Mechanical Properties of Permeable Concrete Reinforced with Polypropylene Fibers for Different Water–Cement Ratios

Abstract

Permeable concrete is a material that allows water filtration, reduces surface runoff, and maintains the natural water cycle. Previous studies have shown that its mechanical properties, particularly its compressive and flexural tensile strengths, are generally lower than those of conventional concrete, with significant variability observed among similar tests. This study investigates the compressive strength, flexural strength, and permeability of polypropylene fiber-reinforced permeable concrete specimens at two water–cement ratios (0.30 and 0.35). The mix design was conducted using the ACI 522R-10 method. Forty-eight cylinders measuring 200 mm × 100 mm were fabricated for permeability and compression tests. Additionally, 12 beams measuring 100 mm × 100 mm × 350 mm were produced and subjected to simple flexural testing in accordance with ASTM C78 guidelines. Compressive strength versus permeability and load versus deflection graphs were plotted, and the fracture energy was calculated for various deflections. The results indicate that the addition of fibers increased permeability and tensile strength but decreased compressive strength. Furthermore, an increase in the water–cement ratio led to higher compressive and flexural tensile strengths.

1. Introduction

Concrete is the most widely used construction material globally, with its versatility and strength forming the foundation of most modern structures. However, the extensive use of conventional concrete can lead to significant environmental consequences, including increased surface water runoff and high CO₂ emissions, among others [1]. Surface runoff can significantly disrupt the water cycle by impeding the natural recharge of water sources [2]. To mitigate this issue, sustainable urban development systems (SUDS) have been developed, including porous pavements that utilize permeable concrete [3,4]. This material has gained traction in countries such as the United States and Japan due to its environmental benefits, which include the control of surface runoff, facilitation of groundwater recharge, and reduction of water [5]. Permeable concrete has been employed in numerous structures such as walkways, parking lots, and recreational areas, and even as a granular sub-base for roads [6,7,8].

Permeable concrete is a special type of concrete with a high filtration capacity, achieved by reducing the amount of fine aggregate in the mix, resulting in a high porosity content ranging between 15 and 30% of the element’s volume [9,10]. Its production involves essentially the same materials as traditional concrete, namely, Portland cement, aggregate, water, and optional additives [11]. However, the amount of cement paste in the mix must be controlled as an excess can lead to pore blockage [12,13]; thus, the recommended paste values are 15–30% of the specimen’s volume. Its water–cement ratio (w/c) differs from that of traditional concrete, being relatively low, typically ranging from 0.28 to 0.40 [14]. Consistency is crucial; a very low w/c ratio fails to provide the necessary cohesion for particle bonding, while a high ratio results in a very fluid mixture where particles are unable to form the necessary network [15].

The porosity of such concretes depends on various factors such as the type and size of aggregate used and even the compaction method. Coarse aggregate size for this type of concrete can range from 19 to 10 mm [16,17] with minimal or no sand presence. This allows for the creation of an interconnected network forming the pores. The most relevant properties of this material include permeability, varying from 0.2–1.2 cm/s, and compressive strength, ranging from 3.5–28 MPa [18,19]. However, as it is often used as pavement, its flexural strength is also important, typically ranging from 0.68 to 2.15 MPa [20,21].

Permeable concrete, due to its high void content, typically exhibits lower compressive and flexural strengths compared to traditional concrete [22]. Previous research has demonstrated an inverse relationship between permeability and mechanical strength; increasing permeability requires a higher pore quantity, thereby reducing the effective stress-resisting area [23]. Consequently, a key challenge in permeable concrete design is to find an optimal balance between permeability and strength to meet specific project requirements.

Studies suggest that the addition of small quantities of polypropylene fibers, approximately 0.15% to 0.2% by volume, enhances the compressive strength of permeable concrete relative to non-fiber mixes [24]. Polypropylene fiber-reinforced concrete has attracted significant research interest, particularly for high-temperature applications, due to the fibers’ strengths, elasticity, and resistance to harsh environments. These lightweight fibers, characterized by their large surface area, form a three-dimensional reinforcing network within the concrete matrix, improving overall performance. The incorporation of polypropylene fibers has been shown to enhance various physical and mechanical properties of concrete, including increased crack and impact resistance, improved delamination resistance, enhanced compressive and tensile strength, increased durability, reduced surface abrasion, improved impact toughness, mitigation of shrinkage and cracking, and increased frost and water resistance [25,26,27,28].

Despite the sustainable advances of permeable concrete in pavement constructions and the numerous benefits offered by fiber reinforcement, research on polypropylene fiber-reinforced permeable concrete remains limited. This scarcity of data contributes to significant variability in research outcomes and a lack of standardized testing protocols. These factors complicate result comparison and analysis, ultimately hindering the widespread adoption of this technology [29].

This research presents an analysis of the physical and mechanical properties of permeable concrete reinforced with polypropylene fibers, with different water-to-cement ratios (w/c). Compression strength and permeability tests were conducted using three coarse aggregate sizes (19 mm, 13 mm, and 9.5 mm). Based on the initial results, the 13 mm aggregate was selected for further experimentation. Compression and flexural strength tests were performed on mixtures with w/c ratios of 0.30 and 0.35 incorporating polypropylene fibers at 0 and 0.6 kg/m³. Compressive strength versus permeability and load versus deflection relationships were plotted. Fracture energy was calculated for various deflection levels.

Key findings include a direct relationship between permeability and porosity. Moreover, an inverse relationship between porosity and compressive strength was identified. The effects of polypropylene fiber addition and w/c ratio variation on permeability, flexural tensile strength, and fracture energy are discussed.

2. Materials and Methods

Initially, 18 cylindrical specimens of permeable concrete (200 mm × 100 mm) were prepared, using three coarse aggregate sizes (9.5 mm, 13 mm, and 19 mm), and subjected to compression and permeability tests. The aim was to determine the optimal coarse aggregate size that would provide adequate compressive strength and permeability. Based on these results, the 13 mm aggregate was selected for further experimentation. Subsequently, 48 permeable concrete cylinders were fabricated as follows: 24 cylinders with a water–cement ratio of 0.30 (12 with polypropylene fibers and 12 without fibers). Additionally, other 24 cylindrical specimens with a water–cement ratio of 0.35 were produced (12 with polypropylene fibers and 12 without fibers). These samples were evaluated for porosity, permeability, and compressive strength. Furthermore, 12 beam samples (100 mm × 100 mm × 350 mm) were prepared for each water–cement ratio of 0.30 and 0.35 (6 beams with polypropylene fibers and 6 beams without fibers). These beams were used to analyze flexural behavior and fracture energy. Polypropylene fibers measuring 50 mm in length were used in all fiber-reinforced samples.

2.1. Materials

Based on a review of previous research, and common construction industry practices, siliceous aggregate was used in three sizes: 19 mm, 13 mm, and 9.5 mm. The properties of these aggregates are described in

Table 1. Properties of stone aggregates.

Property	Coarse Aggregate (Gravel)			Fine Aggregate (Sand)
	19 mm	13 mm	9.5 mm
Fineness Modulus (%)	-	-	-	2.530
Real Density (g/cm3)	2.739	2.508	2.53	2.157
Absorption Capacity (%)	1.940	2.280	2.50	2.440
Loose Bulk Density (kg/dm3)	1.296	1.301	1.31	1.578
Compacted Bulk Density (kg/dm3)	1.444	1.497	1.51	1.643

. The physical properties of the aggregates, necessary for the design of the mixture, were determined using tests of particle size distribution [30], volumetric weight [31], and relative density and absorption capacity of fine and coarse aggregate [32,33]. Polypropylene microfibers (50 mm in length) were employed, with properties as outlined in

Table 2. Polypropylene microfiber properties.

Polypropylene Fiber	Properties
Length (mm)	50
Shape	Straight
Density (g/cm3)	0.91 (±0.01%)
Modulus of Elasticity (MPa)	≥5000
Tensile Strength (MPa)	≥500
Elongation at Brake (%)	≥20
Surface	Rough

, along with general-purpose Portland cement type GU.

2.2. Coarse Aggregate Selection

Eighteen cylindrical samples of permeable concrete (200 mm × 100 mm) were prepared, using three coarse aggregate sizes (9.5 mm, 13 mm, and 19 mm) to determine the optimal particle size for subsequent stages. The mix design followed the ACI 522R-10 method [20], with the following composition: 10% cement paste content, 10% fine aggregate, and a water-to-cement ratio (w/c) of 0.41, as described in

Table 3. Dosages for 3 sizes of coarse aggregate.

Dosage	P-1	P-2	P-3
Particle size (mm)	19.00	13.00	9.50
Number of Cylinders	6.00	6.00	6.00
w/c	0.41	0.41	0.41
Coarse Aggregate (kg/m3)	1310.03	1364.26	1376.76
Fine Aggregate (kg/m3)	143.69	150.06	151.88
Water (kg/m3)	110.98	109.71	113.98
Cement (kg/m3)	265.12	265.12	265.07

. The cylinders were prepared in accordance with ASTM C31 [34], compacted in 2 layers with 25 strokes per layer, and then cured by submersion in a tank at 23 ± 2 °C for 28 days. Subsequently, compression tests were conducted using a Shimadzu model 2000X universal testing machine (load capacity 2000 kN), in accordance with ASTM C39 [35].

Based on the results of the preliminary permeability and compression tests, it was observed that the 9.5 mm aggregate provided the highest compressive strength and the lowest permeability. In contrast, the 19 mm aggregate showed the highest permeability and the lowest compressive strength. Therefore, it was decided to use the 13 mm aggregate as it offers an intermediate balance between compressive strength and permeability. Following aggregate selection, mix designs were prepared for water–cement (w/c) ratios of 0.30 and 0.35, in accordance with previous research suggesting optimal values near 0.32.

For each w/c ratio, 24 cylinders (200 mm × 100 mm) were fabricated, 12 with fibers and 12 without fibers (48 cylinders in total). Additionally, 12 beams in total (100 mm × 100 mm × 350 mm) were prepared, 3 with fibers and 3 without fibers for both w/c ratios. The mix proportions for these samples are detailed in

Table 4. Dosage for different water-cement ratios.

Dosage	1PC	1PCF	2PC	2PCF
Aggregate Size (mm)	13.00	13.00	13.00	13.00
w/c Ratio	0.30	0.30	0.35	0.35
Coarse Aggregate (kg/m3)	1300.34	1300.34	1299.99	1299.99
Fine Aggregate (kg/m3)	231.87	231.87	226.35	226.35
Water (kg/m3)	104.94	104.94	113.41	113.41
Cement (kg/m3)	349.79	349.78	324.03	324.03
Fiber (kg/m3)	-	0.60	-	0.60
Plasticizer (kg/m3)	1.75	1.75	1.62	1.62

. Samples prepared were labelled as follows: 1PCF permeable concrete, w/c ratio 0.30 with polypropylene fibers; 1PC permeable concrete without fibers, w/c 0.30; 2PCF permeable concrete, w/c ratio 0.35 with polypropylene fibers; and 2PC permeable concrete without fibers, w/c 0.35.

All samples were subjected to compression, permeability, and flexural strength tests at 28 days of age.

2.3. Permeability

A variable head permeameter made of polyvinyl chloride (PVC) was used to determine the permeability, following the Neithenatath model [17,20,36]. This instrument has a cylinder to immerse the samples and a valve to allow water flow, as shown in Figure 1.

Before the test, the samples were covered with plastic to prevent lateral leaks, and the permeability index was determined using Darcy’s formula.

$$\mathrm{k}={\displaystyle \frac{\mathrm{Atube}\times \mathrm{L}}{\mathrm{Acylinder}\times \mathrm{t}}}\times \ln \left({\displaystyle \frac{\mathrm{ho}}{\mathrm{h}1}}\right)$$

(1)

The void volume was calculated using Archimedes’ principle. Each sample was immersed in a 15 L water-filled container causing water displacement. The volume of displaced water, equivalent to the volume of the porous concrete samples, was measured. The percentage of voids was then calculated as the difference between the samples’ geometric volume and the measured displaced volume, as shown in Equation (2).

$$\%\mathrm{V}=\left(V_{\mathrm{T}}-V_{\mathrm{M}}\right)\times {\displaystyle \frac{100}{{\mathrm{V}}_{\mathrm{T}}}}$$

(2)

2.4. Compressive Strength

Compressive strength tests were conducted on 48 permeable concrete cylinders using a Shimadzu 2000X testing machine. There were 24 cylinders with a w/c ratio of 0.30 (12 with fibers, 12 without fibers), and 24 cylinders with a w/c ratio of 0.35 (12 with fibers, 12 without fibers). To address the irregular surface characteristic of permeable concrete, resulting from the low fines content in its mix design, neoprene caps were employed during testing, in accordance with ASTM C39 [35]. The samples were loaded to failure following ASTM C1231 [37] protocol, as illustrated in Figure 2. Comparative graphs of compressive strength were plotted as a function of the w/c ratio to analyze the results.

2.5. Flexural Strength

Twelve beams (100 mm × 100 mm × 350 mm) were prepared. The tests were conducted at 28 days using a Shimadzu model 2000X universal testing machine, following the 4-point bending method as specified in ASTM C78 [38]. Steel supports were used to position the samples in the machine; the supports were placed at the third point of each sample’s span, as shown in Figure 3.

The flexural testing procedure varied based on sample composition: In the concrete samples without fibers, load was applied until failure occurred, while for samples reinforced with fibers, testing was stopped upon reaching 2 mm of deflection. Residual stresses were calculated at L/600 and L/150, in accordance with ASTM C1609 [39]; load (KN) versus deflection (mm) curves were plotted for analysis. Additionally, fracture energy was calculated for both 1 mm and 2 mm deflections using Equation (3).

$$R={\displaystyle \frac{W}{b\times d}}$$

(3)

The results obtained from each stage of experiments were processed using Excel Microsoft Office 365 version 2408 spreadsheets and are presented in tables and figures throughout this paper.

3. Analysis and Discussion of Results

3.1. Coarse Aggregate Selection

Eighteen cylinders, incorporating three different sizes coarse aggregate, were tested for permeability and compressive strength. Figure 4 and Figure 5 present the average results from six samples for each aggregate size. The standard deviations for the permeability test were 0.028 cm/s for the 19 mm aggregate, 0.027 cm/s for the 13 mm aggregate, and 0.005 cm/s for the 9.5 mm aggregate. Meanwhile, for the compression tests, the standard deviations were 0.075 MPa for the 19 mm aggregate, 0.054 MPa for the 13 mm aggregate, and 0.086 MPa for the 9.5 mm aggregate. As illustrated in Figure 4, the 19 mm aggregate exhibited the highest permeability, while the 9.5 mm aggregate showed the lowest. The reason behind this can be attributed to the spatial distribution of particles: Small particles tend to pack more efficiently, resulting in smaller interstitial voids that can be partially filled by cement paste, thereby reducing permeability.

A comparative analysis of permeability and compressive strength was conducted for the three coarse aggregate sizes, as shown in Figure 5. It is observed that the 19 mm aggregate exhibits the highest permeability index; however, its compressive strength results are the lowest. On the other hand, the 13 mm aggregate shows average strength and permeability compared to the other two aggregates. The 9.5 mm aggregate presented the highest strength; nevertheless, its permeability was the lowest (although within the recommended range). The inverse relationship between compressive strength and permeability is generally expected, as higher permeability implies greater porosity and, consequently, a reduced load-bearing cross-section. This results in a lower capacity to resist compressive stresses, as observed in the 19 mm aggregate. Based on these results, the 13 mm aggregate was selected for subsequent phases of the study, as it provided an optimal balance between strength and permeability. This selection aligns with findings from similar studies [40].

3.2. Permeability

Twenty-four cylindrical samples (20 cm height) were fabricated using the 13 mm aggregate to assess permeability. The samples were divided into two groups based on w/c ratios: 12 samples with w/c ratio of 0.30 (1PC, 1PCF), and 12 samples with w/c ratio of 0.35 (2PC, 2PCF). Figure 6 illustrates the relationship between porosity and permeability index. A linear relationship was observed, with the correlation coefficient (r) approaching 1.0; this suggests that increased porosity corresponds to a greater volume of voids through which water can permeate, consistent with findings in previous studies [41]. As key observations, it can be mentioned that (1) 1PCF mix (with fibers, w/c = 0.30) presents the highest porosity (22.55%) and (2) porosity increases by 5% for both samples with fibers.

The porosity for 1PC (without fibers, w/c = 0.30) is 21.37%, while 2PCF (with fibers, w/c = 0.35) has a porosity of 21.97% and 2PC (without fibers, w/c = 0.35) has a 20.90% porosity. The porosity values obtained in this study were compared with the limits specified by ACI 522R-10 [20] and NBR 16416/2015 [42] standards. It is important to mention that all samples fell within the recommended range of 15–30%, as shown in

Table 5. Recommended normative values.

Standard	Compressive Strength	Flexural Strength	Porosity	Permeability Index
	MPa	MPa	%	(cm/s)
ACI 522R-10	6.8–25.0	2.8–3.6	15–30	>0.1
NBR 16416/2015	20.0–35.0	>1.00	15–30	>0.1

.

The permeability index results for different mix designs are summarized as follows: (1) With a w/c ratio of 0.30, for the 1PC (0.285 cm/s) and 1PCF (0.33 cm/s) samples, the addition of fibers in 1PCF increased the permeability by 16%. (2) With a w/c ratio of 0.35, the 2PC (0.265 cm/s) and 2PCF (0.31 cm/s) samples showed a permeability increase of 17% due to the fiber addition.

The obtained porosity and permeability results were compared, as shown in Figure 6, obtained from ACI 522R-10 [20], which illustrates the relationship between porosity and permeability. According to this figure, 20% porosity corresponds to an expected permeability of 0.21 cm/s, while 23% porosity corresponds to an expected permeability of 0.36 cm/s. The results obtained for both w/c ratios fall within the range of values consistent with ACI guidelines. The results were also compared using the Brazilian standard NBR 16416/2015 [42]; the porosity falls between 15 and 30%, and the permeability is greater than 0.1 cm/s, as recommended by the standard. These results are summarized in Table 5.

3.3. Compressive Strength

Figure 7 and Figure 8 illustrate the compressive strength and permeability results for samples with water–cement (w/c) ratios of 0.30 and 0.35, both with and without fiber reinforcement.

For samples with a w/c ratio of 0.30, the average compressive strengths were 11.50 MPa for 1PC and 9.70 MPa for 1PCF. For samples with a w/c ratio of 0.35, the average compressive strengths were 12.26 MPa for 2PC and 10.98 MPa for 2PCF.

Previous investigations [43] reported that the compressive strength of permeable concrete reinforced with polypropylene fibers was 9.78 MPa for a w/c ratio of 0.30 and 10.94 MPa for a w/c ratio of 0.35, which is consistent with the values obtained in this study.

The analysis indicates that the addition of polypropylene fibers resulted in a 16% reduction in compressive strength for the w/c ratio of 0.30 and an 11% reduction for the w/c ratio of 0.35. This tendency has also been observed in other studies on both permeable and conventional concrete [44,45].

Comparing the specimens without fibers (1PC and 2PC), the variation in compressive strength resulted in 0.76 MPa, representing a 6% increase. For the samples with fibers (1PCF and 2PCF), the variation resulted in 1.28 MPa, representing a 13% increase. From these results, is observed that there is a direct relationship between compressive strength and w/c ratio in permeable concrete, with higher w/c ratios leading to increased compressive strength, contrary to what is observed in traditional concrete [46,47,48]. For the lowest w/c ratio, the mix became too dry and brittle, despite the use of a plasticizer, suggesting that further testing is recommended to investigate the optimal w/c ratio for this type of concrete.

Compressive strength was compared with the permeability index and porosity. Figure 7 and Figure 8 show that the samples with a higher compressive strength exhibit a lower permeability, and vice versa. As mentioned above, compressive strength and permeability are generally opposite properties, as greater permeability implies a sample with greater porosity and, consequently, a less resistant section.

The results of permeability and compressive strength (Figure 7 and Figure 8) were compared with those provided by the ACI 522R-10 standard [20], as listed in Table 5. It can be observed that for both w/c ratios, and for both fiber-reinforced and fiber-free concrete, the results are acceptable since the permeability exceeds 0.1 cm/s and the compressive strength ranges between 6.8 and 25.0 MPa. However, according to the NBR 16416/2015 standard [42], the specimens do not meet the minimum recommended compressive strength of 20 MPa.

3.4. Flexural Strength

Figure 9 shows the flexural behavior of permeable concrete without fibers. It is observed that after reaching its maximum strength capacity, the material exhibited a brittle failure due to its limited deformation capacity, a characteristic behavior of unreinforced concrete. In contrast, Figure 10 illustrates that after reaching the maximum strength capacity, concrete with fibers continues to deform. In this case, the fibers provide ductility and post-cracking strength, allowing the material to continue supporting loads even after crack formation.

The difference in flexural strength between specimens 2PC (w/c = 0.35) and 1PC (w/c = 0.30) was 0.80 MPa, indicating that the strength of mix 2PC was nearly double that of 1PC. Similarly, for fiber-reinforced permeable concrete, Figure 10 shows a difference of 0.98 MPa, meaning that the strength of mix 2PCF (w/c = 0.35) was 88% greater than that of 1PCF (w/c = 0.30). These results suggest a positive correlation between flexural strength and w/c ratio, a result similar to that found by [41]. As mentioned early in the study with compressive strength, additional testing is suggested to further investigate this relationship.

Comparing the maximum flexural strength values with those recommended by the ACI 522R-10 standard [20] and NBR 16416/2015 [42], as shown in Table 5, it is observed that none of the four mixes reach the minimum flexural strength value recommended by the ACI 522R-10 standard of 2.8 MPa. However, when compared with the Brazilian standard NBR 16416/2015, most samples meet the standard’s recommendations, except for 1PC, which does not reach the minimum value of 1 MPa.

Comparing Figure 9 with Figure 10, it is observed that samples with fibers (1PCF, 2PCF) show an increase in maximum tensile stress for both w/c ratios. For mix 1PCF, there is a 0.28 MPa increase compared to mix 1PC, representing a 33% increase. Mix 2PCF is 0.40 MPa higher than 2PC, indicating a 24% increase. The addition of fibers resulted in an enhanced flexural tensile strength, contrasting with the decrease observed in compressive strength (Figure 7 and Figure 8).

Facture Energy

Figure 11 shows the calculation of fracture energy for different strain levels. Fracture energy is directly related to the area under the load–deflection curve, allowing for the simultaneous evaluation of tensile strength and deformation capacity. It is evident that the 1PC sample has the lowest fracture energy at failure compared to the other samples. The difference in energy between 1PC and 1PCF is 2.47 N/m, with 1PCF exhibiting higher energy. Mix 2PCF shows an increase of 5.72 N/m over 2PC, indicating that fiber-reinforced mixes have greater fracture energy at failure. This is attributed to the fibers enhancing flexural strength at failure while maintaining similar deformations.

Analyzing the fracture energy results at failure for beams without fibers, the mix with a w/c ratio of 0.30 (1PC) and the mix with a w/c ratio of 0.35 (2PC), it is observed that the fracture energy in mix 2PC increased by 46%, being higher in 2PC. For beams with fibers (1PCF w/c = 0.30, 2PCF w/c = 0.35), fracture energy was calculated for deflections of 1 mm and 2 mm. The 2PCF mix shows a 31.82% increase for a deflection of 1 mm and 26.70% for a deflection of 2 mm compared to the 1PCF samples. These results highlight the influence of w/c ratio on fracture energy, with a higher fracture energy observed in the samples with higher w/c ratios, attributed to the increase in flexural tensile strength.

4. Conclusions

Permeability, compressive strength, and flexural strength tests were conducted on permeable concrete samples with and without fiber reinforcement. The samples were prepared using different coarse aggregate sizes and water/cement ratios, allowing for the evaluation of permeable concrete behavior based on these factors.

The permeability and compressive strength tests demonstrated that the selection of coarse aggregate size plays a crucial role in achieving a balance between these two properties. Porosity is directly related to permeability, while both porosity and permeability can vary inversely with the water/cement ratio. Additionally, the addition of polypropylene fibers to permeable concrete leads to an increase in porosity and permeability.

Analysis of the compressive strength test results confirms an inverse relationship between porosity and compressive strength. The addition of polypropylene fibers results in a reduction in compressive strength, while an increase in the water/cement ratio causes an increase strength.

Flexural tests revealed that the inclusion of fibers produces a significant increase in tensile strength and ductility in the post-cracking zone. It was found that, similar to compressive strength, an increase in the w/c ratio can produce up to double the flexural tensile strength, which is contrary to observations in conventional concrete. To confirm this relationship, further testing is recommended to evaluate these values more comprehensively. Fracture energy calculations indicate that increasing the water-cement ratio and adding fibers to permeable concrete cause an increase in fracture energy, due to greater strength and ductility.

The main novelty of this research lies in the analysis of the physical and mechanical properties of permeable concrete for two water–cement ratios. The results show that some properties exhibit behavior opposite to that of conventional concrete, as observed in this study, where certain properties increase as the w/c ratio increases. The information presented provides scientific evidence that helps reduce the scatter of results surrounding permeable concrete.

The studies conducted in this research correspond to a specific fiber content and material mixtures. For future research, it is recommended to investigate different fiber types and volume fractions across a broader range of water–cement ratios.