Keywords

1 Introduction

Concrete volume contains 70–80% of aggregates, and during construction of structures, several tons of aggregates are required in the form of coarse aggregates (CA) and fine aggregates (FA). The aggregates used in concrete works are non-renewable resource which can deplete one day and to overcome that some alternative is required in the future. Nowadays, trend is increasing to find new alternative for the replacement of the concrete constituent so that scarcity of the raw materials can be controlled so plastic waste can be the one solution to be used in concrete as aggregates. The plastic waste utilization in concrete will not only dazed the scarcity of the aggregates, it also helps in lessen the issue of dumping lands and their negative effect to the environment [1]. Since plastic has made its versatile use in our daily practice, the amount of plastics annual consumption is growing gradually. Plastics are used in majority for packing, pipes and plumbing, toys, bottles and in electronic sector [2]. In India, average per capita consumption of plastic is 11 kg and it will go up to 22 kg per capita by 2022 [3] and India uses about 43% plastic for the packaging purpose. With the increase in population, consumption of plastic is also increasing; however, excess consumption of plastic results in generation of large amount of the plastic waste heaps which creates bad scenario and also open dumping attract diseases [4]. Plastics are obtained by monomer polymerization to make elongated chain of hydrocarbons either by condensation or additional reactions [5] Plastic being non-biodegradable and chemically unreactive it releases toxic compounds in the air, water and soil under firm conditions which causes long-term environmental pollution [6]. The plastic waste has been disposed or reused traditionally by burning at 850℃ which releases toxic and harmful gases which can cause cancer or other diseases to living beings. Moreover, end product of after burning of plastic waste must be buried safely in pits to avoid the spread of plastic pollution. Therefore, polyethylene terephthalate (PET) and high-density polyethylene (HDPE) were the most frequently used plastic for concrete mix design as they are less prone to environment in their burning process [7, 8]. The use of plastic waste in concrete as a aggregates based on their sizes (coarse or fine) aids to overcome the landfills due to plastic waste in pits and also reduces the scarcity of natural aggregates (NA) which in result supports to attain sustainable and eco-friendly environment. Plastic has lower density as compared to other ingredients of concrete incorporation of plastic can be used to prepare lightweight members. The plastic waste is crushed or processed in the form of aggregates base on their size (coarse or fine) called as plastic aggregates (PA). In line to this, PA has lower water absorption than NA due to their hydrophobic nature which in result excess water present inside the concrete matrix helps in refining the workability of concrete [9]. Belmokaddem et al. [10] studied the impact of three wastes such as polypropylene PP, high-density polyethylene HDPE, and polyvinylchloride PVC in concrete at a replacement level of 25%, 50% and 75% as CA and FA. They concluded that with the higher content of plastic waste in concrete, compressive strength and ultrasonic pulse velocity decreases due to non-cohesive property of PA. Bahij et al. [11] also suggested that higher content of plastic waste in concrete deteriorate the strength properties. Further, workability and strength properties depend upon the of regularity of particles of plastic waste, i.e. workability and compressive strength of concrete incorporate with irregular plastic has higher value than inclusion of regular units of PA in concrete [12]. The plastic waste can also be used as reinforcement in the form of fibre to make durable concrete. Foti [13] used PET bottles fibres as a reinforcement in concrete partially to replace steel reinforcement. Frigione [14] reported that FA produced from PET bottles in concrete tends to decrease strength parameters at high proportion and give marginal results at low content.

The literature studies reveal that plastic waste was used in concrete in the different form of aggregates to decrease the influence of plastic waste to the atmosphere and to get desirable strength and durability of concrete. Similarly, in current investigation plastic waste was used as FA to get desirable results of the concrete. The main objective of the current study is to optimize the benefits of using post-consumed waste plastics (PET Bottles) in concrete as PA for the partial replacement of FA.

2 Experimental Programme

2.1 Materials Used and Their Properties

In this paper during experimental investigation, ordinary Portland cement (OPC) of 43 grade was consumed as a binder and intermixed with CA and FA to form concrete mix. The obtained physical properties of OPC are given in Table 1. The PA is substituted with FA at a replacement level of 0, 5, 10 and 15%. Firstly, PA was prepared by melting PET bottles to 80–100 mm boulder and further crushed into fine particles and sieved to get particles less than 4.75 mm. The PA used in the study has nearby similar particle distribution of FA as per Indian Standard IS 383-2002 [15]. Further, observed physical properties of CA, FA and PA are shown in Table 2.

Table 1 Physical properties obtained for OPC
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Table 2 Physical properties observed for CA, FA and PA
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2.2 Mix Proportions

The mix proportion of concrete was prepared using Indian Standard IS 10262-2019 [16]. The different concrete mix with different proportion are given in Table 3. The PA is replaced with FA using volumetric approach. The 0.45 water/binder ratio was used for all mixes. For each concrete mix, for individual test three specimens were casted and average has been taken for every test. The slump value of concrete increases with the accumulation of PA in concrete mix as the water absorption of PA is 0.30 due to their hydrophobic nature.

Table 3 Mix proportions of concrete mixes in kg per cubic metre
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2.3 Testing Methods

Compressive Strength. The compressive strength of 100 mm cube was determined using compressive testing setup of capacity 2000 kN as per IS 516-1959 [17] after 7, 14 and 28 days of curing period. The load was applied until first crack has been produced on specimen to find compressive strength.

Split tensile strength. The strength was determined using split load setup for cylinder specimen of size 100 mm (D) × 200 mm (H) using standards IS 5816-1999 [18]. The test was carried out after curing period of 7, 14 and 28 days.

Flexure strength. The flexure strength is determined using two-point load test using flexural testing machine as per IS 516-1999. The beam size of 500 mm (L) × 100 mm (B) × 100 mm (H) was used for casting and tested after ageing of 7, 14 and 28 days.

3 Results and Discussions

3.1 Compressive Strength Test Results

The test results of compressive strength of all concrete mixes are shown in Fig. 1.

Fig. 1
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Compressive Strength test results of concrete mixes with varying percentage of PA

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The strength of control mix, i.e. CRPA0, obtained was 31 N/mm2. The results in Fig. 1 show that the strength start decreasing with the higher content of PA in concrete mix because PA act as a barrier to adhere cement paste with natural aggregates [19]. For 5% replacement of FA with PA, i.e. for CRPA5 mix, compressive strength decreases by 8% and 12% after 7 and 14 days of curing, respectively, relative to conventional mix. After 28 days curing, strength decreased by 15% as compared to control concrete. The compressive strength declines due to infirm bond between PA and mortar paste [10, 20]. Moreover, hydrophobic property of PA confines water which obstruct the hydration process and in result compressive strength decreases [9]. Further, for CRPA10 mix, compressive strength decline by 27%, 20% after curing period of 7 and 14 days, respectively, and after 28 days strength reduced by 26% as compared to CRPA0. The decrease in strength for CRPA10 is 10% as compared to CRPA5 after 28 days curing. Furthermore, for CRPA15 mix the strength reach only up to 60% of control concrete strength for all curing days.

3.2 Split Tensile Strength Test Results

The split tensile strength test results for various concrete mixes are given in Fig. 2.

Fig. 2
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Split tensile strength test results of concrete mixes with varying percentage of PA

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The split tensile strength has same trend as compressive strength it also declined with the higher content of PA in concrete. For CRPA5, split tensile strength decreases by 10% after 7 days curing and further reduced by 21% after 28 days curing as compared to CRPA0. Similarly, for CRPA10 mix, strength decline by 24% after 28 days of curing. The decrease in the strength is due to non-cohesion of PA with cement and conventional aggregates. Furthermore, for CRPA15, split tensile decreases by 27% after curing of days relative to CRPA0. Rahmani et al. [19] show 18% decrease in tensile strength for 15% replacement of PET particles after 28 days curing due to smooth and high surface area of PET particles in concrete. The decline in split tensile strength is smaller than the compressive strength for CRPA15, i.e. split tensile reaches near about 73% of CRPA0 after curing of 28 days.

3.3 Flexure Strength Test Results

The results obtained after flexure testing of all mixes are in Fig. 3.

Fig. 3
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Flexure strength test results of concrete mixes with varying percentage of PA

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The flexure strength of CRPA0, i.e. control mix, is 4.4 N/mm2 after 28 days curing. The flexure strength of CRPA5 decreases by 11% after 7 days curing and 5% after 14 and 28 days relative to control mix. Murugan et al. [21] also reported 5% decrease in flexure strength with 5% replacement of FA with PA. Further, for CRPA10 mix, the flexure strength decreased by 18% and 10% as compared to CRPA0 after 7 and 28 days of curing, respectively. Furthermore, decrease in flexure strength after 15% replacement of FA with PA, i.e. CRPA15 reduced to 3.66 N/mm2, i.e. 17% reduction, after 28 days curing as compared to the conventional mix.

3.4 Dry Density Test Results

The observed values of dry density are shown in Table 4 for all mixes. The dry density of CRPA0 is reported as 2395 kg/m3. Further with 5% replacement of FA with PA, i.e. for CRPA5 mix, dry density reduced marginally. Further, for 10% and 15% replacement of FA with PA dry density decreased by 5% and 8%, respectively. The marginal decrease in density is because of nearby similar specific gravity of PA and FA.

Table 4 Dry density values of all concrete mixes
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3.5 Correlation Between Mechanical Properties

The correlation among compressive, split tensile and flexure strength has been presented in Fig. 4.

Fig. 4
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Correlation between strength properties

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The regression analysis was carried out between compressive and split tensile strength and shows a good fit with R2 = 0.78. Similarly, for correlation of flexure strength with compressive found to be a R2 = 0.98. Results show that split tensile and flexure strength decrease in same trend as compressive strength declines with the presence of PA in concrete. The split tensile and flexure strength range in between 15 and 20% for the all concrete mixes relative to strength obtained from compression loading.

4 Conclusions

The findings in this study with the utilization of plastic waste as a FA conclude that PA can be used in concrete in low content so that mechanical properties of concrete would not be affected significantly. Moreover, lower water absorption and hydrophobic nature of PA affect the workability properties. In present investigation, for compressive and split tensile strength show 15% and 20% reduction in strength up to 5% content of PA, respectively. However, flexure strength drops nearby 10% after 10% replacement of FA with PA. Further, there is fringe decline in dry density with 15% content of PA in concrete. In future studies, plastic waste can be employed more efficiently to improve fresh and mechanical properties of concrete. Moreover, the utilization of plastic waste in concrete helps to boost eco-friendly environment and to reduce air pollution and global warming.