D.P.; Song, Z.; Wang, Y.; Qi, C.; Chen, J. Study on engineering properties of sand strengthened by mixed fibers and polyurethane organic polymer. Bull. Eng. Geol. Environ. 2020, 79, 3049–3062. [Google Scholar] [CrossRef]
  2. Jiang, H.; Cai, Y.; Liu, J. Engineering Properties of Soils Reinforced by Short Discrete Polypropylene Fiber. J. Mater. Civ. Eng. 2010, 22, 1315–1322. [Google Scholar] [CrossRef]
  3. Li, H.; Senetakis, K.; Khoshghalb, A. On the small-strain stiffness of polypropylene fibre-sand mixtures. Geosynth. Int. 2019, 26, 66–80. [Google Scholar] [CrossRef]
  4. Liu, C.Y.; Lv, Y.; Yu, X.; Wu, X. Effects of freeze-thaw cycles on the unconfined compressive strength of straw fiber-reinforced soil. Geotext. Geomembr. 2020, 48, 581–590. [Google Scholar] [CrossRef]
  5. Yixian, W.; Panpan, G.; Shengbiao, S.; Haiping, Y.; Binxiang, Y. Study on Strength Influence Mechanism of Fiber-Reinforced Expansive Soil Using Jute. Geotech. Geol. Eng. 2016, 34, 1079–1088. [Google Scholar] [CrossRef]
  6. Hejazi, S.M.; Sheikhzadeh, M.; Abtahi, S.M.; Zadhoush, A. A simple review of soil reinforcement by using natural and synthetic fibers. Constr. Build. Mater. 2012, 30, 100–116. [Google Scholar] [CrossRef]
  7. Pradhan, P.K.; Kar, R.K.; Naik, A. Effect of Random Inclusion of Polypropylene Fibers on Strength Characteristics of Cohesive Soil. Geotech. Geol. Eng. 2012, 30, 15–25. [Google Scholar] [CrossRef]
  8. Lirer, S.; Flora, A.; Consoli, N.C. On the Strength of Fibre-Reinforced Soils. Soils Found. 2011, 51, 601–609. [Google Scholar] [CrossRef]
  9. Silva dos Santos, A.P.; Consoli, N.C.; Baudet, B.A. The mechanics of fibre-reinforced sand. Géotechnique 2010, 60, 791–799. [Google Scholar] [CrossRef]
  10. Consoli, N.C.; Casagrande, M.D.; Coop, M.R. Effect of Fiber Reinforcement on the Isotropic Compression Behavior of a Sand. J. Geotech. Geoenviron. Eng. 2005, 131, 1434–1436. [Google Scholar] [CrossRef]
  11. Kanchi, G.M.; Neeraja, V.S.; Babu, G.L.S. Effect of Anisotropy of Fibers on the Stress-Strain Response of Fiber-Reinforced Soil. Int. J. Geomech. 2015, 15, 06014016. [Google Scholar] [CrossRef]
  12. Tang, C.S.; Wang, D.Y.; Cui, Y.J.; Shi, B.; Li, J. Tensile strength of fiber-reinforced soil. J. Mater. Civ. Eng. 2016, 28, 04016031. [Google Scholar] [CrossRef]
  13. Li, H.; Senetakis, K. Dynamic properties of polypropylene fibre-reinforced silica quarry sand. Soil Dyn. Earthq. Eng. 2017, 100, 224–232. [Google Scholar] [CrossRef]
  14. Orakoglu, M.E.; Liu, J.; Niu, F. Dynamic behavior of fiber-reinforced soil under freeze-thaw cycles. Soil Dyn. Earthq. Eng. 2017, 101, 269–284. [Google Scholar] [CrossRef]
  15. Festugato, L.; Consoli, N.C.; Fourie, A. Cyclic shear behaviour of fibre-reinforced mine tailings. Geosynth. Int. 2015, 22, 196–206. [Google Scholar] [CrossRef]
  16. Güllü, H.; Khudir, A. Effect of freeze–thaw cycles on unconfined compressive strength of fine-grained soil treated with jute fiber, steel fiber and lime. Cold Reg. Sci. Technol. 2014, 106, 55–65. [Google Scholar] [CrossRef]
  17. Hasanzadeh, A.; Shooshpasha, I. Influences of silica fume particles and polyethylene terephthalate fibers on the mechanical characteristics of cement-treated sandy soil using ultrasonic pulse velocity. Bull. Eng. Geol. Environ. 2021, 81, 14. [Google Scholar] [CrossRef]
  18. Ghadakpour, M.; Fakhrabadi, A.; Janalizadeh Choobbasti, A.; Soleimani Kutanaei, S.; Vafaei, A.; Taslimi Paein Afrakoti, M.; Eisazadeh, N. Effect of post-construction moisture condition on mechanical behaviour of Fiber-reinforced-cemented-sand (FRCS). Geomech. Geoengin. 2022, 17, 1852–1864. [Google Scholar] [CrossRef]
  19. Haghighatjoo, S.M.; Zolfegharifar, S.Y. Effects of fibre type and content on unconfined compressive strength of fibre-reinforced lime or cement-stabilised soils. Geomech. Geoengin. 2022, 17, 1962–1972. [Google Scholar] [CrossRef]
  20. Olgun, M. Effects of polypropylene fiber inclusion on the strength and volume change characteristics of cement-fly ash stabilized clay soil. Geosynth. Int. 2013, 20, 263–275. [Google Scholar] [CrossRef]
  21. Tang, C.; Shi, B.; Gao, W.; Chen, F.; Cai, Y. Strength and mechanical behavior of short polypropylene fiber reinforced and cement stabilized clayey soil. Geotext. Geomembr. 2007, 25, 194–202. [Google Scholar] [CrossRef]
  22. Sukontasukkul, P.; Jamsawang, P. Use of steel and polypropylene fibers to improve flexural performance of deep soil–cement column. Constr. Build. Mater. 2012, 29, 201–205. [Google Scholar] [CrossRef]
  23. Correia, A.A.S.; Venda Oliveira, P.J.; Custódio, D.G. Effect of polypropylene fibres on the compressive and tensile strength of a soft soil, artificially stabilised with binders. Geotext. Geomembr. 2015, 43, 97–106. [Google Scholar] [CrossRef]
  24. Venda Oliveira, P.J.; Correia, A.A.S.; Teles, J.M.N.P.C.; Custódio, D.G. Effect of fibre type on the compressive and tensile strength of a soft soil chemically stabilised. Geosynth. Int. 2016, 23, 171–182. [Google Scholar] [CrossRef]
  25. Consoli, N.C.; Moraes, R.R.; Festugato, L. Split tensile strength of monofilament polypropylene fiber-reinforced cemented sandy soils. Geosynth. Int. 2011, 18, 57–62. [Google Scholar] [CrossRef]
  26. Consoli, N.C.; Moraes, R.R.; Festugato, L. Parameters Controlling Tensile and Compressive Strength of Fiber-Reinforced Cemented Soil. J. Mater. Civ. Eng. 2013, 25, 1568–1573. [Google Scholar] [CrossRef]
  27. Consoli, N.C.; Moraes, R.R.; Festugato, L. Variables controlling strength of fibre-reinforced cemented soils. Proc. Inst. Civ. Eng.—Ground Improv. 2013, 166, 221–232. [Google Scholar] [CrossRef]
  28. Consoli, N.C.; Vendruscolo, M.A.; Fonini, A.; Rosa, F.D. Fiber reinforcement effects on sand considering a wide cementation range. Geotext. Geomembr. 2009, 27, 196–203. [Google Scholar] [CrossRef]
  29. Park, S.S. Unconfined compressive strength and ductility of fiber-reinforced cemented sand. Constr. Build. Mater. 2011, 25, 1134–1138. [Google Scholar] [CrossRef]
  30. Kumar, A.; Gupta, D. Behavior of cement-stabilized fiber-reinforced pond ash, rice husk ash–soil mixtures. Geotext. Geomembr. 2016, 44, 466–474. [Google Scholar] [CrossRef]
  31. Correia, A.A.S.; Venda Oliveira, P.J.; Teles, J.M.N.P.C.; Pedro, A.M.G. Strength of a stabilised soil reinforced with steel fibres. Proc. Inst. Civ. Eng.—Geotech. Eng. 2017, 170, 312–321. [Google Scholar] [CrossRef]
  32. Akbari, H.R.; Sharafi, H.; Goodarzi, A.R. Effect of polypropylene fiber inclusion in kaolin clay stabilized with lime and nano-zeolite considering temperatures of 20 and 40 °C. Bull. Eng. Geol. Environ. 2021, 80, 1841–1855. [Google Scholar] [CrossRef]
  33. Venda Oliveira, P.J.; Correia, A.A.S.; Teles, J.M.N.P.C.; Pedro, A.M.G. Effect of cyclic loading on the behaviour of a chemically stabilised soft soil reinforced with steel fibres. Soil Dyn. Earthq. Eng. 2017, 92, 122–125. [Google Scholar] [CrossRef]
  34. Venda Oliveira, P.J.; Correia, A.A.S.; Cajada, J.C.A. Effect of the type of soil on the cyclic behaviour of chemically stabilised soils unreinforced and reinforced with polypropylene fibres. Soil Dyn. Earthq. Eng. 2018, 115, 336–343. [Google Scholar] [CrossRef]
  35. Chauhan, M.S.; Mittal, S.; Mohanty, B. Performance evaluation of silty sand subgrade reinforced with fly ash and fibre. Geotext. Geomembr. 2008, 26, 429–435. [Google Scholar] [CrossRef]
  36. Yang, C.; Cui, Y.J.; Pereira, J.M.; Huang, M.S. A constitutive model for unsaturated cemented soils under cyclic loading. Comput. Geotech. 2008, 35, 853–859. [Google Scholar] [CrossRef]
  37. Viana da Fonseca, A.; Rios, S.; Amaral, M.F.; Panico, F. Fatigue Cyclic Tests on Artificially Cemented Soil. Geotech. Test. J. 2013, 36, 1–9. [Google Scholar] [CrossRef]
  38. Subramaniam, P.; Banerjee, S. Factors affecting shear modulus degradation of cement treated clay. Soil Dyn. Earthq. Eng. 2014, 65, 181–188. [Google Scholar] [CrossRef]
  39. Sharma, S.S.; Fahey, M. Degradation of Stiffness of Cemented Calcareous Soil in Cyclic Triaxial Tests. J. Geotech. Geoenviron. Eng. 2003, 129, 619–629. [Google Scholar] [CrossRef]
  40. Venda Oliveira, P.J.; Anunciação, G.R.; Correia, A.A.S. Effect of Cyclic Loading Frequency on the Behavior of a Stabilized Sand Reinforced with Polypropylene and Sisal Fibers. J. Mater. Civ. Eng. 2022, 34, 06021008. [Google Scholar] [CrossRef]
  41. Festugato, L.; Fourie, A.; Consoli, N.C. Cyclic shear response of fibre-reinforced cemented paste backfill. Géotechnique Lett. 2013, 3, 5–12. [Google Scholar] [CrossRef]
  42. Dall’Aqua, G.P.; Ghataora, G.; Ling, U. Behaviour of fibre-reinforced and stabilized clayey soils subjected to cyclic loading. Stud. Geotech. Et Mech. 2010, 32, 3–16. [Google Scholar]
  43. Khattak, M.J.; Alrashidi, M. Durability and mechanistic characteristics of fiber reinforced soil–cement mixtures. Int. J. Pavement Eng. 2006, 7, 53–62. [Google Scholar] [CrossRef]
  44. Maher, M.H.; Ho, Y.C. Behavior of Fiber-Reinforced Cemented Sand Under Static and Cyclic Loads. Geotech. Test. J. 1993, 16, 330–338. [Google Scholar] [CrossRef]
  45. Ahmed, A.; Naggar, M.H. Effect of cyclic loading on the compressive strength of soil stabilized with bassanite–tire mixture. J. Mater. Cycles Waste Manag. 2018, 20, 525–532. [Google Scholar] [CrossRef]
  46. Yasuhara, K.; Yamanouchi, T.; Hirao, K. Cyclic Strength and Deformation of Normally Consolidated Clay. Soils Found. 1982, 22, 77–91. [Google Scholar] [CrossRef]
  47. Zhou, J.; Gong, X. Strain degradation of saturated clay under cyclic loading. Can. Geotech. J. 2001, 38, 208–212. [Google Scholar] [CrossRef]
  48. Moses, G.G.; Rao, S.N.; Rao, P.N. Undrained strength behaviour of a cemented marine clay under monotonic and cyclic loading. Ocean Eng. 2003, 30, 1765–1789. [Google Scholar] [CrossRef]
  49. Nguyen, L.D.; Fatahi, B.; Khabbaz, H. A constitutive model for cemented clays capturing cementation degradation. Int. J. Plast. 2014, 56, 1–18. [Google Scholar] [CrossRef]
  50. Wang, K.; Zhuang, Y. Characterizing the permanent deformation Response-Behavior of subgrade material under cyclic loading based on the shakedown theory. Constr. Build. Mater. 2021, 311, 125325. [Google Scholar] [CrossRef]
  51. Yang, D.; Zhuang, X.; Tao, G.; Li, X.; Fang, J. Cumulative plastic strain and shakedown analysis in loess subgrades under intermittent loads. Soil Dyn. Earthq. Eng. 2025, 190, 109224. [Google Scholar] [CrossRef]
  52. Abdullah, H.H.; Shahin, M.A.; Walske, M.L.; Karrech, A. Cyclic behaviour of clay stabilised with fly-ash based geo-polymer incorporating ground granulated slag. Transp. Geotech. 2021, 26, 100430. [Google Scholar] [CrossRef]
  53. ASTM-D2487; Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System). ASTM International: West Conshohocken, PA, USA, 1998.
  54. EN-197-1; Cement—Part 1: Composition, Specifications and Conformity Criteria for Common Cements. European Committee for Standardization: Brussels, Belgium, 2000.
  55. Taylor, H. Cement Chemistry; Thomas Telford: London, UK, 1997. [Google Scholar]
  56. Goulart, D.S. Influence of the Fiber Type in the Mechanical Behavior of a Cemented Sandy Soil Under Static and Dynamic Actions. Master’s Thesis, Univ. of Coimbra, Coimbra, Portugal, 2020. [Google Scholar]
  57. Carvalho, R.; Fangueiro, R.; Neves, J. Durability of Natural Fibers for Geotechnical Engineering. Key Eng. Mater. 2014, 634, 447–454. [Google Scholar] [CrossRef]
  58. Xie, Q.; Li, F.; Li, J.; Wang, L.; Li, Y.; Zhang, C.; Xu, J.; Chen, S. A new biodegradable sisal fiber–starch packing composite with nest structure. Carbohydr. Polym. 2018, 189, 56–64. [Google Scholar] [CrossRef]
  59. Chand, N.; Hashmi, S.A.R. Mechanical properties of sisal fibre at elevated temperatures. J. Mater. Sci. 1993, 28, 6724–6728. [Google Scholar] [CrossRef]
  60. Agboola, O.; Sadiku, E.R.; Popoola, P.; Fayomi, O.S.I.; Ayeni, A.O.; Dick, D.T.; Adegbola, A.T.; Moropeng, L.; Ramakhokhovhu, M. Surface roughness of ternary blends: Polypropylene/chitosan/sisal fiber membranes. Mater. Today Proc. 2021, 38, 2342–2346. [Google Scholar] [CrossRef]
  61. Silveira, M.V.; Casagrande, M.D.T. Effects of Degradation of Vegetal Fibers on the Mechanical Behavior of Reinforced Sand. Geotech. Geol. Eng. 2021, 39, 3875–3887. [Google Scholar] [CrossRef]
  62. Ramakrishna, G.; Sundararajan, T. Studies on the durability of natural fibres and the effect of corroded fibres on the strength of mortar. Cem. Concr. Compos. 2005, 27, 575–582. [Google Scholar] [CrossRef]
  63. Tolêdo Filho, R.D.; Scrivener, K.; England, G.L.; Ghavami, k. Durability of alkali-sensitive sisal and coconut fibres in ce-ment mortar composites. Cem. Concr. Compos. 2000, 22, 127–143. [Google Scholar] [CrossRef]
  64. Zhao, L.; Zhu, S.; Wu, H.; Liang, H.; Liu, C.; Liu, W.; Zhou, W.; Song, Y. The improved resistance against the degradation of sisal fibers under the environment of cement hydration by surface coating of graphene oxide (GO) based membranes. Con-Struction Build. Mater. 2021, 205, 124694. [Google Scholar] [CrossRef]
  65. Wei, J.; Ma, S.; Thomas, D.G. Correlation between hydration of cement and durability of natural fiber-reinforced cement composites. Corros. Sci. 2016, 106, 1–15. [Google Scholar] [CrossRef]
  66. Klerk, M.D.; Kayondo, M.; Moelich, G.M.; Villiers, W.I.; Combrinck, R.; Boshoff, W.P. Durability of chemically modified sisal fibre in cement-based composites. Constr. Build. Mater. 2020, 241, 117835. [Google Scholar] [CrossRef]
  67. EuroSoilStab. Development of design and construction methods to stabilise soft organic soils: Design guide soft soil stabilisation. In Industrial and Materials Technologies Programme (Brite-EuRam III); European Commission: Brussels, Belgium, 2001; p. 94. [Google Scholar]
  68. Correia, A.A.S. Applicability of Deep Mixing Technique to the Soft Soil of Baixo Mondego. PhD Thesis, Univ. of Coimbra, Coimbra, Portugal, 2011. [Google Scholar]
  69. Consoli, N.C.; Foppa, D.; Festugato, L.; Heineck, K.S. Key Parameters for Strength Control of Artificially Cemented Soils. J. Geotech. Geoenviron. Eng. 2007, 133, 197–205. [Google Scholar] [CrossRef]
  70. EN-13286-42; Unbound and Hydraulically Bound Mixtures. Test Method for the Determination of the Indirect Tensile Strength of Hydraulically Bound Mixtures 2011. European Committee for Standardization: Brussels, Belgium, 2011.
  71. NBR-7222; Concrete and Mortar—Determination of the Tension Strength by Diametrical Compression of Cylindrical Test Specimens. ABNT—Brazilian Association of Technical Standards: Rio de Janeiro-RJ, Brazil, 2011.
  72. EN-12390-6; Testing Hardened Concrete. Tensile Splitting Strength of Test Specimens. European Committee for Standardization: Brussels, Belgium, 2011.
  73. Wang, T.; Ye, J.; Zhu, C. Effect of Bi-modulus characteristic on the Brazilian disc test: Insights from numerical study. Int. J. Rock Mech. Min. Sci. 2023, 169, 105447. [Google Scholar] [CrossRef]
  74. Ye, J.; Wu, F.Q.; Sun, J.Z. Estimation of the tensile elastic modulus using Brazilian disc by applying diametrically op-posed concentrated loads. Int. J. Rock Mech. Min. Sci. 2009, 46, 568–576. [Google Scholar]
  75. Ye, J.H.; Wu, F.Q.; Zhang, Y.; Ji, H.G. Estimation of the bi-modulus of materials through deformation measurement in a Brazilian disk test. Int. J. Rock Mech. Min. Sci. 2012, 52, 122–131. [Google Scholar] [CrossRef]
  76. Milliken, W.F.; Milliken, D.L. Race Car Vehicle Dynamics; SAE international: Warrendale, PA, USA, 1995; Volume 400. [Google Scholar]
  77. EN-13286-7; Unbound and Hydraulically Bound Mixtures—Part 7: Cyclic Load Triaxial Test for Unbound Mixtures. European Committee for Standardization: Brussels, Belgium, 2004.
  78. EN-206-1; Concrete—Part 1: Specification, Performance, Production and Conformity. European Committee for Standardization: Brussels, Belgium, 2007.
  79. Duong, N.T.; Satomi, T.; Takahashi, H. Potential of corn husk fiber for reinforcing cemented soil with high water content. Constr. Build. Mater. 2021, 271, 121848. [Google Scholar] [CrossRef]
  80. Consoli, N.C.; Arcari Bassani, M.A.; Festugato, L. Effect of fiber-reinforcement on the strength of cemented soils. Geotext. Geomembr. 2010, 28, 344–351. [Google Scholar] [CrossRef]
  81. Huang, K.; Ma, Q.; Ma, D. Effect of Basalt Fiber on Static and Dynamic Mechanical Properties of Metakaolin-Based Cement Clay. Adv. Civ. Eng. 2020, 1359163. [Google Scholar] [CrossRef]
  82. Hernández-Olivares, F.; Barluenga, G.; Bollati, M.; Witoszek, B. Static and dynamic behaviour of recycled tyre rubber-filled concrete. Cem. Concr. Res. 2002, 32, 1587–1596. [Google Scholar] [CrossRef]
  83. Shao, S.; Khonsari, M.M.; Wang, J.; Shamsaei, N.; Li, N. Frequency dependent deformation reversibility during cyclic loading. Mater. Res. Lett. 2018, 6, 390–397. [Google Scholar] [CrossRef]
  84. Yao, X.; Huang, G.; Wang, M.; Dong, X.Q. Mechanical Properties and Microstructure of PVA Fiber Reinforced Cemented Soil. KSCE J. Civ. Eng. 2021, 25, 482–491. [Google Scholar] [CrossRef]
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Figure 1. Grain size distribution curve of the sandy soil.
Figure 1. Grain size distribution curve of the sandy soil.
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Figure 2. Fibers used in the investigation: (a) polypropylene fibers; (b) sisal fibers.
Figure 2. Fibers used in the investigation: (a) polypropylene fibers; (b) sisal fibers.
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Figure 3. Preparation and testing of the samples. (a) rectification of the top surface of the sample; (b) sample after unmolding; (c) axial cyclic load test machine (GDS Dynamic Triaxial Testing System); (d) sample at the end of an STS test.
Figure 3. Preparation and testing of the samples. (a) rectification of the top surface of the sample; (b) sample after unmolding; (c) axial cyclic load test machine (GDS Dynamic Triaxial Testing System); (d) sample at the end of an STS test.
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Figure 4. Effect of the frequency on the accumulated plastic displacement with the number of load cycles for: (a) unreinforced stabilized soil; (b) stabilized soil reinforced with PP fibers; (c) stabilized soil reinforced with sisal fibers.
Figure 4. Effect of the frequency on the accumulated plastic displacement with the number of load cycles for: (a) unreinforced stabilized soil; (b) stabilized soil reinforced with PP fibers; (c) stabilized soil reinforced with sisal fibers.
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Figure 5. Effect of the frequency on the accumulated plastic displacement for 5000 loading cycles, for unreinforced stabilized soil and stabilized soil reinforced with PP and sisal fibers.
Figure 5. Effect of the frequency on the accumulated plastic displacement for 5000 loading cycles, for unreinforced stabilized soil and stabilized soil reinforced with PP and sisal fibers.
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Figure 6. Load-displacement curves of the static (monotonic) STS tests performed prior to the cyclic stage for the unreinforced stabilized soil and for the stabilized soil reinforced with polypropylene and sisal fibers.
Figure 6. Load-displacement curves of the static (monotonic) STS tests performed prior to the cyclic stage for the unreinforced stabilized soil and for the stabilized soil reinforced with polypropylene and sisal fibers.
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Figure 7. Influence of the frequency on the tensile load-displacement curves of the splitting tensile strength tests performed prior to (STS) and after the cyclic loading stage (STSpc) for the following materials: (a) stabilized soil without fiber reinforcement; (b) soil stabilized and reinforced with PP fibers; (c) soil stabilized and reinforced with sisal fibers.
Figure 7. Influence of the frequency on the tensile load-displacement curves of the splitting tensile strength tests performed prior to (STS) and after the cyclic loading stage (STSpc) for the following materials: (a) stabilized soil without fiber reinforcement; (b) soil stabilized and reinforced with PP fibers; (c) soil stabilized and reinforced with sisal fibers.
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Figure 8. Effect of the frequency on the splitting tensile strength (fct) evaluated through tests carried out before (STS) and after (STSpc) the cyclic stage for unreinforced stabilized soil and stabilized soil reinforced with PP or sisal fibers.
Figure 8. Effect of the frequency on the splitting tensile strength (fct) evaluated through tests carried out before (STS) and after (STSpc) the cyclic stage for unreinforced stabilized soil and stabilized soil reinforced with PP or sisal fibers.
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Figure 9. Influence of the frequency on the brittleness index (IB) evaluated from splitting tensile strength tests performed both prior to (STS) and after (STSpc) the cyclic loading stage for stabilized soils without fiber reinforcement and those reinforced with polypropylene or sisal fibers.
Figure 9. Influence of the frequency on the brittleness index (IB) evaluated from splitting tensile strength tests performed both prior to (STS) and after (STSpc) the cyclic loading stage for stabilized soils without fiber reinforcement and those reinforced with polypropylene or sisal fibers.
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Table 1. Summary of the experimental program and quantity of tests performed (STS, Cyc, STSpc).
Table 1. Summary of the experimental program and quantity of tests performed (STS, Cyc, STSpc).
Type of FibersType of TestMonotonic StageCyclic Stage—Frequency (Hz)
0.251.02.04.0
UnreinforcedSTS2--------
Cyc--2222
STSpc--2222
Polypropylene fibers
(10 kg/m3)		STS2--------
Cyc--2222
STSpc--2222
Sisal fibers
(10 kg/m3)		STS2--------
Cyc--2222
STSpc--2222
STS: STS test without a cyclic stage; Cyc: Cyclic stage; STSpc: STS test carried out after the cyclic stage.
Table 2. Characteristics of the constituent materials: binder, polypropylene (PP), and sisal (S) fibers.
Table 2. Characteristics of the constituent materials: binder, polypropylene (PP), and sisal (S) fibers.
Portland Cement Type I 42.5 R *
CaO
(%)		SiO2 (%)Al2O3 (%)Fe2O3 (%)SO2
(%)		MgO (%)K2O
(%)		Na2O (%)
62.88195.153.193.142.161.290.1
Fibers
L
(mm)		D
(mm)		L/D
(-)		fct
(MPa)		E
(GPa)		Surface Texture Roughness &Biodegradabilityρ
(g/cm3)
Polypropylene *12323752503.5–3.9LowerNot biodegradable0.905
Sisal #121408655826HigherBiodegradable≈1.4
L—Length; D—diameter; L/D—aspect ratio; fct—tensile strength; E—elasticity modulus; ρ—density. * manufacturer’s data. # Refs. [56,57,58,59]. & Ref. [60].
Table 3. Tensile load of the STS and STSpc tests.
Table 3. Tensile load of the STS and STSpc tests.
TestTensile Load, F (N)
T1T2AverageDrel * (%)
Soil without fibersSTS (Monotonic)9028.18855.28941.70.97%
STSpc (f = 0.25 Hz)9310.78495.98903.34.58%
STSpc (f = 1.0 Hz)9135.19804.59469.83.53%
STSpc (f = 2.0 Hz)7870.47640.07755.21.49%
STSpc (f = 4.0 Hz)8438.39140.68789.44.00%
Soil + PP
fibers		STS (Monotonic)9521.99519.29520.50.01%
STSpc (f = 0.25 Hz)10,805.811,370.811,088.32.55%
STSpc (f = 1.0 Hz)9414.910,918.310,166.67.39%
STSpc (f = 2.0 Hz)9568.59741.49655.00.90%
STSpc (f = 4.0 Hz)9631.69639.89635.70.04%
Soil + Sisal
fibers		STS (Monotonic)8737.38734.58735.90.02%
STSpc (f = 0.25 Hz)10,970.310,487.510,728.92.25%
STSpc (f = 1.0 Hz)13,428.212,937.213,182.71.86%
STSpc (f = 2.0 Hz)11,431.111,096.511,263.81.49%
STSpc (f = 4.0 Hz)11,532.710,479.311,006.04.79%
(*) relative deviation from the mean = T i − T ¯ / T ¯ .
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Correia, A.A.S.; Goulart, D.S.; Venda Oliveira, P.J. Tensile Behavior of a Fiber-Reinforced Stabilized Soil—Cyclic Loading Frequency Study. Appl. Sci. 2025, 15, 8825. https://doi.org/10.3390/app15168825

AMA Style

Correia AAS, Goulart DS, Venda Oliveira PJ. Tensile Behavior of a Fiber-Reinforced Stabilized Soil—Cyclic Loading Frequency Study. Applied Sciences. 2025; 15(16):8825. https://doi.org/10.3390/app15168825

Chicago/Turabian Style

Correia, António A. S., Daniel S. Goulart, and Paulo J. Venda Oliveira. 2025. "Tensile Behavior of a Fiber-Reinforced Stabilized Soil—Cyclic Loading Frequency Study" Applied Sciences 15, no. 16: 8825. https://doi.org/10.3390/app15168825

APA Style

Correia, A. A. S., Goulart, D. S., & Venda Oliveira, P. J. (2025). Tensile Behavior of a Fiber-Reinforced Stabilized Soil—Cyclic Loading Frequency Study. Applied Sciences, 15(16), 8825. https://doi.org/10.3390/app15168825

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