Experimental investigation on mechanical and durability properties of M30 concrete with HDPE plastic waste as partial coarse aggregate replacement

1 Introduction

Excessive utilization of these natural aggregates has created significant problems to the environment, including the depletion of natural resources, loss of natural habitats, damage to subsoil condition and ecological imbalance. Hence, the sustainable and environment friendly alternatives for the manufacturing of concrete have become a big concern in the field of civil engineering. Meanwhile, the issue of plastic waste production has grown into an environmental problem on a global scale. Due to their lightweight, durable, corrosion proof and chemical resistant properties, plastics are vastly used in packing, household goods, construction materials and industrial products. But plastics are not biodegradable, which results in a long-lasting presence in the environment, particularly in landfill sites and water and soil systems, where they become a massive pollution problem. Incorporation of plastic waste in concrete, which is one of the promising approaches for natural aggregate substitution is among the potentially effective materials.

Sau et al. (2023) explored partial use of natural aggregates by incorporating plastic waste into concrete to evaluate its feasibility and performance. The study revealed that strength decreased with increased content of plastic, while some durability properties in the concrete increased and the density of the concrete decreased. The authors discovered that achieving sustainable concrete production was possible with optimal levels of plastic replacement. (Varghese et al., 2025) investigated the use of sand-coated reclaimed HDPE and E-plastic aggregates as a partial substitute for coarse aggregate. Results indicated that the bond between plastic aggregates and cement paste was enhanced by sand coating and satisfactory strength was obtained. (Miah and Islam, 2026) studied the effect of plastic waste aggregates on the strength of concrete carried out with machine learning models. The researchers found that up to 5% plastic replacement allowed performance to be maintained or slightly enhanced, but greater plastic replacement led to a decrease in performance. (Lopez et al., 2019) explored the incorporation of recycled HDPE as a replacement for coarse aggregate in pervious concrete that includes an acrylic additive. Results indicated that there was an improvement in porosity and permeability while a reduction was observed in compressive and flexural strength. The optimum mix of 10% HDPE with 15% acrylic additive gave satisfactory performance.

Lokeshwari et al. (2019) investigated the substitution of fine aggregate and coarse aggregate in concrete blocks with the use of waste polypropylene plastic. Results indicated that the mechanical properties decreased as the amount of plastic increased, but the concrete was still acceptable for some applications. The study proved that the plastic waste can be used as sustainable aggregate material. (Radhi et al., 2022) studied flexural properties of reinforced concrete beams with HDPE waste as partial coarse aggregate replacement. The results demonstrated that flexural strength and stiffness were reduced as the proportion of HDPE was increased, whereas moderate replacement levels would yield acceptable structural strength. The study found that at limited replacement ratios, HDPE can be used in reinforced concrete. (Tafheem et al., 2018) explored the properties of concrete with PET and HDPE waste serving as coarse aggregate substitutes. The results demonstrated that the concrete exhibited lower compressive strength and reduced weight compared to the control mix. The authors pointed out the possibility of using plastic waste to make lightweight concrete.

Rana (2025) investigated the substitution of aggregate in concrete with HDPE and PET waste. The best combination of 2% HDPE and 9% PET had better compressive, tensile and flexural strength than the normal concrete. The study successfully demonstrated the possibility of incorporating plastic waste into concrete production. (Suvidha et al., 2024) studied the use of waste plastics (HDPE and PP) as a partial replacement of fine aggregate in M30 and M40 grade concrete. The results have shown that a 5% PP and 7.5% HDPE replacement level gave satisfactory strength and durability with reduced thermal conductivity. The study was in favor of using plastic waste in the sustainable concrete applications. (Mashaan and Ouano, 2025) reviewed the structural behavior of concrete containing HDPE, LDPE, PVC, and PP wastes for rigid pavements. The study concluded that the addition of HDPE and PP can improve the flexural strength and fracture resistance of concrete thereby boosting its overall structural performance and durability. The authors highlighted the advantages of plastic waste utilization in concrete from an environmental point of view.

Ammari et al. (2025) investigated the effects of different post-consumer plastics on concrete properties. The results indicated that the density and compressive strength of concrete reduced with increasing plastic content and the degree of reduction was dependent on the type of plastic employed. The study proposed the replacement of plastic in order to produce sustainable lightweight concrete. (Ridha, 2025) evaluated plastic waste materials such as PP, PET, LDPE, and HDPE as additives in concrete mixtures. Low replacement percentages were found to provide excellent compressive strength, while higher percentages led to a decrease in strength. The authors have drawn the following conclusions: plastic waste can be used to produce concrete as an environmentally sustainable supplementary material. (Rao et al., 2025) examined the use of mixed plastic waste as a partial replacement for natural aggregates in concrete production. The strength in general declined as the content of plastic increased, and the study stated that techniques of surface treatment could enhance the strength. It was indicated that plastic aggregate concrete has positive environmental and sustainability effects. (Dias et al., 2024) examined the utilization of alternative aggregates including waste plastics and reused materials in concrete production. The results demonstrated their ability to reduce environmental impacts and foster sustainable construction practices at appropriate replacement rates. Their importance for the promotion of circular economy practices was highlighted.

Wattanavichien and Iwanami (2024) studied the incorporation of fine PET aggregates as a replacement of natural fine aggregates in concrete. The study indicated that the compressive and tensile strengths of the PET aggregate were reduced, whereas the chloride resistance and durability of the overall PET aggregate increased. The authors concluded that PET aggregates can be used in sustainable concrete applications if durability is an important factor. (Dawood et al., 2021) examined the physical and mechanical properties of concrete with PET waste as a partial substitute of fine aggregate. The results indicated that replacing PET with a 5%–12.5% level led to an enhancement in compressive, tensile and flexural strengths, whereas higher PET replacement levels resulted in a decrease in performance. The study suggested a maximum of 15% PET content for optimum results. (Kangavar et al., 2022) explored the possibility of using recycled PET granules as a partial replacement for fine aggregate in concrete. The results showed that 10% PET replacement was the most favorable replacement ratio for mechanical properties and more ductile. The study findings revealed that lower replacement levels of PET granules are feasible in the sustainable production of concrete.

Mahmoudi et al. (2026)suggested a framework for incorporating recycled plastic waste into concrete using the principles of ESG. The study demonstrated the potential for recycled plastics to have a positive “effect on' the environment, carbon emissions, and sustainable construction methods. The authors pointed out that the governance policy is crucial in the utilization of plastic wastes. (Haigh, 2024) investigated the mechanical properties of waste plastic fibre of milk bottle reinforced concrete using silica fume. Surface-treated fibres created a better bond between the fibre and cement, and increased the compressive strength, tensile strength, and flexural strength. (Almohana et al., 2022) discussed the recycling of plastic waste in the making of sustainable concrete. The review identified that plastic waste can be used to create eco-friendly lightweight concrete with better thermal and sound insulation properties.

The incorporation of plastic aggregates is found to create lower density for concrete and work well to improve some properties such as ductility and impact resistance in previous investigation. In general, however, an increase in the proportion of plastic replacement in the compound, resulted in a greater reduction of compressive strength because of weak bonding between plastic particles and the cement paste. In the present study, experimental investigations were conducted in M30 grade concrete incorporating HDPE plastic waste as a partial replacement of coarse aggregate with replacement percentages varying from 10% to 50% have been done. The aim of this study is to investigate the effect of the incorporation of HDPE on the mechanical properties of concrete such as 28-day compressive strength, split tensile strength and flexural strength. Moreover, durability-related properties, such as water uptake, acid resistance and sulphate resistance tests are studied for the desired water reduction. This investigation is aimed to encourage the construction industry to implement environmentally responsible construction practices by decreasing the amount of plastic waste being disposed of and conserving the natural aggregate resources.

2 Materials used in concrete mix

All the concrete mixes were prepared using Ordinary Portland Cement (OPC) of 53 Grade as the main binder. The fine aggregate used in the study was manufactured sand (M-sand) which meet zone-II requirement as given in IS 383:2016 (Bureau of Indian Standards, 2016). In the control mix, natural crushed coarse aggregate used with a nominal maximum size of 20 mm. Pre-consumer recycled waste, in the form of High-Density Polyethylene (HDPE) bottles, containers and plastic pellets, was gathered and treated prior to its use. Collected plastic waste was cleaned and then cut to the size of 5–10 mm irregular particles. The processed HDPE particles were added to the concrete mixes as a substitute for the coarse aggregate, and were used as a partial replacement by volume.

3 Mix design

The mix design of concrete was designed for M30 grade as per the specifications of IS 456:2000 (Bureau of Indian Standards, 2000) and IS 10262:2019 (Bureau of Indian Standards, 2019). The proportion of the components of the mix (cement, water, fine aggregate and coarse aggregate) is determined and is listed in Table 1.

TABLE 1. Mix proportion.

Figure 1 depicts the normal coarse aggregate, processed HDPE plastic waste as partial replacement material and the resultant concrete mix after precise blending. The HDPE plastic waste was incorporated as partial replacement of coarse aggregate at varying replacement levels of 10%, 20%, 30%, 40% and 50% by volume. The replacement levels were determined to assess the effect of HDPE on the mechanical properties of M30 grade concrete.

Figure 2 depicts the various types of concrete specimens made and tested during this research. The specimens of 150 mm × 150 mm × 150 mm cube were casted for the compressive strength test. Split tensile strength test was performed on cylindrical specimens of diameter 150 mm and height 300 mm. The beam specimens of 150 mm × 150 mm × 900 mm were constructed for testing for flexural strength. All specimens were prepared by using different percentages of HDPE waste plastic as partial replacement of coarse material. After casting, the specimens were cured under normal conditions and then tested. Acid resistance and sulphate resistance durability tests were carried out on 100 mm cube. All specimens were cured in water tanks for 28 days before testing. For each mix proportion, average value was reported for three specimens.

4 Experimental methodology

4.1 Slump test

A concrete slump test is used to measure the workability and consistency of concrete variation in strength of HDPE modified concrete. This is to check whether the concrete is too wet or too dry and to make sure that the mix can flow adequately into the formwork and surround the reinforcement sufficiently without compromising its strength. The slump value was measured by using a slump cone of 100 mm top diameter, 200 mm bottom diameter and 300 mm height as per IS 1199 (Part 2): 2018 (Bureau of Indian Standards, 1199).

4.2 Compressive strength

Compressive strength test was conducted to examine the variation in strength of HDPE modified concrete. The casting size of the cube specimens was 150 × 150 × 150 mm and all these were cured in the water tank for 28 days. The experimental setup shown in Figure 3. This compression testing was done using the compression testing machine of 2000 kN compression testing machine (CTM) and the tests were performed following IS 516 (Part-1/Sec-1):2021 (Bureau of Indian Standards, 2021). The load was applied in a gradual manner and then continuously until failure occurred. Compressive strength was calculated by dividing the failure load on the cube test specimen by the loaded area of the specimen.

4.3 Split tensile strength

Split tensile strength test was performed to investigate the tensile characteristics and crack resistance in HDPE modified concrete. The Split tensile strength test conducted in cylindrical specimens with diameter of 150 mm and height of 300 mm, and 28 days of tank curing. The experimental setup used in the experiments is given in Figure 4. The test was conducted as per IS 516 (Part-1/Sec-1):2021 in a 2000 kN capacity compression testing machine. A uniform load was applied to the cylinder all along its length until the failure point was reached. The split tensile strength was determined as per IS 516 (Part-1/Sec-1):2021.

4.4 Flexural strength

Flexural strength test was performed on the HDPE modified concrete in order to assess the flexural behavior of a controlled and the HDPE modified concrete. Specimens of a size of 150 × 150 × 900 mm were cast and cured for 28 days. This test carried out according to IS 516: 2021in a 200 kN flexural testing machine. The experimental setup shown in Figure 5. The specimens of the beam were loaded under the supporting rollers and applied very slow loading to make the specimens fail for flexural testing. The flexural strength was determined by the maximum load that the specimen could bear before cracking and failure.

4.5 Water absorption

The Water Absorption properties of the HDPE modified concrete were evaluated by conducting water absorption test. The test was performed according to the procedure outlined in ASTM C642-21 (ASTM C642-21, 2021). Before being put in a desiccator, specimens were dried in oven at 105 °C ± 5 °C. Cautions were taken in measuring the dry weight of each specimen. The dry weight was recorded after which the specimens were placed in water for a certain period of time. The gain in weight was determined as a percentage of the dry weight. The density of high-density polyethylene (HDPE) is 943 kg/m.³

4.6 Acid resistance

The acid resistance test was conducted to investigate the durability of HDPE modified concrete in the acidic environment. The samples were taken in the form of cubes of 100 mm × 100 mm × 100 mm, cured for 28 days, and subsequently immersed in sulphuric acid solution for another 28 days shown in Figure 6. The test was conducted as per the procedure given in ASTM C1898-20 (ASTM C1898-20, 2020). Initial weight and initial compressive strength were obtained prior to the immersion. The samples were then removed from the acid solution, gently cleaned and reweighed to calculate the loss of mass. Consequently these specimens were further tested for compressive strength to ensure that the acid attack had effected the strength of the specimens.

4.7 Sulphate resistance

The sulphate resistance test was carried out to investigate the performance of HDPE modified concrete in sulphate environment. The 100 mm × 100 mm × 100 mm cube specimens were cured for 28 days and then immersed in the sodium sulphate solution in the laboratory for an additional 28 days shown in Figure 7. The initial weight and compressive strength of the specimens were taken before the exposure. The specimens were then taken out, cleaned, reweighed and retested after the exposure period to obtain the final weight and remaining compressive strength. Sulphate attack effects on the performance of concrete were taken into account by measuring the loss of weight and compressive strength in percentage terms.

5 Results

The mechanical properties of HDPE modified concrete were studied by conducting compressive strength, split tensile strength and flexural strength tests at the recommended curing ages. The results obtained were used to identify the best HDPE replacement amount, which was selected for further durability investigation. Then, the durability properties of the optimum mix were investigated by performing water absorption, acid resistance and sulphate resistance tests to study the resistance of the mix to ingress of moisture and aggressive chemical environment. The results of these tests give a complete picture of the mechanical and long-term durability performance of the HDPE-modified concrete.

5.1 Slump test

Figure 8 shows the average slump values of HDPE modified concrete at different replacement percentages. With increase in percentage of HDPE replacement, the slump value decreased continuously. The slump reduction might be due to the poor interaction between HDPE and cement paste which reduces the flowability of the fresh concrete. The irregular distribution of HDPE particles may also the reason for reduction in workability. A comparatively lower slump value was observed for 10% HDPE replacement among the different replacement levels which is very close to control concrete indicating that satisfactory workability is at the lower replacement level. In general, the results indicated that the increase of the HDPE replacement percentage negatively affects the workability of the fresh concrete.

5.2 Compressive strength

The average compressive strength of the HDPE modified concrete after 28 days for various percentages of replacement is shown in Table 2. The compressive strength decreased continuously with an increase in HDPE replacement percentage. The controlled concrete specimens failure is brittle and HDPE modified concrete is ductile. The loss of strength could be due to the weaker bond between the particles of HDPE and cement paste, and also to the softer nature of plastic aggregates. However, the 10% replacement demonstrated compressive strength values that are comparatively near to those of normal concrete, and a satisfactory performance was attained at this lower replacement level.

TABLE 2. Compressive strength results at 28 days.

5.3 Split tensile strength

The average split tensile strength of HDPE modified concrete at 28 days for different percentages of replacement of HDPE is presented in Table 3. The control concrete specimens showed a brittle failure with an abrupt splitting fracture while the HDPE modified concrete specimens showed a more ductile response with controlled crack development and increased resistance to sudden failure during the split tensile strength test. Split tensile strength also decreased with the increasing amount of HDPE. The main reasons for this reduction were due to interfacial bonding and crack propagation. But the moderate tensile performance has been achieved at a low replacement level. The Split Tensile Strength values of the 10% replacement are relatively close to the standard concrete.

TABLE 3. Split tensile strength results at 28 days.

5.4 Flexural strength

The flexural behaviour of the HDPE modified concrete was investigated in flexural testing machine 200 kN capacity. Beam specimens of size 150 × 150 × 900 mm were cast and cured for 28 days. This test has been conducted as per IS 516:2021. The flexural strength data for 28-day cured HDPE modified concrete specimens are given in Table 4. The flexural strength property generally decreased as a function of increasing HDPE replacement. The control concrete beams failed in brittle fracture immediately after reaching the peak load. However, the HDPE-modified concrete beams exhibited more ductile failure behaviour with delayed crack propagation and higher energy absorption prior to eventual collapse. The decrease has been attributed to the decreased rigidity and bonding properties of plastic aggregates. The decrease in flexural strength, however, was relatively small when the lower percentages were used. The 10% replacement comes close to the typical concrete in terms of flexural strength ratings.

TABLE 4. Flexural strength results at 28 days.

5.5 Water absorption

Based on the mechanical performance, the HDPE-10 is the optimum combination and was chosen for the water absorption test. The mean value of water absorption for traditional and HDPE-modified concrete sample is presented in Table 5. The water absorption of HDPE modified concrete was little higher than normal concrete. The rise is related to the incorporation of plastic aggregates, which are characterized by a larger void content and a weaker interfacial transition zone (ITZ) between the cement paste and the plastic particles. Moreover, the smooth surface texture and hydrophobicity of HDPE reduce the bonding efficiency of the cement matrix, which leads to an increase in porosity and permeability. Therefore, the concrete with HDPE modified has more water absorption than the original concrete because of the larger void content.

TABLE 5. Water absorption results.

5.6 Acid resistance test

Based on the mechanical performance, the HDPE-10 mix was found as the optimum replacement level and was therefore chosen for the acid resistance test. In order to evaluate the durability performance of HDPE modified concrete in an acid environment, the acid resistance test was carried out. Cube specimens of size 100 × 100 × 100 mm were used for this test. The specimens were immersed in acid solutions. The weight loss and strength loss is presented in Table 6. All the specimens after curing for 28 days were transferred into sulphuric acid solution. Acid resistance test results indicated that the strength loss of the HDPE concrete is higher than that of the conventional concrete exposed to acids. The traditional loss of strength was observed to be 5.22%–6.60% in case of HDPE-10 concrete, here as concrete was observed to be between 8.40% and 9.19%. The use of this HDPE slightly lowered the resistance to acidic environment.

TABLE 6. acid resistance test results.

5.7 Sulphate resistance test

The optimum replacement level determined was HDPE-10 mix from the mechanical performance and was selected for Sulphate Resistance Test. The sulphate resistance test was carried out to examine the performance of the HDPE modified concrete under sulphate environment. The specimens were cured for 28 days and then immersed in sodium sulphate solution for 28 days. The weight loss and strength loss is presented in Table 7. Pre-exposure initial weight and Compressive strength of the specimens was recorded. In the case of conventional concrete, the strength decreased by about 3.51%–4.14%. The loss of strength for HDPE-10 concrete was observed between 5.94% and 6.44%. The reduction in strength of HDPE concrete was found to be greater than control concrete with 10% replacement of HDPE concrete but not beyond the acceptable limits.

TABLE 7. sulphate resistance test results.

6 Discussion

Experimental investigation carried out on M30 grade concrete using HDPE plastic waste as partial replacement of coarse aggregate revealed that the use of plastic aggregates also affects the mechanical and durability properties of concrete. Different replacement percentages (10%, 20%, 30%, 40% and 50%) were located and several physical tests, such as compressive strength test, split tensile strength test, flexural strength test, water absorption, acid resistance and sulphate resistance, were performed on each replacement percentage.

From the compressive strength test results, the strength decreased gradually with an increase in HDPE replacement percentage. The main reason for this decrease in strength is the hydrophobicity of the HDPE particles which decreases the bonding efficiency between the plastic aggregates and the cement paste. Plastic particles have smooth surfaces and are not stiff, which leads to a lower stiffness in transition zones of the concrete matrix compared to natural aggregates. With the rise in HDPE percentage, the capacity of the concrete to hold compressive load also decreased.

In the split tensile strength test results, the same trend was noticed. The tensile strength showed a continuous decrease as the content of HDPE was increased as a result of poor bonding characteristics and lesser resistance to crack propagation. Weak layers were found inside the concrete composite as a result of the presence of plastic aggregates, which influenced the resistance of the concrete to tensile stresses. However, lower percentages of replacement still had excellent tensile qualities and no sudden or brittle failure features.

The bending resistance (flexural strength) results also showed a decrease in flexural strength as the percentage of HDPE increased. Lightweight plastic aggregates have resulted in lower overall rigidity in the concrete due to their influence on the internal bonding and stiffness of the concrete matrix. However, replacement levels at 10% appeared to have relatively stable flexural characteristics, suggesting that using reduced amounts of HDPE in some parts of the construction could be possible.

10% HDPE replacement yielded the best overall performance with regard to mechanical properties. The strength of the materials at this replacement ratio was comparable to the strength of conventional concrete for compressive, split tensile and flexural strength. This shows that incorporation of HDPE plastic waste in small amounts can maintain structural performance without significant deterioration. However, a replacement level greater than 20% led to a significant drop in strength properties, making them less suited to structural applications that require high strength.

Furthermore, durability testing showed the effect of HDPE on the durability of the concrete. The water absorption test revealed that a higher absorption of water was recorded in concrete built with HDPE modification than in conventional concrete. This increment might be correlated with the generation of new voids and weak bond locations around the plastic particles, thereby increasing the permeability and porosity of the concrete matrix.

The result of the acid resistance test showed that after acid treatment, the strength loss of the concrete made of HDPE was greater than that of conventional concrete. The cement matrix was degraded by acid attack and poor bonding at the interface between the HDPE particles and the cement further lowered the strength. In the same manner, the sulphate resistance tests revealed that the strength loss of the HDPE concrete under sulphate exposure conditions was relatively higher. The use of HDPE modified concrete resulted in a higher rate of deterioration than conventional concrete, but acceptable levels were attained for some practical applications up to 15% replacement.

The results of the overall study show that technology can be used to introduce HDPE plastic waste as a partial substitute for coarse aggregate in concrete production, which makes the use of these wastes possible from an environmental perspective and provides good management of plastic wastes. The study, however, also focuses on the need for optimum replacement rates to preserve sustainability and structural performance.

7 Conclusion

In the present experimental investigation, the effect of HDPE plastic waste on mechanical and durability properties of M30 concrete for various replacement levels (10%, 20%, 30%, 40%, 50%) of coarse aggregate has been studied. This experiment provided the results of slump value, compressive strength, split tensile strength, flexural strength, water absorption, acid resistance, and sulphate resistance which revealed that the use of HDPE plastic waste did have a definite effect on the performance of concrete.

The results showed that the slump value, compressive strength, split tensile strength and flexural strength of concrete decreased as the amount of HDPE replacement increased. The decrease in the strength characteristics has largely been attributed to the low bonding of HDPE plastic particles with cement paste and the impermeability and rigidity of plastic particles in comparison to cement particles.

Concrete with 10% HDPE exhibited the best overall workability properties and strength characteristics, which are relatively close to those of conventional concrete among all the levels of HDPE replacement studied. Replacement percentages in excess of 20% have been seen to significantly compromise strength properties, showing higher percentages of HDPE to be less desirable for structural applications that demand higher load carrying capability.

Water absorption tests were conducted on HDPE concrete and it was concluded that the water absorption values were higher than that of conventional concrete, which indicates the concrete to be more porous in nature and have greater permeability. In a similar manner, there was higher strength loss among the HDPE modified concrete specimens compared to the conventional concrete specimens in the acid resistance and sulphate resistance tests. Within these decreases in durability performance, however, there was still a sufficient level of durability for some sustainable construction uses.

In conclusion, the study supports the successful utilization of a small fraction of natural coarse aggregate to replace HDPE plastic waste, which can be implemented as an alternative method in the concrete industry to offset the environmental damage and pollution caused by traditional production processes. The use of HDPE waste in concrete is also helping to conserve the use of natural aggregate. So, using HDPE waste plastics in optimum limits in concrete can be considered an eco-friendly replacement material for some construction applications.

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Footnotes

Edited by: Matteo Sambucci, Sapienza University of Rome, Italy

Reviewed by: Dhondy Rupesh Kumar, Osmania University, India

Kriti Vaid, DPG, India