A Comparative Study of Porous Asphalt Strength Reinforced with Expanded Polystyrene Foam and Ash-Based Fillers: Cantabro Test Findings

This research sought to evaluate the effects of incorporating extruded polystyrene (XPS) into porous asphalt mixtures and to understand the role of various filler combinations, specifically coconut shell ash (CSA) and rice husk ash (RHA), on the mixture’s performance. For this purpose, asphalt mixtures were subjected to the Cantabro test under both unconditioned and conditioned modes. Mixtures were treated with XPS in varying proportions ranging from 7% to 11%. The filler combinations were further varied, with mixtures containing 7% XPS showing Cantabro loss results of 35.71% for 1SD:3CSA and 43.44% for 1SD:1RHA, and those with 11% XPS demonstrating significant reductions to 19.24% and 18.93% respectively. The findings indicate that introducing XPS notably enhances the mixture’s stability and resistance to abrasion and disintegration. CSA-based mixtures generally showcased a more pronounced positive effect on stability than those with RHA. When subjected to moisture conditioning, all mixtures exhibited an increased sensitivity, though the 1SD:1RHA mixture showed the highest resilience against moisture damage. In conclusion, integrating XPS in porous asphalt mixtures can lead to significant performance improvements. The choice of filler, its proportion, and its interaction with XPS are critical factors in determining the mixture’s overall performance, especially its resistance to moisture and abrasion.


Introduction
The road infrastructure construction industry is of paramount importance on a global scale, as it has a substantial impact on economic development.However, the process of constructing and maintaining roads can lead to significant environmental consequences that include resource consumption, energy usage, and greenhouse gas emissions [1].As a result, there is an increasing demand for environmentally sustainable approaches in road infrastructure construction to effectively tackle these ecological challenges [2].In recent years, there has been increasing interest in using waste materials as construction materials as an alternative to traditional methods [3].This approach not only addresses waste management issues but also contributes to sustainability.One such waste material is expanded polystyrene foam, commonly known as styrofoam, which is a non-biodegradable material with potential environmental hazards due to its slow decomposition in soil [4].Incorporating XPS into porous asphalt mixtures for road construction presents a viable solution that tackles waste 1303 (2024) 012037 IOP Publishing doi:10.1088/1755-1315/1303/1/012037 2 management challenges while promoting sustainable practices [5].Furthermore, the utilization of ash powder generated from agricultural and industrial activities can serve effectively as filler material in porous asphalt mixtures, thereby mitigating the environmental impact associated with waste generation [3], [6].
Porous asphalt mixtures are widely used in road pavement construction because they facilitate water drainage and decrease noise levels.In response to environmental concerns, various research studies have explored incorporating waste materials as fillers in porous asphalt mixtures.For instance, a study analyzed the utilization of plastic waste as a filler material and determined that it had no significant impact on the mechanical properties of the porous asphalt mixture [7].Similarly, another investigation investigated waste tire rubber as an additive material and observed enhanced performance results for the porous asphalt mixture [8].Insufficient research has been carried out on using expanded polystyrene foam and ash powder as fillers in porous asphalt mixtures.A comprehensive study examined the substitution of XPS waste as an asphalt replacement material in the Asphalt Concrete Wearing Course layer with varying percentages of substitution.The findings indicated that incorporating XPS significantly impacted various properties of the asphalt, including penetration, softening point, flash point, specific gravity, and viscosity [9].
Furthermore, a comprehensive investigation conducted by researchers discovered that the inclusion of extruded polystyrene in asphalt binder led to notable alterations in the properties of the binder.The ductility ratio between aged and unaged samples varied from 0.84 to 0.92, while the penetration ratio ranged from 0.75 to 0.97 for aged and unaged samples, respectively.Additionally, increased styrofoam-to-asphalt percentage resulted in higher values for rotational viscosity and complex shear modulus (G*) [10].Although there has been a growing trend in utilizing waste materials as fillers in road pavement construction, there is a lack of comprehensive research on using XPS and ash powder fillers, specifically in porous asphalt mixtures.The limited studies conducted so far have not thoroughly examined the impact of varying substitution percentages of XPS or compared the mechanical properties of porous asphalt mixtures incorporating these fillers to traditional ones.Thus, an important research gap exists that calls for further investigation into assessing the mechanical properties associated with using these fillers in porous asphalt mixtures.The primary challenge addressed in this study is the performance of porous asphalt mixtures, especially when incorporating XPS and alternative fillers such as coconut shell ash (CSA) and rice husk ash (RHA).Conventional porous asphalt mixtures often face stability, resistance to disintegration, and abrasion issues.By integrating XPS and alternative fillers, we aimed to enhance these properties and provide a more sustainable solution for road construction.
This study aims to fill a research gap by investigating the potential use of expanded polystyrene foam and ash powder as fillers in porous asphalt mixtures for road pavement construction.The performance of these alternatives will be compared with traditional porous asphalt using Cantabro tests conducted under both dry and wet conditions.Different combinations of fillers and percentages of XPS substitution will be examined, following the Australian Asphalt Pavement Association specification guidelines.In addition to stone dust, coconut shell ash, and rice husk ash were used as alternative fillers for an asphalt binder additive.The mixtures consisted of varying percentages of XPS substitution, ranging from 7% to 11%, to analyze the influence of these additives on the mechanical properties of the mixture.The filler combination was combined with conventional stone dust at ratios of 1:1 and 1:3.Two stages of testing were conducted, including unconditioned (dry) and conditioned (wet), to assess how moisture affects the mechanical properties of the porous asphalt mixtures.This study's findings can potentially contribute valuable to sustainable and eco-friendly solutions in road infrastructure construction.Furthermore, it provides valuable insights into the feasibility of utilizing waste materials in constructing road pavements.

Materials
The present study analyzes the key properties of the asphalt binder, as presented in Table 1.The consistency of the binder is indicated by a penetration value of 64.50 (0.1 mm), determined through the ASTM D5 test with a load of 100 g applied for 5 seconds at 25°C.Thermal susceptibility is evaluated through the softening point test using ASTM D36, which yielded a value of 48.50°C.Specific gravity measurements conducted according to ASTM D79 provide insight into the mass-tovolume ratio, resulting in a value of approximately 1.03 gr/cm³.Furthermore, flexibility is assessed via ductility testing using ASTM D113 and found to be approximately 130 cm at room temperature (25°C).These parameters collectively offer valuable information on the essential characteristics underlying this analysis's asphalt binder assessments.Table 2 provides an overview of the essential properties of the aggregate used in this study.The table concisely displays the results of standard ASTM test methods used to evaluate key characteristics of the aggregate, including relative density (2.74 gr/cm³, ASTM C127), absorption (1.74%, ASTM C127), abrasion (16.44%,ASTM C131), impact (6.49%, ASTM C131), flakiness index (9.83%,ASTM D4791), and elongated index (9.63%,ASTM D4791).These parameters offer valuable insights into the quality and suitability of the aggregate for its intended application.
The aggregate gradation for porous asphalt shown in Figure 1 is an open gradation following AAPA 2004 OGA 14 specification, containing a higher percentage of coarse aggregate compared to fine aggregate.The purpose of using an open-graded aggregate in the design of porous asphalt mixtures is to increase the porosity and permeability of the pavement.Additionally, the open-graded structure of the mixture enhances the infiltrating capacity of the cementitious grouts into the layer.The gradation curve depicted in Figure 1 for the porous asphalt mixture with a maximum aggregate size of 14mm showcases the higher air voids achieved through an open gradation.Additionally, the gradation was carefully managed to stay within the prescribed limits for open-graded aggregate gradation.Specifically, the proportion of coarse aggregate varied between 90% and 95%, while the sand content fell between 4% and 5%.Additionally, filler content ranged from 2% to 4%.Thus, this chosen gradation guarantees that air voids in the open-graded asphalt mixture remain at a desired range of 25% to 35%, thereby facilitating adequate penetration of cementitious grouts into the layer.The XPS material investigated in this research was sourced from discarded food packaging items: disposable cups and food containers.Subsequently, the waste XPS underwent a series of treatments to convert it into foam particles measuring approximately 2-5 mm in diameter.The XPS was incorporated at different percentages of 7%, 9%, and 11% relative to the total weight of the asphalt.
The rice husk ash used in the study was obtained as a byproduct from the rice milling industry, where it is typically discarded and burnt.Similarly, coconut shell ash was collected from a restaurant that uses coconut shells for charcoal and then disposed of.To prepare both types of ash for use in the porous asphalt mixtures, they were processed to achieve a fine powder consistency.This involved sieving the RHA and CSA to remove larger particles and ensure an even distribution of particle sizes throughout the mixtures (pass sieve #200).Furthermore, rice husk ash and coconut shell ash powder were employed as filler substitutes for the asphalt mixture, which was to be blended with aggregate and the XPS, rice husk ash, and coconut shell ash powder.The laboratory data were recorded on the provided testing form.The filler materials used in this study consisted of stone dust and a combination of rice husk ash and coconut shell ash powder.The stone dust passed through sieve No. 200 (0.074 mm), with proportions of 1:3 and 1:1, respectively, based on the total weight of the filler.In the asphalt and aggregate mixture, XPS was added at varying percentages of 7%, 9%, and 11%.The waste XPS was initially cleaned to remove any impurities and subsequently cut into small pieces and blended.The dry process method was used in this study, whereby the XPS, rice husk ash, and coconut shell ash powder were added to the preheated aggregate, followed by hot asphalt.Three replicate specimens were prepared for each combination of materials.This approach was adopted to ascertain the test results' repeatability and provide a robust basis for the conclusions drawn from the study.

Cantabro Test Evaluation
The Cantabro test was conducted to determine the weight loss of test specimens after the Los Angeles abrasion test.The test specimens were compacted with 50 strokes on each side and placed in the Los Angeles test device, which rotated 300 times without a steel ball.The compacted test specimens were kept at room temperature for 48 hours before the test in the unconditioned testing mode.The test specimens were then placed in the Los Angeles machine without using steel balls.The Los Angeles abrasion testing device was operated at a speed of between 30-33 rpm for 300 rotations.After completion of the test, the weight after abrasion was obtained by weighing the test specimens.The weight loss of each test specimen was then calculated as a percentage of the initial sample weight before the test.In the conditioned testing mode, the compacted specimen was soaked for approximately 48 hours and left to rest at 25°C.The initial weight of the test specimen was recorded before subjecting it to the Los Angeles abrasion test with 300 revolutions.After that, it was placed in the Los Angeles abrasion testing device without steel balls, which was also run at a speed of between 30-33 rpm for 300 rotations.The weight loss of each test specimen was then calculated as a percentage of the initial weight.

Comparison of the Cantabro Test results for the unconditioned mode
The results indicate that adding XPS to porous asphalt mixtures significantly affects the Cantabro test results, as shown in Figure 2. As the XPS content increases from 7% to 11%, the Cantabro test results generally decrease, indicating improved resistance to abrasion and disintegration.Comparing the mixtures with 7% XPS and various filler combinations, the addition of XPS decreased the Cantabro Sieve size (mm) upper limit lower limit used gradation loss results, which were 35.71% for 1SD:3CSA, 40.99% for 1SD:1CSA, 33.49% for 1SD:3RHA, and 43.44% for 1SD:1RHA.Similarly, for the mixtures with 11% XPS and the same filler combinations, the Cantabro loss results decreased significantly to 19.24%, 18.04%, 18.36%, and 18.93%, respectively.These findings suggest that adding XPS can significantly enhance the mixture's stability and resistance to disintegration and abrasion.The improvement mechanism could be attributed to the XPS particles' ability to distribute stress evenly throughout the mixture, resulting in a more uniform and stable structure.Additionally, XPS's low thermal conductivity could alleviate thermal stresses in the mix, thus further improving its overall performance.Moreover, mixtures with a higher proportion of SD (at a 1:1 ratio) exhibit higher Cantabro test results than those with a 1:3 ratio of SD and CSA or RHA.This outcome indicates that including CSA and RHA fillers can enhance the integration of porous asphalt mixtures.Comparing different filler combinations shows that mixtures containing CSA generally display lower Cantabro loss results than those including RHA.For instance, in mixtures with 9% XPS and 1:1 CSA and SD ratios, the Cantabro loss results for 1SD:1CSA is 33.54%, while for RHA and 1CSA with 3:1 ratio, the cantabro loss results are 35.83%and 35.51%, respectively.These findings suggest that CSA may have a more pronounced positive effect on the mixture's stability, resistance to disintegration, and abrasion than RHA.
Coconut shell ash (CSA) is renowned for its high silica and carbon content, which can potentially enhance the performance of porous asphalt mixtures.As shown in Figure 2, mixtures with a higher proportion of CSA (at a 1:3 ratio) in combination with SD display a decrease in Cantabro test results as the XPS content increases.This finding suggests that utilizing CSA may improve the stability of the mixture.This trend could be attributed to the high silica content of CSA, which can react with the asphalt binder, resulting in a stronger bond and enhancing the mixture's resistance to disintegration and abrasion.Furthermore, rice husk ash (RHA), obtained from the combustion of rice husks, is also rich in silica and has a high specific surface area, potentially enhancing the performance of porous asphalt mixtures.Mixtures with a higher RHA ratio in combination with SD similarly exhibit a decrease in Cantabro test results as the XPS content increases.Similar to CSA, this trend suggests that RHA may positively impact the stability of porous asphalt mixtures.The possible mechanism underlying this improvement could be RHA's high specific surface area, which can increase the contact area between the filler and asphalt binder, leading to enhanced bonding and adhesion.The high silica content in RHA may also contribute to forming a stronger bond between the binder and filler, further improving the mixture's resistance to disintegration and abrasion.

Comparison of the Cantabro Test results for the conditioned mode
After comparing the Cantabro loss results presented in Figure 3, distinct differences emerge.At 7% XPS content, the 1SD:3CSA and 1SD:1CSA mixtures exhibit a 1.43% difference, while the 1SD:3RHA and 1SD:1RHA mixtures display a 2.91% difference.In addition, there is a further 2.91% difference between the 1SD:3CSA and 1SD:3RHA mixtures and a 4.39% difference between the 1SD:1CSA and 1SD:1RHA mixtures.As the XPS content increases to 9%, the differences in Cantabro loss results are as follows: 1.78% between the 1SD:3CSA and 1SD:1CSA mixtures; 7.28% between the 1SD:3RHA and 1SD:1RHA mixtures; 0.72% between the 1SD:3CSA and 1SD:3RHA mixtures; and 6.22% between the 1SD:1CSA and 1SD:1RHA mixtures.At 11% XPS content, the differences in Cantabro loss results are 2.11% between the 1SD:3CSA and 1SD:1CSA mixtures, 3.32% between the 1SD:3RHA and 1SD:1RHA mixtures, 2.06% between the 1SD:3CSA and 1SD:3RHA mixtures, and 0.85% between the 1SD:1CSA and 1SD:1RHA mixtures.The calculated percentage differences indicate that the performance of porous asphalt mixtures varies depending on the combination of fillers and XPS content.Generally, mixtures that utilize CSA as the alternative filler exhibit a smaller percentage difference in cantabro loss compared to those containing RHA at the same XPS content levels.At 7% XPS content, mixtures with CSA as the alternative filler outperform those with RHA in Cantabro loss.However, as the XPS content increases to 9% and 11%, the differences between the CSA and RHA mixtures become less distinct.The observed percentage differences in cantabro loss results imply that the interaction between conventional and alternative fillers and XPS content is crucial in determining the mixtures' performance.The observed differences may be attributed to various factors, such as the fillers' adhesion properties, specific surface area, and pozzolanic activity, which may impact the mixtures' overall strength, durability, and abrasion resistance.This study aims to discuss the differences in the results and evaluate the mixtures' sensitivity to moisture.The unconditioned test results demonstrate the baseline performance of the asphalt mixtures without exposure to moisture, while the conditioned test results show the performance of the asphalt mixtures after soaking in a water bath for 48 hours at room temperature.The conditioning process simulates the impact of moisture on the mixtures, enabling the assessment of their durability and moisture sensitivity.The differences between the unconditioned and conditioned test results measure the mixtures' moisture sensitivity.A comparison of the two tables reveals that the Cantabro loss values increase for all filler combinations after conditioning, indicating a higher sensitivity to moisture.To further illustrate the differences between the unconditioned and conditioned test results, Table 3 displays the ratio of unconditioned and conditioned measurements of the Cantabro loss test.The ratios presented in this analysis illustrate the relative change in the Cantabro loss values between the unconditioned and conditioned tests.A lower ratio indicates a higher sensitivity to moisture, while a higher ratio implies better resistance to moisture damage.Based on the calculated ratios, we can observe that the 1SD:1RHA mixture exhibits the highest resistance to moisture damage, with ratios of 0.67, 0.72, and 0.44 for 7%, 9%, and 11% XPS, respectively.In contrast, the 1SD:3RHA mixture demonstrates the highest sensitivity to moisture, with ratios of 0.49, 0.47, and 0.40 for 7%, 9%, and 11% XPS, respectively.The results suggest that the 1SD:1RHA mixture offers the best resistance to moisture damage, while the 1SD:3RHA mixture is the most sensitive to moisture.

Conclusion
In conclusion, this study has demonstrated a significant improvement in the performance of porous asphalt mixtures by incorporating XPS and alternative fillers, such as CSA and RHA, in terms of stability, resistance to disintegration, and abrasion.The Cantabro test results suggest that increasing XPS content reduces Cantabro loss, indicating improved resistance to abrasion and disintegration.Mixtures with a larger proportion of CSA or RHA, in combination with SD, exhibit improved performance, with CSA mixtures generally outperforming RHA mixtures.These improvements may be attributed to the stress-distribution capabilities of XPS particles, the high silica content and specific surface area of CSA and RHA, and the formation of stronger bonds between the binder and filler materials.Furthermore, the differences in Cantabro loss results between unconditioned and conditioned modes emphasize the significance of understanding the interactions between conventional and alternative fillers and the impact of XPS content in determining the overall performance of porous asphalt mixtures.
However, this study has limitations, including the focus on a limited range of XPS content and filler combinations.Future research could explore the effects of varying XPS content levels, filler types, and proportions on the performance of porous asphalt mixtures under diverse environmental and loading conditions.An in-depth investigation of the mechanisms responsible for the observed improvements in performance could provide valuable insights for developing more sustainable, costeffective, and durable porous asphalt mixtures.Further research could also evaluate these mixtures' long-term performance and environmental impact, including the potential leaching of pollutants from the XPS and alternative fillers.These efforts can contribute to advancing the development and application of more effective and environmentally friendly porous asphalt mixtures in the road construction industry.
The main contribution of this study lies in demonstrating a significant improvement in the performance of porous asphalt mixtures by incorporating XPS and alternative fillers.The Cantabro test results indicate that increasing XPS content reduces Cantabro loss, suggesting improved resistance to abrasion and disintegration.Furthermore, mixtures with a higher proportion of CSA, RHA, and SD exhibit enhanced performance.The study emphasizes the importance of understanding the interactions between conventional and alternative fillers and the impact of XPS content on the overall performance of porous asphalt mixtures.The outcomes of this research can contribute to developing sustainable and environmentally friendly solutions in road infrastructure construction.

Figure 2 .
Figure 2. Cantabro Test results for the unconditioned mode

Figure 3 .
Figure 3. Cantabro Test results for the conditioned mode

Table 1 :
Basic properties of asphalt binder.

Table 2 .
Basic properties of aggregate

Table 3 .
The ratio of unconditioned and conditioned cantabro loss test results