Possibility of Making Plastic Roof Tiles from Waste Plastic, Sand, and Fly Ash

Abstract

The rapid increase in plastic usage today poses a significant threat to our environment and the planet. It contributes to global warming and negatively impacts biodiversity. Most plastic ends up in landfills, where it can take up to 1000 years to decompose. Shockingly, only 9% of the plastic produced annually is recycled, while an astounding 2 million plastic bags are used every minute worldwide. This paper highlights the primary goal of plastic recycling, with a particular focus on using plastic to manufacture roof tiles. The motivation behind this approach is that everyone deserves a decent roof over their heads. To achieve this, a well-balanced mixture of waste polypropylene (PP), quartz sand, and fly ash minerals was utilized in producing plastic roof tiles. The research employed a hot press process to prepare samples of all composite materials, and no cracks or fractures were observed on the surface of these samples. The results of this innovative process exceed the standards set for most building materials in terms of both mechanical and thermal properties, demonstrating a compressive strength of 99.8 MPa, a flexural strength of 35.6 MPa, and an impact energy absorption of 7.93 KJ/m². Importantly, all samples exhibited zero percent water absorption, making these roof tiles ideal for insulation purposes. Additionally, the resulting roof tiles are lightweight and cost-effective compared to conventional options.

1. Introduction

All over the world, plastic waste is one of the biggest problems facing the planet today. According to a Statista survey, people currently produce more than 350 million tons of plastic waste every year. If current policies are not changed, global plastic waste is expected to increase significantly by 2060, to an impressive one billion tons [1]. Plastics in solid waste are an issue of increasing importance. Recycling waste is currently considered the most acceptable long-term disposal method. However, it is known that this route is particularly difficult for plastics [2]. Due to their lightweight, minimal cost, durability, and flexibility, they are used in most of all areas of the modern economy. Since the 1950s, when the mass production of synthetic plastics began, the production and use of plastics have skyrocketed due to these inherent advantages [3].

Plastic comes in different varieties with different materials and qualities. Notable types include polyethylene, polypropylene, polyester, polyvinyl chloride, and polystyrene. The complexity of plastic is generally not as simple as might be assumed [4]. Because of its low cost, adaptability, and excellent properties, PP is utilized in different bundling structures and has supplanted conventional materials like paper and cellophane. It is generally utilized to make beds, bottles, containers, yogurt cups, hot beverage cups, food presses, and so on [5]. According to a Statista study, the global polypropylene market will be around 79 million tons in 2022 [6].

Fly ash is most commonly used as an aluminosilicate fixative in the production of geopolymer concrete and essential mixes as a partial or complete replacement for Portland concrete [7]. Fly ash from coal combustion generated in nuclear power plants is one of the most potent deposits among various modern waste materials. On one side of the planet, coal-fired power generation generates more than 500 million tons of fly ash annually, of which 25 to 30% is reused in various sectors [8].

In the modern world, two industrial wastes that contribute to pollution are fly ash and polypropylene (PP) waste. Re-evaluating industrial waste is therefore essential to lowering pollution [9]. Polypropylene waste can be recycled as much as possible; it is very beneficial to use it as a binder in the construction industry. Even after impact tests, these roof tiles are essentially impermeable with a porosity of less than 1% [10]. According to a study on the behavior of reinforced concrete columns mixed with plastic under axial compression, plastics can be employed in various construction-related applications. Gowri S. et al. [11] Provide all the support in selecting suitable engineering plastics, processes, and designs for converting conventional material into engineering plastics for performance and system cost benefits.

The study conducted by Koppula N. et al. [12] demonstrated a novel approach by producing plastic bricks using waste high-density polyethylene (HDPE), quartz sand, and bitumen. The optimal mixture, featuring a 3:2 ratio of plastic to sand and 2% bitumen, yielded impressive results, boasting a compressive strength of 37.5 MPa. Additionally, the water absorption rate was found to be below 0.45%, surpassing the performance of many conventional bricks. The efflorescence test revealed that the bricks were resistant to alkalis, showcasing their durability. Notably, these bricks exhibited a low density and proved to be cost-effective when compared to traditional bricks. The research strongly supports the potential utilization of waste plastic, quartz sand, and bitumen in the construction industry.

Bicer A. et al. [9] found that the combination of waste polypropylene (PP) and fly ash enhances compressive strength, reduces water absorption, and improves thermal conductivity when used in appropriate proportions and at specific temperatures. The study observed that there was no synthetic reaction between the components during the creation of the fly ash and PP composite. As the production temperature increased, the thermal conductivity coefficient also increased, leading to improved mechanical properties and reduced porosity values. In a separate study by Siddesh Pai et al. [13], waste PP and sand were utilized to create floor tiles, with a composition of 50% plastic and 50% sand. This proportion balanced both mechanical properties (compression, impact, and transverse strength) and physical properties (water absorption). The results showed that these floor tiles outperformed ceramic floor tiles in various tests, confirming their suitability for use in flooring applications.

The compressive strength of composite materials made from post-consumer polyethylene terephthalate (PET) and fly ash increased by up to 53% as the fly ash content rose from 0% to 50%. The highest recorded compressive strength was 93.4 MPa when a composition of 50% PET and 50% fly ash was used. Additionally, the water absorption was below 0.18%, which falls below the critical value for building materials. A noteworthy observation was that linear shrinkage decreased significantly, by a factor of seven, from 3.9% to 0.54%, with an increase in fly ash content from 0% to 50% [14]. In another study, a researcher explored the feasibility of producing tiles using waste polyethylene terephthalate (PET) bottles and fly ash. The study reported on the mechanical properties and chemical resistance of the manufactured PET polymer tiles. Notably, these tiles exhibited low water absorption, with an efficiency that was 80% lower than that of cement and ceramic tiles. The presence of fly ash in PET polymer tiles impacted the porosity value, particularly when it exceeded 10% in a specific mix [15].

In a study conducted by Akid A.D.M. et al. [16], exploration focused on investigating the fresh, mechanical, and durability properties of concrete influenced by the combination of fly ash and polypropylene fiber. Cement was partially substituted with 15% and 30% fly ash by weight, while polypropylene fiber was added to concrete mixes at volumes of 0.06%, 0.12%, and 0.18%. The inclusion of fly ash and polypropylene fiber significantly enhanced the mechanical and durability characteristics of the cement in comparison to the control mixture. Notably, the combination of 15% fly ash and 0.2% polypropylene fiber had a substantial impact on compressive strength, chloride permeability, sorptivity, and water penetration compared to other concrete mixtures. In the construction industry, the potential of fly ash as a viable alternative to cement in structural concrete production has been extensively studied for years [17]. Sarker P. et al. [18] discovered that fly ash not only improves workability but also reduces the hydration rate and cracking potential of concrete during the early stages of the curing process. Two control concrete mixes achieved compressive strengths of 62 and 68 MPa after 28 days. Experimental results indicated that concrete compositions with 30% and 40% cement replacement by fly ash exhibited average 28-day compressive strengths equivalent to 84% and 63% of the strengths observed in their respective control mixtures.

The research of Seghiri M et al. [19] explores the potential of combining recycled high-density polyethylene (HDPE) with sand, a readily available natural resource, to form a composite material designated as a rooftop tile. The experimental test program involved varying percentages of recycled HDPEr in the mixture, ranging from 30% to 80%. Density and breaking load were assessed through experimental tests, including flexural and impermeability tests. Throughout this study, the density of the polymer rooftop tile exhibited a range from 1.379 to 1.873 g/cm³. The breaking strength, determined through flexural testing, was found to be below the threshold of traditional clay rooftop tiles. However, the impermeability of the polymer rooftop tile proved to be commendable when compared to the control roof-top tile.

In a study conducted by Omosebi Taiwo O et al. [20], an investigation was carried out on tiles crafted from a blend of waste polyethylene terephthalate (PET), fly ash, and sand aggregates. PET waste was incorporated into various mixtures at 30%, 50%, 70%, 90%, and 100% by weight. The assessment of both physical and mechanical properties revealed that tiles containing 30% plastic waste exhibited superior performance compared to other waste fractions in terms of material density, weight, and flammability. The composite tile with 30% PET, 35% fly ash, and 35% sand (designated as PT1) demonstrated notably low porosity values ranging from 2.9% to 0.11%, surpassing those of cement or ceramic tiles. Furthermore, PT1 showcased lower flammability with a linear firing rate of 7.68 mm/min and a higher compressive strength of 11.07 N/mm2. Importantly, there was no significant change in weight observed after immersion in various acidic and basic solutions for seven days. Finally, the tiles had good compressive strength, flammability, and water absorption and were mostly environmentally friendly. This alternative not only holds the potential to lower building material costs but also contributes to waste reduction, mitigating the environmental impact associated with plastic waste disposal [21].

The primary aim of this study is to manufacture roof tiles utilizing waste polypropylene (PP), sand, and fly ash, evaluating their suitability as construction materials. Significantly, all materials are sourced from waste streams, offering substantial benefits in terms of solid waste disposal and environmental preservation. As a result, these plastic roof tiles stand out as the ideal option for replacing both roof and floor tiles. They offer remarkable compressive strength, flexural strength, low water absorption, high energy absorption, very low density, and minimal heat absorption. Additionally, using these tiles helps to gradually reduce plastic waste, making them a sustainable and effective alternative. This research paper follows with materials and methods, methodology, test equipment, test parameters, results, and discussion and ends with a conclusion.

2. Materials and Methods

2.1. Materials Used

2.1.1. Polypropylene

Polypropylene (PP) stands out as a polyolefin derivative with slightly higher toughness than polyethylene. This popular plastic has low density and excellent heat resistance. Its outstanding characteristics, combined with ease of processing, have established polypropylene as a highly versatile and widely used plastic that outperforms several competitors. Its applications are broad, ranging from packaging to automotive, consumer products, pharmaceuticals, and cast film production. Arrow Plastics, situated in Landau, Germany, supplied recycled PP.

Table 1. Properties of polypropylene [9].

Property	Units	Value
Density	g/cm3	0.90–0.92
Thermal conductivity coefficient	W/m K	0.56
Glass transition temperature	°C	20
Specific heat gravity	Kj/kg K	0.44
Water absorption	%	0.01
Melting point	°C	150–160

summarizes the features of polypropylene.

2.1.2. Quartz Sand

Premium quality, meticulously picked, and delicately treated natural quartz stone yields high-purity silica sand with silica dioxide concentration ranging from 99.5% to 99.9% and iron oxide percentage less than 0.001%. This high-purity silica sand is used in a variety of industrial applications, including glass, refractories, ferrosilicon fluxes, ceramics, abrasives, and molding silica sand. It is extremely resistant to acid and chemical erosion, making it an important component in the manufacture of acid-resistant concrete. For experiments, a particle size range of 0.1–0.3 mm was particularly selected. Silica sand, noted for its chemical resilience and higher melting temperature than metals, is used as foundry sand and in the construction of bricks. The silica sand was given by Hochschule Kaiserslautern in Pirmasens, Germany.

Table 2. Properties of quartz sand [12].

Property	Units	Value
Specific gravity	-	2.43
Water absorption	%	1.90
Density	g/cm3	2.65

.

2.1.3. Fly Ash

Fly ash is a finely divided waste formed during the burning of coal dust and carried away from the combustion chamber by exhaust gases. Currently, about 20 million tons of fly ash are used annually in a variety of technical situations. Portland cement concrete (PCC) is commonly used in road construction to stabilize soil and roadbeds, as well as for flowable fills, grouts, structural fills, and asphalt fills. Fly ash is mostly used as a pozzolan in PCC applications. Pozzolan is a silicate or silicate-containing substance that, when finely divided, interacts with calcium hydroxide at room temperature in the presence of water to produce a cementitious compound. This study used EFA-Füller^®, a certified hard coal fly ash used as a concrete addition in the concrete industry. The pulverized hard coal melts at a boiler temperature of around 1300 °C, yielding a spherical and amorphous composition. This unique fly ash was obtained from Baumineral Kraftwerkstoffe, which is located in Herten, Germany.

Table 3. Chemical composition of fly ash.

Composition	Mass Percentage
SiO2	47–57
Al2O3	20–28
Fe2O3	5–13
CaO	3–10
MgO, Na2O, K2O	1–3

summarizes the chemical makeup of fly ash. Density ranges from 2 to 2.2 g/cm³.

2.2. Methodology

2.2.1. Mold Design

The experiment used rectangular plates with dimensions of 100 mm × 100 mm × 4 mm. Two of these plates were chosen and firmly attached together using thermal-resistant tape. Figure 1 depicts the design of the mold.

2.2.2. Manufacture of Tiles

To make the formulations shown in

Table 4. Composition of samples.

Polypropylene	Sand	Fly Ash	Samples
70%	30%	0%	PPSF 1
	20%	10%	PPSF 2
	10%	20%	PPSF 3
50%	50%	0%	PPSF 4
	40%	10%	PPSF 5
	30%	20%	PPSF 6
30%	70%	0%	PPSF 7
	60%	10%	PPSF 8
	50%	20%	PPSF 9

, the materials were combined in a kneader and heated to 165 °C while rotating at a speed of 40 rpm, as seen in Figure 2. After a few minutes, the mixture melted and was collected by taking it outside. After a few minutes, lumps formed. Then, using a granulator, these lumps were crushed into small particles that ranged in size from 0.2 mm to 0.4 mm. To make sample removal easier, a mold release spray was applied to a rectangular mold. After that, the mass determined by combining the density and volume of the grains was put into the mold. Granule-filled, the mold was sandwiched between two hot press plates with a constant temperature of 180 °C and pressure of 60 bar. The sample was made after an hour, and it was then allowed to sit inside the mold for a further half hour to allow the gas to escape and cure. After that, the sample was demolded and given ten minutes to cool as shown in Figure 3. Abrupt air cooling resulted in the modest bending of several samples’ surfaces, especially when the plastic content was higher. For every composition, 45 samples were created, with 5 samples in each set. After that, a cutter was used to cut these samples to standard sizes so that they could be tested further—including bending, compression, and impact tests.

2.3. Test Equipment and Test Parameters

2.3.1. Compression Test

The compression strength of plastic roof tiles was evaluated following the DIN EN ISO 604 standard [22]. A total of 45 samples were subjected to testing. Each sample was precisely cut into pieces measuring 12 mm × 12 mm × 8 mm and assessed using a compression machine. A Zwick roll universal testing machine was employed for the test, with a maximum force capacity of 20 KN and a testing speed of 1 mm/min. The load was applied until the specimen either broke or deformed. The ultimate stress at which the sample exhibited failure or deformation was recorded and the compression strength was calculated using Equation (1).

$$\mathrm{Compression} \mathrm{strength}={\displaystyle \frac{\mathrm{F}}{\mathrm{A}}}$$

(1)

Here, F represents the maximum load and A denotes the area of the sample.

2.3.2. Water Absorption Test

The objective of the test was to determine the percentage of water absorbed by samples after a three-day immersion. A lower water absorption percentage indicates better performance. The samples were initially weighed, and excess moisture was removed by placing them in an oven. After two days with no change in weight, the samples were considered ready for the water absorption test. Cuboid-shaped samples, measuring 50 mm × 50 mm × 8 mm, weighed, noted as W_D, and immersed in water for three days. Following the immersion period, the samples were wiped with a dry cloth, reweighed, and recorded as W_S. The difference in water absorption was calculated using Equation (2).

$$\mathrm{Water} \mathrm{absorption}={\displaystyle \frac{{\mathrm{W}}_{\mathrm{S}}-{\mathrm{W}}_{\mathrm{D}}}{{\mathrm{W}}_{\mathrm{D}}}}\times 10$$

(2)

where W_S = saturate weight of specimen after submersion and W_D = dry weight of the specimen.

2.3.3. Flexural Test

The flexural tests were carried out following the DIN EN 178 standard [23] and utilizing a Zwick universal testing machine as shown in Figure 3. Each composition underwent testing with a total of five samples. The test parameters included a preload of 1 MPA, a 1 mm/min speed, and a 5 mm/min test speed. Test Xpert II testing software was employed to determine the breakpoint’s flexural strength, flexural modulus, and elongation. Standardized dimensions of 80 mm × 10 mm × 4 mm were maintained for the samples to ensure a consistent evaluation of material performance under bending forces.

$$\mathrm{Flexural} \mathrm{strength}\hspace{1em}\hspace{1em}{\mathsf{\sigma }}_{\mathrm{b}}={\displaystyle \frac{3\mathrm{F}{\mathrm{L}}_{\mathrm{v}}}{2\mathrm{b}{\mathrm{d}}^2}}$$

(3)

Here, F = Force, L = length, b = width, and d = thickness of the specimen.

2.3.4. Impact Test

Charpy impact tests were conducted following DIN EN ISO 179 standard [24]. The apparatus used was defined by specific parameters, including an impact energy of 4 joules, an impact velocity of 2.9 m/s, a hammer weight of 0.951 kg, and a measurement unit for impact energy in KJ/m². In this test, no notch was introduced, and the sample dimensions were maintained at 80 mm × 10 mm × 8 mm. A total of five samples underwent testing, and the values were recorded by calculating the mean from the results of the five samples.

$$\mathrm{Impact} \mathrm{work}\hspace{1em}\hspace{1em}{\mathrm{a}}_{\mathrm{n}}={\displaystyle \frac{{\mathrm{A}}_{\mathrm{n}}}{\mathrm{b}\mathrm{h}}}$$

(4)

Here, A_n = impact work, b = width, and h = thickness of the specimen.

2.3.5. Thermal Conductivity Test

The measurement of thermal conductivity was carried out using a specially designed measuring cell in accordance with ASTM E 1225-04 standard [25]. Circular samples with a diameter of 5 cm and a thickness of 8 mm were prepared for the experiment. To ensure proper coupling and minimize interfacial thermal resistance, the samples were coated with thermal conductivity paste. Four distinct temperature zones were established with temperature ranges from 90 k to 1300 k, and the pasted samples were positioned below these zones. Subsequently, the values obtained were displayed on the screen and duly recorded after a certain period.

$$\mathrm{Thermal} \mathrm{conductivity}\hspace{1em}\hspace{1em}\mathrm{k}={\displaystyle \frac{\mathrm{Q}\mathrm{d}}{\mathrm{A}\mathsf{\Delta }\mathrm{t}}}$$

(5)

Here, Q = the amount of heat transferred, d = distance between two isothermal planes, A = area of the surface, and ∆t = temperature difference.

2.3.6. Density

Density measurements were conducted by weighing the samples to identify the composition with the lowest density. A total of 27 samples were tested for 9 compositions to measure density, by taking average values from 27 values.

3. Results

3.1. Water Absorption

The experiment involved weighing all 45 samples in a dry state. Subsequently, the samples were submerged in water for 72 h, as illustrated in the accompanying Figure 4. Following this immersion period, the samples were carefully dried using a dry cloth and then reweighed. Remarkably, none of the samples exhibited any water absorption, attributed to the presence of plastic content and minimal formation of voids or pores. The results as shown in Figure 4 indicate impermeability, making it a favorable outcome for applications such as roof insulation and areas where direct contact with water is anticipated. These findings suggest that these roof tiles display resilience against moss and other weather-related material changes.

3.2. Density

The density measurements of the polypropylene roof tiles revealed values of 1.199, 1.168, 1.246, 1.657, 1.295, 1.372, 1.441, 1.658, and 1.567 g/cm³ for PPSF 1 through PPSF 9, respectively. These densities were significantly lower compared to various building materials, as illustrated in Figure 5. Among the composite tiles, those with 70% plastic content had the lowest density at 1.168 g/cm³, while those with 30% plastic content had the highest density at 1.658 g/cm³. Density decreases when fly ash is used in place of sand, but excessive amounts of fly ash cause an increase in density. Additionally, a reduction in plastic content and changes in the proportions of sand and fly ash lead to higher density due to the naturally higher density of sand compared to both recycled polypropylene and fly ash, with fly ash also contributing to slight density variations.

3.3. Impact Energy

The incorporation of sand and fly ash, coupled with a reduction in plastic content, leads to decreased energy absorption in the samples due to the inherently brittle nature of the composite materials. Figure 6 illustrates the impact strength of the specimens, revealing a noticeable decline in energy absorption as both fly ash and sand percentages increase while plastic content decreases. Among all the specimens, PPSF1 demonstrated the highest impact strength, impressively absorbing 8.76 kJ/m² of energy, surpassing the other samples. PPSF2 exhibited a result of 7.93 kJ/m², representing a 9.47% decrease compared to PPSF1. Conversely, PPSF9 displayed the lowest absorption at 3.34 kJ/m², which was 62% less than PPSF1. The remaining samples—PPSF3, PPSF4, PPSF5, PPSF6, PPSF7, and PPSF8—absorbed energy at rates of 6.8, 6.5, 6.03, 5.86, 4.18, and 3.66 kJ/m², respectively.

3.4. Flexural Test

Figure 7 illustrates the three-point bending strength of PPSF composite materials with varying sand and fly ash contents. The flexural strength of these materials follows a pattern of initial increase at 70% plastic content, followed by a decline with an increasing sand percentage. PPSF2, featuring 70% plastic, 20% sand, and 10% fly ash, exhibits the maximum flexural strength at 35.6 MPa, while PPSF7 displays the minimum at 20.2 MPa. In descending order, the flexural strengths are PPSF1 (34.48 MPa), PPSF3 (34.38 MPa), PPSF4 (23.3 MPa), PPSF5 (30.28 MPa), PPSF6 (27.875 MPa), PPSF8 (21.44 MPa), and PPSF9 (20.03 MPa). In comparison to PPSF2, the flexural strength of PPSF1, PPSF3, and PPSF5 decreases by 3.1%, 3.4%, and 14.9%, respectively. For PPSF4, PPSF6, PPSF7, PPSF8, and PPSF9, the reduction is more substantial at 34.5%, 21.7%, 43.2%, 39.77%, and 43.7%, respectively.

3.5. Compression Strength

Among all the mechanical properties obtained, the most crucial one is the compression strength, as depicted in Figure 8. In the case of 70% plastic content, the addition of fly ash, ranging from 0% to 20%, led to a significant increase in compressive strength from 98.28 to 104 MPa for PPSF3. The results for PPSF1 and PPSF2 were 98.28 and 99.8 MPa, respectively, which were 5.5% and 4.07% lower than PPSF3. For 50% plastic content, the compressive strength increased from 87.9 of PPSF 4 to 98.6 MPa with the addition of 10% fly ash for PPSF5 and then decreased from 98.6 to 82.82 MPa with 20% fly ash for PPSF6. Meanwhile, for 30% plastic content, the compressive strength for PPSF7, PPSF8, and PPSF9 was 85.68, 78.4, and 74.44 MPa, respectively. It is noteworthy that the compressive strength for all samples is two to three times higher than the minimum requirements for traditional roof tiles. Specifically, for 70% plastic content, deformation was observed without cracks or rupture, while for 50%, small cracks were observed. Finally, for 30% plastic content, the samples experienced distortion when the ultimate load was reached, indicating a more brittle behavior as the plastic content decreased.

3.6. Thermal Conductivity

As the concentration of plastic decreased in the samples, there was a noticeable increase in their thermal conductivity, as shown in Figure 9. Samples with 70% plastic content exhibited significant heat resistance, similar to typical roof insulation, indicating a direct correlation. For instance, PPSF1 had the lowest conductivity at 0.284 W/m K, while PPSF2 and PPSF3 showed higher values of 0.376 and 0.532 W/m K, respectively, representing a 32% and an 87% increase compared to PPSF1. For samples with 50% plastic content, PPSF4, PPSF5, and PPSF6 displayed thermal conductivity values of 0.622, 0.597, and 0.572 W/m K, respectively. Finally, with 30% plastic content, the samples absorbed more heat than those with 70% and 50% plastic content. For example, PPSF7, PPSF8, and PPSF9 had thermal conductivity values of 0.985, 0.971, and 1.023 W/m K, respectively. An increase in sand percentage corresponded with higher thermal conductivity. However, when the proportions of plastic, sand, and fly ash were appropriately balanced, the sample functioned as an effective insulator, exhibiting poor heat conductivity.

4. Discussion

4.1. Discussion of Results

The adoption of plastic roof tiles instead of traditional ones aims to prioritize plastic recycling and minimize harm to natural resources. This research primarily focuses on plastic recycling, maintaining a consistent proportion of plastic while varying the ratios of sand and fly ash. Acknowledging the escalating environmental impact of sand mining, particularly its adverse effects on biodiversity and aquatic habitats, the study seeks to address these concerns. A significant environmental benefit can be achieved by substituting just 1% of sand with fly ash, contributing to environmental conservation and reducing the overall demand for sand. The proportions of fly ash were restricted to 10% and 20% due to concerns related to strength.

Both sand and fly ash played integral roles in this study, influencing the workability, setting behavior, and properties of plastic roof tiles. The obtained results demonstrate favorable outcomes when compared with the standards of existing traditional roof tiles. The compressive strength of polypropylene roof tiles reached the highest values, particularly 104 MPa for PPSF 3 and 99.8 MPa for PPSF 2. Importantly, the compressive strength for all samples is two to three times higher than the minimum requirements for traditional roof tiles. For a plastic content of 70%, the deformation was observed without cracks or rupture, while at 50%, small cracks were observed. Finally, at 30% plastic content, the samples experienced distortion when the ultimate load was reached, indicating a more brittle behavior as the plastic content decreased. When the plastic content was high, the samples deformed. However, when the sand content was increased, the samples did not deform; they broke directly.

The flexural strength for PPSF 2 was 35.6 MPa, and for PPSF 9, it was 20.03 MPa. Observing the results confirms that for samples with 50% and 30% plastic content, the outcomes were significantly lower compared to those with 70% plastic content. As the plastic content decreases and the proportions of sand and fly ash vary, the results exhibit variability. Notably, fly ash dominated the results when the content was at 10% and 20%. This suggests that incorporating up to 10% fly ash is suitable with an appropriate amount of PP and sand content. However, an excess of fly ash and an imbalance in plastic and sand contents lead to a significant decrease in adhesion between molecular bonds. The highest flexural strength in PPSF 2 can be attributed to the presence of quartz in both sand and fly ash, enhancing the stress transfer at the interface between the PP matrix, sand, and fly ash [26,27,28]. Consequently, the optimal mixing ratio is determined to be 10% fly ash and 20% sand, as deviations from this ratio, either higher or lower, result in a decrease in flexural strength. The roof tiles exhibited varying impact strengths depending on the composition. The highest impact strength was 8.76 kJ/m² for PPSF 1, while the lowest was 3.34 kJ/m². When a balanced mixture of plastic and sand was used, the sample displayed ductile behavior, absorbing more energy. However, with the addition of fly ash and variations in plastic and sand contents, the samples absorbed less energy due to a gradual shift from ductile to brittle behavior.

In terms of thermal conductivity, PPSF 1 with the highest plastic content showed very low conductivity at 0.284 W/m K. On the other hand, samples with a high sand content and the inclusion of fly ash absorbed more heat energy, with PPSF 9 recording a high thermal conductivity of 1.023 W/m K. The increase in thermal conductivity values was attributed to quartz sand, which has higher thermal conductivity compared to plastic and fly ash. Consequently, low thermal conductivity indicates good insulation properties, implying the material’s inefficiency in conducting heat and reduced heat transfer ability.

In the study by Omosebi Taiwo et al. [16], roof tiles made from polyethylene terephthalate (PET), sand, and fly ash achieved a maximum compressive strength of 11.07 MPa, with a density of 1.3 g/cm³ for tiles containing 70% PET. In contrast, roof tiles produced from waste polypropylene (PP), quartz sand, and fly ash demonstrated a significantly higher compressive strength of 104 MPa, with a density of 1.1 g/cm³ for 70% plastic content. The results for impact strength, water absorption, thermal conductivity, and flexural strength confirmed that these roof tiles are not only thermally insulated but also exhibit excellent mechanical and thermal properties, making them a highly effective composite roofing material.

4.2. Comparison with Clay and Concrete Roof Tiles

Table 5. Comparison of PPSF 2 with conventional roof tiles.

Properties	Clay Roof Tiles	Concrete Roof Tiles [29]	PPSF 2 Roof Tile
Density (Kg/m3)	1620–2402	2000–2500	1168
Impact energy (Kj/m2)	3–3.2	2	7.93
Water absorption (%)	6	13	0
Flexural strength (MPa)	6.8–17.2	4–6	35.6
Compressive strength (MPa)	55–65	13.7–41.3	99.8
Thermal conductivity (W/m K)	0.710	1–1.8	0.376

below presents a comparison between traditional roof tiles and plastic roof tiles, highlighting the exceptional mechanical and thermal properties of the tiles containing 10% fly ash in all samples, particularly PPSF 2, which outperforms conventional options like clay and concrete roof tiles. The data clearly demonstrate the superior strength and thermal resistance of the composite material compared to the other two types of roof tiles, making it an excellent choice for roof insulation.

The study utilized recycled polypropylene (PP), sand, and fly ash to manufacture these roof tiles, revealing significant improvements in strength while also reducing their weight. Additionally, the cost analysis shows that a single plastic roof tile, especially the PPSF 2 tile, costs only EUR 3.5 (This cost is based on the composition of 700 g of plastic at EUR 3, along with 200 g of sand and 100 g of fly ash, each costing EUR 0.25). These cost-effective prices not only benefit the environment and consumers but also provide relief to the government, supporting efforts to reduce plastic usage and recycle plastic.

5. Conclusions

To evaluate the potential use of various waste materials such as polypropylene (PP), fly ash (FA), and sand for improved setting behavior and enhanced strength, composite materials known as PPSF composites were created using different ratios of PP, FA, and sand. The fabrication process involved a hot press machine that applied both pressure and temperature. The study explored the characterization, as well as the thermal and mechanical properties of these composites. The key findings are summarized below:

A range of PPSF composites was successfully produced using a hot press machine with varying proportions of materials. These composites had a fine texture and smooth surface, free of any cracks or pores.

The composites had low-density values compared to many construction materials, and all samples exhibited zero water absorption, indicating favorable setting behavior.

In terms of mechanical properties, the optimal mix of plastic and sand resulted in high energy absorption in the samples. The inclusion of the right amount of fly ash and sand also enhanced the bending and compressive strength.

Regarding thermal properties, samples with higher plastic content showed increased heat resistance. However, when fly ash and sand were added and the plastic content was reduced, the thermal conductivity values increased.

Roof tiles play a critical role in protecting homes from diverse weather conditions, including heat, cold, rain, and storms. Therefore, it is essential that they effectively withstand the elements. Plastic roof tiles, such as PPSF2, exhibit impressive properties with a compressive strength of 99.8 MPa, a flexural strength of 35.6 MPa, an impact strength of 7.93 kJ/m², zero water absorption, and a thermal conductivity of 0.37 W/m·K. These attributes ensure that PPSF2 meets all the necessary standards for ideal household roofing, surpassing the performance of traditional roof tiles.

In summary, incorporating 10% fly ash is considered optimal as a filler, as exceeding this threshold tends to weaken the strength properties of the other materials. The findings from the nine different proportions tested show that these plastic roof tiles outperform traditional clay and concrete tiles. As a result, these plastic tiles emerge as the best choice for replacing both roof and floor tiles. They offer exceptional compressive strength, flexural strength, energy absorption, very low density, minimal heat absorption, and zero water absorption. Additionally, using these tiles helps reduce plastic waste, making them a sustainable and an efficient alternative.

While recycling plastic in this way is commendable, it is important to recognize that plastic can emit greenhouse gases when exposed to high temperatures. Therefore, it is recommended to conduct this process in a vacuum to prevent the formation of harmful compounds such as CO and CO₂, which could negatively impact the environment.

Furthermore, similar ratios can be applied by substituting plastics like high-density polyethylene (HDPE) and polyethylene terephthalate (PET) while maintaining the same proportions of sand and fly ash. This approach aims to determine whether HDPE or PET can surpass the properties of polypropylene roof tiles. Conducting such experiments could significantly reduce plastic waste and enhance plastic recycling efforts.