An Experimental Study to Mitigate Environmental Impacts by Transforming Waste Plastic Bags into Paving Blocks and Roof Tiles

Abstract

The world’s plastic bag problem adversely impacts the environment daily. Plastic bags decompose after years, and some may take centuries, leading to pollution. Society relies on plastic bags for every task, which causes many problems for humans and aquatic life. Focusing on Sustainable Development Goal 12 (SDG 12), this research used waste plastic bags melted in a boilery to develop plastocrete to cast plastocrete paving blocks and roofing tiles. Compressive and split tensile strength tests were performed on plastocrete paving blocks, while a thermal insulation test was performed on roofing tiles in the Concrete Lab of our Department. The compressive strength test on plastocrete showed that it can easily replace concrete pavement blocks after giving good compressive strengths compared with concrete blocks. Being very low in tensile strength, plastocrete is not recommended for flexure members. The thermal insulation test results indicate that using plastic bags as roofing tiles decreases thermal conductivity compared with a controlled reinforced slab. Hence, it is concluded that plastocrete will help reduce pollution in the terrestrial and aquatic environment and can be an effective waste disposal solution. The plastocrete-led paving blocks and roofing tiles not only help economically but also help preserve nature and the environment from land pollution.

1. Introduction

Plastic is a rapidly growing segment of municipal solid waste. One of the serious problems that is being faced by the world is the disposal of waste material, including waste plastic bags, as these are non-biodegradable because hundreds of years are required for biodegradation [1]. Due to the existence of plastic bags on land for an extended period, these can cause rising problems of land pollution. Plastic bags are a significant source of water pollution. These can quickly enter water bodies, as people throw away bags carelessly on roads, rivers, etc. Plastic bags can also badly disturb aquatic life to a greater extent [2]. Usually, plastic bags are polyethylene and contain long chains of ethylene monomers. Shopping bags are either low-density polyethylene or high-density polyethylene [3]. Pakistan has the sixth largest population in the world and is one of the developing countries [4]. According to the Environmental Protection Department surveying report, almost 55 billion plastic bags are used annually in Pakistan, and the increase in plastic bag usage is nearly 15% yearly. The manufacturing units of plastic bags in Pakistan are about eight thousand—the average daily production capability of one unit ranges from 260 kg to 500 kg [5]. According to the Environmental Protection Department surveying report, the worldwide consumption of plastic bags is 5.5 trillion tons. The number of plastic bags, estimated at 14 million tons, affects aquatic life. Due to swallowing plastic, the loss of the lives of marine animals is around 0.2 million [6]. Plastic bags are fabricated of HDPE. These white plastics have low-temperature resistance permeability and sound rigidity and strength. Wear and tear occur quickly in this type of plastic bag with normal force. Pakistan produces a massive amount of shopping bags, an enormous amount of grocery bags, and an excessive amount of trash bags, and they are mainly preferred because they possess sound strength and are economical [7,8,9,10].

Whenever two systems meet each other, there must be a transfer of heat from one system to another. The heat transfer process continues until an equilibrium is established between the two systems. The temperature flows from higher to lower potential until they become equal [11]. Sustainable temperatures will be maintained in a building in summer and winter, which artificially impacts a country’s economy adversely as heat is transmitted across confined airspaces by radiation, convection, and conduction [12]. Any type, size, and surface finish of various thermal insulation materials can prevent thermal insulation integrity from damage and enhance the structure’s appearance [13]. For the insulation of buildings, it is necessary to use low-cost and high-insulating property products [14]. Thermal insulation of a building is the superior way to protect it from the flow of heat because the material used for insulation of a building is good at lowering the flow of heat, and the function of insulation in a building is to attain energy conservation by reducing heat loss or gain [13]. In summer, heat flows into buildings; in winter, heat flows through openings in buildings or residences [15].

Many previous researchers investigated the reuse of plastic waste using different techniques [16,17]. Three paver blocks of ratios 1:4, 1:5, and 1:6 were prepared. They concluded that increasing the percentage of sand and aggregate decreased the compressive strength of paver blocks with plastic waste. In that research, the paver block of ratio 1:4 had the maximum compressive strength due to the smaller proportion of coarse aggregate and sand [3]. In 2019, Avinash et al. [10] utilized waste plastic to manufacture paver blocks. Paver blocks were made by adding 50%, 60%, and 70% of plastic waste by weight with sand. Different tests like compressive strength and water absorption tests were performed on the block samples. They concluded that increasing the waste plastic proportion with sand gives a high resistance against compressive strength. On the other hand, the water absorption value was less for high plastic waste. Recycled plastic was used by M. Achitra et al. [18] in concrete paver blocks in different proportions in 2018. A synthetic material made from a wide range of organic polymers such as polyethylene, polyvinyl chloride (PVC), nylon, etc., was used, having a specific gravity of 1.5 and water absorption of 0.18 in concrete in the ratio of 1:2:2 with four proportions of 0.5%, 1%, 1.5%, and 2% of plastic waste and coconut fiber used in concrete. Several paver blocks were cast with these proportions. By comparing results, they determined that 0.5% coconut fiber and plastic waste gave a compressive strength after 7 and 28 days of 19.170 and 30.021, respectively. Similarly, 1% coconut fiber and plastic waste gave a compressive strength after 7 and 28 days of 17.746 and 28.096, respectively. All the test results show that 0.5% coconut fiber and plastic waste added to concrete blocks gave good compressive, flexural, and split tensile strengths.

In 2018, Mohan et al. [19] used different ratios of plastic waste with fine aggregates and quarry dust. The percentage of plastic and fine aggregates was 1:3. Many cubes were cast. These cube samples were tested for compressive strength, split tensile strength, and water absorption. The results showed that the block consisted of 60% to 70% quarry dust, fine aggregate, and plastics, and from the above observation, it was calculated that the use of 20% recycled plastics did not affect the properties of the block. In a similar study, Ganesh Tapkire et al. [20] recycled plastic in different proportions with the replacement of aggregates in concrete with plastic aggregates having 10%, 20%, and 30% Portland cement of grade 43 (IS:269-1969) and coarse aggregates of size 10 mm used in a mix design. Several tests were performed on these aggregates for water absorption, density, and sieve analysis. A compressive strength test was carried out on these cubes, and the results were compared. The sample’s compressive strength with 30% plastic waste was 25.43 N/mm² and 37.77 N/mm² after 14 and 28 days. They concluded that 20% plastic waste could be used with 70–80% cement and sand coarse aggregates in paving blocks without affecting the strength, which satisfies the I.S.456-2000.

In 2019, Rahman et al. [21] recycled waste plastics into pavement blocks and studied their characteristics. The materials used for paver blocks were plastic bags, quarry dust, fine aggregates, and cement as a binder. Fine aggregates at a size of 1.7 mm with ratios (P: F.A) 1:3 mix design were prepared to check the material’s workability. A water absorption test was performed on the sample, which showed that the model with the maximum plastic portion had a maximum water absorption capacity. Their results showed that 20% recycled plastic could be used without affecting the properties of concrete blocks. It also resulted in a 15% weight loss reduction in the paver block. In 2021, Surkar et al. [22] produced low-density polyethylene (LDPE) bonded sand blocks and pavers. Several samples were cast to investigate the mechanical properties of specimens with plastic waste. A compressive test, split tensile test, and water absorption test were performed. After the tests, it was observed that the compressive strength and split tensile strength decreased by almost 25% of the specimen with low sand content by increasing the sand content.

In 2021, Kazi et al. [23] used plastic waste with fine aggregates and cement in different proportions. In their project, paver blocks were prepared with aggregate that was partially replaced with plastic waste in different proportions, i.e., 0%, 2%, 4%, 6%, 8%, and 10%, and they found the effects on compressive strength and water absorption of the plastic block compared to conventional concrete paver blocks. The result showed that when they increased the percentage of waste plastic, the water absorption of paving blocks increased by 1.44%, 1.50%, 1.55%, 1.59%, 1.64%, 1.70%, and 1.76%, respectively. In 2019, Raju et al. [24] used waste plastic to replace cement in paver blocks. The cement was replaced with plastic waste, quarry waste, and M-Sand. Three paver blocks were cast. After casting the blocks, they remained dry for 24 h and were then removed from the mold for testing. The plastic blocks were tested for compressive strength and water absorption. They concluded that the block with 0.50% quarry dust had a maximum compressive strength and water absorption with 0.25% quarry dust and 1% plastic waste maximum. The same research was also carried out by [25,26,27,28,29,30].

Hence, focusing on Sustainable Development Goal 12 (SDG 12), i.e., “Ensure sustainable consumption and production patterns” [31], it is necessary to protect the environment from pollution because, in comparison with all other factors, plastic pollution is increasing daily due to plastic waste. Plastic bags are the central problem of the world for pollution. Special care for the environment must be taken, and we must find new methods to reuse this plastic waste to make some products to decrease plastic and protect the environment. Thus, this study makes plastocrete using plastic bag waste. The purposes of this research are to investigate the mechanical properties of plastocrete and to find a way to reuse plastic bag waste by reducing environmental challenges related to plastic waste. Plastocrete is a term used when waste plastic bags are heated at a high temperature in a boiler, where, upon heating, solid plastic bags melt into liquid form. Then, this liquid is allowed to settle and cool down in any desired mold.

2. Materials and Methods

The following hierarchy was followed to complete this research, as elaborated in Figure 1.

2.1. Plastic Bags

In Pakistan, people mostly use plastic bags to carry groceries from the market to their homes. Plastic is used to wrap things, including car parts, toys, and other electronic appliances like refrigerators, televisions, etc. Plastic bottles and many products are being made from plastic nowadays. Plastic bags are cheap and are being used in Pakistan on a large scale. After using plastic bags, people throw these bags on streets and roads, polluting the environment. In Pakistan, millions of tons of plastic are drastically polluting the land and water bodies. Plastic bags are utilized for packaging and transporting goods and are also economical because they are cheap. Figure 2 shows waste plastic bags thrown on the streets of Mirpur AJK.

The plastic bags used for casting plastocrete were collected locally as waste plastic bags outside the shops and streets of Mirpur AJK. Plastic bags are made from an ever-available polymer known as polyethylene. The polymer starts out with ethylene commonly extracted from natural gases. Waste plastic was brought to the Concrete Lab of the Civil Engineering Department, Mirpur University of Science and Technology (MUST), Mirpur AJK, and was made ready to use for the project, as shown in Figure 3.

Some properties of plastic bags are given below in the

Table 1. Properties of HDPE Plastic Bags.

Property	HDPE
Density	0.95–0.97 g/cm3
Melting point	~135 °C
Young’s modulus	600–1400 MPa
Tensile strength	20–32 MPa
Toughness	3–5 MPa m1/2
Softening temperature	120–130 °C

[32].

2.2. Apparatus

2.2.1. Boilery

A boilery (Figure 4) is a mechanical machine or apparatus made up of iron. It is used for heating or melting material like plastic waste, bitumen, etc. In this study, a boilery was used for melting plastic bags to make them useable for casting. Parts of the boilery include a material chamber to store the plastic bags. Its size is about 3 × 2 × 3 (ft³). A burning chamber is under the material chamber. Its basic purpose is to heat up the material chamber. Its size is 3 × 2 (ft²). A suction pump sucks out the material that is melted and pumps it out from the chamber. A chimney is used during the melting or burning of plastic bags, which releases toxic gasses that are very dangerous to human health. The function of the chimney is to exhaust these gasses at some known height that is more than normal human height.

2.2.2. Molds

Molds are used to give shape to material that is used to study the properties. Paving block molds and tile molds are used for casting plastocrete.

2.2.3. Paving Block Molds

Paving blocks of size 4″ × 8″ × 3″ are used for casting to prepare for testing. This is the conventional size mostly used in the market. Molds (Figure 5) for paving blocks are lubricated with oil or use butter paper so that they can easily be remolded.

2.2.4. Roofing Tile Molds

Tile molds (Figure 6) of size (12″ × 12″ × 1.5″) are used for casting plastocrete for roofing tiles. Tile molds are also lubricated with oil.

2.2.5. Scoop

A spoon-like metal apparatus, having a short handle and a deep bowl, is used for shifting dry or semi-solid substances from a container. We used it for shifting melted plastic material from the container.

2.3. Casting Methodology

2.3.1. Casting Procedure

The plastic bags were cleaned and the boilery was filled with the waste plastic bags. Upon heating, solid plastic bags melt into liquid form. The plastic bags began to melt at 110 to 130 °C, but in this study, the consistency needed was for casting paving blocks, and this consistency was achieved at the temperature of 200 to 250 °C. This temperature was measured at the time of casting the specimen. During this study, wood was used for heating purposes. There was no temperature-controlling mechanism installed in the boilery. The temperature was taken with the help of an infrared handheld thermometer at the time of casting the specimen.

Oil can be used for lubricating paving block molds and tile molds for easy de-molding. First, paving blocks are cast with plastic bags. Molted product from the boilery is then transferred to the molds. With the help of a compressor machine, the molds are compressed to remove pores from the product. Tiles are also cast with only waste plastic bag molten material and compressed the same as the paving blocks. Both paving blocks and tiles are placed in normal atmosphere for 24 h to make them cool and to convert into solid form. After 24 hours, the specimens are de-molded and tested.

2.3.2. Casting of Paving Blocks

Paving blocks of size 4″ × 8″ × 3″ are cast. Paving blocks, P_1, P₂, and P₃ are cast with the same proportion of HDPE and LDPE (1:1) waste plastic bag molten material, as shown in Figure 7 and Figure 8.

2.3.3. Casting of Roofing tiles

Roofing tiles of size 12″ × 12″ × 1.5″ are cast. Each mold is cast with waste from the plastic bags, as shown in Figure 9 and Figure 10.

2.3.4. De-Molding

After molding, both the paving blocks and tiles are placed in normal atmosphere for 24 h to make them cool and harden so that these molds are ready to use for testing. Then, the paving blocks and tiles are de-molded and tested [30].

2.4. Testing Methodology

2.4.1. Compressive Strength Test

A compressive strength test (Figure 11) was performed on casted plastocrete paving blocks after 24 h and locally made concrete paving blocks, in accordance with BS 1881-116 [33]. Basically, the aim was to reduce plastic waste by making paving blocks and using plastocrete blocks instead of concrete blocks. So, a comparison of compressive strength was made to check whether the idea would work or not. The specimens were tested at a specified loading rate using a compression testing machine in the direction from any depth in paving blocks. Compressive strength was calculated using Equation (1).

Compressive strength, C= P/A

(1)

where

• C = Compressive strength of the specimen;
• P = Maximum load indicated by the testing machine;
• A = Area of the specimen.

Figure 11. Compressive strength test: Concrete Lab.

Figure 11. Compressive strength test: Concrete Lab.

2.4.2. Split Tensile Strength Test

A split tensile test (Figure 12) was performed on casted plastocrete paving blocks after 24 h and locally made concrete paving blocks, in accordance with BSEN 1338 [34]. Split tensile strength was calculated using Equation (2).

Split tensile strength:

T= 0.637 × K × P/L × T

(2)

where

• T = Split tensile strength;
• K = Correction factor for thickness;
• P = Maximum load indicated by the testing machine;
• L = Length of paver block;
• T = Thickness of paver block.

Figure 12. Split tensile strength test: Concrete Lab.

Figure 12. Split tensile strength test: Concrete Lab.

2.4.3. Heating/Cooling Thermal Cycle Test

A heating and cooling thermal cycle test (Figure 13) of specimens was carried out in the chamber, as shown in Figure 13. This setup can test one single specimen at a time. The chamber walls are made up of a wooden chip, and inside the wall, there is an additional layer of thermophore covered with aluminum foil to seal the flow of heat. A tile can be placed in the middle of the chamber. At the top of the chamber, an infrared 100-Watt bulb is fixed, which is used as a heat source during the test process. To record the temperature of the bottom surface of the slab, lower chamber, open environment, and upper chamber, four temperature sensors T1, T2, T3, and T4, respectively, are used, which are connected in their respective places, and then it is sealed properly. The data logger is placed aside with the chamber on the tripod, and time interval is set in seconds [35]. Equation (3) explains the temperature effect on thermal conductivity.

Q = K (ΔT/L)

(3)

where

• T = T2–T4;
• qL = K(ΔT);
• K = qL/ΔT.

Figure 13. Schematic system of the heating/cooling thermal cycle: Concrete Lab.

Figure 13. Schematic system of the heating/cooling thermal cycle: Concrete Lab.

qL is the heat flux and is taken as a constant because the flow of heat is uniform throughout the cycle. T4 is the tile bottom surface temperature, T2 is the temperature of the upper chamber, and ‘K’ is the thermal conductivity. If we take qL as constant, then K α 1/ΔT. As time t is constant and the heat produced from the source is constant, then T2 is constant. According to Equation (3), thermal conductivity, K, is inversely proportional to ΔT; then, if T4 is increased, ΔT will be reduced, and in turn, K will be increased, and vice versa.

2.4.4. Controlled Reinforced Slab

Before placing the 1.5″ slab inside the chamber on its specified point, a 1″ clay mortar was applied on its top surface, the chamber was sealed properly after placing the slab inside the chamber, the data logger was mounted on a balanced tripod stand, and the temperature sensors were connected to it. All the necessary settings were set properly including date, time, temperature unit, etc. To ensure thermal uniformity, a dummy cycle was run, and the temperature of the bottom surface of the slab (T1) was raised to 25 °C, the heat source (bulb) was turned off, and the temperature was allowed to become normal (29.2 °C). Later, to start the actual heating cycle, the data logger, heat source, and stopwatch were turned on simultaneously. The heat source remained on until T1 reached 55 °C. T1 achieved a temperature of 55 °C in 116 min, the bulb was turned off after 116 min, and the temperature was allowed to normalize to room temperature without any external assistance while the data logger was still noting the time and temperature. When the temperature became normal, the data were taken from the data logger and saved for further analysis.

2.4.5. Plastocrete Roofing Tiles (1.5″)

A similar procedure was used for the controlled reinforced slab above after placing a 1.5″ roofing tile on top of the clay surface of the slab on each test day, respectively. The data for these tiles were taken from the data logger and stored for further analysis.

2.4.6. Plastocrete Roofing Tiles (1/2″)

A similar procedure was used for the controlled reinforced slab above after placing a 1/2″ roofing tile on top of the clay surface of the slab on each test day, respectively. The data for this tile were taken from the data logger and stored for further analysis.

3. Results

3.1. Compressive Strength

The results found after calculating the compressive strength of plastocrete paving blocks are given in

Table 2. Compressive strength of plastocrete paving blocks.

Sr No.	Specimen	Length (L) (mm)	Width (W) (mm)	Load (KN)	Correction Factor	Thickness (T) (mm)	Compressive Strength (N/mm2)
1	P1	203.2	101.6	84.3	1.06	70	4.08
2	P2	203.2	101.6	92.4	1.12	78	4.47
3	P3	203.2	101.6	88.7	1	63	4.29

. For the comparison of the compressive strength of plastocrete paving blocks, the locally available concrete blocks from the market were brought to the lab where their specifications were tested under the same conditions. Their observed compressive strengths are detailed in

Table 3. Compressive strength of concrete blocks.

Sr No.	Specimen	Area (A11) (mm2)	Area (A12) (mm2)	Avg. Area (mm2)	Load (KN)	Correction Factor	Thickness (T) (mm)	Compressive Strength (N/mm2)
1	P11	196 × 92	200 × 100	19,016	234	1.06	60	12.03
2	P12	196 × 92	200 × 100	19,016	274.7	1.06	60	14.44
3	P13	196 × 92	200 × 100	19,016	260.7	1.06	60	13.70

.

The compressive strength of concrete blocks was higher because only plastic waste was used in the plastocrete paving blocks. Keeping different thicknesses with different loads while having the same dimensions, the compressive strength of specimen P1 cast with waste from plastic bags is 4.08 N/mm² at a load of 84.3 KN. The compressive strength of specimen P2 cast with waste from plastic bags is 4.47 N/mm² at a load of 92.4 KN. The compressive strength of specimen P3 cast with waste from plastic bags is 4.29 N/mm² at a load of 88.7 KN. Table 3 shows the compressive strength of locally available concrete blocks from the market, and it is evident that the concrete blocks have more compressive strength compared with the plastocrete paving blocks. The compressive strength of specimen P11, locally made with concrete, is 12.03 N/mm² at a load of 234 KN. The compressive strength of specimen P12 is 14.44 N/mm² at a load of 274.7 KN. The compressive strength of specimen P13 is 13.70 N/mm² at a load of 260.7 KN. A graphical representation for the comparison of the compressive strength of concrete paving blocks and plastocrete blocks is shown in Figure 14.

Although the compressive strength of concrete blocks is almost 60% more than plastocrete, the compressive strength of plastocrete cannot be ignored. Thus, it can replace concrete blocks in walking tracks and parking where less load is required because of its lower compressive strength. It should be kept in mind that the ratio for locally made concrete blocks was unknown because these samples were not especially cast for this research; the samples were purchased/collected from the market to compare the mechanical properties of concrete paving blocks with plastocrete. Correction factors were used to correct systematic errors [36].

Two types of products were used for this study. The first was paving blocks. This product is recommended for walkways, for which its strength is sufficient. However, its strength may be increased by using an efficient pressing mechanism to remove voids and increase density. The second was roofing tiles. The low strength of the specimens is not an issue as these are designed to be used as an overlay over existing accessible roofs. The following are recommendations for an accessible roof: (a) it may be protected by 1.5” burnt clay roofing tile in 1:3 C/s mortar and (b) provide a 1.5” concrete screed over it. In this study, the strength of concrete after the heating and cooling cycle was not evaluated. There was no sign of distress, i.e., no discoloration, cracks, or chipping. Further dried samples were used for the heating and cooling cycle. The movement of moisture at elevated temperatures was the main cause of distress.

3.2. Split Tensile Strength

The split tensile strengths of the specimen cast with plastocrete and locally made concrete paving blocks were found using a testing machine. Tabular results of the split tensile strength of plastocrete paving blocks are given below in

Table 4. Split tensile strength of plastocrete paving blocks.

Specimen	Length (mm)	Thickness (mm)	Correction Factor	P (Max. Load) (KN)	Split Tensile Strength (MPa)
Block (P1)	194	78	1.12	21.97	0.924
Block (P2)	200	70	1.06	29.9	1.27
Block (P3)	196	63	1	16.74	0.75

. Similarly,

Table 5. Split tensile strength of locally made concrete paving blocks.

Specimen	Length (mm)	Thickness (mm)	Correction Factor	P (Max. Load) (KN)	Split Tensile Strength (MPa)
Block (P11)	200	60	1.06	11.73	0.567
Block (P12)	200	60	1.06	12.18	0.56
Block (P13)	200	60	1.06	9.07	0.42

depicts the tabular results of the split tensile strength of locally made concrete paving blocks, while Figure 15 shows a graphical representation of the comparison of the split tensile strength of concrete paving blocks and plastocrete blocks.

It is evident from the above results that the tensile strength of plastocrete paving blocks is almost 50 times greater than that of concrete paving blocks. Tensile strength is very low, so this product is not suitable for flexure members. Even the tensile strength of concrete is very low. The plastocrete blocks were made up of plastic waste, which is why the plastocrete was very weak in tension.

3.3. Thermal Cycle Test

3.3.1. Controlled Reinforced Slab (1.5″)

Figure 16 shows that the temperature of the bottom surface of the slab (T1) of the controlled reinforced slab starts at 29.2 °C, increases smoothly to 60 °C in 116 min, and then the temperature starts to decrease gradually. After 24 h, the temperature reaches 19 °C.

3.3.2. Plastocrete Roofing Tiles (1.5″)

Figure 17 shows that for sample 1, the temperature of the bottom surface of the slab (T1) of the plastocrete roofing tile starts at 29.2 °C and rises suddenly to a temperature of 33.5 °C. After this, the temperature increases smoothly to a maximum temperature of 43 °C and then starts to decrease gradually to normal temperature. This 43 °C temperature was due to the thickness of the tile. After 24 h, the temperature reaches 24 °C. The thermal insulation test was performed on plastocrete roofing tiles to ensure that these roofing tiles would sustain fire and would be reliable if used instead of concrete tiles. The findings show a satisfactory response.

Figure 18 shows that for sample 2, the temperature of the bottom surface of the slab (T1) of the plastocrete roofing tile starts at 29.2 °C and rises suddenly to a temperature of 33.5 °C. After this, the temperature increases smoothly to a maximum temperature of 43 °C and then starts to decrease gradually to normal temperature. This 43 °C temperature was due to the thickness of the tile. After 24 h, the temperature reaches 23 °C.

Figure 19 shows that for sample 3, the temperature of the bottom surface of the slab (T1) of the plastocrete roofing tile starts at 29.2 °C and rises suddenly to a temperature of 33.5 °C. After this, the temperature increases smoothly to a maximum temperature of 43 °C and then starts to decrease gradually to normal temperature. This 43 °C temperature was due to the thickness of the tile. After 24 h, the temperature reaches 22 °C.

3.3.3. Plastocrete Roofing Tiles (1/2″)

Figure 20 shows that the temperature T1 of the plastocrete roofing tile starts from 29.2 °C and suddenly increases at a temperature of 33.5 °C. After this, the temperature increases smoothly to a maximum temperature of 44 °C and then gradually decreases to normal temperature. This 44 °C temperature was due to the minimum thickness of the tile. After 24 h, the temperature reaches 19 °C.

4. Discussion

During a heating–cooling thermal cycle test, the plastocrete roofing tile (1.5″) had a maximum attained temperature of 43 °C, which is 17 °C lower than the controlled slab, and the plastocrete roofing tile (1/2″) had a maximum attained temperature of 44 °C, which is 16 °C lower than the controlled slab. After comparing roofing tiles (i.e., 1.5″ and 1/2″), it was observed that roofing the tile with minimum thickness has a temperature difference of 1 °C compared with the maximum thickness roofing tile. So, the optimum thickness for a roofing tile is 1/2″. When increasing the size and thickness of roofing tiles, the temperature must be reduced.

All the data show that a minimum reduction in temperature was achieved at approximately 17 °C by installing modified roofing tiles with plastic waste compared with the controlled tile and the R.C.C slab, respectively. The literature shows that as the temperature decreases, it increases the efficiency of A.C. usage and reduces utility bills annually. For example, reducing 1 °C temperature saved 1300 units annually [37].

In comparison to the literature, in 2019, Avinash et al. [10] utilized waste plastic to manufacture paver blocks. Paver blocks were made by adding 50%, 60%, and 70% plastic waste by weight with sand. They concluded that increasing the waste plastic proportion with sand gives a high resistance against compressive strength. In 2018, recycled plastic was used by M. Achitra et al. [18] in concrete paver blocks in different proportions. A synthetic material made from a wide range of organic polymers such as polyethylene, PVC, nylon, etc., was used. By comparing the results, they determined that 0.5% coconut fiber and plastic waste gave a compressive strength after 7 and 28 days of 19.170 and 30.021, respectively. Similarly, 1% coconut fiber and plastic waste gave a compressive strength after 7 and 28 days of 17.746 and 28.096, respectively. All the test results showed that 0.5% coconut fiber and plastic waste added to concrete blocks results in good compressive, flexural, and split tensile strengths.

Iswahyuni et al. [38] also performed similar research and concluded that a paving block mixture with a ratio of 1:4 exhibited the best physical–mechanical properties as revealed by a fine surface with no defect and no cracks. A compressive strength of 17.4 MPa, a friction resistance of 0.138 mm/s, and water absorption of 2.518% could be achieved, which is suitable for parking area construction.

5. Conclusions

Waste plastic bags are a major problem in the world, which is damaging the environment continuously, day by day. Plastic bags decompose after several years, and some plastic bags may not decompose after hundreds of years, which is the cause of increasing pollution. Focusing on Sustainable Development Goal 12 (SDG 12), this study utilized waste plastic bags that were melted in a boilery to create plastocrete, which was subsequently used to produce paving blocks and roofing tiles. The authors observed after the experimental research that using plastic bags to manufacture plastocrete is an effective way to reduce plastic bag waste. The thermal insulation test was performed on plastocrete roofing tiles to ensure that these roofing tiles would sustain against fire and would be reliable if used instead of concrete tiles. The test results showed a satisfactory response. These tiles can be used in sewer and canal lining units or where a chemical attack is expected. These paving blocks can be used in walkways, non-traffic and light-traffic roads, home gardens, and parks. These roofing tiles are suitable for thermal insulation of roofs and exterior walls. By increasing the thickness of the roofing tile, thermal conductivity was lowered significantly. Less time is required to manufacture plastocrete composite. These blocks were ready for use after 24 h. The weight of these plastocrete paving blocks was lighter than concrete paving blocks.

It is concluded that using waste plastic bags in the construction industry is the best option for their disposal. Certain additives/fluxes may be investigated to reduce the melting time and enhance the consistency of the molten paste. Other plastic wastes like bottles and hospital waste may be investigated using a similar methodology. Thermal conductivity was evaluated using a heating/cooling thermal cycle test during this research. It may be evaluated directly using a thermal conductivity meter. Further research can be carried out to be more specific. The studied paving blocks are recommended for walkways, for which their strength is sufficient. However, their strength may be increased using an efficient pressing mechanism to remove voids and increase density.