An Experimental Study of Permeable Asphalt Pavement Incorporating Recycled Concrete Coarse Aggregates

Abstract

Urban waterlogging due to sudden rainfall leads to critical issues. This study aims to develop sustainable porous asphalt pavement by incorporating different proportions of recycled coarse aggregate. Recycled coarse aggregate from waste laboratory-tested concrete in 19, 12.5, and 9.5 mm sizes was prepared for a porous asphalt mix series (Mix-Types 1-9). The study showed that optimal aggregate ratios performed well in porous asphalt mixes. Mix-Type-3 with the aggregate ratio of 19:12.5:9.5 mm (1:1:0.5) achieved an optimal stability of 8.88 kN at the minimum flow rate. The movement of water flow results revealed that permeability decreases with time. The Mix-Type-3 permeability reductions were found to be 16.75% and 30.14% at 6 and 12 months, compared to the permeability of fresh mixes. The study results revealed that the Mix-Type-3 retained the highest stability level, and the permeability fell within the standard values. Hence, it is concluded that Mix-Type-3 balances in all parameters and is a viable choice for effective and sustainable urban water management.

1. Introduction

For urban waterlogging, the development of permeable pavement has emerged as an innovative option in advanced pavement technologies, particularly over the last few decades. Its capacity to allow rainwater to drain from surfaces has led to its growing popularity in road surfacing efforts worldwide [1,2,3]. Additionally, using porous asphalt pavement (PAP) offers various ecological benefits, such as reducing urban waterlogging and aiding in groundwater replenishment, which is crucial in promoting environmentally responsive city development [4,5]. With ongoing developments in PAP systems, this technology has become a key element in managing stormwater in diverse weather regions in developed nations. Its flexibility is demonstrated through frequent implementation in urban projects such as parking lots, roundabouts, and other infrastructure. The safe urban infrastructure can be developed by applying the PAP management in all small and big cities [6,7]. Recent advancements have increased the focus on improving PAPs’ effectiveness and environmental performance. The role of PAP in urban stormwater control is primarily due to its ability to pass the water flow and reduce surface runoff, thereby helping prevent flooding in urban areas [6,8].

The stability of a PAP is mainly governed by the proportion of bitumen to aggregate ratios. Although the Marshall stability method is a standard approach for mixed design in regions such as Asia and Europe, the United States typically adopts alternative methods, highlighting regional differences in construction practices and technologies. In the PAP design, the emphasis is placed on optimizing both porosity and mechanical strength. Aggregate gradation is a key factor in achieving this, and it contributes significantly to the mixture’s characteristic non-uniform porosity [9,10]. In the aggregate gradation, appropriately engineered particle size distributions can enhance structural integrity while improving water transmission efficiency. Moreover, sustainable waste additives such as recycled coarse aggregates (RCAs), crumb rubber (CR), fly ash (FA), and silica fume (SF) have shown benefits in PAP mixes studied in [3,11]. Using RCA offers a promising solution to waste recycling and reduces environmental impacts by decreasing waste material and supporting resource conservation [12,13]. The studies have demonstrated the multifaceted advantages of PAP when incorporating the RCA gradation techniques. The most important feature is that high air void content greatly enhances water infiltration, improving road safety during heavy rainfall by reducing surface water, minimizing splash, lowering the risk of skidding, and enhancing driver visibility. The RCA’s sustainable PAP encourages more sustainable construction practices. This approach supports environmental preservation efforts by promoting the reuse of industrial and construction waste [14,15,16]. The mechanical performance of PAP incorporating mineral fillers and hydrated minerals was studied. The Marshall stability with fillers was reported as approximately 8 kN, compared to mixes containing hydrated lime, which showed a slightly higher stability of 8.2 kN. Including calcium oxide in silicate filler materials boosts the mixture’s ability to withstand applied loads [17,18]. Al-Jumaili [19] evaluated the laboratory performance on modified PAP. The results show that the peak stability value was achieved at 10.1 kN when the flow was 3.3 mm, and the stiffness was 3.06 kN/mm, respectively. The study results concluded that the developed PAP with polymer revealed the best strength and higher resistance to rutting. Putri and Vasilsa [20] developed the PAP by incorporating high-density polyethylene (HDPE). The results reported that at 4% HDPE, the stability value reached about 8.5 at the optimum binder content of 5.54%. It shows that using HDPE as an additive improves the stability value of the developed PAP. Nakanishi et al. [21] exhibited the mechanical properties of the newly designed porous asphalt pavement. The study results revealed the relationship between mechanical properties, such as dynamic stability and shearing strength. The study results concluded that the higher the shearing strength, the better the mechanical properties. Hardiman [22] studied the stability and permeability of PAP mixes by incorporating natural coarse aggregate (NCA). The results show satisfactory stability with good permeability values. The most promising sample initially exhibited a permeability of almost 4000 × 10⁻⁶ m/s, which decreased to 2500 × 10⁻⁶ m/s over a year, likely due to the effects of environmental conditions. This alteration highlights the significant impact of environmental conditions on the permeability of PAP with time. The recently published results of the studies [3,5,23,24] showed that the stability value of PAP mixes with RCA addition has satisfactory results in stability and permeability values. Hence, the RCA can be utilized in the PAP development.

Despite these findings, a limited understanding exists of how RCA affects the permeability and load-bearing capacity of PAP when combined with various gradation methodologies. Further investigation is necessary to fill these gaps and support the broader adoption of PAP in sustainable infrastructure projects. It has been determined from the literature review that some studies have utilized RCA in permeable mixes. However, no study has used RCA from waste laboratory-tested concrete cubes and cylinders to produce PAP mixtures. To bridge these gaps, this study will use graded RCA in PAP design mixes. Nine unique mix formulations (Mix-Type-1 to Mix-Type-9) were developed, with each blend being assessed for aggregate composition, Marshall stability, and permeability to determine its suitability in PAP mixes. The model established in this study was subsequently applied to analyze the permeability behavior of newly mixed PAP blends and core samples extracted from a university parking area at 6 and 12 months post-installation.

2. Experimental Methodologies and Material Properties

2.1. Development of Recycled Coarse Aggregates

2.1.1. Preparation of Recycled Coarse Aggregate from Tested Concrete Waste

Tested concrete waste was collected from quality control (QC) labs, and recycled coarse aggregate was prepared at Abin Construction Company’s crushing plant, as shown in the systematic diagram in Figure 1. The RCA was prepared to meet the requirements specified in [25,26]. After fulfilling the required standards, the RCAs were transported to a QC pavement lab for further physical testing. The process used in this study for preparing the RCA is outlined in Figure 1. RCA fragments exceeding 25 mm in size were omitted from the final blend. As shown in panel Figure 1, the aggregates were categorized by size into X = (25–19.0 mm), Y = (19–12.5 mm), and Z = (12.5–9.5 mm). The aggregate passes the higher number and returns to the lower number. This gradation technique in this study yields more significant results in producing higher permeability with different X, Y, and Z proportions utilized in the PAP design.

2.1.2. Properties of Graded Recycled Coarse Aggregate

The details of the parameters, such as unit weight, relative density, moisture, crushing strength, and resistance to wear, of the developed RCA are mentioned in

Table 1. Prepared coarse aggregate physical properties.

Tests	Standards	Minimum (%)	Maximum (%)	Results
	ASTM C29/C29M	_	_
Bulk density (BD)				2.656
Saturated surface density (SSD)				2.707
Apparent surface density (ASD)				2.759
Percentage of water absorption				1.90% < 2
RCA abrasion	ASTM C131	-	30%
X				14.2%
Y				16.7%
Z				19.3%
Soundness	ASTM C88
Sodium Sulfate		-	10	7.1
X		-		7.5
Y				7.9
Z
Elongation and& Flakiness Index	ASTM D4791	-	10%
X		-	10%	5.3%
Y				6.8%
Z				7.9%
Fractured Faces	ASTM D5821		-
2ff		90%	-	100%
1ff		100%		100%

. RCA’s relative density and bulk weight fall within acceptable specified limits for natural coarse aggregates (NCAs), suggesting that RCA could effectively substitute NCA for these physical attributes. In addition, the RCA demonstrates resistance to crushing and surface wear, with values recorded at 14.2%, 16.7%, and 19.3%, all of which remain below the NCA standard’s allowable upper limit of 30%. These results indicate that the RCA possesses sufficient strength and durability for applications requiring high resistance to crushing and abrasion. The comprehensive details for the coarse aggregate properties are provided in Table 1.

2.1.3. Sieve Analysis Tests on Developed Recycled Coarse Aggregate

Figure 2 presents the gradation profiles of prepared RCA from waste-tested cubes and cylinders of laboratory wastes incorporated into nine unique PAP formulations, identified as Mix-Type-1 to Mix-Type-9. These distribution graphs illustrate how different particle sizes correspond to the percentage of material that passes through each sieve, benchmarked against the specification range of both upper and lower thresholds outlined in ASTM C33 [27]. Figure 2 illustrates the gradation profiles corresponding to each mix (Mix-Type-1 to Mix-Type-9) that meets the minimum specifications outlined in ASTM C33 [27]. The observed differences result from employing distinct RCA proportions and choosing specific particle sizes—X = (25–19.0 mm), Y = (19–12.5 mm), and Z = (12.5–9.5 mm)—and are inconsistent with standard grading requirements. Even though the Mix-Type-1 to Mix-Type-9 blends do not entirely satisfy the specifications set by ASTM-C33 [27], their gradation profiles remain near the acceptable boundary of the standard. The RCA employed in this research is appropriate for producing the various PAP mixes (Mix-Type-1 to Mix-Type-9). The gradation curve falls close to the permissible range, completely fulfilling the standards specified by ASTM-C33 [27]. Therefore, Mix-Type-1 to Mix-Type-9 are suitable for PAP design as their gradations fall within the established limits.

2.2. Properties of Asphalt and Optimal Binder Content

The bituminous binder’s behavior at temperatures exceeding 93 °C becomes predominantly viscous, resembling the flow characteristics of lubricants like engine oil—Narayan et al. [17]. On the other hand, when exposed to freezing or sub-zero temperatures, the binder responds more like a flexible solid, regaining its original shape once the applied stress is removed. At intermediate temperatures, bituminous binder demonstrates the dual behavior of a deformable liquid and a resilient solid. For this investigation, bitumen classified within the (60–70) penetration range was sourced from Abdin Construction Co., Ltd., Tabuk, Saudi Arabia, and analyzed at the Amana testing facility in Tabuk, Saudi Arabia. The specifications for this type of binder are outlined in Table 1. Test results confirmed that the binder meets the 60–70 grade asphalt criteria defined by the AASHTO standards codes in

Table 2. Specifications of 60–70 grade asphalt.

Experimental Values	Study’s Results	60–70 Grade Recommended Values	Standards
Penetration at 25 °C, 100 g, 5 s	65	60–70 (1/10 mm)	AASHTO T 49, 2019
Flash point, Cleveland Open Cup	258	Min 232 °C	AASHTO T 48, 2015
Ductility at 25 °C, cm	118	Min 100 cm	AASHTO T 51, 2018
Solubility in trichloroethylene	106	Min 99.0%	AASHTO T 44, 2014
Thin film oven 3.2 mm, 163 °C, 5 h loss on heating	0.7	Max 0.75%	AASHTO T 179, 2009
Penetration of the residual % of the original	64	Min 54%	AASHTO T 49, 2019
Ductility of residue at 25 °C, 5 cm/min	62	Min 50 cm	AASHTO T 51, 2018
Viscosity, at 60 °C, poise, min	2605	Min 2400 poise	AASHTO T 202, 2019, 2000
Kinematic viscosity (centistokes) at 135 °C	270	Max 400 centistokes	AASHTO T 201, 2015
The softening point, ring, and ball apparatus	47	46–54 °C	AASHTO T 53

.

Figure 3 shows that the optimal binder content (OBC) correlates with the different characteristics to evaluate the actual value of OBC for this study. These include (a) the volume fraction of voids in the composition, (b) the load-bearing strength, (c) the volume of voids in the mineral aggregate (VMAs), and (d) the voids filled with asphalt (VFAs). These four crucial parameters were taken into consideration when deciding on OBC. As the new RCA is developed, determining the right amount of OBC depends on practical experience with porous asphalt mix design, after several trials of the mixes against the parameters reported in Figure 3a–d. This study shows slightly higher OBC than conventional mixtures. This is due to the utilization of the newly developed RCA. The possible causes of this include higher roughness and angularity of RCA. In addition, the RCA’s porous nature could be another reason for a higher amount of OBC than in the regular asphalt mixes. The OBC’s 6% amount was most suitable for blending the materials without losing their strength.

Finally, for this study, an OBC of 6% is the most effective binder content for creating porous asphalt mix formulations ranging from Mix-Type-1 to Mix-Type-9. According to the Asphalt Institute’s MS-2 manual guidelines, the selected binder content is deemed the most suitable when achieving the highest stability and desired air voids midpoint. This research effectively met all the standards outlined in the MS-2 guidelines issued by the Asphalt Institute.

2.3. Design Criteria, Mix Types, and Formulating Permeable Asphalt Mixtures

This study involved the development of PAP mixtures using uniformly graded RCA. According to AASHTO T96 specifications, coarse aggregates are acceptable when their wear percentage does not exceed 40%. Regulations further stipulate that coarse aggregates must be devoid of clay clods, deleterious materials, organic contaminants, and elongated particles with aspect ratios exceeding 3:1. At the same time, flat-shaped pieces should not make up more than 8.0% of the total aggregate content. The RCA utilized in this study satisfied all specified criteria, as outlined in

Table 3. Mix-Type-1 to Mix-Type-9 design mix compositions.

PAP Mixes	Prepared Recycled Aggregate Gradation for This Study			Recycled Aggregate Proportion			RCFP (75-2μ)	SF	WPF	CR	Binder	Total Weight
				X	Y	Z
	X = 19 mm	Y = 12.5 mm	Z = 9.5 mm	%	%	%	%	%	%	%	%	%
				g	g	g	g	g	g	g	g	g
Mix-Type-1	0.5	1	1	17.70	35.40	35.40	1	1	0.5	3	6	100
				212.40	424.8	424.8	12	12	6	36	72	1200
Mix-Type-2	1	0.5	1	35.40	17.70	35.40	1	1	0.5	3	6	100
				424.8	212.4	424.8	12	12	6	36	72	1200
Mix-Type-3	1	1	0.5	35.40	35.40	17.7	1	1	0.5	3	6	100
				424.8	424.8	212.4	12	12	6	36	72	1200
Mix-Type-4	0	1	1	0.0	44.25	44.25	1	1	0.5	3	6	100
				0.0	531	531	12	12	6	36	72	1200
Mix-Type-5	1	0	1	44.25	0.00	44.25	1	1	0.5	3	6	100
				531	0.0	531	12	12	6	36	72	1200
Mix-Type-6	1	1	0	44.25	44.25	0.0	1	1	0.5	3	6	100
				531	531	0.0	12	12	6	36	72	1200
Mix-Type-7	0	2	1	0.0	55.32	33.18	1	1	0.5	3	6	100
				0.0	663.84	398.16	12	12	6	36	72	1200
Mix-Type-8	2	0	1	55.32	0.0	33.18	1	1	0.5	3	6	100
				663.84	0.0	398.16	12	12	6	36	72	1200
Mix-Type-9	0	1	2	0.0	33.18	55.32	1	1	0.5	3	6	100
				0.0	398.16	663.84	12	12	12	36	72	1200

RCFP = recycled concrete fine powder, SF = silica fume, WPF = waste polythene fiber, CR = crumb rubber.

, verifying its appropriateness in the composition of PAP mixtures.

According to the standards in [28,29,30,31], a porous asphalt mix design was prepared. Table 3 presents the weight-based component ratios for the PAP mix designs developed in this study, ranging from Mix-Type-1 to Mix-Type-9. The optimum binder content for this study was taken as 6% on the basis of asphalt content vs. different standards results, as mentioned in Figure 3. The study also establishes the recommended proportions for various waste materials, including 1% recycled concrete fine powder (RCFP), 1% silica fume (SF), 1% waste polythene fiber (WPF), and 3% crumb rubber (CR). This research examines various RCA levels within the PAP blends to determine the most effective mix. Assessing these variations is crucial for achieving the targeted functional properties of the PAP. These included waste materials with several advantages, including a dust-free composition, smooth texture, uniform consistency, and the absence of clumping, as noted by Saoud et al. [32]. Jin et al. [33]’s study reported that shredded rubber material and waste polythene fibers enhance the strength and permeability characteristics of the permeable PAP mixes. The material’s natural viscoelastic properties enhance the binder’s ability to flex and resist deformation, thereby reducing the risk of cracking and stress from traffic loads.

It also plays a role in refining the internal air void structure, promoting an effective balance between water permeability and mechanical stability. Despite being added at only 3% by total weight, CR significantly reinforces the mixture and supports the study’s aim of advancing environmentally sustainable pavement solutions, as discussed by Duan et al. [34]. It is essential to distinguish between the specified aggregate gradations of 9.5 mm, 12.5 mm, and 19.0 mm when designing the permeable asphalt mixes in this study. The gradation influences the pavement’s structural stability and permeability, affecting its performance. Figure 2 summarizes the specific grading of different RCA size distributions, offering an in-depth depiction of the PAP mix designs by incorporating RCA.

2.4. Fabrication of PAP Blend Specimens

The sample preparation procedure used in this research is outlined in Figure 4. A total of 1200 g of the mixture was heated to 160 ± 5 °C, according to the guidelines outlined in the SP-2 publication by the Asphalt Institute [30]. This heating temperature, 160 ± 5°C, was set to ensure the mixture was thoroughly blended and homogeneous, ensuring uniform material characteristics. The mixing process began by placing the preheated aggregate into a standard container, with the timing of each step carefully observed, as illustrated in Figure 4. The complete 24 h oven preheating stage was carried out before molding. It also visually represents the mixing procedure, where, at approximately 160 °C, asphalt aggregate and other ingredients were blended. Each sample was compacted with a Marshall Hammer following mixing, delivering 75 strikes per side to achieve adequate densification. Moreover, Figure 4 includes various test specimens, such as porous asphalt specimens undergoing curing at 60 °C. These fabricated samples in Figure 4 were finalized and ready for subsequent testing. Eighty-one specimens were developed, corresponding to nine unique PAP mixtures labeled Mix-Type-1 to Mix-Type-9. A total of 6 specimens were produced for each mixture type, resulting in 54 samples, to perform tests assessing stability and flow; an additional three samples per mix, making up 27 specimens for the permeability test.

2.5. Marshall Stability Method

No separate method is available for the design of PAP mixes. That is why the Marshall stability for regular asphalt pavement is utilized in this research. This research employs the Marshall method on the developed PAP mixes to evaluate the Marshall stability of each mix. Marshall stability aims to determine the resistance of developed PAP mixes against applied load. This study employed the traditional Marshall testing procedure to assess the Marshall stability of PAP mixes (Mix-Type-1 to Mix-Type-2) and evaluate their structural robustness. The test method ASTM D5581 [35] measured the plastic flow of cylindrical bituminous specimens using the Marshall instrument. This method can be used for the maximum nominal size of 37.5 mm aggregate. In regular asphalt mixes, critical tests, including the density of the materials, air void levels, structural integrity, and strain behavior of the mixes, were evaluated, as noted by Weatherbee [36]. This study utilized the maximum size of 19 mm of the developed RCA. The Marshall stability assessed the maximum load on the PAP mixes at which samples failed. Simultaneously, flow was measured against each peak load. The Marshall stability apparatus is shown in Figure 4.

3. Results and Discussion

3.1. Stability and Flow Relationship

As presented in Figure 5, the stability values for the formulations ranging from Mix-Type-1 through Mix-Type-9 were recorded as 8.15, 7.9, 8.88, 7.8, 6.32, 3.88, 7.1, 5.04, and 7.4 kN, respectively. The porous asphalt mixes, with varying graded ratios, demonstrated high stability. This investigation’s selected gradation approach for coarse aggregates strengthened the interaction between the aggregate material and the bituminous binder, contributing to improved load-bearing performance. Among all the mixes, the Mix-Type-3 mixture, which had a 1:1:0.5 aggregate ratio, exhibited the highest stability performance at 8.88 kN.

The Marshall test indicated maximum load-bearing capacity combined with minimal deformation. For the mixtures ranging from Mix-Type-1 to Mix-Type-9 with a binder content of 5.5%, the flow values were measured as 4.4, 4.8, 4, 4.4, 5.1, 5.7, 4.4, 5.1, and 4.9 mm, as outlined in Figure 5. As shown in Figure 5, the Mix-Type-3 blend comprising aggregates in a 1:1:0.5 proportion demonstrated the most significant structural strength along with reduced deformation under load. It indicates that the composition of the aggregate affects the mechanical attributes of the permeable asphalt mixtures when subjected to a load. Since porous asphalt is not designed to withstand intense traffic pressure, evaluating specimen deformation through the flow test is suitable for assessing its performance. Nevertheless, the mixtures developed in this study conform to the necessary specifications for porous asphalt mixes.

3.2. Stability Loss Analysis

The remaining strength ratio (RSR) was utilized to measure the decrease in stability, which gauges the pavement’s resilience after being submerged. The formula for this measure is provided in Equation (1).

$$\mathrm{R}\mathrm{S}\mathrm{R}=S_1/S_2\times 100$$

(1)

where

• RSR = Remaining strength ratio;
• $S_1$ = Post-immersion stability after 24 h;
• $S_2$ = Pre-immersion stability.

Table 4. Outcomes of the present study.

Types of Porous Asphalt Mixes	Percentage of Voids	Mixes Stability (kN)		Loss of Stability (%)	Mixes Flow (mm)
		After 30 min, Stability	After 24 h of Stability
Mix-Type-1	19.64	8.15	4.38	46.26	4.4
Mix-Type-2	18.60	7.9	4.26	44.81	4.8
Mix-Type-3	17.90	8.88	5.44	38.74	4
Mix-Type-4	18.75	7.8	4.38	43.85	4.4
Mix-Type-5	20.05	6.32	3.35	46.99	5.1
Mix-Type-6	21.52	3.88	1.58	59.28	5.7
Mix-Type-7	18.88	7.1	4.05	42.96	4.4
Mix-Type-8	21.09	5.04	2.66	46.82	5.1
Mix-Type-9	19.70	7.4	3.86	47.43	4.9

presents the stability reduction determined using Equation (1). The highest stability loss, based on the Marshall Stability Test MOC-MRDTM 410 [37,38], was observed. Since there are no specific guidelines for stability loss in porous asphalt mixes, the standard values from traditional asphalt mix designs were used as a point of reference for comparison. The threshold for standard asphalt mix design tests is up to 25% MOC-MRDTM 410 [37,38]. The findings of this study indicate values exceeding those recommended by MOC-MRDTM 410 [37,38]. The higher reduction in Marshall stability can be explained by the fact that the specimens used in this research are composed of permeable asphalt, which contains more air voids, as shown in Table 4.

3.3. Permeability Coefficient (k)

In PAP blends, the hydraulic conductivity (k) is a critical parameter for evaluating how fluid passes through the open structure of the material. The rate at which liquid travels through the material measures flow capacity within the permeable asphalt. This property sets permeable asphalt apart from conventional asphalt. Due to the critical role permeability plays in the performance of permeable asphalt surfaces, there has been a need to develop improved methods for accurately measuring drainage capacity. This research aimed to develop a standardized method for assessing the ease with which fluids can pass through porous asphalt materials. Equation (2) was used to measure the permeability of newly produced samples alongside core sections extracted after 6 and 12 months of field exposure.

$$k=2.3{\displaystyle \frac{aL}{At}}\mathit{log}\left({\displaystyle \frac{h_1}{h_2}}\right)$$

(2)

The symbol (k) represents the permeability coefficient. In contrast, (A) represents the specimen’s area, (a) stands for the tube’s cross-sectional area, (L) indicates the height of the sample, (t) indicates time, and h₁ and h₂ are the water levels. The falling head permeability method was utilized to measure the permeability of fresh samples and the core samples extracted after 6 and 12 months of casting. Figure 6 shows the setup of this study’s falling permeability test.

3.3.1. Permeability (Mix-Type-1 to Mix-Type-9) Mixes

As depicted in Figure 7, the coefficient of permeability (k) was determined through experimental evaluation for the freshly produced PAP mixtures, and the core specimens extracted after 6 and 12 months of casting were identified as Mix-Type-1 through Mix-Type-9. Permeability measurement is primarily used to assess the compaction of the mixes (Mix-Type-1 to Mix-Type-9), which is vital for maintaining both the durability of the structure and the effectiveness of fluid movement. Proper compaction is vital to ensure the pavement can withstand light traffic without compromising its durability, especially given its primary function as a drainage solution.

Furthermore, the research was conducted to understand conditions, such as regular dust particles and frequent low and high windstorms, which transport fine particles that may alter the attributes of the permeable asphalt pavement materials. This environmental factor played a significant role in testing the samples under natural conditions, providing a long-term evaluation of permeability in real-world scenarios. The study effectively replicated their expected performance and permeability over time in the open environments by subjecting the pavements to such conditions.

The PAP blends were designed to assess their permeability values (Mix-Type-1 to Mix-Type-9). The findings indicated that greater coarse RCA in the mix enhanced permeability levels. For example, Mix-Type-8, which incorporated an RCA blend ratio of 2:0:1 and contained roughly 55.32% of X proportions aggregate ranging from 25 mm to 19.0 mm in size, recorded the maximum permeability rate of 2510 × 10⁻⁶ m/s. On the other hand, Mix-Type-5, which had an RCA ratio of 1:0:1, displayed a lower permeability of 900 × 10⁻⁶ m/s. The outcomes indicate a distinct correlation between the permeability values (Mix-Type-1 to Mix-Type-9) and the RCA gradation incorporated in the mixes. The aggregate size distribution and specific properties of the RCA used affect the flow capacity of PAP mixtures. Aggregate gradation influences particles’ sizing and spatial arrangement, directly affecting the pavement’s void network and water movement. Due to its uneven texture and angular form, RCA boosts permeability by promoting better interconnection between void spaces. This effect is especially noticeable in mixtures that contain a higher proportion of larger RCA particles; for instance, Mix-Type-8 exhibited superior permeability performance, primarily attributed to its inclusion of 19 mm aggregate particles. Hence, the optimal permeability performance of porous asphalt mixtures is primarily governed by the aggregates’ particle size distribution and the RCA’s inherent characteristics.

The permeability range for PAP mixtures spans from 347 × 10⁻⁶ to 1157 × 10⁻⁶ m/s, as recommended by DOTMNC standards. Figure 7 displays the results of permeability evaluations conducted on mixtures ranging from Type-1 to Mix-Type-9, with values spanning from 900 × 10⁻⁶ to 2510 × 10⁻⁶ m/s. These results showed that some samples exceeded the higher limit recommended by DOTMNC guidelines, while others were within the limits and validated by the most recent published studies, which range from 400 to 2000 × 10⁻⁶ m/s [3,39,40,41]. Hence, this study’s coefficient of permeability results depend on the RCA size and proportions decided in Table 1. Therefore, the selected sizes X, Y, and Z of RCA in different gradation proportions in the design mixes (Mix-Type-1 to Mix-Type-9) are exceedances in permeability due to differences in gradation design.

Core samples were retrieved 6 and 12 months following the initial placement of PAP in the university parking lot. The permeability values (k) for these samples (Mix-Type-1 to Mix-Type-9) at each interval are illustrated in Figure 7. A comparison was made between the original permeability values and those after 6 and 12 months of exposure. After 6 months, the permeability coefficient decreased to 802, 726, 1740, 848, 788, 827, 1640, 1880, and 1420 × 10⁻⁶ m/s. After 12 months of exposure, the permeability values were 751, 618, 1460, 794, 721, 768, 1460, 1620, and 1270 × 10⁻⁶ m/s. The percentage reduction in permeability for the mixes after 6 and 12 months ranged from 10% to 25% and 17% to 39%, respectively. This study utilizes waste polythene fiber (WPF) with hot asphalt mixtures. Upon blending WPF with heated asphalt, it integrates with the aggregates and facilitates uninterrupted water movement within the mixture. Previous studies have not done this. That was one reason for the sample’s higher permeability values in the present study.

The changes in permeability coefficient (k) values have been inconsistent and influenced by multiple factors, including climate, traffic volume, the composition of the mix, and the methods used during installation, which impact the fluid flow characteristics within the asphalt. In certain instances, permeability can remain constant for up to five years when subjected to traffic conditions, while in others, a significant decrease occurs within a year. Previous studies have not offered a definitive or consistent explanation of how permeability evolves. Field investigations generally reveal a slight decrease in permeability within porous asphalt. Hardiman [22] noted that increased void content in PAP mixtures, when filled with dust and debris from storms, gradually decreases the rate of fluid movement as a function of time.

Recent studies [42,43,44,45] have focused on finding the permeability of asphalt pavement and concrete mixes and interpreting the data. Several factors impact the permeability coefficient and affect the permeability of PAP and asphalt concrete. Many numerical models, theoretical assessments, and empirical and semi-empirical studies have been done. The shortcomings of many studies have been reviewed. The studies revealed some correlation in the laboratory measurement, but the effective field permeability data are unavailable for analysis. Most permeability test methods are based on laminar flow, which is unconvincing for PAP. Those studies that attempt to measure correlations between the permeability and air voids are more meaningful than the mathematical models.

3.3.2. Correlation Analysis Between Permeability and Stability

Figure 8 shows the correlation between stability and permeability results. As illustrated in Figure 8, no evident correlation or pattern exists between the stability and permeability coefficient values. The stability figures remain unaffected by the permeability coefficient (k). It suggests that stability and the permeability coefficient (k) do not correlate directly. However, the research proposes an ideal mix of aggregate proportions that may strike a desirable balance between the stability vs. permeability relationship.

The aggregate gradation utilized in this study significantly impacts the permeability coefficient (k). As shown in Figure 8, the maximum stability achieved was 8.88 kN at the aggregate ratio of (X = 1, Y = 1, Z = 0.5) in Mix-Type-3. The higher the amounts of X and Y, the higher the proportion of permeability compared to Y and Z. This demonstrates that aggregates’ dimensions and distributions considerably impact permeability. The research found Mix-Type-3 to be the most suitable option, providing the ideal balance between permeability and stability. It achieved a maximum stability of 8.88 kN and an initial permeability value of 2.09 × 10⁻⁶ m/s, surpassing the criteria established by DOTMNC.

At the 6-month and 12-month intervals, Mix-Type-2 exhibited the most significant decrease in permeability, with reductions of 27.4% and 38.2%, respectively. This drop in permeability was notably higher compared to the initial values. However, despite these reductions, Mix-Type-3 retained the highest stability level, with permeability reductions of 16.75% and 30.14% at 6 months and 12 months, respectively. The primary cause of the reduced permeability is the buildup of dust and fine desert particles, which block the voids and hinder water movement.

PAP core samples’ permeability coefficient (k) was measured 6 and 12 months after casting. Figure 8 illustrates a noticeable decrease in permeability over time. The reduction in permeability values varies between the 6-month and 12-month core samples. Due to the compact structure of PAP mixtures, they typically have a shorter lifespan, leading to lower durability. The PAP design, as explored by Hardiman [22], includes natural coarse aggregates. The research highlighted the correlation between stability and permeability in mixtures containing. Examining the current literature reveals a lack of comprehensive understanding regarding the relationship between stability and permeability. Moreover, there has been limited research on PAP mixtures using RCA. This study aims to address these gaps, contributing new insights to the field.

The buildup of small particles in porous materials can notably impact the permeability characteristics of both synthetic and natural porous structures. This alteration can influence a range of material properties and environmental processes that rely on the flow behavior of these substances. For instance, the permeability of PAP can be notably reduced due to clogging from the accumulation of small particles, particularly during rainy or waterlogged conditions. In desert areas, the movement of tiny particles during dust storms may contribute to the blockage of pore throats, resulting from depressurization under such extreme conditions. Moreover, the impact of fine particles from recycled aggregates on the flow properties of PAP has not been thoroughly investigated.

4. Significance, Limitations, and Prospective

4.1. Significance

This experimental research highlights the considerable promise of permeable asphalt pavement in promoting sustainable urban stormwater management practices, thereby reducing the likelihood of flooding in urban areas. This feature supports the goals of sustainable urban drainage systems, focusing on managing rainwater at its source. Permeable asphalt pavement facilitates water infiltration into the subsurface, allowing for the replenishment of groundwater reserves and the maintenance of the urban water cycle. Beyond its benefits in permeability, permeable asphalt pavement helps reduce pollution from surface runoff by trapping and filtering particles and other pollutants, preventing them from reaching drainage systems.

Incorporating recycled coarse aggregates prepared from waste-tested laboratory samples into permeable asphalt pavement contributes to its environmental sustainability by preserving resources and minimizing waste. This study demonstrates enhanced water flow capacity and significant durability, making them suitable for urban environments where effective stormwater mitigation is paramount.

4.2. Limitations

The findings suggest that utilizing recycled RCA prepared from waste-tested laboratory samples in permeable asphalt surfaces has the potential for environmentally friendly urban water management. Nevertheless, the data reveal that such pavements could be vulnerable to blockage caused by fine particles, such as desert sand and airborne dust, which can impair the long-term functionality of the drainage system and necessitate regular maintenance and monitoring. Inconsistencies in the characteristics and performance of recycled concrete materials can pose a significant constraint for long-term applications. The study’s other limitations include higher maintenance costs than conventional pavement analysis, the lack of real traffic simulation, and the absence of accelerated aging tests. Furthermore, the results may also vary across regions with divergent climatic conditions, such as heavy precipitation or low temperatures.

4.3. Prospective Avenues for Further Investigation

To overcome the limitations of the present study and explore the combined use of appropriate waste materials, upcoming investigations should undertake in-depth evaluations of PAP’s functional characteristics, including aspects like surface friction, heat transfer capability, and environmental impact over its lifespan. Such detailed analyses would provide critical knowledge to support the development and refinement of permeable asphalt formulations. Moreover, expanding the research to incorporate additional tests, such as fatigue and rutting on PAP by incorporating graded RCA, could further enhance the quality of PAP characteristics. In addition, the cost-effectiveness of PAP can also be analyzed. Exploring methods for mitigating the clogging issue in PAP is crucial, as it would help improve its functionality and long-term durability can also be added.

5. Conclusions

This study developed and proposed PAP mixes by RCA prepared from laboratory-tested cubes and cylindrical concrete waste. A new grading technique was utilized to develop RCA at the optimum gradation level, significantly affecting the pre-graded mixes’ stability and permeability results (Mix-Type-1 to Mix-Type-9). The research findings are summarized pointwise as follows.

• The developed RCA from tested laboratory cubes and cylindrical concrete waste produced successful experimental results in designing PAP mixes.
• The OBC for the PAP mixes of this study was reported to be 6%, which is slightly higher than that of natural aggregates.
• The highest Marshal stability, 8.88 kN, and lowest flow, 4.0, were reported in Mix-Type-3 with the optimal gradations of X = 1, Y = 1, and Z = 0.5, respectively.
• The highest permeability value was observed in the freshly mixed samples. After 6 months and 12 months, the core samples showed a reduction in permeability.
• It has been concluded that the most effective PAP mix in the study was Mix-Type-3. The mix has reported the highest stability and good permeability at the tested time of fresh samples. In the long term, 6 and 12 months also achieved the acceptable limits of DOTMNC.